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Approaches to Automotive Emissions Control

In Approaches to Automotive Emissions Control; Hurn, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1974.


Approaches to Automotive Emissions Control R i c h a r d W . H u r n , Editor

A symposium co-sponsored by the Division of Fuel Chemistry and the Division of Petroleum Chemistry at the 167th Meeting of the American Chemical Society, Los Angeles, Calif., A p r i l 1-2, 1974.

ACS

AMERICAN

SYMPOSIUM

CHEMICAL

WASHINGTON,

D.

C.

SERIES

SOCIETY 1974


1

Library of Congress CIP Data Approaches to automotive emissions control. ( A C S symposium series; 1) Includes bibliographical references and index. 1. Automobile exhaust gas—Congresses. 2. Motor vehicles—Pollution control devices—Congresses. I. H u m , R . W . , 1919- ed. II. American Chemical Society. III. American Chemical Society. A C S symposium series; 1. TD886.5.A66 I S B N 0-8412-0212-5

Copyright ©

629.2'53 ACSMC8

74-22443 1 1-207 ( 1 9 7 4 )

1974

American Chemical Society A l l Rights Reserved P R I N T E D IN THE U N I T E D S T A T E S O F

AMERICA


ACS Symposium Series Robert F. Gould, Series Editor


FOREWORD The A C S S Y M P O S I U

a medium for publishing symposia quickly in book form. The format of the SERIES parallels that of its predecessor, A D V A N C E S I N C H E M I S T R Y SERIES, except that in order to save time the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. As a further means of saving time, the papers are not edited or reviewed except by the symposium chairman, who becomes editor of the book. Papers published i n the A C S S Y M P O S I U M SERIES are original contributions not published elsewhere in whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation.


PREFACE

The

course of automotive emissions control has profound influence both on attaining improved environmental quality and on meeting the energy needs of the transport sector. Thus this symposium, "Approaches to Automotive Emissions Control," simultaneously addresses two issues that w i l l dominate the national research and development effort for a long time. The symposium wa and critical examination and energy requirements. Taken together, the papers provide excellent background for insight into the interplay of automotive emissions control, fuel economy, and overall energy requirement. These elements of transportation technology have been considered independently for too long. N o w , because of the potentially critical problems i n meeting fuel demand, a reasonable balance must be drawn between control requirements and the preservation of potential for improved fuel economy. RICHARD W.

Bartlesville, Okla. September 9, 1974

ix In Approaches to Automotive Emissions Control; Hurn, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1974.

HURN

1 The Influence of Fuel Composition on Total Energy Resources G . P. H I N D S , JR. and W . A. B A I L E Y ,

JR.

Shell Development Co., Deer Park, Tex. 77536

A meaningful discussio only possible within predefine in the form of e l e c t r i c i t y generated by solar power or nuclear fusion, fuel composition i s of no significance. However, since chemical fuels, particularly liquid chemical fuels, represent a convenient and inexpensive way of storing large amounts of energy i n a small, light container, it i s probable that they w i l l be used for self-propelled vehicles at least for many years to come. The air pollution problems associated with their use are well on the way to being solved. The chemical fuels can be easily distributed and handled and they can be synthesized from available raw materials. This discussion will be limited to chemical fuels. Since the combustion products of fuels for oxidation processes must be capable of being handled by the biosphere without damaging it, the useful elemental compositions are limited. Elements whose oxidation products are i r r i t a t i n g or toxic (for example sulfur) cannot be considered nor can those whose scarcity precludes their general use. Thus chemical fuels must probably be compounds of carbon, hydrogen, oxygen, and perhaps nitrogen, although inclusion of nitrogen compounds under some circumstances creates problems. Obviously, during the twentieth century the most widely used liquid fuels have been hydrocarbons, and these compounds have many advantages as chemical fuels. Their physical properties vary widely, making possible the tailoring of fuels to meet varying combustion requirements. Since they have been manufactured i n quantity, the technology for their efficient distribution and use has been developed. Most importantly, their energy content per unit mass is higher than that of other e l i g i b l e compounds. Figure 1 shows the net heat of combustion i n Btu/# as a function of molecular weight for hydrocarbons, and some oxygen, nitrogen and sulfur compounds. As would be expected, as the oxygen content of a molecule increases the heat of combustion decreases.

1 In Approaches to Automotive Emissions Control; Hurn, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1974.

2

AUTOMOTIVE

EMISSIONS C O N T R O L

For hydrocarbons, the net heat of combustion i s essentially a function of hydrogen content, Figure _2. The curve of Figure _2 i s defined by the equation: H

c

« 14,100 + 402.5 χ %w H - 4.26 (%w H )

2

(1)

This equation can be generalized to give an approximation of the heat of combustion of other organic compounds of interest. The generalized equation i s :

Net H

" l " l o o " ^ ^ ï o ô - ï o ô ) 14,100 + 402.5 1

c

/ (% H -

\Z

Zfi

C + % H -

100 ν

/ (% H -

^=2/

\

g

V

*

2J>) 100\

2.

^/ J

+ 82 χ % S (2)

Although the equation i s based on compounds containing only one kind of hetero atom, i t can be used to estimate the heat of combustion of kerogen, shale o i l s , coal, etc., from the elemental composition. Figure j3 illustrates the agreement between measured and calculated heats of combustion for some hydrocarbons and non-hydrocarbon compounds. Points representing two coals are also shown. As has been pointed out previously (1), many other properties of hydrocarbons, specific gravity, refractive index, smoke point, etc., can be related to the hydrogen content. Even a property as sensitive to molecular structure as viscosity correlates i n a general way with this parameter - consider the difference between graphite and methane. This trend can be illustrated qualitively by the viscosity on the C 2 6 saturated hydrocarbons synthesized by API Research Project 42 at Pennsylvania State University (2) - Figure 4_. Here the absolute viscosity i n centipoise at 210° F i s plotted against the number of rings i n the molecule. The average value and range of data are indicated. Essentially the same curve can be drawn for aromatic rings, so that hydrogen content alone does not determine viscosity, but the trend of increasing viscosity with decreasing hydrogen content is obvious. (Also certain specific highly s t e r i c a l l y hindered structures have been synthesized. The inclusion of data on these structures increases the scatter of the points, but does not affect the general conclusion.) The manufacture of chemical fuels from crude o i l , i . e . , petroleum refining, can be considered as the process of adjusting the molecular weight and hydrogen content of the hydrocarbons present to meet product specifications, and the amount of high valued products which can be manufactured from a given crude i s limited by the amount of hydrogen available. Nearly a l l crude o i l s contain less hydrogen than the most desirable product mix. Typical data for crudes and currently acceptable fuels are shown in Table 1· Only residual fuel o i l and asphalt contain less


Fuel Composition

HINDS A N D B A I L E Y

20,000 c

nH2n+?

CnH2n-6— O-

BENZENE θβ-~-0

PHÎ&THRÉNE 15,000

10,000

100

MOLECULAR WEIGHT

Figure I.

150

Heat of combustion as a function of molecular weight

"i—!—ι—ι—ι—!—ι—ι—ι—ι—r 22,000

20,000

18,000

12,000

10,000

0

-J

2

1

4

I

6

«

8

10

»

12 14

«

16

% WT H

18

20

22

24

2

Figure 2. Heat of combustion as a function of hydrogen content


A U T O M O T I V E EMISSIONS C O N T R O L

Figure 3.

Calculated and measured heats of combustion

2

3

NUMBER OF RINGS/MOLECULE

American Petroleum Institute

Figure 4. Viscosity of saturated pure hydrocarbons with 26 carbon atoms/molecule



Fuel Composition

Table 1 Hydrogen Contents of F o s s i l Fuels and Some Current S p e c i f i c a t i o n Products

Typical

(Range)

Crude O i l s

12.3

(10-14)

Residues from Crudes

11.8

(9.5-12.5)

N a t u r a l Gas

22.5

L i q u i f i e d Petroleum Gases

17.5

"Regular" Gasoline

14.3

"Premium" Gasoline

13.7

A i r c r a f t Turbine F u e l

13.8

D i e s e l F u e l - No. 2 Furnace O i l

12.3

R e s i d u a l F u e l - No. 6 F u e l

10.0

Asphalt

11.2


6


hydrogen than the residue from which many products must be made. When fuels are derived from other sources, shale, tar sands, or coal, the problem i s aggravated. Not only are these materials poorer i n hydrogen than most crude o i l s , but they also contain higher concentrations of sulfur and nitrogen. Compounds of these elements must be removed to comply with a i r pollution regulations, and at the present state of knowledge, their removal can be accomplished practically only by hydrogénation. Unless the chemical fuels of the future can be of high molecular weight, high viscosity, and of poor burning quality, i t seems probable that their production w i l l require the generation of hydrogen. The usable hydrogen content of the raw material from which a fuel i s to be made has a significant effect on the energy required to produce i t . The energy required to deliver by pipeline to a Gulf Coast refinery a pound of hydrogen combined with carbon i n crude o i generate the same poun would require 85,000 Btu. When the starting material contains sufficient hydrogen so that auxiliary generation i s not needed, the efficiency of energy resource use can be high. The importance to current refining practice of efficient use of hydrogen is obvious. When fuels are to be manufactured from raw materials of lower hydrogen content than that desired i n the finished product, additional hydrogen must be generated, probably from water and excess carbonaceous material. The production of pure hydrogen from coke i s a commercially practical, i f expensive, process. Such a process might achieve a thermal efficiency, defined as the net heat of combustion of the hydrogen produced divided by the net heating value of the coke needed for the reaction and to provide the power required for the oxygen plant, separation equipment, etc., of about 55%. (Current efficiencies are i n the range of 46-47%.) This would be equivalent to the consumption of 6.7 pounds of coke for each pound of hydrogen produced. Using this efficiency, the weight of fuel of a given hydrogen content which can be produced from a unit weight of coke can be calculated by simple stoichiometry. (The heat of formation of hydrocarbons i s sufficiently small so that i t can be neglected i n this context.) Figure 5 shows this relationship. The assumptions used i n this and subsequent calculations are summarized i n Table _2. By combining this curve with that relating heat of combustion to hydrogen content, Figure 2_ a curve relating fuel hydrogen content to the fractional reduction i n total available energy can be constructed for the synthesis of hydrocarbon fuels from coke, a i r and water, Figure 6. From this curve i t i s obvious that unaltered carbon should be used as a source of energy whenever this i s feasible without serious efficiency penalty. The generation of methane from coke carries with i t a penalty of about 38% of the energy reserves. The preceding picture i s greatly oversimplified. Coals, not coke, are usually available, and these contain sulfur, which must 9


1.

Fuel Composition


7

Table 2 Assumptions Used i n Energy Calculations Thermal Efficiency of Hydrogen Generation: Gasification of coal or coke to - 55% hydrogen only Steam-Hydrocarbon Reforming

62%

To Remove S, N, or 0 by Hydrogénation Hydrogen require Thiophene desulfurizatio Hydrogen required for Ν - 4 1/2 moles H2/mole Ν - Ν removal - from Pyridine and Pyrrole Hydrogen required for 0 - 2 1/2 moles ^/mole removal - from Esters, Furans, Phenols

0-0

The additional Η not associated with H 2 S , NH3 and H 0 i s incorporated i n the fuel. 2

Hydrogen i n coal or shale o i l available to react with impurities. A l l char-carbon gasified before additional coal used. Net Heat of Combustion of fuels:

/ (% Η - 4.26 χ \% C + % H -

10θ\

—-

2

Ί + 82 χ % S J

A l l % are weight


8



1.

9 HINDS A N D B A I L E Y

Fuel Composition

be removed before or after combustion, as well as oxygen and nitrogen. Shale o i l contains more hydrogen than coal, but i s also rich i n sulfur and nitrogen compounds which require hydrogen for their elimination. Practical conversion processes produce a range of compounds of varying hydrogen contents rather than a single, most desirable one. Literature data on coal hydrogénation i n pilot plant equipment show products ranging from H S, N H 3 and CH^, to residual fuel (3). The presence of impuri t i e s , and the limitations of reaction mechanisms, qualitatively increase the hydrogen requirements to produce fuels of given properties, and thus reduce the fraction of energy recoverable. Analyses of the organic material i n o i l shale (4) and of the o i l derived therefrom by retorting (5), have been published, as have elemental compositions of several coals (3)· Table _3 shows typical data. In the case of shale i t i s not unreasonable to assume that the hea combustion of the unrecovere that the i n i t i a l raw material i s the retorted o i l . By making the assumptions shown i n Table 2^ i t i s possible to calculate the fuel yield and the fraction of the original energy recovered from shale o i l as a function of hydrogen content of the f i n a l fuel. Figures 7 and 8* show these relations. Similar calculations can be made for coals of varying compos i t i o n , and curves for an I l l i n o i s No. 6 bituminous and a Wyoming subbituminous are included i n Figures _7 3 1 1 ( 1 ϋ· curves are based on dry, ash-free coals, and represent an idealized situa tion. It has been assumed that the oxygen, sulfur and nitrogen in the coal can be removed by reaction with a portion of the hydrogen present, and that the remaining hydrogen can be included i n the hydrocarbon fuel manufactured. Only excess carbon i s gasified (with a thermal efficiency of 55%) to produce hydrogen. The curves i n Figures _7 and _8 extend between a point equivalent to the hydrogen content of the oxygen, sulfur and nitrogen^free raw material, and the composition of methane. The actual raw material points (at 100% recovery) are also shown. Obviously, the higher the usable hydrogen content of the starting material, the higher w i l l be the percent of the original energy recovered. Because of the relatively high costs associated with the processing schemes discussed, i t i s logical to assume that only fuels of high value, synthetic natural gas, LPG, gasoline, and light fuel o i l s should be produced by these costly synthetic routes. Since these fuels are the most probable ones for small self-propelled vehicles, the remainder of this discussion w i l l consider only the manufacture of them. Several studies have been made over the years which have attempted to evaluate octane number of gasoline which minimizes the cost of transportation to the motorist. In each case the approach has been similar. F i r s t i t i s necessary to establish a relationship between compression ratio and mileage at a constant level of performance; second, to relate octane number 2

T

h

e



%w C

80.5 84.25

79.50

75.46

Elemental Composition

Kerogen - Mahogany Zone Green River Formation

Shale O i l - NTU Retort

I l l i n o i s No. 6 Coal - Dry (ash free basis)

Wyoming Subb ituminous Coal - Dry (ash free basis) 4.71

5.53

11.41

10.3

%w H

Table 3

1.10

1.02

2.02

2.4

%w Ν

0.66

3.54

0.72

1.0

%w S

18.07

10.41

1.61

5.8

%w 0

Fuel Composition


I

201

\

2

4

\

\

\

\

\

\

I

1

1

6

8

10

12

14

16

18

20

22

I

1 24

% WT H IN FUEL

Figure 7. Weight recovery of hydrocarbons synthesized from shale and coal

20

I

I

|

I

I

I

I

I

I

I

1

i

2

4

6

8

10

12

14

16

18

20

22

l

_

J

24

% WT H IN FUEL

Figure 8.

Energy recovery in hydrocarbons synthesized from shale and coal


12

A U T O M O T I V E EMISSIONS

CONTROL

requirement to compression ratio for the average car on the road; and third, to estimate the relation between gasoline octane number and cost. From these data, the gasoline cost per mile can be calculated as a function of octane number. Duckworth, et a l (fi) and Kavanagh et a l (2), i n 1959 concluded that the minimum cost was reached at an average research octane level of 97 to 98.5 for a l l grades of leaded gasoline. Studies on unleaded gasolines were carried out by Corner and Cunningham (8), and Wagner and Russum (9). The former suggest that the optimum value for the unleaded pool research octane number of motor gasoline i s about 97; the latter concluded that the optimum motor octane number i s about 87. Both studies agree that at least two grades of differing octane number (and thus differing costs) are desirable. While these studies do not exactly agree, since the average pool gasoline sensitivity (research octane number - motor octane number discrepancy between them that unleaded octane numbers as high as these represent a true optimum. However, other publications (10), while not specifying optimum octane ratings, agree that the 91 research octane number level mandatory for unleaded gasoline i n 1974 w i l l probably eventually be exceeded. The optimization studies mentioned are based on the t o t a l costs of manufacturing gasoline from crude o i l , and thus involve charges for capital and operating costs, as well as raw materials. Thus they may not reflect exactly an optimum fuel composition to maximize total energy resources. However, since the most practical route to increasing the octane quality of motor gasolines i s to increase the aromatic content, which results i n a decrease i n total hydrogen content, i t appears that the manufacture of light, low octane number fuels does not represent a desirable direction for energy conservation. ( E l l i s has calculated that, even i n the absence of catalytic mufflers, an increase i n gasoline aromatics does not cause a proportionate increase i n reactive exhaust hydrocarbons (10).) It i s not chemically reasonable to postulate a process based on a reaction so specific that i t w i l l produce only a single hydrocarbon from a variety of starting materials. Some data are available i n the literature on the products obtained by coal hydrogénation, and the properties of the various products Q) · Table 4· i s based on data on the hydrogénation of b i t u minous coal, and shows yields, properties, and estimated hydrogen content for the various fractions. (The hydrogen contents and heats of combustions have been estimated from limited physical property data.) From these data and the assumptions i n Table 2, weight and energy recoveries can be calculated. The reported product distribution contains heavy fuels which do not meet current specifications. I f these fractions are freed of sulfur and nitrogen, and upgraded to current ATF and No. 2 (diesel) gas o i l quality, their hydrogen content must be



14.0

NH

81.98

10.70

11.56

11.57

11.43

1.51

0.0

0.74

1.13

5.9

1.51

-0.72

12.2

14.5

2.0

0.24

0.80 12.3

6.0 0

12.5

0.41

12.3

8.9

0.3° -20.0°

0.35 -0.04

107.9

16.7

10.7

26.8 12.5

0.56

13.8

11.4

18.5 0

15

21.1°

1.72 1.49

10.2 0

21

Yield %w

21.0

f

Add l H Needed

As siomed Minimum %w H

Est. %w H

15.0

API Gravity

49.2°

1.59

H Yield from Gasification of Char = 1.61#

Total

2

HS

105.9

10.7

Char-Carbon

2

12.3

975°F +

H0

12.7

680°-975°F

3

27.5

400°-680°F 3.13

2.78

15.72

18.5

24.37

2.14

8.06

c

10.2

C

l ~ 3 Cz+ - 400° F

Component

Basis: 100# Coal Charge # H Yield Added # H # C %w

Data from Hellwig, et a l

Table 4

14


increased, and additional hydrogen must be generated. For this case, and for increasing levels of hydrogen i n the products, weight and energy recoveries can be calculated i n a similar manner. These results are shown graphically i n Figures _9 and 10. The curve for bituminous coal from Figures _7 and j8 are repeated for reference. Point A, calculated from the reported data, l i e s slightly above the reference curves, since the products i n this case s t i l l contained significant quantities of nitrogen and sulfur (0.60 and 2.10%, respectively). Point Β for the hetero atom-free hydrocarbon product meeting high valued fuel specifications f a l l s below the reference curve. In the real process sufficient char or hydrogen-free carbon could not be generated to produce a l l of the hydrogen necessary, and additional coal had to be fed to the gasifier. The hydrogen i n this coal i s not recovered and the coal's heating value i s considerably lower tha of the curves for thes Some design estimates for commercial plants for hydrogénation of I l l i n o i s No. 6 coal have been published (3), (11) and from these data weight and energy recoveries can be calculated. Point C on Figures J9 and 10 i s based on a plant estimated by Hellwig, et a l , while Point D has been calculated from the design developed by O Hara,et a l . Both " r e a l " cases show much lower efficiencies than the hypothetical curves calculated. Coal as delivered contains both water and ash which must be removed and disposed of. Sulfur and nitrogen must be removed from products i n a way which does not give rise to pollution. Hydrogénation units require large amounts of power for compression, pumps, etc., and the generation of this power consumes energy. It i s interesting, though perhaps coincidental, that both real cases show essentially the same ratio of their thermal efficiency to that of the reference curves at the same product hydrogen content. The dashed curve through these two points i s drawn on the assumption that this same ratio would hold at other levels of hydrogen input. If new and better technology i s developed, thermal e f f i ciencies superior to those shown on the dashed curve i n Figure 10 may be realized - although i t must be emphasized that the two " r e a l " cases are based on some assumptions which may prove to be optimistic. In any case, the general shape of the curve w i l l not change, and the thermal efficiency of fuel synthesis processes w i l l decrease as fuel hydrogen content increases. Solid fuels are not well suited to small self-propelled vehicles, and the transportation of fuel from source to point of consumption requires energy. Published studies (12) have indicated that the cost of transporting e l e c t r i c a l power i s far higher than that of moving an equivalent amount of energy i n the form of o i l and gas. Thus, i t would appear that the conversion of coal to a f l u i d fuel suitable for pipeline transport should minimize overall energy losses. The f l u i d f u e l f


1.


Fuel Composition


15

16


which i s produced should be as poor i n hydrogen as can be tolerated by the equipment i n which i t i s to be consumed. To make maximum use of f o s s i l fuel resources, engines should be designed which can operate e f f i c i e n t l y on highly aromatic hydrocarbon mixture, preferably of low v o l a t i l i t y . The s t r a t i fied charge engine described by Coppoc, et a l , might be a possibility (13). The methane and other light hydrocarbon gases which must probably be produced i n any synthesis plant should be used for home distribution (synthetic natural gas) and petrochemical feedstocks. By assuming that future plants may achieve a thermal efficiency midway between that of the "real" cases and the "theoretical" line i n Figure 10, that these plants are designed to produce only the specified f u e l and the minimum amount of light gases associated with i t , and that this minimum amount i s as low (basis hydrogen input) for coal hydrogénation at cracking low end poin turing various types of liquid fuels from coal can be calculated. Since SO2 emissions must be restricted, the total heating value of this coal cannot be used as a base. However, high sulfur residual fuels (and therefore presumably coal) can be burned for power generation without pollution problems with a thermal efficiency of 90 to 95% (14). Thus a base recovery of 93% has been used. A hypothetical plant; producing conventional gasolines and diesel fuels - 14 %w hydrogen,would lose 28% of the original energy - having a thermal efficiency of 67%. The plant would also produce 9 %w light gases. If the l i q u i d fuel to be manufactured contained only 9.5% H (the level of xylenes or of an aromatic gas o i l ) , the energy loss would be reduced to 21%, and the light gas make to 4 %w. To produce a given amount of liquid fuel, the gasοline-diesel plant would have to process 15% more coal than the one producing the aromatic fuel, and would obviously be more expensive. Thus i t would appear that when liquid fuels must be synthesized from coal, energy resources w i l l be conserved to the greatest extent i f these fuels can be low i n hydrogen content - and thus highly aromatic. It must be kept i n mind that the nature of the raw material from which fuels are to be synthesized governs the nature of the fuel which w i l l best u t i l i z e the energy available i n that raw material. The manufacture of a highly aromatic liquid f u e l from a hydrogen-rich paraffinie crude o i l would require so much additional processing that the energy recovery would undoubtedly be lower than i f more conventional products were made. But since i t seems probable that future raw materials w i l l be low in usable hydrogen, aromatic fuel manufacture may represent one way to conserve natural resources.


1.


Fuel Composition

17

Stmmiary It seems probable that for a considerable time f l u i d fuels w i l l be desirable at least for self-propelled vehicles, and that these fuels w i l l have to be synthesized from raw materials low in hydrogen, e.g., shale o i l , coal or coke. Under these c i r cumstances, fuel composition has a significant influence on the theoretical and practical thermal efficiency of the con version process, and this affects the fraction of the total energy resources which i s available. The manufacture of highly aromatic, low hydrogen content fuels rather than paraffinie materials conserves available energy.

Literature Cited 1.

Hinds, G. P., J r . Hydrogenative Processing , Proceeding Eighth World Petroleum Congress, Volume 4, pp. 235-244.

2.

"Properties of Hydrocarbons of High Molecular Weight Synthesized by Research Project 42 of the American Petroleum Institute 1940-1966", Pennsylvania State University, University Park, Pa.

3.

Hellwig, K. C., Chervnak, M. C., Johanson, E. S., Stotler, Η. Η., and Wolk, R. H., "Convert Coal to Liquid Fuels with Η-Coal", Chem. Eng. Progress Symposium Series, 85, Volume 64, (1968), pp. 98-103.

4. Thorne, Η. Μ., Stanfield, Κ. Ε., Dinneen, G. U., and Murphy, W. I. R., " O i l Shale Technology - A Review", U. S. Bureau of Mines Information Circular 8216. 5.

Cody, W. E. and Seelig, H. S., "Composition of Shale O i l " , Ind. Eng. Chem., 44, No. 11 (1952), pp. 2636-2641.

6. Duckworth, J . B., Kane, E. W., Stein, T. W., and Wagner, T. O., "Economic Aspects of Raising Compression Ratio and Octane Quality", Proceedings of the F i f t h World Petroleum Congress, Section VI, pp. 91-99. 7.

Kavanagh, F. W., MacGregor, J . R., Pohl, R. L., and Lawler, M. B., "The Economics of High-Octane Gasolines", SAE Transactions, Volume 67, (1959), pp. 343-350.

8. Corner, E. S. and Cunningham, A. R., "Value of High Octane Number Unleaded Gasoline i n the U. S.", presented before the Division of Water, A i r and Waste Chemistry, American Chemical Society, Los Angeles, California, March 28 - A p r i l 2, 1971.


18


9.

Wagner, T. O. and Russian, L. W., "Optimum Octane Number for unleaded Gasoline", presented before the Automobile Engineering Meeting of the Society of Automotive Engi neers, Detroit, Michigan, May 14-18, 1973, SAE Preprint 730552.

10.

E l l i s , J . C., "Gasolines for Low Emission Vehicles", presented before 1973 SAE Section Meetings, SAE Preprint 730616.

11.

O'Hara, J . B., Jentz, Ν. E., Rippee, S. Ν., and M i l l s , Ε. Α., "Preliminary Design of a Plant to Produce Clean Boiler Fuels from Coal", presented at the American Institute of Chemical Engineer 66th Annual Meeting Philadelphia, Pa.

12.

Linden, H. R., "The Case for Synthetic Pipeline Gas from Coal and Shale", Chem. Eng. Progress Symposium Series, 85, Volume 64, (1968), pp. 57-72.

13.

Coppoc, W. J . , Mitchell, B., and Alperstein, Μ., "A Stratified Charge Engine Meets 1976 U. S. Standards", presented before the 38th Midyear Meeting of the American Petroleum Institute, Philadelphia, Pa., May 16, 1973, Preprint 46-73.

14.

Kuhre, C. J . and Sykes, J . Α., J r . , "Clean Fuels from Low-Priced Crudes and Residues", presented before the 74th National Meeting of the American Institute of Chemical Engineers, New Orleans, La., March 11-15, 1973.


2 Impact of Automotive Trends and Emissions Regulation on Gasoline Demand DAYTON H,

CLEWELL

Mobil Oil Corp., New York, Ν. Y. 10017 WILLIAM J. KOEHL Mobil Research and Development Corp., Paulsboro, N. J, 08066

Gasoline i n Perspectiv In these days of energy shortages, gasoline is probably our most visible source of energy and the automobile, our most conspicuous consumer. In this paper we will trace some automotive trends that have contributed to rising gasoline demand in the past and that can be expected to affect it in the future. We will also point out some opportunities for moderating the future growth of gasoline demand. To put gasoline consumption into the perspective of the overall energy picture, Figure 1 shows total 1971 energy consumption broken down into its major sources and consuming sectors(1). On an equivalent energy b a s i s , g a s o l i n e r e p r e s e n t e d about 17% o f t h e energy consumed in 1971, or about 38% of the oil. Virtually all of the gasoline was consumed by the transportation sector, but not all by automobiles. Gasoline supplied about 68% of the energy required for all transportation. Focusing on the automobile, statistics illus trated in Figure 2 show that gasoline consumption by passenger cars amounted to 74% of total gasoline demand(1,2) or about 13% of total energy. Light trucks, up to 6000 lbs. gross vehicle weight, are estimated to consume about 10% as much g a s o l i n e as a u t o m o b i l e s , o r 7% o f t h e total (3). Although they frequently are used interchangeably with automobiles, we will exclude them from this discussion because they are treated separately from

*Numbers i n p a r e n t h e s e s d e s i g n a t e r e f e r e n c e s a t end o f paper. 1Û



20

U.S. Department of Transportation

Figure 1.

Patterns of fuel and energy consumption

OTHER, 19% 4—LIGHT TRUCKS 7%* BILLION GALLONS PASSENGER CARS 74% [13% OF TOTAL ENERGY]

1950

1970

1960 YEAR

* Estimated Figure 2.

Gasoline consumption, 1950-1971


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CLEWELL AND KOEHL

Automotive Trends and Emissions Regulations

21

p a s s e n g e r c a r s i n e m i s s i o n s r e g u l a t i o n s f o r 1 9 7 5 and beyond, and because t h e y appear t o be e x c l u d e d from p r o p o s a l s under d i s c u s s i o n i n Washington f o r r e g u l a t i n g f u e l economy. Car

Trends

The i n c r e a s e i n g a s o l i n e demand shown i n F i g u r e 2 r e f l e c t s changes i n p a s s e n g e r c a r s a l e s and usage. Based on d a t a from t h e U.S. Department o f T r a n s p o r t a t i o n (4), F i g u r e 3 shows t h a t r e g i s t r a t i o n s i n c r e a s e d 45% from 1960 t o 1970 w h i l e m i l e s t r a v e l e d were up s l i g h t l y more a t 51%. G a s o l i n e consumption by p a s s e n g e r c a r s i n c r e a s e d 60% i n d i c a t i n g an i n c r e a s e i n average f u e l consumption p e r m i l e o v e r t h e p e r i o d Over t h e same 1 9 6 a r e shown t h r o u g h 1972) a s p e c t s o f new c a r d e s i g n t h a t caused f u e l consumption to increase. As i l l u s t r a t e d i n F i g u r e 4, v e h i c l e weight (_5_) , engine d i s p l a c e m e n t (6J , and t h e p e r c e n t a g e o f a u t o m a t i c t r a n s m i s s i o n s (JJ a l l i n c r e a s e d , b u t n o t by l a r g e f a c t o r s . A t t h e same time these f u e l consuming t r e n d s were o f f s e t somewhat by t h e f u e l s a v i n g t r e n d s o f i n c r e a s i n g compression r a t i o ( 6 ) and g r e a t e r s a l e s o f i m p o r t e d c a r s (_8) . Only a i r c o n d i t i o n e r i n s t a l l a t i o n s ( 7 ) showed a s t e e p i n c r e a s e , but t h e r e s u l t i n g i n c r e a s e i n f u e l consumption was a t a much lower r a t e because a i r c o n d i t i o n i n g i s n o t used a l l o f t h e time. In a d d i t i o n t o t h e t r e n d s shown i n F i g u r e 4, e x h a u s t e m i s s i o n c o n t r o l s emerged w i t h t h e 1968 models (1966 f o r c a r s s o l d i n C a l i f o r n i a ) as a new a s p e c t o f car design. These have had an i n c r e a s i n g l y i m p o r t a n t e f f e c t on g a s o l i n e demand; by 1970 they had r e d u c e d f u e l economy o f new c a r s by about 3%. F o r t h e 1 9 7 3 models, we e s t i m a t e t h a t the t o t a l l o s s i n f u e l economy caused by e m i s s i o n c o n t r o l s averaged about 15%. In t h e f u t u r e , c a r d e s i g n t r e n d s w i l l c o n t i n u e t o i n f l u e n c e average f u e l economy and t o t a j . g a s o l i n e consumption. We e x p e c t e m i s s i o n c o n t r o l s t o c o n t i n u e t o be an i m p o r t a n t f a c t o r . Of t h e f a c t o r s t r a c e d i n F i g u r e 4, w e i g h t c o u l d i n c r e a s e because o f s a f e t y and d a m a g e a b i l i t y regul a t i o n s ; however, t h i s t r e n d may be c o u n t e r a c t e d by i n c r e a s i n g emphasis on w e i g h t r e d u c t i o n wherever p o s s i b l e t o improve f u e l economy. On t h e a v e r a g e , we e x p e c t v e h i c l e w e i g h t t o d e c r e a s e because o f t h e growing p r o p o r t i o n o f s m a l l e r c a r s among new c a r sales. A u t o m a t i c t r a n s m i s s i o n i n s t a l l a t i o n s appear



22

% 100 9 0

v

AUTOMATIC _ TRANSMISSIONS, % ^

- ^ + " 7s

COMPRESSION RATIO*

80 AIR CONDITIONED, % y

PERCENT

SHIPPING WEIGHT, lbs*

f

I

IMPORTS, %

^

1 65

3

0

0

260

DISPLACEMENT Cu.in.*

L 70

•WEIGHTED A V E R A G E , U.S. C A R S O N L Y .

YEAR Figure 4. New car design and equipment trends, 1960-1972


2.

CLEWELL AND KOEHL


23

t o have l e v e l e d o f f and a i r c o n d i t i o n e r i n s t a l l a t i o n s p r o b a b l y cannot i n c r e a s e much more w i t h o u t deep p e n e t r a t i o n i n t o the s m a l l c a r and c o o l e r c l i m a t e markets. Compression r a t i o has a l r e a d y s u f f e r e d a d r a s t i c r e d u c t i o n s i n c e 1970. T h i s change, made t o f a c i l i t a t e i n t r o d u c t i o n o f unleaded g a s o l i n e f o r 1975 c a t a l y t i c e m i s s i o n c o n t r o l systems, a c c o u n t s f o r n e a r l y h a l f o f the 15% f u e l economy l o s s a s s o c i a t e d w i t h e m i s s i o n c o n t r o l s through 1973. Some f u r t h e r r e d u c t i o n i n compression r a t i o c o u l d o c c u r i n the next y e a r o r two t o p r o v i d e adequate knock p r o t e c t i o n i n c a r s u s i n g 91 octane unleaded g a s o l i n e . In the l o n g e r term, a f t e r e m i s s i o n c o n t r o l development has s t a b i l i z e d , compress i o n r a t i o c o u l d be and performance; however grade h i g h e r octane f u e l s . Engine d i s p l a c e m e n t w i l l p r o b a b l y i n c r e a s e somewhat i n g i v e n c a r f a m i l i e s t o compensate f o r performance l o s s e s due t o e m i s s i o n c o n t r o l s , but on average, i t may d e c r e a s e because o f the s h i f t t o s m a l l e r c a r s . L a t e r i n t h i s paper we s h a l l make some p r o j e c t i o n s o f growth i n f u t u r e g a s o l i n e demand as a f u n c t i o n o f the two v a r i a b l e s t h a t we see as most i m p o r t a n t i n the s h o r t term - e m i s s i o n c o n t r o l r e g u l a t i o n s and average v e h i c l e weight. The l a t t e r w i l l be d e s c r i b e d i n terms o f the s h i f t from l a r g e r c a r s t o s m a l l e r ones t h a t can be seen d e v e l o p i n g r a p i d l y i n the new c a r market t o d a y . P r o j e c t i o n s o f the p o t e n t i a l e f f e c t s o f e m i s s i o n r e g u l a t i o n s are a l s o t i m e l y , not o n l y i n the c o n t e x t o f t h i s symposium, but a l s o i n the c o n t e x t o f c u r r e n t d e l i b e r a t i o n s on p o s s i b l e changes i n the C l e a n A i r A c t . Gasoline

Trends

B e f o r e p r o j e c t i n g g a s o l i n e demand, l e t us l o o k b r i e f l y at gasoline q u a l i t y trends. These a l s o have been and w i l l c o n t i n u e t o be i n f l u e n c e d by v e h i c l e trends. A l o n g w i t h compression r a t i o , g a s o l i n e o c t a n e q u a l i t y r e a c h e d i t s h i g h e s t l e v e l s i n the l a t t e r h a l f o f t h e l a s t decade; w h i l e g a s o l i n e v o l a t i l i t y showed r e l a t i v e l y l i t t l e change (9J. S i n c e 1970, however, i m p o r t a n t changes i n g a s o l i n e q u a l i t y have begun t o t a k e p l a c e i n response to emissions r e g u l a t i o n s . S e v e r a l marketers i n t r o duced u n l e a d e d grades o f lower o c t a n e than t r a d i t i o n a l r e g u l a r i n 1970 and 1971 as new c a r s w i t h lower compression r a t i o e n g i n e s were i n t r o d u c e d . By J u l y 1, 1974, v i r t u a l l y a l l m a r k e t e r s must o f f e r an u n l e a d e d g a s o l i n e o f a t l e a s t 91 r e s e a r c h o c t a n e number (RON)


24


i n a n t i c i p a t i o n o f c a t a l y s t e q u i p p e d 1975 c a r s ( 1 0 ) . As c a r s r e q u i r i n g u n l e a d e d g a s o l i n e r e p l a c e t o d a y ' s c a r s which can use l e a d e d g a s o l i n e , the average o c t a n e q u a l i t y o f the g a s o l i n e p o o l w i t h o u t l e a d w i l l have t o i n c r e a s e from r e c e n t l e v e l s o f a p p r o x i m a t e l y 88 RON t o 91 RON. Recent r e g u l a t i o n s w i l l a c c e l e r a t e the i n c r e a s e i n the c l e a r p o o l o c t a n e l e v e l by f o r c i n g a r e d u c t i o n i n the l e a d c o n t e n t o f e x i s t i n g r e g u l a r and premium g r a d e s . EPA has o r d e r e d t h a t the l e a d c o n t e n t o f the l e a d e d grades o f g a s o l i n e be reduced from t h e i r r e c e n t average l e v e l s o f about 2 t o 2.5 g / g a l t o a l e v e l such t h a t the average l e a d c o n t e n t o f a l l grades i n c l u d i n g the unleaded g a s o l i n e w i l l not exceed 1.7 g / g a l a f t e r J a n u a r y 1, 1975. Th limit will b reduced i fou more s t e p s t o 0.5 g / g a Turning to v o l a t i l i t y , expec y larg changes i n the f u t u r e . A l t h o u g h some had been p r o p o s e d t o m i n i m i z e c o l d s t a r t e m i s s i o n s from f u t u r e low e m i s s i o n c a r s , we have n o t seen c o n v i n c i n g e v i d e n c e t h a t t h i s i s the b e s t a l t e r n a t i v e f o r e f f e c t i v e e m i s s i o n c o n t r o l . Advances are b e i n g made i n c a r b u r e t o r and m a n i f o l d d e s i g n t o f a c i l i t a t e f u e l e v a p o r a t i o n and i n d u c t i o n , and a c c o m p l i s h the same objective. Today's g a s o l i n e v o l a t i l i t y e v o l v e d t h r o u g h many y e a r s o f o p t i m i z a t i o n o f v e h i c l e p e r formance and e f f i c i e n t u t i l i z a t i o n o f g a s o l i n e blending stocks. Any d r a s t i c change i n t h e d i s t i l l a t i o n s p e c i f i c a t i o n s , p a r t i c u l a r l y r e d u c i n g the h i g h e r b o i l i n g components o f g a s o l i n e , would r e q u i r e w a s t e f u l changes i n r e f i n i n g schemes. I t would deny r e f i n e r s the f l e x i b i l i t y t o make optimum use o f a v a i l a b l e b l e n d i n g components and would r e q u i r e c o n v e r s i o n o f l e s s v o l a t i l e s t o c k s t o more v o l a t i l e ones w i t h a t t e n d a n t y i e l d l o s s e s and i n c r e a s e s i n crude runs and c o s t s . T h i s would be u n a d v i s e d i n the p r e s e n t energy l i m i t e d environment. P r o j e c t i n g Future

Gasoline

Demand

In o r d e r t o r e l a t e the c a r t r e n d s d i s c u s s e d i n t h i s paper t o g a s o l i n e demand, we have d e v i s e d a m a t h e m a t i c a l model i n which the c a r p o p u l a t i o n i s d e s c r i b e d by means o f parameters which a r e r e l a t e d t o f u e l economy. The c a r p o p u l a t i o n i s t r e a t e d as b e i n g composed o f f i v e c l a s s e s o f c a r s : f u l l size, i n t e r m e d i a t e , compact, d o m e s t i c sub-compact, and imported. H i s t o r i c a l d a t a a r e used t o d e t e r m i n e the f r a c t i o n o f t o t a l new c a r s a l e s i n each c l a s s i n each model y e a r , and a l s o t o c a l c u l a t e s a l e s w e i g h t e d


2.

CLEWELL AND KOEHL


25

averages f o r t h e parameters used t o d e s c r i b e each class. P r o j e c t i o n s o f f u t u r e s a l e s f r a c t i o n s and o f v a l u e s o f t h e parameters a r e made from t h e h i s t o r i c bases. The main d e t e r m i n a n t o f demand growth i n t h e model i s t h e growth i n annual v e h i c l e m i l e s . Changes i n t h e c a r parameters and s a l e s s h i f t s between c a r c l a s s e s cause p e r t u r b a t i o n s on t h e b a s i c demand growth c u r v e . For t h e growth c u r v e o f annual v e h i c l e m i l e s , we have used t h e p r o j e c t i o n o f t h e Department o f T r a n s p o r t a t i o n which was g i v e n i n t h e J a n u a r y 1972 r e p o r t o f t h e Committee on Motor V e h i c l e E m i s s i o n s ( 1 2 ) . This curve, i l l u s t r a t e d i n F i g u r e 5, may now be l e s s v a l i d because o f f u e l s h o r t a g e s and p r i c e i n c r e a s e s . S t i l l i t does not seem u n r e a s o n a b l projections. I t project an average o f 3.4% p e r y e a r t h r o u g h 1980 and 1.9% from 1980 t o 1990; w h i l e , t h e l a b o r f o r c e i s p r o j e c t e d t o i n c r e a s e a t 1.6% and t h e number o f households a t 2.2% p e r y e a r from 1970 t o 1990 (13). In any c a s e , i t w i l l s e r v e as a b a s i s on which t o a s s e s s t h e r e l a t i v e impacts o f p o t e n t i a l changes w i t h i n and among c a r classes. To c a l c u l a t e t o t a l f u e l consumption i n any y e a r , the average f u e l economy o f each model y e a r i n t h e c a r p o p u l a t i o n and t h e m i l e s t r a v e l e d by c a r s o f each model y e a r must f i r s t be o b t a i n e d . T o t a l annual miles are o b t a i n e d from F i g u r e 5, d e s c r i b e d above. The f r a c t i o n o f t h e m i l e s t r a v e l e d by each model y e a r i n t h e popul a t i o n i s t a k e n from a Department o f T r a n s p o r t a t i o n estimate o f r e l a t i v e annual miles versus c a r age(12). The average f u e l economy o f each model y e a r i s c a l c u l a t e d u s i n g the f i v e c l a s s breakdown o f c a r s a l e s i n t h a t model y e a r and t h e parameters d e s c r i b i n g each class. T h i s m a t h e m a t i c a l model was used t o p r o j e c t g a s o l i n e demand t h r o u g h 1985 and t o e x p l o r e p o t e n t i a l e f f e c t s o f e m i s s i o n s l i m i t s , c a r s i z e , and p o s s i b l e e f f i c i e n c y improvements on t h e growth i n f u t u r e g a s o l i n e demand. P o t e n t i a l E f f e c t s of Emission

Controls

Based on p u b l i s h e d i n f o r m a t i o n , p r i m a r i l y s t a t e ments by t h e a u t o m o b i l e m a n u f a c t u r e r s a t r e c e n t C o n g r e s s i o n a l h e a r i n g s (see Appendix) and on o u r own e n g i n e e r i n g assessment o f the c o n t r o l systems l i k e l y t o be used i n t h e coming y e a r s , we b e l i e v e t h a t e m i s s i o n c o n t r o l r e g u l a t i o n s w i l l l e a d t o t h e f u e l economy changes shown i n F i g u r e 6. Compared w i t h u n c o n t r o l l e d



BILLION MILES

I—REPORTED

PREDICTED-

_L

60

70

90

80 YEAR

National Academy of Sciences

Figure 5. +10

Growth in vehicle miles traveled/year

CONTROL TECHNOLOGY INTRODUCED: -ENGINE MODIFICATIONS -EXHAUST GAS RECIRCULATION

FUEL ECONOMY CHANGE, ~

J—OXIDATION CATALYSTS 1

ΝΟχ CONTROL METHOD UNCERTAIN

0

% -20

-30 EMISSION HC LIMITS, CO g/mi(1975 CVS) NO

1967

x

1974

1973 ~"\/ 3.0 28 3.1

1975

1975

1977

1978

1.5 15 3.1

.9 9 2.0

.41 3.4 2.0

.41 3.4 .4

1

Figure 6. Effect of emission standards on fuel economy


2.

CLEWELL

AND KOEHL

Automotive Trends and Emissions Reguhtions

27

c a r s o f 1967, we see a 15% l o s s i n f u e l economy i n t h e 1973 models. Some improvement appears t o have o c c u r r e d i n 1974, and i n 1975 models o u t s i d e o f C a l i f o r n i a , we e x p e c t a 3% improvement o v e r 1974. In F i g u r e 6, t h e d a t e s a s s i g n e d t o t h e s t a n d a r d s shown beyond 1975 a r e t h e e a r l i e s t model y e a r s i n which we would e x p e c t them t o a p p l y i n view o f r e c e n t a c t i o n s i n Congress (22). The l o s s through 1973 i s a t t r i b u t e d t o changes i n spark t i m i n g and a i r - f u e l r a t i o , and t o i n t r o d u c t i o n o f exhaust gas r e c i r c u l a t i o n , changes made t o c o n t r o l p o l l u t a n t f o r m a t i o n i n t h e e n g i n e , as w e l l as t o r e d u c t i o n o f compression r a t i o i n a n t i c i p a t i o n o f 91 octane unleaded g a s o l i n e . With t h e i n t r o d u c t i o n o f c a t a l y s t s i n t h e exhaus and carbon monoxide 1975 4 9 - s t a t e s i n t e r i m s t a n d a r d s , engine c a l i b r a t i o n s can be p a r t i a l l y r e s t o r e d t o more e f f i c i e n t s e t t i n g s t o r e g a i n a s m a l l p a r t o f t h e f u e l economy l o s t because of emission c o n t r o l s . However, beyond t h e s e 1975 l i m i t s , f u e l economy l o s s e s w i l l a g a i n i n c r e a s e and c o u l d r i s e t o 30% i f t h e most s t r i n g e n t s t a n d a r d s s e t by t h e C l e a n A i r A c t o f 1970 must be met. Our p r o j e c t i o n o f d i m i n i s h i n g f u e l economy a t t h e more s t r i n g e n t e m i s s i o n l e v e l s beyond 1975 p a r a l l e l s p u b l i s h e d e s t i m a t e s by G e n e r a l Motors C o r p o r a t i o n and F o r d Motor Company (see A p p e n d i x ) . With t h e 1975 i n t e r i m C a l i f o r n i a s t a n d a r d s and the s t a n d a r d s i n d i c a t e d f o r 1977, we e x p e c t t h e f u e l economy l o s s e s r e l a t i v e t o u n c o n t r o l l e d c a r s t o be 14 and 18%, r e s p e c t i v e l y . These a r e a s s o c i a t e d w i t h r e t a r d e d spark t i m i n g , r i c h e r a i r - f u e l r a t i o s , and exhaust gas r e c i r c u l a t i o n r e q u i r e d p r i m a r i l y f o r N 0 control. Least c e r t a i n o f attainment are the s t a t u t o r y l i m i t s o f 0.4 g/mi. f o r h y d r o c a r b o n s , 3.4 f o r carbon monoxide, and 0.4 f o r o x i d e s o f n i t r o g e n u l t i m a t e l y r e q u i r e d by t h e C l e a n A i r A c t . Because adequate t e c h n o l o g y has n o t y e t been i d e n t i f i e d f o r meeting t h e s e s t a n d a r d s , o u r e s t i m a t e s o f t h e f u e l economy p e n a l t y ranges from 20% t o as much as 30% r e l a t i v e t o 1967 c a r s . Our o p t i m i s t i c p r o j e c t i o n assumes d e v e l o p ment o f a n i t r i c o x i d e r e d u c t i o n c a t a l y s t which cannot p r e s e n t l y be r e g a r d e d as t e c h n i c a l l y f e a s i b l e i n t h e context o f the r e g u l a t i o n s ; while our p e s s i m i s t i c p r o j e c t i o n assumes N 0 c o n t r o l c o u l d be a c h i e v e d through t h e maximum degree o f exhaust gas r e c i r c u l a t i o n t h a t i s c o n s i s t e n t w i t h engine o p e r a t i o n . Some auto i n d u s t r y p r o j e c t i o n s f o r the n i t r i c oxide r e d u c t i o n c a t a l y s t are c l o s e r t o our p e s s i m i s t i c estimate. X

X


28


In t h i s assessment, we have t r i e d t o i s o l a t e t h e e f f e c t o f e n g i n e changes made p r i m a r i l y f o r e m i s s i o n control. Compression r a t i o r e d u c t i o n i s i n c l u d e d among t h e s e changes. We have a l s o endeavored t o compare systems on a c o n s t a n t performance b a s i s . In e v a l u a t i n g v e h i c l e t e s t d a t a , one must be c a r e f u l t o s e p a r a t e e m i s s i o n c o n t r o l e f f e c t s from c o u n t e r a c t i n g e f f e c t s o f o t h e r changes, such as r e d u c e d a c c e l e r a t i o n performance, h i g h energy i g n i t i o n systems, improved carburetors, r a d i a l t i r e s , or s h i f t s to smaller cars. These changes would y i e l d f u e l economy improvements r e g a r d l e s s o f t h e e m i s s i o n c o n t r o l system chosen. To compare the p o t e n t i a l e f f e c t s o f the e m i s s i o n l i m i t s shown i n F i g u r e 6, we have used the c o r r e sponding f u e l econom change i math model Th new c a r s a l e s mix ( f u l sub-compact, and imported) year t o be t h e same as i n 1973, w h i l e the parameters d e s c r i b i n g t h e new c a r s i n each f u t u r e y e a r were a l s o held at current values. A n n u a l v e h i c l e m i l e s were a l l o w e d t o i n c r e a s e as p r o j e c t e d i n F i g u r e 5. The p r o j e c t e d growth i n g a s o l i n e demand t h r o u g h 1985 a t each e m i s s i o n l e v e l i s t r a c e d i n F i g u r e 7. For a l l o f t h e s e p r o j e c t i o n s , the g a s o l i n e i s assumed t o be 91 o c t a n e u n l e a d e d g a s o l i n e . The f u e l economy d e b i t s a t t r i b u t e d t o each e m i s s i o n l e v e l were h e l d c o n s t a n t t h r o u g h the p e r i o d o f the p r o j e c t i o n s i n F i g u r e 7. E v o l u t i o n a r y improvements can r e a s o n a b l y be e x p e c t e d t h a t would reduce the f u e l economy d e b i t s as m a n u f a c t u r i n g and s e r v i c e e x p e r i e n c e grows; however, such improvements ought t o be a p p l i c a b l e i n some degree a t a l l o f t h e e m i s s i o n l e v e l s so t h a t on a r e l a t i v e b a s i s , our g a s o l i n e demand p r o j e c t i o n would not change s i g n i f i c a n t l y . The g a s o l i n e demands p r o j e c t e d i n F i g u r e 7 f o r t h e y e a r 1985 a r e summarized i n the t a b l e below a l o n g w i t h t h e p e r c e n t a g e changes i n 1985 from a base case i n which 1973/74 e m i s s i o n s t a n d a r d s a r e assumed t o a p p l y t o a l l model y e a r s t h r o u g h 1985. In computing the demand f o r any y e a r , each e m i s s i o n l i m i t i s a p p l i e d from i t s y e a r o f i n t r o d u c t i o n u n t i l i t i s superseded by a subsequent, more r e s t r i c t i v e s t a n d a r d .


2.

C L E W E L L AND

Emission


KOEHL

Limits

Year o f Introduction

HC,

1973

3,

CO,

Ν0 * χ

28,

3.1

1985 P r o j e c t i o n o f 91 Octane Unleaded Gasoline Required f o r Automobiles Change from billion Base, % gal. 121

Base

117

- 3

122

+ 1

1975

49-States

1.5,

1975

California

.9,

1977

Proposed

.41,

3.4,

2

128

+ β

1978

Statutory

.41,

3.4,

.4

132

+ 9

*g/mi. on

1975

CVS

15, 9,

3.1

2

29

test basis.

F o r p e r s p e c t i v e , the maximum demand i n c r e m e n t w i t h the most s e v e r e e m i s s i o n s l i m i t s (29 b i l l i o n g a l l o n s a n n u a l l y o r 1.9 m i l l i o n b a r r e l s p e r day) i s g r e a t e r than the g a s o l i n e s h o r t f a l l o f 1.4 m i l l i o n b a r r e l s per day a n t i c i p a t e d d u r i n g the embargo on shipment o f A r a b i a n o i l t o the U n i t e d S t a t e s i n the W i n t e r o f 1973-1974 (3). While the f u e l s a v i n g p r o j e c t e d f o r the 1975 system r e l a t i v e t o p r e s e n t c o n t r o l s may be l e s s t h a n p r o j e c t e d by o t h e r s , the i m p o r t a n t p o i n t i s t h a t moving t o more s t r i n g e n t e m i s s i o n l i m i t s than the 1975 i n t e r i m l i m i t s w i l l r e q u i r e s u b s t a n t i a l l y more g a s o l i n e . T h e r e f o r e , i t seems r e a s o n a b l e t o s e t e m i s s i o n s t a n d a r d s a t l e v e l s t h a t are j u s t i f i a b l e i n terms o f a t t a i n i n g d e s i r e d ambient a i r q u a l i t y l e v e l s , n o t a t a r b i t r a r y l e v e l s t h a t a r e unduly r e s t r i c t i v e and demanding o f energy. Prospects

f o r Moderating Gasoline

Demand Growth

Even w i t h the lowest demand growth c u r v e s i n F i g u r e 7, which are based on new c a r p o p u l a t i o n s as i n 1973, we p r o j e c t an i n c r e a s e i n g a s o l i n e demand f o r a u t o m o b i l e s o f a l m o s t 50% from 1973 t o 1985. This can be compared w i t h the 50% growth from 1970 t o 1985 p r o j e c t e d by the T r a n s p o r t a t i o n Energy Panel(15) and w i t h growth i n t o t a l energy r e q u i r e m e n t s p r o j e c t e d by others. F o r example, the N a t i o n a l P e t r o l e u m C o u n c i l p r o j e c t e d growth o f 70 t o 90% from 1970 to 1985 (14) and the Bureau o f Mines p r o j e c t e d about 70% over a similar period(16).


30

AUTOMOTIVE

EMISSIONS

CONTROL

What are the p r o s p e c t s f o r s u b s t a n t i a l l y r e d u c i n g , o r even a v o i d i n g , t h i s p r o j e c t e d 50% growth i n g a s o l i n e demand f o r a u t o m o b i l e s ? With the t e c h n o l o g y a v a i l a b l e now, two m o d e r a t i n g t r e n d s are o b v i o u s p o s s i b i l i t i e s , and b o t h c o u l d be seen t o be t a k i n g some e f f e c t i n r e c e n t months. One i s r e d u c t i o n i n v e h i c l e m i l e s t r a v e l e d , the o t h e r i s r e p l a c e m e n t of l a r g e c a r s w i t h s m a l l e r ones. In the l o n g e r term, improvements i n automotive t e c h n o l o g y can be e x p e c t e d t o p r o v i d e a d d i t i o n a l f u e l economy b e n e f i t s . These w i l l come through improved engine and d r i v e t r a i n e f f i c i e n c i e s , l i g h t e r weight components, improved e f f i c i e n c y i n power a c c e s s o r i e s , and improvements i n body aerodynamics. We w i l l e x p l o r e a few o f t h e s e o p t i o n s . Reduced V e h i c l seen a f o r c e d r e d u c t i o n i n c a r usage because t h e r e has not been enough g a s o l i n e a v a i l a b l e t o l e t us d r i v e as much as we would l i k e . People are a d j u s t i n g to l i f e w i t h l e s s g a s o l i n e and l e s s c a r t r a v e l , but not w i t h o u t i n c o n v e n i e n c e and even h a r d s h i p . Since even r e c r e a t i o n a l d r i v i n g i s i m p o r t a n t t o the p e r s o n accustomed t o i t , and e s p e c i a l l y t o the p e r s o n whose l i v e l i h o o d depends on i t , c a r usage can be e x p e c t e d to r e t u r n t o more normal l e v e l s w i t h i n c r e a s i n g s u p p l i e s o f g a s o l i n e now becoming a v a i l a b l e . In the l o n g e r term g a s o l i n e p r i c e s w i l l i n f l u e n c e p e o p l e t o s w i t c h t o more e f f i c i e n t c a r s t h a t w i l l e n a b l e them to d r i v e the r e q u i r e d m i l e s . Consequently, there i s u n l i k e l y t o be a r e d u c t i o n i n a n n u a l c a r m i l e s which, by i t s e l f , would have a s u b s t a n t i a l e f f e c t i n r e d u c i n g g a s o l i n e demand. O p p o r t u n i t i e s f o r some m i l e a g e r e d u c t i o n s appear to e x i s t i n i n c r e a s e d c a r p o o l i n g and the use o f p u b l i c t r a n s p o r t a t i o n . The Department o f T r a n s p o r t a t i o n e s t i m a t e s t h a t p o t e n t i a l s a v i n g s from i n c r e a s e d c a r p o o l i n g , and i n c r e a s e d usage o f urban t r a n s i t , and i n t e r c i t y bus and r a i l would be o n l y 1 . 2 , 1.0 and 0.5%, r e s p e c t i v e l y , of n a t i o n a l t r a n s p o r t a t i o n f u e l requirements after five years(3). These s a v i n g s could increase to 8 . 3 , 1.7, and 1 . 3 % , r e s p e c t i v e l y , i n 15 y e a r s Q ) . S h i f t to Smaller Cars. U s i n g our math model, we have e s t i m a t e d the p o t e n t i a l 1985 g a s o l i n e demand w i t h a s h i f t o f new c a r s a l e s from l a r g e c a r s t o s m a l l e r ones as compared t o m a i n t a i n i n g the 1973 new c a r s a l e s mix. The base 1973 new c a r s a l e s mix and a f u t u r e new c a r mix a c h i e v e d w i t h i n c r e a s i n g p e n e t r a t i o n o f s m a l l c a r s are shown i n F i g u r e 8 i n terms o f the c a r c l a s s e s



C L E W E L L AND K O E H L

ANNUAL DEMAND, BILLION GALLONS

1970

1975

1980

1985

YEAR Figure 7. Gasoline demand projections for automobiles —effect of emission standards

50 40 30 20 PERCENT OF NEW CAR

10

SMALL CARS

SUB-COMPACT - (U.S. & IMPORTS)

lr*—" "

'Ί973"ΜΙΧ-[--ΐ

COMPACT 1970

FUTURE MIX=j

1 1 1 11975 1 1 11 I1980 1 1 1 1 1985 1 YEAR

Figure 8. Hypothetical future new car sales mixes for projecting gasoline demand


32

AUTOMOTIVE

EMISSIONS

CONTROL

used i n our model. F i g u r e 9 shows the g a s o l i n e demand growth c u r v e s c a l c u l a t e d f o r the two c a s e s . I t can be seen t h a t i f the p o s t u l a t e d s h i f t t o s m a l l e r c a r s were a c h i e v e d , g a s o l i n e consumption by a u t o m o b i l e s would i n c r e a s e o n l y about 37% o v e r t h a t c a l c u l a t e d f o r 1973 v e r s u s 51% i f the 1973 new c a r s a l e s mix were maintained. T h i s r e p r e s e n t s a p o t e n t i a l s a v i n g i n 1985 o f 9%. F o r t h i s comparison, 1973/74 e m i s s i o n c o n t r o l s were assumed t o be i n e f f e c t t h r o u g h 1985. With 1975 e m i s s i o n c o n t r o l s , the s a v i n g would be about the same, but the g a s o l i n e demand o f the p o s t u l a t e d f u t u r e mix would be about 3% lower t h a n shown i n F i g u r e 9. The f u l l b e n e f i t o f t h e p o s t u l a t e d s h i f t t o s m a l l e r c a r s would n o t be seen u n t i l 1990 o r l a t e r when n e a r l y a l l pre-198 F i g u r e 9 a l s o show c i a t e d w i t h the s h i f t i n s a l e s mix t h a t o c c u r r e d from 1970 t o 1973 as the P i n t o , the Vega, and the G r e m l i n were i n t r o d u c e d . With the 1970 new c a r mix a d j u s t e d to the same e m i s s i o n l e v e l s as the 1973 mix, t h i s would r e p r e s e n t an e s t i m a t e d s a v i n g o f 6% i n 1985. Our p o s t u l a t e d r e d u c t i o n o f the b i g c a r segment ( f u l l s i z e and i n t e r m e d i a t e ) o f the new c a r market from about 58% i n 1973 t o 40% by 1980 does n o t seem u n r e a s o n a b l e i n l i g h t o f the r e d u c t i o n from 68% i n 1970 t h a t has a l r e a d y o c c u r r e d . According to recent news s t o r i e s , F o r d has i n d i c a t e d t h a t s m a l l c a r s c o u l d amount t o 50 t o 60% o f the market as soon as September, 1974 (17); and G e n e r a l Motors has i n d i c a t e d t h a t s m a l l c a r p r o d u c t i o n c a p a b i l i t y i n 1975 would be 30% g r e a t e r than i n 1974 and c o u l d be d o u b l e d i n 1976, i f necessary(18). Improved V e h i c l e E f f i c i e n c y . Improvements i n e n g i n e and d r i v e t r a i n e f f i c i e n c y ( e x c l u d i n g i n c r e a s e d compression r a t i o which w i l l be d i s c u s s e d l a t e r ) c o u p l e d w i t h weight r e d u c t i o n i n c a r components and improved aerodynamics might r e a s o n a b l y be e x p e c t e d t o a f f o r d a f u r t h e r 10 t o 15% i n c r e a s e i n f u e l economy when f u l l y implemented. R a d i a l t i r e s and improved e f f i c i e n c y i n power a c c e s s o r i e s c o u l d a l s o c o n t r i b u t e to t h i s s a v i n g . Assuming t h a t t h e s e improvements l e a d to 10% b e t t e r f u e l economy i n 1980 models and 15% i n 1985 models, we p r o j e c t a p o t e n t i a l g a s o l i n e s a v i n g i n 1985 o f 11%. T h i s e s t i m a t e i s based on 1973/74 e m i s s i o n l e v e l s and t h e s h i f t t o s m a l l e r c a r s p o s t u l a t e d above. As i n the case o f the s h i f t t o s m a l l e r c a r s , the f u l l 15% b e n e f i t o f t h e p o s t u l a t e d improvements would n o t be r e a l i z e d u n t i l a l l l e s s e f f i c i e n t c a r s are r e p l a c e d .


2.

CLEWELL AND KOEHL


33

Our p o s t u l a t e d 10 t o 15% e f f i c i e n c y improvement i s a l s o c o r r o b o r a t e d by F o r d and G e n e r a l Motors p r e d i c t i o n s t h a t the minimum f u e l economy o f f u t u r e s t a n d a r d s i z e c a r s i s l i k e l y t o be 13 t o 15 mpg(18); as c o n t r a s t e d t o 11.5 mpg and l e s s f o r the average 1970 t o 1974 f u l l s i z e c a r s i n our model. As s t a t e d e a r l i e r , we e s t i m a t e t h a t about h a l f o f the f u e l economy l o s s a s s o c i a t e d w i t h e m i s s i o n c o n t r o l s (7 o f the 15% f o r 1973 systems) i s due t o the r e d u c t i o n i n compression r a t i o t h a t was made t o accommodate 91 o c t a n e u n l e a d e d g a s o l i n e . T h i s energy l o s s c o u l d be r e c o v e r e d i n p a r t by use o f h i g h e r octane unleaded g a s o l i n e i n engines of i n c r e a s e d compression r a t i o . I t c o u l d be r e c o v e r e d i n f u l l , and even beyond, i f the r e t a i n e d , or i f lea o r e m i s s i o n c o n t r o l systems were d e v e l o p e d t o meet more s t r i n g e n t s t a n d a r d s . Then l e a d e d g a s o l i n e c o u l d c o n t i n u e t o be used, and compression r a t i o c o u l d be increased. Of c o u r s e , the r e c e n t l y p u b l i s h e d r e g u l a t i o n s ( 1 1 ) r e q u i r i n g a phase-down o f the l e a d c o n t e n t o f g a s o l i n e would have t o be r e v o k e d t o a l l o w the f u l l f u e l s a v i n g p o t e n t i a l o f l e a d t o be r e a l i z e d . If a i r quality s t a n d a r d s f o r l e a d p a r t i c u l a t e s were t h e n e s t a b l i s h e d , d e v i c e s t o remove l e a d from v e h i c l e e x h a u s t c o u l d be a p p l i e d t o meet them. S e v e r a l companies have r e p o r t e d v e r y marked p r o g r e s s i n the development o f t h e s e d e v i c e s which shows t h a t t h e y are f e a s i b l e f o r 80% removal o f l e a d p a r t i c u l a t e s from e x h a u s t ( 1 9 , 2 0 ) . Our s t u d i e s i n d i c a t e t h a t adding 2.5 g o f l e a d p e r g a l l o n t o the 91 o c t a n e unleaded g a s o l i n e t h a t w i l l soon be a v a i l a b l e because o f c u r r e n t r e g u l a t i o n s (10, 11) would p e r m i t an o c t a n e number i n c r e a s e t o 98 and an engine e f f i c i e n c y i n c r e a s e o f up t o 13%. A t the 1973/74 e m i s s i o n s l e v e l w i t h the 1973 new c a r s a l e s mix, the 1985 g a s o l i n e demand o f 121 b i l l i o n g a l l o n s c o u l d be reduced by up t o 16 b i l l i o n g a l l o n s , i f the f u l l f u e l s a v i n g p o t e n t i a l o f l e a d e d g a s o l i n e were e x p l o i t e d by t h a t time. I n our p o s t u l a t e d s c e n a r i o o f i n c r e a s i n g penet r a t i o n o f s m a l l e r c a r s a l o n g w i t h o t h e r f u e l economy improvements, the added e f f e c t o f l e a d i n m o d e r a t i n g the growth i n g a s o l i n e demand c o u l d be as shown i n F i g u r e 10. F o r t h i s p r o j e c t i o n , 1973/74 e m i s s i o n s t a n d a r d s were assumed t o a p p l y a l o n g w i t h the 10 t o 15% e f f i c i e n c y improvement d i s c u s s e d above. The compression r a t i o i n c r e a s e which would be e q u i v a l e n t t o a 13% i n c r e a s e i n e f f i c i e n c y was assumed t o be phased i n from 1976 through 1979. The r e s u l t a n t s a v i n g



130 120

ANNUAL DEMAND, BILLION GALLONS

110

AT 1973/74 EMISSION LEVELS . BASE - 1973 NEW CAR MIXFUTURE NEW CAR MIXENGINES! VEHICLE IMPROVEMENTS IN FUTURE MIX

. ALL WITH 91 OCTANE UNLEADED GASOLINE 90 h

100

80 70

1970

» INCREASED COMPRESSION RATIO AND 98 OCTANE LEADED GASOLINE • 1980 NEW CAR MIX 1980

1975

1985

YEAR

Figure 10. Gasoline demand projections for automobiles— effect of efficiency improvement


2.

C L E W E L L AND KOEHL


35

i n 1985 c o u l d be 10% b u t t h e f u l l b e n e f i t would n o t be r e a l i z e d u n t i l sometime l a t e r when a l l lower compression r a t i o c a r s c o u l d be r e p l a c e d . Summary Based on p a s t t r e n d s , g a s o l i n e demand has been p r o j e c t e d t o i n c r e a s e about 50% from 1973 t o 1985 a t c u r r e n t o r 1975 4 9 - s t a t e s e m i s s i o n l e v e l s , and maybe as much as 90% i f t h e s t a t u t o r y NO e m i s s i o n s t a n d a r d o f 0.4 g/mi. i s r e t a i n e d and can be approached o n l y by EGR. These p r o j e c t i o n s assume t h a t t h e mix o f v e h i c l e types on t h e r o a d w i l l remain t h e same as i n 1973 and t h a t f u t u r e c a r usage w i l l grow as p r o j e c t e d before the current rate of increase i are a l r e a d y a t work t h a t c o u l d moderate i t . The p r e s e n t l y e v i d e n t t r e n d toward s m a l l e r c a r s , i f i t c o n t i n u e s , a l o n g w i t h development o f t e c h n o l o g y t o implement t h e improvements i n v e h i c l e e f f i c i e n c y t h a t appear f e a s i b l e c o u l d s u b s t a n t i a l l y reduce t h e r a t e o f growth i n g a s o l i n e demand. Choosing v e h i c l e emiss i o n s t a n d a r d s w i t h due c o n c e r n f o r a t t a i n m e n t o f a i r q u a l i t y s t a n d a r d s and c o n s e r v a t i o n o f f u e l s h o u l d p r e v e n t unnecessary i n c r e a s e s i n demand. P o t e n t i a l 1985 g a s o l i n e s a v i n g s p r o j e c t e d i n t h i s paper a r e summarized below. I f i t were p o s s i b l e t o implement a l l o f them, a u t o m o b i l e s meeting the 1973/74 e m i s s i o n s t a n d a r d s and u s i n g l e a d e d g a s o l i n e might r e q u i r e o n l y 10% more g a s o l i n e i n 1985 t h a n c a l c u l a t e d f o r 1973; w h i l e t h o s e meeting 1975 i n t e r i m 4 9 - s t a t e s s t a n d a r d s w i t h unleaded g a s o l i n e might r e q u i r e o n l y 19% more. A t more s t r i n g e n t s t a n d a r d s , t h e growth would be g r e a t e r . x


36


Emission Level HC, CO, NO , g/mi. x

1973/74 3,28,3.1

1975 49-States 1.5,15,3.1

1985 Demand w i t h Uncons t r a i n e d Growth, b i l . g a l . I n c r e a s e o v e r 1973 Demand o f 80 b i l . g a l .

121

117

51%

46%

1985 S a v i n g w i t h S h i f t t o Smaller Cars, b i l . g a l .

11.3

10.8

1985 S a v i n g w i t h Improved Engine and D r i v e T r a i n E f f i c i e n c y and V e h i c l e Weight R e d u c t i o n , 1985 S a v i n g w i t h Leaded G a s o l i n e and I n c r e a s e d Compression R a t i o , b i l . gal.

1985 Demand i f a l l S a v i n g s are R e a l i z e d , b i l . g a l . Increase over C a l c u l a t e d 1973 Demand o f 80 b i l . gal.

9.5

Not a v a i l a b l e i f catalysts a r e used

88.2

94.9

10%

19%

Our o p t i m i s t i c p r o j e c t i o n t h a t the 1985 g a s o l i n e demand f o r automobiles a l o n e c o u l d be h e l d t o 10 t o 20% more than i n 1973 i s dependent, as d i s c u s s e d above, on changes i n promulgated e m i s s i o n s r e g u l a t i o n s , c o n t i n u a t i o n o f t h e t r e n d t o s m a l l c a r s , and o t h e r improvements i n f u e l economy. I t would r e p r e s e n t a s u b s t a n t i a l p o t e n t i a l g a s o l i n e s a v i n g and would be e q u i v a l e n t i n energy t o about two m i l l i o n b a r r e l s p e r day l e s s crude o i l t h a n p r o j e c t e d by t h e uncons t r a i n e d demand c u r v e . Compared t o t o t a l p r o j e c t e d 1985 p e t r o l e u m r e q u i r e m e n t s o f 25 m i l l i o n b a r r e l s p e r y ( 1 4 , 2 1 ) , i t r e p r e s e n t s a s a v i n g o f about 8% and r e l a t i v e t o t o t a l 1985 energy p r o j e c t i o n s o f 58 m i l l i o n b a r r e l s p e r day o i l e q u i v a l e n t ( 2 1 ) , a s a v i n g o f about 3%. These l a s t comparisons show t h a t w h i l e t h e p r o j e c t e d g a s o l i n e s a v i n g c o u l d be v e r y s u b s t a n t i a l i n a b s o l u t e terms, i t would s t i l l be a r e l a t i v e l y s m a l l s a v i n g i n t o t a l energy r e q u i r e m e n t s . Therefore, w h i l e h i g h l y d e s i r a b l e , i t s h o u l d n o t be viewed as t h e complete answer t o our n a t i o n a l energy problems. Cons e r v a t i o n i n o t h e r consuming s e c t o r s i s a l s o needed. d a


2.

CLEWELL AND KOEHL


37

I n a d o p t i n g energy c o n s e r v a t i o n p o l i c i e s f o r t h e f u t u r e , we s h o u l d remember t h a t l i q u i d h y d r o c a r b o n f u e l s are i d e a l l y s u i t e d f o r t r a n s p o r t a t i o n a p p l i cations. C u r r e n t s h o r t a g e s a r e due n o t o n l y t o r i s i n g demand f o r a l l f u e l s b u t a l s o t o s u b s t i t u t i o n o f p e t r o l e u m f u e l s f o r h i g h e r s u l f u r c o a l and f o r s c a r c e gas. To c o n s e r v e p e t r o l e u m and m i n i m i z e t h e economic and p o l i t i c a l c o s t s o f i m p o r t i n g o i l , we s h o u l d t r y not o n l y t o moderate t h e r i s i n g demand f o r f u e l s b u t a l s o t o r e s e r v e l i q u i d p e t r o l e u m f u e l s f o r premium a p p l i c a t i o n s such as t r a n s p o r t a t i o n w h i l e f i n d i n g e n v i r o n m e n t a l l y a c c e p t a b l e ways t o use d o m e s t i c c o a l and n u c l e a r energy i n a p p l i c a t i o n s such as power generation that are adaptable to a v a r i e t y o f f u e l s . Acknowledgment We g r a t e f u l l y acknowledge t h e a b l e a s s i s t a n c e o f Drs. C. R. Morgan and M. Ohta o f M o b i l Research and Development C o r p o r a t i o n who d e v e l o p e d t h e m a t h e m a t i c a l model used i n t h i s s t u d y . Literature Cited 1.

"Energy Statistics, A Supplement t o t h e Summary of National Transportation Statistics," U. S. Department o f T r a n s p o r t a t i o n , Report No. DOT-TSC-OST-73-34, September, 1973.

2.

Annual Statistical Reviews, U. S. P e t r o l e u m Industry Statistics, American P e t r o l e u m Institute; and, 1972 N a t i o n a l P e t r o l e u m News Factbook I s s u e , and earlier issues.

3.

W h i t f o r d , R. K. and H a s s l e r , F. L., "Some T r a n s p o r t a t i o n Energy O p t i o n s and T r a d e - O f f s : A F e d e r a l View," p r e s e n t e d a t California Institute o f Technology, January 8, 1974.

4.

Highway Statistics - 1960 through 1970 i s s u e s , U. S. Department o f T r a n s p o r t a t i o n , F e d e r a l Highway A d m i n i s t r a t i o n , Bureau o f Public Roads.

5.

C a l c u l a t e d u s i n g s h i p p i n g w e i g h t d a t a from Automotive I n d u s t r i e s Statistical I s s u e , 1960 t h r o u g h 1972, and M o b i l e s t i m a t e o f c a r popudistribution.

6.

B r i e f Passenger C a r Data, E t h y l Corp., 1960 t h r o u g h 1970; 1971 and 1972 N a t i o n a l P e t r o l e u m News Factbook I s s u e .

lation



38

7.

Ward's Automotive Ward's Automotive

Year Book, 1960 through 1970; R e p o r t s , September 25, 1972.

8.

Ward's Automotive

R e p o r t s , F e b r u a r y 26,

9.

M i n e r a l I n d u s t r i e s S u r v e y s , Motor G a s o l i n e s , U. S. Department o f the Interior, Bureau o f Mines.

1973.

10. R e g u l a t i o n o f F u e l s and F u e l A d d i t i v e s , F e d e r a l R e g i s t e r , January 10, 1973, p. 1254. 11. R e g u l a t i o n o f F u e l s and F u e l A d d i t i v e s , F e d e r a l R e g i s t e r , December 6, 1973, p. 33734. 12. Semiannual Repor Vehicle Emissions t o the E n v i r o n m e n t a l P r o t e c t i o n Agency, January 1, 1972. 13. A Guide t o Consumer Markets 1973/74, Report No. 607, The Conference Board, I n c . , New York, Ν. Υ., 1973. 14. U. S. Energy O u t l o o k , A Summary R e p o r t o f the N a t i o n a l P e t r o l e u m C o u n c i l , December 1972. 15.

"Research and Development O p p o r t u n i t i e s for Improved T r a n s p o r t a t i o n Energy Usage - Summary T e c h n i c a l Report o f the T r a n s p o r t a t i o n Energy R&D Goals P a n e l , " U. S. Department o f T r a n s p o r tation, September 1972.

16. The P o t e n t i a l f o r Energy C o n s e r v a t i o n : A Study, E x e c u t i v e Office o f the P r e s i d e n t , o f Emergency P r e p a r e d n e s s , October 1972. 17. Automotive

News, January

21, 1974,

p.

18. Automotive

I n d u s t r i e s , March 1, 1974,

Staff Office

1. p. 17 and

18.

19. C a n t w e l l , Ε. Ν., J a c o b s , Ε. I . , Kunz, W. G. and Liberi, V. Ε . , S o c i e t y o f Automotive E n g i n e e r s , N a t i o n a l Automobile E n g i n e e r i n g M e e t i n g , D e t r o i t , M i c h i g a n , May 1972, Paper 720672. 20. H i r s c h l e r , D. Α., Adams, W. E. and Marsee, F. J., N a t i o n a l Petroleum Refiners A s s o c i a t i o n Annual M e e t i n g , San A n t o n i o , Texas, April 1-3, 1973, Paper AM-73-15.


2.

C L ÉW E L L A N D K O E H L


39

21. DuPree, W. G., " U n i t e d S t a t e s Energy Requirements t o the Year 2000," American S o c i e t y o f M e c h a n i c a l E n g i n e e r s , p r e s e n t e d a t I n t e r s o c i e t y Conference on T r a n s p o r t a t i o n , Denver, C o l o r a d o , September 1973, Paper No. 73-ICT-105. 22.

S2589 (Energy Emergency A c t ) Conference December 1973.

Report,

APPENDIX E f f e c t o f E m i s s i o n C o n t r o l s on F u e l Economy In F i g u r e A - l l o s s e s a s s o c i a t e d w i t h e m i s s i o n c o n t r o l s i s compared w i t h p u b l i s h e d e s t i m a t e s from s e v e r a l s o u r c e s . The F o r d r e p o r t o f a 13% l o s s i n c i t y - s u b u r b a n f u e l economy i n 1973 r e l a t i v e t o u n c o n t r o l l e d c a r s i s based on a n a l y s i s o f a l a r g e number o f c a r s i n a f l e e t whose c o m p o s i t i o n was c o n s t a n t through the period (A-l). E f f e c t s o f e m i s s i o n c o n t r o l s were s e p a r a t e d from e f f e c t s o f changes i n v e h i c l e weight, engine d i s p l a c e m e n t , r e a r a x l e r a t i o , and a c c e s s o r y equipment. P r o j e c t i o n s f o r the f u t u r e y e a r s are made from t h i s 1973 base (A-2). Note t h a t F o r d e x p e c t s a 3% g a i n from 1974 t o 1975 i n t e r i m 4 9 - s t a t e s s t a n d a r d s i n c a t a l y s t - e q u i p p e d v e h i c l e s b u t a 5% l o s s i n v e h i c l e s without c a t a l y s t s . The C h r y s l e r e s t i m a t e f o r 1973 i s based on an a n a l y s i s o f a t y p i c a l i n t e r m e d i a t e s i z e c a r (A-3), w h i l e t h o s e f o r 1974 and 1975 are based on t e s t i m o n y t o the Senate Subcommittee on P u b l i c Works (A-4). G e n e r a l M o t o r s statement t o the Senate Committee on P u b l i c Works i n d i c a t e s a 15% l o s s due t o e m i s s i o n c o n t r o l s i n 1973 r e l a t i v e t o u n c o n t r o l l e d c a r s , a f t e r weight e f f e c t s are s u b t r a c t e d (A-5). From 1973 t o 1974, i t shows a 1% g a i n based on the average o f t y p i c a l h i g h volume models [the p o i n t (x) i n F i g u r e A - l ] , but a 1% l o s s based on a s a l e s weighted average a f t e r c o r r e c t i n g f o r v e h i c l e weight i n c r e a s e s . In g o i n g from 1974 t o 1975 i n t e r i m 4 9 - s t a t e s s t a n d a r d s , GM e s t i m a t e s range from 10% t o about 20%. The GM statement shows a 13% improvement i n c i t y t r a f f i c economy on an average b a s i s a t an e q u i v a l e n t v e h i c l e weight. In o r a l t e s t i m o n y GM i n d i c a t e d t h a t the improvement a t t r i b u t a b l e t o the e m i s s i o n c o n t r o l s a l o n e was o n l y 10% (A-6). In c o n t r o l l e d t e s t s w i t h one l a r g e 1


40


Figure A-l.

Effect of emission standards on fuel economy


2.

C L ÉW E L L A N D K O E H L

Automotive Trends and Emissions Régulations

41

c a r , a 21% improvement was i n d i c a t e d i n c i t y f u e l economy r e l a t i v e t o an average f o r new 1973 p r o d u c t i o n models o f t h i s c a r ; f o r highway economy t h e improvement was o n l y 6% (A-5). I n F i g u r e A - l , we have p l o t t e d b o t h the 10% e s t i m a t e and t h e one-car r e s u l t s t o e s t a b l i s h the range o f GM e s t i m a t e s f o r the 1975 4 9 - s t a t e s standard. F o r more s e v e r e s t a n d a r d s than t h e 1975 4 9 - s t a t e s s t a n d a r d , t h e one-car r e s u l t s show t h e downward t r e n d i n f u e l economy. The DuPont assessment (A-7) f o r 1973 i s based on measurements w i t h a c o n s t a n t f l e e t o f s i x p r o d u c t i o n cars. I t i s a d j u s t e d f o r weight changes. F o r b o t h 1975 e m i s s i o n l e v e l s t h e e s t i m a t e s a r e based on t h e e x t e n t t o which c a r b u r e t i o n and spark t i m i n g c o u l d be changed t o improve economy w h i l e s t i l l meeting t h e NO s t a n d a r d s . Th t e s t s w i t h c a r s equippe m a n i f o l d s , o x i d i z i n g c a t a l y s t s f o r 1977 and b o t h o x i d i z i n g and r e d u c i n g c a t a l y s t s f o r 1978. The Esso Research and E n g i n e e r i n g Company e s t i m a t e s (A-8) have been used by R u s s e l l T r a i n , A d m i n i s t r a t o r o f t h e EPA, i n a p r e s e n t a t i o n t o t h e House o f R e p r e s e n t a t i v e s (A-9). These e s t i m a t e s appear t o be based on o p t i m i s t i c e x p e c t a t i o n s f o r t h e e f f i c i e n c y o f r e d u c i n g c a t a l y s t s and a t h e o r e t i c a l assessment o f o p t i m i z e d exhaust r e c y c l e systems which i n v o l v e advancing spark t i m i n g , d e c r e a s i n g a i r - f u e l r a t i o , and l i m i t i n g EGR r a t e i n p r o p o r t i o n t o engine air. The M o b i l e s t i m a t e f o r 1973 i n c l u d e s f u e l economy d e b i t s f o r compression r a t i o r e d u c t i o n , r e t a r d e d spark t i m i n g and exhaust gas r e c i r c u l a t i o n (A-10). For the 1975 4 9 - s t a t e s s t a n d a r d , i t i s somewhat lower t h a n t h e average o f t h e p u b l i s h e d e s t i m a t e s shown i n F i g u r e A - l , because we e x p e c t t h a t compression r a t i o w i l l be reduced f u r t h e r o r spark t i m i n g w i l l be r e t a r d e d t o p r o v i d e an a c c e p t a b l e l e v e l o f octane s a t i s f a c t i o n i n 1975 c a r s u s i n g 91 o c t a n e unleaded g a s o l i n e . These changes would reduce f u e l economy. Beyond t h e 1975 i n t e r i m 49-states standard, our estimate o f d e c r e a s i n g f u e l economy p a r a l l e l s most o f t h e p u b l i s h e d e s t i m a t e s shown i n F i g u r e A - l . x

REFERENCES FOR APPENDIX A-1.

L a P o i n t e , C., " F a c t o r Affecting Vehicle Fuel Economy," S o c i e t y o f Automotive E n g i n e e r s N a t i o n a l M e e t i n g , Milwaukee, W i s c o n s i n , S e p t . 1973, Paper No. 730791.


42


A-2.

Statement o f H. L. M i s c h , F o r d Motor Co., t o the U. S. House o f R e p r e s e n t a t i v e s , Subcommittee on P u b l i c H e a l t h and Environment, Dec. 4, 1973, Washington, D. C.

A-3.

Huebner, G. J . and G a s s e r , D. J., "Energy and the Automobile - G e n e r a l F a c t o r s A f f e c t i n g V e h i c l e F u e l Consumption," S o c i e t y o f Automotive E n g i n e e r s , 1973 N a t i o n a l Automobile E n g i n e e r i n g M e e t i n g , D e t r o i t , M i c h i g a n , May 1973, Paper No. 730518. R i c c a r d o , J . J., C h r y s l e r Corp., Testimony b e f o r e the U. S. Senate Committee on P u b l i c Works, Nov. 5, 1973, Washington, D. C.

A-4.

A-5.

" F u e l Econom 7 of General the U. S. Senate Committee on P u b l i c Works, Nov. 5, 1973, Washington, D. C.

A-6.

C o l e , Ε. Ν., G e n e r a l Motors Corp., Testimony t o t h e U. S. House o f R e p r e s e n t a t i v e s , Subcom m i t t e e on P u b l i c H e a l t h and Environment, Dec. 4, 1973, Washington, D. C.

A-7.

C a n t w e l l , Ε. Ν., "The Effect o f Automotive Exhaust E m i s s i o n C o n t r o l Systems on F u e l Economy," Ε. I. duPont de Nemours and Co., P e t r o l e u m L a b o r a t o r y , J a n . 14, 1974.

A-8.

P e r s o n a l communication - L. E. F u r l o n g , E s s o Research and E n g i n e e r i n g Co.

A-9.

T r a i n , R. Ε . , Statement and Attachments p r e s e n t e d t o the U. S. House o f R e p r e s e n t a t i v e s , Subcommittee on P u b l i c H e a l t h and Environment, Dec. 3, 1973, Washington, D. C.

A-10.

C l e w e l l , D. Η., M o b i l Oil Corp., Addendum t o Testimony b e f o r e the U. S. Senate Committee on P u b l i c Works, Nov. 5, 1973.


3 Gaseous Motor Fuels—Current and Future Status W. H. FINGER —Humble Oil and Refining Co., Baytown, Tex. 77520 D. S. GRAY—American Oil Co., Whiting, Ind. 46394 W. J. KOEHL—Mobil Research and Development Corp., Paulsboro, N. J. 08066 P. E. MIZELLE—Cities Service Oil Co., Cranbury, N. J. 08512 Α. V. MRSTIK—Atlantic Richfield Co., Harvey, 111. 60426 S. S. SOREM—Shell Oil Co., San Francisco, Calif. 94104 J. F. WAGNER—Gulf Research and Development Co., Harmarville, Pa. 15238

Some o f the e a r l f o r a c h i e v i n g and m a i n t a i n i n quality s t a n d a r d s i n c l u d e d p r o v i s i o n f o r the mandatory c o n v e r s i o n t o gaseous f u e l s o f certain groups o f motor v e h i c l e s . A l s o , i n the S t a t e o f California, there were legislative proposals for similar retrofit pro grams. Because o f the w i d e s p r e a d interest i n t h i s sub ject, the Engine F u e l s Subcommittee o f t h e American P e t r o l e u m I n s t i t u t e Committee f o r E n v i r o n m e n t a l Affairs undertook an assessment o f p u b l i s h e d i n f o r m a t i o n on the potential impact o f a d o p t i o n o f such a gaseous f u e l s retrofit program. T h i s assessment has been p u b l i s h e d and is available in its entirety as an API P u b l i c a t i o n . (1) T h i s p r e s e n t a t i o n summarizes the API p u b l i c a t i o n . To demonstrate the i n c e n t i v e f o r retrofit t o gaseous f u e l s , a typical s e t o f e m i s s i o n c u r v e s will be p r e s e n t e d . (2) F i g u r e 1 shows the total hydrocarbon e m i s s i o n from an e n g i n e o p e r a t e d a t o n e - h a l f throttle on t h r e e different fuels: g a s o l i n e , propane and n a t u r a l gas. The r e d u c t i o n i n the h y d r o c a r b o n e m i s s i o n which can be a c h i e v e d by s w i t c h i n g t o a gaseous f u e l is the p r i m a r y i n c e n t i v e f o r the retrofit proposals. Not o n l y are the hydrocarbon e m i s s i o n s n e a r l y c u t in half as we s w i t c h from g a s o l i n e t o the gaseous f u e l s b u t the e m i t t e d hydrocarbons tend t o be l e s s r e a c t i v e when gaseous fuels are used. (2), (3), ( 4 ) , (5) F u r t h e r , note t h a t as we approach the l e a n m i s f i r e limits the h y d r o c a r b o n e m i s s i o n s s t a r t t o i n c r e a s e rapidly. With the gaseous f u e l s , t h e air/fuel e q u i v a l e n c e ratio a t which we g e t i n t o lean misfire problems is c o n s i d e r a b l y f a r t h e r out and thus we can o p e r a t e a t 43


44


l e a n e r mixtures without increases i n t o t a l hydrocarbon emission. A reason why we may w i s h t o o p e r a t e a t l e a n e r m i x t u r e s i s i l l u s t r a t e d i n F i g u r e 2 which shows the n i t r o g e n o x i d e e m i s s i o n s as a f u n c t i o n o f a i r / f u e l equivalence r a t i o . Here we see t h a t s u b s t a n t i a l r e d u c t i o n s i n n i t r o g e n o x i d e s e m i s s i o n s can be a c h i e v e d w i t h o u t any s i g n i f i c a n t p e n a l t y w i t h r e s p e c t t o h y d r o carbon e m i s s i o n s by u t i l i z i n g t h e l e a n o p e r a t i n g c a p a b i l i t y o f the gaseous f u e l s . F i g u r e 3 shows t h e carbon monoxide e m i s s i o n as a f u n c t i o n o f the a i r / f u e l e q u i v a l e n c e r a t i o . Here you w i l l see t h a t the e m i s s i o n o f t h i s p o l l u t a n t i s subs t a n t i a l l y u n a f f e c t e d i n the o p e r a t i n g range o f interest. Shown i o u t p u t as a f u n c t i o You w i l l n o t e t h a t t h e s e h a l f - t h r o t t l e d a t a i n d i c a t e t h a t t h e r e w i l l be some s a c r i f i c e i n power o u t p u t o p e r a t i n g a t the l e a n e q u i v a l e n c e r a t i o s . Because o f the d e f i n i t i o n of h a l f - t h r o t t l e used i n t h i s i n v e s t i g a t i o n , the horsepower d a t a f o r the s e p a r a t e f u e l s are n o t s u f f i c i e n t l y d i f f e r e n t t o j u s t i f y p l o t t i n g separate l i n e s . However, a t f u l l - t h r o t t l e , t h e r e i s a d e f i n i t e power l o s s upon c o n v e r t i n g t o gaseous f u e l s . On propane c o n v e r s i o n s power l o s s e s u s u a l l y less t h a n 10% have been r e p o r t e d . (.3) , (6_) , {!_) On n a t u r a l gas c o n v e r s i o n s the power l o s s e s have g e n e r a l l y been i n the 10% t o 15% range, (3) , (7) # (8) a l l r e l a t i v e t o gasoline. These power l o s s e s are due p r i m a r i l y t o the f a c t t h a t a t f u l l t h r o t t l e the maximum charge o f comb u s t i b l e m i x t u r e e n t e r i n g the engine c y l i n d e r i s e s s e n t i a l l y a c o n s t a n t number o f moles i f a l l o f the f u e l i s i n the gaseous s t a t e . W i t h the lower mole weight f u e l s the energy p e r u n i t volume o f charge i s l e s s . (4) G a s o l i n e / a i r m i x t u r e s n o t o n l y have t h e h i g h e s t average m o l e c u l a r w e i g h t b u t some p o r t i o n o f the g a s o l i n e may a c t u a l l y e n t e r the combustion chamber i n the form o f l i q u i d d r o p l e t s , thus f u r t h e r i n c r e a s i n g the maximum q u a n t i t y o f energy p r o d u c i n g charge which may be i n t r o d u c e d i n t o the c y l i n d e r . Having e s t a b l i s h e d an i n c e n t i v e f o r a gaseous f u e l r e t r o f i t program we w i l l next l o o k a t what i s i n v o l v e d i n r e t r o f i t t i n g a v e h i c l e . T a b l e 1 g i v e s some o f the p e r t i n e n t p r o p e r t i e s o f the t h r e e f u e l s i n q u e s t i o n . For this p r e s e n t a t i o n the s i m p l i f i c a t i o n has been made


Gaseous Motor Fuels

SOREM E T A L .

NATURAL 6AS 0.8

I

0.9

L_

i

l

1.0 l.l 1.2 1.3 A I R - F U E L EQUIVALENCE

l

l

1.4 1.5 RATIO

1.6

Bureau of Mines

Figure 1. Hydrocarbon emissions as a function of air-fuel equiva lence ratio at 50Ψο throttle

7,000 6,000 Ε

ο. 5,000

f

LEAN MISFIRE LEAl LIM ITS PROPANE

1.5

1.6

A I R - FUEL EQUIVALENCE RATIO Figure 2. Nitrogen oxide emissions as a function of air-fuel equivalence ratio at 50% throttle


46


Table I Physical

P r o p e r t i e s of Methane, Propane, and G a s o l i n e

Property

Methane

M o l e c u l a r Weight 16 B o i l i n g P o i n t , °F -259 C r i t i c a l Temp, °F -116 Vapor P r e s s u r e @ — 100°F, p s i Heat o f V a p o r i z a t i o n , BTU/lb G r o s s Heat o f Combustio BTU/lb ( g a s ) > Heat o f Combustion, (LNG)84,000 BTU/gal as s t o r e d (CNG)33,400 on v e h i c l e (Gross) Density of Liquid @ 60°F, l b / g a l Density of Liquid @ -260°F, l b / g a l 3.52 D e n s i t y o f gas @ 2000 p s i , 60°F, 1.4 lb/gal Stoichiometric A i r / fuel Ratio l b s a i r / l b Gas 17. 1 Ft a i r / f t Gas 9. 5 2 Explosive Limits, % V o l in A i r (3) Lower 5. Upper 13. A u t o i g n i t i o n Temp ( 3 ) 999

Propane

Gasoline (approx)

44 -44 207

100 100-400

190

8-14

91,300

125,000

—

(1

3

3

4.22

15.6 23.82

14.7

2.37 9.5 871

1.3 6.0 495

(1) P e r r y ' s C h e m i c a l E n g i n e e r s Handbook, F o u r t h E d i t i o n , p g . 3-142. (2) Energy D e n s i t y (see T a b l e I I I f o r Energy E q u i v a lents) . (3) Lange*s Handbook o f C h e m i s t r y , 1 4 t h E d i t i o n .


3.

SOREM E T A L .

Gaseous Motor Fuels

47

t h a t n a t u r a l gas can a d e q u a t e l y be r e p r e s e n t e d by methane and LPG ( l i q u e f i e d p e t r o l e u m gases) can a d e q u a t e l y be r e p r e s e n t e d by propane. As t h e s e hydrocarbons u s u a l l y c o n s t i t u t e 95% o f t h e r e s p e c t i v e f u e l s i n t h e m a r k e t p l a c e , t h i s s i m p l i f i c a t i o n would n o t be expected t o i n t r o d u c e any s i g n i f i c a n t b i a s o r e r r o r s . The v a l u e s f o r g a s o l i n e a r e approximate i n t h a t t h e r e are c o n s i d e r a b l e v a r i a t i o n s among today's commercial products. The f i r s t items t o be n o t e d a r e t h e vapor p r e s s u r e s and b o i l i n g p o i n t s . G a s o l i n e h a v i n g a vapor p r e s s u r e o f l e s s than a t m o s p h e r i c i s n o r m a l l y s t o r e d on t h e v e h i c l e i n a l i g h t weight s h e e t m e t a l tank subjected to pressure p e r square i n c h abov Propane w i t h a b o i l i n g p o i n t o f -44°F can have a vapor p r e s s u r e e x c e e d i n g 200 l b s . p e r square i n c h i n a tank s t a n d i n g i n t h e h o t sun. The ASME code f o r s t o r a g e tanks f o r t h i s f u e l r e q u i r e t h e tanks t o be d e s i g n e d f o r 312 pounds p e r square i n c h p r e s s u r e w h i l e t h e F e d e r a l Department o f T r a n s p o r t a t i o n r e g u l a t i o n s r e q u i r e t h a t v e h i c l e tanks be d e s i g n e d f o r a s e r v i c e p r e s s u r e o f 240 pounds p e r square i n c h w i t h a s a f e t y f a c t o r o f 4. Thus we have a requirement f o r a heavy, h i g h p r e s s u r e tank. F u r t h e r , you w i l l n o t e t h a t t h e h e a t o f combustion o f a g a l l o n o f LPG i s s u b s t a n t i a l l y l e s s than t h e h e a t o f combustion o f g a s o l i n e . C o n s e q u e n t l y , an LPG tank w i t h a c o r r e s p o n d i n g l y l a r g e volume must be p r o v i d e d t o p e r m i t t h e same v e h i c l e range o r range must be s a c r i f i c e d . T u r n i n g t o n a t u r a l gas w i t h a c r i t i c a l temperatur o f -116°F, t h e tankage p r e s e n t s an even more d i f f i c u l t problem. We have t h e c h o i c e o f e i t h e r c a r r y i n g t h e f u e l as CNG (compressed n a t u r a l gas) a t v e r y h i g h p r e s s u r e s , u s u a l l y i n i n d u s t r i a l gas c y l i n d e r s , a t p r e s s u r e s up t o 2500 p s i o r c a r r y i n g t h e m a t e r i a l as a cryogenic l i q u i d . LNG ( l i q u e f i e d n a t u r a l gas) has a vapor p r e s s u r e o f one atmosphere a t -259°F and a vapor p r e s s u r e o f 45 atmosphere a t i t s c r i t i c a l temper a t u r e o f -116°F. Hence, a h i g h l y i n s u l a t e d and e x p e n s i v e tank i s r e q u i r e d . F u r t h e r , p r o v i s i o n must be made f o r s a f e l y v e n t i n g b o i l e d o f f f u e l as t h e temperature r i s e s i n a p a r k e d v e h i c l e . These s p e c i a l tanks need t o be c y l i n d r i c a l because o f s t r e n g t h c o n -


48

AUTOMOTIVE

EMISSIONS

CONTROL

s i d e r a t i o n s and they need t o be l a r g e r t h a n the p r e s e n t tank i f e q u i v a l e n t c r u i s i n g ranges are t o be a c h i e v e d . These s p e c i a l tank shapes and s i z e s can n o t be accommodated i n the spaces u s u a l l y a l l o t t e d t o the normal g a s o l i n e tank. Hence, the gaseous f u e l tank i n the most u s u a l c a s e u s u r p s some o f the o t h e r w i s e u s e f u l l o a d space. F u r t h e r , i t i s n e c e s s a r y t o p r o v i d e s p e c i a l v e n t i l a t i o n o f t h i s l o a d space f o r s a f e t y reasons i f i t i s an e n c l o s e d space. F i g u r e 4 i l l u s t r a t e s s c h e m a t i c a l l y the necessary components o f a r e t r o f i t LPG f u e l system. From the s p e c i a l f u e l tank, the f u e l p a s s e s f i r s t t h r o u g h an a u t o m a t i c s h u t - o f f v a l v e , r e q u i r e d by law i n most s t a t e s , thence t h r o u g pressure regulator t f u e l i s c o n v e r t e d t o the vapor s t a t e . The source o f h e a t f o r the v a p o r i z e r i s u s u a l l y the engine c o o l a n t though t h e r e are i n s t a n c e s where engine exhaust o r engine i n t a k e a i r has been used. From the v a p o r i z e r t h e vapor p a s s e s t h r o u g h a second s t a g e , low p r e s s u r e r e g u l a t o r and thence t o a c a r b u r e t o r where i t i s mixed w i t h a i r and i n t r o d u c e d i n t o the engine m a n i f o l d . Hardware packages a r e a v a i l a b l e where the h i g h p r e s s u r e r e g u l a t o r , e v a p o r a t o r and low p r e s s u r e r e g u l a t o r a r e a l l i n c o r p o r a t e d i n a s i n g l e u n i t r e f e r r e d t o as a converter. Gaseous f u e l c a r b u r e t o r s a r e a v a i l a b l e i n c o n f i g u r a t i o n s which can be a t t a c h e d atop e x i s t i n g g a s o l i n e c a r b u r e t o r s where a d u a l f u e l , gas o r gasoline,, c a p a b i l i t y i s d e s i r e d f o r emergency o r f o r l o n g - d i s tance t r a v e l . In the d u a l f u e l i n s t a n c e t h e r e i s u s u a l l y an e l e c t r i c i n t e r l o c k s o l e n o i d v a l v e system t o p r e v e n t the f l o w o f b o t h f u e l s a t the same time. N a t u r a l gas f u e l systems r e q u i r e the same f u n c t i o n a l components e x c e p t t h a t t h e CNG system needs no evaporator. The d e s i g n r e q u i r e m e n t s o f t h e components up t o the low p r e s s u r e r e g u l a t o r are much more demanding i n the n a t u r a l gas systems because o f the v e r y low temperatures and/or v e r y h i g h p r e s s u r e s . The r e t r o f i t m o d i f i c a t i o n s j u s t d e s c r i b e d a r e s u f f i c i e n t t o c o n v e r t a s t a n d a r d g a s o l i n e engine t o use gaseous f u e l s . Further, r e t r o f i t modifications a r e p o s s i b l e and n e c e s s a r y i f one wishes t o o p t i m i z e the performance on t h e new f u e l . S e v e r a l of these f u r t h e r m o d i f i c a t i o n s become q u i t e e x p e n s i v e and a r e


SOREM E T AL.

Gaseous Motor Fuels

KEY

A I R - F U E L EQUIVALENCE

RATIO

Figure 3. Carbon monoxide emissions and engine power as functions of air-fuel equivalence ratio at 50% throttle

Figure 4. LPG fuel system


50

AUTOMOTIVE

EMISSIONS

CONTROL

seldom employed. They a r e touched upon i n some d e t a i l i n the r e f e r e n c e (1) p u b l i c a t i o n . F o r v e h i c l e s which have been r e t r o f i t t e d b o t h performance b e n e f i t s and shortcomings have been r e ported. G e n e r a l l y , d r i v e a b i l i t y o f gaseous f u e l e d v e h i c l e s i s v e r y good. S i n c e the f u e l reaches the c a r b u r e t o r i n a gaseous s t a t e , f u e l / a i r m i x t u r e s can be q u i t e u n i f o r m . C o l d s t a r t i n g i s good, i d l i n g i s smooth, warm-up i s q u i c k e r and t h e r e i s no p a r t t h r o t t l e surge i f the a i r / f u e l r a t i o adjustments have been p r o p e r l y s e t . I f t h e adjustments have been i m p r o p e r l y made o r i f ΝΟχ e m i s s i o n c o n t r o l has been over-emphasized, d r i v e a b i l i t y problems s i m i l a r t o those found i n s i m i l a As p r e v i o u s l y mentione a b l e l o s s e s i n the maximum power and hence a c c e l e r a t i o n c a p a b i l i t y o f the e n g i n e . (3_) , (4) # (8a) Further, because o f the lower v o l u m e t r i c h e a t i n g v a l u e o f the f u e l , there i s a s u b s t a n t i a l l o s s i n miles per g a l l o n and an even g r e a t e r l o s s i n m i l e s p e r tank f i l l i n g f o r the u s u a l i n s t a l l a t i o n . On a m i l e s p e r ΒTU b a s i s , LPG c o n v e r t e d v e h i c l e s have been r e p o r t e d t o g i v e f u e l consumptions from 20% b e t t e r ( 4 ) t o 30% p o o r e r (_3) than f o r g a s o l i n e . T h i s wide range o f r e s u l t s gener a l l y comes from comparing one o p t i m i z e d v e r s i o n a g a i n s t one n o t s i m i l a r l y o p t i m i z e d on the a l t e r n a t e f u e l . On a l o n g e r term b a s i s we a g a i n f i n d b e n e f i t s and d e t r i m e n t s from c o n v e r t i n g t o a gaseous f u e l system. Spark p l u g s , o i l and o i l f i l t e r , exhaust system and even engine l i f e improvements have been r e p o r t e d . ( 4 ) , (.6) , (7) , (8), (9) , (10) In some i n s t a n c e s , t h e s e b e n e f i t s have been e s t i m a t e d t o save 1% t o Ι^Φ p e r m i l e o v e r t h e t o t a l o p e r a t i n g l i f e o f the v e h i c l e . However, exhaust v a l v e r e c e s s i o n ( 4 ) , (_7) has been en c o u n t e r e d i n gaseous f u e l e d e n g i n e s which do not have p r o p e r v a l v e s and v a l v e s e a t m e t a l l u r g y f o r such con versions. F u r t h e r , the f u e l systems b e i n g a t h i g h p r e s s u r e a r e much more prone t o l e a k a g e problems. (4) The d r i v e r o f a gaseous f u e l e d v e h i c l e may have problems i n o b t a i n i n g a f u e l s u p p l y . The technology and the hardware f o r t h e d i s p e n s i n g o f LPG are w e l l d e v e l o p e d b u t the number o f the d i s p e n s i n g l o c a t i o n s may be a l i m i t i n g f a c t o r i n many i n s t a n c e s . Thus v e h i c l e s which can be most c o n v e n i e n t l y c o n v e r t e d t o


3.

SOREM E T A L .

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51

b u r n gaseous f u e l s would be f l e e t v e h i c l e s which oper ate on s h o r t t r i p s from c e n t r a l t e r m i n a l s where a s u i t a b l e r e f u e l i n g f a c i l i t y c o u l d b e m a i n t a i n e d as p a r t o f the f l e e t s e r v i c e . Compressed n a t u r a l gas i s u s u a l l y h a n d l e d under a p r e s s u r e o f about 2250 pounds p e r square i n c h . T h i s r e q u i r e s h i g h p r e s s u r e compressors, t a n k s and l i n e s . F o r LNG c o n d e n s a t i o n b y r e f r i g e r a t i o n i s required t o y i e l d a l i q u i d product t o f i l l the f u e l tank. Keeping t h i s m a t e r i a l i n t h e l i q u i d phase r e q u i r e s heavy i n s u l a t i o n o f a l l s t o r a g e f a c i l i t i e s . While t h e t e c h n o l o g y f o r t h e compression o r l i q u e f a c t i o n and d i s p e n s i n g o f n a t u r a l gas f u e l s i s known, hardware f o r t h i s s e r v i c e may n o t be r e a d i l y a v a i l a b l e from o f f - t h e - s h e l f i t e m s The comparativ eous f u e l s s h o u l d be mentioned. The r e l a t i v e l y un known, and t h e r e b y fearsome t o t h e u n i n i t i a t e d , a s p e c t s of h a n d l i n g f u e l a t h i g h p r e s s u r e s and low temperatures can be c o u n t e r a c t e d b y adequate t r a i n i n g and p r o p e r hardware. The gaseous f u e l s have w i d e r ranges o f ex p l o s i v e m i x t u r e l i m i t s than does g a s o l i n e , t h e r e b y p o s s i b l y p r e s e n t i n g a g r e a t e r h a z a r d i n open f u e l spills. However, t h e f a s t e r r a t e a t which t h e s e low m o l e c u l a r weight f u e l s w i l l d i s s i p a t e i n t h e atmosphere tends t o o f f s e t t h i s w i d e r e x p l o s i v e range problem. In g e n e r a l , i t can b e s a i d t h a t b o t h l i q u i d and gas eous f u e l s c a n be h a n d l e d s a f e l y i f p r e c a u t i o n s i n i n s t a l l a t i o n , o p e r a t i o n and maintenance o f t h e f u e l system a r e t a k e n . ( 4 ) , (Τ) , (11) The r e l a t i v e c o s t s o f r e t r o f i t and gaseous f u e l operation are c r i t i c a l i n determination o f the a c c e p t a b i l i t y o f r e t r o f i t i n programs t o t h e g e n e r a l public. The c o s t o f c o n v e r s i o n o f a v e h i c l e t o gas eous f u e l depends p r i m a r i l y on t h e p a r t i c u l a r f u e l and s e c o n d a r i l y on t h e r e q u i r e d l a b o r c o s t f o r i n s t a l l a t i o n and adjustment. When r e a s o n a b l e l a b o r and o v e r head c o s t s a r e used w i t h t h e c o n v e r s i o n equipment ex pensed i n t h e c u r r e n t y e a r t h e e s t i m a t e d c o s t f o r c o n v e r s i o n o f each v e h i c l e a r e $500 f o r an LPG system, $600 f o r a CNG system and between $700 and $1,200 f o r t h e LNG system. (I) The h i g h e r c o s t f o r t h e l i q u i d n a t u r a l gas i s a t t r i b u t a b l e t o t h e need f o r c r y o g e n i c s t o r a g e and t h e range o f c o s t i s due t o t h e minimal information i n t h i s area. ( A l l p r i c e e s t i m a t e s and


52


c o s t s mentioned i n t h i s paper r e p r e s e n t 1 9 7 2 d o l l a r s and m a t e r i a l c o s t s . These are now e s c a l a t i n g r a p i d l y and a t d i f f e r e n t r a t e s f o r d i f f e r e n t i t e m s . Hence, i n any u p d a t i n g o f the economics, the r e a d e r must p i c k the c o s t s a p p l i c a b l e on a p a r t i c u l a r day on which he hopes the e s t i m a t e s w i l l be r e l e v a n t . ) F u e l c o s t r e p r e s e n t s the most h i g h l y v a r i a b l e i t e m i n p u b l i s h e d economic s t u d i e s . Two r a t h e r comprehen s i v e s t u d i e s were s e l e c t e d f o r c o m p a r a t i v e a n a l y s i s o f r e l a t i v e f u e l economy. The U n i t e d S t a t e s G e n e r a l S e r v i c e A d m i n i s t r a t i o n s t u d y (GSA), b a s e d on a t w e l v e month, 2 4 - v e h i c l e comparison, (12) and the i n s t i t u t e o f gas t e c h n o l o g y s t u d i e s (IGT) ( 6 ) undertaken f o r t h e EPA. N e e d l e s s t o say do not agree w i t h eac d i f f e r e n t b a s i c assumptions a f f e c t i n g f u e l c o s t . When f u e l c o s t s were n o r m a l i z e d u s i n g the same p u b l i s h e d p r i c e s i n b o t h s t u d i e s the d i f f e r e n c e s between the two were reduced b u t n o t t o t a l l y e l i m i n a t e d . (1) The GSA n o r m a l i z e d r e s u l t s i n d i c a t e d compressed n a t u r a l gas t o be a more e c o n o m i c a l f u e l t h a n g a s o l i n e i n Los A n g e l e s , Houston, and C h i c a g o b u t more e x p e n s i v e i n New York C i t y . The IGT n o r m a l i z e d r e s u l t s i n d i c a t e d t h a t none o f the gaseous f u e l s was more e c o n o m i c a l than gasoline. T h i s d i f f e r e n c e i n economics i s due p r i m a r i l y t o assumed compression c o s t s a t 3 3 Φ p e r 1 , 0 0 0 s t a n d a r d c u b i c f e e t f o r l a r g e compressed n a t u r a l gas i n s t a l l a t i o n and 6 8 Φ t o 7 8 Φ p e r 1 , 0 0 0 s t a n d a r d c u b i c f e e t compression c o s t i n s m a l l i n s t a l l a t i o n s v i s u a l i z e d i n the IGT r e p o r t . In a number o f economic s t u d i e s s u b s t a n t i a l f u e l c o s t advantages were c l a i m e d f o r gas eous f u e l s b u t i n most e v e r y i n s t a n c e t h i s advantage c o u l d be a t t r i b u t e d t o s p e c i a l t a x c o n c e s s i o n s (13)or o t h e r s p e c i a l s i t u a t i o n s which r e s u l t e d i n a lower than normal c o s t f o r the gaseous f u e l . W i t h the w i d e l y v a r y i n g f l u c t u a t i o n s i n f u e l p r i c e s today, i t would be f u t i l e t o attempt t o draw any f i r m c o n c l u s i o n s r e g a r d i n g r e l a t i v e f u e l economy. However, i t i s q u i t e c l e a r t h a t t h e r e i s no u n i v e r s a l economic advantage f o r any f u e l f o r a l l v e h i c l e s . T h e r e f o r e , s e l e c t i o n o f the most economic f u e l must be b a s e d upon the u n i q u e economic p o s i t i o n o f f u e l s u p p l y and d i s t r i b u t i o n as w e l l as l o c a l and f e d e r a l t a x a t i o n f o r each f l e e t o p e r a t i o n .


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In r e g a r d t o s o u r c e s and a v a i l a b i l i t y o f gaseous f u e l s , l i t t l e needs t o be s a i d a t t h e p r e s e n t time t o i l l u s t r a t e t h e c u r r e n t s h o r t a g e s o f b o t h n a t u r a l gas LPG as w e l l as g a s o l i n e . L e t me summarize t h i s a s p e c t of t h e study w i t h two s t a t e m e n t s . 1) S i n c e s u p p l i e s o f n a t u r a l gas and LPG a l r e a d y l a g b e h i n d demand, any c o n v e r s i o n o f automotive type v e h i c l e s from g a s o l i n e t o gaseous f u e l s can be a c c o m p l i s h e d o n l y by w i t h d r a w i n g t h e gaseous f u e l s u p p l i e s from t h e c u r r e n t p r i o r i t y u s e r s . 2) New d i s t r i b u t i o n and d i s p e n s i n g f a c i l i t i e s would be r e q u i r e d f o r g r e a t e r u t i l i z a t i o n o f LPG, CNG, or LNG, t h e r e b y r e q u i r i n g s u b s t a n t i a l c a p i t a l i n v e s t ment b y an i n d u s t r t h i s area t o suppl future. In an e f f o r t t o a r r i v e a t an e s t i m a t e o f t h e impact o f such a r e t r o f i t program upon t h e automotive c o n t r i b u t i o n o f p o l l u t a n t s t o t h e atmosphere we have f i r s t assumed t h a t t h e average performance o f a r e t r o f i t t e d v e h i c l e would be e q u a l t o t h e average o f t h e some 150 v e h i c l e s which have been r e t r o f i t t e d and f o r which e m i s s i o n measurements have been p u b l i s h e d . Figure 5 i l l u s t r a t e s the i n d i v i d u a l emission f a c t o r s used. The d o t t e d l i n e s r e p r e s e n t t h e average e m i s s i o n s from t h e 150 r e t r o f i t t e d v e h i c l e s j u s t mentioned. The average h y d r o c a r b o n e m i s s i o n l e v e l i s 2.8 grams p e r mile. The average CO l e v e l i s 12.2 grams p e r m i l e and t h e average NO l e v e l 3.5 grams p e r m i l e . The s t e p p e d s o l i d l i n e s r e p r e s e n t t h e s t a n d a r d s t o which new v e h i c l e s are being b u i l t . Those o f you who a r e f a m i l i a r w i t h r e c e n t EPA d e c i s i o n s w i l l know t h a t t h e l a s t s t e p s have been extended one y e a r t o 1976 f o r hydrocarbon and CO and t o 1977 f o r N 0 . Meanwhile, t h e r e are some s m a l l e r s t e p s due t o new i n t e r i m s t a n d a r d s f o r 1975. The upper c u r v e d l i n e s r e p r e s e n t t h e w e i g h t e d average e m i s s i o n r a t e f o r a l l g a s o l i n e v e h i c l e s i n u s e . I t w i l l b e n o t e d from t h i s c h a r t t h a t t h e r e i s very l i t t l e hydrocarbon i n c e n t i v e f o r r e t r o f i t t i n g v e h i c l e s beyond t h e 1972 models. Starting w i t h t h e 1975 models, t h e s t a t u t o r y l i m i t a t i o n on h y d r o c a r b o n e m i s s i o n s w i l l be a c t u a l l y below t h a t a c h i e v a b l e by gas r e t r o f i t t e d o l d e r v e h i c l e s . In t h e c a s e o f CO, t h e r e i s some i n c e n t i v e f o r r e t r o f i t o f a l l x

X


54


1970

1975

1980

1985

Figure 5. Emission factors for gasoline and gas powered vehicles. Passenger cars and light trucks—g/mile (1972 CVS basis).


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v e h i c l e s up t o those which meet t h e 1975 s t a t u t o r y s t a n d a r d s o r even t h e 1975 i n t e r i m s t a n d a r d s which a r e n o t p l o t t e d on t h i s graph. With r e g a r d t o N 0 t h e r e i s no i n c e n t i v e f o r gas r e t r o f i t beyond t h e 1973 models. To a r r i v e a t t h e motor v e h i c l e e m i s s i o n c a l c u l a t i o n s which a r e i l l u s t r a t e d i n t h e n e x t f i g u r e , No. 6, i t has been n e c e s s a r y t o make a number o f f u r t h e r assumptions. 1. The r e t r o f i t program w i l l be l i m i t e d t o h i g h m i l e a g e v e h i c l e s i n f l e e t s o f 10 o r more o p e r a t i n g l a r g e l y i n urban a r e a s . I t w i l l b e completed i n 1975. 2. The f u e l consumption o f t h e t o be r e t r o f i t t e d v e h i c l e s r e p r e s e n t s 12% o f t h e n a t i o n a l g a s o l i n e consumption. 3. The gaseou f l e e t s w i l l be withdrawn from t h e i n d u s t r i a l u s e r s and r e p l a c e d b y 0.2% s u l f u r c o n t a i n i n g No. 2 d i s t i l l a t e . Demand f o r t h i s d i s t i l l a t e would as a r e s u l t i n c r e a s e by about 21% b y 1975. The r a t i o n a l e f o r t h e s e assumptions i s p r e s e n t e d i n t h e f u l l p u b l i c a t i o n . (JL) F i g u r e 6 i l l u s t r a t e s t h e impact on t h e t o t a l v e h i c l e e m i s s i o n s o f u t i l i z a t i o n o f gaseous f u e l s as j u s t d e s c r i b e d . The t o p o f t h e lower l i n e r e p r e s e n t s t h e e s t i m a t e d r e d u c t i o n i n e m i s s i o n r a t e from t h e average g a s o l i n e powered motor v e h i c l e assuming p r e s e n t e m i s s i o n s t a n d a r d s on new v e h i c l e s a r e adhered t o . The bottom o f t h i s lower l i n e r e p r e s e n t s t h e average e m i s s i o n r a t e f o r a l l motor v e h i c l e s i f t h e h y p o t h e t i c a l r e t r o f i t program o u t l i n e d above were a c t u a l l y implemented and completed by t h e end o f 1975. The t h i c k n e s s o f t h i s lower l i n e i s i n t e n d e d t o r e p r e s e n t t h e b e n e f i t i n terms o f reduced e m i s s i o n s which would be a c h i e v e d as a r e s u l t o f t h i s r e t r o f i t program. A t t h e i r maximum, t h e s e r e d u c t i o n s would be a 3.9% r e d u c t i o n i n h y d r o c a r b o n s , a 9.3% r e d u c t i o n i n carbon monoxide and a 1.6% r e d u c t i o n i n n i t r o g e n o x i d e s . Due t o the phasing out o f o l d e r v e h i c l e s these b e n e f i t s would be e x p e c t e d t o s u b s t a n t i a l l y d i s a p p e a r i n t h e e a r l y 1980's. F i g u r e 7 i l l u s t r a t e s t h e s e r e d u c t i o n s i n another way. On t h e r i g h t - h a n d s i d e we see b a r s r e p r e s e n t i n g t h e maximum r e d u c t i o n s o f e m i s s i o n s from t h e t r a n s p o r t a t i o n s e c t o r t o be a c h i e v e d b y t h i s h y p o t h e t i c a l X


56


1970

1975

1980

1985

Figure 6. Motor vehicle emission improvements. Fleet use of gas in urban areas by 1975 (million tons/yr).

TRANSPORTATION SECTOR - REDUCTIONS I

INDUSTRIAL S E C T O R - ADDITIONS

0.24

I

I

I

CO NOx -3.9% -9.3% -1.6% G A S E O U S F U E L S IN U R B A N F L E E T S

NOx +2.7%

+1.6% +4.9% DISTILLATE F U E L OIL

Figure 7. Net effect of gas-powered vehicles on pollutant emissions. Transportation and industrial energy sectors—1975 (million tons/yr.).


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r e t r o f i t program. On t h e r i g h t hand s i d e we see t h e i n c r e a s e s i n e m i s s i o n s by t h e i n d u s t r i a l s e c t o r which would r e s u l t i f t h e i n d u s t r i a l gaseous f u e l s were r e p l a c e d b y a 0.2% s u l f u r c o n t a i n i n g d i s t i l l a t e . We would be t r a d i n g o f f t h e h y d r o c a r b o n and c a r b o n monoxi d e tonnages i n d i c a t e d f o r i n c r e a s e s i n s u l f u r d i o x i d e and p a r t i c u l a t e m a t t e r . The n e t e f f e c t on n i t r o g e n o x i d e s would be n e a r l y a s t a n d o f f b u t even h e r e some d e t e r i o r a t i o n would be e x p e c t e d . The n e t h e a l t h e f f e c t o f such changes i n p o l l u t a n t e m i s s i o n c a n be c a l c u l a t e d on t h e b a s i s o f s e v e r a l published techniques. Using the three techniques summarized i n t h e RECAT (14) r e p o r t , we have c a l c u l a t e d health e f f e c t s rangin 2.5% d e t e r i o r a t i o n numbers a r e m e a n i n g f u l . Summarizing t h i s assessment o f t h e p r o p o s e d r e t r o f i t program f o r s u b s t i t u t i o n o f gaseous f u e l s f o r gasol i n e , we would e x p e c t t h a t : 1) S i g n i f i c a n t r e d u c t i o n s o f h y d r o c a r b o n , CO and N 0 e m i s s i o n s from o l d e r v e h i c l e s would r e s u l t . Howe v e r , t h e s e r e d u c t i o n s would be s m a l l as a p e r c e n t o f t h e e m i s s i o n o f t h e t o t a l v e h i c l e p o p u l a t i o n and t h e y would v a n i s h by t h e e a r l y 1980's. 2) U t i l i z a t i o n o f gaseous f u e l s i n t h e t r a n s p o r t a t i o n s e c t o r would r e q u i r e s u b s t i t u t i o n o f h e a v i e r l i quid f u e l i n the i n d u s t r i a l sector r e s u l t i n g i n i n c r e a s e d i n d u s t r i a l e m i s s i o n s o f SO2, NO and p a r t i c u late. 3) A n e t e n v i r o n m e n t a l e f f e c t o f t h e r e d u c t i o n s o f h y d r o c a r b o n s and CO e m i s s i o n s and t h e i n c r e a s e s i n SO2, NO and p a r t i c u l a t e a n t i c i p a t e d as a r e s u l t o f such a program cannot be u n e q u i v o c a l l y e s t a b l i s h e d . 4) W h i l e t h e economics o f c e r t a i n e x i s t i n g g a s eous f u e l r e t r o f i t s appear a t t r a c t i v e , t h e s e u s u a l l y i n v o l v e f u e l tax concessions or other s p e c i a l circums t a n c e s r e s u l t i n g i n low f u e l c o s t s . 5) I n any mandatory r e t r o f i t program expanding t h e use o f gaseous f u e l s , t h e economy would have t o b e a r t h e c o s t s o f new f u e l s u p p l y and d i s p e n s i n g f a c i l i t i e s , r e t r o f i t t i n g c o s t s f o r b o t h v e h i c l e s and f o r i n d u s t r i e s from w h i c h t h e gaseous f u e l s have been withdrawn and the r e b a l a n c i n g o f r e f i n e r y f a c i l i t i e s t o meet t h e changed p r o d u c t s l a t e . X

x

x


58


Literature

Cited

1. Gaseous Motor F u e l s - An Assessment o f the C u r r e n t and F u t u r e S t a t e s -- American P e t r o l e u m I n s t i t u t e , Committee on E n v i r o n m e n t a l Affairs, API P u b l i c a t i o n No. 4186, August (1973). 2. A l l s u p , J . R. and F l e m i n g , R. D., " E m i s s i o n Characteristics o f Propane as Automotive F u e l " , Bartlesville Energy R e s e a r c h C e n t e r , Bureau o f Mines Report o f I n v e s t i g a t i o n s 7672, (1972). 3. Genslak, S. L., " E v a l u a t i o n o f Gaseous F u e l s f o r A u t o m o b i l e s , " SAE Paper 720125, January (1972). 4. Gaseous F u e l e d V e h i c l e s and the Environment, GSA Symposium, May 24-26 5. B a x t e r , M. C., "Ho E m i s s i o n s , " The Compressed Gas I n d u s t r y and I t s R e l a t i o n s h i p t o the Environment, 58th Annual Meeting, J a n u a r y (1971). 6. E m i s s i o n R e d u c t i o n U s i n g Gaseous F u e l s f o r V e h i c u l a r P r o p u l s i o n , I n s t i t u t e o f Gas Technology, June (1971), PB-201410. 7. B i n t z , L. J . , Kramer, Μ., and Tappenden, Τ. A., "LP-Gas and t h e A u t o m o b i l e C l u b o f Southern California," ASTM-NGPA, NLPGA Symposium on LP-Gas Engine F u e l s , Los A n g e l e s , California, June 27, (1972). 8· McJones, R. W., "Method and System f o r Reducing Oxides o f N i t r o g e n and Other P o l l u t a n t s from I n t e r n a l Combustion E n g i n e s , " U. S. P a t e n t 3,650,255, March 21, (1972). 8a. E n v i r o n m e n t a l P r o t e c t i o n Agency, P o s i t i o n Paper C o n v e r s i o n o f Motor V e h i c l e s t o Gaseous F u e l t o Reduce Air P o l l u t i o n , April (1972). 9. Douglas, L. Α., "Dual F u e l Systems D e s i g n - CNG/ G a s o l i n e , " The Compressed Gas I n d u s t r y and I t s R e l a t i o n s h i p t o t h e Environment, 58th Annual Meeting, January (1971). 10. Diamond, R., "LPG A Now Answer t o Air Pollution," SAE Automotive E n g i n e e r i n g E x p o s i t i o n , January (1971). 11. California I n s t i t u t e o f Technology, E n v i r o n m e n t a l L a b o r a t o r y , " C a l t e c h C l e a n Air C a r P r o j e c t -- Gaseous F u e l s Manual," March 1, (1972). 12. Pollution R e d u c t i o n w i t h C o s t S a v i n g s , U. S. Government G e n e r a l S e r v i c e s A d m i n i s t r a t i o n , GSA DC 7110828.


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SOREM E T A L .

Gaseous Motor Fuels

13. Sagan, V. R., " C u r r e n t and Pending Legislation for Gaseous F u e l s , " ASTM-NGPA-NLGPA Symposium on LP-Gas Engine F u e l s , Los A n g e l e s , California, A p r i l (1972). T h i s paper i s a summary o f API p u b l i c a t i o n No. 4186 w i t h t h e same t i t l e and a u t h o r s f o r p r e s e n t a t i o n to t h e Symposium on C u r r e n t Approaches t o Automotive E m i s s i o n C o n t r o l - ACS M e e t i n g , Los A n g e l e s , A p r i l 1, 1974. The f u l l p u b l i c a t i o n i s a v a i l a b l e from t h e American P e t r o l e u m I n s t i t u t e , 1801 Κ S t r e e t , N.W., Washington, D.C. 20006.


59

4 Fuel Volatility as an Adjunct to Auto Emission Control R. W . H U R N , B. H . E C C L E S T O N , and D . B.

ECCLESTON

Bartlesville Energy Research Center, Bureau of Mines, Bartlesville, Okla. 74003

Abstract Late-model vehicles were used i n an experimental study of the interaction of fuel v o l a t i l i t y with emissions and associated fuel economy. V o l a t i l i t y characteristics of the test fuels ranged between 7 and 14 pounds Reid vapor pressure; 50 pet point between 130° and 240° F; and 90 pct point between 190° and 370° F. Choke settings of each vehicle were adjusted as needed for choke action appropriate to each fuel's v o l a t i l i t y . Midrange and back-end v o l a t i l i t y were found to influence emissions but in a possibly complex interaction of the two. The principal influence i s upon emissions during cold start and warmup. Within the vapor pressure limits traditional of U.S. fuels, vapor pressure and fuel front-end v o l a t i l i t y were found to have only slight effect upon either emissions or fuel economy. Results show that i n this study, reduced hydrocarbon and carbon monoxide emissions are associated with the fuels of lower back-end v o l a t i l i t y . Among the fuels tested higher fuel economy values were found with the heavier fuels. However, the d i f f e r ences in fuel economy may--and probably do--result from d i f f e r ences i n mixture stoichiometry and fuel heating value rather than from differences i n fuel v o l a t i l i t y , per se. Introduction In 1967, the Bureau of Mines, in cooperation with the American Petroleum Institute, began a series of experiments to obtain more comprehensive information on the effects of fuel v o l a t i l i t y on exhaust emissions. Results of the API-sponsored studies showed that fuel v o l a t i l i t y does affect exhaust emissions but only i n a complex relationship in which vapor pressure mid-range and back-end v o l a t i l i t y interact. Briefly, i t was concluded from the 1967-71 studies that, for the 1966-69 model year cars that were tested, and for operation at moderate ambient temperatures—

60


4.

HURN ET AL.

Fuel Volatility

1.

61

Exhaust hydrocarbon (HC) and carbon monoxide (CO) were increased when vapor pressure was decreased below 9 pounds Reid vapor pressure (EVP), and 2. HC and CO generally were decreased by increasing mid-range v o l a t i l i t y as compared with typical current practice. With this work having established evidence of a strong relationship between fuel v o l a t i l i t y and exhaust emissions, the Bureau conducted follow-on studies to delineate more clearly the effects of mid-range and back-end v o l a t i l i t y . The work sought answers to two questions i n particular: 1. If fuel v o l a t i l i t y i s increased, what i s the l i k e l y effect on emissions and fuel economy for vehicles currently on the road? 2. If fuel v o l a t i l i t y i s increased, and with minor modifications to carburetion, can emissions be held the same or lowered while increasing fue To provide some answer questions, experiment designed to use 12 fuels i n 3 cars: (1) A compact car with a 250-CID engine and single-barrel carburetor, (2) a light sedan with 350-CID engine and 2-bbl carburetor, and (3) an intermediate sedan with 350-CID engine and 4-bbl carburetor. A l l were equipped with automatic transmission and with power options typically sold with that class of vehicle. The fuels were designed to represent, insofar as possible, options for v o l a t i l i t y change selectively within the front, midrange, or back-end portion of the fuel boiling range. Combinations of these selective changes also were designed into the fuels. Emissions were measured using analytical instruments and the driving cycle as specified for the 1975 Federal test procedure. A l l work was done at controlled temperature and humidity; data were taken at test temperatures of 20°, 55°, and 90° F. This i s a summary report of findings, and except for one reference to test data taken at 90 F, references are limited to the data obtained at 55° F as being i l l u s t r a t i v e of trends that were represented generally. e

Discussion Turning now to a more detailed discussion of the study, l e t me f i r s t review b r i e f l y the v o l a t i l i t y characteristics of the 12 test fuels. Vapor pressures of the fuels ranged roughly between 7% and 14 pounds. Higher vapor pressure fuels were excluded from the 90° F test; the lower vapor pressure fuels were excluded from tests made at 20° F. The 10 pet boiling points of the fuels ranged from about 100° F i n one of the more v o l a t i l e f u e l s t o 146° F i n one of the least v o l a t i l e . The 50 pet points of the fuels ranged between about 130° and 250° F among the 12 fuels; the 90 pet point was varied between roughly


62


185° and 375° F. As indicated earlier, various combinations of these fuel characteristics were used in designing the 12 fuels. The range of characteristics i s summarized below. Test Fuels V o l a t i l i t y Characteristics Range of Values Vapor Pressure, RVP, l b .

7.4

-

14.0

10 pet point, °F

100.0

-

146.0

50 pet point, °F

130.0

-

254.0

90 pet point, °F

184.0

376.0

Total of 12 fuel A detailed inspection of the emissions data showed unmistakable differences attributable to fuels. No one v o l a t i l i t y characteristic (i.e., RVP, 10 pet point, 50 pet point, or 90 pet point) was shown to act alone i n a dominant fashion. However, the combination of the 50 pet and 90 pet boiling points, a measure of v o l a t i l i t y across the f u l l back half, does permit correlation with emissions. At least the combination appears to exert a greater influence than any other one v o l a t i l i t y characteristic or any other combination of vapor pressure, and 10, 50, or 90 pet boiling point. In this paper we have, therefore, elected to show the relationship that was found to exist between emissions and the v o l a t i l i t y of the fuel back-end as expressed i n the sum of the 50 pet and 90 pet boiling points. In figure 1 and i n following figures, v o l a t i l i t y as expressed by the sum of the 50 pet and 90 pet boiling points w i l l be shown as a horizontal variable. The observed emissions are shown as the v e r t i c a l coordinate. Also, in figure 1 as in those following, the data points are shown for one vehicle, a compact car. The trend of data for the other cars, the intermediate and the light sedan, are shown by the dashed curves. These data reflect a general trend, but although the trend is real, there i s nonetheless only a loose relationship between the v o l a t i l i t y characteristics and exhaust emissions. If the data i n figure 1 were the only measurements available, they would not be significant in indicating the trends. However, as i s to be seen in the figures to follow, other measurements also indicate trend lines, and taken together there i s a high degree of confidence in the trends that are shown. Therefore, we conclude that HC emissions tend to be somewhat increased with back-end v o l a t i l i t y either increased or decreased from the intermediate range of the v o l a t i l i t y characteristic.


4.

HURN E T AL.

Fuel Volatility

63

Oxides of nitrogen (NO ) also i s shown to be responsive to the fuel back-end v o l a t i l i t y characteristic (Fig. 2). The data are internally self-consistent and consistent between automobiles, and as earlier indicated, we believe that the trends exist as shown. The explanation for increased NO with the lower v o l a t i l i t y fuels probably relates not to volatiïity characteristic, per se, but rather to the stoichiometry of the a i r - f u e l mixture and to heat content of the fuel. This point i s explored further i n discussions to follow. Carbon monoxide data (Fig. 3) follow the same general trends as shown for hydrocarbon; however, the effect does appear to be somewhat more pronounced i n showing CO increased with the fuels that have 50 pet plus 90 pet point values below the 450° to 500° F range. Also consistent with the hydrocarbon data, CO emissions were found t increas with back-end v o l a t i l i t decreased well beyond th In general, trends fo y consistent i n that CO and HC move together and increased Ν 0 emissions are associated with decreased CO and HC. The effect of increased emissions with fuels of d i s t i n c t l y heavier back-ends i s shown accentuated i n the 90° F data for the light sedan (Fig. 4). In the case of these data, i f the two deviated points "A" and "Β" are not considered, emissions are shown to increase i n a consistent pattern. However, i f the backhalf v o l a t i l i t y i s characterized by low mid-point v o l a t i l i t y , but combined with high back-end v o l a t i l i t y , point "A", emissions are increased over that of a fuel typically more representative. If, on the other hand, the same average v o l a t i l i t y characteris tics are achieved by combining high mid-range with low back-end v o l a t i l i t y , point "B", CO emission i s decreased. This effect appeared to be consistent with the three vehicles; therefore, we conclude that emissions reduction i s best served by incor porating high mid-range v o l a t i l i t y i n the fuel. One question to be answered from results of the tests was whether minor modifications to the carburetion system—to be made i n connection with increased v o l a t i l i t y — c o u l d be used advantageously as an emissions control measure. To obtain information on this point, emissions were measured on the vehicles both as set to standard specifications and with the choke schedule modified to effect less choking and more rapid choke release. The results were, i n a l l cases, to realize marked reduction i n emissions during cold starts by modifying the choking schedule toward less choking. Using a standard choke installation, CO emissions were increased by about 4 grams per mile (over the emissions measured with the reference fuel) by increasing fuel v o l a t i l i t y at the 10 pet point. However, with a modified choke schedule (and s t i l l achieving satisfactory vehicle operation), CO emissions from the fuel with v o l a t i l i t y increased at the 10 pet point decreased by about 4 grams per mile from the level measured with the reference fuel. In like manner, χ



40 55°F ambient

35

ω 125

I

''S

>ν Compact

in

Intermediate

^

•

•

20

Ρ

Standard

Μ

"5 10

300

ι

I

ι

I

ι

I

400 500 600 SUM OF 50 8 9 0 % POINTS, F ^ Higher volatility e

Figure 1. Hydrocarbon emissions response to mid-range and back-end volatility 10

55° F ambient

a. m

8

.·= Ε

7

Intermediate

m

Ε

S 6 ο

ζ

Standard 5

Compact 300

I

ι

400 500 600 SUM OF 50 a 9 0 % POINTS, F «* Higher volatility e

Figure 2. NO response to mid-range and back-end volatility x


4.

Fuel Volatility

HURN E T AL.

65

40 55°F ambient 35

10

300

400 500 600 SUM OF 50 8 9 0 % POINTS, °F Higher volatility

Figure 3. Carbon monoxide response to mid-range and back-end volatility 35 30

9 0 ° F ambient Std. sedan

S 25 σ> ΐ 20

Low mid-range vol. Λ High back-end vol. J

%

Α

in

Ε

15 ο ο

10 High mid-range vol. Low back-end vol.

300

400 500 600 SUM OF 50 ft 9 0 % POINTS, °F Higher volatility

Figure 4. Carbon monoxide response to mid-range and back-end volatility


66


significant reduction i n CO emissions was achieved using a modified choke schedule when fuel v o l a t i l i t y was increased at the 50 pet point, and also when v o l a t i l i t y was increased throughout the back half of the boiling curve. However, consistent with earlier evidence, increasing v o l a t i l i t y at the 90 pet point reduced emissions less significantly than did the other fuel modifications just cited. These relationships of v o l a t i l i t y adjustments to emissions are summarized below: Effect of V o l a t i l i t y Change i n CO Emissions—55° F Ambient Cold Start Fuel Modification

Effect on CO Emissions (gm/mile) Standard

Modified

V o l a t i l i t y increased at 10 pet point

+4.2

- 3.8

at 50 pet point

-3.0

-17.4

at 90 pet point

+4.6

- 2.0

throughout midrange

+9.8

- 9.8

Fuel economy was determined for a l l of the tests. Results showed unmistakable response to fuel change. As i s to be observed from the curves of figure 5, fuel economy improved measurably with the heavier fuels and the effect was consistent among the three vehicles. Conceivably, the change i n economy could be associated with v o l a t i l i t y characteristics, per se; but there i s no evidence that this i s the case. Quite the contrary, i t would appear to be due to change i n air-fuel ratio and to differences i n heating value between the fuels. When associated with mixture ratio, fuel economy was found to be directionally consistent with the change i n a i r - f u e l ratio that was measured for each of the tests (Fig. 6). More s i g n i ficant, however, fuel economy i s believed to respond to the energy content of the respective fuels as shown estimated i n figure 7. As a measure of the rough correspondence found between fuel economy and heating value, i t i s noted that fuel economy between the worst and best cases differed by about 11 pet. The corresponding difference i n heating value of the fuels i s about 17 pet. We conclude, therefore, that there i s no evidence that fuel v o l a t i l i t y , per se, affected fuel economy, but that the observed differences are due to variations i n heating value of the fuel and associated influence upon the stoichiometry of the a i r - f u e l mixture.


4.

HURN E T AL.

Fuel Volatility

67

55° F ambient

Compact 11% increase

Intermediate

Standard

_1_ 300

J_

400 500 600 SUM OF 50 8 9 0 % POINTS, °F Higher volatility

Figure 5. Fuel economy at 55 F ambient



300

400 500 SUM OF 50 a 9 0 % POINTS, °F

600

Higher volatility

Figure 6.

Relationship of fuel economy to volatility. Data from compact car.

130 Lu

125 I20h-

2 Ζ LU Ο

ο >ο or Lu

115 I 10 Ι05Η 100 300

400 500 SUM OF 50 a 9 0 % POINTS, °F Higher volatility

Figure 7.

600

—

Energy content of test fuels


5 Pre-engine Converter Ν. Y. C H E N

and

S. J.

LUCKI

Mobil Research and Development Corp., Princeton

I.

08540

and Paulsboro

08066, N. J.

Introduction

D u r i n g t h e p a s t decade, efforts t o reduce vehicu lar pollutant e m i s s i o n have i n c l u d e d s u g g e s t i o n s for the removal o f l e a d from g a s o l i n e o r for use of alter native fuels such as H and low m o l e c u l a r weight hy d r o c a r b o n s which a r e known t o have h i g h octane v a l u e s and good b u r n i n g characteristics ( 1 ) , (2), (3). Lead removal, which is a l r e a d y b e i n g implemented, r a i s e s t h e octane r e q u i r e m e n t o f t h e fuel. The i n c r e a s e d s e v e r i t y r e q u i r e d in refining t o produce such h i g h o c t a n e g a s o l i n e d e c r e a s e s t h e g a s o l i n e yield p e r bar rel o f crude and, t h e r e f o r e , i n c r e a s e s crude oil con sumption and demands more refining c a p a c i t y in t h e f a c e o f an impending energy crisis. Use o f low molec ular weight h y d r o c a r b o n s is difficult t o implement because o f s a f e t y h a z a r d s and l a c k o f n a t i o n w i d e stor age and distribution systems. The c o n c e p t o f a t t a c h i n g a catalytic reactor to an internal combustion engine c o n v e r t i n g liquid hydro carbons t o gaseous f u e l was d i s c l o s e d i n a p a t e n t i s s u e d t o Cook (4) in 1940. R e c e n t l y , it has r e c e i v e d some renewed a t t e n t i o n . Newkirk et al (2), (3) de s c r i b e d their c o n c e p t o f an on-board p r o d u c t i o n o f C O / H m i x t u r e by steam r e f o r m i n g o f g a s o l i n e fuel. A U.S. p a t e n t was i s s u e d t o W. R. Grace Company in 1972 (5) on a m o b i l e catalytic c r a c k i n g u n i t in c o n j u n c t i o n w i t h a mobile internal combustion e n g i n e . I n 1973, Siemens Company (6) o f Germany announced a "splitting c a r b u r e t o r " which b r e a k s up g a s o l i n e and related f u e l s i n t o burnable gases. The jet p r o p u l s i o n l a b o r a t o r y o f NASA (7) is investigating t h e c o n c e p t o f t h e gener a t i o n o f hydrogen f o r use as an a d d i t i v e t o g a s o l i n e in internal combustion e n g i n e s . While little technical data are available, these 2

2

2

69


70

AUTOMOTIVE

EMISSIONS

CONTROL

developments appear t o r e p r e s e n t d i f f e r e n t approaches of adapting e s t a b l i s h e d i n d u s t r i a l c a t a l y t i c processes d e s i g n e d f o r a narrow range o f o p e r a t i n g c o n d i t i o n s t o moving v e h i c l e s which must o p e r a t e from i d l i n g t o f u l l throttle. To d e s i g n a r e a c t o r system c a p a b l e o f o p e r a t i n g s a t i s f a c t o r i l y under f u l l t h r o t t l e c o n d i t i o n s r e q u i r e s e i t h e r a l a r g e r e a c t o r o r an u n u s u a l l y a c t i v e and e f f i c i e n t c a t a l y s t . A s t a n d a r d 300 cu. i n . automotive engine a t f u l l t h r o t t l e consumes f u e l a t a r a t e o f about 10 c c / s e c . I f t h e r e a c t o r were o p e r a t i n g a t 1-2 LHSV ( v o l / v o l / h r . ) , i . e . , a t t h e t h r o u g h p u t o f an average i n d u s t r i a l r e a c t o r , t h e engine would r e q u i r e a c a t a l y s t bed volume o f 18-36 l i t e r s (4.8 - 9.5 gallons) - f a r l a r g e r than the carburetor i t r e p l a c e s The n e c e s s i t y o f a operation plus accessor p r e h e a t e r , e t c . , would make t h e system i m p r a c t i c a l l y b u l k y and t o o slow t o warm up. T h e r e f o r e , a workable system c l e a r l y depended on t h e d i s c o v e r y o f new c a t a lysts o f high a c t i v i t y . To reduce t h e s i z e o f t h e r e a c t o r t o t h a t o f a c a r b u r e t o r , an i n c r e a s e i n c a t a l y t i c a c t i v i t y by a f a c t o r o f a t l e a s t 50-100 i s necessary. In a d d i t i o n t o t h e problem o f t h e c a t a l y t i c r e a c t o r volume, t h e l i f e o f t h e c a t a l y s t i s a l s o o f c r i t i c a l importance. Most i n d u s t r i a l c a t a l y s t s r e q u i r e p e r i o d i c o x i d a t i v e r e g e n e r a t i o n i n a m a t t e r o f minutes a f t e r operation t o maintain t h e i r effectiveness. A c a t a l y t i c c r a c k i n g c a t a l y s t , s u c h as t h a t p r o p o s e d i n the p a t e n t i s s u e d t o Grace (5), r e q u i r e s f r e q u e n t regeneration. An example d e s c r i b e d i n t h i s p a t e n t s t a t e s t h a t w i t h a z e o l i t e - c o n t a i n i n g c a t a l y s t , 2% o f the f u e l was c o n v e r t e d t o coke i n the c a t a l y t i c converter. We e s t i m a t e t h a t under t h e p r o p o s e d o p e r a t i n g c o n d i t i o n s , each volume o f c a t a l y s t c o u l d p r o c e s s no more t h a n 10 volumes o f f u e l b e f o r e s u f f i c i e n t coke (20%) would have d e p o s i t e d on t h e c a t a l y s t t o d e a c t i v a t e i t . Thus, even i f t h e c a t a l y s t were a c t i v e enough t o o p e r a t e a t 100 LHSV, no more t h a n 6 minutes o f c o n t i n u o u s o p e r a t i o n between o x i d a t i v e r e g e n e r a t i o n s would be f e a s i b l e . In t h i s p a p e r we p r e s e n t e x p e r i m e n t a l s t u d i e s w i t h a c a t a l y s t t h a t overcomes many o f t h e s e l i m i tations. II.

Experimental

1. Equipment. To demonstrate t h e performance o f the new c a t a l y s t system, t h e c a t a l y t i c r e a c t o r was


5.

CHEN

AND

LUCKI

Vre-engine Converter

71

a t t a c h e d t o a s t a n d a r d motor knock T e s t E n g i n e , Method IP44/60 ( 8 ) , b y p a s s i n g t h e c a r b u r e t o r . F i g u r e 1 shows a s c h e m a t i c diagram o f t h e c a t a l y t i c u n i t . The r e a c t o r c o n s i s t e d o f two 3/4 i n c h O.D. χ 18 i n c h e s s t a i n l e s s s t e e l c y l i n d e r s mounted v e r t i c a l l y , one on t o p o f t h e o t h e r , and c o n n e c t e d i n s e r i e s . The t o p chamber s e r v i n g as t h e p r e h e a t e r c o n t a i n e d 82 c c o f 3 mm diam e t e r g l a s s beads? t h e c a t a l y s t bed (5 i n c h e s long) i n t h e bottom chamber c o n s i s t e d o f 24 c c o f 20/30 mesh c a t a l y s t mixed w i t h 12 c c o f 8/14 mesh V y c o r c h i p s . D u r i n g t h e r m a l r u n s , V y c o r c h i p s were s u b s t i t u t e d f o r the c a t a l y s t . Both c y l i n d e r s were e l e c t r i c a l l y h e a t e d . Liquid f u e l f l o w was metered w i t h a r o t a m e t e r . Air-fuel r a t i o was m o n i t o r e d by O r s a t a n a l y s i s o f t h e exhaust 2. Test Fuels used: (1) an 86 r e s e a r c h o c t a n e (R+0) and 79.5 motor o c t a n e (M+0) r e f o r m a t e o b t a i n e d from M o b i l ' s P a u l s b o r o Refinery containing: 23.4 wt. % n - p a r a f f i n s , 33.9% branched p a r a f f i n s , 1.2% o l e f i n s , 1.0% naphthenes and 40.5% a r o m a t i c s , and (2) a Kuwait naphtha o f 40.5 c l e a r motor o c t a n e (M+O). III.

R e s u l t s and D i s c u s s i o n s

1. Upgrading o f a C5-4Q0°F r e f o r m a t e . The experiments were c a r r i e d o u t by c h a r g i n g t h e l i q u i d f u e l s t o r e d i n a p r e s s u r i z e d r e s e r v o i r (4500 cc) a t 38 cc/min. c o n t i n u o u s l y f o r about 2 hours t h r o u g h the c a t a l y t i c c o n v e r t e r d u r i n g which time t h e motor octane number o f t h e r e a c t o r e f f l u e n t was d e t e r m i n e d e v e r y 30 m i n u t e s . A t t h e end o f 2 h o u r s , t h e r e a c t o r was c o o l e d t o 800°F w i t h purge n i t r o g e n w h i l e t h e f u e l r e s e r v o i r was b e i n g r e f i l l e d . *The experiment was t h e n repeated. Two c a t a l y s t s were examined, v i z . , a new s t a b l e z e o l i t e c a t a l y s t (12 gms) and a commercial z e o l i t e c r a c k i n g c a t a l y s t (16 gms), which had p r e v i o u s l y been aged f o r 2 hours i n a t e s t d e s c r i b e d later. The f e e d r a t e c o r r e s p o n d s t o a weight h o u r l y space v e l o c i t y o f 140 and 93, r e s p e c t i v e l y . The r e a c t o r was m a i n t a i n e d a t between 910 and 920°F. Octane r a t i n g o f t h e r e a c t o r e f f l u e n t as a f u n c t i o n o f t h e c u m u l a t i v e on-stream time i s shown i n F i g u r e 2. During the f i r s t 2 hours, the s t a b l e z e o l i t e r a i s e d t h e o c t a n e number from t h e t h e r m a l v a l u e o f 79.6 t o 85 M+0. The octane dropped 2 numbers d u r i n g t h e n e x t two hours and m a i n t a i n e d above 82 M+0 f o r t h e next seven h o u r s . The aged commercial z e o l i t e c a t a l y s t , on t h e o t h e r hand, produced no a p p r e c i a b l e c o n v e r s i o n


72

AUTOMOTIVE

EMISSIONS

CONTROL

I. FUEL RESERVOIR 2. ROTAMETER 7—

3. PREHEATER

7-

5. EFFLUENT LINE TO INTAKE MANIFOLD 6. THERMOWELLS

7—

7. THERMOCOUPLES Θ. NITROGEN 9. FUEL LINE Figure 1. Diagram of the catalytic unit

86

82

80

» NEW STABLE ZEOLITE

, COMMERCIAL ZEOLITE CRACKING CATALYST » THERMAL

8 10 12 ON STREAM TIME: HR.

Figure 2. Effect of on-stream time on octane rating—knock test engine. 79.5 M + Ο, C -4O0 reformate, 915°F, 95 LHSV. 5


5.

CHEN

AND

LUCKI

Pre-engine Converter

73

under the e x p e r i m e n t a l c o n d i t i o n s , i . e . , a t t h i s h i g h space v e l o c i t y . 2. Upgrading o f a C£-350 Kuwait naphtha. After 12 hours o r o p e r a t i o n w i t h o u t r e g e n e r a t i o n u s i n g r e f ormate as t h e f e e d , t h e f u e l was s w i t c h e d t o the low o c t a n e v i r g i n naphtha and t h e t e s t c o n t i n u e d o v e r t h e aged s t a b l e z e o l i t e c a t a l y s t f o r an a d d i t i o n a l two 2-hours runs b e f o r e t h e experiment was t e r m i n a t e d due t o a m e c h a n i c a l m a l f u n c t i o n . The r e s u l t o f t h e napht h a t e s t i s summarized i n F i g u r e 3. Shown i n t h e same f i g u r e a r e t h e r e s u l t s o v e r a f r e s h commercial c a t a l y s t and the t h e r m a l r u n . I t i s i n t e r e s t i n g t o note t h a t a b o o s t o f 22 motor o c t a n e numbers was r e g i s t e r e d by the aged s t a b l e z e o l i t e c a t a l y s t w h i l e the f r e s h commercial z e o l i t e run recorded a g a i tively. 3. Shape S e l e c t i v e C r a c k i n g . I n a d d i t i o n t o t h e i r excellent burning q u a l i t i e s , i . e . , non-polluting combustion, l i g h t hydrocarbons have volume b l e n d i n g o c t a n e r a t i n g s ranged between 100 and 150 r e s e a r c h c l e a r numbers (R+0). Thus low octane l i q u i d s s u c h as v i r g i n naphtha and m i l d l y reformed r e f o r m a t e can be upgraded by p a r t i a l l y c o n v e r t i n g them t o l i g h t h y d r o carbons i n t h e p r e - e n g i n e c o n v e r t e r , and f e e d i n g the e n t i r e r e a c t o r e f f l u e n t d i r e c t l y i n t o the engine. A t y p i c a l d i s t r i b u t i o n of reaction products i s shown i n T a b l e I f o r t h r e e samples c o l l e c t e d when a b l e n d o f C6 h y d r o c a r b o n s was p a s s e d o v e r t h e s t a b l e z e o l i t e c a t a l y s t a t 1 atm. and 900°F. The r e s u l t s c l e a r l y show t h a t t h e c a t a l y s t e x h i b i t e d p r e f e r e n t i a l shape s e l e c t i v e c r a c k i n g i n the o r d e r o f n- > monomethyl- > dimethyl-paraffins. Thus isomers h a v i n g the lower o c t a n e r a t i n g s a r e p r e f e r e n t i a l l y c r a c k e d . The C4 minus c r a c k e d p r o d u c t s a r e h i g h l y o l e f i n i c and some C7+ a r o m a t i c s a r e formed by secondary r e a c t i o n s . The added advantage o f shape s e l e c t i v e c r a c k i n g i n the o r d e r o f o c t a n e r a t i n g i s i l l u s t r a t e d by the c r a c k i n g o f a 61 r e s e a r c h o c t a n e Udex r a f f i n a t e , a low o c t a n e p r o d u c t from t h e s o l v e n t e x t r a c t i o n o f aromati c s from a r e f o r m a t e . I n F i g u r e 4, c u r v e 1 shows the c a l c u l a t e d o c t a n e number o f t h e r e a c t o r e f f l u e n t v s . wt. % l i q u i d c r a c k e d t o C4" l i g h t h y d r o c a r b o n s . To produce a 91 R+0 f u e l , about 4 9 % o f t h e l i q u i d i s cracked. E x a m i n a t i o n o f the c o m p o s i t i o n o f the r a f f i n a t e shows t h a t the s t r a i g h t c h a i n p a r a f f i n s h a v i n g an average o c t a n e r a t i n g o f 17 R+0 r e p r e s e n t 27% o f the l i q u i d . Curve I I shows t h a t when t h e s e



+

ΔΟΝ/%

Conversion

C4~% C o n v e r s i o n

ΔΟΝ

R+0

9

Methane Ethane, Ethene Propane Propene Butanes Butènes 2,2-D i m e t h y l b u t a n e 2,3-Dimethylbutane 2-Methylpentane Hexane 1-hexene Benzene C 7 Aromatics

wt. %

—

—

77.1

—

9.1 5.4 13.5 24.5 47.5

—

—

—

—

—

—

Feed

14.9 18.9

19.7 25.8

0.79

92.0

96.8

0.76

0.4 2.5 6.1 5.8 1.5 2.6 8.6 5.4 10.7 10.4 40.8 5.1

100

0.6 3.3 9.7 7.0 2.1 3.1 8.6 5.4 8.5 6.9 38.1 6.7

55

WHSV

0.93

8.0

7.4

84.5

0.2 0.8 1.1 3.6 0.3 2.0 8.6 5.4 11.7 16.1 44.4 5.6

200

P r o d u c t D i s t r i b u t i o n a t 90Q°F

TABLE I

5.5 0.0 37.0 71.8 19.8

55

5.5 0.0 20.7 57.6 14.1

100

5.5 0.0 13.3 34.3 6.5

200

% Conversion

5.

CHEN

AND

LUCKI


75

65

, AGED STABLE ZEOLITE

Ο +

2 55 COMMERCIAL ZEOLITE CRACKING CATALYST

1.0

Figure 3.

1.5

J

2.0 2.5 3.0 ON STREAM TIME: HR.

I

3.5

I

L

Effect of on-stream time on octane rating. 405 Μ + Ο, Kuwait naph tha, 915°F, 95 LHSV.


76

AUTOMOTIVE

EMISSIONS

CONTROL

n - p a r a f f i n s a r e s e l e c t i v e l y c r a c k e d , t h e octane r a t i n g o f t h e f u e l c a n be b o o s t e d t o ~ 90 R+0 w i t h o n l y 27% c o n v e r s i o n . An i d e a l shape s e l e c t i v e c r a c k i n g would y i e l d c u r v e I I I w h i c h r e p r e s e n t s t h e most e f f i c i e n t route o f upgrading. The o c t a n e r a t i n g o f t h e f u e l i s b o o s t e d t o 100 R+0 w i t h l e s s t h a n 4 0 % conversion. 4. C a t a l y s t l i f e and s t a b i l i t y toward o x i d a t i v e reqene r a t i o n . P r e l i m i n a r y d a t a o b t a i n e d i n bench s c a l e m i c r o - r e a c t o r (9) s t u d i e s u s i n g t h e r e f o r m a t e o v e r b o t h t h e f r e s h c a t a l y s t s and t h e r e g e n e r a t e d c a t a l y s t s showed t h a t t h e c a t a l y s t was s t a b l e toward a i r r e g e n e r a t i o n and c a t a l y s t a c t i v i t y was r e s t o r e d a f t e r regeneration A t 100 WHSV t h e c a t a l y s t ap p e a r e d t o have a u s e f u corresponding t o processing pound pe pound o f c a t a l y s t . A t lower space v e l o c i t i e s , t h e c y c l e l i f e appeared t o be much l o n g e r than 7 hours, a l t h o u g h t h e amount o f f u e l p r o c e s s e d o v e r t h e same l e n g t h o f o p e r a t i n g hours was l e s s than t h a t a t 100 WHSV. IV.

Conclusions

A h i g h l y a c t i v e , s t a b l e and shape s e l e c t i v e zeol i t e c r a c k i n g c a t a l y s t overcomes a major p r o b l e m i n the a p p l i c a t i o n o f t h e c o n c e p t o f p r e - e n g i n e convers i o n t o a moving v e h i c l e . The c a t a l y s t i s a c t i v e enough t o o p e r a t e a t above 100 LHSV and 900°F. The volume o f a c a t a l y s t b e d f o r a 300 cu. i n . engine capable o f o p e r a t i n g s a t i s f a c t o r i l y a t f u l l t h r o t t l e would be l e s s than 360 c c - a manageable volume from b o t h s i z e and warm-up c o n s i d e r a t i o n s . The c a t a l y s t has t h e c a p a c i t y o f p r o c e s s i n g more t h a n 700 volumes o f f u e l p e r volume o f c a t a l y s t . F o r a 360 c c c a t a l y s t bed, t h i s c o r r e s p o n d s t o p r o c e s s i n g 66.5 g a l l o n s o f f u e l o r about a d r i v i n g range o f 800 t o 1000 m i l e s b e f o r e a i r r e g e n e r a t i o n would be n e c e s s a r y . The c a t a l y s t appears s t a b l e toward o x i d a t i v e r e g e n e r a t i o n and i t s c a t a l y t i c a c t i v i t y c a n be f u l l y r e s t o r e d . Since t h e r e q u i r e d volume o f c a t a l y s t b e d i s s m a l l enough, segmented o r m u l t i p l e r e a c t o r s c o u l d be used t o accomp l i s h c r a c k i n g o p e r a t i o n and r e g e n e r a t i o n a t a l l times. Literature Cited 1.

C o r b e i l , R. J. and G r i s w o l d , S. S., P r o c . Int. C l e a n Air Congr., 2nd 1970, p . 624 (1971).


5.

CHEN

2.

3. 4. 5. 6. 7. 8. 9.

AND

LUCKI


Newkirk, M. S. and A b e l , J. L., p a p e r No. 720670 p r e s e n t e d a t New E n g l a n d S e c t i o n M e e t i n g , S o c i e t y o f Automotive E n g i n e e r s , November 2, 1971. U. S. P a t e n t 3,682,142 a s s i g n e d t o I n t e r n a t i o n a l M a t e r i a l s Corp., August 8, 1972. U. S. P a t e n t 2,201,965 t o John T. Cook, May 21, 1940. U. S. P a t e n t 3,635,200 a s s i g n e d t o W. R. Grace and Company, J a n u a r y 18, 1972. New York Times, F e b r u a r y 11, 1973. New York Times, September 17, 1973. IP S t a n d a r d for P e t r o l e u m and its P r o d u c t s , P a r t II, 2nd Ed. I n s t . Petrol., London, 1960. Chen, Ν. Y. and L u c k i , S. J., I n d . Eng. Chem. P r o c e s s Des. D e v e l o p (1971) 10 71


^7

6 Low Emissions Combustion Engines for Motor Vehicles H E N R Y K.

NEWHALL

Chevron Research Co., Richmond, Calif. 94802

During the past 10-15 years, very significant advances i n controlling exhaust emissions from automobile power plants have been made. I n i t i a l l y , careful readjustment an (1). More recently, highly effective exhaust treatment devices requiring a minimum of basic modification to the already highly developed internal combustion engine have been demonstrated. These are based on thermal and/or catalytic oxidation of hydrocarbons (HC) and carbon monoxide (CO) i n the engine exhaust system (2,3,4). Nitrogen oxide (NO ) emissions have been reduced to some extent through a combination of retarded ignition timing and exhaust gas recirculation (EGR), both factors serving to diminish severity of the combustion process temperature-time history without substantially altering design of the basic engine (5). Basic combustion process modification as an alternative means for emissions control has received less attention than the foregoing techniques, though it has been demonstrated that certain modified combustion systems can i n principle yield significant pollutant reductions without need for exhaust treatment devices external to the engine. Additionally, it has been demonstrated that when compared with conventional engines controlled to low emissions levels, modified combustion processes can offer improved fuel economy. Nearly all such modifications involve engine designs permitting combustion of fuel-air mixtures lean beyond normal i g n i tion limits. As will be shown, decreased mean combustion temperatures associated with extremely lean combustion tend to limit the rate of n i t r i c oxide (NO) formation and, hence, the emission of NO . At the same time, the relatively high oxygen content of lean mixture combustion products tends to promote complete oxidation of unburned HC and CO provided that combustion gas temperatures are sufficiently high during late portions of the engine cycle. The purpose of this paper i s to present an overall review of the underlying concepts and current status of unconventional X

X


6.

N E W H A L L

Low Emissions Combustion Engines

79

engines employing modified combustion as a means for emissions control. Detailed findings related to specific power plants or to specific applications w i l l be treated by the papers which follow. Throughout the paper exhaust emissions w i l l be compared with emissions standards legislated for the years 1975 and 1976. As a result of Environmental Protection Agency (EPA) actions suspending the 1975 HC and CO standards and the 1976 N0 standard, several sets of values exist. These are l i s t e d i n Table I and i n the text X

Table I Federal Exhaust Emissions Standards, Grams/Mile 1

Statu tory HC CO Ν0

1

χ

0.41 3.4 3.0

1975 Interi U.S. California 0.9 9.0 2.0

1.5 15 3.1

tory

U.S.

California

tory

0.41 3.4 0.4

0.41 3.4 2.0

0.41 3.4 2.0

0.41 3.4 0.4

As measured using 1975 CVS C-H procedure.

w i l l be referenced either as statutory (original standards as set by the Clean A i r Act Amendment of 1970) or as interim standards as set by the EPA. Theoretical Basis for Combustion Modification Figure 1 has been derived from experimental measurements (6) of the rate of NO formation i n combustion processes under condi tions typical of engine operation. This figure demonstrates two major points related to control of N0 emissions: f i r s t , the slow rate of NO formation relative to the rates of major combus tion reactions responsible for heat release and, second, the strong influence of fuel-air equivalence ratio on the rate of NO formation. Experimental combustion studies (7) employing "well-stirred reactors" have shown that hydrocarbon-air combustion rates can be correlated by an expression of the form X

Ν

, Gram-Moles/Liter-Second 0

2

=4 8

y-F""

ÂS?7*


80

AUTOMOTIVE

EMISSIONS

CONTROL

where: β

Ν moles reactants consumed per second V = combustion volume ρ = total pressure For conditions typical of engine operation, this expression yields a time of approximately 0.1 ms for completion of major heat release reactions following ignition of a localized parcel of fuel-air mixture within the combustion chamber. Comparison with Figure 1 shows that the time required for formation of s i g n i f i cant amounts of NO i n combustion gases i s at least a factor of 10 greater. Thus, i n principle, energy conversion can be effected i n times much shorter than required for NO formation. In the con ventional spark ignition engine, the relatively lengthy flame travel process permits peratures s u f f i c i e n t l y Figure 2, which consolidates the data of Figure 1, indicates that maximum rates of NO formation are observed at fuel-air equivalence ratios around 0.9 (fuel lean). For richer mixtures, the concentrations of atomic and diatomic oxygen, which p a r t i c i pate as reactants i n the formation of NO i n combustion gases, decrease. On the other hand, for mixtures leaner than approxi mately 0.9 equivalence ratio, decreasing combustion temperatures result i n lower NO formation rates. Figure 2 serves as a basis for combustion process modifica tion. Operation with extremely r i c h fuel-air mixtures (Point A of Figure 2), of course, results i n low N0 emissions since the maximum chemical equilibrium NO level i s greatly reduced under such conditions. However, the resultant penalties i n terms of impaired fuel economy and excessive HC and CO emissions are well known. An alternative i s operation with extremely lean mixtures (Point B) - lean beyond normal ignition limits. Combustion under such conditions can lead to low N0 emissions while at the same time providing an excess of oxygen for complete combustion of CO and HC. Operation of internal combustion engines with extremely lean overall fuel-air ratios has been achieved i n several ways, employing a number of differing combustion chamber configurations. One approach involves ignition of a very small and localized quan t i t y of fuel-rich and ingitable mixture (Point A of Figure 2), which i n turn serves to inflame a much larger quantity of sur rounding fuel-air mixture too lean for ignition under normal c i r cumstances. The bulk or average fuel-air ratio for the process corresponds to Point Β of Figure 2; and, as a consequence, reduced exhaust emissions should result. A second approach involves timed staging of the combustion process. An i n i t i a l r i c h mixture stage i n which major combustion reactions are carried out i s followed by extremely rapid mixing of rich mixture combustion products with dilution a i r . The X

X


6.

NEWHALL

81


4

Γ Chemical Equilibrium

I 0.6

ι

ι

ι

ι

ι

0.7

0.8

0.9

1.0

1.1

Fuel-Air

Equivalence

ι 1.2

Ratio

Figure 1. Rate of nitric oxide formation in engine combustion gases ( 6 )

F u e l - A i r Equivalence

Ratio

Figure 2. Influence of fuel-air ratio on nitric oxide formation rate


82

AUTOMOTIVE

EMISSIONS

CONTROL

transition from i n i t i a l Point A to f i n a l Point Β i n Figure 2 i s , in principle, sufficiently rapid that l i t t l e opportunity for NO formation exists. Implicit here i s u t i l i z a t i o n of the concept that the heat release reactions involved i n the transition from Point A to Point Β can be carried out so rapidly that time i s not available for formation of significant amounts of NO. Reciprocating spark ignition engines designed to exploit the foregoing ideas are usually called s t r a t i f i e d charge engines, a term generally applied to a large number of designs encompassing a wide spectrum of basic combustion processes. Open-Chamber Stratified Charge Engines Stratified charge engines can be conveniently divided into two types: open-chambe chamber s t r a t i f i e d charg interest. Those engines reaching the most advances stages of development are probably the Ford-programmed combustion process (PROCO) Ç8) and Texaco's controlled combustion process (TCCS) (9). Both engines employ a combination of inlet a i r swirl and direct timed combustion chamber fuel injection to achieve a local fuelr i c h ignitable mixture near the point of ignition. The overall mixture ratio under most operating conditions i s fuel lean. The Texaco TCCS engine i s illustrated schematically i n Figure 3. During the engine inlet stroke, an unthrottled supply of a i r enters the cylinder through an inlet port oriented to promote a specified level of a i r swirl within the cylinder and combustion chamber. As the subsequent compression stroke nears completion, fuel i s injected into and mixes with an element of swirling a i r charge. This i n i t i a l fuel-air mixture i s spark ignited, and a flame zone i s established downstream from the nozzle. As injection continues, fuel-air mixture i s continuously swept into the flame zone. The total quantity of fuel consumed per cycle and, hence, engine power output, are controlled by varying the duration of fuel injection. Under nearly a l l engine operating conditions, the total quantity of fuel injected i s on the lean side of stoichiometric. The TCCS system has been under development by Texaco since the 1940 s. To date, this work has involved application of the process to a wide variety of engine configurations. Like the TCCS engine, the PROCO system (Figure 4) employs timed combustion chamber fuel injection. However, i n contrast to the TCCS system, the PROCO system i s based on formation of a premixed fuel-air mixture prior to ignition. Fuel injection and inlet a i r swirl are coordinated to provide a small portion of r i c h mixture near the point of ignition surrounded by a large region of increasingly fuel-lean mixture. Flame propagation proceeds outward from the point of ignition through the leaner portions of the combustion chamber. f


6.

N E W H A L L


83

4 - Combustion Products

Figure 3.

Texaco-controlled combustion system (TCCS)

Fuel Injector

Figure 4. Ford-programmed combustion (PROCO) system


84

AUTOMOTIVE

EMISSIONS

CONTROL

Both the TCCS and PROCO engines are inherently low emitters of CO, primarily a result of lean mixture combustion. Unburned HC and N0 emissions have been found to be lower than those typical of uncontrolled conventional engines, but i t appears that additional control measures are required to meet statutory 1976 Federal emissions standards. The U.S. Army Tank Automotive Command has sponsored develop ment of low emissions TCCS and PROCO power plants for light-duty Military vehicles. These power plants have been based on con version of the 4-cylinder, 70-hp L-141 Jeep engine. The vehicles i n which these engines were placed were equipped with oxidizing catalysts for added control of HC and CO emissions, and EGR was used as an additional measure for control of N0 . Results of emissions tests on M i l i t a r y Jeep vehicles equipped with TCCS and PROCO engines are l i s t e d i n Table I I (10) At low X

X

Average Emissions from Military Jeep Vehicles with Stratified Engine Conversions (Reference 10) Emissions, g/Mile CO HC 2

Engine L-141 Ford PROCO L-141 TCCS

1

2

Miles 1

Texaco

1

ΝΟχ

Low 17,123

0.37 0.64

0.93 0.46

0.33 0.38

Low 10,000

0.37 0.77

0.23 1.90

0.31 0.38

CVS Fuel Economy, mpg 18.5-23

16-22

Engines equipped with oxidation catalysts and exhaust gas recirculation.

1975 CVS C-H test procedure.

mileage these vehicles met the statutory 1976 emissions standards. Deterioration problems related to HC emission would be expected to be similar to those of conventional engines equipped with oxidizing catalysts. This i s evidenced by the increase i n HC emissions with mileage shown by Table I I . N0 and CO emissions appear to have remained below 1976 levels with mileage accumulation. X


6.

N E W H A L L


85

Table III Average Low Mileage Emissions Levels - Ford PROCO Conversions (Reference 10) z

Emissions, g/Mile HC CO N0 PROCO 141-CID Capri Vehicles

1

0.12 0.13 0.11

0.46 0.18 0.27

0.32 0.33 0.32

20.4 25.1 22.3

2500

1

0.30

0.37

0.37

14.4

4500

1

0.36 0.36

0.13 1.08

0.63 0.39

12.8

PROCO 351-CID Torino Vehicle PROCO 351-CID Montego Vehicles

1

2

X

CVS Fuel Inertia Economy, Weight, mpg Lb

— —

A11 vehicles employed noble metal exhaust oxidation catalysts and exhaust gas recirculation.

1975 CVS C-H test procedure.

Table III presents emissions data at low mileage for several passenger car vehicles equipped with PROCO engine conversions (10). These installations included noble metal catalysts and EGR for added control of HC and ΝΟχ emissions, respectively. A l l vehicles met the statutory 1976 standards at low mileage. Fuel consumption data, as shown i n Table III, appear favorable when contrasted with the fuel economy for current production vehicles of similar weight. Fuel requirements for the TCCS and PROCO engines differ sub stantially. The TCCS concept was i n i t i a l l y developed for multifuel capability; as a consequence, this engine does not have a significant octane requirement and i s flexible with regard to fuel requirements. In the PROCO engine combustion chamber, an end gas region does exist prior to completion of combustion; and, as a consequence, this engine has a f i n i t e octane requirement. Prechamber Stratified Charge Engines A number of designs achieve charge s t r a t i f i c a t i o n through division of the combustion region into two adjacent chambers. The emissions reduction potential for two types of dual-chamber engines has been demonstrated. F i r s t , i n a design traditionally called the "prechamber engine," a small auxiliary or ignition


86

AUTOMOTIVE

EMISSIONS

CONTROL

chamber equipped with a spark plug communicates with the much larger main combustion chamber located i n the space above the piston (Figure 5). The prechamber typically contains 5-15% of the t o t a l combustion volume. In operation of this type of engine, the prechamber i s supplied with a small quantity of fuelr i c h ignitable fuel-air mixture while a very lean and normally unignitable mixture i s supplied to the main chamber above the piston. Expansion of high temperature flame products from the prechamber leads to ignition and burning of the lean main chamber fuel-air charge. The prechamber s t r a t i f i e d charge engine has existed i n various forms for many years. Early work by Ricardo (11) i n d i cated that the engine could perform very e f f i c i e n t l y within a limited range of carefully controlled operating conditions. Both fuel-injected and carbureted prechamber engines have been b u i l t A fuel-injected design the subject of extensiv nearly a decade (13,14). Unfortunately, the University of Rochester work was undertaken prior to widespread recognition of the automobile emissions problem; and, as a consequence, emissions characteristics of the Brodersen engine were not determined. Another prechamber engine receiving attention i n the early I960 s i s that conceived by R. M. Heintz (15). The objectives of this design were reduced HC emissions, increased fuel economy, and more flexible fuel requirements. I n i t i a l experiments with a prechamber engine design called "the torch ignition engine" were reported i n the U.S.S.R. by Nilov (16) and later by Kerimov and Mekhtier (17). This designation refers to the torchlike j e t of hot combustion gases issuing from the precombustion chamber upon ignition. In the Russian designs, the o r i f i c e between prechamber and main chamber i s sized to produce a high velocity j e t of combustion gases. In a recent publication (18), Varshaoski et a l . have presented emissions data obtained with a torch engine system. These data show significant pollutant reductions relative to conventional engines; however, their interpretation i n terms of requirements based on the Federal emissions test procedure i s not clear. A carbureted three-valve prechamber engine, the Honda Compound Vortex-Controlled Combustion (CVCC) system, has received considerable recent publicity as a potential low emissions power plant (19). This system i s i l l u s t r a t e d schematically i n Figure 6. Honda's current design employs a conventional engine block and piston assembly. Only the cylinder head and fuel inlet system differ from current automotive practice. Each cylinder i s equipped with a small precombustion chamber communicating by means of an o r i f i c e with the main combustion chamber situated above the piston. A small inlet valve i s located i n each prechamber. Larger inlet and exhaust valves typical of conventional automotive practice are located i n the main combustion chamber. Proper proportioning of fuel-air mixture between prechamber and 1


N E W H A L L


Figure 5. Schematic of a prechamber charge engine

Environmental Protection Agency

Figure 6. Honda CVVC engine ( 1 9 )


88

AUTOMOTIVE

EMISSIONS

CONTROL

main chamber i s achieved by a combination of throttle control and appropriate i n l e t valve timing. Inlet ports and valves are oriented to provide specific levels of a i r swirl and turbulence i n the combustion chamber. In this way, a relatively slow and uniform burning process giving rise to elevated combustion tem peratures late i n the expansion stroke and during the exhaust process i s achieved. High temperatures i n this part of the engine cycle are necessary to promote complete oxidation of HC and CO. It should be noted that these elevated temperatures are neces s a r i l y obtained at the expense of a fuel economy penalty. Results of emissions tests with the Honda engine have been very promising. The emissions levels shown i n Table IV for a number of lightweight Honda Civic vehicles are typical and demonstrate that the Honda engine can meet statutory 1975-1976

Honda CVCC Powered Vehicle Emissions (Reference 19) 1

Emissions,^ g/Mile ΝΟχ HC CO

Fuel Ε conomy, mpg 1975 FTP 1972 FTP

Low Mileage Car No. 3652

3

0.18

2.12

0.89

22.1

21.0

50,000-Mile Car No. 2034

4

0.24

1.75

0.65

21.3

19.8

x

Honda Civic vehicles.

2

1975 CVS C-H procedure with 2000-lb i n e r t i a weight.

3

Average of five tests.

^Average of four tests. HC and CO standards and can approach the statutory 1976 ΝΟχ standard (10). Of particular importance, durability of this system appears excellent as evidenced by the high mileage emis sions levels reported i n Table IV. The noted deterioration of emissions after 30,000-50,000 miles of engine operation was slight and apparently insignificant. Recently, the EPA has tested a larger vehicle converted to the Honda system (20). This vehicle, a 1973 Chevrolet Impala with a 350-CID V-8 engine, was equipped with cylinder heads and


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induction system of Honda manufacture. Test results are presented i n Table V for low vehicle mileage- The vehicle met the present 1976 interim Federal emissions standards though N0 levels were substantially higher than for the much lighter weight Honda Civic vehicles. X

Table V Emissions from Honda CVCC Conversion of 350-CID Chevrolet Impala (Reference 20) 1

Test 1 2 3 4

2

3

Emissions, g/Mile N0 HC CO 0.2 0.23 0.80 0.32

5.01 2.64 2.79

1.95 1.51 1.68

Fuel Economy, mpg

11.2 10.8 10.2

1975 CVS C-H procedure, 5000-lb i n e r t i a weight. z

Carburetor float valve malfunctioning.

3

Engine stalled on hot start cycle.

Fuel economy data indicate that efficiency of the Honda engine, when operated at low emissions levels, i s somewhat poorer than that typical of well-designed conventional engines operated without emissions controls. However, EPA data for the Chevrolet Impala conversion show that efficiency of the CVCC engine meeting 1975-1976 interim standards was comparable to or slightly better than that of 1973 production engines of similar size operating i n vehicles of comparable weight. I t has been stated by automobile manufacturers that use of exhaust oxidation catalysts beginning i n 1975 w i l l result i n improved fuel economy relative to 1973 pro duction vehicles. In this event fuel economy of catalystequipped conventional engines should be at least as good as that of the CVCC system. The apparent effect of vehicle size (more precisely the ratio of vehicle weight to engine cubic inch displacement) on N0 emis sions from the Honda engine conversions demonstrates the generally expected response of ΝΟχ emissions to increased specific power demand from this type of engine. For a given engine cubic inch displacement, maximum power output can be achieved only by enrich ing the overall fuel-air mixture ratio to nearly stoichiometric X


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proportions and at the same time advancing ignition timing to the MBT point. Both factors give r i s e to increased N0 emissions. This behavior i s evidenced by Table VI, which presents steady state emissions data for the Honda conversion of the Chevrolet Impala (20) . At light loads, N0 emissions are below or roughly comparable to emissions from a conventionally powered 1973 Impala. This stock vehicle employs EGR to meet the 1973 N0 standard. I t i s noted i n Table VI that for the heaviest load condition reported, the 60-mph cruise, W emissions from the Honda conver sion approached twice the level of emissions from the stock vehicles. This points to the fact that i n sizing engines for a specific vehicle application, the decreased a i r u t i l i z a t i o n (and hence specific power output) of the prechamber engine when operated under low emissions conditions must be taken into consideration. X

X

X

K

Steady State Emissions from Honda CVCC Conversion of 350-CID Chevrolet Impala (Reference 20)

Vehicle Speed, mph 15 30 45 60

Emissions, g /Mile N0 CO HC 350 350 350 350 350 350 CVCC Stock CVCC Stock CVCC Stock X

0.15 0.00 0.00 0.01

0.60 1.22 0.51 0.32

3.30 0.65 0.19 0.53

7.26 9.98 4.71 2.48

0.37 0.53 1.00 3.00

0.52 0.37 0.93 1.78

Divided-Chamber Staged Combustion Engine Dual-chamber engines of another type, often called "dividedchamber" or "large-volume prechamber" engines, employ a two-stage combustion process. Here i n i t i a l r i c h mixture combustion and heat release ( f i r s t stage of combustion) are followed by rapid dilution of combustion products with relatively low temperature a i r (second stage of combustion). In terms of the concepts previously devel oped, this process i s i n i t i a t e d i n the v i c i n i t y of Point A of Figure 2. Subsequent mixing of combustion products with a i r i s represented by a transition from Point A to Point B. The object of this engine design i s to effect the transition from Point A to Point Β with sufficient speed that time i s not available for formation of significant quantities of NO. During the second low temperature stage of combustion (Point Β ) , oxidation of HC and CO goes to completion.


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An experimental divided-chamber engine design that has been b u i l t and tested i s represented schematically i n Figure 7 (21,22). A dividing o r i f i c e (3) separates the primary combustion chamber (1) from the secondary combustion chamber (2), which includes the cylinder volume above the piston top. A fuel injector (4) supplies fuel to the primary chamber only. Injection timing i s arranged such that fuel continuously mixes with a i r entering the primary chamber during the compression stroke. At the end of compression, as the piston nears i t s top center position, the primary chamber contains an ignitable fuel-air mixture while the secondary chamber adjacent to the piston top contains only a i r . Following ignition of the primary chamber mixture by a spark plug (6) located near the dividing o r i f i c e , high temperature rich mix ture combustion products expand rapidly into and mix with the relatively cool a i r contained i n the secondary chamber. The resulting dilution of ture reduction rapidly time, the presence of excess a i r i n the secondary chamber tends to promote complete oxidation of HC and CO. Results of limited research conducted both by university and industrial laboratories indicate that ΝΟχ reductions of as much as 80-95% relative to conventional engines are possible with the divided-chamber staged combustion process. Typical experimentally determined ΝΟχ emissions levels are presented i n Figure 8 (23). Here ΝΟχ emissions for two different divided-chamber configura tions are compared with typical emissions levels for conventional uncontrolled automobile engines. The volume ratio, $, appearing as a parameter i n Figure 8, represents the fraction of total com bustion volume contained i n the primary chamber. For 3 values approaching 0.5 or lower, ΝΟχ emissions reach extremely low levels. However, maximum power output capability for a given engine size decreases with decreasing β values. Optimum primary chamber volume must ultimately represent a compromise between low emissions levels and desired maximum power output. HC and particularly CO emissions from the divided-chamber engine are substantially lower than conventional engine levels. However, further detailed work with combustion chamber geometries and fuel injection systems w i l l be necessary to f u l l y evaluate the potential for reduction of these emissions. Table VII presents results of tests cited by the National Academy of Sciences (10). Emissions from the divided-chamber engine are compared with those from a laboratory PROCO s t r a t i f i e d charge engine, the com parison being made at equal levels of N0 emissions. ΝΟχ emis sions were controlled to specific levels by addition of EGR to the PROCO engine and by adjustment of operating parameters for the divided-chamber engine. These data indicate that the divided-chamber engine i s capable of achieving very low N0 emissions with relatively low HC and CO emissions. X

X


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5000

Ζ

EMISSIONS

MBT Ignition Timing Wide Open Throttle

3000

= Fraction of Total Combustion Volume in Primary Chamber

2000

Divided Chamber, ^ = 0.85 1000

Divided Chamber, β = 0.52 0.5

0.6

0.7

0.8

0.9

LL 1.0

1.1

Overall F u e l - A i r Equivalence Ratio American Institute of Chemical Engineers Figure 8.

Comparison of conventional and

divided combustion chamber ~ΝΟ emissions χ

(23)


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Table ¥11 Single-Cylinder Divided Combustion Chamber Engine Emissions Tests (Reference 10)

N0 Reduction Method X

Engine

Emissions, g/ihp-hr CO HC

Fuel Economy, Lb/ihp-hr

PROCO Divided Chamber

EGR None

1.0 1.0

3.0 0.4

13.0 2.5

0.377 0.378

PROCO Divided Chamber

EGR None

0.5 0.5

4.0 0.75

14.0 3.3

0.383 0.377

As shown by Table VII, fuel economy of the divided-chamber staged combustion engine i s comparable to that of conventional piston engines without emissions controls. When compared with conventional piston engines controlled to equivalent low ΝΟχ emissions levels, the divided-chamber engine i s superior i n terms of fuel economy. The Diesel Engine The diesel engine can be viewed as a highly developed form of s t r a t i f i e d charge engine. Combustion i s i n i t i a t e d by com pression ignition of a small quantity of fuel-air mixture formed just after the beginning of fuel injection. Subsequently, injected fuel i s burned i n a heterogeneous diffusion flame. Over a l l fuel-air ratios i n diesel engine operation are usually extremely fuel lean. However, major combustion reactions occur l o c a l l y i n combustion chamber regions containing fuel-air mix tures i n the v i c i n i t y of stoichiometric proportions. The conventional diesel engine i s characterized by low levels of CO and light HC emissions, a result of lean mixture operation. On a unit power output basis, N0 emissions from diesel engines are typically lower than those of uncontrolled gasoline engines, a combined result of diffusion combustion and, i n an approximate sense, low mean combustion temperatures. Work devoted to mathe matical simulation of diesel combustion has shown that NO forma tion occurs primarily i n combustion products formed early i n the combustion process, with the later portions of diffusioncontrolled combustion contributing substantially less (24). Table VIII presents emissions levels for three diesel-powered passenger cars as reported by the EPA (25). These vehicles, a Mercedes 220D, Opel Rekord 2100D, and Peugeot 504D, were powered by 4-cylinder engines ranging i n size from 126-134 CID with power ratings ranging from 65-68 bhp. Two of the diesel-powered X


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vehicles were capable of meeting the 1975 statutory emissions standards, ΝΟχ emissions were i n excess of the original Federal 1976 standards but were well within present interim standards. Table VIII Automotive Diesel Engine Emissions (Reference 25)

Vehicle Mercedes 220D Mercedes 220D (Modified) Opel Rekord 2100D Peugeot 504D

Emissions» g/Mile HC Inertia HC (Cold (Hot Weight, Bag) FID) CO NO* Lb

0.16

0.40

1.03

3.11

1.16 3.42

1.34 1.07

3000 3000

Fuel Economy, mPS 1975 1972 FTP FTP

23.8 25.2

23.2 24.2

The preceding data do not include information on particulate and odorant emissions, both of which could be important problems with widespread diesel engine use i n automobiles. Complete assessment of the environmental potential for the diesel engine would have to include consideration of these factors as well as emission of polynuclear aromatic hydrocarbons. A l l are the sub ject of ongoing research. Fuel economy data referred to both 1972 and 1975 Federal test procedures are presented i n Table VIII. As expected, diesel engine fuel economies are excellent when compared with gasoline engine values. However, a more accurate appraisal would probably require comparison at equal vehicle performance levels. Powerto-weight ratios and, hence, acceleration times and top speeds for the diesel vehicles cited above are inferior to values expected i n typical gasoline-powered vehicles. Gas Turbine, S t i r l i n g Cycle, and Rankine Cycle Engines Gas turbine, S t i r l i n g cycle, and Rankine engines a l l employ steady flow or continuous combustion processes operated with fuellean overall mixture ratios. In a s t r i c t sense, the gas turbine i s an internal combustion engine since high temperature combustion products serve as the cycle working f l u i d . Rankine and S t i r l i n g engines are external combustion devices with heat exchanged between high temperature combustion gases and the enclosed cycle working f l u i d .


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In contrast to the situation with conventional spark i g n i tion piston engines, the major obstacles related to use of con tinuous combustion power plants are i n the areas of manufacturing costs, durability, vehicle performance, and fuel economy. The problem of exhaust emissions, which involves primarily the com bustion process, has been less significant than the foregoing items. As a consequence of lean combustion, these continuous com bustion power plants are characterized by low HC and CO emissions. Several investigators have reported data indicating that existing combustion systems are capable of approaching or meeting statutory 1975 and 1976 vehicle emissions standards for HC and CO (26,27). For a given power output, ΝΟχ emissions appear to be lower than those of conventional uncontrolled gasoline engines. How ever, i t has been show that existin combustor probabl w i l l not meet the statutory vehicles (26). The formation of N0 i n continuous-flow combustors has been found to result from the presence of high temperature zones with l o c a l fuel-air ratios i n the v i c i n i t y of stoichiometric condi tions. Approaches suggested for minimizing N0 formation have involved reduction of these localized peak temperatures through such techniques as radiation cooling, water injection, and p r i mary zone a i r injection. Other approaches include lean mixture primary zone combustion such that l o c a l maximum temperatures f a l l below levels required for significant NO formation. Laboratory gas turbine combustors employing several of these approaches have demonstrated the potential for meeting the 1976 standards (28). With a laboratory S t i r l i n g engine combustor, Philips has measured simulated Federal vehicle test procedure emissions levels well below 1976 statutory levels (29). X

X

Conclusion As an alternative to the conventional internal combustion engine equipped with exhaust treatment devices, modified combus tion engines can, i n principle, yield large reductions i n vehicle exhaust emissions. Such modifications include s t r a t i f i e d charge engines of both open and dual chamber design. On an experimental basis, prototype s t r a t i f i e d charge engines have achieved low exhaust emissions with fuel economy superior to that of conven tional engines controlled to similar emissions levels. The diesel engine i s capable of achieving low levels of light HC, CO, and ΝΟχ emissions with excellent fuel economy. Potential problems associated with widespread diesel use i n light-duty vehicles are i n i t i a l cost, large engine size and weight for a given power output, the possibility of excessive particulate and odorant emissions, and excessive engine noise. Several power plants based on continuous combustion processes have the potential for very low exhaust emissions. These include


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the gas turbine, the Rankine engine, and the S t i r l i n g engine. However, at the present time major problems i n the areas of manu facturing costs, r e l i a b i l i t y , durability, vehicle performance, and fuel economy must be overcome. As a consequence, these systems must be viewed as relatively long range alternatives to the piston engine. Literature Cited 1.

Beckman, E. W., Fagley, W. S., and Sarto, J . O., Society of Automotive Engineers Transactions (1967), 75.

2.

Cantwell, Ε. Ν., and Pahnke, A. J., Society of Automotive Engineers Transactions (1966), 74.

3.

Bartholomew, Ε., Societ Paper 660109.

4.

Campion, R. M., et a l . , Society of Automotive Engineers (1972), Publication AP-370.

5.

Kopa, R. D., Society of Automotive Engineers (1966), Paper 660114.

6.

Newhall, Η. Κ., and Shahed, S. Μ., Thirteenth Symposium (International) on Combustion, p. 365, The Combustion Institute (1971).

7.

Longwell, J . P., and Weiss, Μ. Α., Ind. Eng. Chem. (1955), 47, p. 1634-1643.

8.

Bishop, I. Ν., and Simko, Α., Society of Automotive Engineers (1968), Paper 680041.

9.

Mitchell, E., Cobb, J . Μ., and Frost, R. Α., Society of Automotive Engineers (1968), Paper 680042.

10. "Automotive Spark Ignition Engine Emission Control Systems to Meet Requirements of the 1970 Clean A i r Amendments," report of the Emission Control Systems Panel to the Committee on Motor Vehicle Emissions, National Academy of Sciences, May 1973. 11. Ricardo, H. R., SAE Journal (1922), 10, p. 305-336. 12. U.S. Patent No. 2,615,437 and No. 2,690,741, "Method of Operating Internal Combustion Engines," Neil O. Broderson, Rochester, New York.


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13. Conta, L. D., and Pandeli, D., American Society of Mechanical Engineers (1959), Paper 59-SA-25. 14. Conta, L. D., and Pandeli, D., American Society of Mechanical Engineers (1960), Paper 60-WA-314. 15. U.S. Patent No. 2,884,913, "Internal Combustion Engine," R. M. Heintz. 16. Nilov, Ν. Α., Automobilnaya Promyshlennost No. 8 (1958). 17. Kerimov, Ν. Α., and Metehtiev, R. I., Automobilnoya Promyshlennost No. 1 (1967), p. 8-11. 18. Varshaoski, I. L. Konev B F. and Klatskin Aubomobilnaya Promyshlennos

V B.

19. "An Evaluation of Three Honda Compound Vortex-Controlled Combustion (CVCC) Powered Vehicles," Report 73-11 issued by Test and Evaluation Branch, Environmental Protection Agency, December 1972. 20. "An Evaluation of a 350-CID Compound Vortex-Controlled Combustion (CVCC) Powered Chevrolet Impala," Report 74-13 DWP issued by Test and Evaluation Branch, Environmental Protection Agency, October 1973. 21. Newhall, Η. Κ., and E1-Messiri, I. Α., Combustion and Flame (1970), 14, p. 155-158. 22. Newhall, Η. Κ., and E1-Messiri, I. Α., SAE Trans. (1970), 78, Paper 700491. 23. E1-Messiri, I. A., and Newhall, Η. Κ., Proc. Intersociety Energy Conversion Engineering Conference (1971), p. 63. 24. Shahed, S. Μ., and Chiu, W. S., Society of Automotive Engineers, Paper 730083, January 1973. 25. "Exhaust Emissions from Three Diesel-Powered Passenger Cars," Report 73-19 AW issued by Test and Evaluation Branch, Environmental Protection Agency, March 1973. 26. Wade, W. R., and Cornelius, W., General Motors Research Laboratories Symposium on Emissions from Continuous Combustion Systems, p. 375-457, Plenum Press, New York (1972). 27. Brogan, J . J . , and Thur, Ε. Μ., Intersociety Energy Conversion Engineering Conference Proceedings, p. 806-824 (1972).


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28. White, D. J., Roberts, P. Β., and Compton, W. A., Intersociety Energy Conversion Engineering Conference Proceedings, p. 845-851 (1972). 29. Postma, N. D., VanGiessel, R., and Reinink, F., Society of Automotive Engineers, Paper 730648 (1973).


7 Alternative Automotive Emission Control Systems Ε . N . C A N T W E L L , E . S. J A C O B S , and J. M . P I E R R A R D Ε . I. du Pont Nemours and Co., Wilmington, Del. 19898

Abstract Relationships developed between automotive exhaust emissions and ambient air quality levels have been used to establish the degree of emission control needed to meet the ambient air quality standards in major urban areas. Interim emission standards already established for 1975 appear to be more than adequate for congested urban areas and the existing 1974 standards appear more than adequate for the remainder of the country. The very low levels mandated by the 1970 Amendments to the Clean Air Act do not appear necessary. Emission control systems based on engine modifications and thermal reactors have been shown to provide the degree of emission control needed to achieve the ambient air quality goals and are compatible with the continued use of leaded gasoline. Exhaust lead traps have been shown to be a practical means to reduce lead emissions to the environment should such control be needed. The lead tolerant control systems used with high compression ratio engines are shown to have the potential to improve fuel economy to a greater degree than proposed catalytic systems used with unleaded gasoline and low compression ratio engines. Both approaches are shown to impose severe fuel economy penalties at the very stringent emission standards mandated by the 1970 Amendments to the Clean Air Act. Introduction The 1970 Amendments to the Clean Air Act directed the Environ mental Protection Agency to set hydrocarbon and carbon monoxide exhaust emission standards for 1975 vehicles which were 90% lower than the standards for 1970 vehicles. These amendments also required a nitrogen oxides emission standard for 1976 vehicles which was 90% lower than the level of 1971 vehicles. In response to this mandate by Congress, EPA issued vehicle emission standards for 1975 and 1976 which were 99


100

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subsequently postponed one year to 1976 and 1977. At the time the standards were postponed, EPA issued interim emission standards for 1975 which called for reductions in hydrocarbons and carbon monoxide, but not to the degree required by the 1970 Amendments to the Clean Air Act. The 90% reduction required by the 1970 Amendments to the Clean Air Act coupled with the reductions achieved up to 1970 provided for overall reductions of 97% for hydrocarbons, 96% for carbon monoxide, and 93% for oxides of nitrogen below pre-emission control levels. In April, 1971 EPA promulgated national ambient air quality standards for hydrocarbons, carbon monoxide, nitrogen dioxide, and photochemical oxidants as required by the 1970 Amendments to the Clean Air Act. These air quality standards were set to protect the public health and welfare from any known or anticipated adverse effects of air pollution. Interestingly, automotiv carbon monoxide, and nitroge establishment of ambient air quality standards. Actually, the process should have been reversed. Air quality standards should have been established first and then studies should have been carried out to determine what levels of automotive emissions were needed to meet the air quality standards. Since this was not done, we now find ourselves in the position of examining the legislated automotive standards to see if the degree of control being called for is consistent with the air quality goals. In the absence of any other consideration, it is desirable to attain the lowest automotive emission levels which are technologically achievable. Gasoline consumption and control hardware costs, however, increase with the degree of emission control imposed (1)*. In view of the critical energy situation, it is imperative that an appropriate balance be struck between required emission levels and fuel consumption penalties. Automotive emission standards must be soundly related to the ambient air quality standards, so that we are not paying for more control than is needed to achieve the established air quality standards. The purpose of this paper is to report on the progress being made in major programs carried out at Du Pont designed to answer three questions derived from these concerns. These questions are: •

What automotive exhaust emission standards are needed to achieve the air quality standards ?

•

What automotive emission control systems can meet these needed automotive emission standards?

•

Which emission control system minimizes consumption of energy while still meeting needed standards ?

* Numbers in parentheses refer to references at end of paper.


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Scope of Du Pont Studies The process of selecting the proper course of action for air pollu tion control to achieve the objectives of the Clean Air Act consists of an orderly series of decisions as diagramed in Figure 1. First, pollutant effects on human health and welfare including the aesthetic qualities of life as well as damage to plants, animals, and inanimate objects of value must be determined. Using this information, Step A can be taken to establish the needed levels of air quality. Establishment of these air quality levels is not precise because all of the needed knowledge is not and probably never will be available. The degree of safety required is based on judgement and is subject to the interpretation of the adequacy and accuracy of the medical and environmental studies. Debates on these issues arise from the recognitio more stringent and thus mor As discussed earlier, EPA set ambient air quality standards in 1971. The adequacy of these standards has been vigorously debated (2}. Some critics contend that air quality standards are too high to protect public health while others contend that they are lower than can be supported based on medical evidence. Still others point out that some of the standards are below natural background levels and thus are impossible to attain. For the purposes of this paper, the national ambient air quality standards promulgated by EPA have been accepted as necessary goals for achieving clean air. Once air quality standards have been set, then the question becomes one of deciding what degree of control of emission sources is needed to meet these standards. The ratio of existing and desired air quality levels gives the percentage reduction which is needed in source emis sions. In order to carry out this part of the process, information is needed on air quality levels in critical areas of the country and a detailed knowledge of emission levels from various sources. At the time Con gress enacted the Clean Air Act Amendments, information of this type was limited and Step Β was side-stepped by Congress in enacting the degree of automotive controls required to meet ambient air quality standards. Since then, data have become available which make it possible to carry out this step and the first part of this paper presents a logical basis for establishing automotive emission standards. The final step in the overall process is selecting the most effective means to meet emission standards. Once again this step is not precise because the costs in terms of economic, social, and environmental factors have not been quantified. This is due in part to inadequate data on alternative control measures. Identification of preferred control measures allows specific emission control strategies and technology to be scheduled for implementation.


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The third and final section of this paper provides an assessment of the effect of various emission control systems on energy consumption using the most recent data on vehicle fuel economy. The uncertainties inherent in Steps A and B, coupled with the uncertainty in Step C prevent quantitative assessment of the cost effectiveness of various implementation plans. Because of this, it is vital that each alternative be examined thoroughly before a final decision on implementation is made. The purpose of this paper is to provide an analysis of available data to arrive at a reasonable strategy for automotive emission control to achieve air quality to protect public health. Air Quality and Emission Standards In order to calculat air quality standards, D the EPA's Continuous Air Monitoring Program (CAMP) for gaseous pollutants in the central business districts of six large cities. Carbon monoxide was chosen for initial study because, unlike other motor vehicle exhaust pollutants, most carbon monoxide in urban areas comes from motor vehicles, and it is chemically inert in the atmosphere. In our studies, we have examined various proposed relationships between automotive emission rates and atmospheric levels of carbon monoxide. It was recognized that once a relationship was established for carbon monoxide, it then could be extended to other pollutants. Simple Rollback Approach. Practical estimates of the automotive emissions reductions needed to achieve ambient air quality standards have been made on the basis of the so-called "rollback" approach first used by California and later by EPA. This approach assumes that the pollutant concentration is proportional to the emission rate of that pollutant in an air basin, with a small correction for the background level of the pollutant. We tested this assumption for Chicago, using data from the EPA CAMP station in the central business district, and from outlying air sampling stations operated by the City of Chicago. Two of these sites were in residential areas, and the other two near expressways, at distances from 2.5 to 12 miles from the center city CAMP station. The analysis, described in detail in Reference JL showed that daily average CO concentrations at the five stations were essentially unrelated. This indicated that ambient carbon monoxide levels should be related to nearby, not remote, traffic activity. Therefore, Chicago central business district traffic, rather than metropolitan area traffic, must be considered to explain air quality measured at the CAMP station. This analysis also pointed up a problem in applying rollback, namely


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the proper choice of the traffic growth factor. Cordon traffic counts verified that traffic saturation exists in the Chicago central business district around the CAMP station, as illustrated in Figure 2. No large increase of vehicle use can reasonably be expected in other large urban business districts either. Therefore, it appears that simple rollback cannot be applied to develop projections of air quality in mature urban regions on the basis of anticipated growth in fringe regions. Modified Rollback* Because of the limitations of simple rollback, recent EPA air quality projections have been based on a "modified" rollback model, as discussed in Reference 4. The modifications introduced by EPA were: 1. consideration of six source categories, each with its own growth rat control, and 2.

inclusion of a factor for each source category which weights the emissions according to their stack height. With EPA s cooperation in providing us with copies of their input data and computer program, we have conducted tests of the ability of the modified rollback model to predict air quality. This was done by taking as a starting point, a measured air quality condition of, say, five years ago, and then using this value to calculate present air quality using the modified rollback model. The modified rollback model does not appear to be a good predictor since calculated values did not agree with measured values as shown in Figure 3. Based on our earlier analysis of the relationship between urban CO emissions and air quality, we believe the inability of the modified rollback to predict is due to the assumption which calls for equal weighting of CO emissions originating anywhere within the air quality control region (AQCR). The Federal AQCR s are geographically very large, and therefore sources near the boundaries cannot be expected to have any significant influence on air quality in the central metropolitan area. For example, the areas of the Chicago, Philadelphia, and National Capitol AQCR s are, respectively, 6,087, 4,585, and 2,326 square miles. If these regions were circular, their outer boundaries would be 44, 38, and 27 miles from the center. As the regions are not circular, their farthest points are at even greater distances than those listed above. Yet, the simple rollback, and the current modified rollback assume that all sources contribute to air quality at a receptor point in proportion to their emission rate, regardless of distance from the receptor. !

!

T

Air Quality Trend Analysis. There is an alternative to the simple rollback approach which can be used to establish needed vehicle emission


AUTOMOTIVE

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Medical and Environmental Studies to Determine the Effects of Air Pollutants on Health and Welfare Step A - What Levels of Air Quality Are Needed to Protect Public Health and Welfare?

Primary and Secondary Ambient Air Quality Standards Step Β - How Much Must Emissions Be Reduced to Achieve the Air Quality Standards in the Desired Time?

Alternative Emissio a nd Source Category Standards Step C - What Are the Most Cost Effective Emission Control Measures?

Implementation of Control Strategies and Emission Control Technology

Figure I.

Sequence of steps required to achieve control of air pollution

500 r

62

65

68

71

YEAR Figure 2.

Weekday traffic activity in the Chicago central business district


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standards to satisfy air quality standards. This approach, developed in our studies, and described in References J. and_4, uses aerometric data records for cities with long term measurement bases, to establish what air quality changes have taken place over the years. By relating these changes to vehicle CO emission rates it is possible to predict needed vehicle emission rates to meet air quality standards. An examination of CAMP data over the last ten years shows a general improving trend in CO air quality. Over the same period of time the average CO emission rate of vehicles on the road has decreased. This decrease has resulted from retirement of older, uncontrolled cars, and their replacement with new models, which have met increasingly stringent emission standards. In the preceeding section, it was shown that Chicago central business district traffic is constant generally accepted as characteristi which coincide with the regions of expected maximum CO concentration, and with the locations of CAMP sampling stations. Because traffic can be considered constant, the value of average CO emission rate per mile can be used as an index of total CO emissions in the vicinity of the air monitoring station. A comparison of average vehicle CO emission rate and the highest 8-hour nonoverlapping average CO concentration in each month of record for the Chicago CAMP station is shown in Figure 4. A projection of the trends shown in Figure 4 predicts that a value of 40 g/mile average CO emission rate for all vehicles on the road would allow attainment of the CO air quality standard for Chicago in the mid1970* s. While there is no reason to disagree with this finding, a comprehensive analysis of the predictive value of this approach to determination of emission standards, given in Reference j£, shows that projections on the basis of such trend envelopes are subject to large uncertainty. The sensitivity of trend line location to a few extreme values led us to the search for a more stable parameter describing air quality, which is discussed in the next section. Use of Annual Mean for Predicting Emission Standards. Air quality standards for CO, hydrocarbons, and photochemical oxidant are specified as concentration levels, over given averaging times, not to be exceeded more than once a year. Therefore, demonstration that the standards are being achieved, or evaluation of progress toward achievement of the standards, requires a high degree of confidence that the air quality measurements used to estimate the frequency distribution of pollutant concentrations are representative. Unless truly continuous measurements are made, the confidence of an estimate of the frequency of occurrence of a rare event, such as is implied by the air quality standard, is degraded. However, if it could be shown that a definite relationship exists between


AUTOMOTIVE

•:

EMISSIONS

CONTROL

ι

• •· · ··· ·· · s

·

ι .

0

10

!

· ·

· · · ·

: ι

20

30

40

OBSERVED CO, PPM Figure 3. Comparison of carbon monoxide concentration pro jected by "modified rollback air quality impact analysis'" with observed concentrations. Annual second highest 8-hr. nonoverlapping average value.

YEAR Figure 4. Comparison of vehicle carbon monoxide emission rate and monthly maximum carbon monoxide values in Chicago


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the number of violations of the concentration level of the standard, and a less sensitive property of the distribution, such as a long period mean, then that mean can be used to determine appropriate emission reductions needed to meet air quality standards. By analysis of an aggregate of 51 years of data from the six CAMP cities, we established that a relationship does hold between the number of times per year that the air quality standard is exceeded and the annual average CO concentration. The details of the analysis are reported in Reference 3. From this relationship, the annual average CO which will result in only one annual occurrence of the 9 ppm - 8-hour average CO concentration was computed. This value is 2.3 ppm. An independent, strictly empirical analysis also gives a value of 2.3 ppm, with better than 98% confidence. The annual average C and Philadelphia were clos level in 1971. The other cities were still above the required 2.3 ppm annual average by varying amounts, although trending downward. The only exception, Denver, has shown an increase of ambient CO since 1969, which apparently is attributable to an excessive vehicle population mean CO emission rate resulting from the interpretation of the antitampering provision of the Clean Air Act Amendments to mean that altitude-tuning of carburetors is prohibited. Vehicles at Denver's 5, 000 foot elevation are running richer resulting in higher CO emissions. This explanation is verified by a recently reported EPA-sponsored survey of exhaust emissions from a total of 1, 020 vehicles of the 19571971 model years which showed that hydrocarbon and carbon monoxide emissions in Denver were significantly higher, and oxides of nitrogen emissions significantly lower, than in the other cities studied (5). As shown in Table 2, the Denver 1971 vehicle population mean CO emission rate is nearly double that for Washington, D. C. The second column in Table 2 was calculated from the reported 1971 annual mean CO for each city, and the requirement for a 2. 3 ppm annual average to meet the air quality standard as derived earlier. When the percent reduction figures from column two are applied to the population mean CO emission rates in column one, the values in the last column are obtained, showing the CO emission rate consistent with achievement of the ambient air quality standard in each of the cities. There is good agreement among the values for Denver, Los Angeles, St. Louis, and Washington. The more stringent standard calculated to be necessary to meet the air quality standard in Chicago may well be the result of the meteorological peculiarity of that city s pronounced lake breeze effect discussed in Reference ϋ. For the worst case city, Chicago, a vehicle CO emission rate of 29 g/mile is needed to meet air quality standard. This value, obtained 1


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Table 1 CAMP City Ambient Carbon Monoxide Trends Annual Average CO Concentration, ppm Year Chicago Denver Washington Cincinnati St. Louis Philadelphia 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972

12.1 17.1 12.5 8.8 6.2 8.2 6.9 5.4

-

5.3 6.9 5.7 3.7 3.3 4.9

7.3 7.9 7.6 5.4 4.6 6.5 6.7 6.3

7.1 6.1 4.0 4.9 5.6

-

3.8 3.5

2.3

-

-

6.4 6.5 5.8 5.6

7.2 8.1 6.8 6.4

4.4 4.4 4.4

4.1 2.6

-

Table 2 Vehicle CO Emission Standards Calculated By Air Quality Trend Analysis, Using Measured 1971 Vehicle Population Mean CO Emission Rates

City Chicago Denver Los Angeles St. Louis Washington, D. C.

CO Emission Rate Of Cars On Road In 1971, g/Mile 66 112 74 75 62

Reduction of 1971 Annual Mean Vehicle CO Ambient CO Emission Rate Required to Meet Needed To Meet Air Quality Air Quality Standard, % Standard, g/Mile 57 66 52 48 34

29 38 36 39 41

by statistical treatment of all the air quality data, is a more reliable value than that derived from Figure 4, where the trend line is dependent on only a few peak values.


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Traffic Volume and Allowable CO Emission Rate. Another approach which can be taken to establish vehicle emission standards consists of treating an urban area as a box into which is injected carbon monoxide. The amount injected is directly proportional to the number of vehicle miles travelled in the area and the vehicle emission rate. This amount, defined as the CO flux density, is responsible for the ambient level of CO which occurs. The ratio of the observed CO level and the desired 9 ppm ambient air standard determines the degree of control or reduc tion in flux density which is needed. This would then apply for existing traffic conditions. If traffic saturation is then assumed, a vehicle standard can be derived which would apply in the worst case. This approach has been applied using data from a number of metropolitan areas and a value of 26 grams of CO per mile to meet the ambient air quality standard was obtained in the following paragraphs Traffic volume data for the most heavily trafficked sections of each metropolitan area listed in Table 3, except Chicago, were obtained from EPA Transportation Control Strategy reports (6^. For six of these areas, the authors of the individual reports had computed values of CO emission flux density. We calculated CO emission flux densities for Chicago, Denver, and Philadelphia using reported area traffic volume data (3} (6^, appropriate values for the 1971 population mean CO emission rate [5^, and the equation F = 10 VR where F = CO Emission Flux Density in metric tons of CO square miles χ day V = Area Traffic Volume in vehicle miles square miles χ day R = Mean CO Emission Rate in grams of CO vehicle mile The air quality used in this analysis was the annual second-highest 8-hour running mean CO value (computed hourly) for each location, obtained from the Transportation Control Strategy reports and the CAMP data described in Reference J*. Assuming a linear relationship between CO emission flux density and ambient CO, we calculated the needed CO emission flux density to achieve the 9 ppm CO air quality standard for each area, as listed in the last column of Table 3.


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Table 3 CO Emission Flux Density Needed For Achievement Of Running Mean Eight-Hour CO Air Quality Standard

City

Year

F Actual

Ambient 8-Hour CO, ppm,

Boston Kenmore Square Science Park Chicago Denver Minneapolis Philadelphia Pittsburgh St. Paul Spokane

1970 1970 197 197 1971 1970 1972 1971 1970-71

13.18 14.19

16.0 18.4

7.41 6.94

17.09 16.86 23.26 16.83 15. 71

17.5 19.0 21.2 21.6 20.0

8.79 7. 98 9.88 7.01 7.07

Average S. D.

F Needed

7.83 1.05

The spread of values is small, considering the variety of locations and the fact that the air quality values range from less than two to more than three times the 9 ppm level. This indicated that the mean value of CO emission flux density could be used as the basis for deriving the vehicle population mean CO emission rate needed to achieve the air quality standard as a function of traffic volume. Given the value of CO emission flux density, F, of 7. 83, the vehicle population mean CO emission rate, R (grams/mile), needed to meet the air quality standard was calculated for various levels of daily average area traffic volume, V (vehicle miles traveled per square mile per day). The results of these calculations are given in Table 4 for four values of daily average area traffic volume ranging up to the estimated traffic saturation value of 300,000 vehicle miles per day per square mile (3). These vehicle emission rates would meet the 8-hour CO air quality standard on the running mean basis. At traffic volumes below the saturation value, higher vehicle population mean CO emission rates would still permit achievement of the 8-hour running mean air quality standard. The area traffic volume in the most heavily traveled portions of the most metropolitan centers is below 200,000 vehicle miles per square mile per day as shown in Table 5. These extreme levels of traffic activity are encountered in only a few congested urban areas of the country.


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Table 4 Needed Vehicle CO Emission Rate To Meet Air Quality Standard As A Function Of Traffic Volume Traffic Volume, Vehicle Miles Per Day Per Square Mile

Vehicle CO Emission Rate Needed To Meet A i r Quality Standard, g/Mile

150,000 200,000 250,000 300,000

52 39 31 2 Table 5

Daily Area Traffic Volumes In Heavily Trafficked Regions Of Metropolitan Centers

City

Year

Area Traffic Volume, Vehicle Miles Per Day Per Square Mile

Boston Kenmore Square Science Park Chicago CBD Denver CBD Minneapolis CBD Philadelphia CBD Pittsburgh CBD St. Paul CBD Spokane CBD

1970 1970 1971 1971 1971 1970 1972 1971 1970-71

159,000 172,000 300,000 187,000 207,000 234,000 281,000 204,000 190,000

Calculations then were made to predict how the value of the CO emission standard chosen for 1976 and later will affect the year in which the air quality standard for CO would be met in the most heavily trafficked portions of urban areas. First, the future vehicle population mean CO emission rates were computed for each year through 1985 for a series of levels of the 1976 automotive emission standard for CO according to the procedure described by EPA (7^. Values from this reference were used for projected vehicle replacement rates, annual miles traveled, emission rate, and deterioration of emission control by vehicle model year and age.


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By this procedure a family of curves - one for each assumed 1976 CO emission standard - was developed showing the trend of vehicle population mean CO emission rate as a function of calendar year. From this family of curves, it was determined when the mean CO emission rate would decrease to the needed level for a given value of area traffic volume, assuming introduction of various CO emission standards beginning with the 1976 models. These values of CO air quality standard attainment date versus 1976 CO emission standard are plotted in Figure 5 for four assumed levels of traffic activity ranging up to 300, 000 vehicle miles per day per square mile. As Figure 5 illustrates, the attainment date of the CO air quality standard is only slightly advanced by a 1976 CO emission standard lower than the current standard of 28 grams per mile for areas with average daily area traffic volume per day. At higher level advance with lower 1976 standards, but only at the estimated saturation level is there a marked improvement in attainment date with a 1976 CO emission standard as low as 15 grams per mile. It is important to recognize that the extremes of traffic volumes are encountered only in a limited number of locations. In general, only the most heavily-trafficked square mile or two of a metropolitan area has these area traffic volume values. Another point to be kept in mind in interpreting Figure 5 is that, even with a 1976 emission standard of 3.4 g/mile, the air quality standard will not be achieved before 1978 in areas of near-saturation traffic activity. Therefore, only through traffic control to reduce traffic volume to roughly 200, 000 vehicle miles per square mile per day can the air quality standard be achieved by the statutory deadline of 1977. Once such traffic control measures are in force, no advantage is gained from a 1976 emission standard lower than the current level of 28 g/mile. Implication of Air Quality Studies. The air quality trend analysis for CO indicated a level of 29 g/mile would be satisfactory to meet ambient CO air quality standard. A second method based on traffic saturation conditions and maximum CO flux density in major urban areas resulted in a value of 26 g/mile. In view of the large difference between these values and the 3.4 g/mile mandated by the Amendments to the Clean Air Act of 1970, a serious review of the standards is in order Although our results to date have been restricted to the case of CO, others have reexamined the HC and NO emission standards in relation to the air quality standards for NO2 and photochemical oxidants. In the joint report by the panels on emission standards and atmospheric chemistry of the Committee on Motor Vehicle Emissions of the National Academy of Sciences (8), it is concluded that the Federal emission standards of x


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0.41 gram/mile for HC and 0.4 gram/mile for Ν Ο seem too stringent by a factor of about 3. The panels estimated that emission rates needed to achieve the NO2 and oxidant air quality standards should be of the order of 1.3 grams/mile of HC and 1. 5 grams/mile of NO . However, in an appendix to the joint panel s report, the argument is developed that very substantial reductions of hydrocarbon emissions may be required to achieve the oxidant air quality standard. This is because laboratory studies show that NO acts as an inhibitor, and NO2 as a promoter of the photochemical smog reaction, and NO is converted to NO2 when hydrocarbons and sunlight are present. Therefore, since most ΝΟχ enters the atmosphere as NO rather than as NO2, a conceivable strategy for oxidant standard achievement is hydrocarbon emission reduction without NO emission reduction. In either event, the mandate appears more stringent tha sive stringency is furnished by the EPA statement that because faulty analytical techniques led to incorrect ambient NO2 levels, the vehicle ΝΟχ emission standard should be revised upward (9^. Revision of this standard would significantly widen the scope of choices among options for future vehicle emission control. Among the expected benefits of revised standards - still consistent with achievement of the air quality standards - would be improved system reliability, reduced maintenance costs, and improved fuel economy. The later sections of this paper deal with these considerations. χ

x

1

Alternate Automotive Emission Control Systems Automobile exhaust emission standards required by the 1970 Amend ments to the Clean Air Act as well as the 1975 interim standards are lower than the emission levels from current cars. The domestic auto motive manufacturers have indicated they will use catalytic devices to achieve these interim as well as the statutory automotive emission standards. These catalytic systems, however, will require lead-free gasoline. Anticipating the use of catalysts and the need for lead-free gasoline, the engine compression ratios of cars built since 1970 were reduced to allow use of lower octane unleaded gasoline without knock. This compression ratio reduction has resulted in higher vehicle fuel consumption. Thus, the decision to use catalysts requiring unleaded fuel resulted in increased use of refinery crude oil because of a decrease in vehicle fuel economy and the need to make unleaded gasoline. On the other hand, if the standards recommended in the previous section were adopted, then alternative emission control systems could be considered. As an example, the emission control systems based on thermal reactors can be used. These non-catalytic systems are


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compatible with leaded fuel and high compression ratio engines and could be used to give improved fuel economy. Thus, it is desirable to consider the performance of alternate control systems capable of meet ing the less stringent standards, particularly in view of the fuel savings which may be possible. Du Pont Total Emission Control System. The Du Pont emission control system consists of three major elements and appropriate engine modifications to optimize emission control and fuel economy. As indicated in Figure 6, the first component consists of an exhaust mani fold thermal reactor which replaces the conventional exhaust manifold. The reactor provides a high temperature zone where exhaust gases mix with air supplied by an air pump and in which the hydrocarbons and carbon monoxide are oxidize component consists of a when coupled with modifications to the carburetor metering and ignition timing, controls nitrogen oxides. The EGR device returns a portion of the exhaust gas to the carburetor to dilute the air-fuel mixture, which in turn reduces peak combustion temperatures and reduces nitrogen oxides formation. Finally, a muffler lead trap is used in place of the conven tional exhaust muffler to remove most of the particulate lead from the exhaust gas before it leaves the tail pipe. When combined, these com ponents form the Du Pont Total Emission Control System or TECS. First and second generation thermal emission control systems, TECS I and TECS II, were described in earlier publications (10) (11). The TECS I vehicles were designed in 1969 and 1970 to meet the then existent exhaust emission standards for the 1975 model cars set forth by the U.S. government and by the State of California. After the passage of the 1970 Amendments to the Clean Air Act, a second generation system, TECS II, was developed in an attempt to meet the more stringent emis sion levels mandated by the Act. More recently, the TECS ΙΠ and IV systems have been developed to meet emission levels compatible with attainment of the ambient air quality standards while minimizing the fuel consumption penalty. The first generation emission control system, TECS I, was success ful in meeting the goals of the earlier 1975 U. S. and California standards. Six 1970 Chevrolets equipped with TECS I were operated in a 10-month field test by the California Air Resources Board. The fleet average emission levels remained below the former 1975 standards throughout this test. Extended operation of the TECS I vehicles revealed two major problems. First, fuel consumption was significantly higher than com parable unmodified production 1970 vehicles. During the 10-month test conducted in California, TECS I vehicles used 17% more fuel than un modified production vehicles. The second problem was excessive wear


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L Ο

A

A

A

A

I

10

20

30

40

50

1976 CO EMISSION STANDARD, g/MILE

Figure 5. Date o/ achievement of air quality standard for carbon monoxide as a function of vehicle emission standards and traffic activity

AIR PUMP

THERMAL REACTORS

Figure 6. Du Pont total emission control system (TECS)


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on various parts of the engine caused by the recirculation of metal oxides from the exhaust system back into the engine with the exhaust gas re circulation gases. This excessive wear problem was overcome by system modifications employed in TECS III and IV. Vehicles equipped with the second generation emission control system, TECS II, included a full-size Chevrolet sedan equipped with a V-8 engine and automatic transmission, and a sub-compact Pinto equip ped with a small four-cylinder engine and manual transmission. These vehicles approached but did not meet the emission levels required by the 1970 Amendments to the Clean Air Act. Hydrocarbon levels were below 0.25 gram per mile but carbon monoxide levels were about 6 grams per mile and nitrogen oxide levels were about 0. 6 gram per mile. To meet the very low nitrogen oxide levels, carbutetors were operated very rich which increased fuel consumption more fuel and the Pinto 20 unmodified production vehicles. In view of the growing concern over the increased consumption of fuel by low emission cars, it was decided to develop improved total emission control systems and evaluate internal engine modification for emission control. The goal of this program was to achieve emission levels adequate to meet ambient air quality standards in major urban areas while minimizing the fuel consumption penalty which usually accompanies the attainment of such low emission levels. The designs, emission control, and fuel economy achieved with these systems are discussed in succeeding sections. Design of TECS ΠΙ. The same general emission control systems used for TECS I and II were used in TECS III and IV. The major differ ence in the later systems is the emphasis on fuel economy and the use of high compression ratio engines with TECS IV vehicles. A 1971 Pinto and a 1971 Chevrolet were chosen for the development of the TECS III because of our experience with these vehicles and the fact that they represented both current production standard size vehicles with V-8 engines and automatic transmissions as well as the sub-compact cars representative of both domestic and foreign production. A description of the vehicles and the type of control system installed is summarized in Table 6. The TECS III system installed on the 1971 Chevrolet is shown sche matically in Figure 6. The exhaust manifold reactors shown in Figure 7 were modifications of the Type VIII insulated reactor previously des cribed (11). The interior core of the reactor was a large diameter open chamber with a single baffle located across the outlet pipe. The exhaust gases entered the core through extended exhaust ports and exited from these ports through rectangular slots which contain directional vanes.


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The core consisted of concentric, double walled cylinders to reduce the heat loss from the inner core to the outer shell of the reactor. To further reduce heat loss, the outer shell and outlet pipe from the reactor were covered with a one-half-inch layer of fibrous ceramic insulation. Secondary air was injected into the exhaust ports and into the ends of the reactor to provide an overall oxidizing atmosphere. Table 6 TECS III Vehicles 1971 Chevrolet Vehicle Engine Transmission Thermal Reactor

EGR Traps Carburetion Spark Timing

Four-doo 4, 50 350 CID V-8 3 Speed automatic Modified Type VIIÏ, insulated, with air injection Below throttle, ~ 10% None Moderately enriched, fast release choke Modified vacuum advance on start up

1971 Pinto

1600 cc In-line 4 cylinders 4 Speed manual Type V, shielded with air injection Above throttle, 13% Muffler lead trap Moderately enriched, fast release choke Modified vacuum advance on start up

The exhaust gas recirculation system for the Chevrolet TECS III vehicle utilized two 1973 production EGR valves for this make vehicle. Exhaust gas was taken from the exhaust pipe ahead of the muffler on one side of the dual exhaust system, routed through the two EGR valves in parallel, and introduced below the secondary throttle plates of the fourbarrel carburetor. The EGR valves were operated by manifold vacuum obtained from a port in the carburetor and were turned off at idle and at wide- open-thr ottle. Changes were made to the carburetor metering, spark advance characteristics, and exhaust gas recirculation rates of the 1971 Chevrolet to improve fuel economy while maintaining low exhaust emission levels. A modified version of the production four-barrel carburetor normally used for this engine was employed. Metering was set to give a maximum vacuum air-fuel ratio at idle and a gradual leaning of the air-fuel ratio at mid-speed cruise range to give air-fuel ratios of 13.5 to 14:1. A production 1970 distributor was used with the basic timing advanced 8° from the manufacturers specifications for the 1970


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model to improve fuel economy. The production intake manifold was replaced with a dual-passage Offenhauser manifold and the intake system heat was supplied by engine coolant routed directly from the outlet of the engine through the internal passages in the intake manifold. The TECS III system installed on the 1971 Pinto is shown schematically in Figure 8. The thermal reactor, shown in Figure 9, was a Type V exhaust manifold reactor. Appropriate modifications to the reactor port spacing, flanges, and the exhaust outlet were made to fit this design to the 1.6 liter Pinto engine. The reactor contained an inner core to promote mixing of the air and the exhaust gases and a double walled heat shield to reduce heat loss to the outer shell. No external insulation was used. All interior parts were made of Inconel 601 and the outer shell was 304 stainless steel. The air injection syste off the crankshaft at a pump-to-engin varied from about 3 cfm at idle to 15 cfm at 55 mph). The air from the pump was injected into each exhaust port. The exhaust gas recirculation system for the Pinto is shown schematically in Figures 9 and 10. The exhaust gas was withdrawn from the exhaust ports in the immediate vicinity of the exhaust valve. The individual lines from each of the four ports were manifolded together to take advantage of the exhaust blowdown process to force the exhaust gas through the EGR line. A vacuum operated on-off valve prevented exhaust gas recirculation during cold start up. Exhaust gas was delivered to the carburetor below the venturi and above the throttle plate. The air injection tubes were located approximately one inch downstream from the exhaust gas recirculation pick up tubes in the exhaust ports. The recirculated exhaust contained about 25% injected air. A total of 18% exhaust gas and injected air was recirculated to the carburetor resulting in a true exhaust gas recirculation rate of 13% in terms of the air-fuel mixture delivered to the engine. The carburetor used on the Pinto was selectively enriched throughout the metering range to aid in control of nitrogen oxide emissions. The air-fuel ratio varied from 13.5 to 14.0:1 over mid-speed range. The idle speed was increased from a standard 900 to 1000 rpm. A vacuum spark advance control system sensitive to coolant temperature was incorporated to prevent manifold vacuum advance during cold starts until the coolant reached normal operating temperatures. Design of TECS IV. The TECS IV system was installed on a 1973 Chevrolet equipped with a 350 CID, V-8 engine as shown in Figure 6. The engine compression ratio was increased to 9.25:1 by use of 1970 350 CID engine heads. Otherwise, TECS IV was quite similar to the TECS III installed on the low compression ratio 350 CID engine of the 1971


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Figure 7. Modified Type VIII thermal reactor for 350 CIO Chevrolet

AIR PUMP

THERMAL REACTOR

Figure 8. Du Pont TECS III installed on a IS liter Pinto vehicle

Figure 9,

Type V thermal reactor for a 1.6 liter Pinto


119

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Chevrolet. The thermal reactor shown in Figure 11 was a Type LX. The interior core was changed to enhance exhaust gas mixing to provide improved combustion under lean operating conditions. Again, a modified version of the production 4-barrel carburetor normally used with this engine was employed and the metering was set to give lean operation with air-fuel ratio of approximately 15:1. The basic ignition timing was advanced 10° from the manufacturer's specification to improve fuel economy. Emission Control With TECS III and IV. The Pinto equipped with the Du Pont TECS III system was driven successfully for 100, 000 miles using leaded gasoline. The road mileage accumulation consisted first of a 4, 000-mile, cross-country trip from the east coast to Denver, to the continental divide, and bac test, the vehicle was drive driving route in the South Jersey area. During the evening and nighttime hours, mileage was accumulated on a programmed chassis dynamometer following a simulated turnpike driving schedule with speeds varying between 40 and 60 mph with an average speed of 50 mph. An unmodified production version of the 1971 Pinto was run as a companion car with all of its mileage being accumulated in a similar manner except for the cross-country road trip. Commercial gasoline containing 2.2 grams of lead per gallon and conventional multigrade lubricating oils meeting the manufacturers specifications were used for these tests. The gaseous exhaust emission levels of hydrocarbons, carbon monoxide, and nitrogen oxides for the TECS III Pinto measured at intervals during the 100,000-mile test are shown in Figure 12. As can be seen, the average emission levels were below both the 1975 U. S. and the more stringent California interim emission standards for the entire test. The average emission levels during the 100,000-mile test as measured by the 1975 CVS Federal Test Procedure are given in Table 7. Mechanical failures such as burned valves and worn clutches occurred in both the companion unmodified and TECS Pintos. Some minor mechanical problems such as broken reactor core pins and cracks in the welds of the outer casing of the thermal reactor occurred at 51,000 and 84,000 miles. The pins were replaced, the welds repaired and the test continued. These failures were due to mechanical design problems which could be easily rectified in commercial designs. The interior reactor core and shield and all other hot parts remained in good condition throughout the test. The average emission levels from replicate emission tests for the TECS III on the 1971 Pinto and a 1971 Chevrolet are given in Table 7. In addition, the results for the modified 1973 Chevrolet with TECS IV tuned to meet different emission levels are included.


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Alternative Automotive Emission Control Systt

ON-OFF VALVE \ J (J

Ç=^==T=^

Î>

! CARBURETOR

Figure 10. Exhaust gas recirculation system for 1.6 liter Pinto

Figure 11. Type IX thermal reactor for 350 CID Chevrolet


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1975 Federal Test Procedure Emission Standards

2.0

1975 U. S. (1.5)

I! S£ Ο

1.0

1975 California (0.9)

-

(Λ

LJ

' i

0.5

0.8

50 75 Thousands of Miles

100

>£ 25

J

1976-1977 U. S. (0.41)

1975 U.S. (15.0)

1975 California (9.0)

—

25

50 75 Thousands of Miles

1976-1977 U.S. (3.4)

100

1975 U.S. (3.1)

/1975 California (2.0) 11976 U.S.

1977 U. S. (0.4)

25

50

75

100

Thousands of Miles Figure 12.

Exhaust emission levels of TECS- equipped Pinto during 100,000-mile road test


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Table 7 Emission Levels of Vehicles With TECS ΙΠ and TECS IV

Vehicle 1971 1971 1973 1973

Pinto 1.6 Liter Chevrolet 350 CID Chevrolet 350 CID Chevrolet 350 CID

1975 Interim Standards U.S. 49-State California

Control System TECS III TECS III TECS IV TECS IV

Emissions, Grams Per Mile NO HC CO χ 5.9 0.5 1.3 0.4 7.0 1.0 1.5 0.4 8.0 11.3 2.3 0.4

0.9

9.0

2.0

Fuel Economy. The fuel economy of all vehicles was measured over a 26-mile city-suburban course which included approximately 9 miles of city traffic and 17 miles of suburban roads and interstate highways. The average speed was 30 mph. The test vehicles were fueled from auxiliary tanks located in the trunk and the fuel consumption was determined by weight difference. The emission control vehicles and the standard pro duction vehicles used for comparison were driven in convoy in order to insure that variations in traffic and thus variations in average speed on the course did not influence results. The drivers and the position of the cars were rotated and at least four replicate tests were made. A l l results are reported as an average of these replicate determinations. Modifications of carburetion and ignition timing incorporated in the TECS ΙΠ and TECS IV vehicles have improved fuel economy compared with the earlier emission control systems. In addition, the higher com pression ratio engine used with the TECS IV vehicle gave greater im provement in fuel economy than obtained with the TECS III vehicle at similar emission levels. As shown in Table 8, the fuel economy was significantly better with the TECS vehicles than with the 1973 unmodified production vehicle. As shown in Table 9, the 1. 6 liter 1971 Pinto equipped with the TECS III system had an average fuel economy penalty of 6.9% as com pared with the unmodified production vehicle. A recent change in the city portion of the driving course to avoid more congested streets explains the greater fuel economy for both cars at the 100,000-mile test point. However, the percent difference in fuel economy remained about the same as for earlier tests. The fuel economy of the TECS III Pinto was 6% better than that measured for two unmodified 1973 Pintos. Minor improvements in ignition timing, carburetion, and, most importantly, a


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significant reduction in the pressure drop across the muffler lead trap when compared with the lead trap incorporated in the TECS II vehicle resulted in a significant improvement in acceleration time for the TECS III vehicle. When compared with the unmodified vehicle, the TECS III car had an 11% increase in wide-open-throttle acceleration time. Table 8 Fuel Economy of Chevrolets Equipped With TECS III and TECS IV Fuel Economy Miles/Gallon % Gain* Unmodified 1973, 35 Chevrolet, 8.2:1 C.R. 1971 Chevrolet With TECS III 8.2:1 C.R. Meeting 1975 California Standards 1973 Chevrolet With TECS IV, 9.25:1 C.R. Meeting 1975 U.S. Standards 1973 Chevrolet With TECS IV 9.25:1 C.R. Meeting 1975 California Standards

13.2

13.8

4.5

14.6

11

14.1

8

* Compared with 1973 Table 9 Fuel Economy of 1971 Pinto With and Without TECS III

Vehicles Miles 0 25,000 50,000 75,000 100,000*

Fuel Economy, mpg Unmodified Pinto TECS III Pinto 25.0 25.3 24.0 24.9 29.0

*

% Change

22.4 -10.4 24.2 - 4.4 22.8 - 5.0 22.8 - 8.4 27.2 - 6.2 Average -6.9

Course change


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During the course of developing emission control systems based on thermal reactors, a program was undertaken to determine what levels of emission control could be achieved without any form of exhaust aftertreatment. The possibility that less stringent standards might be satisfactory for achieving desired air quality gave added impetus for proceeding with this program. The incentive for doing this was the belief that markedly improved fuel economy could be obtained. A standard 1970 Chevrolet with a 350 CID, V-8 engine was modified by (a) changing cylinder heads to increase the compression ratio to 10.5 to 1 and provide a fast burn chamber, (b) installing head land pistons and rings to reduce the quench zone to reduce unburned hydrocarbons, (c) installing a leaner 4-barrel carburetor, (d) installing a production 1973 intake manifold to provide 1973 production EGR to reduce nitrogen oxides, (e) optimizing camshaft timing ignition timing was advance a 1970 model and the transmission control spark system was deactivated. The camshaft was advanced about 5° from standard for the 1970 Chevrolet. Carburetor metering was set to give lean operation with air-fuel ratio ranging from 16 to 17:1. No air injection, add-on thermal or catalytic reactors, special high energy ignition system or special choke were used. All components used in the modification were stock parts and easily obtained. The results to date with only "internal" engine modifications show striking improvements in fuel economy, driveability, and reduced emissions. As shown in Table 10, the emission levels were well below the 1974 emission standards and except for the hydrocarbon levels, were below the 1975 U.S. interim emission standards. The fuel economy, Table 11, was 6% better than a comparable 1967 model and 21% better than a 1973 model as measured in replicate tests on the Du Pont citysuburban road course. Table 10 Emissions With Only Engine Modifications No Thermal Or Catalytic Reactor

Vehicle 1970 Chevrolet 350 CID 10.5:1 C.R. 1974 Standards 1975 Standards U. S.

Emissions, Grams Per Mile 1975 CVS Test Procedure HC CO NO 2.0 3.0 1.5

6.1 28 15

2.2 3.1 3.1


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Table 11 Fuel Economy Obtained With Standard and Modified High Compression Ratio Chevrolet

Vehicle Unmodified 1973 Chevrolet Modified 1970 Chevrolet With 10.5:1 C.R.

Fuel Economy Miles/Gallon % Change vs. 1973 13.3 16.1

+ 21

Lead Tolerant Emission Control Systems. Based on the results presented in the above sections emission control systems on both large and small vehicles to values which are compatible with meeting the national ambient air quality standards. Furthermore, these emission control systems exhibit fuel economy and vehicle performance characteristics which are better than current production vehicles. These systems can be used with leaded gasoline and thus provide the motorist with the benefits of less expensive gasoline and higher compression ratio, more efficient engines. If lead continues to be used in gasoline at current levels and it is prudent to reduce vehicle lead emissions to avoid any potential health risk, lead traps could be used. The performance of the Du Pont lead traps is described in the next section. Du Pont Lead Traps Design and Performance. The Du Pont muffler lead traps have been developed to reduce the level of particulate lead material emitted in the exhaust of vehicles operated on conventional leaded gasoline. The muffler lead trap, shown in Figure 13, is a single unit, sized and shaped like a conventional muffler, and located in the same position under the car. The trap contains a bed of alumina pellets which induces agglomeration and growth of lead particulate to larger particles. These large lead particles eventually flake off the alumina pellets and are reentrained in the exhaust gas stream. The exhaust gas then passes into two parallel inertial cyclone separators which separate and retain the lead particles in collection chambers. The collection chambers can be sized to hold all the exhaust particulate matter collected during 100,000 miles of operation on conventional leaded gasoline. The Du Pont muffler lead trap has been used on a wide variety of cars - both current production vehicles as well as those equipped with advanced emission control systems.


7.

CANTWELL

ET

AL.


127

Identical muffler lead traps were installed in place of the exhaust muffler on each of four 1970, 350 CID Chevrolets. These cars were operated on laboratory chassis dynamometers according to the Federal mileage accumulation schedule using gasoline containing 2.2 grams of lead per gallon. During this mileage accumulation, the total lead emissions were measured according to the procedure previously described (12). The average total lead emission rate for each vehicle during the life of the test is summarized in Table 12. Table 12 Du Pont Muffler Lead Traps On 1970 Chevrolet

Vehicle C-82 C-83 C-85 C-130

Miles 52,669 48,735 50,102 12,440

Weighted Mean

Grams/Mile

Due to Trap*

0.015 0.015 0.015 0.012

87 87 87 89

0.015

88

* Average lead emission rate of production Chevrolets is 0.116 g Pb/mile (Ref. 12, Table 1) In addition to reducing the total amount of lead emitted, the muffler lead traps also reduce the amount of the small, air-suspendible lead particles emitted to the atmosphere. The effectiveness of the lead traps in reducing the emission of lead particles of various sizes at 15,000 and 50,000 miles is shown in Table 13. As expected, the lead traps with their inertial separators were effective in removing almost all of the large particles which for the most part flaked off the walls of the> exhaust system. Of special interest is the 68% reduction in the submicron particles. The reduced emission of these small particles is most important since these particles tend to remain airborne and correspond to the size of lead particles found in the atmosphere of urban areas. The efficiency of the traps for capturing these small particles was about the same at 15, 000 miles and 50, 000 miles. This indicates that the alumina pellets did not deteriorate with mileage. It also indicates that fresh alumina surface is not required which is good, since the pellets tend to become coated with lead salts with extended mileage. High surface area and optimum temperature appear to be much more important factors in trapping the lead.


128

AUTOMOTIVE

EMISSIONS

CONTROL

Table 13 Muffler Lead Trap Performance On 1970 Chevrolet s

Vehicle

Mileage

Standard Car* Trap Cars C-82 C-83 C-85

14,500 3,300 9,00

Lead Emission Rate, g/Mile Particle Size, Microns >9 1 to 9

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Air Pollution Effects on Plant Growth: A Symposium Sponsored by the Division of Agricultural and Food Chemistry at the 167th Meeting of the American (Acs Symposium Series, 3.)

Hydrocracking and Hydrotreating.. A Symposium Sponsored by the Division of Petroleum Chemistry

Mechanism of pesticide action: A symposium sponsored by the Division of Pesticide Chemistry at the 167th meeting of the American Chemical Society, Los ... April 2-3, 1974 (ACS symposium series ; 2)

Physiological effects of food carbohydrates: A symposium co-sponsored by the Division of Carbohydrate Chemistry and the Division of Agricultural and Food ... 11-12, 1974 (ACS symposium series ; 15)

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Metal-DNA Chemistry (Acs Symposium Series)

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Extended interactions between metal ions in transition metal complexes: A symposium sponsored by the Division of Inorganic Chemistry at the 167th meeting ... April 3-5, 1974 (ACS symposium series ; 5)

Platinum Group Metals and Compounds;: A symposium sponsored by the Division of Inorganic Chemistry at the 158th meeting of the American Chemical Society (Advances in chemistry series 098)

Analytical Chemistry of Bacillus thuringiensis (Acs Symposium Series)

Chemistry of Wine Flavor (ACS Symposium Series, No. 714)

Bioregulators: Chemistry and Uses (ACS Symposium Series, Volume 257)

Adsorption at interfaces : papers from a symposium honoring Robert D. Vold and Marjorie J. Vold sponsored by the Division of Colloid and Surface Chemistry at the 167th meeting of the American Chemical Society, Los Angeles, Calif., April 2-5, 1974

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Arsenical pesticides: A symposium sponsored by the Division of Pesticide Chemistry at the 168th meeting of the American Chemical Society, Atlantic City, N.J., Sept. 9, 1974 (ACS symposium series ; 7)

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