Approaches to Automotive Emissions Control - ACS Publications

3 Gaseous Motor Fuels—Current and Future Status W. H. FINGER —Humble Oil and Refining Co., Baytown, Tex. 77520

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on May 15, 2018 | https://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/bk-1974-0001.ch003

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 y v e r s i o n s o f implementation plans f o r a c h i e v i n g and m a i n t a i n i n g the n a t i o n a l ambient a i r 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

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


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

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 n t h e same F i g u r e i s the horsepower o u t p u t 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 . 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 220 G r o s s Heat o f Combustion 23,861 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

—

—

184 21,646

20,500

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 .



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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 subj e c t e d t o p r e s s u r e s u s u a l l y n o t more than one pound p e r square i n c h above o r below a t m o s p h e r i c p r e s s u r e . 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 -



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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 h a f u e l f i l t e r and a h i g h p r e s s u r e r e g u l a t o r t o a v a p o r i z e r where a l l o f the 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



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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 r g a s o l i n e engines have r e s u l t e d . As p r e v i o u s l y mentioned t h e r e a r e f r e q u e n t l y n o t i c e 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



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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 comparative s a f e t y o f g a s o l i n e and t h e gas 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, the r e s u l t s o f t h e s e two s t u d i e s do not agree w i t h each o t h e r a t t r i b u t a b l e p r i m a r i l y t o 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 y f a c i n g c r i t i c a l requirements i n t h i s a r e a t o s u p p l y t h e g a s o l i n e needed i n t h e near 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 gaseous f u e l s used f o r t h e s e r e t r o f i t t e d 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



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1975

1980

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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 h e a l t h e f f e c t s r a n g i n g from a 2.1% improvement t o a 2.5% d e t e r i o r a t i o n . I t seems d o u b t f u l i f any o f t h e s e 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, (1972). 5. B a x t e r , M. C., "How Does LP Gas Reduce Exhaust 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.


3.

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.


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Approaches to Automotive Emissions Control - ACS Publications

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