National Academies Press: OpenBook

Report by the Committee on Motor Vehicle Emissions (1973)

Chapter: ALTERNATIVE SYSTEMS FOR LOW-EMISSION AUTOMOBILES

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Suggested Citation:"ALTERNATIVE SYSTEMS FOR LOW-EMISSION AUTOMOBILES." National Research Council. 1973. Report by the Committee on Motor Vehicle Emissions. Washington, DC: The National Academies Press. doi: 10.17226/11096.
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Suggested Citation:"ALTERNATIVE SYSTEMS FOR LOW-EMISSION AUTOMOBILES." National Research Council. 1973. Report by the Committee on Motor Vehicle Emissions. Washington, DC: The National Academies Press. doi: 10.17226/11096.
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Page 105
Suggested Citation:"ALTERNATIVE SYSTEMS FOR LOW-EMISSION AUTOMOBILES." National Research Council. 1973. Report by the Committee on Motor Vehicle Emissions. Washington, DC: The National Academies Press. doi: 10.17226/11096.
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Page 106
Suggested Citation:"ALTERNATIVE SYSTEMS FOR LOW-EMISSION AUTOMOBILES." National Research Council. 1973. Report by the Committee on Motor Vehicle Emissions. Washington, DC: The National Academies Press. doi: 10.17226/11096.
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Page 107
Suggested Citation:"ALTERNATIVE SYSTEMS FOR LOW-EMISSION AUTOMOBILES." National Research Council. 1973. Report by the Committee on Motor Vehicle Emissions. Washington, DC: The National Academies Press. doi: 10.17226/11096.
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Page 108
Suggested Citation:"ALTERNATIVE SYSTEMS FOR LOW-EMISSION AUTOMOBILES." National Research Council. 1973. Report by the Committee on Motor Vehicle Emissions. Washington, DC: The National Academies Press. doi: 10.17226/11096.
×
Page 109
Suggested Citation:"ALTERNATIVE SYSTEMS FOR LOW-EMISSION AUTOMOBILES." National Research Council. 1973. Report by the Committee on Motor Vehicle Emissions. Washington, DC: The National Academies Press. doi: 10.17226/11096.
×
Page 110
Suggested Citation:"ALTERNATIVE SYSTEMS FOR LOW-EMISSION AUTOMOBILES." National Research Council. 1973. Report by the Committee on Motor Vehicle Emissions. Washington, DC: The National Academies Press. doi: 10.17226/11096.
×
Page 111
Suggested Citation:"ALTERNATIVE SYSTEMS FOR LOW-EMISSION AUTOMOBILES." National Research Council. 1973. Report by the Committee on Motor Vehicle Emissions. Washington, DC: The National Academies Press. doi: 10.17226/11096.
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Page 112

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6. ALTERNATIVE SYS TEMS FOR LOW-EMISS ION AUTOMOB ILES The Committee a l s o cons idered p ower sys tems other than Otto­ cyc le ga s o l ine engines . It became apparent quite ear ly in t his s tudy tha t no a l terna t ive power sys tem could be produced in sufficient num­ bers by 19 75 or 19 76 to d is p lace an appre c iable part o f present engine­ produc t ion quant ities . S evera l p ower sys tems ( e . g . , Rank ine , S t ir l ing , b a t t e r ies , fue l ce l l s ) show promi se for eventua l ly mee t ing 19 76 s tan­ dards , but deve lopment time and co s t reduct ion are nece s s ary be fore the s e can become competit ive . Two engine s ( d ie s e l and gas turb ine ) s how promise o f meet ing 19 75 emi s s ion s t and ard s . However , even though such eng ine s have a lready been adapted to p a s s enger cars , l i t t le deve l ­ ment is be ing done o n them for 19 75 and 19 76 because they are cos t ly and have other detra c t ive chara c ter is t ic s . The pre sent d ie s e l is heavy , tends to smoke , and its exhaus t is odorous . The gas turb ine ha s poor fue l economy a t part load , and the NO emi s s ions are not pre s ­ x ent ly control l ab le to low enough leve l s . A l though it is unl ike ly tha t any a l terna t ive eng ine will be in a p pre c iab le ma s s product ion by 19 75 or 1 9 76 , some o f them wi l l b e p h a s e d i n within the next decade . Thus , s umma r ies o f the find ings con­ cerning the various sys tems are g iven b e l ow . 6.1 D ie s e l Engine s Recent data show tha t severa l current four - s t roke , and one two­ s troke , d ie s e l eng ine s can mee t 19 7 5 s tandards for carbon monoxide and unburned hydrocarbons . A typ ica l NO va lue for a current Mercede s Benz X 220D under the CVS -CH tes t is 1 . 65 g/mile . There have been no resu l t s ob ta ined o n d iesel engine s s howing a b i l ity to mee t the 19 76 NO s tan­ x dard o f 0 . 4 g / mile . Da imler-Benz e s t ima tes tha t the lowe s t NO leve l s X achievab le for d ie s e l s at the pre s ent s ta te o f the art would be ab out 0 . 8 g / mile . - 1 04 - Digitized by Coogle

New deve lopments in d ie s e l eng ines , such a s a two - s troke engine with a new , low-emis s ion combus t ion me thod , and the use of pos i t ive­ d i s p lacement rotary pr ime movers , such as the Wanke l -engine configura ­ t ion , o f fer the future pos s ib i l ity o f meet ing , or near ly mee t ing , 19 76 s tandard s with an eng ine tha t is sma l ler and cheaper than the pres ent ( 19 70 ) ga s o l ine engine . Much work mus t s t i l l be d one to prepare even suitable prototype s o f the se concep ts . There is a good pos s ib i l ity tha t a d ie s e l eng ine o f suffic ient power d ens ity , l ight enough we ight , and emis s ions near ly s a t is fac tory for 19 76 automob i le can be bui l t . But much engineering work mus t s t i l l b e done be fore there can b e a p roven concep t . Potent ia l prob lems o f smoke , wh ite smoke , odor , and no i s e s t i l l rema in . It appears tha t good s ingle pro to types of the advanced eng ine wi l l not be ava ilable be fore 19 75 . L imited product ion might be pos s ib le by 1980 . A pa s s enger-car d i e s e l eng ine d e s igned accord ing to exi s ting technology may have a po s s ib le d isadvantage in s l ightly greater weight and larger s ize over a s park- ignit ion engine of comparable output . It may cos t more ba s ica l ly , but the d ifference shr inks when the emi s s ion control s for ga s o l ine engine s are added in , s ince the add-ons for d ie s e l s to mee t 19 75 s tand ard s are minima l . It wi l l g ive better fue l economy and requ ire les s ma intenance , which should quickly make up any fir s t-cos t d i f ference . The effic ient d ie s e l wil l to lera te a wide range of fue l s and becomes of gre a ter intere s t as our concerns with energy conserva t ion increase . Becaus e fue l o f lower vo l a t i l ity is used , d ie s e l eng ine s have an addit iona l sa fe ty factor , and a ls o there would be le s s fue l -vapor emi s s ions at the fi l l ing s ta t ion. 6.2 Ga s Turb ine s Ga s turb ines are a fea s ib l e me thod o f propuls ion for s tandard­ s ize U . s . p a s senger cars . In pro to type form, they have demons trated accep table or super ior we ight , s ize , fuel consump t ion , dr ive ab i l ity , - 105 - Digitized byGoogle

ma inta inab i l i ty , re s is tance to abuse and neglec t , and s a fe ty . Carbon monoxide and hydrocarbon emi s s ions are below the 19 7 6 s tandards ; NO X emis s ions are pres ent ly above the 19 76 l imit s , but s evera l approache s have shown that it is technica l ly fea s ib le t o lower NO to 19 76 re quire- x ments e s p e c ia l ly for low-pres s ure-ra t io engine s . The concep t s can probab ly be incorporated in a pro t o type by 19 76 . The added c ontrol s o r cos t s o f rea ching 19 76 NO s t andard s are no t ye t known . X Ga s turb ines to d a te have a l l shown poor fue l consump t ion a t low d e s ign power and whi le opera t ing a t low frac tions o f the d e s ign power . Highly regenerated unit s tend to l imit the e f fect , but the po s s ib i l ity o f economic ga s turb ines having des ign power be low 150 horsepower and opera t ing under l ight ly loaded cond it ions is s ti l l a controvers ia l ma tter . The ret a i l cos ts o f future ga s turbine s ins t a l led in automob iles are highly uncertain. E s t imat e s made by various highly q ua l i fied ind i­ vidua l s or organiz a t ions run from a price be low tha t of the c leaned-up s park- ignit ion engine to one three or four times higher . Thes e e s t i­ ma tes are based on the use o f ma ter ia l s s imilar to those in today ' s engine s . Future pos s ib i l i t ie s for ga s turb ines improve a s the use o f ceramic s for many par t s is proven. I f ceramics become widely avail· ab le for the ho t parts o f gas turbines , i t i s genera lly agreed that the engines would eventua l ly co s t l e s s than the spark- ignition a lterna t ive . In add ition , the emp loyment o f critical resources would be grea t ly reduced . A rea l i s tic s chedule for advanced ga s turb ine s t o be produced in q uant ity would be for a dvanced l imited-product ion eng ines by 1 9 8 2 , fo l l owed by ma s s product ion by 1984 . - 106 - Digitized byGoogle

6.3 Stirl ing Engines A t the present state of development , S t irling engines are very efficient engine s tha t could allow high-performance full-size automobiles to meet the 19 76 emission standards. Any form of heat energy or fuel source can be used to opera te it . The engineering problems that remain to be solved be fore it would be poss ible to adop t them as pract ical engines for limited applica tion relate to the reliability of sealing the working fluid ins ide the engine, to the cost and rel iability o f the heater a s sembly , and to the development of a simple, ver s a t ile power­ output control system. Considerably more engineering is necessary to allow the engine to be considered as an entirely suitable automobile power plant. Add itional developments necessary to make this poss ible relate to cost, opera tion in the hands of the customer, and integra tion into the automobile. The two se ts of problems are best attacked simul­ taneously and may involve changes in the present form of the engine. The potent ial of the engine goes well beyond its present state. S ize, we ight, producibility , sa fe ty, response to abuse and neglect, starting ease , driveability and versa t ility , control ease, fuel eco­ nomy , noise , emissions , and cos t potent ial all show indications of being competitive with or better than diesels in the present generation of development , and equal to or better than gasoline engine s in the next genera tion of development. Thus, the engine could fit into the auto industry, truck industry , and other segments of the transportat ion industry , independent of the eventual outcome of the energy cr isis or the fuel controversy. Approximately 4 to 10 years of addi tional devel­ opment will be required to solve the out standing engineer ing problems and produce a prototype advanced Stirling eng ine suitable for present­ type automobiles. - 107 - Digitized byGoogle

6.4 E le c tr ica l ly Driven Vehicles E lectrica l ly dr iven vehicles in pr inc ip le provide freedom from p o l lution and are character ized by high energy e f ficiency , flexib i l i ty o f per formance , good durab i l i ty , and low ma intenance re qu irement s . At p re s ent , the l imit ing factor re lat ing t o the te chnica l and economic fea s ib i l ity of e l e c tric vehic les is the vehicular power source . E lec­ tric drive sys tems (mo tor and contro l s ) having exce l lent character i s t ic s have been demons tra ted ; d evelopment o f o p t ima l drive sys tems is not c on­ s idered to be l imiting in the u l t ima te rea l i z a t ion of e lectr i c automo­ b iles . Fue l - cel l - powered electric veh ic les in wh ich the free energy o f fo s s i l fue l s i s d irec t ly conver ted into e lec tr ical energy for mo t ive power do not emit CO or NO ; unused hydrocarbons c an be eas ily removed X from the exhau s t . Fue l cel l s are no t hea t eng ines and are no t sub j e c t t o the Carnot l imi tat ion . For th is reason they may opera te a t very h igh energy-convers ion e f f ic iency , resu l t ing in s uper ior fue l economy . Although some fue l - ce l l sys tems have been succes s fu l ly dep loyed in space mis s ions , these are no t a d a p table for app l ica tions where low ,.- cos t i s impor tant . Current advanced developments directed toward s t a ­ tionary a p p l icat ions i n commer c ia l and consumer marke t s are in the fie l d - t e s t s ta ge . The s e repre sent important co s t reduction and per for­ mance improvements rela tive to the aero s p a ce uni t s . With further s ig­ ni ficant cos t and performance improvement s , vehicular app l ica tions in smal l quant i t ie s may become fea s ib l e wi thin 10 to 15 years . V ehicle s that emp loy rechargeab le b a t terie s a s a power source do no t have emi s s ions re s ul t ing from the combus t ion of fue l s ; the s ite of emis s ions is trans ferred to centra l power s tat ions where such emis­ s ions are under s tood to be more e ffec t ive ly contro l led , and a t a lower co s t . Because o f the high e fficiency o f batteries and o f e lectric dr ives , the net fuel economy of s uch vehicles promises to be be t ter - 108 - Digitized byGoogle

.J than tha t o f pres ent automob i l e s . Fur thermore , if we move toward an e le c tric economy , bat ter ie s may a s s ume a unique role in the trans porta­ tion sy s tem. In contra s t to fuel cel l s , extens ive exper ience exis ts with re­ s pec t to the performance charac teris t ic s o f a t lea s t one bat tery sys tem­ lead/ ac id . Th is b a t tery is rugged , e f f ic ient , rel iab le , and can res pond ins tantaneous ly to l arge changes in load . Pre s ently ava i lab le s pe c i a l ­ purpo s e veh icles can provide ranges of up t o 50 mi les and modes t acc e l ­ era tion marg ina l ly acc ep tab le under urban dr iving cond i t ions , at a high cos t . Other currently available rechargeab le bat teries , such as z inc/ s i lver- ox ide and cadmium/ nicke l - oxide , wh i le super ior in some r e s pec ts to the lead / a c id sys tem , are inherent ly uns u itab le for vehicu l ar a p p l ic a t ions becaus e o f cos t and / or l imi ted ava i labi l i ty o f materia l s . S t i l l o ther ba t tery sys tems concurrent ly in var ious s tage s o f deve l o p­ ment o f fer s ignificant performance improvements , and may mee t the cos t and ma teria l s requ irements for vehicular app l ic a t ions . The z inc / nicke l - oxide bat tery is expec ted to a l l ow a vehic le des ign wi th ac cep table acce lerat ion and a range of abou t 80 mi les be­ tween recharge s . The mos t promis ing o f the advanced bat tery sys tems are sod ium/ su l fur and l ithium/ s u l fur bat teries , wh ich operate a t tempera ture s in 0 the range 300-400 C , and are mainta ined at operat ing tempera ture by the ir re j ec t hea t and appropriate thermal insul ta t ion. The s e batteries are expec ted to have s pe c i f ic energ ie s of 100 wa tt-hours / pound and spec ific powers of 100- 200 wa t t s / pound , permi t t ing the de s ign and cons truc tion of e lec tric vehicles with excel lent accelerat ion capab i l ­ i t ies and a range of about 200 mi les between recharge s . Abou t 7 o r 8 year s o f o p t imum e f for t wil l probably be requ ired for the deve l opment of p i l o t quant ities of the se b a t teries for veh ic le te s t purpo ses . Still o ther promis ing nonaqueous sys tems are i n early s t ages of exp lora t ion. - 109 - Digitized by Coogle

Hybrid e l e c tr ic/ hea t- engine powerp lants are c l aimed to enab le reduct ion o f the emi s s ion of a ir po l lutant s . The expec ted improvement in dr iveab il ity by us ing the e l e c tric mo tor for power surges should al low the he a t eng ine to operate c l eanly and economical ly at one s e t t ing or wi th a s l owly vary ing s e t t ing over a range . There are s ignif icant pena l t ies in the areas of c o s t and comp lexity that mus t be overcome before the hybr id can be cons idered a viab le contender . Even if the technic al and economic cr iter ia c an be me t , it is doub tful whe ther in­ troduc t ion of this new and complex power- p l ant scheme wi l l repre sent any more than an inter im solution with res pec t to po l lu t ion aba tement and e ffec t ive use of na tural resources . 6.5 Rankine Engines Tes ts made on Rankine-eng ine component s have s hown that the 1 9 7 6 s tand ard s could probably be met wi th Rankine-eng ine-powered , s tan­ dard- s ize automob iles . Var ious approaches to the de s ign ind icate that Rankine engines can be made to f i t into ful l- s ize automob iles . The s e f indings are to b e demons tra t ed with working unit s i n rea l automobiles by 1 9 75 . Eng ine no ise promis e s to be low excep t for the co ndenser fans , which could be troub lesome due to large air- flow re q uirements . S tart­ ing should be easy , al though t ime-consuming ( one minute being a practi­ ca l e s t imate ) . The dr iveabi l ity of Rankine-powered automob iles should be s a t is fac tory i f a su ffic ient ly h igh p ower- to-we ight rat io can be ach ieved . One ful l - s ize automob i l e ha s been fit ted with a !50-horsepower s team engine . Emi s s ions did not meet 19 76 s tandard s and there were o ther detracting fea tures , which can be traced par t ly to the under­ deve loped na ture of the engine . Lower-power s team eng ines have been fitted into compac t-s ize automob iles and demons trated . Low power dens i ty is a genera l character i s tic o f these engine s , traceab l e to poor e f ficiency . - 1 10 - Digitized by Coogle

Newer form8 o f Rankine eng ines tha t use organic f luids f l owing through e i ther reciprocating or turb ine mach inery offer the pos s ib i l i ty of trouble- free opera tion ( no freez ing , easy s tart ing ) a t the expense o f poorer fue l economy as compared with s team. These uni t s wi l l be l arger and more d ifficul t to integrate than wil l s team eng ines . The Rankine cyc l e in any vers ion will tend to have re l a t ive ly uniform s pec ific fue l consump t ion over the operat ing range . Th is lead s t o reasonab le fue l economy ( b u t les s than tha t of gasol ine- powered auto­ mobiles o f s imil ar s i z e ) over typ ical dr iving schedules when s te am , or the bes t organic- f l u id , eng ines are cons idered . T o achieve an eng ine wi th reas onab le fue l economy , the contro l s have to b e c omplex and the eng ine has to b e a s l arge a s po s s ible within the a l l owable enve lope . Thus , any Rankine engine wil l be pushed to the allowab le l imits on s ize , weigh t , and cos t for a g iven app l ic a t ion , and the au tomobile wil l be cons id erab ly underpowered and overpriced as compared with a gas o l ine engine in the s ame application . Des p ite its po tent ial ly good emis s ions , dr iveab i l i ty , and low no ise , most o f the o ther rea l is t ic evaluation fea tures for automob ile eng ines ( such as s ize , we igh t , cos t , fue l economy , and s tarting t ime ) are mi s sed by the Rankine eng ine , independent of type . I t is prob l ema t ic whe ther even l imited produc t ion o f ful l - power eng ines could be feas ib le before 1 9 80 . Limi ted produc t ion o f exi s t ing des igns for low- power app l ic a t ions could beg in by 1976- 7 7 . Maj or que s t ions remain to be answe red a f f irmat ively with respe c t t o s afe ty , operab i l i ty , rel iab i l i ty , and overal l dr iving ver s a t i l ity in the hand s of the pub l ic . Unit c o s t and the ab i l i ty to be phased into produc t ion pre sent even l arger que s t ions for which a f f irmat ive answer s are l acking . - 111 - Digitized byGoogle

A s u i table ful l - s ize , proto type Rankine engine wil l no t be ava i l ab le unt i l 1 9 7 5 (EPA schedule ) . Deve l opment o f a manufac turab l e pro to type mu s t fo l low th is b y sever a l year s , wh ich mu s t i n turn be fo l l owed by normal deve l opment . 6.6 O ther Engines A wide var iety o f o ther eng ine s with some po tent ial advantage over the gasol ine eng ine or d ie s e l eng ine h ave been cons idered over the years . Mo s t of the se have no t been developed even as far as the au tomob ile gas turb ine , Rankine eng ine , or S t irl ing eng ine . None o f them seem t o o f fer a c le ar-cut advantage in emi s s ions over the o ther types , and they a l l o f fer some increase in comp lexity , we ight , vo lume , and probably cos t . Sy s tems us ing pos i tive d is p l acement mach inery but with combus t ion taking pl ace out s ide the cy l inder ( o ut- o f - cy l inder combu s t ion sy s tems ) have been s tud ied for eng ine s o perat ing on the d ie s e l cyc l e , the O t to cyc l e , the Bray ton cyc le , and many var i a t ions . They a l l s u f fer from l owered e f f ic iency , l a rger s i ze , and probab le h igh NO va lues . None X o f the se sy s tems appear to offer any bas ic advantage that c anno t be ach ieved ul t �ately by d ie s e l s , gas turb ine s , and S t ir l ing eng ine s , a l l o f wh ich show promise o f l ower co s t . - 1 12 - Digitized byGoogle

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