缸内直喷汽油机的HC排放特性分析及未来排放法规对其的挑战性_英文_

1、Article ID : 100420579 ( 2001) 0320278207HC Emission Anal ysis ofGa sol ine D irect Inject ion Engines an d Challenge Faced by Such Engines in Meet ing Futures Emission Stan dardHUAN G Ying , GE Yun2shan , ZHAN G Fu2jun , ZHAO J ing2wei( School of Vehicle and Transportatio n Engineering , Beijing In

2、stit ute of Technology , Beijing 100081 ,China)Abstract : Based o n t he int roductio n of t he basic co mbustio n co ncep t of gasoline direct injectio n ( GD I) engine and it s operatio n under different operating co nditio ns , HC emissio n mechanisms of t he GD I engine are analyzed. And HC emis

3、sio n characteristics of t he GD I engine are co m2 pared wit h t he PF I engine via a co mpariso n test based o n t he F TP275 driving cycle. It can beco ncluded t hat t he GD I engine is facing a big challenge in meeting t he f ut ures HC emissio nstandard . Reaso ns for t he higher HC emissio ns

4、of t he GD I engine are discussed and t he ways forHC emissio n co nt rol are given.Key words : gasoline direct injectio n ( GD I) ; emissio n ; cold start ; gasoline engineCLC number : T K 411153 Document code : AWit h gasoline direct injectio n ( GD I) engine , bot h f uel eco no my and drive abil

5、it y can be achieved simultaneo usly. So me wo rld leading co mpanies have p ut t heir GD I engines into t he mar2 ket , such as Mit subishi and Toyota . However t he p ropert y of t he exhaust emissio n is not clear fo r t his engine .It is well know n t hat t he vehicle emissio n standard is beco

6、ming mo re and mo re st ringent wo rldwide. Acco rding to UL EV , Tier 2 , Euro and Euro , t he f urt her reductio n of HCemissio ns must be achieved. And refering to F P T275 test cycle and N EDC ( new European driving cycle) test cycle , tailpipe emissio ns will be measured f ro m starting up , wi

7、t h acceleratio n loading at 21 s and 11 s respectively. It means t hat exhaust emissio ns during cold start have been taken into acco unt 1 .In t his paper mechanisms of HC emissio ns of t he GD I engine are analyzed. And t he HC emissio n characteristics of t he GD I engine and t he P F I engine a

8、re co mpared based o n so me experi2 mental result s. So t he big challenge w hich t he GD I engine is f acing in meeting t he f ut ure emissio nstandard can be figured o ut .Received 2000206212Biogra phy HUAN G Ying ( 1967 - ) ,associate p rofesso r .1 Ba sic Concept of GD I Engine111 GD I Engine P

9、erf ormance RequirementsA t ypical engine operatio n map fo r a st ratified charge GD I engine is show n in Fig. 1 . In o rder to achieve excellent perfo r mances of eco no my , drive abilit y and emissio n , different f ro m P F I en2 gines , bot h st ratified charge and ho mogeneo us co mbustio n

10、st rategies are employed in GD I en2 gines. U nder t he of ten running operatio n co nditio n , bot h st ratified co mbustio n and ho mogeneo us co mbustio n are adop ted. When t he engine speed is below t he middle and partly loaded , t he st rati2 fied co mbustio n will be adop ted. When t he engi

11、ne is f ully loaded o r t he engine speed is highert han t he middle , t he ho mogeneo us co mbustio n will be adop ted.Fig. 1 GD I operating range requirementThe engine start is a special operatio n co nditio n . When t he GD I engine start s and war ms up , usually t he stoichio met ric ho mogeneo

12、 us co mbustio n p rocess is employed. In t his case , t he power o utp ut can be increased so t hat engine start beco mes easy , and also t he exhaust gas temperat ure will be higher so t hat t he catalyst can light off mo re quickly.112 Combust ion SystemThe basic co ncep t of t he GD I engine is

13、p rimarily deter mined by t he requirement s of t he st rat2 ified charge operatio n , i . e . t he co mbustio n chamber shape , charge motio n and t ype and arrange2 ment of t he f uel injecto r must be matched in such a way t hat t he desired charge st ratificatio n wit h rich mixt ure near t he s

14、par k plug at t he time of ignitio n can be achieved and maintained till t he time of co mbustio n . Fo r t his task a do minant charge flow in t he co mbustio n chamber is required. This can eit her be a basically swirling o r a basically t umbling charge motio n2 ,3 .Fig. 2 show s t he st ratified

15、 charge fo r matio n co ncep t of t he Mit subishi GD I engine . To achieve t he st ratified charge , t he f uel is injected during t he co mp ressio n st ro ke . The f uel sp ray is directed toward t he pisto n surf ace and af ter impinging o n t he sp herical pisto n cavit y , it is reflected towa

16、rd t he spar k plug. Up right st raight intake po rt s generate an intensive reverse t umble , t hatis , a t umble wit h a rotatio nal directio n oppo site to t hat of t he t umble generated by co nventio nal ho rizo ntal intake po rt s. Wit h t he help of t he reverse t umble , t he gaseo us f uel

17、is moved toward t hespar k plug af ter impinging o n t he pisto n cavit y.Fig. 2 St ratified charge fo r matio n of Mit subishi GD I engineThe sp herical co mbustio n chamber is designed so as to cap t ure t he f uel sp ray and t he gaseo us f uel and to direct t he reflected gaseo us mixt ure to t

18、he spar k plug. The spar k plug was located att he perip hery of t he co mbustio n chamber . The air f uel mixt ure and t he flame sho uld t ravel to t he center of t he sp herical chamber w here a large amo unt of air exist s. This was realized by t he in2 tense squish flow generated by t he squish

19、 area o n t he exhaust side . During t he later stage of co m2 bustio n , t he reverse squish flow p ropagates t he flame to t he exhaust side . The wall of t he sp heri2 cal bowl at t he exhaust side changes t he dow nward liner side airflow to an up ward flow af ter im2 pinging o n t he pisto n .

20、Therefo re t his design is app rop riate fo r enhancing t he reverse t umble . Fur2 t her mo re , t he shape of t he bowl is suitable fo r p reserving t he rotatio nal mo ment um of t he reverset umble until t he end of t he co mp ressio n st ro ke .2 HC Emission Mechan isms of GD I EngineCo mpared

21、wit h CO and NO x emissio ns , HC emissio ns mechanisms are t he mo st co mplicated fo r spar k ignitio n engines. L ets t hink of t he total hydrocarbo n emissio ns ( E THC) p rocess as oc2curring in t wo largely sequential stages. First t here are t he HC so urces : t he several different mechanis

22、ms w hich p revent a f ractio n of t he f uel inco rpo rated into each cylinder f ro m bur ning dur2 ing t he no r mal flame p ropagatio n . Then , fo r t he f uel , w hich has escaped f ro m t he no r mal co m2 bustio n p rocess to beco me engine hydrocarbo n emissio ns , it must remain unbur ned w

23、it hin t he cylinder t hro ugh t he rest of expansio n and exhaust st ro kes , must exit f ro m t he cylinder , and mustremain unbur ned in t he exhaust po rt and manifold.211 HC Format ion Mechan isms of GD I Engine21111 HC So urcesJ ust like t he t raditio nal P F I engine , t he inco mplete flame

24、 p ropagatio n , wall quenching , crevice and wall wet ting etc. , are also main HC so urces fo r t he GD I engine . However , because of it s special co mbustio n system , w hich differs a lot f ro m t he P F I engine , t here are so me differences in ter ms of each so urce especially fo r wall wet

25、 ting.Wall wett ing When t he engine start s , t he f uel is injected in t he intake st ro ke . Because t hetemperat ure of pisto n and cylinder liner is very low , lot s of f uel adheres to t he pisto n wall and lin2 er causing wall wet ting. The evapo ratio n of t he f uel o n t he pisto n wall an

26、d liner during expansio n st ro ke causes increasing of HC emissio n .When t he engine war ms up , fo r t he P F I engine , because wet ting takes place at t he intake po rt , af ter t he engine war ms up , t he wall wet ting will not affect t he HC emissio ns. But fo r t he GD I engine , because wa

27、ll wet ting takes place in t he cylinder , t he time fo r t he fo r matio n of air f u2 el mixt ure is very sho rt . This will affect HC emissio ns during t he w hole engine operatio n p rocess. Refering to t he p resent research result s , different wet ting po sitio ns such as t he pisto n cavit y

28、 , liner under t he intake valve and liner under t he exhaust valve will p ro duce different amo unt s of HC emissio ns. Acco rding to experiment s , wet ting t he liner under t he exhaust valves is t he wo rst case , wet ting t he liner under t he intake valves is t he best case , and wet ting t he

29、 pisto n top is notquite as bad as wet ting t he liner under t he exhaust valves. And HC emissio ns due to t he cylinders inner wet ting are almo st independent of injectio n timing4 .D irect burn ing of f uel droplet Fo r t he GD I engine , t he direct bur ning of t he f uel droplet is so mew hat a

30、 unique HC so urce . As we know , fo r t he GD I engine t he f uel evapo rates and mixes wit h air in a very sho rt perio d. Due to poo r evapo ratio n , a part of t he f uel takes part in bur ning directly causing unbur ned hydrocarbo n emissio n .Combust ion system In o rder to reduce HC emissio n

31、s due to p revio us so urces , t he co mbus2 tio n system design is a very impo rtant aspect . However , fo r t he GD I engine , it has to operate bot h in t he st ratified charge co mbustio n and in t he ho mogeno us co mbustio n . So t he t rade2off must be do ne , and it will increase t he HC emi

32、ssio n especially under t he ho mogeno us co mbustio n opera2 tio n co nditio n .21112 In2Cylinder Oxidatio nCo mpared wit h t he P F I engine , t he air f uel ratio of t he GD I engine is leaner . So t he co m2 bustio n temperat ure is relatively lower t han t he P F I engines. This leads to poo r

33、ness of o xidizing unbur ned hydrocarbo n in t he cylinder . Therefo re t he engine2o ut HC emissio n increases. Due tot he same reaso n , it is difficult fo r t he catalyst to light off . So t he tailpipe HC emissio n fo r t heGD I engine during t he cold p hase is of very high level .3 Comparison

34、an d Anal ysis of HC Emission Characterist ics of GD I 5an d PFI Engine Ba sed on ExperimentArgo nne Natio nal L abo rato ry did a co mpariso n test fo r GD I engine and P F I engine . A Mit2subishi 118 L GD I engine was tested fo r emissio ns , and t he result s were co mpared wit h t ho se fo r210

35、 L P F I Do dge Neo n . Bot h engine 2o ut and tailpipe emissio ns were collected to analyze varia2tio ns in t he co mbustio n p rocess and variatio ns in t he catalytic co nverters.Test s were run o n t he EPAs F TP275 and highway f uel eco no my cycles. Test result s are as follow s.311 Bag Emissi

36、onsFig. 3 co mpares engine2o ut emissio ns of GD I vehicles to t ho se of P F I vehicles bot h running o n Indolene . Refer to t he figure , total weighted2average HC emissio ns f ro m GD I vehicles were abo ut t hree times mo re t han t ho se f ro m P F I vehicles. We also noted t hat , fo r t he P

37、 F I vehicle bag2 and bag 3 HC emissio ns are less t han t ho se of bag 1 . But fo r t he GD I vehicle bag 2 t he HC e2 missio n is even mo re t han t hat of bag 1 . It means t hat af ter t he engine war ms up t he HC emissio n of t he GD I engine is not imp roved like t hat of t he P F I engine .Fi

38、g. 4 co mpares t he tailpipe emissio ns f ro m t he GD I engine and P F I engine , bot h engines running o n Indolene . It is noted t hat t he tailpipe HC emissio ns of GD I vehicles were much wo rset han t hat of P F I vehicles. And mo re t han half of HC emissio ns is f ro m bag 1 .Fig. 3 Engine2o

39、 ut T HC emissio n co mpariso n bet weenMit subishi GD I and Neo n PF I vehicles duringF TP275 cycle312 Second2by2Second EmissionsFig. 4 Tailpipe T HC emissio n co mpariso n bet weenMit subishi GD I and Neo n PF I duringF TP275 cycleSince mo st of t he HC is emit ted during t he cold start and war m

40、2up perio ds , o nly bag 1 of t he F TP cycle is p resented fo r understanding t he emissio ns characteristics of t he GD I and P F I en2 gines.Fig. 5 show s t he seco nd2by2seco nd engine2o ut HC emissio ns of t he bag 1 fo r t he t wo vehicles , bot h running o n Indolene . The bag 1 engine2o ut h

41、ydrocarbo n emissio ns of t he GD I engine are210 % higher t han t ho se of t he P F I engine . However , during t he first 120 s , t he emissio ns of t heGD I engine are o nly 103 % mo re t han t ho se of t he P F I engine . In t he remainder of bag 1 , t heemissio ns of t he GD I engine are 239 %

42、mo re t han t ho se of t he P F I engine . This implies t hat t he HC emissio ns f ro m t he P F I engine are affected mo re serio usly by a cold start t han t ho se f ro m t he GD I engine .Fig. 6 show s t he seco nd2by2seco nd tailpipe total HC ( T HC) emissio ns of t he bag 1 fo r t het wo vehicl

43、es. These t races show t hat t he catalyst o n t he P F I engine beco mes effective in t he first100 - 200 s of operatio n . The catalyst o n t he GD I vehicle requires abo ut 250 - 300 s to beco me ef2fective .Fig. 5 Engine2o ut T HC emissio n co mpariso n bet weenMit subishi GD I and Neo n PF I ve

44、hicles duringF TP cold start4 Concl usionsFig. 6 Tailpipe T HC emissio n co mpariso n bet weenMit subishi GD I and Neo n PF I vehicles duringF TP cold p haseAcco rding to t he test result s , up to now t he GD I engine can not meet t he f ut ure HC emis2sio n standard , and it even has a lo ng way t

45、o go . Reaso ns fo r t he GD I engines poo r HC emissio n characteristics are as follow s :a1 The engine2o ut HC emissio n is high . It is difficult fo r t he GD I engine to achieve bot h goo d st ratified co mbustio n and ho mogeneo us co mbustio n in t he same system. So different f ro m t he P F

46、I engine , af ter t he engine war ms up t he HC emissio n of t he GD I engine is still not very goo d ; The exhaust gas temperat ure is lower t han t hat of t he P F I engine , so it is difficult fo r t he unbur nedHC to be o xidized in t he expansio n and exhaust st ro kes6 .b1Mo re time is needed to make t he catalyst light off . So t he tailpipe HC emissio n during coldstart and war m2up is much wo rse alt ho ugh t he engine2o ut HC emissio n of t he GD I engine is in a bet ter sit uatio n t han t hat of t he P F I engine7 .Ways to imp rove t he GD I engines HC emiss