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UNIT7

EMISSIONCONTROLSYSTEMS

TEXTA

OverviewofEmissionControlSystems

PROFESSIONALENGLISHUNIT7

EMISSIONCONTROLSYSTEMS

TEXTA

OverviewofEmissionControlSystems

PCVSystem

EGRSystem

EvaporativeControlSystem

AirInjection

CatalyticConverterPROFESSIONALENGLISH本次课学习目标掌握排放控制系统的组成掌握排放控制系统的原理掌握有关的英文专业术语了解翻译技巧—重复NEWWORDSdilute[dai'lju:t]v.冲淡,变淡,变弱,稀释crossover['krɔsֽouvə]n.转线路,天桥,交叉channel['t∫ænl]n.海峡,水道,信道,频道,通道route[ru:t]n.路线,路程,通道;v.发送lean(out)[li:n]v.贫化,变瘦thermal['θə:məl]a.热的,热量的transducer[trænz'dju:sə]n.传感器,变频器,变换器orifice['ɔrifis]n.孔,口,节流孔linear['liniə]a.线的,直线的,线性的potentiometer[pəֽten∫i'ɔmitə]n.电位计,电势计fume[fju:m]n.(浓烈或难闻的)烟,气体;v.用烟熏,冒烟,发怒prohibit[prə'hibit]v.禁止,阻止adhere[əd'hiə]v.粘附,胶着,坚持pop[pɔp]n.砰的一声,爆裂声,流行乐曲,流行艺术a.流行的,热门的,通俗的v.发出爆裂声,爆开,射击,突然出现diverter[dai'və:tə]n.分流器,换向器,分流阀divert[di'və:t]v.转移,转向catalytic[ֽkætə'litik]a.催化的muffler['mʌflə]n.消声器NEWWORDSpellet['pelit]n.小球honeycomb['hʌnikoum]n.蜂房,蜂巢platinum['plætinəm]n.白金,铂palladium[pə'leidiəm]n.钯catalyst['kætəlist]n.催化剂render['rendə]v.致使,表演,实施NEWWORDS

PHRASESANDEXPRESSIONS

脉宽调制pulsewidthmodulationEGR阀位置(EVP)传感器EGRvalveposition(EVP)sensor锥形端taperedtip通气孔bleedport背压backpressure大节气门开度(简写为WOT)wide-openthrottle废气再循环阀EGRvalve节气门开度throttleopening在最坏的情况下atworst空气喷射airinjection催化转换器catalyticconverter空气泵airpump分流阀divertervalve清污阀purgevalve与…一道(同时),以及,除…之外(还)alongwith活性炭罐charcoalcanister

PHRASESANDEXPRESSIONS

Tominimizepollutionoftheatmospherefromincompletelyburnedandevaporatinggasesandtomaintaingooddriveabilityandfueleconomy,anumberofemissioncontrolsystemsareusedonallvehicles.Theyincludepositivecrankcaseventilation(PCV)system,evaporativeemissioncontrol(EVAP)system,exhaustgasrecirculation(EGR)system,airinjection(AIR)systemandthree-waycatalyticconverter(TWC)system.PCVSystemThepurposeofthepositivecrankcaseventilation(PCV)systemistotakethevaporsproducedinthecrankcaseandpistonblow-by,andredirectthemintotheair/fuelintakesystemtobeburnedduringcombustion.Thesevaporsdilutetheair/fuelmixture,theyhavetobecarefullycontrolledandmeteredsoasnottoaffecttheperformanceoftheengine.Thisisthejobofthepositivecrankcaseventilation(PCV)valve.

OverviewofEmissionControlSystems

Atidle,whentheair/fuelmixtureisverycritical,justalittleofthevaporsareallowedintotheintakesystem.Athighspeedwhenthemixtureislesscriticalandthepressuresintheenginearegreater,moreofthevaporsareallowedintotheintakesystem[1].Whenthevalveorthesystemisclogged,vaporswillbackupintotheairfilterhousingoratworst,theexcesspressurewillpushpastsealsandcreateengineoilleaks[2].Ifthewrongvalveisusedorthesystemhasairleaks,theenginewillidlerough,oratworstengineoilwillbesuckedoutoftheengine.EGRSystemExhaustgasrecirculation(EGR)systemsreducetheamountofoxidesofnitrogenproducedduringthecombustionprocess.TheEGRsystemdilutestheair/fuelmixturewithcontrolledamountsofexhaustgas.Sinceexhaustgasdoesnotburn,thisreducesthepeakcombustiontemperatures.

OverviewofEmissionControlSystems

OverviewofEmissionControlSystems

Atlowercombustiontemperatures,verylittleofthenitrogenintheairwillcombinewithoxygentoformNOX.Mostofthenitrogenissimplycarriedoutwiththeexhaustgases.Fordriveability,itisdesirabletohavetheEGRvalveopening(andtheamountofgasflow)proportionaltothethrottleopening.DriveabilityisalsoimprovedbyshuttingofftheEGRwhentheengineisstartedupcold,atidle,andatfullthrottle.SincetheNOXcontrolrequirementsvaryondifferentengines,thereareseveraldifferentsystemswithvariouscontrolstoprovidethesefunctions.EGRValvesMostofthesesystemsuseavacuum-operatedEGRvalvetoregulatetheexhaustgasflowintotheintakemanifold.Exhaustcrossoverpassagesundertheintakemanifoldchanneltheexhaustgastothevalve.(Somein-lineenginesroutetheexhaustgastothevalvethroughanexternaltube.)TypicalmountingoftheEGRvalveiseitherona

plateunderthecarburetorordirectlyonthemanifold.

OverviewofEmissionControlSystems

TheEGRvalveisavacuum-operated,flowcontrolvalve.OpeningtheEGRvalvebycontrolvacuumatthediaphragm,allowsexhaustgasestoflowthroughthevalveandintotheintakemanifold.Here,theexhaustgasmixeswiththeair/fuelmixture.Theeffectistodiluteorleanoutthemixture,sothatitstillburnscompletelybutwithareductionincombustionchambertemperatures.

TherearealsovariousdesignsofEGRvalves.ThepositivebackpressureEGRvalvehasableedportandvalvepositionedinthecenterofthediaphragm.Alightspringholdsthisbleedvalveopen,andanexhaustpassageisconnectedfromthelowerendofthetaperedvalvethroughthestemtothebleedvalve.Whentheengineisrunning,exhaustpressureisappliedtothebleedvalve.Atlowenginespeeds,exhaustpressureisnothighenoughtoclosethebleedvalve.Ifcontrolvacuumissuppliedtothediaphragmchamber,thevacuumisbledoffthroughthebleedport,andthevalveremainsclosed.

(略)

OverviewofEmissionControlSystems

InanegativebackpressureEGRvalve,anormallyclosedbleedportispositionedinthecenterofthediaphragm.Anexhaustpassageisconnectedfromthelowerendofthetaperedvalvethroughthestemtothebleedvalve.Whentheengineisrunningatlowerspeeds,thereisahigh-pressurepulseintheexhaustsystem.However,betweenthesehigh-pressurepulsestherearelow-pressurepulses.Astheenginespeedincreases,morecylinderfiringsoccurinagiventime,andthehigh-pressurepulsesbecomeclosertogetherintheexhaustsystem.(略)

AdigitalEGRvalvecontainsuptothreeelectricsolenoidsthatareoperateddirectlybythePCM.Eachsolenoidcontainsamovableplungerwithataperedtipthatseatsinanorifice.Whenanysolenoidisenergized,theplungerisliftedandexhaustgasisallowedtorecirculatethroughtheorificeintotheintakemanifold.Thesolenoidsandorificesaredifferentsizes.ThePCMcanoperateone,two,orthreesolenoidstosupplytheamountofexhaustrecirculationrequiredtoprovideoptimum

controlofNOxemissions.Fig.7-2AelectronicEGRsystem

OverviewofEmissionControlSystems

Fig.7-2AelectronicEGRsystem

OverviewofEmissionControlSystems

InternalExhaustGasRecirculation(EGR)EGRreducesthelevelsofoxidesofnitrogen(nitricoxideNO,andsmallquantitiesofnitrogendioxideNO2,collectivelyreferredtoasNOX)inengineexhaustgasesatpartload.TheaimofaninternalEGRsystemistocontroltherecirculationofexhaustgaswithouttheuseofexternalpipeworkontheengine.Inaconventionalplenumthrottledengine,atpartthrottlethereisapressuredifferentialbetweentheinletandexhaustports.Towardstheendoftheexhauststrokeonafourstrokeengine,theinletvalveopensandaperiodfollowswheninletandexhaustvalvesareopensimultaneously.Duringthisvalveoverlapperiod,theinletportdepressioncausesresidualexhaustgasinthecombustionchambertoflowbackintotheinletport.Theresultantpressuredropinthecombustionchambercausesgasesintheexhaustporttoflowbackintothecombustionchamber.Theseresidualexhaustgasesdilutetheincomingair/fuelcharge.

OverviewofEmissionControlSystems

OverviewofEmissionControlSystems

Thisdilutionofthechargereducesthepeakcombustiontemperaturesandpressures,whichreducestheamountofNOXintheexhaustgases.Excessdilutioncanleadtoincompleteorunstablecombustionwhichresultsinanincreaseinhydrocarbon(HC)levels.Theoptimumamountofdilutionvarieswithenginespeedandload.Conventionally,thedilutionrequirementsforoptimizedrunningconditionsareachievedbyusinganexternalEGRsystemwhichrecirculatesmeteredquantitiesofexhaustgasbyexternalpipesandacontrolvalve.EvaporativeControlSystem

Gasolineevaporatesquiteeasily.Inthepasttheseevaporativeemissionswereventedintotheatmosphere.20%ofallHCemissionsfromtheautomobilearefromthegastank.In1970legislationwaspassed,prohibitingventingofgastankfumesintotheatmosphere.Anevaporativecontrolsystemwasdevelopedtoeliminatethissourceofpollution.Thefunctionofthefuelevaporativecontrolsystemistotrapandstoreevaporativeemissionsfromthegastankandcarburetor.

OverviewofEmissionControlSystems

Acharcoalcanisterisusedtotrapthefuelvapors.Thefuelvaporsadheretothecharcoal,untiltheengineisstarted,andenginevacuumcanbeusedtodrawthevaporsintotheengine,sothattheycanbeburnedalongwiththefuel/airmixture.Thissystemrequirestheuseofasealedgastankfillercap.Thiscapissoimportanttotheoperationofthesystemthatatestofthecapisnowbeingintegratedintomanystateemissioninspectionprograms.Pre-1970carsreleasedfuelvaporsintotheatmospherethroughtheuseofaventedgascap.Todaywiththeuseofsealedcaps,redesignedgastanksareused.Thetankhastohavethespaceforthevaporstocollectsothattheycanthenbeventedtothecharcoalcanister.Apurgevalveisusedtocontrolthevaporflowintotheengine.Thepurgevalveisoperatedbyenginevacuum.Onecommonproblemwiththissystemisthatthepurgevalvegoesbadandenginevacuumdrawsfueldirectlyintotheintakesystem[3].Thisenrichesthefuelmixtureandwillfoulthesparkplugs.

OverviewofEmissionControlSystems

Mostcharcoalcanistershaveafilterthatshouldbereplacedperiodically.Thissystemshouldbecheckedwhenfuelmileagedrops.Insomeengines,thepowertraincontrolmodule(PCM)allowsintakemanifoldvacuumtodrawvaporsintothecombustionchambersduringcertainoperatingconditions.Alloftheseenginesuseadutycyclepurgesystem.ThePCMcontrolsthevaporflowbyoperatingthedutycycleEVAPpurgesolenoid(Fig.7-3).Fig.7-3AnECM-controlledEVAPsystem

OverviewofEmissionControlSystems

OverviewofEmissionControlSystems

AirInjectionSincenointernalcombustionengineis100%efficient,therewillalwaysbesomeunburnedfuelintheexhaust.Thisincreaseshydrocarbonemissions.Toeliminatethissourceofemissionsanairinjectionsystemwascreated.Combustionrequiresfuel,oxygenandheat.Withoutanyoneofthethree,combustioncannotoccur.Insidetheexhaustmanifoldthereissufficientheattosupportcombustion,ifweintroducesomeoxygenthatanyunburnedfuelwillignite.Thiscombustionwillnotproduceanypower,butitwillreduceexcessivehydrocarbonemissions.Unlikeinthecombustionchamber,thiscombustionisuncontrolled,soifthefuelcontentoftheexhaustisexcessive,explosions,whichsoundlikepopping,willoccur.Therearetimeswhenundernormalconditions,suchasdeceleration,whenthefuelcontentisexcessive[4].Undertheseconditionswewouldwanttoshutofftheairinjectionsystem.a)coldmodeFig.7-4Airmanagementsystemoperation

OverviewofEmissionControlSystems

b)wormmodeFig.7-4Airmanagementsystemoperation

OverviewofEmissionControlSystems

OverviewofEmissionControlSystems

Thisisaccomplishedthroughtheuseofadivertervalve,whichinsteadofshuttingtheairpumpoff,divertstheairawayfromtheexhaustmanifold.Sinceallofthisisdoneafterthecombustionprocessiscomplete,thisisoneemissioncontrolthathasnoeffectonengineperformance.LaterversionsoftheairinjectionsystemareunderECMcontrol(Fig.7-4).Whentheengineiscold,theECMenergizesacontrolsolenoid.Thisallowsairtoflowtoanairswitchingvalve.Theairswitchingvalveisenergizedtodirectairtotheexhaustports.Onawarmengine,orin"closedloop"mode,theECMde-energizestheairswitchingvalve,directingairbetweenthebedsofthecatalyticconverter.ThisprovidesextraoxygenfortheoxidizingcatalysttodecreaseHCandCOlevels,whilekeepingoxygenlevelslowinthefirstbedoftheconverter.Thisenablesthereducingcatalysttoeffectivelydecreasethelevelsofoxidesofnitrogen(NOX).CatalyticConverterAutomotiveemissionsarecontrolledinthreeways.Oneistopromotemorecompletecombustionsothattherearefewerby-products.Thesecondistoreintroduceexcessivehydrocarbonsbackintotheengin

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