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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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