汽車排放物檢測與控制英文

Vehicleemissionscontrol

Writers:Rosen,ErwinM

Company:ManufacturersofEmissionControlsAssociation

Abstract

Keywords:

Vehicleemissionscontrolisthestudyandpracticeofreducingthemotorvehicleemissions,especiallyinternalcombustionengines.Emissionsofmanyairpollutantshavebeenshowntohavevarietyofnegativeeffectsonpublichealthandthenaturalenvironment.Throughoutthe1950sand1960s,variousfederal,stateandlocalgovernmentsintheUnitedStatesconductedstudiesintothenumeroussourcesofairpollution.In1970,thefederalUnitedStatesEnvironmentalProtectionAgencywasestablished.Bothagencies,aswellasotherstateagencies,nowcreateandenforceemissionregulationsforautomobilesintheUnitedStates.SimilaragenciesandregulationswerecontemporaneouslydevelopedandimplementedinCanada,WesternEurope,Australia,andJapan.ThefirsteffortatcontrollingpollutionfromautomobileswasthePCV.Advancesinengineandvehicletechnologycontinuallyreducethetoxicityofexhaustleavingtheengine,butthesealonehavegenerallybeenprovedinsufficienttomeetemissionsgoals.Therefore,technologiestodetoxifytheexhaustareanessentialpartofemissionscontrol.

Vehicleemissionscontrol,airpollutants,negativeeffects,PCV

Vehicleemissionscontrolisthestudyandpracticeofreducingthemotorvehicleemissions,especiallyinternalcombustionengines.

Emissionsofmanyairpollutantshavebeenshowntohavevarietyofnegativeeffectsonpublichealthandthenaturalenvironment.Emissionsthatareprincipalpollutantsofconcerninclude:1.Hydrocarbons-Aclassofburnedorpartiallyburnedfuel,hydrocarbonsaretoxins.Hydrocarbonsareamajorcontributortosmog,whichcanbeamajorprobleminurbanareas.Prolongedexposuretohydrocarbonscontributestoasthma,liverdisease,lungdisease,andcancer.Regulationsgoverninghydrocarbonsvaryaccordingtotypeofengineandjurisdiction;insomecases,"non-methanehydrocarbons"areregulated,whileinothercases,"totalhydrocarbons"areregulated.Technologyforoneapplication(tomeetanon-methanehydrocarbonstandard)maynotbesuitableforuseinanapplicationthathastomeetatotalhydrocarbonstandard.Methaneisnotdirectlytoxic,butismoredifficulttobreakdowninacatalyticconverter,soineffecta"non-methanehydrocarbon"regulationcanbeconsideredeasiertomeet.Sincemethaneisagreenhousegas,interestisrisinginhowtoeliminateemissionsofit.2.Carbonmonoxide(CO)-Aproductofincompletecombustion,carbonmonoxidereducestheblood'sabilitytocarryoxygen;overexposure(carbonmonoxidepoisoning)maybefatal.CarbonMonoxidepoisoningisamajorkiller.3.Nitrogenoxides(NOx)-Generatedwhennitrogenintheairreactswithoxygenatthehightemperatureandpressureinsidetheengine.NOxisaprecursortosmogandacidrain.NOxisamixtureofNO,N2O,andNO2.NO2isextremelyreactive.Itdestroysresistancetorespiratoryinfection.NOxproductionisincreasedwhenanenginerunsatitsmostefficientpartofthecycle.4.Particulatematter-Sootorsmokemadeupofparticlesinthemicrometresizerange:Particulatemattercausesnegativehealtheffects,includingbutnotlimitedtorespiratorydiseaseandcancer.5.Sulfuroxide(SOx)-Ageneraltermforoxidesofsulfur,whichareemittedfrommotorvehiclesburningfuelcontainingsulfur.ReducingtheleveloffuelsulfurreducesthelevelofSulfuroxideemittedfromthetailpipe.Refineriesgenerallyfightrequirementstodothisbecauseoftheincreasedcoststothem,ignoringtheincreasedcoststosocietyasawhole.6.Volatileorganiccompounds(VOCs)-Organiccompoundswhichtypicallyhaveaboilingpointlessthanorequalto250°C;forexamplechlorofluorocarbons(CFCs)andformaldehyde.VolatileorganiccompoundsareasubsectionofHydrocarbonsthatarementionedseparatelybecauseoftheirdangerstopublichealth.

Throughoutthe1950sand1960s,variousfederal,stateandlocalgovernmentsintheUnitedStatesconductedstudiesintothenumeroussourcesofairpollution.Thesestudiesultimatelyattributedasignificantportionofairpollutiontotheautomobile,andconcludedairpollutionisnotboundedbylocalpoliticalboundaries.Atthattime,suchminimalemissioncontrolregulationsasexistedintheU.S.werepromulgatedatthemunicipalor,occasionally,thestatelevel.Theineffectivelocalregulationsweregraduallysupplantedbymorecomprehensivestateandfederalregulations.By1967theStateofCaliforniacreatedtheCaliforniaAirResourcesBoard,andin1970,thefederalUnitedStatesEnvironmentalProtectionAgencywasestablished.Bothagencies,aswellasotherstateagencies,nowcreateandenforceemissionregulationsforautomobilesintheUnitedStates.SimilaragenciesandregulationswerecontemporaneouslydevelopedandimplementedinCanada,WesternEurope,Australia,andJapan.

ThefirsteffortatcontrollingpollutionfromautomobileswasthePCV(positivecrankcaseventilation)system.Thisdrawscrankcasefumesheavyinunburnedhydrocarbons—aprecursortophotochemicalsmog—intotheengine'sintaketractsotheyareburnedratherthanreleasedunburnedfromthecrankcaseintotheatmosphere.Positivecrankcaseventilationwasfirstinstalledonawidespreadbasisbylawonallnew1961-modelcarsfirstsoldinCalifornia.Thefollowingyear,NewYorkrequiredit.By1964,mostnewcarssoldintheU.S.weresoequipped,andPCVquicklybecamestandardequipmentonallvehiclesworldwide.

Thefirstlegislatedexhaust(tailpipe)emissionstandardswerepromulgatedbytheStateofCaliforniafor1966modelyearforcarssoldinthatstate,followedbytheUnitedStatesasawholeinmodelyear1968.Thestandardswereprogressivelytightenedyearbyyear,asmandatedbytheEPA.

Bythe1974modelyear,theemissionstandardshadtightenedsuchthatthede-tuningtechniquesusedtomeetthemwereseriouslyreducingengineefficiencyandthusincreasingfuelusage.Thenewemissionstandardsfor1975modelyear,aswellastheincreaseinfuelusage,forcedtheinventionofthecatalyticconverterforafter-treatmentoftheexhaustgas.Thiswasnotpossiblewithexistingleadedgasoline,becausetheleadresiduecontaminatedtheplatinumcatalyst.In1972,GeneralMotorsproposedtotheAmericanPetroleumInstitutetheeliminationofleadedfuelsfor1975andlatermodelyearcars.Theproductionanddistributionofunleadedfuelwasamajorchallenge,butitwascompletedsuccessfullyintimeforthe1975modelyearcars.AllmoderncarsarenowequippedwithcatalyticconvertersandleadedfuelisnearlyimpossibletobuyinmostFirstWorldcountries.

Engineefficiencyhasbeensteadilyimprovedwithimprovedenginedesign,morepreciseignitiontimingandelectronicignition,moreprecisefuelmetering,andcomputerizedenginemanagement.

Advancesinengineandvehicletechnologycontinuallyreducethetoxicityofexhaustleavingtheengine,butthesealonehavegenerallybeenprovedinsufficienttomeetemissionsgoals.Therefore,technologiestodetoxifytheexhaustareanessentialpartofemissionscontrol.

Airinjection(Mainarticle:Secondaryairinjection):Oneofthefirstdevelopedexhaustemissioncontrolsystemsissecondaryairinjection.Originally,thissystemwasusedtoinjectairintotheengine'sexhaustportstoprovideoxygensounburnedandpartiallyburnedhydrocarbonsintheexhaustwouldfinishburning.Airinjectionisnowusedtosupportthecatalyticconverter'soxidationreaction,andtoreduceemissionswhenanengineisstartedfromcold.Afteracoldstart,anengineneedsafuel-airmixturericherthanwhatitneedsatoperatingtemperature,andthecatalyticconverterdoesnotfunctionefficientlyuntilithasreacheditsownoperatingtemperature.Theairinjectedupstreamoftheconvertersupportscombustionintheexhaustheadpipe,whichspeedscatalystwarmupandreducestheamountofunburnedhydrocarbonemittedfromthetailpipe.AirInjectionisasecondarytechnology,usedinsupportofthemaintechnologiesonsomeengines.

Exhaustgasrecirculation:IntheUnitedStatesandCanada,manyenginesin1973andnewervehicles(1972andnewerinCalifornia)haveasystemthatrou