王建昕+清华+缸内直喷发动机氧化模型预测(2)

3152F.Zhangetal./ProceedingsoftheCombustionInstitute33(2011)3151–3158

chemicalkineticmechanismsformethanoloxida-tionshouldberesearched.Thereareabout10kindsofmethanoloxidationmechanismsshowninthepastliterature.Bowman[2]developedthe rstdetailedmechanismsbasedonshock-tubeexperiments,despitefacingdi cultiesinpredict-ingmethanolignitiondelayperiodinlowtemper-ature(<1800K)causedbyalackofelementaryratedata.Subsequently,WestbrookandDryer[3]developedthe rstcomprehensivekineticmodelofmethanoloxidation,whichhadasuc-cessfulveri cationwith ow-reactorandshock-tubedatainawidetemperaturerange.TheshortageisthatsomeelementaryrateconstantandreactionpathinformationwerelackedandCH3Owasneglectedinthemechanism.NortonandDryer[4]undatedtheWestbrookandDryermechanismusingmorecurrentrateconstantsandthermochemicalparameters,andidenti edtheimportanceoftheHO2radicalinthemethanolcombustionprocess.Anewsetof ow-reactordatawasusedtoverifythemechanism.Themeth-anoloxidationmechanism,madebyEgolfopoulosetal.[5],hadanexcellentagreementwiththeexperimentallaminarspeedand ow-reactordataoverarangeofinitialtemperaturesandpressures.However,therewasabadpredictionofmethanolignitiondelayperiodcomparedwithBowman’sshock-tubemeasurements.Grotheeretal.[6–8]subsequentlydevelopedacomprehensivemecha-nism,whichcouldpredictbothlaminarburningvelocitiesandauto-ignitioninspark-ignition(SI)engines.Accordingtosensitiveanalysis,itcon-cludedthatsomereactionshadagreatimpactonlaminarburningvelocities,suchasthebranch-ingratiobetweenreactionsCHandCH3OH+OH=CH2OH+H2Oradical3OH+OH=CHHspeciessuchas3O+2O.AlthoughCH,CH2(S),andCH2(T)wereomittedintheHeldandDryer[9]mechanism,ithasagoodagreementwithshock-tube, ow-reactor,andpremixedlam-inar amesexperimentaldataoverawideapplica-blerange.Lindstedtetal.[10,11]providedamethanoloxidationmechanism,containingCH,CH2(S),andCH2(T)radicalspecies.Itcanbeusedtocalculatethelaminar ameburningspeed,ignitiondelayperiod,andvariousemissions.BasedontheHeldandDryermechanism,LiandWilliams[12,13]constructedaclassi edmeth-anoldetailedmechanism,usingCO/H2O/H2/O2,CH2O,andCH3OHreactionsandnewreactionrateconstantandthermodynamicdata.Christianetal.[14]hadstudiedtheoxidationofmethanolina ow-reactorexperimentallyunderdiluted,fuel-leanconditionsat650–1350K,overawiderangeofOout2concentrations(1–16%),andwithandwith-thepresenceofnitricoxide.Atpresenttheresearchontheoxidationmechanismofmetha-nol-gasolineblendedfuelisrare.Casimiretal.[15]developedadetailedchemicalkineticreactionmechanismresultingfromthemergingofvali-

datedkineticschemesfortheoxidationofthecomponentsofthepresentM85(methanol-gaso-lineblendedfuelcontaining85%methanol)surro-gate.GoodagreementbetweentheexperimentalresultsandthecomputationswasobservedunderthepresentJSRconditions.

Inthisstudy,adetailedcomprehensivemetha-noloxidationmechanismwasdeveloped,basedonpresentreactionrateconstantandpathinforma-tion.Thein uenceofCH,CHicalspeciesandnitricoxidewas2(S),andCHconsidered2(T)rad-inthemechanism.Shock-tubeand ow-reactordatawereusedtovalidatethemechanism.Inordertoconstructamethanol-gasolinemechanism,anoxi-dationmechanismofgasolinesurrogatewascom-binedwiththemethanolmechanism.Thegasolinesurrogatemechanismwasformedwithiso-octane(iso-para nrepresentative),toluene(aromaticrep-resentative),and1-hexene(ole nrepresentative).Themethanol-gasolinemechanismwasvalidatedbythejet-stirredreactor(JSR)experimentdata.Sequentially,theBoostenginecyclemodelwasestablishedandcoupledwiththemethanol-gasolinemechanismtosimulatetheformaldehydeandnitricoxideemissionsofthelow-percentmethanol-gaso-lineblendedfuelsfromaSI(Sparkignition)engine,andalsoappliedtopredicttheemissionsofthehigh-percentblendedfuels.TheexperimentaldatafromtheSIenginewereobtainedbytheFTIR(Fouriertransforminfrared)spectrometer.Numericalsimu-lationsofallsystemswereconductedbyCHEM-KIN-basedprograms.2.Methanolmechanism

Themethanolmechanismisbasedonthatpro-posedpreviouslyfortheoxidationofmethanol.Theproposedkineticreactionmechanismhas46speciesand247reversiblereactions.ThebasicC/H/Oreactionrateconstantsandpathinforma-tionoftheproposedmechanismarebasedontheHeldandDryer[9]mechanism.Theclassi edCO/H2O/H2/O2,CH2O,andCHmechanism3OHreactionsfromtheLiandWilliams[12,13]areadded.ThereactionsinvolvingCH,CH(T)radicalspeciesarebasedontheLindstedt2(S),andCHetal.2[10,11]mechanism.ThereactionsrelatedwithnitricoxidefromtheChristianetal.[14]mecha-nismarealsoaddedintotheproposedmechanism.Thefullmechanism,includingthermochemicaldata,isavailableasSupplementalmaterial.

Predictionsutilizingthepresentmethanoloxi-dationmechanismhavebeencomparedwiththeexperimentaldata.Forhightemperaturecombus-tion,shock-tubeexperimentsareoperatedatthehighertemperaturerangeof1500–2500K.Formethanoloxidationconditions,theexperimentaldataofBowman[2]weremodeledbythepresentmethanolmechanism.Theshock-tubecon gura-tionwasnumericallysimulatedasanadiabatic,