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Simulation of quasi-dimensional model for diesel engine working process

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Simulation of quasi-dimensional model for diesel engine working processof,OF,model,for,Model

    Simulation of quasi-dimensional model for

    diesel engine working process

    J.Cent.SouthUniv.Techno1.(2010)17:868872

    D0I:10.1007/sl1771O10-0569-2Springer

    Simulationofquasidimensionalmodelfordieselengineworkingprocess

    QIKunpeng(齐鲲鹏),FENGLiyan(~),LENGXianyin(冷先银),

    TIANJiangping(田江平),LONGWuqiang(隆武强)

    SchoolofEnergyandPowerEngineering,DalianUniversityofTechnology,Dalian116024,China

    CentralSouthUniversityPressandSpringerVerlagBerlinHeidelberg2010

    Abstract:Inordertosarisfythedemandofvalidityandrea1timeoperatingperformanceofdieselenginemode1usedinhardwarein

    the

    loopsimulationsystem.asimplifiedquasi.dimensionalmodelfordieselengineworkingprocesswasproposed.whichwasbased

    onthephase.dividedspraymixingmode1.ThesoflwareMATLAB/Simulinkwasutilizedtosimulatedieselengineperformance

    parameters.Thecomparisonsbetweencalculatedresultsandexperimentaldatashowthattherelativeerrorofpowerandbrake

    specificfuelconsumptionislessthan2.8%.andtherelativeerrorofnitricoxideandsootemissionsislessthan9.1%.Atthesame

    time.theaveragecomputationa1timeforsimulationofoneworkingprocesswiththenewmode1is36s.whichpresentsgoodreal

    timeoperatingperformanceofthemode1.Thesimulationresultsalsoindicatethatthenozzleflowcoefficienthasgreatinfluenceon

    thepredictionprecisionofperformanceparametersindiese1enginesimulationmode1. Keywords:dieselengine;phase--dividedspraymixingmodel;quasi?-dimensionalmodel;

MATLAB/Simulink;predictionprecision

    1IntrOductiOn

    Thehardware..in._the..loopsimulationsystemof dieselengine[2iscomposedofthehardwareof

    dieselenginecontrolsystemandthesimulationmodel fordieselengineworkingprocessrunninginthe computer.Withtheaidofhardware?-in?-the--loop simulationsystem,manyexpenslveandtimeconsuming

    testsarereplacedbyutilizationofthesimulationmodel fordieselengineworkingprocess,andthedevelopment periodofdieselenginecontrolsystemislargely reduced.

    Currently,thequasidimensionalmodelfordiesel

    engineworkingprocessisoneofthemostpopular modelsappliedtosimulatingthedieselengineworking processanditscentralpartisthespraymixingmode1. Varietiesofquasi-dimensionalmodelsfordieselengine workingprocesshavebeenproposedduringpastdecades [39].Althoughthesemodelshavedifferent

    organizationsandcomputationalmethods,alloftheir centralspraymixingmodelsweredevelopedonthebasis ofoneofthethreeclassicspraymixingmodels,which werecalledasfueldropletsevaporationmodel[36],

    transientgaseousflowmodel[7-8]andtwophaseflow

    evaporationmodel[9.Inthefueldropletsevaporation model,combustionwasassumedtobecontrolledby evaporationrate.Therefore,atomizationprocessaswell asevaporationprocessoffueldropletswastakeninto account.Sincethespraywasdividedintoalargenumber ofzonesandevaporationrateoffueldropletshadtobe

    calculatedineachtimestep.thecalculationwiththeruel dropletsevaporationmodelwasverytime.consuming.In thetransientgaseousflowmodel,onlythegaseousphase fue1existedinthecombustionchamberduetothehigh pressureinitwhichcausedthefue1dropletsevaporated instantaneously,thusthecombustionwasdeterminedby themixingoffuelvaporandfleshair.Becausethespray wassimplifiedasagaseoussprayinthismodel,the computationofmode1wassimpler,buttheinstantaneous evaporationofthefueliniectedintothecombustion chamberwasnotquiteaccurate.Inthetwophaseflow

    evaporationmode1.theevaporationofthefueldroplets wasconsideredandthemovementbetweenthefuel dropletsandentrainedfleshairwasneglected.Itwas assumedthatthefuelinonecombustionzonebecame approximatedisoconcentrationaftersometimeandthe twodimensionalflowwassimplifiedasaone

    dimensionalflow.Butthemodelwasstillcomplexfor fueldropletsevaporationcomputationalthoughthespray mixingprocesswassimplified.

    Inthiswork,tomeettherequirementsofthe

    validityandrealtimeoperatingperformanceofdiesel enginemodelusedinhardwareintheloopsimulation

    system,aphasedividedspraymixingmodelwas

    developedtocalculatethefuelairmixingprocessin

    ordertosimplifythequasi.dimensionalmodelfordiesel engineworkingprocess.Additionally,theinfluenceof Foundationitem:Project(2006A10GX059)supportedbytheScienceandTechnologyPlano

    fDalian,China

Receiveddate:2009——08——28;Accepteddate:2009——12——17

    Correspondingauthor:LONGWuqiang,Professor;Tel:+8613889538768;E

    mail:longwq@dlutedu.cn

    J.Cent.SouthUniv.Techno1.(2olo)17:868872869 parametersincalculationoffleshairentrainmentonthe predictionprecisionofperformanceparametersindiesel enginesimulationmodelwasanalyzed.

    2Modelingofquasi-dimensionalmodelfor

    dieselengineworkingprocess

    2.1Phasedividedspraymixingmodel

    ExperimentalresultsinRef.10]showedthatthe

    fueliniectedintocombustionchamberexperiencedtwo phases:thefue1dropletsandthegaseousfuelair

    mixture.Thefueldropletsonlyexistedaroundthenozzle Withtheevaporationofthefueldropletsandthe diffusionofspray,thefueldropletsbecamegaseousin shorttimeandthefuelairmixtureformed.Basedonthis

    experimentalphenomenon,aphase?dividedspraymixing mode1wasdevelopedinthiswork.Inthisphasedivided

    spraymixingmode1.thefue1incombustionzoneswas liquidduringbreakupperiodandbecamegaseousafter

    break.uptime.Thefleshairbegantoentrainintothe combustionzonesafterbreak..uptimeandthetwo.. dimensionalflowwassimplifiedasflone.dimensional flow.

    Thebasicassumptionsinthephase-dividedspray mixingmodelasfollows:f11Thecombustionchamberis dividedintoanairzoneAandmanycombustionzonesB thataremadeupofthefuelinjectedintocombustion chamber,thefleshairentrainedintothezone,andthe

    combustionproductsateachcalculationtimestep.f21 Duringbreakupperiod,theinjectedfuelatomizesand evaporates.Nofreshairisentrainedintocombustion zonesinthisperiod.andfleshairentrainmentisassumed tostartafterbreakuptime.Thefuelairmixturebecomes

    isOc0ncentratiOnafterbreakuptime.andthe

    twodimensionalflowissimplifiedasaonedimensiona1

    flow.f31Theamountoffleshairentrainedintothe combustionzoneiscalculatedbasedonthefuel momentumwhenitisiniectedandthemomentum remainsthesameduringmixingprocess.(4)Fuelis mixedbythefreshairentrainmentaccordingtothe equivalentfuelairratioincombustionzones.andpavial burningisneglectedhere.(5)Thereisnofreshair entrainedintocombustionzoneafterthefue1inthiszone isburntout.Fig.1showstheschematicdiagramofzone Fig.1Schematicdiagramofzonedivisionofphasedivided

    spraymixingmodel

    divisionofthephasedividedspraymixingmode1.The

    boundariesofB1,B2,B3,andB4areclearlyshownas isochronesinthefigure,sincethefuelinthesezoneshas experiencedbreakupprocessandmixedwithfreshair. Onthecontrary,thefuelinotherzonesisstill undergoingbreakupprocessandtheirboundariescannot beshown

    2.2Quasidimensionalmodelfordieselengine

    workingprocess

    Thequasi.dimensionalmodelfordieselengine workingprocessisdividedintosixsub-models,namely

compressionsubmodel,combustionsubmodel,

    expansionsubmode1.exhaustsubmode1.inletand

    outletvalveoverlapsubmodelandintakesub.mode1.

    Thesimulationresults.whichincludeinstantaneousdata suchaspressure,temperature,massandperformance parameterssuchaspower,brakespecificfuelconsumption (BSFC),nitricoxideandsootemissions,areobtainedby solvingtheenergyconservationequations,themass conservationequationsandtheidealgasstateequations f1114].Inthequasi.dimensionalmodel,thecombustion sub.mode1isdividedintobreak.uptimecalculation. freshairentrainmentcalculation,ignitiondelayperiod calculation,heattransferringcalculation,thermo

    dynamicscalculation,combustionproductscalculation andemissionscalculation.Thebreak.uotimecalculation andfreshairentrainmentcalculationareformulatedin detai1inthefollowingsections.

    2.2.1Breakuptimecalculation

    Thebreakuptime(tb)iscalculatedaccordingto

    HIROYASUequation[15],butwithdifferentdefinition onthefuelphaseafterbreak.uDtime.Inthephase. dividedspraymixingmode1.itisassumedthatthefue1 dropletsexperienceatomization,gasification,and becomegaseousafterbreakuptime.

    h28?654Pa

    (Pinj-Pa)(1)

    wherePListhedensityofliquidfuelattheexitofthe nozzlehole;doisthediameterofthenozzlehole;Pais thedensityoffreshairinthecylinder;Pinjisthefuel injectionpressure;andpaisthein?cylinderpressure.

2.2.2Freshairentrainmentcalculation

    Thequantityoffleshairentrainedintocombustion zoneiscalculatedinaccordancewiththemomentum conservationprinciple[9]:

    mfiHof=(mr/+ma,)"(2)

    aai(j1)+Ama(3)

    wheremf/istheithzonalfuelquantity;"0isthefthzonal initialvelocityattheexitofthenozzlehole;maisthe quantityoffreshairentrainedintotheithzonefromstart 870J.

    Cent.SouthUniv.Techno1.(2010)17:868-872 timewhenthefuelisinjectedintothecombustion chambertothejthcalculationtimestep;",istheh

    zonalaveragevelocityduringthejthcalculationtime step;andAmj,isthetheoreticalquantityoffleshair entrainedintothefthzoneduringthejthcalculationtime step.

    Whentheflameoccurs

    isareductionoftheflesh

    mode1.Thequantityofflesh

    combustionzoneisgivenby

    Ama'=c.Ama

    inacombustionzone,there

    airentrainmentrateinthe

    airentrainedintoaburning

    whereAm;,isthefactualfleshairquantityintheith zoneduringthejthcalculationtimestep;andcisthe correctcoefficientrepresentingtheeffectofflameon freshairentrainment.

    3Simulationofquasi-dimensionalmodelfor

dieselengineworkingprocess

    MATLAB/Simulinkwasutilizedtosimulatethe quasidimensionalmodelfordiese1engineworking process.WiththeaidofMArLAB/Simulink.itiseasy foruserstounderstandtheant/typeofsystemquickly, adjusttheparametersofsimulationsystemconveniently andimprovethedevelopmentefficiencyofsimulation systemobviously.

    Experimentaldatawereobtainedfromthe1135 naturallyaspirateddieselengineforcomparisonwiththe calculatedresults.Thespecificationsofthedieselengine are1istedasfollows:thecylinderboreisl35mm.the strokeis150mm,theconnectingrodlengthis265mm. thecompressionratiois17:l,thedisplacementvolumeis 2.147L,theratedpoweris14.7kW,andtherated rotationspeedis1500r/min.

    3.1Realtimeoperatingperformanceofmodel Becausethecomputationalcostofspraymixing processinthephasedividedspraymixingmodelis

    largelydecreasedcomparingwiththatofotherspray mixingmodels,therealtimeoperatingperformanceof simulationsystemisgreatlyimproved.Theaverage computationaltimeforoneworkingprocessofthe simulationmodeldevelopedinthisworkis36sinthe computerequippedwithaCPUofAMD2500+I.83GHz and512Mmemory.

    3.2Validationofmodel

    Fig.2showsthecomparisonsofcalculatedresults andexperimentaldataofincylinderpressureandheat

    releaserateinratedcondition.Thecomparisonsof

    calculatedresultsandexperimentaldataofdieselengine Crankangle/(.)

    Crankangle/(.l

    Fig.2Comparisonsofcalculatedresultsandexperimentaldata ofincylinderpressure(a)andheatreleaserate(b)inrated condition

    performanceparametersatratedspeedindifferentload conditionsareshowninTable1.

    Fig.2(a)showsthatthecalculatedmaximum

    pressureiS7.048MPaat11.ATDCraftertopdead center),correspondingtotheexperimentalmaximum pressureof6.962MPaat12.ATDCandthetwo

    incylinderpressurecurvesareconsistentwitheachother inratedcondition.Fig.2(b1indicatesthatthecalculated andexperimentalheatreleaseratesshowgoodagreement inratedcondition.Thesawtoothinthecurveof calculatedheatreleaserateisduetothevariationof zonesinvolvedincombustionanddifierentquantitiesof thefile1ineachzoneparticipatedincombustionduring eachcalculationstep.Also.itcanbeobservedfrom Table1thatthecalculatedresultsandexperimentaldata agreewel1.TherelativeerrorofpowerandBSFC betweencalculatedresultsandexperimentaldatais1ess than2.8%.andtherelativeerrorofnitricoxideandsoot emissionsbetweencalculatedresultsandexperimenta1 dataislessthan9.1%atratedspeedindifferentload conditions.Theseresultsindicatethattheassumptionsin phasedividedspraymixingmodelarereasonableandthe ?』n?器Jdpu一『^3-,一一一.J.J/0.808I_I

:::!:!!!

    TablelComparisonsofcalculatedresultsandexperimental dataofdieselengineperformanceparametersatratedspeedin 871

    different1oadconditions

    Nitricoxideemission/10

    L.d/%E

    xperimenta1

    data

    Calculated

    results

    Relative

    error/%

    Note:BSUisBoschsootunit

    predictionofdieselengineperformanceparametersis accurateenough,whichmeansthatthequasi

    dimensionalmodelfordieselengineworkingprocessis validatedtobeappliedtothehardware--in?-the?-loop simulationsystem.

    3.3Influenceofnozzleflowcoefficientonmodel's predictionprecision

    BecausethefuelinzoneBisfullygasifiedandthe spraymixtureforcombustionisformedafterbreakup

    timeinphase-dividedspraymixingmodel,the combustionprocessiscontrolledbythecalculationof fleshairentrainmentinquasi.dimensionalmode1for dieselengineworkingprocess,whichhassignificant effectonthepredictionprecisionofthemodel's performanceparameters.

    Eq.(2)showsthatthequantityoffreshairentrained

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