HybridpneumaticICE.docx

HybridpneumaticICE.docx

《HybridpneumaticICE.docx》由会员分享，可在线阅读，更多相关《HybridpneumaticICE.docx（25页珍藏版）》请在冰点文库上搜索。

HybridpneumaticICE

TypePaperNumberHere

OneDimensionalModelingandExperimentalValidationofSingleCylinderPneumaticCombustionHybridEngine

PascalBREJAUD,PascalHIGELIN,AlainCHARLET,YannCHAMAILLARD（DoNOTenterthisinformation.ItwillbepulledfromparticipanttabinMyTechZone）

Affiliation（DoNOTenterthisinformation.ItwillbepulledfromparticipanttabinMyTechZone）

Copyright©2011SAEInternational

ABSTRACT

Theobjectiveofthispaperistopresentandtovalidateanumericalmodelofasingle-cylinderpneumatic-combustionhybridengine.Themodelpresentedinthispapercontains0-Dsub-modelsfornon-spatiallydistributedcomponents:

Enginecylinder,Airtank,wallheatlosses.1-Dsub-modelsforspatiallydistributedcomponentsareappliedonthecompressivegasflowsinpipes（intake,exhaustandcharging）.Eachpipeisdiscretized,usingtheTwo-StepsLax-Wendroffscheme（LW2）includingDavisT.V.D.TheboundariesconditionsusedatpipeendsareMethodOfCharacteristics（MOC）based.Inthespecificcaseofavalve,anoriginalintermediatevolumeMOCbasedboundaryconditionisused.Thenumericalresultsprovidedbytheenginemodelarecomparedwiththeexperimentaldataobtainedfromasinglecylinderprototypehybridengineonatestbenchoperatingin4-strokepneumaticpumpand4strokepneumaticmotormodes.Ineachmode,thepredictionofthemassflowrates,amplitudeandtimingofthechargingpipewavesaresatisfactory,withoutusinganydischargecoefficient.Indicatedworkandp-Vdiagramsaresimilarbetweensimulationandmeasurementsinthecaseofpneumaticpumpmode.Forthepneumaticmotormodethemodelunderestimatescylinderpressureduringthechargingprocess.

INTRODUCTION

Figure1:

SchematicrepresentationofaSingleCylinder

Theconceptofthepneumatichybridengine

（1）

（2）isbasedonaconventionalinternalcombustionengineinwhichoneadditionalvalve,calledthechargingvalve,connectsthecombustionchambertoanairtank.SeeFigure1.Inordertoreducecosts,theintakeandexhaustvalveremaincamshaft-drivenandonlythechargingvalveismovedbyafullyvariableactuator（3）.Asaresult,thenewmajormodesallowedbythisadditionalvalve（pneumaticpump,pneumaticmotorandsupercharged）remains4-Strokescycles:

∙PneumaticPump:

Thismodetransformsvehiclekineticenergyintoare-usablepneumaticenergy.Thecyclebeginswithaconventionalintakestroke.Thechargingvalveopensduringcompressionstrokesassoonasthein-cylinderpressurereachesthatofthechargingport.ThevalveclosesshortlyafterT.D.C,andthecyclefinisheswithconventionalexpansionandexhauststrokes.

∙PneumaticMotor:

Thismodeisusedtotransformpneumaticenergyintomechanicalworkwithoutanycombustion.Thecyclebeginswithclassicalintakeandcompressionstrokes.ThechargingvalveopenswhenapproachingTDC,andremainsopenduringpartoftheexpansionstrokeinordertomaintainpressureatahighlevelandgeneratethedesiredindicatedwork.Thecyclefinisheswithaconventionalexhauststroke.

∙PneumaticSuperchargedmode:

Thismodeisusedtocompensateforthe"turbolag"effect,whiletemporarilyboosttheengineduringastrongaccelerationtransient.Thechargingvalveopensshortlyafterintakevalveclosure,andcloseswhenthedesiredadditionalairmasshasflowedintothein-cylinder.Theendofthecycleremainsthesameasaconventionalfourstrokeone.

Severalpreviouspublications（4）（5）（6）haveshownthattheconceptofapneumatic-combustionhybridenginecouldprovidebenefitsintermsoffuelconsumptionandgreenhousegasemissionsthatarecomparablewiththoseofanelectrichybridvehicle（7）butwithlowerweightandpresumablylowercost（6）.Toimprovetheperformanceandefficiencyofthehybridpneumaticconcept,thedevelopmentmainlyconsistsindeterminingthetimingofopeningandclosingofthechargingvalve,foragivenoperatingmode（pneumaticmotormode,pneumaticpumpmode,superchargedmode）andforagivenobjective（maximizationornominalcontrolofmechanicalwork,maximizationornominalcontrolofmassorenthalpytransferred,maximizationofglobalefficiencyetc.）.Ithasbeenexperimentallyshown（8）thatlargeamplitudepressurewaves（near2barsofamplitude）arecreatedinsidethechargingpipeasaresultofthechargingvalveopeningandclosure.Inordertotakethispressurewavephenomenonintoaccounta1Dsimulationplatformisneeded.

However,thewayinwhichgastransferbetweenthecylinderandtheAirtankisperformeddependsonmanyparameters,suchas:

chargingpipelengthandcrosssection,airtankmeanpressure,airtanktemperature,chargingvalvehydraulicdiameterandnumber,chargingpiperoughness,chargingvalvelift.Thelargenumberofparameterstobeexploredforeachoperatingmodeandeachobjectivemakesoptimizationalmostimpossibletoperformexperimentally.Areliable,flexible,andfastnumerical1Dmodelisthereforeneededinordertodevelopcontrollaws.Twopreviousstudies（9）（10）haveuseda1-Dcommercialsimulationsoftwareforenginesimulations,butdonotpresentanycomparisonbetweenexperimentalandsimulatedresultsforwavetimingsandamplitude,massflowratesetc.Fromourpointofview,theuseofsuchcommercialcodeforapneumatichybridengineposesoneproblemandleavesonequestionunanswered.Theproblemisthatthesoftwarerequiresapreciseknowledgeofthedischargecoefficientversusliftofeachsimulatedvalve（11）.Thesecoefficientarrayshavetobedeterminedbyexperimentsthusaprototypecylinderheadisrequired.Anestimateddischargecoefficientwillthereforebemoreorlesserroneous,leadingtoseriousdiscrepanciesbetweensimulationsandfuturemeasurements.Theunansweredquestionisthatthevalveboundaryconditionimplementedinthiskindofsoftwareisseldomvalidatedonpressureratiosashighasthoseencounteredinapneumatichybridengine（upto22）.Tocircumventthepreviouspoints,authorshavedevelopedtheirownMOCvalveboundaryconditionthatobviatesinmanycasestheuseofaCoefficientofdischargeandhasbeenexperimentallyvalidatedonavalvegasdynamicstestbench（12）.Theobjectiveofthepaperisnowtopresentthecompleteenginemodelthatembedsthisvalveboundarycondition,andtocompareexperimentsversussimulations.

Thepaperisorganizedasfollows:

Firstly,0Dcomponentsmodelsaredescribed:

thecylinderandtheairtankmodel.Secondly,the1Dsubmodelsforspatiallydistributedcomponentsaredescribed:

theLW2numericalschemeandthesimplifiedTVDschemeproposedbyDavisarepresented,followedbytheIntermediateVolumeValveboundarycondition.Thirdlytheresultsproducedbythecompletesinglecylinderhybridenginearepresentedandcomparedtomeasurementsobtainedwithaprototypeengine.

Quasi-dimensionalcomponentsoftheenginemodel

Airtank:

TheairtankthermodynamicstateshownonFigure1isdeterminedusingthefirstlawofthermodynamics:

Becausethetankhasaconstantvolume,

.AccordingtoJoule'slaw

with

thetemperatureofthegasescontainedintheTank.Theairtankisassumedtobeadiabatic,then

.Foraperfectgas,thespecificenthalpyisgivenby

with

thetemperatureoftheflowinggases.Finally,are-arrangementofEq.

（1）gives:

Theairflowmass

isdeterminedattheopenendboundary（seecorrespondingsectionofthispaper）usingthemethodofcharacteristics（M.O.C）.Aclassicalnumericalintegrationthenprovidesthetotalairmassinsidethetank.UsingEq.

（2）,theelementarytemperatureriseinthetankisdetermined.Applyinganumericalintegration,thenewtanktemperatureiscomputed.Finally,usingtheperfectgaslaw（pV=mrT）,themeantankpressureisdetermined.

Enginecylinder

Thecylinderisthecentralpartofthesystem.Itexchangesheatandmasswiththeoutside.Itsthermodynamicstateisdeterminedusingthefirstlawofthermodynamics（Eq

（1））.

Wisthemechanicalworkgeneratedbythemovingwalls,Qisthetotalheat,mthemassandHistheenthalpy.Subscriptiindicatesanintakeflow,cindicatesachargingpipeflowandeindicatesanexhaustflow.Then:

Eachmassflowrateisdeterminedusingavalveboundarycondition（Seecorrespondingsectionofthispaper）.Aclassicalnumericalintegrationtechniquethenyieldsthenewtotalmassinsidethecylinder.

Thetotalheat

isthesumofacombustionheat

andconvectiveheattransferthroughcylinderswalls

.

and

arerespectivelydeterminedusingtheWoshni（13）andWiebe（14）models.Theseclassicalcorrelationsarenotdetailedinthispaper.Re-arrangingEq

（1）finallygives:

Anumericalintegrationgivesthenewtemperatureofthecylinder.Thevolumeisdeterminedfromtheenginegeometryandcrankshaftposition（15）.Thepressureisthencalculatedusingidealgaslaw.

One-dimensionalcomponentsoftheenginemodel

Fundamentals

Figure2:

ControlVolume

Flows,ineachpipe,areassumedtobemonodimensional.Theidealcompressivegasisassumedtobeinviscid.Threeconservationlawsarewrittenforacontrolvolume,respectivelythemass,momentumandenergy.Figure2showstheflowofanidealcompressiblegasthroughaninfinitesimalsectionofpipe.

and

arerespectivelythepressure,thedensity,thevelocity,thetime,thespaceandthecrosssectionarea.

Continuityequation:

Therateofchangeofmasswithinthecontrolvolumeisequaltonetmassflowratethroughtheelement.Thisprincipleleadsto（16）（17）:

Momentumequation:

Therateofchangeofmomentumwithinthecontrolvolumeisequaltothesumoftheforcesappliedonthecontrolvolume.Inordertomodelthefrictionbetweentheflowandthewa