Studyonturbocompoundsystemforaheavy-dutydieselenginebycombiningmatchinganalysiswithexperiments.docx

ProclMechEPartD:DOI: 10.1177/09544070221104350S SageReviewArticIeStudyonturbocompoundsystemforaheavy-dutydieselenginebycombiningmatchinganalysiswithexperimentsYinYong1,2®,WuZhijun1zZhaoRongchao3GzZhugeWeilin4andHuZongjie1AbstractJAutomobiteEngineering2023,Vol.237(8)1775-1789IMechE2022Articlereuseguidelines:Inthiswork,toimprovethefueleconomyoflong-haulcommercialvehicles,theeffectsofturbocompoundsystemmatchingonengineperformancewerenumericallyandexperimentallystudied.Firstly,aIDGT-POWERsimulationmodelofan11Lheavy-dutydieselenginewasestablishedandverifiedbytheexperimentaldata.Secondly,theperformancesoftheturbocompoundenginematchingwithdifferentsizesoffixedgeometryturbine(FGT)andpowerturbineswereanalyzed.Itwasfoundthattheexhaustenergydistributionbetweentheturbochargerturbineandpowerturbinehadasignificantimpactonengineperformance,andthesizeoftheturbochargerturbinehadamorenoticeableimpactthanthepowerturbine.BasedontheFGTturbocompoundsystemsimulationresult,anappropriatevariablegeometryturbocharger(VGT)andthreewastegateturbochargers(WGT)wereselectedforfurthersimulationandexperimentalresearch.Inaddition,theimpactsofthetransmissionratiobetweenthepowerturbineshaftandtheenginecrankshaft,andthefuelinjectiontimingontheengineperformancewereexperimentallystudied.Theenginetestresultshowedthatthefueleconomywasimprovedby1.6%underEuropeanSteadyState(ESC)cyclewhilekeepingtheweightedNOxemissionthesameastheoriginalengine.Finally,theturbocompoundenginewithWGTwasinstalledonaheavy-dutylong-haulcommercialvehicleforroadtests.Thefueleconomyofthevehiclewasimprovedby2.54%underthe80km/hconstantspeedroadtest.KeywordsTurbocompoundsystem,heavy-dutydieselengine,variablegeometryturbine,wastegateturbine,powerturbineDatereceived:27October2021;accepted:2May2022IntroductionDieselengineshavebeentheprimarypowersourcesforcommercialvehiclesandengineeringmachineryforalongtimebecauseoftheirexcellentadaptability,highefficiency,andreliability.Itisimportanttofurtherimprovethedieselengine'sthermalefficiency.Thein-cylindercombustionprocessofdieselengineshasbeendramaticallyimprovedbytechnologiessuchashigh-pressurecommon-rail,high-efficiencyturbocharging,andexhaustgasrecirculation(EGR).Dieselengines'brakethermalefficiency(BTE)hasreachedmorethan45%.However,ithasbecomeincreasinglydifficulttoimproveBTEonlybyoptimizingtheincylindercombustionprocess.Wasteheatrecoveryisgenerallyacceptedtoimprovetheengine'soverallefficiency.Themaintechnologiesofwasteheatrecoverj,includeOrganicRankineCycle(ORC),1ThermoelectricGeneration(TEG),2andturbocompounding.3ComparedwithORCandTEGtechnology,turbocompoundinghastheadvantagesofrelativelysimplestructureandgoodenergy-savingperformance.Inaddition,theenginebackpressurecanbeincreasedsignificantlyduetoapowerturbinedownstreamoftheturbochargerturbine.Asaresult,ahigherEGRratecanbeadoptedtoreduceNitrogenOxides(NOx)emission.Furthermore,theengineexhaustenergyisabundantforlong-haulcommercialvehiclesbecausetheir1TongjiUniversity,Shanghai,China2DongfengCommercialVehicleCo.Ltd.,Wuhan,China3SouthChinaUniversityofTechnology,Guangzhou,China4TsinghuaUniversity,Beijing,ChinaCorrespondingauthor:ZhaoRongchao,SouthChinaUniversityofTechnology,381WushanRoad,TianheDistrict,Guangzhou510640,China.Email:merczhaoenginesmainlyoperateathighspeedsandhighloadscomparedwithpassengercarengines.Therefore,itisconducivetoreducingfuelconsumptionbyapplyingturbocompoundtechnologyinlong-haulcommercialvehicles.Inaturbocompoundengine,apowerturbineisusedtorecovertheexhaustenergyandturnitintomechanicalworkorelectricity.Therearethreemainconfigurationsforthepowerturbineandturbocharger,includingseries,parallelandintegratedlayouts.Weietal.4comparedtheperformanceofa1.8LturbochargedgasolineenginewiththreeIurbocompoundlayoutsunderdrivingcycles.Itwasshownthattheparallelturbocompoundlayouthadthebestfuelsavingperformance.However,theexhaustmassflowratiobetweenthepowerturbineandturbochargerturbineneedstobeadjustedusingtwovalvesaccordingtotheengineoperatingcondition.Sincetheoperationconditionfrequentlychangesontheroad,theparallelconfigurationisunsuitableforvehicleapplication.Inintegratedlayouts,5amotor/generatorisintegratedwiththeturbocharger.Itactsa$amotortoacceleratetheturbochargeratlowenginespeedconditionsforbettertransientresponseandasageneratortorecoverthewasteheatforlowerfuelconsumptionathigh-speedconditions.Thematchingandcontrolmethodfortheintegratedturbocompoundsystemiscrucialtogethighoverallefficiency.Yangetal.6proposedamatchingguidelinefortheintegratedturbocompoundsystemandappliedittoatwo-strokelowspeedmarineengine.Resultsshowedthatthefuelconsumptioncouldbereducedby2%-3%althreeloadprofiles.Joshietal.78proposedanovelsystemconsistingofsupercharging,turbocompounding,andelectrification.Thepowerflowcouldbeoptimallymanagedinthislayoutbyemployingaplanetarygearsetaccordingtotheroadconditions.Resultsshowedthatthefueleconomywasimprovedby11.1%.ThemainchallengeforanintegratedIurbocompoundsystemistodevelopareliablehigh-speedmotorbecauseoftheextremelyhighturbochargerspeed.Theturbine'shightemperaturealsorisksdamagingtheelectricmachine.Seriesturbocompounddrawsthemostattentioninvehicleapplication.9Thepowerturbineisgenerallyplaceddownstreamoftheturbochargerturbineinthisconfiguration.Thepowerdistributionbetweenthetwoturbinesismainlydecidedbytheexpansionratiosofthetwoturbines.Theenginebackpressurewillbeincreasedduetotheextractpressuredropinthepowerturbine.Briggsetal.,°foundthattheoptimalratedpowerofthepowerturbinefora2.4Lturbochargeddieselenginewas7.0kWatfullengineloads.Theengine'sBSFCandBMEPimprovedby2.41%and2.21%,respectively.Mamatetal.1112designedapowerturbinewithalowexpansionratioof1.1,whichcouldreducetheimpactontheenginebackpressure.Thetestresultsshowedthatamaximumbreakspecificfuelconsumption(BSFC)reductionof2.6%wasachievedattheenginespeedof2500rmin.Theoptimalexpansionratioiscloselyrelatedtotheengineparameters.Zhaoetal.13establishedananalyticalmodelwiththerelationshipamongtheseparameters,includingturbineexpansionratio,efficiency,exhausttemperature,enginefuelconsumption,etc.Basedontheanalyticalmodel,theoptimumvalueofthepowerturbineexpansionratiowasdisclosed.Sincetheoptimumexpansionratiosoftheturbochargerturbineandpowerturbinevariedastheengineoperationconditionchanged,avariablegeometryturbinewasadoptedtoregulatetheturbineexpansionratioforhigherengineperformanceatdifferentenginespeeds.14Jyeetal.15establishedanumericalsimulationmodeltostudytheinfluenceofseriesturbocompoundontheperformanceoftraditionalturbochargeddieselengines.Itshowedthattheengine,smaximumpowercouldincreaseby7%athighenginespeed.Onthecontrary,theenginepowerwouldbereducedby4.7%atlowspeedduetoincreasedexhaustbackpressure.Thenegativeeffectofthepowerturbinecouldbereducedbybypassingtheexhaustflowinthepowerturbine.Finally,theaveragefuelconsumptioncanbereducedby1.9%underallengineworkingconditions.Thespeedofthepowerturbinecanalsobeadjustedaccordingtotheoperationconditionforthebestengineperformance.Katsanosetal.16studiedtheinfluenceofpowerturbinespeedonengineperformancebasedonanumericalmodel.Itwasfoundthattheoptimalpowerturbinespeeddecreasedwiththedecreaseofengineload.Theoif-designperformanceoftheenginecouldbeimprovedbyadjustingthepowerturbinespeed.Heetal.17proposedacontrollableturbo-compoundingsystemincludingvariabletransmissionandapowerturbinebypassvalve.Thetransmissionratiobetweenthepowerturbineshaftandenginecrankshaft,andtheopeningdegreeofthepowerturbinebypassvalvewereoptimizedunderoff-designconditions.Thefuelconsumptionwasreducedby2%and3.4%underthehighwayfueleconomylestandTianjin503drivingcycles.Insummary,Iurbocompoundtechnologycanimprovetheengine'sfueleconomyby2%-10%inaspecificworkingcondition.However,thepowerturbineincreasestheexhaustbackpressure,increasingthepumpinglossanddeterioratingtheenginefueleconomy.Iftherecoveredexhaustenergybythepowerturbineisinsufficienttooffsetthepowerlossoftheengine,theengine,soperatingperformancewilldeteriorate.Theheavy-dutydieselonthelong-haulcommercialvehiclemainlyoperatesathighspeedsandhighloads.Theexcellentmatchingoftheturbocompoundsystemfortheseoperatingconditionsisessentialfortheengine'sfuelefficiencyandotherperformances.However,theimpactsofFGT,VGT,WGTmatchingwithpowerturbine,andthetransmissionfactoroftheturbocompoundingontheoff-designperformancehavenotbeenthoroughlyanalyzedinpreviousstudies.Thispaperfocusesonthematchinganalysisandexperimentalstudyofturbocompoundsystemsforheavy-onlyonemainfuelinjectionatfullloadconditions.BecausethisstudymainlyfocusesonFigure 2. Performance map of the power turbine.Figure1.Schematicoftheseriesmechanicalturbocompoundengineandenginetestbench.dulydieselengines.AcomparisonoflheimpactsofFGT,VGT,andWGTontheturbocompoundengineoff-designperformancewasperformed.ThematchingprocesswillbedisclosedfortheVGTandWGTcoupledwiththepowerturbinetoimproveengineperformance.ThematchinganalysisinthispaperisbasedonthetypicalseriesturbocompoundsystembyIDenginesimulationandenginetests.Aftertheanalysis,theengineequippedwithWGTwaschosenforfurtherexperimentalstudyandoptimization.Themechanicaltransmissionratiobetweenthepowerturbineshaftandenginecrankshaft,andthefuelinjectiontimingwereexperimentallyoptimized.Inaddition,theturbocompoundenginewasinstalledinaheavydutytruck,androadtestswerecarriedout.Thisworkcanprovideasystematicreferenceforturbocompoundsystemsimulation,matching,andoptimization.EnginesimulationandtestbenchTheschematicoftheseriesmechanicalturbocompoundengineispresentedinFigureI.Thepowerturbineisfitteddownstreamoftheturbochargerturbine.Itconvertspartoftheexhaustenergyintorolationalkineticenergyoftheenginecrankshaftbythegearsandhydrauliccoupler.Thehydrauliccouplerwasintegratedwithanoverrunningclutch.Itreducesthetorsionalvibrationbetweenthehighspeedpowerturbineshaftandlow-speedenginecrankshaft.Inaddition,itcanpreventreverseworkdonebytheengineatlowpowerturbinespeed.ThepowerturbineinthispaperwasfromCummins(HP841).Itsmaximumpoweroutputis30kW.ThemapofthispowerturbineisshowninFigure2.Allexperimentswereconductedinan11L,fourstroke,six-cylinder,turbochargedheavy-dutydieselengineequippedwithahigh-pressurecommon-railinjectionsystem.Anelectroniccontrolunit(ECU)madebyBoschwasusedtocontrol(hefuelinjectionparameters.ThereisTable1.Specificationsofthetestengine.ParameterDescriptionEnginedisplacement11.12LRatedpower303kW1900r/minMaximumtorque1850Nm1200-1700r/minCompressionratio18Bore3Stroke(mm)123mm3156mmCombustionchamberRe-entranttypeTurbochargerFixedGeometryTurbineMaximuminjectionpressure1800barEmissionscomplianceChinaVtheeffectoftheturbocompoundsystemonengineperformance,thereisnoengineexhaustafter-treatmentsysteminthetest.Butaback-pressurevalvewasfitteddownstreamofthepowerturbineintheexhaustpipetosimulatetheback-pressurecausedbytheaftertreatmentsystem.Theback-pressurewaskept25kPaattheratingcondition.Andtheengine,srawNOxemissionwaskepttheTable 2. Main equipment and their uncertainties of engine test bench.EquipmentModelUncertaintiesDynamometerHORIBA WS700FSpeed: 65 rminz Torque: 60.5% FSFuel consumption meterHORIBA FQ-3200CR60.12% FSAirflow meterAVL Flow Sonix Air61%Gas emission analyzerHORIBA MEXA 7100DEGR60.5%Cooling systemEME 42061Csameastheoriginalengine.ThemainspecificationsoftheengineareshowninTable1.TheprimarytestequipmentanditsuncertaintiesareshowninTable2.Apiezoelectricpressuresensor(Kistler6125CU20)coupledwithachargeamplifier(AVL365C01)wasemployedtomeasurein-cylinderpressure.Thepressuredataacquisitionwastriggeredbyanopticalcrankshaftangleencoder(AVL365CC)witharesolutionof0.5CA.Theincylinderpressuretracewasutilizedtoverifythecombustionmodel.Theenginespeedandtorquewerecontrolledandmeasuredbyaneddydynamometer.Thegaseousexhaustemissionsandlambdaweremeasuredbyagasemissionanalyzer.AsimulationmodeloftheturbocompoundengineisdevelopedbasedoncommercialsoftwareGT-POWER,asshowninFigure3.Theengineperformancesatfullloadweresimulatedinthissimulation.TheheatreleaseinthecylinderismodeledusingtheWiebefunctionasshowninequation(1),whereDjandSarethecombustiondurationandshapefactor,respectively.u()isthecrankshaftanglecorrespondingtothestartofignition.Sincethisstudymainlyfocusesonfueleconomy,pilotandpostinjectionwerenotusedinthisexperiment.Thefuelisinjectedonlyonceinoneengineworkingcycle.Asaresult,asingleWiebefunctioncanbeused.dQbQbUUOs=6:9s+1PduDuDu"uUaS+i#61Dexp6:9DuwhereDiscylinderdiameter,pisin-cylinderpressure,Tistheaveragetemperature,andCmisthemeanvelocityofthepiston.Figure3.Enginesimulationmodelwithturbocompoundsystem.Theenergydistributionbetweentheturbochargerturbineandthepowerturbineaffectstheengine'soverallperformance.Theturbochargerandpowerturbineenergyarecalculatedfromequation(4)toequation(7).Intheseequations,thesubscript"O"means“total,“andthenumberfrom1to6representsthelocationofthemeasurepointfromtheturbochargercompressorinlettothepowerturbineoutlet,whichisshowninFigure1.Thepoweroutputoftheturbochargerturbine(Wcr)iscalculatedinequation(4):：k41Wc= mi CpjToi (p02=p01) k 1 =hc 351>Theheattransfertothewallsinsidethecylinderisobtainedaccordingtoequation(2).dQwdu=aAwT½TP2PwhereAwistheareaofthecontactwall,andthecoefficientaiscalculatedusingtheWoschnimodel,18aspresentedinequation(3).a=3:26Do：2po：8To：55Cm63DWct=hcr114cp,4T041(p5=p04)md4Dwherem4istheexhaustmassflowratethroughtheturbine,cp,4isthespecificheatatconstantpressureoftheexhaust,T04isthegastotaltemperatureattheturbochargerturbineinlet,hcisturbineefficiency,p5issialicpressureaftertheturbine,PNistotalpressurebeforetheturbine,k4isthespecificheatratiooftheexhaust,whichis1.33.Thepowerconsumedbythecompressor(Wc)isgiveninequation(5).kll100012001400160018002000Engine speed (rmin)1716 (EN) nbJOH190(MWS ouls(dwheremisintakeairmassflowratethroughthecompressor;cp.isthespecificheatatconstantpressureoffreshair;ToisthegastotaltemperatureattheFigure 4 Simulationmodelvalidation.compressorinlet;hciscompressorefficiency;pandp02istotalpressureatthecompressorinletandexit,respectively,kisthespecificheatratioofair,whichis1.4.Accordingtotheenergybalanceoftheturbocharger,equation(6)canbeobtained.Wc=hmWc6PInequation(6),hnisthemechanicalefficiencyoftheturbocharger.Thetheoreticalpoweroutputofthepowerturbine(WPT)iscalculatedusingequation(7).k4lWpT=hprm5Cp.5To5I(p6=p05)m1Pwherem$isexhaustmassflowratethroughthepowerturbine;cp,5isthespecificheatatconstantpressureoftheexhaust;h11istheefficiencyofthepowerturbine;To5isthetotaltemperatureatthepowerturbineinlet;POSandp6isthetotalpressureatthepowerturbineinletandstaticpressurealthepowerturbineexit,respectively.TheaccuracyoftheGT-POWERsimulationmodelinFigure3isverifiedbyexperimentaldata.ThecomparisonbetweenthesimulationresultsandexperimentalresultsisshowninFigure4.Regardingtheenginetorqueandspecificfuelconsumption,itisshownthatthedifferencesarewithin5%betw