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1、ExperimentalThermalandFluidScience18(1998)231±243Turbulencecharacteristicsoftumble¯owinafour-valveenginea,*bKernY.Kang,JeH.BaekaHeadofLowEmissionEngineLaboratory,KoreaInstituteofMachineryandMaterials(KIMM),171,Jang-dong,Yuseong,Daejon305-600,SouthKoreabAssociateProfessor,Department
2、ofMechanicalEngineering,PohangUniversityofScienceandTechnology(POSTECH),P.O.Box125,Pohang,Kyungbuk,SouthKoreaReceived30March1997;receivedinrevisedform9February1998;accepted27April1998AbstractTumble¯owhasbeenadoptedtoincreasetheprecombustionturbulencelevelinfour-valveengines,sinceit
3、canbeeectivelygeneratedwithnegligibleadverseeectonthe¯owcoecient.Inthisstudy,turbulencecharacteristicsofthetumble¯owinafour-valveenginewereinvestigatedbylaserDopplervelocimetry(LDV)andanalyzedbymeansofturbulenceintensity,integraltimeandlengthscales,andenergyspectrum.Thedataratewass
4、ucientlyhightoallowthebulkvelocitytobecharacterizedinindividualcyclesat500and1000rpmfortwodierentintakeports.Theintegraltimescalesobtainedbythreekindsofdierentde®nitionsandtheircharacteristicswerecompared.Theresultsshowthattumblecausesturbulenceintensitytoincreaseconsiderablyduring
5、thecompressionstrokeanditsdistributiontobehomogeneous.Theeectoftumbleonintegraltimescaleisnegligible,whilethein-tegrallengthscaleincreasesbytumble.Ó1998ElsevierScienceInc.Allrightsreserved.Keywords:Internalcombustionengine;Tumble¯ow;Intakeport;LDVmeasurement;Cycle-resolvedanalysis;
6、Turbulenceintensity;Turbulencescales1.Introductionpressionstrokes,orbythesquishmotionoccurringneartopdeadcenter(TDC)ofcompressionincertaincom-Itiswellknownthattheturbulent¯owinthecylin-bustionchambergeometries.However,infour-valvederofanengineplaysanimportantroleindeterminingengine
7、ssquishisveryweakanditseectasaturbulencethecombustioncharacteristicsandthermaleciencyofpromoterislimitedaswellaslocalizedaroundthetheengine.Automotiveengineershaveendeavoredtosquishlip[3].Tumblehasbeenconsideredtooermoreutilizetheturbulencebychangingtheshapeoftheadvantagesinfour-va
8、lveenginesequippedwithpent
