Combustion Process in a Spark Ignition Engine Dyna

arXiv:nlin/0312067v1[nlin.CD]28Dec2003CombustionProcessinaSparkIgnitionEngine:DynamicsandNoiseLevelEstimationT.Kami´nskiandM.WendekerDepartmentofCombustionEngines,TechnicalUniversityofLublin,Nadbystrzycka36,PL-20-618Lublin,PolandK.UrbanowiczFacultyofPhysics,WarsawUniversityofTechnology,Koszykowa75,PL-00-662,Warsaw,Poland.G.LitakDepartmentofMechanics,TechnicalUniversityofLublin,Nadbystrzycka36,20-618Lublin,Poland(Dated:September30,2003)AbstractWeanalysetheexperimentaltimeseriesofinternalpressureinafourcylindersparkignitionengine.Inourexperiment,performedfordifferentsparkadvanceangles,apartfromusualcyclicchangesofenginepressureweobservedoscillations.Theseoscillationsarewithlongertimescalesrangingfromonetoseveralhundredenginecyclesdependingonengineworkingconditions.Basingonthepressuretimedependencewehavecalculatedtheheatreleasedpercycle.Usingthetimeseriesofheatreleasetocalculatethecorrelationcoarse-grainedentropyweestimatedthenoiselevelforinternalcombustionprocess.Ourresultsshowthatforasmallersparkadvanceanglethesystemismoredeterministic.1Acombustionprocessinsparkignitionenginesisknownasnonlinearandnoisyone.Combustioninstabilitiesareoccurringasacycle-to-cyclevariationsofin-ternalcylinderpressureeffectingdirectlyonthepoweroutput.Examinationofthesevariationscanleadtobetterunderstandingoftheirsourcesandhelpintheireliminationsinfuture.Improvingengineefficiencyrequiresachiev-ingbettercombustionconditionswithoutintroducingadditionaldisturbances.Inthepresentpaperweanalysethedynamicsandestimatethenoiselevelincombustionprocessbasingonexperimentaltimeseriesofinternalpressureandcalculatedfromthemheatrelease.Inthefollowinganalysisweapplythenon-linearmultidimensionalmethodswhichcandistinguishrandomvariationsfromadeterministicbehaviour.I.INTRODUCTIONCombustioninfourstrokesparkignition(SI)enginesisacomplexcyclicprocesscon-sistedofairintake,fuelinjection,compression,combustion,expansionandfinallygasex-haustphases(Fig.1)whereburnedfuelpoweristransmittedthroughthepistontothecrankshaft.InearlybeginningofSIenginedevelopmenttherewereobservedinstabilitiesofcombustion1.Theseinstabilitiesarecausingfluctuationsofthepoweroutputmakingitdifficulttocontrol2,3.TheproblemsoftheirsourcesidentificationandtheireliminationhavebecamethemainissuesinSIenginestechnologiesengineeringandtheyhavenotbeensolveduptopresenttime4.AmongthethemainfactorsofinstabilitiesclassifiedbyHeywood5areaerodynamicsinthecylinderduringcombustion,amountsoffuel,airandrecycledexhaustgassuppliedtothecylinderandalocalmixturecompositionnearthesparkplug.Recently,Dawetal.6,7andWendekeretal.8havedonethenonlinearanalysisofsuchpro-cess.Changinganadvancesparkangletheyobservedtheconsiderableincreaseofpressurefluctuationslevel8claimingthatitisduetononlineardynamicsoftheprocess.Intheotherwork9Wendekerandcoworkershaveproposedintermittencymechanismtoexplaintherouttoeventuallychaoticcombustion.Promptedbythesefindingswedecidedtoanalysethethecorrelationentropyofthecombustionprocessindifferentworkingconditionsoftheengine.Withahelpofentropyproducedbythedynamicalsystemwecanquantifythelevelofmeasurementordynami-2FIG.1:Schematicpictureofacombustioncycleinafourstrokesparkignitionengine.calnoise10.Inthepresentpaperweshallstartouranalysisfromexaminingexperimentalpressuretimeseries.Itshouldbenotedthatpressureisthebestknownquantitytoanalyseenginedynamics.Cylinderpressuretogetherwithvolumedatacanbeusedtoobtainindicatedmeaneffectivepressure(IMEP),calculatetheenginetorque,indicatedefficiencyandalsoburnrate,bulktemperatureandheatrelease.Moreover,statisticalanalysisofthepressuredatacanalsoprovideinformationaboutcombustionprocessstability.However,inpractice,Itisnoteasytoperformdirectmeasurementofpressure11,asoneneedsagoodsensorpersistenttohighttemperaturestobeplacedinsidetheenginecylinder.Thereforetoobtaininformationaboutpressuresomeresearchersdevelopedalternativenon-directmeasurementsprocedures12.Inourcasewehavebeendealingwithnovelpressurefibreopticalsensors13.Duetoapplyingthemnoisefrommeasurementisverylow,comparingtotraditionalpiezo-electricones14.Thisenabledustoexaminethedynamicsmoreeffectivelythanitwaspossibleinearlierinvestigations.Thepresentpaperisdividedinto6sections.Afterpresentintroduction(Sec.1),wewillprovidethedescriptionofourexperimentalstandingandmeasurementprocedureinSec.2.Therewepresentsomeexamplesofcycle-to-cyclevariationsinpressureinsideoneofcylinder.InSec3.weexaminethepressurewithmoredetail.Wealsoperformspatio-temporalanalysiscomparingthefluctuationsofpressureinsucceedingcyclesfordifferentadvanceangles.InSec.4wecalculatetheheatreleasepercycle.FinallyinSec.5weanalyseitstimedependenceandshowourmainresulti.e.levelofnoise.Weendupwith3FIG.2:Experimentalstand.conclusionsandlastremarks(Sec.6).II.EXPERIMENTALFACILITIESANDMEASUREMENTSOFINTERNALPRESSUREInourexperimentalstand(Fig.2)pressurewasmeasureddirectlyinsidecylinderbytheuseoftheopticalfibresensor13.Suchequipmentprovidesoneofthemostdirectmeasuresofcombustionqualityinaninternalcombustionengine.InternalpressuredatawereobtainedfromEngineLaboratoryofTechnicalUniversity