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1、Article history:Received 6 April 2015Revised 18 June 2015Accepted 19 June 2015 Availableonline 21 July 2015Keywvak:Cool amcsFlame speedExtinction limitDinieihyl etherOzoneNumericalsimulationsofpremixedcoolflamesofdimethylether/oxygenmixturesYiguangJu,ChristopherB.Reuter,SangHeeWonDepartmentOfMechani
2、calandAerospaceEngineering,PfiMegnUnNersiiy,PrbWeion.Nl08X4,USAarticleinfoThCformationanddynamicsofpremixedCoOlIlamcsarenumericallyinvestigatedbyusingadetailedkineticmechanismofdimethylethermixturesinbothfreely-propagatingandstretchedcounterflowflameswithandwithoutozonesensitization.Thepresentstudyf
3、ocusesonthedynamicsandtransitionsbetweenCOOInanleSandhightemperatureflames.Theimpactsofmixturetemperature,inertgastemperature,andozoneconcentrationonlowtemperatureignition.COOl11ameformation,and11amnubleregionsofdiHerent11ameregimesareinvestigated.Forthefreely-propagating11ames,threedifYerentflameSi
4、niciures(hightemperature11anes,doubleflames,andCOOlflames)arefound.ThepresentstudyshowsthattheflammabilitylimitofdimethyletherisSigniflCanllyextendedbytheappearanceofcoolflamesandthattheconventionalconceptofthe(Iamniabilitylimitofahightemperatureflameoughttobereconsidered.Furthermore,theresultsdemon
5、stratethatthecoolamepropagationspeedcanbesignificantlyhigherthanthatofncar-limithightemperatureflamesandthatozoneadditiondramaticallyacceleratesCheformationofcool11anesatlowtemperaturesandextendstheflammabilitylimit.Aschematicofamodified11ammabilitylimitdiagramincludingbothhightemperatureflamesandCO
6、OInameSisproposed.Forstretchedcounterflowflanes.the*sulsalsoshowthatmultipleameregimesexistwithandwithoutozoneaddition.Itisdemonstratedthatatthesamemixtureenthalpy,ozoneadditionkineticallyextendsthecoolflameextinctionlimit(oahigherstretchrale.Moreover,withozoneaddition,twodierenicoolflametransitionr
7、egimes:alowtemperatureignitiontransitionandadirectcool11amctransitionwithoutanignitionlimitathighertemperature,arcpredicted.ThepresentresultssuggestthatCoOltlamescanbeanimportantcombustionprocessinaffectingIlammabilitylimitsandflameregimesasthemixturetemperature,turbulentmixing,andradicalProductioiV
8、recirculationareincreased.Theresultsalsoprovideguidanceinobservingself-sustainingpremixedcl11anesinexperiments.2015TheCombustionInstitute.PublishedbyElscvicrInc.Allrightsrcser,cd.IUre/pressuredomainwereobtained112.I4.Nevertheless,fewstudieshavebeencarriedoutonCOOlflamedynamics,extinction,andabstract
9、CooIflameshavelongbeenconsideredakeyprocessresponsibleforengineknockandarealsoanimportantphenomenonforfiresafetyl-6.Sincethefirstdiscoveryofclflamestwocenturiesago7.8,extensiveeilbrtshavebeenmadetoobservecoolflamesbyusingvariousflamegeometriesincludingheatedsurfacesandheatedburners8-11,stirredreacto
10、rs112-14,heatedflowreactors1.8,I5-17J,rapidCOmPreSS沁nmachinesI8,counterflowflames119,droplets16.20.211.andplasma-assistedflames22.23.Despitethatmanyoftheobservedclflameswereoscillatory,transient,andstronglyaffectedbyflame-surfaceinieraciion.insightsintocoolIlamespectroscopy,negativetemperaturecoeffi
11、cient(NTC)chemistry,heatrelease,andthecoolflamepeninsulainthetempera-BCocrespondingauthor.Fax:+16092586233.E-mailaddress：yjuprirKeion.edu(Y.Ju).h(ipdx.doi.org10.1016,j.conbusflanfe.2015.06.014flammabilitylimits.Muchofourknowledgetodayaboutamepropagationspeeds,amestructures,extinctionlimits,andflamma
12、bilitylimitsisstilllimitedtohightemperatureflames24.Duetothedifficultyinestablishingself-sustainingclflames,adetailedandfundamentalunderstandingofclflamedynamicbehaviorshasnotbeenwellestablished.Recently,aself-sustainingn-heptanecooldiffusionflamewasexperimentallyobservedforthefirsttimebyusingozones
13、ensitizationinacounterflowflameoverabroadrangeofflowresidencetimes19).Theflamestructuresandextinctionlimitswerequantitativelymeasuredinthisstudy.Theresultsshowedthatozoneadditionextendedtheflammableregionofcoolflamesandallowedselfsustainingclflamestobeobservedonalaboratoryflamescale.Inotherstudies.L
14、awandZhaonumericallymodeledtheNTCeffectonn-heptane/airignitioninadiffusioncounterflowflame25.ThcirresultsdemonstratedtheexistenceofNTC-affectedignition.Inn-heptanedropletcombustionexperiments.Nayagametal.6reportedthedualmodesofcombustionandextinctionandpresentedahypothesisofclflameformationinamicrog
15、ravityenvironment.Inarelatedn-heptanedropletstudy,Farouketal.211numericallymodeledOSCiHalOryCoOlflamesgovernedbyradiationheatlossandconductiveheatlossfromflametodroplet.However,theabovestudieswerealllimitedtodiffusionflames.Forpremixedcoolflames.Marutaandcoworkersrecently16,17Jstudiedthestabilizatio
16、nlimitsofclflamesbyusingabumerteatedmicrochannel.Unfortunately,inthisgeometrythewalltemperaturegradientandflame-wallcouplingstronglydictatetheflamestability,makingitditYiculttoaddresshowfastaclflamecanpropagateandwhattherelationisbetweentheflammabilitylimitsofhightemperaturetlamesandcoolflames.Withtheexpectedincreasesinpressureandinitialmixturetemperatureinfutureengines,(hereisa
