Numerical simulations of premixed cool flames of dimethyl ether／oxygen mixtures.docx

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1、Artic1ehistory:Received6Apri12015Revised18June2015Accepted19June2015Avai1ab1eon1ine21Ju1y2015Keywvak:Coo1amcsF1amespeedExtinction1imitDinieihy1etherOzoneNumerica1simu1ationsofpremixedcoo1f1amesofdimethy1ether/oxygenmixturesYiguangJu,ChristopherB.Reuter,SangHeeWonDepartmentOfMechanica1andAerospaceEng

2、ineering,PfiMegnUnNersiiy,PrbWeion.N108X4,USAartic1einfoThCformationanddynamicsofpremixedCoO1I1amcsarenumerica11yinvestigatedbyusingadetai1edkineticmechanismofdimethy1ethermixturesinbothfree1y-propagatingandstretchedcounterf1owf1ameswithandwithoutozonesensitization.Thepresentstudyfocusesonthedynamic

3、sandtransitionsbetweenCOOInan1eSandhightemperaturef1ames.Theimpactsofmixturetemperature,inertgastemperature,andozoneconcentrationon1owtemperatureignition.COO1ameformation,andamnub1eregionsofdiHerentameregimesareinvestigated.Forthefree1y-propagatingames,threedifYerentf1ameSiniciures(hightemperaturean

4、es,doub1ef1ames,andCOO1f1ames)arefound.Thepresentstudyshowsthatthef1ammabi1ity1imitofdimethy1etherisSignif1Can11yextendedbytheappearanceofcoo1f1amesandthattheconventiona1conceptofthe(Iamniabi1ity1imitofahightemperaturef1ameoughttobereconsidered.Furthermore,theresu1tsdemonstratethatthecoo1amepropagat

5、ionspeedcanbesignificant1yhigherthanthatofncar-1imithightemperaturef1amesandthatozoneadditiondramatica11yacce1eratesCheformationofcoo1anesat1owtemperaturesandextendsthef1ammabi1ity1imit.Aschematicofamodifiedammabi1ity1imitdiagraminc1udingbothhightemperaturef1amesandCOOInameSisproposed.Forstretchedco

6、unterf1owf1anes.the*su1sa1soshowthatmu1tip1eameregimesexistwithandwithoutozoneaddition.Itisdemonstratedthatatthesamemixtureentha1py,ozoneadditionkinetica11yextendsthecoo1f1ameextinction1imit(oahigherstretchra1e.Moreover,withozoneaddition,twodierenicoo1f1ametransitionregimes:a1owtemperatureignitiontr

7、ansitionandadirectcoo1amctransitionwithoutanignition1imitathighertemperature,arcpredicted.Thepresentresu1tssuggestthatCoO1t1amescanbeanimportantcombustionprocessinaffectingI1ammabi1ity1imitsandf1ameregimesasthemixturetemperature,turbu1entmixing,andradica1ProductioiVrecircu1ationareincreased.Theresu1

8、tsa1soprovideguidanceinobservingse1f-sustainingpremixedc1anesinexperiments.2015TheCombustionInstitute.Pub1ishedbyE1scvicrInc.A11rightsrcser,cd.IUre/pressuredomainwereobtained112.I4.Neverthe1ess,fewstudieshavebeencarriedoutonCOO1f1amedynamics,extinction,andabstractCooIf1ameshave1ongbeenconsideredakey

9、processresponsib1eforengineknockandarea1soanimportantphenomenonforfiresafety1-6.Sincethefirstdiscoveryofc1f1amestwocenturiesago7.8,extensiveei1brtshavebeenmadetoobservecoo1f1amesbyusingvariousf1amegeometriesinc1udingheatedsurfacesandheatedburners8-11,stirredreactors112-14,heatedf1owreactors1.8,I5-17

10、J,rapidCOmPreSS沁nmachinesI8,counterf1owf1ames119,drop1ets16.20.211.andp1asma-assistedf1ames22.23.Despitethatmanyoftheobservedc1f1ameswereosci11atory,transient,andstrong1yaffectedbyf1ame-surfaceinieraciion.insightsintocoo1I1amespectroscopy,negativetemperaturecoefficient(NTC)chemistry,heatre1ease,andt

11、hecoo1f1amepeninsu1ainthetempera-BCocrespondingauthor.Fax:+16092586233.E-mai1address：yjuprirKeion.edu(Y.Ju).h(ipdx.doi.org10.1016,j.conbusf1anfe.2015.06.014f1ammabi1ity1imits.Muchofourknow1edgetodayaboutamepropagationspeeds,amestructures,extinction1imits,andf1ammabi1ity1imitsissti111imitedtohightemp

12、eraturef1ames24.Duetothedifficu1tyinestab1ishingse1f-sustainingc1f1ames,adetai1edandfundamenta1understandingofc1f1amedynamicbehaviorshasnotbeenwe11estab1ished.Recent1y,ase1f-sustainingn-heptanecoo1diffusionf1amewasexperimenta11yobservedforthefirsttimebyusingozonesensitizationinacounterf1owf1ameovera

13、broadrangeoff1owresidencetimes19).Thef1amestructuresandextinction1imitswerequantitative1ymeasuredinthisstudy.Theresu1tsshowedthatozoneadditionextendedthef1ammab1eregionofcoo1f1amesanda11owedse1fsustainingc1f1amestobeobservedona1aboratoryf1amesca1e.Inotherstudies.1awandZhaonumerica11ymode1edtheNTCeff

14、ectonn-heptane/airignitioninadiffusioncounterf1owf1ame25.Thcirresu1tsdemonstratedtheexistenceofNTC-affectedignition.Inn-heptanedrop1etcombustionexperiments.Nayagameta1.6reportedthedua1modesofcombustionandextinctionandpresentedahypothesisofc1f1ameformationinamicrogravityenvironment.Inare1atedn-heptan

15、edrop1etstudy,Farouketa1.211numerica11ymode1edOSCiHa1OryCoO1f1amesgovernedbyradiationheat1ossandconductiveheat1ossfromf1ametodrop1et.However,theabovestudieswerea111imitedtodiffusionf1ames.Forpremixedcoo1f1ames.Marutaandcoworkersrecent1y16,17Jstudiedthestabi1ization1imitsofc1f1amesbyusingabumerteated

16、microchanne1.Unfortunate1y,inthisgeometrythewa11temperaturegradientandf1ame-wa11coup1ingstrong1ydictatethef1amestabi1ity,makingitditYicu1ttoaddresshowfastac1f1amecanpropagateandwhatthere1ationisbetweenthef1ammabi1ity1imitsofhightemperaturet1amesandcoo1f1ames.Withtheexpectedincreasesinpressureandinitia1mixturetemperatureinfutureengines,(hereisachancethatcoo1t1amescou1dno