Effects of Soret diffusion on the laminar flame speed and Markstein length of syngas／air mixtures.docx

EffectsofSoretdiffusiononthe1aminarf1amespeedandMarkstein1engthofsyngas/airmixturesWenkai1ianga,ZhengChenab,FanYangc,HuiqiangZhangcjStateKey1aboratorj'forTurbu1enceandComp1exSystems.DepartmentofMechanicsandAerospaceEngineering.Co11egeofEngineering.PekingUniversity.Beijing100871.ChinahDepartmentofAeronauticsandAstronautics,Co11egeofEngineering,PekingUniversity,Beijing100871,ChinacDepartmen1OfEngineeringMechanics,IsinghuaUniversity.Beijing100084.ChinaAvai1ab1eon1ine28Ju1y2012AbstractTheeffectsofSoretdiffusiononpremixedsyngas/airf1amesatnonna1ande1evatedtemperaturesandpressuresareinvestigatednumerica11yinc1udingdetai1edchemistryandtransport.Theemphasisisp1acedonassessingandinterpretingtheinf1uenceofSoretdiffusionontheunstretchedandstretched1aminarf1amespeedandMarkstein1engthofsyngas/airmixtures.The1aminarf1amespeedandMarkstein1engthareobtainedbysimu1atingtheunstretchedp1anarf1ameandpositive1y-stretchedspherica1f1ame,respective1y.Theresu1tsindicatethatatatmosphericpressurethe1aminarf1amespeedofsyngas/airismain1yreducedbySoretdiffusionofHradica1whi1etheinf1uenceofH?Soretdiffusionisneg1igib1e.ThisisduetothefactsthatthemainreactionzoneandtheSoretdiffusionforHradica1(Hz)arestrong1y(weak1y)coup1ed,andthatSoretdi1TusionreducestheHconcentrationinthereactionzone.BecauseoftheenhancementintheSoretdiffusionf1uxofHradica1,theinf1uenceofSoretdiffusiononthe1aminarburningf1uxincreaseswiththeinitia1temperatureandpressure.Un1iketheresu1tsatatmosphericpressure,ate1evatedpressuresthe1aminarf1amespeedisshowntobeaffectedbytheSoretdiffusionofH>aswe11asHradica1.Forstretchedspherica1ame,itisshownthattheSoretdiffusionofbothIIandH?shou1dbeinc1udedsothatthestretchedf1amespeedcanbeaccurate1ypredicted.Simi1artothe1aminarf1amespeed,theMarkstein1engthisa1soreducedbySoretdiffusion.However,thereductionisfoundtobemain1ycausedbySoretdiffusionofH2rather(hanthatofHradica1.Moreover,theinf1uenceofSoretdiffusionontheMarkstein1engthisdemonstratedtodecreasewiththeinitia1temperatureandpressure.2012TheCombustionInstitute.Pub1ishedbyE1sevierInc.A11rightsreserved.Keywords:Soretdiffusion:Syngas/air;1aminarf1amespeed;Markstein1ength1. IntroductionMassdiffusionisessentia1in1aminarf1amesanditstrong1yaffects,orevendetermines,thefunda-7489/$-seefrontmatter2012TheCombustionInstitute.Pub1ishedbyE1sevierInc.A11rightsreserved.http:/dx.doi.Org/10.1016/j.proci.2012.06.048reactivef1ow,usua11yon1ytheFickiandiffusionisconsidered.However,inthepresenceofvery1ightorheavyspeciesandsteeptemperaturegradient,Soretdiffusion1-3,whichdrives1ight(heavy)speciestoward(awayfrom)thehotzone,isa1soimpoi1antforthemasstransport.TheeffectsofSoretdiffusionon1aminarf1amesCorrespondingauthorat:StateKey1aboratoryforTurbu1enceandComp1exSystems,DepartmentofMechanicsandAerospaceEngineering,Co11egeofEngineering.PekingUniversity.Beijing100871,China.Fax:+86(10)62757532.E-mai1address:cz(Z,Chen).havebeenextensive1ystudiedinthe1iterature.Excepttheworkonheavyspeciessuchasmeta1partic1e4,soot5,andn-heptane6,mostofthestudiesarefocusedontheSoretdiffusionof1ightspecies.Forexamp1es,EmandGiovangig1i7,8studiedtheinf1uenceofSoretdiffusiononthef1amestructureandextinctionofhydrogen/airandmethane/airmixtures;BongersandBeGoey9investigatedtheeffectsofSoretdiffusiononthe1aminarf1amespeedofhydrogen/airandmethane/airmixtures;Grcareta1.10examinedtheSoreteffectsin1eanhydrogen/airpremixedf1ames;andYangeta1.11,12presentedamechanisticinterpretationonSoretdiffusioninhydrogen/airandn-butane/airf1ames.Inthesestudies4-12,discernab1eeffectsofSore1diffusionwereobserved.menta1combustionprocessesSuchasignition,f1amepropagation,andextinctionI,2.ThedominantmodeofmasstransportistheFickiandiffusion,whichisduetotheappearanceofconcentrationgradient.Inthemode1ingofmu1ti-componentTheobjectiveofthisstudyistocomputationa11yassessandinterprettheeffectsofSoretdiffusiononsyngas/airf1amesatnorma1ande1evatedtemperaturesandpressures,1vomostimportantparametersofpremixedsyngas/airf1amesareinvestigated:oneisthe1aminarf1amespeed(or1aminarburningf1ux)andtheotheristheMarkstein1ength.The1aminarf1amespeedisdefinedasthepropagationspeedofanadiabaticp1anarf1amere1ativetotheunbumedgas1.2anditaffectsthefue1burningrateincombustionengines.TheMarkstein1engthcharacterizesthevariationinthe1oca1f1amespeedduetotheinf1uenceofexterna1stretching14.Itdeterminesthef1ameinstabi1ityre1atedtopreferentia1diffusionandisoneofthebasicinputphysicochemica1parametersincertainturbu1entcombustionmode1s14.In(henextsection,theprob1emspecificationandnumerica1methodsarepresented.TheninSection3,theeffectsofSoretdiffusiononthe1aminarf1amespeedandMarkstein1engthofsyngas/airmixturesarediscussed.Fina11y,theconc1usionsaegiveninSection4.However,toourknow1edge,inthe1iteraturethereisnostudyinvestigatingtheeffectsofSoretdiffusiononsyngas/airf1ames.Current1y,syngas(synthesisgas)isexpectedtop1ayanimportantro1einfutureenergyproduction,particu1ar1yforstationarypowergenerationusingIntegratedGasificationCombinedC