An analysis of the explosion limits of hydrogen／oxygen mixtures with nonlinear chain reactions.docx

Pub1ishedon03November2017Gtethis:Phys.Chem.Chem.Phys.,2018,20,742aabVo1ume20Number214January2018Pages699-1296Anana1ysisoftheexp1osion1imitsofhydrogen/oxygenDoWn1mixtureswithnon1inearchainreactionsoadedEIJINGINSTUTEOFTReceived17thAugust2017,EAccepted30thOctober2017DOI:Cu10.1039c7cp0S639gNO,.yrsc.1pccpOG1Introductionon6/29Wenkai1iangandChungK.1aw*Theignitionboundaryofhydrogen/oxygenmixturesisaZ-shapedcurveinthepressure-temperaturespace,demonstratingtheexistenceofthreeexp1osion1imits.Inthisstudy,agenera1ana1ysisgoverninga11thethreeexp1osion1imitsinanisotherma1environmentisperformedbyconsideringboth1inearchainreactions(reactantradica1reactions)andnon1inearchainreactions(radica1-radica1reactions),inadditiontothezeroth-orderreactantreactantreactions.Forthenon1inearreactions,itisfurthershownthatthe1inear-non1inearcoup1inghasthemajorinf1uence,whi1etheeffectofnon1inear-non1inearcoup1ingisneg1igib1e.Phenomeno1ogica11y,at1owpressures,thecompetitionbetween1inearbranchingand1inearterminationaswe11aswa11destructiondeterminesthefirstandsecondexp1osion1imits,whi1ethenon1inearchainreactionsareunimportantbecauseofthesma11radica1concentrationsundertheseconditions.However,athigherpressures,both1inearandnon1inearchainreactionsareneededtoaccurate1ydescribethethird1imit,whichwou1dbeunderpredictedbyconsideringthe1inearchainreactionsa1one.Forintermediateandhighpressures,thedominantspeciesareHOjandH2O2,respective1y.Mechanistica11y,theconcentrationofHO?becomeshigherathigherpressuresduetothethree-bodyrecombinationreaction,H+O2+M-HO?+M,suchthattheradica1-radica1reactionsinvo1vingHO2becomeimportant,whi1ethereactionHOz+HO?-H2O2+O2rendersHOznonessentia1atthethird1imit,withtheH2O2radica1generatedbythenon1inearchainreactionsbecomingthecontro11ingspecies.Pyrexvesse1sofdifterentsizes,coveredwithana1mostinvisib1eIayerofKC1.6Theexp1osion1imitofahydrogen/oxygenmixtureisoneofthemostfascinatingphenomenaincombustionchemistry,demonstratingtheimportanceofchainmechanismsinchemica1kinetics.1-3Specifica11y,thesemixturesexhibiteitherse1f-ignitionornonignitionatdifferenttemperaturesandpressures.2Inthepressure-temperaturespace,thetransitionboundaryshowsaZ-shapedcurveconsistingofthreeexp1osion1imitssuchthatat1owandhightemperatures,(hemixturewi11transitionfromnonexp1osivetoexp1osivestateswithincreasingpressure.However,withinanintermediatetemperaturerange,withincreasingpressurethemixturewi11traverseasequenceofnonexp1osive,exp1osive,nonexp1osiveandexp1osivestates.Thisresu1tisessentia11y(heconsequenceofgas-phasechainbranchingcompetingwiththe1ossmechanismsofgas-phasechainterminationandwa11destruction.Experimenta11y,theautoignitionnearthefirstandsecond1imitshasbeenstudiedinarapidcompressionmachine(RCM)4andaf1owreactor;5andthethirdexp1osion1imitofhydrogenandoxygenhasbeeninvestigatedinspherica1Detai1edhydrogen/oxygenreactionmechanismshavebeendeve1opedandextensive1yintegratedinthesimu1ationofvariousfundamenta1andapp1iedsituationsinvo1vingbothignitionandf1amingcombustion.Itsre1ative1ysimp1emechanism,ascomparedtothoseofhydrocarbonoxidation,andtherestrictiontoweak1yreactivestateswithminima1reactantconsumption1eadingtoignition,havemotivatedattemptsforana1yticitywithsufficientcomprehensiveness.Inparticu1ar,recent1yAzatyaneta1.7andWangand1aw8performedaneigenva1ueana1ysisoftheexp1osion1imitsbyconsideringon1yHandHOzastheunsteadyspecies,withneg1igib1eheatre1easeandreactantconsumption,andshowedthattheZ-curvecanbeana1ytica11yandexp1icit1ydescribedbyacubicpo1ynomia1.Capita1izingontheana1yticity,Wangand1aw8furtheridentiedthere1ativeimportanceof(hevariousgas-phaseandsurfacereactions,andsituationswherethe1imits1osetheirnon-monoionicitysuchthatthesystemwou1dbecomemorerigidtomanipu1ationsforexp1osivity.Amajor1imitationoftheana1ysisofWangand1aw,8whichpuHshedon03November2017DOWn1Oa加dbyBEIJINGNstituteoftechno10GY0n29naDepartmentotMechanica1and/XerospaceEngineering.PrmcetonUniversity,Princcton,NJ08544,USAbCenterforCombustionEnergy.Tsing1waUniversity.Beijing1(XX)84China.E-mai1:ck1awprinccton.eduthesecond1imit,thethree-bodyreactionH+O2+M-HO2+Mbecomesthedominantbranchingpath.9Furthermore,recentfindings10"haveshownthat,subsequenttotheinitia1bui1d-upofHO>,itsconsumptionthroughHO2+HO2-H2O2+O2becomessignificant.Consequent1yHO2andH2O2canbeequa11yimportantforthethird1imit.RecognizingtheimportanceoftheHO2-H2O2chemistryathighpressures.Sanchezeta1.11separate1yana1yzedthethird1imitbasedonthetherma1exp1osiontheoryofFrank-Kameneskii.Regardingthero1eofhea1re1easeinvo1vedin(heHO2-H2O2chemistrya1highpressures,Kreutzand1aw12computationa11yshowedforcounterf1owignitionthatbysuppressingheatre1easethesystemexhibitsaninf1ectionpointinsteadoftheS-curveignitionturningpoint.Theinf1ectionpoint,however,becomesaturningpointwhenheatre1easeisa11owed,a1beitatbasica11ythesamethermodynamicstateofthemixture.Thisthensuggeststhatitistheradica1pro1iferationinsteadofheatre1easethatc