Page 133 - konishipaper

COLDTEMPERATUREVALLEYINPULSATINGFLAMESPREAD 2821
LSPTandSTTechniques
Ahigh-spedcamera(50frames/swithashuter spedof0.2ms)wi也 anultravioletlensandanim- ageintensifierwasusedtoobtainthevelocityofpar- ticles. A schema世 c of the ap paratus was shown in om:earlierpapers[1，13]andisnotavailablehere. Therearetwolasersintheaparatus:a4W Ar-ion 1aseranda75mW He-Ne1aser.TheAr-ion1aser wasusedtomeasuregas-phaseflowve10cityand也e He-Ne1asertomeasureliquid-phaseflow.Eachla- serformedrough1ya0.8m mthickshetofthe1aser 1ightwi出 a450 openingang1ebypぉsingthrOlψits owncylindrica11ens.Formeasurementofthegas- phaseconvec世on，talcparticlesweredisperseduni- form1yoverthefue1surface.Formeasurementof theliquidconvection，aluminumparticlesof10to 20μmdiameterweresprinkledontotheliquidsu子 face;somealuminumparticlesfloatedontheliquid surface，andothersenteredintotheliquid.These aluminumparticlesweighedles也an0.01gintota1 sothattheyhadlitleefectonthechangein也er目 mophysicalpropertiesofliquid.
Thesuperimposedimageoftheliquidandgas 丑owcanbesenfromthetop.Thatimagewassepa- ratedbyabeamspliter10catedoverthefuelsurface. Thegas-phaseflow(Ar-ionlaser)datawerepased th1'oughthebeamspli社erandrecordedbyadigital videocamera，whiletheliquid-phaseflow(He-Ne laser)datawerereflectedbythebeamspli仕erand recordedbyanotherdigitalvideocamera.Thesetwo videocamerasweresynchronizedtoobtainasplit imageofgasandliquidflowinasingleTVmonitor.
DWHIFueZConcentrationMeasuremeηts
ThebasicplinciplesofDWHIarethesameas those fo1' sing1e holographic interferomehy [4，14，15].ThedetailsofDWHItechniquearepro- videdinourpreviousstudies[1，14].Themajordiι ferencebetweenthese.twosystemsisthatDWHI hastwo(50mW He目 Neand75mW Ar-ion)lasers andthesing1eHIhasone(50mW Hか Ne)laser. DWHIisanonintrusivemeasurementtechnique 也atissuitabletomeasu1'etwo-dimensiona1fuelcon- centrationprofileswi出 alesthanmicrosecondre- sponsetimeandabeterthan30μmspatialreso- lution. When our flame conditions satisfy aproximate1ywi也 thetwo-dimensionalnature，as shown in out previous s加 dy [1 1，14，] D W H I is ac- curate over the microsampling technique [16，] whosespatia1resolutionisroughlyseveralmilime- tersandwhoseresponsetimeison也eorderofa secondor10nger.
TheDWHItechniqueissusceptibletosmaler- rorsbecausetheG1adstone-Daleconstantsareon1y weakfunctionsofwavelength.Theacuracyofread- ingthefringenumbershiftrequiresanorderofone- thousandthtokeptheaproximateerorwithin
:!:5%，resultinginourtaskbeingimpractical.In目 steadweusedtheequa世onofsing1ewavelengthin- terferometryforeachlaser.Thisaproxima世onsim- plified our experimental procedures and a1so is ptovedtobeacurate叩eno∞u悼ghD白oro町u1汀rme伺asuremen pur中pose日[1日].
Dualwavelength(DW)ho1ogramscontainho1o-
g1'amsoftwodiferentwavelengths，oneforfuelcon centra世onandtheotherfortemperatureprofiles. AfterD Whologramswererecordedonafilm，the twoimageswereseparatedusingatechniqueex- p1ainedinourearlypape1'[1].
IRSurfaceTemperatureMeasurements
Aninfraredcame1'awasusedtomeasuretransient two-dimensionalprofilesofliquidsurfacetempera- ture.Theinfra1'edcamerawぉ calibratedagainsta 75μmdiameterChrome1-Alumelthermocouplethat wasplaced1m mbelowthefuelsurface;theemis- siviザofn-propanolwasdeteninedtobe0.95.This infraredcamerawasusedinourpreviousstudy[17] andhadadetectorspectralrangeof8-12μm，tem- peratureresolutionof0.1oC，andtimeresolu世onof 30ms.OurIRthermographcanmeasurethecon- densed-phasetemperaturebyeliminatinginterfer- enceoftheflame(sot，CO2，andH20)efect[17].
ResultsandDiscusion
Figure1showsschematicsofthefourdiferent steps(athroughd)，whilethefinalstep(e)wasnot includedbecause社 issimilartoStep[a].Eachstep containstopandsideviewsof1iquidandgasflow structures也atwereconstructedfromLSPTandST resu1ts.Inthefolowingwebrieflydescribethema~ jorfoursteps.
Step{a}:OnsetofPulsation
Thereisnoflowintheliquidphase，whereasthere isairflow也atisinducedbybuoyancyaheadof也e flameleadingedge.Theleanflamabilitylimit(2.2 fue1vaporvol% inairforn-propanol)liesaproxi- mばe砂1m mabovethefue1surface;belowthat heightthefuelvaporiswi出intheflammab出句， limit， andthe宜ameisabletospread;whileabovethat heightthefuelvaporisleanerthanthefl出 nmab血.ty limit，andtheflameisnotab1etospread.TheIR measuredfue1surfacetemperaturereached30oC (welabovethe23oCflashpoint)，thenrapidlyde- creased with the increase of distance from the flame'sleadingedge.At.2m maheadoftheflame edge，thesurfacetemperaturedropedbelowthe 230C 宜ashpoint.DWHIfuelconcentration(not shownhere)proved也atatpositionsneartheflame 1eadingedgeandinsideada1'kquenchingzone，the leanflamablelimitisnotsatisfied，andindedno flamespreadocuredinthegasphase.
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