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2820 FIRE-IgnitionandFlameSpread
temperatureinanormal-gravityenvironment.Three valuablenewobservationsweremadeinthattest: (1)Evenwithforcedairfiowofthesameorderof magn社udeasthatinducednaturalybybuoyancyat normalgravity，themicrogravity:8.amebehavioris completely dif ferent; (2) the normal-gravi，句 :8.ames producesot，pulsate，andspreadrapidly，whuethe microgravity :8.ames are fre e of so ot and spread stea占lya吋 veryslowly[7];and(3)theabsenceof thehquid-phasebuoyancyinmicrogravityleadstoa- verydiferenthquid-phasesurfacetemper批ure， :8.ow五eld，andcharacteroftheflamespread.
UCINumericalModel
To incorporate progres s made by e守 erimental studies， Schil ler et al. [8] developed a numerical modelwi也 finiteldneticsandvariablethermophys- icalpropertiesinboththegasandhquidphases.The conditionoftheircalculatIonwasinitialyquiescent liquidwithlowspedandoposedforcedairflow [8]，andtheyprovideddetatiedvectorplotsofthe velocityfieldverynearthe:8.amefrontatdiferent 世mesin也epulsatingcycle.Theyconcluded也批 pulsationowesitsexistencetothegas-phasecircu- lationce，Il andthermale守 ansionplaysthemajor roleintheperiodicdestructionofthecirculationcelI inthegasphasewhenthe宜amejumpsforwarddur- ingthepulsatingspread.Itsforma世onocursduring thecrawhngpor世onofthepu1satingflamecycle，and 社 persistsinacumulatingfuelvaporuntua:8.am- mableconcentrationisreachedinsidethecelIand the宜amejumpsagain.WhiletheUniversityofCah- fo凶 a，Irvine，(UC1)modelshowsgoodagrement withseveralexperimentalyobserved:8.ame-spread characteris世cs批 normalgravity，thepredictedpu1- satingspreadinmicrograviザ disagreswiththeex- perimentalfindingsoftheslowquasi-uniformspread [7].Thedisagrementwashypothesizedasatrib- utabletodiferencesintheefectsofthelateralther- malexpansion.
1nthetwo-dimensionalmodel，forwardthermal e守 ansionispredictedtoperiodicalydesh'oytheci子 culationcelandthereforeleadto'pulsation.This efectisreducedintheexperimentbecauselateral expansioncanocurfromatraythatismuchn紅白 rower出 anthesuroundingflowduct.Tosuport thishneofthinldng，mostofthethermalexpansion inthemodelwasremovedbysetingthetermdp/at equaltozerointhepresurecorectiontermofthe continuityequation[6].Agreementwiththemicro回 gravi，句flame-spreadratewasquan世ta出，elyachieved [7].
modeling，thegas-phasecirculationislargerinmi- crogravity，butasoposedtothese-predictionsitwas notfoundtocyclicalyrepeatdestructionandfor- mation.1nrespecttothelateralexpansionefect， smokevisualizationalsorevealedthatthelateraldis- placementofthesmokehnesduetothermalexpan- sionape紅 ssurprisinglysimilartoth批 atnormal gravity.Therefore，usingthedimensionalefectof thehotgase守 ansiontowardthesidestoexplainthe model'sdisagrementwithmicrogravityexpe1ments nowappe訂 sincorect[9].
TheNedfor1γαηsientThre-Di仰 倒 的 αl Eχperiment
Tounderstandthemechanismofpulsa世ngspread， itisclearfromtheabove-mentionedbackground andGarcia-Ybaraetal.'sschlierenexperiments[10] thatweneedthetransientvelocity，temperature，and fuelconcentra世onprofi1es(preferablyalinthre dimensions)nearthemovingflameleading.edge，in thegas，thehquid，anditsinterfacewi也 lesthan1 mmspa世alresolution.
To也atend，weemployedthefivediferentmea- surement techniques mentioned in the abstract: LSPT，DWH1，1R，ST，andHSP.Eachtechnique playedauniquerole也 atise守 l垣 間 dinalatersec- 世on.LSPTandDWH1techniquesweredeveloped inourgroup，whue1R，ST，andHSPtechniques werepreviouslyusedbyotherresearchers[7].
JE!'perimentalMefuodls Aparatus
Thefueltrayusedforthisstudywasthesameas thatusedpreviously[4，11]，havingdimensionsof 250 m m long X 20 m m wide X 25 m m de ep. The fueltraywaslocatedinsidea14cmhighX 15cm wideX 40cmlongglasceltoehminatelaboratory draftandincreaserepeatabihty.Thevolumeofthe glascelIwaslargeenoughtocontainsuficientox- ygenforflamespreadunderaconstantoxygencon- centration.
A75μm占ameterChromel-Alumelthermocouple wasplacedatthecenterand2m mbelowthefuel surfacetomonitortheinitialliquidtemperature. Theambientairtemperaturewasalsomeasuredus- ingthesametypeofthermocouplenearthesideof fueltrayand2m mabovethefuelsurface.Normal propanolwasusedasthebasehnefuel也atalows
1n recent microgravi句T e呼 eriments with the
smoke-wiretechnique，MilIerandRos[9]verified， comparisontothepreviousexpe1ments[4，5，l1，l2]. inagrementwithnumericalmodehng，thatamil- Thefuelwasignitedatoneendofthefueltraybya limeter-sizedgas-pha~e circulationcelI回 stsahead smalpuotflame.Attheendofeachtestrun，high- ofaflamespreadingacrosaflamablehquidas presurenitrogenwasapliedfromanitrogencーメ ocursatnormalgravity.Aspredictedbynumerical inderぬ ex世nguish也eflame.