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ProcedingsoftheCombustionInstitute，Volume28，20/p.2819-2826
l'1HL!E lEF FlEC l' O F A C O L D l'JEMPlER Al'U R1E V A L LlEY O N J?U L S A'f][NG FLAMESPREADOVJERlPROlPANOL
TADASHIKONISHI，lGHASSANTASHTOUSH，2AKIHIKOITO，3AKlRANARUMI4ANDKOZOSAIT02
lOitaNationalColegeofTechnology Oita870-0152，]apan 2UniversityofKentucky Lexington，KY40506，USA 3HirosakiUniversity
Hirosaki036-8561，]apaη 4KanagawaInstituteofTechnology
Atsugi243-02，]apan
Thetransientthre-dimensionalstructuresofvelocityandtemperaturecreatedbyapu1satingfl.ame spreadovernormalpropanolwereconstructedfromfiveindependenttransientmeasurementsusingfive 也ferenttech凶 ques:lasershetparticletracking(LSPT);smoketracing(ST);dualwavelengtholographic interferometry(DWHI);in企aredthermography(IR);andhigh-spedphotography(HSP).Thesemea回 surementsshowed也此也epulsating:8.amespreadconsistsoffive也stinctlydiferentsteps.Thefi凶 step istheonsetofp吐sationcreatedbythestagnationoffl.amespreadovertheliquid，whichisfolowedby thesecondstep，formationofacoldliquidvaleynearthea~me's leadingedge，andthetl1Irdstep，acu- mulationofliquidfuelvaporovertheliquidsurface.Inthefourthstep，出eflamejumpstlrough也e formedpremixedgaslayer，leadingto出e缶lalstep，thecesa世onofspread.Afterthe五fthstep，theproces retumsto也efirststep，completingtheentirepulsationcycle.Ourexperimentaldataconfirmtheforma世on ofasmalgas-phasecircula世oncel，aspredictedbytheU凶.versityofCalifornia，Irvine，numericalmode，l andsuporttheidea也at也epulsatingspreadistrigeredbythesubsurfaceliquidconvection也atafects thegas-phase:8.owandthefuelvaporconcentration.Thesecondresu1tisuniqueandsugeststhatacold temper拭 urevaleyformedon出eliquidsurfacewouldplayanimportantroleinthemechanismofpulsating spread.
In.trodluctioJrl PulsatingFlameSpread
Experimentsoftenusearectangular-shapedopen- topcontainer[1]filedwi也 liquid，ignitingoneend andobservinghowtheflamespreadsover吐leliquid totheotherend.Whentheliquidtemperatureis aboveitsflashpoint(super-flash-pointliq凶 d)，也e flamespreadisfast，dependinglitleonitsinitial liquidtemperature.Whentheliq凶 dtemperatureis below its flash point (sub-丑ash-point liquid)，也 e 丑ame-spreadratedependsstronglyontheini任aliq- uidtemperature[2，3].
When'theliq凶 dtemperatureisslightly'.telowthe flashpoint，也eflamespreadssteadilyover.theliquid; thephenomenonislmown'asuniformspread[2]. The:8.ame句 readrateisdefinedasthespeedofthe :8.ameleadingedgeagainstacordinatefixedtothe stationarγliquidcontainer.Withadecreaseinthe i凶世alliquidtemperature，the:8.amefrontst但 isto pulsateduringspread;thephenomenoniscal1ed pulsatingflamespread，themainfocusofthiss切 dy. Inpulsating丑amespread，theflame-spreadrateis
periodic.Withafurtherdecreasein，theliquidtem- peraturebeyondthepulsa世ngspreadtemperature the:8.amespreadisbelievedtobecomepseudo-u凶- form[2]，buton砂afewexperimentalresultsare availableinthisregion.
Previouslywestudiedthemechanismofuniform :8.amespread[4]usingaholographicinterferometry technique.Inthatstudy，weshowed也atintheuni同 formspreadregion，contr但ア toAkita'searlystudy [2]，subsurface liquid convection is the driving mechanismofflamespread;however，nodetailed discusionwasgiventothemechanismofpulsating spreadbecausewecouldnotacuratelymeasure transientthre-dimensionalvelocityprofilescreated bythepulsatingspread.
FlameSpreadE:χ:perimeηtUnderMicrogravity
NASAconductedasoundingrockete守 eriment [7]，whichprovidedfarlongermicrogravitycon也- tionsthanthoseprovidedbythedroptowerfac出ザ forthefirst-phasetest[5].Inthesoundingrocket， thefueltrayhaddimensions300m mlongX20m m wideX 25m mdeep，andη，目butanolwasusedasthe fuelbecauseitproducespulsa世ng.samesatroom
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