Page 101 - konishipaper

INTRODUCTION
ThephenomenonofflamespreadoverliquidsisofcUITent interestbecauseofitsimportancetofiresafetyandthecuriosity 。ffundamentalmechanismofflamespread.Specialnoteisthe
reviewartic1ebyGlassmanandDryer(1981)andRoss(194a). Nevertheles，inspiteoflaboriousworks，esentialproblems，i.e.， pulsatingspreadmechanismhavestil1tobesolved.
Inthepulsatingspreadregime，theflamespreadrateisperi- odic，andliquid-phaseflowaheadoftheflame，whichisdriven bytheinteractionofthermocapi1laryandbuoyancy，seemstobe akeycontributortothespreadproces.Theconflictingphenom- enologyandcontrol1ingmechanismhavebenproposedforpul- satingregime，indicating;(1)pulsatingspreadowesitsexistence totheperiodicformationanddestructionofthegas-phaserecir- culationceljustabovetheliquidsurface(Schil1ereta，.l196a; RossandMil1er，196b);(2)instabilityinliquid-phaseyieldthe onsetoreliminationofpulsatingflamespread(Garcia，196);(3) forma~ion offlammablevaporlayerduetohotsurfacetension flow(Itoeta，.l191a).
ThesecondphaseofNASA'smicrogravitytestwasfir叫 con- ductedaboardasoundingrocke.tSeveralnovelobservationswere madeinthistests.Evenwithforcedairflowofthesameorderof magnitudeasthatinducednaturalybybuoyancyin19，theμg flamebehaviorwascompletelydiferen.tWhereasthe19flames weresotproducing，andpulsateandspreadrapidly，theμgfl紅 nes werefreofsotandspreadsteadilyandveryslowly.Theab- senceof1iquid-phasebuoyancyinμgleadedtoaverydiferent liquid-phasesurfacetemperature，flowfiled，andflamespread character.
Althoughthelumericalmodel(Schilereta，.l196a，196b) showedagoodagrementwithseveralexperimentalyobserved flamespreadcharacteristicsin19，thepredictedpulsatingspread m μgdisagre edwiththeexperimentalfindingsofslow，quasi- uniformspread(RosandMiler，196b).Thedisagrementwas hypothesizedasatr:ibutabletodi百'erencesintheefectsofther- malexpansion.Inthe2-Dmodel，forwardthermalexpansionis predictedtoperiodicalydestroytherecirculationcel1andthere- foreleadstopulsations，butthisefectisreducedin'theexperi- mentbecauselateralexpansioncanocursincethetrayismuch narowerthanthesuroundingflowduct.Tosuportthislineof thinking，thermalexpansi
Inourpreviousstudies，wemeasuredthedetailedvelocity andfuelconcentrationprofilesinan-propanolpolbyusingpar- tic1etrackvelocimetryanddualwavelengthholographicinterfer- ometry，respectively(Itoeta，.l197b).Then，wefirstsuceded tomeasureaseriesofdetai1edve10cityandvaporconcentration profilesinpulsatingregime，whichconsistsofivestages，[a]onset ofpulsating，[b]developmentofsurfacetensionflow，[c]forma- tionofrecirculationflow，[d]jumping，and[e]endofpulsating. Theseresultselucidatethat(1)gasrecirculationcelisgenerated bytheinteractionofsurfacetensionflowandbuoyancyinduced airflow，(2) fuelvaporconcentrationprofilesaheadofflame edgecanbealteredsubstantialybygasflowvelocityfield.How- ever，onlythesestudiescouldnotgiveanysuficientexplanation aboutpulsatingflamespreadmechanism.
EXPERIMENTALAPPARATUS
Experimentalaparatususedforthisstudyisesential1ythe sameasthatusedinapreviouswork(Itoeta，.1197b).Asshown inFig.1，the25cmlongx2cmwidex2.5cmdepfueltrayis used.ThermocouplesarelocatedinthefuelandsUIToundinggas.
Themeasurementsofthesurfacetemperature訂 eaccom- plishedbyusinganinfraredcamerah~ving aspectralrangeof8-
12μm，temperatureresolutionof0.1Candtimeresolutionof 30msec.Themeasurementtechniqueofinfraredcameraisde- scribedind~tail (Itoeta，.l195c;Konishi，197a).Infraredelec- tromagneticwaveisemitedfromfuelsurfaceandreflectedona goldmiITor，whichislocatedoverthefueltray，andfinal1yitis recordedbyaninfr紅 edcamera.Aninfraredcameraiscalibrated byaChromel-Alumelthermocoupleswitha75μmdiameter， whichislocatedonfuelsurface.Wedeterminedthattheemisiv- ityofn-propanolandn-butanolis0.，Q5.TheteI1operaturerangeof in企 訂 ed camera is dete1TnIned to 20 C and 50 C for n-propanol andn-butanol，respectively.Avideocameraisusedtoobservea realimageofflameandmeasureflamespreadrate.
SCHEMATICILLUSTRATIONOFPULSATINGFLAME SPREADMECHANISM
Figure2showsaschematicil1ustrationofpulsatingflame spreadmechanism，consistingoffivediferentsteps.Step[a]is thebeginingofthepulsationcyc1eandtheprocesmovesonto steps[b]，[c]，[d，][e]，andretumstostep[a]tocompletethecyc1e. Step[a]showstheonsetofpulsationandtheflameprocedsslowly
Gold-coatedmiror
Fueltray
2
Copyrightc919byASME
Therm
Infraredcamera
Figure1Experimentalapparatusformeasuring surfacetemperatureoverliquidfuel.