Page 105 - konishipaper

Thelowestsurfacetemperatureis21 C，wruchisbelowtheflash pointofn-propanol.Theconcentrationprofilesalsoprovesthat thereisnosuficientflamablevaporlayerat3.4m maheadof flameleadingedge.Becauseofthislowconcentrationregiondue totemperaturevaley，the.crawlingflamecanotpropagateingas- phase.
St皇rucl:_Accumulation01flammablevaoor Figures5(a)through(c)showtheacumulationprocesof
flammablevapor.1npreviousstudies(Itoeta，.l197b)，weob- servedthefuly-developedcirculationcelinbothgas-andliq- uid-phase.Thethermographicimageandtemperatureprofiles， whichareshowninFigs.5(a)and(b)，indicates出 attemperature valey，whichexistedinstep[b]，almostdisapearsandtheliquid temperatureaheadofflameleadingedgeexcedstheflashpoint ofn-protano.lTherefore，asthesubstantialflamablevaporlayer formsaheadoff1ameleadingedge，theflamecanpropagatein premixedflammablelayer.However，asshowninFig.5(c)，the concentrationprofilesshownosu百'icientvaporacumulatedin frontoftheflame，whichmightbemistakesinDWHI-measure- men.tDuetothre-dimensionalityofflamespreadphenomena， thechancesarehardlyencounteredtoobtainthesatisfactoryre- sultsamonghundred-timesexperiments.
SteDrdl:Jumoinaoortion Ifthepositionofleanf1ammablelimitexcedsthatof
quenchinglayer，theflamepropagatesinpremixedgas.Ito(1toet al.，197b)showsthatbecauseofasudenincreaseoftheflame spreadrate，athermalexpansionofairhapensinthecirculation zonedestroyingthecirculationcel1andcreatinganewconcur- rentairflow.Thisconcurentairflowaceleratestheliquid-sur- face-tensionflowasflamespreadsalongwiththeflow.τbermo-. graphicimageandtemperatureprofilesshowthejumpingpro- cesinFigs.6(a)and(b).百leconcentrationprofiles，asshownin Fig.6(c)indicatesthatnosubstantialcombustiblegasremains aheadofflameleadingedge.
MlECHANISMOFPSEUDO固 UNIFORMFLAMESPREAD Thepseudo-uniformregimederivesitsnamefromtheposi-
bilitythatpulsationmayocurbuttheirwavelengthsexcedthe traylengthsusedintheexperimentsotheobservedspreadis steady.Howevertherehasbenlitleexperimentationinthislow temperatureregimeandnosuficientexpl加 ationforpseudo-uni- fonnmechanismhasbenmade.
Themechanismforexplainingthepulsatingphenomenaalso
，
ofn-propalol.Althoughtheconcentrationdistributionsinpseudo- uniformregimearenotobtainedforn-propanol，theremightbe nosuficientfuelvaporexistedinfrontoflameassameascrawl- ingphaseofpulsationcycle.
DlSCUSSION AseriesofNASA'smicrogravityexperimentsaboardasound-
ingrocketofersvaluableresultstous.Theyusedn-butanolasa fuelandperformedtheμgexperimentswithforcedairflowof 30cmls.Theexperimentrevealedthatinspiteofgas-recircula- tioncel，thecharacteroftheμgspreadwasuniform，i.e.without pulsation，atavelocityofabout1.5cmlsec.Furthermore，aliq自 uid-phasevortextravelssteadilywiththef1ame，extendsthepre町
canaplytopse
O 5 Distancefromflameleadingedgex[mm]
Figure7(a)Thermographicimage.and(b)sUJl1ace temperatureprofileinpseudo-uniformregime.
.1 1$ r4 15 16 J7 t8 リ
udo-uniformspread，i.e.theexistenceoftem- peratui'evaley.Figures7show(a)athermographicpictureand (b)asurfacetemperatureprofileobtainedatthecenterofthefuel trayinn-propanolpool.Verylargecoldarea，whichislargerthan thatinpulsatingregime，isobservedinfrontoftheflameleading edgeassqpwninFig.7(a).Thesurfacetemperatureofthiscold 創 .'eais15 C，asshowninFig.7(b)，wruchisbelowtheflashpoint
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>'Co~wdir愉tω い Figure8Thermographicpicturefornabutanol inμg，Tf=20.4oC(RossandMiler，196b).
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