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COLDTEMPERATUREVALLEYINPULSATINGFLAMESPREAD 2823 Step[b]
35 と 30
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ro 25
~ 20 ωo
吉~ 15 凶
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25 Distancefromtheflameleadingedgex[mm]
4 3 2
。
FIG.2.Top:TheIRmeasuredupstreamsurface-tem- pera旬 reofn-propanolatStep[b].Botlom:Gas-phasepro- panolconcentra世oninairforStep[b]measuredbyDWHI (Tf=10.1OC).Theoriginisfi.xedattheflameleadingedge andminustotheupstream占rection.
temperaturevalJ.eywheretheminimumliquidtem- peratureis21oC，whichisbelowthe23oC:8.ash pointofn-propanol，existsat5m maheadofthe flameleadingedge.Fig.(botom)showstheDWHI measuredfuelconcentrationprofilesinthevertical directiontothefuelsurfaceandaheadofthe:8.ame leadingedge.Itshowsthatthefuelconcentrationat 3.4m maheadofthe:8.ameleadingedgeisbelowthe lean :8.am mabiliザ limit (2.2 vol % in air); therefore， thecrawling:8.amespreaddidnotocurinthegas phase.
Step[c]:FuelVaporBuildup
Whenthe:8.amespreadingconditionwasatStep [a，]therewasno:8.amespread;whilethecondition wasatStep[b]，theflameadvancedslowlyoverliq- uid. Through both steps，the liquid was local ly heated，causingconvectionanddiametersofboth liquidandgascirculationcelstoincreaserespec-
世ve砂to15.7m mlongX 4.1m mhighand2m m longX 31mhigh.Thecenterofthegas-phasecir- cula世 on cel l was located at 8.5 m m upstream from
Concentration[vol%]
o12~3 45 Concentration[vol%]
FIG.3.Top:D WhologramforStep[d].Botlom:Gas- phasepropanolconcentra世oninairforStep[d]measured byDWHI(T)f=10.lOC).
出eflameleadingedge，whilethecenterofliquid circulationwaslocatedjustbelowtheflameleading edge.AtStep[c]，theupstreamliquidfuelsurface temperatureincreasedtoabovethe23ocB.ashpoint andthecoldtemperaturevaleydisapeared，indi- cating也批 theincreaseoffuelvaporconcentration intheupstre田 nisunderway.
Step[d]:FlameJumpiηg
Thisstepshowsth抗出ecriticalmomentofflame on砂ocurswhentheheightofthe宜am
う泡anlimitexceds出th拭atoft也hequenc恒hlingl1l:匂ye町r.
ofasuddenincreaseoftheB.ame-spread ociatedwi也 也e:8.amejumping，thegas- lrculationcelwasdestroyed，probablydue 'lnalexpansionefect[9]，creatinganewcon-
air:8.ow(Fig.1，Step[d]).Thisconcurent lceleratedtheliquidsurfacetension:8.owas Ireadalongwiththeflow.Thecoresponding ogramisshowninFig.3(top)，andthecon白 川 profile，showninFig.3(bo仕om)，indi-
jumps，noflamablegas mixtureremainsaheadofthe.:8.ame'sleadingedge，
causingtheces sationofthespread.
Compαrisoη oftheEχperimentalResultswithUCI NumericalModel
Schilereta.l[8]predictedthattheexistenceof the pulsating flame spread is dependent upon the
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