Page 87 - konishipaper

Step(a)
Step(b)
S~ep (c)
cm/s，showsafulydevelopedcirculationingasphaseandliquidphase. Thecenterofthegasphasecirculation(15.7m minlength(4.1m min height)islocated8.5m mupstreamfrorntheflarneleadingedge. Fig- ure4(d)showstheflamespreadratetobe14.1cmJsandboththe liquidandgasphasecirculationsdecreasedtheirdiameter.
DWHIResults HighspedvideoandIRphotographstakenfromabovethetray
revealedthatforthe0.5cmwidetray，boththesurface-ternperature distributionandtheshapeoftheflarnefrontareparabolicinnature， whileforthe1，2and4cmwidetrays，srnaltwincirculationswere generatedonthefuelsurface[RosandMiler，196]sugestingthat thecharacteroftheflowprofi1eofthegasphaseflowprofi1eischanged from2-Dto3-Dbyincreasingthewidthofthetray.Arecentstudyby Garcia-Ybara[Garcia-Ybara，eta1.， 196]alsosugestedthe3-Dna.司 印 reofthegas-phaseflowinducedbyaspreadingflameoveralcohols. ToincreasetheacuracyoftheDWHI，the3-Defectnedstobernini- rnized.Weexperirnentalydidthisbytakingaseriesofvideopictures togetherwithD Wholograrnsandidenti勾ingthebest2-D-flameshape fromthevideofilrnandthecorespondingD Wholograrn.
SincethespatialresolutionofourDWHIisbeterforthewider traywidth[Narumi，eta1.]， weuseda40rnrnwidetrayandconducted flamespreadtestsovern-propanolatitsinitialternpera旬 re10oc.How- ever，weconfirmedthattheflamespreadrateoverthe20rnrnwideand 40rnrnwidetraysisaproxirnatelythesarneandtheflamestructure overbothtraysisverysimilarinnature. Figure6showsD Wholo- grarnsandverticalprofilesofpropanolfuelconcentrationforsteps(a， b，andd). Theleanflarnmabilitylirnitforn-propanol-air(2.2mole percent)isshowninasolidlineinFig.6(top). Figure6(botorn) showsthepropanolconcentrationintheareabelowthesolidlinesatis- fiestheleanflarnmabilitylirnit，thus，theflarneisabletospreadthrough aprernixedpropanol-airrnixture.
SUMMARYANDCONCLUSIONS
(1) Previously，wedevelopedauniquePTLSsystemforrneasuring velocityprofilesfortransientflowinaverylimitedspace.Weaplied thisPTLS勾sterntostudythemechanismofthepulsatingflarnespread overpropanolandsucesfulyobtainedaseriesofPTLSflowdiagrams. ThesePTLSflowdiagramsrevealedagas-phasecirculationinthe pulsatingspre戸dregiontogetherwithaliquid-phaseconvection，both ofwhichwerepredictedbyotherresearchers.
(2) WeapliedtheDWHIsysterntorneasuretransientprofilesofthe gas-phasepropanolconcentrationovertheliquid-propanolsurface.We obtainedaseriesofD Whologramsandconfirmedthattheflamespread ocuredonlywhenthepropanolfuelconcentrationoverthefuelsurface ishigherthantheleanflammabi1itylirni.tOurcurentDWHIasumes a2-Dmodel，thustheacuracyoftheDWHInedstobeimproved whenitisapliedto3-Dproblems.
ACKNOWLEDGEMENTS
Thisstudywassuportedinp紅 tbytheNationalInstituteofStan-
dardsandTechnologyunderGrant#60NANB4D1674，inpartbythe NASA-KentuckyEPSCoRProgram，inpartbytheJapaneseMinistry ofEducationunderUS-JapanColaborativeAgreementTravelGrant， andinpartbytheCenterforManufacturingSystemsattheUniversity
S~ep (d1>
Figure 4 Four dif ferent flow visualization photographs obtainedforsteps(a，b，c，andd1).