Flame spread over kerosene soaked sand in a quiescent, atmosphere and an opposed air stream has been examined, and the effects of the air stream on the fl arne spread mechanisms are discussed.The aspects of spreading flames, the flame spread rate, and t.he temperature d i.s t.r i bu ti.ons near leading flame edges were examined for various initial temperatures T. of kerosene soaked sand and free stream velocities U of the opposed i. air stream.As U increases, the flame near Lt.s leading edge approaches the sand surface.The flame spread r a t.e Vf at U=O increases considerably with T..As U increases, V f decreases rapidly and then gradually decreas1?s until U becomes 275 cmls in the Li.mi ts of present e xpe r i.men ts .When U exceeds 275 cm y s , the flame spread becomes unstable and V f decreases rapidly. In the case of U=O, the heat transfer from the flame zone t.o the unburned region ahead of the leading flame edge seems t.o depend largely on the flame radiation.On the other hand in the case of U 0, the heat transfer t.o the unburned region seems to depend largely on t.he heat conduction through the sand layer.The stabil izat ion of the leading flame edge associated with the aerodynamic atru c tur e of the reverse flow region is found t.o be necessary for the stable flame spread.
The behavior of the reverse flow in f r o nt. of t.h e leading flame edge spreading over kerosene-soaked sand in an a i r s t.r e a:n has been examined using a few flow visualization techniques, and r.h e role of t.h e reverse flow in the flame spread is discussed.In a wide range of the free stream velocities U from 30 t.o 210 cm/s, a stable reverse flow region in f r o nt. of the leading flame edge was observed clearly, and its horizontal dimension was found to be almost independent of U.As U increases, the velocity of the reverse flow increases. The reverse flow takes an important role in the stable flame spread in an opposed air stream, although it has no apprec iable e f f e ct. on the f lame spread rate.The reverse f low provides a slow gas stream region, through which gasified fuel as well as heat from the reacteion zone would be transferred in the upstream direction.
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