Flame Spread and Its Limitation along a Thermally Thin Combustible Solid in a High-temperature / Low-oxygen Concentration Opposed-Gas Flow

Abstract

This paper discusses the flame spread and its limitation along a thermally thin combustible solid (a sheet of filter paper) in a high-temperature / low-oxygen concentration opposed-gas flow, based on experimental investigations. The leading flame length along a solid surface for both horizontal flame spread and vertically downward flame spread decreases with decreasing oxygen concentration. Especially the flame becomes to be round shape in high-temperature/low-oxygen concentration gas flow, which is similar to the flame shape in microgravity condition. The flame leading edge retreats and extinction occurs at some oxygen concentration. We defined this oxygen concentration LOC (Low Oxygen Concentration) , as the flame spread limitation. The flame spread rate near the LOC is close to that in microgravity with normal air condition. To clarify the effect of buoyant force on flame spread, the Rayleigh number for spreading flame was examined. The Rayleigh number decreases with decreasing oxygen concentration, and it is less than the critical Rayleigh number near the LOC. The relation between the non-dimensional flame spread rate, V, and the Damköhler number, Da was also examined. The V both of normal gravity and microgravity decreases with decreasing the Da, and reaches to the flame spread limitation at some Da. This paper suggests that it may be possible to simulate the flame spread under microgravity environment by using high-temperature / low-oxygen gas flow under normal gravity.