A Comparison of the Roles Played by Natural and Forced Convection in Opposed-Flow Flame Spreading

A computational model of flame spread down a thermally thin solid in a gravitational environment, in which the acceleration of gravity can be varied from zero to some finite value of the order of the Earth's acceleration, is presented. Information obtained from the model bridges the gap between experimental data that is most generally obtained in normal gravity and in microgravity environments, an understanding of flame spreading in a microgravity environment being essential for understanding the fire safety aspects of space travel Results of the modeling effort show that gravity levels that might be thought of as low enough such that the effects of gravity are negligible, i.e., 10 −2 or 10 −3 times that of the Earth, have a significant effect on the flame spread process. A striking similarity between flame spreading in a naturally induced flow and a forced flow, each opposing the spreading flame, is found. The reason for the similarity is the similarity in the velocity profiles near the surface and flame leading edge. It is this region that determines the spread rate and flame characteristics, regardless of the character of the free stream flow.