Gravitational Influences on Flame Propagation Through Non-Uniform Premixed Gas Systems

Flame spread through uniformly premixed gas systems, while not completely understood, is nevertheless a well-studied problem in combustion science. In contrast, flame propagation through non-uniform premixed gas systems (also called "'layered systems") has been the subject of relatively few previous studies. In a recent theoretical paper Talley lists sprays, flame spread over liquids, and the leading edge of lifted turbulent diffusion flames as applications where flame behavior in layers is important, and goes on to note that, "'Compared with the two better known limiting cases [pure diffusion and pure premixed flames] these intermediate mixtures have so far received relatively little attention." Layered mixtures, however, are ubiquitous in terrestrial fire hazards such as chemical spills, underground mining operations, and automobile and aircraft crashes. The flames in such systems have been shown to carry over fences, and to propagate past the ends of the fuel spill, thus representing a hazardous area beyond that associated with the original fuel location. They also represent a likely fire hazard aboard long-duration spacecraft such as the International Space Station -- perhaps second in probability only to electrical wire/insulation breakdowns - because flammable gases may accumulate near waste storage, laboratory fluids, fuel cells, lasers, etc.