2561 Proceedings of the Combustion Institute, Volume 29, 2002/pp. 2561–2567 GRAVITATIONAL EFFECTS ON FLAME SPREAD THROUGH NON-HOMOGENEOUS GAS LAYERS FLETCHER J. MILLER, 1 JOHN W. EASTON, 1 ANTHONY J. MARCHESE 2 and HOWARD D. ROSS 1 1 National Center for Microgravity Research NASA Glenn Research Center Cleveland, OH 44135-3191, USA 2 Rowan University 201 Mullica Hill Road Glassboro, NJ 08028-1700, USA Flame propagation through non-uniformly premixed gases occurs in several common combustion situ- ations. Compared with the more usual limiting cases of diffusion or uniformly premixed flames, the prac- tical concern of non-uniform premixed gas flame spread has received scant attention, especially regarding the potential role of gravity. This research examines a system in which a fuel concentration gradient exists normal to the direction of flame propagation and parallel with the gravitational vector. This paper presents experimental and numerical results for flame spread through alcohol/air layers formed by diffusive evap- oration of liquid fuel at temperatures between the flash-point temperature and the stoichiometric tem- perature. A gallery, which had either the top and/or one end open to maintain constant pressure, sur- rounded the test section. The numerical simulations and experiments conducted include normal and microgravity cases. An interferometer was used, in normal gravity only, to determine the initial fuel layer thickness and fuel concentration distribution before and during flame spread. Both the model and exper- imental results show that the absence of gravity results in a faster spreading flame, by as much as 80% depending on conditions. This is the opposite effect to that predicted by an independent model reported earlier in this symposium series. Determination of the flame height showed that the flame was taller in microgravity, an effect also seen in the results of the numerical model reported here. Having a gallery lid results in faster flame spread, an effect more pronounced at normal gravity, demonstrating the importance of enclosure geometry. The interferometry and numerical model both indicated a redistribution of fuel vapor ahead of the flame. Numerical simulations show that, despite the rapid flame spread in these systems, the presence of gravity strongly affects the overall flow field in the gallery. Fig. 1. Schematic of flame spread through a non-ho- mogeneous mixture contained in a gallery (not drawn to scale). Darker areas indicate region of higher fuel vapor concentration near surface. Also labeled on the figure are the gallery size and boundary conditions used in the nu- merical model and experiment. Introduction Flame spread through uniformly premixed gas systems is a frequently studied problem in combus- tion science. In contrast, flame propagation through non-uniformly premixed gas systems (also called ‘‘layered systems’’) has been the subject of relatively few studies. Layered mixtures (see Fig. 1), 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 rep- resenting a hazardous area beyond that associated with the original fuel location. They also are a po- tential fire hazard aboard long-duration spacecraft, such as the International Space Station, because flammable gases may accumulate near waste storage, laboratory fluids, fuel cells, lasers, etc. Our hypothesis is that gravity can influence flam- mability and the rate of flame propagation in a lay- ered system in at least three ways: through a hydro- static pressure gradient, through buoyantly induced