SPACE-SHUTTLE BASED MICROGRAVITY SMOLDERING COMBUSTION EXPERIMENTS

Results from four microgravity smoldering combustion experiments condu cted aboard the NASA Space Shuttle are presented in this work. The exp eriments are part of the NASA funded Microgravity Smoldering Combustio n (MSC) research program, aimed to study the smolder characteristics o f porous combustible materials in a microgravity environment. The obje ctive of the study is to provide a better understanding of the control ling mechanisms of smolder for the purpose of control and prevention, both in normal- and microgravity. The microgravity smolder experiments reported here have been conducted to investigate the propagation of s molder through a polyurethane foam sample under both diffusion driven and opposed forced flow driven smoldering. The present experiments, al though limited, are unique in that they provide the only available inf ormation about smolder combustion in microgravity in sample sizes larg e enough to allow the self-propagation of the smolder reaction through out the sample length. Two quiescent tests at ambient oxygen concentra tions of 35% and 40% and two opposed forced flow tests with air as oxi dizer, were conducted aboard the NASA Space Shuttle (STS-69 and STS-77 missions). The MSC data are compared with normal-gravity data to dete rmine the effect of gravity on smolder, and are used to verify present theoretical models of smolder combustion. It is found that for the pr esent test conditions, the microgravity opposed flow smolder reaction temperatures, propagation velocities, toxic compound production and re action extent lie between those of normal-gravity upward and downward tests. Thermogravimetric analysis shows little effect of gravity on th e kinetics of the smolder process in these cases. Neither of the two q uiescent, microgravity cases resulted in self-sustained smolder propag ation, whereas the normal-gravity downward cases propagated vigorously . The difference in these results shows that gravity has a significant effect on smolder combustion, at least for the sample size tested. Co rrelation of the forced flow smolder velocity data with a heat transfe r based model, indicates that simplified heat transfer models of smold er propagation can effectively describe vigorous smolder, away from li miting conditions such as extinction and flaming. (C) 1998 by The Comb ustion Institute.