Propanol droplet flammability and combustion in air-diluent environments under normal and reduced gravity

Reduced gravity and normal gravity combustion experiments were performed with individual fiber-supported propanol droplets with initial diameters that were typically in the 1.2 to 1.3mm range. The environment was composed of an air-inert mixture at 0.1MPa and about 298 K, where helium, carbon dioxide and xenon were separately used as inerts. In the experiments, the amount of inert gas in the environment was progressively increased until droplets could no longer be ignited. Droplet ignitability depended on the gravitational level as well as the inert gas in the environment. In general, the amount of inert gas required to suppress combustion was higher in reduced gravity than normal gravity. Use of xenon required significantly higher mole fractions for suppression of combustion relative to helium or carbon dioxide. Increasing the amount of inert gas generally decreased burning rates and increased flame standoff ratios. The data indicate that ambient gas transport properties play an important role in determining flammability and combustion behaviors of droplets.