Combustion Processes Laboratories

Experiments were conducted to measure the flame propagation rate of a plug-flow flame through a combustible matrix of randomly oriented cubes of polyurethane foam in microgravity and normal gravity as a function of the forced air flow. The experiments in microgravity were conducted at the Japan Microgravity Center (JAMIC) drop tower, which provides 10s of microgravity. The normal gravity experiments were simulations of the microgravity experiments, and by comparison, were used to determine the effect of gravity on the flame propagation process. The experiment was conducted in a cylindrical geometry. Ignition was accomplished by means of a hot-surface igniter brought into direct contact with the foam at one end of the sample holder. The other end of the sample was sealed to a fan drawing air through the sample, which was adjustable using a variable DC power supply. In this configuration the flame propagation is flow-assisted. The flame propagation rate was determined by means of the temperature histories provided by thermocouples placed along the centerline of the sample. It is found that, both in normal and microgravity, as the air flow rate is increased the flame propagation velocity increases. Comparison between the normal and microgravity experiments shows that the microgravity combustion is greatly influenced by the ignition period. In microgravity the time to initiation of flame propagation is significantly longer than the corresponding time in normal gravity. This is due to the contribution of the buoyant flow that assists the forced flow during the initiation period in normal gravity. A simplified analytical model is presented for correlation of the velocity data.