Further observations of flame spread over laboratory-scale alcohol pools

Results are presented for flame spread rate and behavior for alcohol pools in normal and microgravity. The normal gravity experiments concentrated on depth effects in the uniform and pulsating regimes for pool depths of 2, 5, and 10 mm. Extra care was taken in achieving a very uniform initial fuel temperature, and a new video/PC-based flame tracking program was introduced that allowed very detailed graphs of flame position vs. time to be generated. A linear dependence of the average spread rate with pool depth was found in the pulsating regime, with a less-than-linear dependence in the uniform regime. Furthermore, the results show the pulsation wavelength is strongly affected by the pool depth, but not by the temperature. Possible mechanisms for this are discussed. In microgravity we extended earlier experiments to deep pools and examined the extinction limits of flame spread with and without an opposed, forced air flow. The previously reported correspondence between pulsating spread in normal gravity and extinction in a quiescent, microgravity environment for shallow, axisymmetric pools was upheld for deep, linear pools. However, with the imposition of a forced, opposed flow, the flame is sustained, thus opposed flow lowers the limiting oxygen index for pools in microgravity.