he experimental realization of pulsating flame spread across a flammable liquid in microgravity was accomplished for the first time through systematic tests in a forced, opposed flow of oxygen-enriched air across shallow and intermediate-depth pools. In tests with the deeper pools, the sequential transition through all three subflash flame spread regimes―from pseudo-uniform to pulsating to uniform spread behavior―was achieved. Normal gravity tests were performed for many of the same conditions and showed similar behavior. In addition, agreement between a detailed numerical model and experiments in both normal gravity and in microgravity was newly obtained through changes in the mass diffusivity and the addition of a heat loss parameter in the two-dimensional model of flame spread over a subflash pool of 1-butanol. The model now-uniquely captures the differences in flame spread character in going from normal to microgravity and provides quantitative agreement in flame spread rate and surface temperature at either gravity level. An earlier hypothesis that lateral thermal expansion in the gas-phase accounted for the initial discrepancy between the two-dimensional model and the three-dimensional experiment is no longer supported; this is because experiments designed to directly eliminate lateral expansion resulted in flame extinction rather than the desired pulsation.
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