Flame spread over liquid fuels involves a complex coupling between gas-phase combustion and liquid-phase hydrodynamics, often obscured by buoyancy-driven convection. This study uses a fully coupled numerical simulation with detailed chemical kinetics and radiative heat-transfer models to elucidate the controlling mechanisms of flame spread over 1-propanol in microgravity. The results show that radiation is essential for predicting extinction of low-temperature quiescent flames in microgravity. Radiative heat loss weakens the reaction zone, reduces conductive feedback to the liquid surface, suppresses evaporation, and eventually causes flame lift-off and extinction. For higher initial fuel temperatures, however, uniform flame spread can be sustained. In this regime, the spread rate is not controlled by the peak heat release rate, but by thermocapillary-assisted formation and transport of a flammable mixture ahead of the flame front. At lower fuel temperatures, an imposed opposed flow enables flame spread that would otherwise extinguish. The opposed flow enhances oxygen supply and product removal, while also opposing the weak leading flame. This produces a pulsating mode characterized by alternating slow crawling and rapid jumping stages. The crawling stage is controlled by heat and vapor accumulation, whereas the jump stage is governed by rapid consumption of the accumulated premixed layer. These results clarify the regime-dependent mechanisms of liquid-fuel flame spread in microgravity and provide useful guidance for spacecraft fire safety.
Shan et al. (Wed,) studied this question.