Theoretical analysis and predictions of burning in microgravity using a burning emulator

Abstract

Burning experiments are analyzed for 29 steady burning flames using a gas burner (BRE) to emulate condensed-phase burning of 25 mm diameter flat surface. Mixtures of ethylene and nitrogen allow for 23.6 and 47.2 kJ/g heats of combustion (LHV). Ambient conditions range from 21 to 40% oxygen and pressures of 0.56 to 1 bar. The results are compared to predictions from analytic models developed to determine the flame radiation fraction, flame convective and radiative heat fluxes, flame shape, and heats of gasification for steady burning. Steady burning is theoretically decided by ensuring the flame temperature is above a critical value of 1100 K. Good agreement is achieved between experiment and predicted steady results. Further computations are made to determine the effect of ambient pressure and oxygen on burning for heats of combustion of 23.6 and 47.2 kJ/g, diameters up to 100 mm, and vaporization temperatures of 80 and 350 ºC. It is found that for the range of analyzed conditions, heats of gasification of about 1 to 5 kJ/g, steady burning would result over a range of about 1 to 6 g/m2s. Low pressure appears to yield more stable flames. The results have implications on how the fire safety of materials in microgravity should be determined.