A comparison of theoretical and experimental results in flame spread over thin condensed fuels in a quiescent, microgravity environment

Flame spread over thin cellulosic fuel in a quiescent, microgravity environment of a 50/50 volumetric mixture of oxygen (oxygen mass fraction 0.53) and nitrogen at 152 kPa (1.5 atm) has been analyzed theoretically, and the results are compared to a recently conducted experiment in the microgravity environment on board a Space Shuttle flight. Experimental results suggest that the fuel preheat zone upstream of the gas-phase flame is followed by a constant temperature pyrolysis zone, which is followed by a large zone of surface reaction. Because the theory does not treat surface reaction, results of the theory apply only to regions close to the flame leading edge. Although CO2 and H2O radiation is included in the theory, the absorption and emission of radiation by the fuel surface is modeled only approximately. The theory compares well with experiment near the flame leading edge. The flame spread rate, peak surface temperature, and gas-phase temperature at two different locations are predicted within 5%. The success of the theory leads to the conclusion that the flame structure near the flame leading edge determines the flame spread rate and that gas-phase radiation plays a significant role in quiescent, microgravity flame spread.