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Ignition and Transition to Flame Spread Over a Thermally Thin Cellulosic Sheet in a Microgravity Environment.


pdf icon Ignition and Transition to Flame Spread Over a Thermally Thin Cellulosic Sheet in a Microgravity Environment. (806 K)
Nakabe, K.; McGrattan, K. B.; Kashiwagi, T.; Baum, H. R.; Yamashita, H.; Kushida, G.

Combustion and Flame, Vol. 93, No. 4, 361-374, 1994.

Sponsor:

National Aeronautics and Space Administration, Lewis Research Center, Cleveland, OH

Keywords:

microgravity; ignition; flame spread; oxygen; autoignition; cellulose; oxygen concentration

Abstract:

An axisymmetric, time-dependent model is developed describing auto-ignition and subsequent transition to flame spread over a thermally-thin cellulosic sheet heated by external radiation in a quiescent microgravity environment. Due to the unique combination of a microgravity environment and low Reynolds number associated with the slow, thermally induced flow, the resulting velocity is taken as a potential flow. A one-step global gas phase oxidation reaction and three global degradation reactions for the condensed phase are used in the model. A maximum external radiant flux of 5 W/cm2 (Gaussian distribution) with 21%, 30%, and 50% oxygen concentrations is used in the calculations. The results indicate that autoignition is observed for 30% oxygen concentrations but the transition to the flame spread does not occur. For 50% oxygen the transition is achieved. A detailed discussion of the transition from ignition to flame spread is given as an aid to understanding this process. Also, a comparison is made between the axisymmetric configuration and a two-dimensional (line source) configuration.