The behavior of flames spreading over thin solids in microgravity,

Experiments were conducted aboard Space Shuttle Orbiters during five different flights to study flame spread over a thin cellulosic fuel in a quiescent, microgravity environment. Data, which include spread rate and temperature measurements in the gas and solid phases, and also recordings of the flame from ignition to extinction using two 16-mm cameras, were gathered for two different oxygen levels and three different pressures. Detailed observation of the flame evolution is described along with theoretical support from steady and unsteady models that include radiation from CO2 and H2O. Experimental results indicate that the spread rate increases with ambient oxygen level and pressure. The brightness of the flame and the visible soot radiation increases monotonically from the slowest to the fastest spreading flame. Steady-state theory compares well with experiments in the vicinity of the flame leading edge. Trends in temperature, spread rate, and structure of the flame are qualitatively reproduced in this region, but the feature of a flame trailing edge curving back to the fuel surface and flame evolution over time is only captured through an unsteady model.