Mechanism Of Flame Spread Across Solid Fuels In Microgravity And Weakly-Buoyancy Environment

It is of fundamental importance to study on mechanisms of flame spread in microgravity and weakly-buoyancy environment, for it has a great significance in understanding combustion process, developing combustion theory and improving fire safety of spacecraft. In this paper, experiments were conducted on the flame spread over solid fuels in weakly-buoyancy environment and numerical simulation of the flame spread across thermal thin fuels in microgravity were also presented in this thesis.In the first chapter, the state of the arts of the mechanisms of the flame spread over solid fuel surfaces the significance of microgravity combustion were reviewed. Based on the paper review, the topics of the thesis were proposed.In the second chapter, the experiments were conducted in weakly-buoyancy environment. In the first section, we have done the experiments of flame spread across solid thermal thin fuels in the low ambient pressures. The results show that flame spread has the characteristics of flame spread in microgravtiy. The mechanisms of flame spread are analyzed with dimensionless flame spread rate and Damkohler number. In the second section experiments were conducted to study the effects of fuel width, inclination angle and ambient flow on the flame spread over solid thin fuels.In the third chapter, numerical simulations were presented to analyze the mechanism of flame spread over solid thermal thin fuel in the quiescent microgravity environment. Effects of solid surface radiation heat losses on the flame spread characteristics were studied at different ambient oxygen concentrations and ambient pressures. The results show that surface radiation heat losses can considerably affect the flame structure and the spread rate. By radiating heat to the environment, the surface acts as a heat sink for flame. The flame cools, becomes smaller, and moves closer to the surface to supply additional heat to compensate for the radiative loss. When consideringsurface radiation heat loss, the rate of spread increases with the increase of pressure, which agree with the experimental results in microgravity. With the increase of surface radiative emission coefficient, the peak values of the flame temperature decrease. A radiation/conduction parameter is identified that adequately describes the importance of the surface radiation.