Emulation of condensed fuel flames with gases in microgravity

Abstract A gaseous fuel burner has been designed to emulate the burning behavior of liquids and solids. The burner is hypothesized to represent a liquid or solid fuel through four key properties: heat of combustion, heat of gasification, vaporization temperature, and laminar smoke point. Previous work supports this concept, and it has been demonstrated for four real fuels. The technique is applied to flames during 5 s of microgravity. Tests were conducted with a burner of 25 mm diameter, two gaseous fuels, and a range of flow rates, oxygen concentrations, and pressures. The microgravity tests reveal a condition appearing to approach a steady state but sometimes with apparent local extinction. The flame typically retains a hemispherical shape, with some indication of slowing growth, and nearly asymptotic steady flame heat flux. A one-dimensional steady-state theory reasonably correlates the data for flame heat flux and flame length. The burning rate per unit area is found to be inversely dependent on diameter and a function of the ratio of the ambient oxygen mass fraction to the heat of gasification. The flame length to diameter ratio depends on two dimensionless parameters: Spalding B number and the ratio of the heat of combustion per unit mass of ambient oxygen to the heat of combustion of the fuel mixture stream.