Free-Convective Diffusion Flame Sheet in Porous Media

Abstract

Abstract The nonpremixed burning of a condensed fuel with an oxidizer flow, driven by the buoyancy force, adjacent to the wall in porous media is analyzed in the reaction-sheet limit. Because of the distinct flow characteristics in porous media, similarity exists when the problem is scaled by x1/2, where x is the spatial coordinate along the wall, instead of x1/4 as for the conventional gaseous natural convective flow. Results show that the profiles of the temperature and reactants are qualitatively similar to those of the gaseous combustion situation. Quantitatively, the flame temperature is reduced as a consequence of the high effective thermal conductivity, which results in high Lewis numbers. The standoff distance of the reaction sheet is relatively insensitive to the preferential diffusion of the oxidizer but is decresed with increasing Lewis number of the fuel vapor. Interestingly, the vertical induced flow velocity may have one maximum, which is located at the reaction sheet, or two maxima, dependi...