Flame spread over solid fuels in opposite natural convection

The downward spread of a flame along the surface of a thermally thick solid fuel inclined at an angle to the vertical is investigated, The flow and the heat transfer in the flame front region that controls the spread rate are described numerically using a single-step Arrhenius model for the gas-phase reaction. The effect of the finite rate kinetics is discussed in terms of a Damköhler number defined as the square of the ratio of the speed of the planar stoichiometric flame of the fuel vapor to the characteristic speed induced by buoyancy in the flame front region. The computed spread rate is lower when the burning surface faces downward than when it faces upward due to the influence of the pressure gradient parallel to the surface