Model calculation of steady upward flame spread over a thin solid in reduced gravity

Abstract

Steady upward flame spread in two-dimensional laminar flow over a thin solid is solved numerically in reduced gravity based on a combustion model recently formulated for concurrent flows. This flame spread model is more sophisticated than most previous ones because it avoids the boundary layer approximation and uses full elliptic Navier-Stokes equations. In addition, two-dimensional flame radiation treatment is accomplished by using the S-N discrete ordinates method. The emitting gas media are carbon dioxide and water vapor, the combustion products. Computed flow and flame structure are presented. The details of the flame stabilization zone near the solid burnout is resolved. Downstream flame is found to deviate from the self-similar boundary layerscaling relation. The effect of gravity level is studied. Flame length and spread rate increase approximately linearly with gravity level. A low-gravity flame quenching limit is predicted. Gaseous flame radiation is found to be important for flame structure, flame dimension, and extinction limit. Flame radiative feedback is an essential part of the solid surface energy balance. However, predicted flame spread rates have similar magnitudes as those computed by the model neglecting flame radiation.