The Dependence of Flame Propagation on Surface Heat Transfer I. Downward Burning

Abstract

The problem of finding a unique flame propagation rate for a given distribution of surface heat flux is solved analytically for three solid fuel geometries (i) finite slabs, (ii) finite rods (iii), semi-finite fuel bed. The solutions cover a range of fuel thicknesses from the thermally thin limit to the thermally thick limit. The effect of longitudinal heat conduction within the fuel is considered and found to become important as the fuel thickness increases. Experimental results on the downward burning of PMMA sheets are presented for the flame spreading velocity and preheat distance. The preheat distance is found to become independent of fuel thickness for / >0·25 cm. A combination of the analytical and experimental results leads to a determination of the surface heat transfer parameters.