Prediction of horizontal flame spread using a theoretical and experimental approach

Abstract

A new methodology has been developed for obtaining properties that characterize creeping flame spread over solid materials and for predicting creeping flame spread using these properties. These properties have been reduced to two quantities that are deduced from present measurements or from other tests: the convective energy per unit length. E', from the flame to material near the pyrolysis front and the gaseous thermal length, δg, generated by the opposed flow. The convective energy determines the flame, energy input modified by gaseous chemical kinetics. For fast kinetics, it is independent of the opposed flow velocity. The gaseous thermal length depends on magnitude and profile of the opposed flow velocity. For creeping flame spread at normal gravity conditions, the derived convective energy flux, E', was determined to be 31 W/m for particle board and 97 W/m for PMMA. The thermal length, δg, is 1.36 mm for PMMA and 1.22 for particle board. An additional important contribution of this work is a careful consideration of the effect of external heat fluxes on flame spread, including reradiation losses, acting on the pyrolyzing side of flame front. Neglect of these effects has led to misleading or incomplete interpretation of previous creeping flame spread experiments or test methods.