Effects of External Radiation On Solid-Fuel Diffusion Flames

Results of calculations for free-convection diffusion flames are presented for the range of external radiative fluxes encountered in room fires. The specific system studied is PMMA burning in O ₂ /N ₂ atmospheres. It is found that the burning rate shows a linear increase with ambient oxygen concentration at fixed external radiative flux, and shows an almost linear increase with external flux at fixed oxygen concentration. The minimum oxygen concentration required for combustion is found to decrease slowly with increasing external radiation. A criterion for estimating extinction limits based upon a parameter equivalent to a local Damkohler number is proposed.