Bottom Surface Combustion of Polymethylmethacrylate Disks—II. Diffusion Flame Radiative Properties

Abstract

The purpose of this work is to calculate the radiative properties and fluxes at each location through a fully developed “laminar” diffusion flame over the bottom surface of disks of a polymeric material, Le., polymethylmethacrylate.

The temperature, species and soot concentration profiles having been experimentally determined, the radiative properties of the combustion zone have been obtained using a spectral method adapted to this particular scale test and configuration. The results show that for combustion driven by natural convection, the contribution of radiative heat transfer to the burning rate is a “negative” contribution: the solid surface emits much more heat by radiation than it receives from the gas phase. This effect of surface re-radiation allows one to interpret the previously observed linear correlation between combustion rate and characteristic dimension of the samples. In the case of experiments with additional imposed radiative fluxes, the contribution to the burning rate becomes “positive” and this contribution increases logically with the increase of the additional flux. In parallel, an enhancement of the heat blocking effect of the convective flux can be observed.