On the emission of radiation by flames and corresponding absorption by vegetation in forest fires

Abstract

Experimentations have been carried out in the infrared using Fourier transform infrared spectrometers. The obtained data characterize the emission of radiation by flames using vegetation as fuel. In a study conducted in parallel, the absorption of radiation by the vegetation has been investigated for several species. Usual assumptions of an emission equivalent to the one of a high temperature blackbody on the one hand, or of absorption close to the one of a black surface on the other hand, are discussed. Indeed, the emission by flames is strongly governed by hot gases produced by the combustion and the corresponding spectral emission is far from the one of a blackbody. In parallel, the spectral absorption of the vegetation varies with the wavelength, indicating a non-gray behavior. Fine descriptions should therefore involve a spectral modeling of radiation propagation, which is known to require huge computational costs. For simpler models aimed at producing approximate results but with a reduced computational effort, average values of absorptivities are suggested for two species ( Quercus coccifera and Pinus halepensis) on the basis of the present results.