Testing of different skeletal and global mechanisms for modeling combustion of degradation gases involved in wildland fire

Abstract

To simulate forest fires, there is a need of simple models for gas oxidation. The aim of this work is to provide such a model. Using numerical methods, the transient equations for the conservation of mass, momentum, energy and chemical species were solved as well as the radiative transfer equation for a laminar flame. Skeletal and global mechanisms of combustion including the main degradation gases released by forest fuels (CO 2 , CO, CH 4 and H 2 O) were tested. Their evaluation was carried out following two criteria: their computational time and their accuracy. The skeletal mechanisms provide results close to the experiments. However, they require too long computational times whatever the number of reactions. Then, two global mechanisms considering different gases were investigated as they necessitate less computational time. The comparison between the simulated and predicted temperatures points out that the mechanism containing only carbon monoxide as fuel underestimates significantly the temperature in the fire plume. On the contrary, the results obtained with global mechanisms including both methane and carbon monoxide are in good agreement with the experiments. These conclusions lead to the proposal of a simple and reliable combustion model for forest fire simulations, which considers only two reactions steps including methane.