Fire Safety Science Digital Archive

The propagation of a wildfire is simulated numerically from the resolution of the conservation equations (mass, momentum, energy...) of the system formed by the solid phase representing the vegetation and the surrounding gas mixture. The vegetation is represented by a collection of particles composed by a mixture of dry matter (wood), water, coal, plus a mineral residue (ashes). The physical parameters characterizing the various stages of the thermal decomposition of the vegetation (drying, pyrolysis, heterogeneous combustion) are evaluated from experimental data obtained by thermogravimetric analysis. The model describing the decomposition of particles is coupled with the calculation of the reactive turbulent flow resulting from the combustion of the pyrolysis products with the ambient air. The particles/gas coupling is ensured by production/destruction terms in the conservation equations of the chemical species. The drag force induced by the particles as well as the convective and radiative exchanges are also taken into account. The presence of soot particles in the flame and the composition of the gas mixture are taken into account to evaluate the absorption coefficient and the radiative intensity field. Calculations are carried out for various conditions of wind and a fire propagating in a layer of vegetation composed with a mixture of shrubs (Quercus coccifera) and grasses (Brachypodium ramosum) (characteristic of the Mediterranean zones on calcareous ground).