Mathematical Modelling of Forest Fires

Abstract

A burning forest is considered to be a polyphase, multi-layer, porous three-dimensional heterogeneous medium, consisting of dry organic substance (volume fraction φ1), dispersed water (liquid medium water, φ2), solid pyrolysis product (char, φ3), stationary char combustion product (ashes φ4), gas phase φ5), dispersed ash particles (φ6), soot particles φ7), and drops of rain (φ8). Forest fuel elements (thin twigs, conifer needles, foliage) all have the same temperature, while the gaseous and dispersed phases have another. The solid elements (trunks, branches and twigs) sway in the wind. Flexural vibration of these elements, i.e. aero elasticity of the medium, acts only on the resistance value and on the coefficients of heat-and-mass transfer of forest fuel elements with gas phase, the medium being nearly rigid (almost unchangeable in the wind gusts); the thermal energy, resulting from free and forced convection and radiation in the fire front, heats, dries and then decomposes forest fuels. The result are gaseous combustible products, inert gaseous pyrolysis products, and solid combustible pyrolysis products (char). Then the gaseous and solid pyrolysis products are ignited and burnt out, and the process is repeated in the above mentioned order (see Fig.l).KeywordsForest FireForest CanopyFire SpreadCrown FireFire FrontThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.