Most of the vegetal species involved in forest fires produce and emit volatile organic compounds (VOCs). Physical forest fire propagation models do not take into account the combustion of these compounds and the objective of this study is to provide experimental and numerical data in order to better foresee and control fires. The emissions of five vegetal species have been analyzed for different temperatures using a flash pyrolysis apparatus: Thymus vulgaris, Rosmarinus officinalis, Lavandula stoechas, Cistus albidus and Pinus pinea. Laminar burning speeds, Markstein lengths and flame thicknesses of three major VOCs (-pinene, limonene and p-cymene) are determined using the spherical expanding flame technique. Numerical simulations are also performed with the PREMIX code of the CHEMKIN package for similar molecules. Several studies have shown that forest fires can behave in a surprising way, with a sudden increase of the rate of spread and of the released energy. This phenomenon is called accelerating forest fire. A thermochemical explanation, based on the ignition of a premixed VOCs/air mixture accumulated in a canyon, has been proposed. The different experimental data presented in this work can also be useful to study the validity of this approach. Other experimental and theoretical studies on the diffusion direction of VOCs and on their flammability limits are performed to investigate in detail this approach.
Study on the emission and combustion characteristics of volatile organic compounds potentially involved in accelerating forest fires