Piloted ignition of wildland fuels

Piloted ignition of wildland fuel litters was experimentally studied using the FM Global Fire Propagation Apparatus (FPA) with an applied external radiant heat flux up to 30 kW/m2. Fuel types (i.e. Maritime Pine needles and Kermes Oak leaves) and loadings are representative of Mediterranean ecosystems. For the fuel beds considered the inverse of the ignition time was found to be linearly dependent on the imposed heat flux, as observed for thermally-thin solids. A systematic study was carried out to determine the critical (minimum) heat flux for piloted ignition. On the other hand, a dimensionless analysis of the energy equation for the homogeneous equivalent medium was carried out based on the assumptions that the solid and gas phases are in thermal equilibrium and that piloted ignition occurs when the average equivalent medium temperature over the radiation penetration depth reaches a critical value. Using experimental data, a correlation was found between dimensionless ignition time and imposed heat flux.