doi:10.3850/978-981-08-7724-8_14-02

ABSTRACT

This paper presents a study of the ignition of pine needle samples representative of forest floor beds. The litters are a common fuel lying on forest floors. This fuel is primarily involved in wildfire ignition as most of the fires start on the ground before moving to the shrub and tree layers. Samples of pine needle litters were submitted to an external heat flux in the FM-Global Flame Propagation Apparatus. The study has been conducted in two steps. First, a simple model developed for solid fuels has been applied to a broad range of experimental conditions. The model matched the experimental results for closed boundary conditions at the bottom and with the sides of the fuel sample, preventing a flow to occur through the basket, and for natural convection conditions. Then, the model has been adapted to take into account the fuel bed porosity and the cooling due to a forced flow through the porous matrix. The results showed that the new model was able to match the experimental data for low fluxes but not for high fluxes. This is certainly due to other phenomena taking place inside and above the fuel layer, the most likely being a changing in the mixing between pyrolysis gases and air around the pilot flame.

Keywords: Wildland fire, Forest fuel, Time to ignition.

© 2011 CPD Unit, University of Leeds