On the role of bulk properties and fuel species on the burning dynamics of pine forest litters

This work aims to characterize pine needles as a fuel for a better understanding of the burning dynamics of forest floor fuels in wildland fires. Three Mediterranean species of pine have been studied: Pinus halepensis, Pinus pinaster and Pinus laricio. These species have been chosen because they present close but slightly different physical and chemical properties. The study focuses on the influence of the bulk and particle properties on the burning dynamics of pine needles litters. The permeability of the porous fuel beds as well as the physical and chemical characteristics of each fuel have been determined experimentally. The combustion experiments were performed using the FM Global Fire Propagation Apparatus. The heat release rate estimation was done by using oxygen consumption calorimetry with a correction of the energy constant since the composition of the fuels was known. Two kinds of sample holders were used, one with holes to allow different air flow rates to pass through the fuel sample and one blocked to stop the flow at the bottom and the sides of the fuel sample. The different air flow rates were natural convection and different rates of forced flows. A mean value of the energy released during the flaming stage per unit mass loss can be determined for all species under the different flow conditions. This energy is related to the fire-line intensity, which is an important quantity for foresters, and firefighters that allows them to evaluate the fire impact and the means which are necessary to fight a fire. Permeability appears to be an important parameter when analyzing the combustion dynamics of highly porous forest fuel beds. The energy released during flaming depends greatly on permeability but for the same permeability, the fuel species have an influence on the burning dynamics.