This work aims to characterize pine needles as a fuel for a better understanding of the behaviour of forest fuels in wildland fires. It does this in two ways: classify vegetation as a fuel for forest fires and understand the role of transport mechanisms in fuel beds. For this purpose, the physical and chemical characteristics of each fuel are taken into account. Three species of pine needles were studied: Pinus halepensis, Pinus pinaster and Pinus laricio. These were chosen because they are representative of the Mediterranean ecosystem and present different characteristics such as surface-to-volume ratio and chemical composition.
The experiments were performed using the FM-Global Fire Propagation Apparatus with a Fourier transform infrared gas analyser to determine the pyrolysis gases released by the three species. The heat release rate (HRR) was estimated using oxygen consumption calorimetry. Specially constructed porous sample holders were used, with different percentages of basket openings, to allow different air flow rates to pass through the fuel samples. Forced flows of different magnitudes were also imposed through the sample in some cases.
In this study, the focus has been made upon the influence of the two main experimental parameters, i.e. flow conditions through the fuel bed (varying with basket opening and forced flow conditions) and fuel species particularities, on the time dependent variable HRR. Discrete variables such as time to ignition, duration of flames and mean HRR during the flame were also analysed.
Flow conditions appear to be an important parameter when analysing the combustion dynamics of a porous fuel. Fuel species also have an influence on the heat release rate. The role of these parameters and their interaction prove to be more complex than anticipated. Surface-to-volume ratio and fuel packing ratios are not the only parameters governing burning dynamics, even for closely related species such as pine needles. Chemical properties have also proved to have an influence when the oxygen supply in the combustion zone is high.