Experimental study of laminar flames obtained by the homogenization of three forest fuels

Abstract

This work aims to improve the understanding of the parameters involved in the burning of vegetative fuels. As the role of the surface-tovolume ratio is already known, we focused on the influence of other parameters. Three Mediterranean species (Pinus pinaster, Erica arborea and Cistus monspeliensis) were crushed in order to decrease the surface-to-volume ratio effects. The burning of these fuel samples produces unsteady, axisymmetric, non-premixed, laminar flames. The thermal properties and the mass loss of the crushed fuels, the distribution of temperature inside the sample and in the flame, the gases released by the fuels and the flame geometry were investigated. Thanks to these experimental data, the influence of the different fuel properties was underlined. We observed that the mass burning rate of the samples mainly controls the flame dynamics. However, the combustion kinetics in the flame depends on the degradation gases released by the fuels: the reaction zone is shifted and the flame height is changed. It appears that the composition of the degradation gases has to be taken into account to improve forest fire modeling.

Flammability studies for wildland and wildland–urban interface fires applied to pine needles and solid polymers

“…An estimation of the radiative and convective transfers at the interface for T ig provided a very close value (less than 20% difference by assuming the needles to be cylinders). In addition to the properties provided in section 2.2, the density was taken as ρ s = 789 kg/m 3 , the thermal capacity as c ps = 3,100 J/kg K and the absorptivity as a s = 1 [52,53].…”

Heat and Mass Transfer in Fires: Scaling Laws, Ignition of Solid Fuels and Application to Forest Fires

“…The ignition temperature found in literature for pine needles is between 280-350°C [31]. An estimation of "kρC" thanks to literature [31,32] provides a value of 0.09 (kW/m 2 K) 2 s. These values are very different from the values obtained in Table 3, particularly for "kρC", even if one considers a correction factor to estimate the actual values from the effective ones, as done by Mowrer [14]. It should be noticed that the value of the parameters do not represent the actual physical values but the value of the control parameters of the system [33].…”

Experimental study in the infrared of the radiative properties of pine needles

“…For similar species, Vaz et al [7] already presented a study on pine needles, comparing experimental data and predictions for the extinction coefficient. Pine needles have also been studied recently in terms of flame characterization by Tihay et al [8]. Based on the preliminary results presented in [2], a special care has been brought in the present work to the repeatability of the measurements as mentioned above, its analysis and the influence of various parameters, namely ageing of the sample in relation with a weight loss, influence of the sample preparation (thickness of one single needle or set of a layer of several needles).…”