Experimental study of the burning rate of small-scale forest fuel layers

• An experimental study concerning the burning rate of small-scale fuel litters was carried out by using the FPA.
• The mass loss rate is found to exhibit the same behavior no matter the fuel load and the radiant heat flux considered.
• At long time the degradation process can be described by a first order Arrhenius law.
• The long time degradation and the flaming residence time are found to be weakly dependent on radiant heat flux.

An experimental study of the burning rates of small-scale forest fuel layers composed of maritime pine needles is carried out by using the FM-Global Fire Propagation Apparatus (FPA). Three fuel loads, corresponding to fuel volume fractions of about 0.02, 0.04 and 0.08, are exposed to external heat fluxes in the range 15–30 kW/m2. The analysis of the experimental data focuses on the flaming stage. The time evolution of the mass loss rate exhibits the same trend no matter the external radiant heat flux and the fuel load considered. Just after ignition (short time) a linear increase is observed whereas after the peak (long time) the degradation process can be described by a first order Arrhenius law. The flaming residence times and the characteristic chemical time scale for the long time process are found to be weakly influenced by the external radiant heat flux while they increase exponentially with the fuel load. In addition, an analysis of the remaining mass of solid fuel at flame extinction shows that the char oxidation process becomes increasingly important as the fuel volume fraction becomes larger. Finally flame heights, determined from CH* measurements, are found to be consistent with those predicted by the classical correlations of the literature.