Simulation of complete or incomplete biomass degradation under parameterized wildland fire spread conditions

Abstract

Our objective in the present study is to provide fundamental insights into the main factors that control the thermal degradation processes occurring inside the biomass vegetation during wildland fire spread. These processes determine the formation of flammable volatiles through pyrolysis reactions and the intensity of the internal heat release through char oxidation reactions; both aspects are central to flaming and smoldering combustion. We adopt here a simplified framework in which the biomass vegetation is viewed as a population of discrete elongated particles that are made of pine wood, are cylindrical-shaped and feature different diameters. The exposure conditions experienced by these particles in an assumed fire are characterized by a given intensity of the external thermal load, a given duration during which this load is applied, and a given external flow velocity that controls the rates of convective heat transfer and oxygen mass transfer. The response of the biomass particles is studied using a one-dimensional computational model, called the particle burning rate (PBR) model. The PBR model adopts a porous medium formulation, and provides a description of drying, (thermal and oxidative) pyrolysis, and char oxidation. We focus in the present study on the conditions required for complete "fuel consumption", i.e., for complete particle degradation from virgin solid to ash. It is found that in thin biomass particles, complete biomass degradation requires sufficiently high intensities of the external thermal load and sufficiently low external flow velocities; high flow velocities correspond to excessive cooling effects. Similarly, in thick biomass particles, complete biomass degradation requires sufficiently high intensities of the external thermal load, sufficiently long application times of the thermal load, and sufficiently high external flow velocities; low flow velocities correspond to insufficient oxygenation of the (exothermic) oxidative pyrolysis and char oxidation reactions.

Citation

Ahmed, Mohamed Mohsen; Al-Bulqini, Hazem M.; Trouve, Arnaud; Forthofer, Jason; Finney, Mark. 2024. Simulation of complete or incomplete biomass degradation under parameterized wildland fire spread conditions. Journal of Physics: Conference Series. 2885: 012077.