Thermo-mechanical modeling of firebrand breakage on a fractal tree

Firebrand lofting models rely on prescribed size distributions for brands that are available for lofting. Typically, the assumption made is that the balance between aerodynamic forces and weight defines the characteristic size of lofted brands. This work develops a model for predicting the size distribution of brands lofted from a fractal tree using simple mechanical breakage models that are coupled to a simple thermal decomposition model. The breakage model is parameterized by fuel density and strength data that are experimentally generated. Dimensionless parameters are identified to characterize the degradation and breakage processes. The breakage model is then coupled to a plume model to form a description of the breakage, transport, and mass loss of branching vegetative fuel packets in wildland fire scenarios. A Monte Carlo simulation is then performed for branching fuels in a wildland fire case study, and the presence of an optimal branch diameter for mass transport by brand lofting is identified.