Simulations of Fuel Consumption in Wildland Fire Spread at Vegetation and Flame Scales

This study considers simulations of fundamental processes responsible for flame spread and fuel consumption in wildland fires. The computational model uses a classical multiphase formulation in which biomass vegetation processes are treated using a discrete particle burning rate (PBR) model and gas-phase processes are treated using a Computational Fluid Dynamics (CFD) model. The CFD solver comes from an established library called OpenFOAM; the PBR solver is an in-house addition. The PBR model includes a one-dimensional porous medium formulation, and a description of in-particle oxygen transport and exothermic char oxidation; the model thereby allows simulations of smoldering combustion. We consider here a benchmark configuration corresponding to fire spread across a surrogate biomass vegetation bed treated as an array of thin and thick pine wood sticks distributed in flat terrain and exposed to wind; the bed features different patches corresponding to different loads of the thick sticks. The present analysis focuses on degradation processes inside the thick sticks and shows that complete fuel consumption occurs in three consecutive phases: a first external heating phase due to propagating flaming combustion; a second external heating phase due to residual stationary flaming combustion; and a third internal heating phase due to residual stationary smoldering combustion. • A framework to simulate fuel consumption in wildland fires is presented. • The biomass particle model includes a treatment of smoldering combustion. • Simulations show complete or partial fuel consumption in thick biomass elements. • An energy balance analysis quantifies heat gains/losses in thick biomass elements. • The analysis identifies three phases in the process of complete fuel consumption.