A physics-based ignition model with detailed chemical kinetics for live fuel burning studies

This work presents a computationally inexpensive framework for modeling combined pyrolysis and gas-phase combustion of general vegetative fuels, which improves on existing solvers by incorporating detailed chemical kinetics and predicts the ignition behavior. The main motivation for this work is capturing the burning behavior of live wildland fuels, which can differ from those of dead fuels. Existing models are unable to accurately predict the ignition time and temperature variations for the live fuel cases. The kinetics model used here accounts for the non-primary constituents of fuels, or “extractives”, which are expected to play a role in this distinct behavior. Validation studies show that the developed model is a promising tool for understanding the effects of fuel chemistry and spatial variation on ignition and fuel burning behavior. Case studies using the tool suggest that variations in ignition time can be explained by combined effects of variables such as moisture content, initial composition, and density.Novelty and Significance Statement: We address a gap in the literature by developing a model that can simulate the pyrolysis and gaseous ignition of live wildland fuels. Existing methods that focus on pyrolysis and smoldering cannot capture the complex chemical kinetics of either pyrolysis or gas-phase combustion, and do not represent interactions between the solid and gas phases that lead to ignition. Similarly, existing detailed fluid dynamics models for fire behavior do not represent detailed gas-phase chemical kinetics, and do not typically couple with a pyrolysis model. We demonstrate the model’s capability to predict pyrolysis products, temperatures, and ignition times for different plant species, accounting for subtle differences in composition. We examine relationships between fuel composition, moisture content, pyrolysis products, and ignition time.