Predicting volatile gas generation and transport during wildfires using a physics-based conjugate modelling approach

Volatile gas generation from vegetative fuel is a critical process driving ignition, spread, and intensity in wildfire environment. Accurate prediction of this phenomenon is essential for reliable wildfire modelling and mitigation strategies. The current study presents a conjugate heat and mass transfer model to predict the generation and transport of combustible gases from the pine tree under uncontrolled wildfire conditions. Unlike conventional fire model, which merge pyrolysis with combustion, the presented framework isolates pyrolysis as a standalone process, enabling a clearer understanding of gas generation mechanisms. The framework explicitly incorporates both radiative and convective heat transfer, which govern the rate of thermal degradation, and volatile release. The model evaluates the impact of air velocity, surrounding air temperature, as well as trees spatial arrangement on gas generation rate and its distribution to the atmosphere. Simulation results indicate that spacing between burned and unburned tree has significant effect on the volatile gas generation. The gas generation rate and tree temperature were reduced by 10.86% and 163.2 K by increasing the gap by 2 m between the burned and unburned tree, respectively, highlighting the role of spacing in mitigating fire intensity. Moreover, the higher air velocity decreases the gas generation within the tree, however, it increases the gas transfer rate towards the surrounding from the tree. These findings showed the importance of accurately modelling conjugate heat and mass transfer to improve the predictive accuracy of wildfire behaviour. • Developed a physics-based conjugate heat and mass transfer model of pyrolysis. • Convective diffusion dominates molecular diffusion under turbulent flow. • Gas generation rate decreases by increasing tree spacing. • Radiation heat transfer is dominant between the trees at the bottom half. • Convective cooling dominates heat transfer at top of tree canopy.