Drying Process, Thermal Behaviour, and Ignition Patterns of Horizontally aligned Moisturized Cellulosic Leaves: A Computational Study

Abstract: Wildfire occurrence and propagation is influenced by the combustion of various vegetative components, including leaves, twigs, and branches, across different vegetation structural levels. The ignition of individual leaves can significantly contribute to the initiation of a wildfire, potentially leading to large-scale environmental destruction. This research employs advanced computational fluid dynamics (CFD) simulations to meticulously analyze the heating, drying, pyrolysis, ignition, and combustion processes of two horizontally aligned, moisturized, cellulosic leaves exposed to a convective heat source, with two different Fuel Moisture Contents (FMC) of 4%, and 34%. Through this detailed examination, we aim to provide insights into the ignition patterns and underlying physical and chemical mechanisms that play a pivotal role in the initiation of solid fuel combustion. Numerical analyses were conducted using FireFOAM, an advanced Large Eddy Simulation (LES) transient solver from the OpenFOAM platform, to numerically solve the governing equations. Dry out and ignition time of each leaf with different positions and fuel moisture contents were obtained., Our results revealed the upper leaf, which is shielded by the lower leaf, undergoes a reduced rate of convective heat transfer. This results in a slower drying rate for the upper leaf compared to its unshielded counterparts. With a 34% FMC, moisture loss occurs more rapidly in the lower leaf than in the upper leaf; yet, as FMC decreases to 4%, this disparity becomes less marked, although it does not entirely disappear, indicating a nuanced relationship between moisture content and drying rates in varied conditions. Keywords: Fuel Moisture Content (FMC), Large Eddy Simulation, FireFOAM, Fire modelling, Pyrolysis modelling, Ignition