Numerical simulation of firebrand pile burning behaviour under different cross-flows

Background The thermal and burning characteristics of firebrands, particularly temperature, heat flux and heat release rate, have been identified as the key parameters in spot fire ignition and wildfire spread. Aim This study investigated how firebrand pile coverage density under varying wind speeds influences modelled thermal and combustion characteristics of firebrands, and their impact on the underlying substrate. The behaviour of individual firebrands within the pile was also analysed to reveal thermal variations and combustion characteristics. Method Fire Dynamics Simulator (FDS) was used to simulate firebrand pile burning behaviour, incorporating a char oxidation reaction model to represent glowing firebrand combustion. Key results In smouldering piles, increasing the coverage density and wind speed significantly elevated peak substrate heat flux. Wind-facing firebrands showed the highest surface temperature, reaching almost 1200°C, whereas firebrands in the middle and back peaked at ~1000 and 700°C, respectively, for the 0.16 g cm−2 pile, highlighting thermal variation based on location within the pile. Conclusion Notably, despite the model’s simplicity, it successfully captures the general experimental trends observed in firebrand pile combustion. Implications Findings emphasise the influence of pile density and wind speed on firebrand burning, as well as their potential contribution to the ignition of new spot fires.