Background. The thermal and burning characteristics of firebrands, particularly temperature, heat flux, and heat release rate, are identified as the key parameters in spot fire ignition and wildfire spread. Aim. This study investigates how firebrand pile coverage density, under varying wind speeds, influences modelled thermal and combustion characteristics of firebrands, along with their impact on the underlying substrate. The behaviour of individual firebrands within the pile was also analysed to reveal thermal variations and combustion characteristics of individual firebrands within the pile. Method. Fire Dynamics Simulator (FDS) was used to simulate firebrand pile burning behaviour, incorporating a char oxidation reaction model to represent the combustion of glowing firebrands. Key results. In smouldering piles, increasing the coverage density from 0.06 g cm-2 to 0.16 g cm-2 and wind speed from 0.9 m s-1 to 2.7 m s-1 significantly elevated peak substrate heat flux from 18 kW m-2 to 51 kW m-2. The wind-facing firebrands showed the highest surface temperature, reaching to almost 1,200 °C, while middle and back firebrands peaked at around 1,000 °C and 700 °C, respectively, for the 0.16 g cm-2 pile, highlighting thermal variation among individual firebrands 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 emphasize the influence of pile density and wind speed on firebrand burning, as well as their potential contribution to the ignition of new spot fires.
Eissa et al. (Tue,) studied this question.