Intermittent fireline behaviour over porous vegetative media in different crossflow conditions

Background: Reliable wildfire prediction and efficient controlled burns require a comprehensive understanding of physical mechanisms controlling fire spread behaviour. Earlier studies explored the intermittent nature of free-burning fires, but the influence of flame intermittency on fire spread requires further attention. Aims: This research qualitatively explores dynamic fire behaviour and its influence on fire spread. Methods: Fire spread experiments were conducted under varying wind conditions inside a wind tunnel. Various cameras were used for qualitative analysis, verified against velocity and temperature measurements carried out inside the fuel bed. Key results: Dynamic fire behaviour was observed in the form of near-bed flame pulsations. These pulsations caused fluctuating contact between the flame and unburned fuel ahead of the fire front, leading to point ignitions. Under favourable heat transfer conditions, these point ignitions strengthened and merged with the existing fire front, leading to intermittent flame spread in the form of leaps. Conclusions: The transient nature of flame spread was observed during fire spread experiments conducted under steady external conditions. Implications: This research lays the foundation for critical flow and heat transfer analyses required to characterise intermittent flame spread.