Experimental investigation of flame behavior and radiation heat transfer in wind-driven single-tree crown fires

Background Crown fires are one of the most destructive types of wildland fires, significantly threatening forest ecosystems and the wildland–urban interface (WUI), especially under certain wind conditions. Methods A series of controlled burning experiments using real cypress trees with three different crown heights (0.4, 0.6 and 0.8 m) under five wind velocity conditions (0–2.0 m/s) were conducted to investigate the fire behaviors and mechanism of heat transfer from crown fire to the WUI. Key results and conclusions Flame length and radiation heat flux increased with crown height and wind velocity. Under wind conditions, flames leaned significantly, and the tilt angle decreased with increasing crown height. Mass loss rate and flame temperature were higher at greater wind velocities and crown heights, with temperature stratification observed within the flame plume. A modified inclined cylindrical radiation model was developed, incorporating segmented flame temperature and variable emissivity to improve the accuracy of radiation flux predictions. Implications These findings enhance the understanding of crown fire dynamics under varying wind conditions and crown structures and provide improved radiation heat-transfer predictions, offering valuable support for WUI fire-risk assessment and the development of more effective mitigation strategies.