Experimental investigation of fire behaviours and heat transfer in single cypress tree crown fires

Background Crown fires are among the most perilous and challenging types of forest fires to combat, posing a significant hazard to forest ecosystems and the wildland–urban interface. Methods Crown fire experiments were carried out using cypress trees with five different crown heights from 0.4 to 1.2 m to investigate the fire behaviours and heat transfer mechanisms. Key results and conclusions The characteristic values of flame height, mass loss rate and heat flux increased with crown height, whereas flame width increased with crown width. Empirical correlations of mass loss rates were established. Flame temperature varied with flame height and relationships between these were developed based on four dimensionless temperature zones. Flame emissivity was related to crown height and increased exponentially with the heat release rate. This study proposes a modified model to predict the radiation heat flux from crown fires, taking the variations of flame temperature and flame emissivity into account. Implications The findings of this work enhance understanding of fire behaviours and controlling mechanisms of crown fire under different crown heights, and also improve the accuracy of prediction of wildland fire development and spread in the wildland–urban interface.