Upslope fire spread and heat transfer mechanism over a pine needle fuel bed with different slopes and winds

Abstract

The surface fire spread involved slope and wind effects are significantly important in wildland fires, while very limited attention has been paid on the heat transfer mechanism, especially for different fire line conditions. This work experimentally evaluates the effects of slope angle (0˚ to 30˚) and wind velocity (0 to 2 m/s) on spread of surface fire over a pine needle fuel bed. Flame length, flame angle, rate of fire spread, fuel consumption rate and heat flux are acquired and quantitatively analyzed. Two different fireline shapes of sheet and inverted ‘v’ are observed and assumed for different wind velocities and slope angles, respectively. The flame length, rate of spread, mass loss rate and heat flux increase with the increasing wind velocity and slope angle, while flame angle and fuel consumption efficiency vary in the opposite way. The extreme fire can be observed with the external manifestations of a steep increase in flame length, rate of spread and heat flux under conditions of larger wind velocity and slope angle, which is similar to an eruptive fire. In addition, the heat transfer of convection and radiation heat flux is quantitatively analyzed with wind velocity and slope angle to explore heat flux control mechanism. Moreover, the modified models of radiation heat flux considering fire line shape are presented, which demonstrates good effectiveness in predicting radiation heat flux by comparing the calculated values and experimental data.