Ignition of pine needle fuel bed by the coupled effects of a hot metal particle and thermal radiation

Abstract

Spot fire and flame radiation are two important causes of Wildland-Urban interface fire. Previous studies have mainly focused on one single cause. However, the ignition of fuels by firebrands (or hot particles) coupled with flame radiation is unknown due to the lack of experimental and theoretical study. In this paper, the ignition behavior of pine needle fuel bed under the coupled action of a hot particle and thermal radiation was studied for the first time, and the critical ignition conditions were analyzed. The experimental results show that the ignition risk of a hot particle coupled with thermal radiation is much higher than that of a hot particle or thermal radiation alone. Under the coupled condition, the ignition probability increases with the increase of particle temperature and radiation heat flux, and the critical radiation heat flux required for ignition decreases with the increase of particle diameter and temperature. The ignition delay time decreases as the radiation heat flux increases for different particle diameters and temperatures. The theoretical analysis revealed that there is a good linear relationship between the critical radiation heat flux required for ignition and the parameters of the hot particle d(Tp-Tsm). This study may help provide the first step to understand the ignition mechanism of fuels by the coupled effect of firebrands and flame radiation.