Experimental study on flaming ignition of pine needles by simulated lightning discharge

Abstract

Lightning is one of the main natural causes for wildfires, and lightning-caused wildfires are responsible for substantial losses of ecology, property, and lives worldwide. There is very limited research on the ignition process and mechanism by lightning, and significant knowledge gaps still exist. In this work, the flaming ignition process of fine natural fuels (pine needles) by simulated lightning discharge with a long-continuing current was studied experimentally. The 50% ignition probability was predicted by a logistic regression method. It was found that, under the current experimental conditions, the energy of simulated discharge needed for igniting pine needles increases with increasing fuel moisture content. The flaming duration is highly dependent on the fuel moisture content, and the moisture content dominates the risk of lightning-caused ignition when it is high enough. It was visually observed that the ignition underwent a very special process including three stages: discharge heating stage, thermal feedback stage, and self-sustaining flame stage, different from ignitions by firebrands or flame radiation. Discharge energy and fuel moisture content can affect the flaming ignition by dominating the first two stages and the last stage, respectively.