In recent years, forest fires have frequently occurred worldwide, leading to substantial casualties and property losses. Many fires are caused by hot metal particles igniting forest fuels. Therefore, understanding the ignition mechanisms of high-temperature metal particles is critical. Studying how these particles ignite combustible materials is a key focus in current forest fire research, with particular attention to factors such as temperature, size, and material of the metal particles. The nature of the fuel remarkably impacts ignition, with some fuel particles being large and others small. In this study, the particle size of combustibles is characterized by their mesh number. This research examines the influence of the mesh number on the ignition boundary and combustion behavior of hot metal particles. These findings provide a theoretical basis for assessing whether hot metal particles can ignite combustibles of different particle sizes and offer valuable insights for wildfire safety, prevention, and emergency response.

This study investigates the effect of mesh number on the ignition boundary and combustion behavior of hot metal particles. Pine powder with varying mesh numbers was selected as the research object, and steel balls were used as hot metal particles to ignite the pine powder. A serie of ignition experiments was conducted using experimental devices independently developed by the China People's Police University. Experimental phenomena were recorded and analyzed using ordinary and high-speed cameras. Key parameters, such as ignition probability, ignition boundary temperature, ignition delay time, flame height, and flame duration, were studied as functions of mesh numbers. In addition, the mechanism by which mesh number influences the ignition boundary and combustion behavior of hot metal particles was explored.

The minimum ignition temperature of pine wood powder by metal hot particles decreases with increasing mesh number, decreasing from 965℃ at 50 mesh to 910℃ at 300 mesh. The ignition delay time of 1 000℃ high-temperature metal hot particles also decreases as the mesh number decreases, reducing from 49.8 ms at 50 mesh to 41.8 ms at 300 mesh. However, the flame height and duration increase with higher mesh numbers, increasing from 14.78 mm and 12.8 s at 50 mesh to 17.02 mm and 14 s at 300 mesh.

The ignition boundary temperature decreases with increasing mesh. When hot metal particles reach a high temperature of 1 000 ℃, combustibles with various mesh numbers can be ignited. The ignition delay time also decreases with increasing mesh number. However, as the temperature increases, the difference in ignition delay time between different mesh numbers decreases, indicating that the influence of temperature on ignition delay time gradually diminishes. The flame height and flame duration increase as the number of mesh increases, suggesting that an increase in mesh number elevates fire risk by producing taller flames and prolonged combustion.