Study on Flow Field Characteristics and Temperature Evolution of the Moving Train Fire in Naturally Ventilated Tunnels

This work investigates the evolution of gas temperature and flow field characteristics inside the tunnel due to an on-fire moving train at varying speeds and fuel pan sizes. A 1:15 model scale experimental series using methanol liquid has been carried out with a train speed range from 0.0 m/s to 2.0 m/s. The results show that the piston wind and return wind generated due to the moving train had a significant influence on the maximum gas temperature rise of the tunnel. Different from the stationary fire source scenario, the ceiling gas temperature evolution shows a sudden peak followed by a decrease in temperature due to the increased return wind and flame tilt angle. The vertical gas temperature decreases with an increased vertical distance from the tunnel ceiling due to the formation of a smoke layer near the ceiling. At increasing train speed, the increased piston wind disrupts the smoke stratification phenomenon, causing the relative decay rate of vertical temperature to differ. This study helps to understand the gas temperature evolution and flow field characteristics due to a moving train fire in naturally ventilated tunnels.