Influence of tunnel longitudinal ventilation and opening mode of side door on fire temperature field in carriage

A 1∶15 scale train-tunnel coupled experimental model was utilized to investigate the impact of longitudinal ventilation and train side door opening mode on smoke temperature distribution inside a burning carriage. The qualitative analysis focused on the smoke temperature distribution at the ceiling of the carriage, while the quantitative analysis examined data on smoke back-layering length within the carriage. This aimed to reveal the correlation between smoke back-layering length and changes in longitudinal ventilation velocity, side door opening mode, and heat release rate. The research results are drawn as follows. Under different longitudinal ventilation velocities, there is a significant decrease in the temperature distribution of smoke upstream of the fire source at the through door. Moreover, when considering different side door opening modes, it is observed that the rate of temperature attenuation upstream from the fire source is higher when the side door of the burning carriage is opened on both sides compared to when the side door is open on one side. As the number of opened side doors on each side of the carriage increases, the difference in temperature attenuation rate between single-side and double-side opening modes for the burning carriage also increases. Additionally, when the side door of the burning carriage and the non-burning carriage are opened on one side, the variation of smoke back-layering length is greatly affected by the obstruction of the through door. Once the heat release rate reaches 5.7 kW and the longitudinal ventilation velocity exceeds 0.8 m/s, there is no further change in smoke back-layering length with increasing ventilation velocity. When both sides of the side doors on the burning carriage are open and only one side on the non-burning carriage is open, variations in smoke back-layering length follow a pattern of accelerating decay zone, stagnation zone, and slow decay zone. A dimensionless segmented function relationship for smoke back-layering length has been proposed, considering dimensionless longitudinal ventilation velocity, dimensionless side door opening factors, and dimensionless heat release rate within the ‘train-tunnel’ coupling interval. The present results can provide experience and theoretical references for improving the effectiveness of smoke control in trains, strengthening smoke control in tunnel intervals, and enhancing operational safety. © 2024, Central South University Press. All rights reserved.