Numerical Investigation on the Flame Propagation Rate in the High-Speed Train Carriages

Modern high-speed train compartments contain intricate internal configurations. In the event of a fire emergency, the propagation velocity of flames through the passenger cabin is determined by multiple factors, including compartment design, ignition source characteristics, and airflow conditions. This study employed computational fluid dynamics (CFD) and large eddy simulation (LES) to investigate the effects of fire source power, fire source location, and longitudinal ventilation velocity on the rate of flame progression. Unlike simplified homogeneous fuel models, this study incorporates the specific heterogeneous material layout of the CR400AF to capture realistic flame spread dynamics. The simulation results reveal that, under forward ventilation conditions, the magnitude of fire power has a minimal influence on flame propagation speed. However, stronger fire sources lead to earlier initiation of flame spread along the carriage. Central positioning of the ignition source results in bidirectional flame movement toward both ends of the carriage, with faster propagation rates than those of fires originating at the extremities. Longitudinal airflow patterns significantly influence the fire dynamics. When the airflow speed within the tunnel remains below 3 m/s, the impact of longitudinal ventilation on fire propagation speed in the train is minimal under forward ventilation conditions. Conversely, in reverse-ventilation scenarios, the rate of flame advancement shows a positive correlation with increasing ventilation speed. Nevertheless, once tunnel ventilation velocities exceed 3 m/s, combustion propagation within high-speed rail carriages becomes impossible due to intact windows, which create oxygen-deficient conditions that prevent the development of fire. This paper investigates the heat release rate and spread process of vehicle fires. It comprehensively considers the effects of fire source power, fire source location, and longitudinal ventilation rate on the rate of spread. The research results provide data support for the fire-resistant design of rail transit vehicles and for the formulation of emergency evacuation strategies for different fire scenarios, which are vital for enhancing rail vehicle fire safety and ensuring personnel evacuation safety.