Study on Smoke Propagation Characteristics of a Carriage Fire in Longitudinally Ventilated Tunnel

Model-scale experimental tests and numerical simulations were conducted to investigate the characteristics of the smoke overflow at the lateral carriage doors and the smoke temperature below the tunnel ceiling of a carriage fire in a longitudinally ventilated tunnel. Results indicates that the smoke overflows from the carriage into the tunnel through the lateral doors downstream of the fire source under the impact of longitudinal ventilation. Depending on the fire location, the amount of the overflow smoke exhibited either an inverted V-shaped variation or a monotonical increase with the door position. Multiple peaks in the smoke temperature below the tunnel ceiling is attributed to the uneven distribution of the overflow smoke. A dimensional analysis revealed a quantifiable relationship between the heat flow of the overflow smoke and the peak temperatures below the tunnel ceiling. Consequently, an empirical model was developed to predict the maximum smoke temperature below the tunnel ceiling under different heat release rates and longitudinal ventilation velocities. These findings are excepted to enhance the understanding of carriage fires and provide a theoretical guidance for future ventilation and safety designs in subway systems.