An experimental study on the fire temperature characteristic of commuter express carriages with multiple side doors in tunnel of urban rail transit

In extra-long urban rail transit tunnels, fires create a unique double narrow space between the tunnel and the train, making high-temperature smoke discharge difficult and increasing evacuation and rescue distances. This study investigates the temperature distribution of a commuter express carriage fire using a 1:15 scale tunnel model. The effects of heat release rate, number of side doors, and door opening modes were considered. Results show that the fire source's relative position to the side door and the door opening modes significantly influence temperature distribution inside the carriage and tunnel. Three distinct transverse temperature patterns beneath the carriage ceiling were identified. A maximum temperature rise prediction model was developed, incorporating structural correction factors to account for flame deflection under different door opening conditions, achieving an error within 30 %. Additionally, the longitudinal temperature decay beneath the carriage roof follows an exponential trend. A piecewise model was proposed, showing that the decay rate is influenced by the heat release rate, opening factor, and gangway door status. This study provides a quantitative framework for evaluating temperature distribution characteristics during carriage fires in tunnel-train narrow spaces and offers theoretical guidance to improve the safety of passengers and vehicles in extra-long urban rail transit tunnels.