Effect of ambient pressure on smoke movement and temperature distribution in dual-source fire in tunnels

In high-altitude tunnel environments, fire behavior is significantly altered due to reduced ambient pressure and diminished oxygen availability. In this study, full-scale numerical simulations were conducted to investigate the thermal behavior of multiple fire sources in a tunnel under natural ventilation, focusing on the effects of ambient pressure and fire source spacing on smoke temperature distribution. The simulation results reveal that at close spacing, strong thermal interaction between fire sources leads to the formation of a single, unified high-temperature zone. In contrast, at larger spacings, two distinct heat-affected regions emerge with minimal overlap. As ambient pressure decreases, both the overall peak temperature and the intensity of the thermal field decline, while the location of the maximum temperature shifts further downstream. These findings demonstrate that fire source spacing and altitude-induced pressure variation jointly influence the magnitude, geometry, and extent of the thermal hazard zone in tunnel fires. Based on the simulation outcomes, two empirical models are proposed to predict the maximum smoke temperature and ceiling temperature distribution under varying fire configurations and environmental conditions. The models exhibit good agreement with both simulation and experimental data. This study provides a valuable reference for the design and evaluation of fire safety systems in tunnels, particularly those located in high-altitude regions.