Study on air entrainment coefficient for different heat release rates and transverse displacements in a tunnel with unpowered ventilation cap

An automobile accident may cause combustion and release large quantities of toxic smoke in tunnels. This article investigates how the heat release rate and fire displacements affect the air entrainment coefficient during smoke one-dimensional motion stage along the tunnel by using a shaft with unpowered ventilation cap for natural ventilation. The results show that the air entrainment coefficient increases with the heat release rate when plug-holing occurs in the shaft. The correlation between the air entrainment coefficient and heat release rate is analyzed by dimensionless analysis and verified using experimental data. Different transverse fire source locations do not significantly affect the temperature distribution during the one-dimensional horizontal spread of smoke. The air entrainment coefficient exhibits no significant difference for different transverse fire source locations, but is lower for a fire closing to the sidewall than for other locations. The ratio of the air entrainment coefficient for a fire source near the sidewall to that for a fire source at the center of the tunnel is 0.76–0.96. This research contributes to a deeper understanding of smoke dynamics in tunnels, which can ultimately aid in the development of strategies to help trapped people escape.