Study on smoke temperature induced by two fires in a naturally ventilated tunnel

• Numerical study on smoke temperature of tunnel fire with two fire sources. • The influence of burner separation distance on smoke temperature was studied. • Model for predicting the longitudinal temperature distribution was proposed. • Model for predicting the longitudinal maximum temperature rise was developed. The temperature of smoke flow beneath the tunnel ceiling induced by two fires in a naturally ventilated tunnel is studied. The two fires are located in the lateral direction of the tunnel, and the distance between two fires is varied. Both the maximum temperature rise and the temperature distribution beneath the tunnel ceiling are investigated. For temperature distribution in the tunnel longitudinal direction, there is decrease in temperature with the increasing burner separation distance at the near fire region, while at the region far away from the fire location, the smoke temperature gets very close. Results show that the longitudinal temperature distribution exhibits an exponential decay law along the tunnel ceiling. A formula is established to predict the longitudinal temperature distribution and results show that there is good agreement between the numerical data and formula calculations. Comparison of temperature distribution in the tunnel longitudinal direction and transverse direction shows that at separation distance of L = 0 m , there is obvious decrease in temperature with the increasing distance from the zero point both in the tunnel longitudinal direction and transverse direction, while at separation distance of L = 6 m , there is obvious increase in temperature at the near fire location in the transverse direction, and at other regions, the temperature is very close in both directions. The maximum temperature rise in the tunnel longitudinal direction decreases with the increasing burner separation distance. A model by considering the fire heat release rate Q ̇ , the effective tunnel height H ef and the burner separation distance L is proposed to express the maximum temperature rise, and results show that the model can well predict the numerical data. The findings obtained in this work could provide reference for the design of tunnel fire safety with two fire sources.