Study on the maximum ceiling temperature and downstream temperature distribution in inclined tunnel fire

Abstract

Constrained by various factors, including terrain, tunnels frequently exhibit slopes. While existing research on fires in inclined tunnels predominantly focuses on the characteristics of smoke flow in large slope tunnels, there is a notable lack of attention given to the study of micro-slope tunnels and important factors such as induced air inflow. Therefore, in this paper, the numerical simulation method is used to study the maximum ceiling temperature rise and downstream temperature distribution in inclined tunnel fire under the conditions of micro-slope and large slope. The results show that the main factors affecting the ceiling temperature rise are not only the tunnel slope, but also the HRR and the downstream length. These effects can be expressed by the stack effect intensity. When the inclined tunnel fire occurs, the maximum ceiling temperature and the downstream temperature distribution characteristics show two states. When the stack effect in the tunnel is diminished, there is no significant alteration in the maximum ceiling temperature and temperature distribution within the tunnel when compared to a horizontal tunnel. In a tunnel with a strong stack effect, the maximum temperature decreases as the stack effect increases, and the temperature distribution differs greatly from a horizontal tunnel. The theoretical analysis of this paper identifies the demarcation point of the two state changes as the dimensionless induced air inflow velocity of 0.1. On this basis, a piecewise prediction model for the maximum ceiling temperature of the inclined tunnel fire is established. Because the temperature distribution between the fire source and the maximum temperature position is not regular. Thus, using the maximum ceiling temperature as a reference point, an accurate segmented prediction model of temperature distribution is proposed for downstream Region 1. This study offers guidance for designing tunnel structures with high-temperature resistance and assessing safety conditions within the tunnel.