Ceiling temperature rise and critical ventilation velocity under the influence of burner dimensions in tunnel fires

Ceiling temperature rise and critical ventilation velocity are important parameters for tunnel fire safety design. This study analyzed the influence of burner area, burner aspect ratio, and tunnel slope on the maximum ceiling temperature rise and critical ventilation velocity through a series of experiments. It was found that the maximum ceiling temperature rise decreased linearly with the increase of the burner area, while it first sharply increased then slowly decreased with the increasing aspect ratio (L/W) of the burner. When the burner was square (L/W = 1), the maximum temperature rise reached the peak value. On the other hand, the critical ventilation velocity linearly decreased with the increasing area of burners, while it increased with the increasing burner aspect ratio as a logarithmic function. The burner width mainly affected the critical ventilation velocity through changing the air entrainment condition from the aspect of thermodynamic influence. The burner length mainly affected the critical ventilation velocity through changing the initial smoke generating range from the aspect of the geometric influence. Finally, based on experimental data and dimensionless analysis, the optimized prediction models of maximum ceiling temperature rise and critical ventilation velocity were respectively established considering the coupling influence of the area and the aspect ratio of the burner. This study could provide more accurate guidance for the fire protection design of tunnels in engineering.