Experimental Study on Flame Behavior and Temperature Rise Under Ceiling in Single-Lane Tunnel Fire Scenarios

Single-lane tunnels, characterized by narrow and high cross-sections with limited ventilation, present significantly higher fire hazards than conventional multi-lane tunnels. To investigate flame morphology and ceiling temperature evolution in such confined spaces, a comprehensive set of reduced-scale fire tests was conducted using a 1:10 scale tunnel model based on Froude similarity. The effects of the heat release rate (HRR), transverse fire location, and fire source height were systematically analyzed. The results indicate that the transverse fire location critically influences flame behavior: a centerline fire produces a stable, vertically symmetric flame, whereas a wall-attached fire exhibits a periodic oscillation of attachment, elongation, and detachment. The maximum ceiling temperature rise increases with both HRR and fire source height. Notably, compared to a centerline fire, a wall-attached fire can increase the maximum ceiling temperature rise by up to 39% due to sidewall confinement. Based on the experimental data, a predictive correlation for the maximum ceiling temperature rise under centerline fire conditions was established. Furthermore, a global prediction model incorporating a transverse position coefficient was proposed, which shows good agreement with the experimental results. Comparative analysis reveals that the temperature rise coefficient for the single-lane tunnel is approximately 13% higher than that of multi-lane tunnels. These findings provide a theoretical basis for fire risk assessment and safety design in single-lane tunnel infrastructure.