Experimental investigation on the ceiling flame impingement and temperature distribution in tunnel with varying widths and fire source locations

When a tunnel fire occurs, a large amount of heat is generated, which not only has an adverse impact on structural stability, but also seriously threatens the life safety of personnel inside the tunnel, affecting evacuation and rescue operations. Current researches predominantly focus on fixed tunnel section dimensions, while in practical applications, tunnel sections frequently exhibit varying aspect ratios. In this paper, four series of fire tests were carried out using a tunnel model with adjustable sectional dimension to investigate the effect of different tunnel widths on the flame development and temperature distribution of centerline fire and sidewall fire. The results indicate that under the same heat release rate (HRR), sidewall fire extends higher and longer than centerline fire, with 400 K and 600 K identified as the critical temperature at the fire plume impingement point between intermittent and continuous flame impinging on the ceiling. Changing in tunnel width has a relatively small impact on the flame region with high-temperature area, but for the attenuation area beyond the flame extension, the temperature rise under the ceiling increases as the tunnel widths decrease. Furthermore, by introducing the characteristic parameter of cross-sectional aspect ratio, predictive correlations for the longitudinal flame length and ceiling temperature distribution are proposed and verified by the previous data with more extensive tunnel dimensions. We hope that this study could provide valuable references for understanding tunnel fire development and enhancing the fire safety in tunnel.