Experimental investigation on influence of different transverse fire locations on maximum smoke temperature under the tunnel ceiling

In former studies, fires were always assumed to occur at the longitudinal centerline of tunnels. In fact, fires will occur at any locations in tunnels, with different distances to the sidewall. A set of model scale experiments were carried out, to investigate the influence of different transverse fire locations on maximum smoke temperature under the tunnel ceiling. Results show that the restriction effect of the sidewalls of tunnels cause the maximum smoke temperature rise under the ceiling to increase compared with the unconfined space, even fires occurs at the longitudinal centerline. The maximum smoke temperature rises above the fire keep almost unchanged with the fire moving closer to the sidewall at the beginning and then increase significantly after the distance between the fire and the sidewall decreases to a certain value. For small pools of wall fire, the “mirror” effect is reasonable, and for large pools, will bring a relatively large error without considering the influence of the equivalent diameter of a wall fire, resulting in underestimating the mass flow rate of fire plume and then overestimating the smoke temperature. Under all fires, the maximum smoke temperature rise under the ceiling decreases exponentially as the longitudinal distance from fire increases. Correlations for related parameters are proposed.