Experimental study on temperature attenuation of smoke flow driven by dual fire sources in a tunnel

A series of reduced-scale tunnel fire tests were carried out to investigate ceiling smoke temperature attenuation in a naturally ventilated tunnel under double fire sources of various sizes and distances. Experimental results showed that the interactions between the two flames affect excess gas temperature attenuation. Under a given fire size, the ceiling smoke temperature gradually decays more slowly when the spacing between the two fire sources is longer and then goes through a steady stage. Moreover, for different smoke spread regions (i.e., the radial ceiling jet region, the shooting flow region and the one-dimensional tranquil flow region), the ceiling smoke temperature attenuation trends are different. Models of non-dimensional excess ceiling smoke temperature attenuation in the radial ceiling jet and shooting flow regions were proposed using the plume radius at the ceiling level as the characteristic length scale. In the one-dimensional tranquil flow region, an exponential model was developed by theoretical analysis to predict non-dimensional ceiling smoke temperature. The lumped attenuation coefficient k was observed to decrease first and then approach a relatively stable value with an increasing fire spacing. This study is of great significance to the design and protection of tunnel structures under multiple fire sources.