Experimental study on the characteristics of temperature distribution of two pool fires with different transverse locations in a naturally ventilated tunnel

The interaction between multiple fires is complex, in which the theory of single fire is not applicable. This study focuses on the combustion characteristics and temperature distribution of two pool fires with different transverse locations in a model tunnel under natural ventilation. In this study, 84 groups of combustion experiments of two ethanol pool fires were designed by varying the spacing between two pool fires (denoted by S), transverse distance between the geometric center of pool fires and tunnel sidewall (L), and side length of oil pan (D). The experimental results show that when L = 50 cm and L = D/2, mass loss rate decreases along with a bigger S/D, and reaches the minimum for L = 50 cm and the maximum for L = D/2. However, mass loss rate first increases and then decreases with S/D for L = 30 cm and L = 20 cm, which is controlled by the competition between air entrainment and radiant heat feedback. In order to describe the influences of fire source spacing and transverse distance, a prediction model of maximum temperature rise under the tunnel ceiling is developed, which matches the experimental results well. Under the case of no flame merging, longitudinal temperature distribution is insensitive to the transverse location rather than the spacing between the fire sources. Moreover, it is found that the vertical temperature distribution far from the fire sources matches the Gaussian distribution well. The results of this work can provide a significant reference for the risk assessment of tunnel fires with two fire sources.