Experimental study on curved flame characteristics under longitudinal ventilation in a subway tunnel

Curved flame is one of the determining aspects in evaluating the risk of tunnel fire. In this study, a series of experiments are carried out to investigate the characteristics of fires in a reduced-scale tunnel model, including the center-line trajectory, length and tilt angle of curved flame. It can be known from the experiments that the total flame length in the tunnel without longitudinal ventilation is almost equal to that in open space. For the flame in the tunnel with longitudinal ventilation, a third-power relationship is shown in the center-line trajectory equation of the curved flame. Meanwhile the length of curved flame can be obtained by the method of calculus. Based on the experimental data from this study, an empirical model is developed to predict the tilt angle of the curved flame, which is based on Oka's model but with much improved accuracy for the curved flames in the tunnel.