Numerical simulation of a continuously released ethanol spill fire in an inclined tunnel with longitudinal ventilation

Abstract

Under the influences of the chimney effect and longitudinal ventilation, the risks of continuous spill fires in inclined tunnels are catastrophic with great complexity and uncertainty. In this paper, the spread and combustion behaviour of a continuous spill fire under the effect of longitudinal ventilation in an inclined tunnel is studied and compared with that in a horizontal tunnel through fire dynamics simulator (FDS) software. The critical time shrink point (SP) to reach the maximum combustion area (MCA), the change rates of the dimensionless combustion area A* and stable combustion area (SCA), the flame propagation speed, and the dimensionless burning rate W* values and heat transfer mechanisms of the combustion fuel layer, tunnel wall and flame smoke are analysed; the prediction equation between the dimensionless burning rate W* and the dimensionless wind speed V* of the upstream and downstream spill fire are identified. The results show that longitudinal ventilation leads to a nonlinear increase in the MCA, and the longitudinal slope leads to a great decrease in the critical time SP. In the stable combustion stage, the SCA in the downstream spill fire is greater than that in the upstream spill fire. Additionally, there are significant differences in the flame propagation phenomenon of spill fires. On the windward side, the maximum flame propagation speed of the upstream spill fire is 3.8 times that of the downstream spill fire; however, on the leeward side, the maximum flame propagation speed of the upstream spill fire is only 18% of that of the downstream spill fire. According to the prediction equation, with the increase in the dimensionless wind speed V*, the dimensionless burning rate W* decreases gradually; the dimensionless burning rate W* of the upstream spill fire is always greater than that of the downstream spill fire. The increase in thermal feedback caused by the inclined flame is the main reason for the significant difference in the spread of the spill fire in the ventilated inclined tunnel, causing the flame propagation speed of the −10% slope on the leeward side to gradually approach that of the −5% slope.