Experimental study on the smoke movement and flame extension length characteristics of strong fire plumes in a sealed tunnel

Sealing strategy is one of the methods available to extinguish tunnel fires. In this study, based on a 1/10 reducedscale model tunnel, the fire source heat release rate and source-ceiling height were changed, and the sealing walls with various sealing ratios and opening positions were set to study the smoke movement and flame extension length characteristics of strong fire plumes. The results show that for the total sealing ratio of 75%, the competition between smoke overflow and air supplement when the opening position is in the middle area is stronger than that when the opening position is in the upper area or lower area. For the total sealing ratio of 50%, the competition between smoke overflow and air supplement is not obvious due to the large opening area. The flame extension length beneath tunnel ceiling increases with fire source heat release rate and decreases as sourceceiling height increases. When the total sealing ratio is 50%, the flame extension length beneath tunnel ceiling is close to that without sealing, and the flame extension length beneath tunnel ceiling becomes longer when the total sealing ratio is 75%. As the total sealing ratio increases, the stability of the flame extension beneath tunnel ceiling decreases. Based on dimensional analysis, empirical models are developed to predict the flame extension length beneath ceiling in the sealed tunnel.