Experimental investigation of the propagation of deflagration flames in a horizontal underground channel containing obstacles

The deflagration of premixed methane-air gas (concentration of 9.5%) was experimentally investigated in a closed channel (0.2 m × 0.2 m × 6.5 m) containing different obstacles. Rectangular, trapezoidal, and spherical obstacles were employed. Various tests on the deflagration flames were carried out (using schlieren imaging and pressure and flame sensors) and the diverse characteristics of the deflagration flames were analyzed. In this work, we concentrate on the change in shape of the flames as they pass the obstacles, the instantaneous overpressure formed in the local areas in front and behind the obstacles, and the change in velocity of the deflagration flame. The results suggest that extremely complex changes occur when the deflagration flames pass the differently-shaped obstacles in the closed channel. The shape of the obstacle and the structural form of the confined space between the boundaries of the obstacle and channel walls both exert a significant effect on the mechanical characteristics of the deflagration flames as they develop. Obstacles in the channel enhance the propagation of the deflagration flame to unburned areas away from the local area where the flame forefront had been. The flatness of the flame front is therefore broken. A certain amount of flame stagnation appears to occur which results in a larger crosswise span of the flame front. The obstacle's angles and effective barrier area presented to the incoming flow of the deflagration flame have an effect on the propagation of the flame and instantaneous overpressure of the deflagration flame in the local areas just in front and behind the obstacle. Moreover, the correlation between the obstacle angle and mainstream direction of the deflagration flame as it passes the obstacle also has an effect. Of the three obstacles investigated, the trapezoidal obstacle exhibits the weakest ability to strengthen the inertial force of the deflagration flame. Compared to the others, the spherical obstacle most significantly enhances the inertial force of the deflagration flame as it passes through the obstacle's neighborhood.