Experimental study on the influence of obstacle aspect ratio on ethanol liquid vapor deflagration in a narrow channel

Abstract

A series of experimental tests were conducted in a narrow obstructed channel to investigate the influence of obstacle distribution mode (unilateral and bilaterally symmetrical distribution) and obstacle aspect ratio (the width-to-height ratio in flame propagation direction) on vapor deflagration. Rectangular obstacles with different aspect ratios 0.9–2.1 were used. The flame propagation speed, flame front structure, overpressure and local temperature near obstacles were recorded and analyzed. The results indicated that different obstacle distribution modes would not fundamentally alter the propagation mechanism of deflagration flame and overpressure. The shear action of obstacle edges and the confined space structural form between the obstacle and the channel boundaries both exerted a significant effect on deflagration flame propagation. And two acceleration stages existed in the deflagration, and the flame speed peaks appeared above obstacle and near the channel portal, respectively. Specifically, when aspect ratio was 1.8, the maximum flame speed peaked to 102.5 m/s. Moreover, obstacle aspect ratio has shown a significant influence on flame front, and the flame front structure experienced complex changes as it passed through obstacle. What's more, an interesting reverse flame phenomenon was observed, which resulted in a larger area of violent flame combustion. The maximum length of reverse flame decreased firstly and then increased with the increase of obstacle aspect ratio, which probably ascribed to the inertial force of fluid. Accordingly, a simple empirical equation was proposed to predict the reverse flame length during flame propagation in the narrow obstructed channel. This equation performs well in prediction of reverse flame length in current application range. Meanwhile, the local temperature peak is closely related to the local deflagration reaction intensity affected by obstacle aspect ratio. In addition, it is also found that the deflagration overpressure and flame propagation involved the obvious coupling mechanism. Deflagration overpressure and flame speed reached peaks almost simultaneously. This coupling mechanism could significantly expend the impact range of deflagration.