Influence of Different Types of Obstacles on the Propagation of Premixed Methane-Air Flames in a Half-Open Tube

Quan Wang,Shanghao Liu,Yibin Ding,Zhimin Li,Chi-Min Shu

doi:10.3390/en10111908

Abstract

To understand the propagation characteristics of methane-air deflagration flames and in an obstacle-filled tube, a high-speed color video camera, photoelectric sensors, and pressure transducers were used to test the deflagration flame propagating parameters. The tests were run in a 1500 mm long plexiglass tube with a 100 × 100 mm square cross-section. The obstacles included four types of repeated baffles and five forms of solid structure obstacles. The results showed that: (1) the flame front was constantly distorted, stretched, and deformed by different types of obstacles and, consequently, the flame propagating parameters increased; (2) plates and triple prisms increased the speed of the flame and overpressure to the highest extent, whereas cuboids and quadrangulars exerted an intermediate effect. However, the effect of cylindrical obstacles was comparatively limited. It was suggested that the obstacle’s surface edge mutation or curvature changes were the main factors stimulating the flame acceleration; (3) the peak pressure of deflagration was relatively low near the ignition end, increased gradually until it reached the maximum at the middle of the tube, and decreased rapidly near the open end; and (4) the fixed obstacles in front of the flame exhibited a blocking effect on flame propagation during the initial stages; the flame speed and overpressure increased when the flame came into contact with the obstacles. This study is of significance because it explains the methane-air propagation mechanism induced by different types of obstacles. The findings have value for preventing or controlling gas explosion disasters.

Highlights

Underground mining accounts for more than 90% of coal mining in China
The outer surfaces of the rectangular and, the flame propagation velocity was and quadrangular obstacles contained moderate mutation edges or angularities. These results demonstrate that mutation edges or irregularities on the surfaces of two typical edges is >90◦ ) and, the flame propagation velocity was intermediate
The vortices formed around the obstacles are closely related to the flame propagation, which can be clearly seen from the images of high speed video camera

Summary

Introduction

Underground mining accounts for more than 90% of coal mining in China. At a greater mining area and depth, the coal seam containing methane is generally larger. Of mines are gassy mines facing high risk of explosions and are sites of frequent accidents [1,2]. According to the statistics provided by the Chinese government, 24 major accidents occurred in coal mines, killing 3780 people since the founding of the People’s Republic of China in 1949. Of these 24 accidents, 21 were related to fire damp explosions, including gas and coal dust explosions, and the number of deaths in such cases is 3424. Apart from the loss of life, society incurred substantial property losses [3,4,5,6]

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Conclusion