Mechanism of accelerating premixed hydrogen/methane flame with flexible obstacles

Abstract

Low-velocity laminar flames gradually accelerates under the joint action of various mechanisms, and develops from deflagration to detonation, and the mechanism in this process is the focus of explosion dynamics research. This article presents experimental results of the propagation of premixed hydrogen/methane flames in square-section channels with flexible and rigid obstacles at a blockage ratio (BR) of 0.3. Theory and experiment show that the acceleration effect of flexible obstacles on flame is weaker than that of rigid obstacles. The results show that there are many differences in the physical mechanism of flame acceleration. It is mainly reflected in the difference between the two obstacles on turbulence guidance, and the difference in the peak pressure of flame propagation. The flexible obstacles create smaller turbulence and absorbs the transverse waves within the pipe that continuously accelerate the flame. At the same time, compared with rigid obstacles, flexible obstacles can effectively reduce the peak flame tip speed Vmax, and the peak flame tip speed reduction rate is the highest by 22.86%. In addition, unburned pockets formed by obstacles play a key role in the acceleration of the flames. The expansion of gas in the flexible obstacle pocket expands the obstacle spacing, accelerates the fuel combustion in the pocket, and avoids the concentrated release of fuel energy. The intensity of the turbulence and the velocity of the flame are lower after passing through the obstacle area, showing a lower explosion risk than rigid obstacles.