The influence of opening shape of obstacles on explosion characteristics of premixed methane-air with concentration gradients

By installing obstacle plates with different opening shapes in an experimental pipeline, the combined effect of vertical concentration gradients and obstacle shapes on methane-air explosion characteristics was experimentally investigated. The presence of obstacles and concentration gradients induced turbulent flame instabilities, which promoted the positive feedback between the combustible gas flow and combustion process. The combustion process caused the upstream lean methane, lighter than the unburned gas, to propagate through the obstacle and hence bubble-like local disturbances were generated in the central area downstream of the obstacle. Under the action of transverse waves, a g & uml;apa & uml;ppeared in the lower part of the flame front, and the flame front appeared concave. The effect of the concentration gradient and obstacles on the methane explosion gradually weakened, and hence the wrinkled flame surface gradually stabilized. Results show that the square-shaped opening affected the flame propagation and explosion evolution most significantly. As the concentration gradient increased, the combined effect undermined the positive feedback mechanism, and the maximum explosion overpressure and maximum rate of pressure rise were reached for the square-shaped opening at a low concentration gradient (0.5 %), while for the circular-shaped and quadrant-shaped openings the maximum values were reached at a higher concentration gradient (1.0 %). The effect of obstacles was more significant than the effect of concentration gradients with respect to the flame propagation velocity and rate of pressure rise.& nbsp; (c) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.