Effect of ignition position on overpressure in vented explosion of methane-air mixtures

Vented explosion tests were carried out in a 12 m³ concrete chamber filled with premixed methane-air mixture with the methane volume fraction of 9.5%, and the influence of the ignition position on the development of overpressure and the evolution of flame was investigated. The results show that this influence on the rising rate of Δp₁ was nearly negligible but the peak value of Δp₂ increased with the increase of the distance between the ignition position and the vent, and the peak value of Δp₄ was correlated with different ignition positions, i.e. central ignition, rear ignition, front ignition, in an order of descending influence. Moreover, when the venting pressure got bigger, Δp₁ had the same increment at all the ignition positions, whereas Δp₂ vanished in front and central ignitions, and Δp₄ increased with the increase of venting pressure only in center ignition. Besides, the evolution of the external frame was observed to fall into two stages: the fireball formation and the jet frame. The size of the fireball and the maximum length of the external jet flame in rear and central ignitions were larger than those in front ignition.