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 △p2 increased with the increase of the distance between the ignition position and the vent, and the peak value of △p4 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 △p2 vanished in front and central ignitions, and △p4 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.%在12 m3密闭空间内开展了甲烷-空气预混气体(甲烷体积分数为9. 5％)的爆炸试验研究,改变点火位置,分析有泄爆口时点火位置对甲烷-空气爆炸超压和火焰形态的影响.结果表明:点火位置对△p1的升压速度基本没有影响,Δp2的峰值随着点火位置远离泄爆口而增大,Δp4的峰值与点火位置的关系为:中心点火最大,尾部点火次之,前端点火最小.在所有位置,Δp1随着泄爆阈值的增大而增大,且增量相同;Δp2在前端点火和中心点火时随泄爆阈值的增加而消失,仅在尾部点火时出现;Δp4只有在中心点火时随泄爆阈值的增加而增加.外部火焰发展过程可以分为火球阶段和火焰喷射阶段,尾部点火和中心点火的火球大小及火焰喷射长度远大于前端点火.
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