Abstract:

The premixed stoichiometric methane-air deflagration is conducted in a transparent square cross-section duct. Effects of the ignition positions on the overpressure characteristics of the premixed methane-air deflagration flame propagating in the duct closed at one end and open at the opposite end are obtained. The experimental results show that the pressure waveform changes from no oscillation to weak oscillation with the equiamplitude then to sharp oscillation with the exponential increase amplitude as the ignition positions relative to the closed end of the duct are increased. The generation mechanism of the overpressure is closely dependent on the transient flame structures and the overpressure extrema of the oscillating waveforms always correspond to the flame position extrema. The oscillation periods of the overpressure waveforms during the phase of the exponential increase amplitude are linearly decreased with the time since ignition and well correlated with the length of the unburnt gas column. The oscillation is triggered by the venting of the flame front located at the open end of the duct, and then amplified by the flame-sound interaction in the unburnt gas column between the pressure wave and the flame front located at the closed end of the duct.

Key words: methane, explosion, safety, overpressure oscillation, ignition position

摘要：

开展了化学恰当比φ = 1甲烷-空气预混气在透明方形管道内的爆燃实验研究,改变点火源位置,分析在管道一端闭口一端开口条件下,点火源位置对甲烷-空气预混气爆燃超压特征的影响。实验结果表明:当点火源与闭口端之间距离较小时,时间-超压曲线不发生振荡,随着点火源相对于闭口端距离的增加,超压分别呈微弱等幅振荡、振幅指数增长的振荡,且最大超压峰值随之增加;超压波形与火焰瞬态结构存在密切关联,振荡波形超压峰值的极值点总是位于火焰位置的极值点;当超压发生振荡时,振幅指数增长阶段的振荡周期随时间线性减小,振荡周期与未燃气气柱长度呈现较好相关性;超压振荡的原因在于,泄爆口侧的火焰前沿触发了超压振荡,闭口侧火焰前沿与声波(压力波)在未燃气气柱中相互作用放大了超压振荡。

关键词: 甲烷, 爆炸, 安全, 超压振荡, 点火位置