顶部点火下甲烷-空气预混泄爆特性研究

Vented Explosion Characteristics of Premixed Methane-air Gas by Top Ignition

利用自主设计和搭建的1 m 3矩形泄爆系统,开展了顶部点火条件下7%~13%浓度范围的甲烷-空气预混气体泄爆实验,研究甲烷浓度对泄爆过程中火焰演化和内部超压特性的影响规律,并结合压力时程曲线和火焰演化图像等进行机制分析,研究结果表明:浓度对甲烷-空气预混气体的泄爆特性有显著影响,在特定甲烷浓度下,容器内部超压出现双峰现象,在各浓度下均出现压力峰值P 1,而压力峰值P 2仅在浓度为9%出现。各浓度均出现的第一压力峰值P 1随着浓度的增加呈现先增大后减小的趋势,而该峰值出现时间的变化趋势却与之相反,两者均在甲烷浓度10%下取得极值。这一现象主要由初始火焰传播、外部爆炸、亥姆霍兹振荡和泰勒不稳定性等因素综合影响形成。仅在甲烷浓度9%出现由火焰与声波耦合作用诱发产生的声学峰值P 2,该峰值远大于压力峰值P 1;其主要由火焰和声压的相互促进与扰动触发热声耦合作用影响形成。火焰向下传播速度随浓度呈先增加后减小的趋势,在甲烷浓度10%时达到最大值,且稍富燃状态下燃烧速度总体较快。

Experiments of vented explosion were conducted in a 1 m 3 vessel under the conditions of top ignition for premixed methane-air gas with a concentration from 7%to 13%to investigate the influence law of methane concentration on flame evolution and internal overpressure during the vented explosion process.The explosion venting mechanism was analyzed by analyzing the pressure-time curve and the flame evolution image.The results prove that concentration has a significant impact on the explosion venting characteristics of the methane-air premixed gas.The overpressure inside the container presents a double-peak phenomenon with a specific methane concentration.The first pressure peak P 1 can appear at each concentration,while the second pressure peak P 2 only occurs when the concentration is 9%.P 1 increases first and then decreases with the increase of concentration,while the trend of the timing of the peak is the opposite.However,both reach the extreme value at the methane concentration of 10%.This is mainly formed by the combined effects of initial flame propagation,external explosion,Helmholtz oscillation and Taylor instability,etc.The phenomenon that P 2 is much higher than P 1 is mainly formed by the mutual promotion of flame and sound pressure and the thermoacoustic coupling effect triggered by disturbance.The flame downward propagation velocity increases first and then decreases with the concentration,and reaches the maximum value when the methane concentration is 10%,and the combustion velocity is generally faster in the slightly rich combustion state.