约束端面对管内甲烷爆炸特性的影响

为研究不同约束端面下甲烷的爆炸特性，利用自行搭建的实验平台完成了多种约束端面下不同浓度甲烷的爆炸实验。研究表明:约束端面的性质对甲烷的爆炸特性有显著影响，约束端面的承压强度越高，甲烷的爆炸超压越大。单层PVC薄膜作用下，薄膜破裂，不会引起火焰与超压的振荡；而纸膜破裂后，管道内外气流的高速泄放和回流则会引起超压振荡，使火焰前锋波动并发生扭曲变形；两者共同作用时，PVC薄膜会阻碍气流的泄放与回流，加速超压衰减，抑制火焰和超压的振荡。然而，随着纸膜层数增加，破膜时管道内外形成的巨大压差会使约束端面完全破裂，降低PVC薄膜的抑制作用。当破膜难度达到一定程度时，约束端面作用下的泄压峰值成为不同浓度甲烷爆炸的最大超压峰值，且泄爆压力并不随甲烷浓度的改变而改变，因此不同浓度甲烷的爆炸超压在较高的泄爆压力下相同；此时，相同约束端面下不同浓度甲烷的压力振荡曲线在压力衰减的前半个周期内完全重合，管道内外的压差成为主导超压振荡的重要因素，而不同浓度甲烷的燃烧速率对超压振荡的影响则可以忽略不计。

Effect of vented end faces on characteristics of methane explosion in duct

In order to study the characteristics of methane explosion under different vented end faces, explosion tests of methane with different concentrations are carried out in a vertical 5 L quartz duct with the upper end sealed by different films. The results show that the properties of the vented end faces have significant effects on methane explosion. The explosion overpressure of methane with different concentrations is largely dependent upon the vent burst pressure of the vented end faces, which increases with the increasing vent burst pressure. Specially, by covering the end of the duct by a single layer of PVC film, neither the flame nor the overpressure oscillation will be aroused by the rupture of the PVC film, while the rupture of the paper which generates drastic discharge and reflux of the air flow will severely reverse and distort the flame, such that cause the overpressure oscillation in the duct. Moreover, as the two works together, the PVC film will hinder the venting of the air flow, resulting in accelerating the reduction of the overpressure and suppressing the flame and overpressure oscillation. However, this effect gradually decreases with the increasing layers of paper films. Indeed, as the vent burst pressure reaches a certain value, the difference among the explosion overpressure of different concentrations of methane gradually diminishes owing to the same vent burst pressure, which is the maximum pressure of the overpressure history, resulting in a similar overpressure amongst different concentrations of methane. Significantly, the overpressure attenuation curves of methane explosion with different concentrations completely coincide with each other in the first half of the period. At this point, the differential overpressure between the internal and external duct is the key factor leading to the overpressure oscillation, while the influence of the combustion rate of methane with different concentrations on the overpressure oscillation can be ignored.