甲烷与空气质量浓度当量比对火焰结构及传播特性的影响

Effect of CH_4 to air mass concentration ratio on flame structure and propagation characteristic

为研究受限空间内甲烷与空气预混气体火焰结构及传播速度特性,建立小尺寸开口管道燃烧爆炸试验平台。采用高速纹影摄像技术,研究甲烷与空气质量浓度当量比对甲烷预混气体火焰在开口管道内传播结构的影响。根据离子探针技术监测燃烧反应区的离子产物浓度变化,分析燃烧反应区特性。试验结果表明:火焰结构受甲烷/空气预混气体中甲烷的质量浓度当量比的影响较大,在贫燃或富燃条件下,火焰阵面受湍流和浮力的作用效果明显,火焰结构发生不规则变化;甲烷/空气质量浓度当量比达到1.06时,预混气体充分燃烧,火焰传播速度较快,预热区厚度达到最小值,火焰传播速度与预热区厚度存在此消彼长的变化趋势。甲烷与空气预混气体发生完全燃烧时,火焰传播速度较快,引发火灾的危害性较大,降低或增大甲烷浓度均可使燃烧反应不充分,有助于降低危险性。

A small-sized pipe with an open duct system was built to study the CH4/ air mixture flame structure and spreading characteristic in the open space. Changes in flame propagation structure were obtained by using high speed schlieren technique. The characteristic of reaction zone was detected by using ion probe.The results show that flame has a spherical wave structure under stoichiometric ratio,that under condition of lean fuel or rich fuel,the flame front will bave an asymmetric structure. As mass concentration ratio reached1. 06,the combustion of premixed gas was fuller with high flame propagation speed,while preheat zone thickness reaches the minimum value. That preheated zone thickness decreased first and then increased with increase in CH4 gas concentration,and that flame propagation speed is more quick,the harmfulness of fire is bigger when complete combusition occurs,and it is useful to reduce or increase methane concentrations to make combustion inadequate.