障碍物对开敞空间贫燃天然气爆炸特性的影响研究

Effect of obstacles on unconfined methane explosion characteristics under lean-fuel conditions

为揭示贫燃条件下障碍物对开敞空间天然气爆炸特性的影响,试验记录了火焰传播形态和爆炸压力,并对火焰结构和压力空间分布进行了数值分析。结果表明:在无障碍物工况下,火焰近似以球形向外膨胀传播,火焰表面较为连续,火焰传播速度较慢,爆炸压力较低;而在障碍物的湍流扰动下,火焰表面出现较大的“褶皱”结构,火焰燃烧表面积显著增大,火焰传播速度升高,爆炸压力也相应增大。相比于由障碍物引起的火焰加速作用,因流体动力学不稳定性产生的失稳效应可忽略不计。由温度分布可清晰观察火焰表面“褶皱”结构的形成过程,计算所得的爆炸压力达到峰值时间较早,且超压峰值相比试验值较低。

In order to reveal the effects of obstacles on explosion characteristics of unconfined methane explosion under lean-fuel conditions,flame propagation images and explosion overpressure were experimentally recorded.In addition,the simulation software FLACS was applied to observe the flame propagation process and the space distribution of overpressure.The explosion experiments were conducted in a 1 m3 explosion equipment,and the ignition source was fixed in the geometry center of equipment.Transparent thin film was applied to seal the equipment and a circulating pump was used to ensure the uniformity of the premixed methane gas,and the methane concentration was measured by a gas concentration analyzer.A high-speed camera with a 900 nm IR filter was adopted to capture the clear flame image.Three high-accuracy acoustic pressure sensors and a data acquisition instrument were employed to record the pressure variations.Regular-shape obstacles were constructed by a number of square stainless steel tube with both ends blocked.An experiment without obstacles was performed as a comparison.The results showed that the flame propagated outwardly as the shape of a sphere with a continuous surface under no-obstacle condition,and the explosion overpressure was low due to the slow flame propagation velocity.However,when there were obstacles in the explosion space,large wrinkled structures appeared on the flame surface and the flame surface area increased greatly,which enhanced the flame propagation velocity and then the explosion overpressure increased.The effects of flame acceleration caused by the hydrodynamic instability could be ignored compared with the effects of obstacles.Clear developing process of wrinkled flame on the flame surface could be observed with the help of temperature distribution,and the time calculated by simulation software when the explosion overpressure reached the maximum value was earlier than that of experiments.In addition,the calculated explosion pressures were lower than the experimental values.