Explosive characteristics of non-uniform methane-air mixtures in half-open vertical channels with ignition at the open end

In this study, the explosive characteristics of non-uniform methane-air mixtures in a 1.5 m half-opened vertical channel with ignition at the open end were experimentally studied. The results revealed significant oscillation characteristics in the flame image, velocity, and pressure variations. Notably, a strong similarity was observed between the flame velocity and pressure profiles. Furthermore, it was experimentally demonstrated that the explosion characteristics of methane-air mixtures in vertical channels with the same average volume fraction differed. These variations in characteristics were attributed to the degree of non-uniformity, where both the direction and steepness of the methane concentration gradient influenced the explosion flame behavior. When the diffusion time was very short, resulting in a small concentration above the channel and a large gradient, an obvious cusp appeared at the flame front, which was absent in the case of longer diffusion times. In addition, as the methane diffusion time increased, the methane in the vertical channel gradually accumulated upward. Consequently, the time required to reach maximum velocity and pressure after ignition decreased, leading to a larger maximum amplitude. In summary, our study highlights the importance of considering non-uniformity and diffusion time in understanding the explosion characteristics of methane-air mixtures in vertical channels.