Comparative study of the effects of ignition location on the flame propagation characteristics and spectral properties of a methane-air premixed gas in a vertical pipeline

Methane is an explosion hazard during its pipeline transportation and distribution. This study investigated the characteristics of methane explosions in a vertical pipeline for various ignition locations and methane concentrations. Flame propagation properties were more sensitive to methane concentration changes in central ignition than in bottom ignition; in lean fuel -air mixtures, they were more sensitive to methane concentration changes than in rich fuel -air mixtures. Because the central ignition flame burned over a larger area, it shows more explosive intensity than the bottom ignition. At methane concentration of 10 vol%, the maximum pressure (Pmax) and maximum pressure increase ((dP/dt)max) of the central ignition increased by 6.2 % and 44.2 %, respectively, compared with that of the bottom ignition, and the time to reach the peak explosion pressure (tP) was advanced by 14.6 %. Bottom ignition showed faster maximum flame velocity (vmax) and flame pattern change, higher maximum flame temperature (Tmax), and stronger OH center dot peak intensity than central ignition. When the flame velocities were all upward, vmax was most significantly reduced by 64.6 % when the methane concentration was 8 vol% compared with the bottom ignition. At a methane concentration of 10 vol%, Tmax, OH center dot peak signal intensity and OH center dot signal duration increased by 2.2 %, 1.3 %, and 39.5 %, respectively, for the bottom ignition compared to the central ignition. The experimental results of this study can be used as a reference to design targeted measures for preventing methane explosions in pipelines and to develop new methane explosion suppressants.