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 (P_max) 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 (t_P) was advanced by 14.6 %. Bottom ignition showed faster maximum flame velocity (v_max) and flame pattern change, higher maximum flame temperature (T_max), and stronger OH• peak intensity than central ignition. When the flame velocities were all upward, v_max 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%, T_max, OH• peak signal intensity and OH• 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.