Propagation characteristics of methane/air explosions in pipelines under high temperature and pressure

Underground coal gasification (UCG) is a multidisciplinary and integrated technology for energy production. Due to the requirements of the UCG technology and methane harvesting processes, methane is in a high-temperature and high-pressure state in underground transmission pipelines. A model for the deflagration and detonation of methane/air mixtures under ultra-high pressure and ultra-high temperature conditions was established. The experimental validation under various operating conditions demonstrated that this model can accurately assess the deflagration and detonation processes of methane/air mixtures. The structure of detonation waves under ultra-high pressure and ultra-high temperature was observed, and the critical pressure and critical temperature for initiating deflagration-to-detonation transition (DDT) were determined. When the initial pressure exceeds 0.75 MPa, the methane/air mixture undergoes DDT, with the detonation pressure exceeding 10 times the initial pressure. The critical concentration range under ultra-high pressure and ultra-high temperature for initiating DDT was also determined. The results presented in this paper possess significant engineering value for guiding the process safety design of UCG.