Flammability limit and explosion energy of methane in enclosed pipeline under multi-phase conditions

To investigate the regulation of gas explosion characteristics under multi-phase conditions, a series of experiments were conducted in enclosed pipeline with different scenarios of liquid types and liquid height. The criterion for explosion pattern classification, flammability limit, propagation of the maximum explosion pressure and the energy distribution of the explosion wave were studied to provide basic data guidance for explosion accident prevention. The results indicate that the flammability limit of gas has a volume effect and the flammability limit for pure methane in an elongated pipeline with the volume of 76 dm³ is 9%–17%. The deflagration patterns of methane within the flammability limit can be divided into violent deflagration pattern (VDP) and weak deflagration pattern (WDP). In addition, the increase of the flammability limit range under the condition of gas-liquid coexistence increases the risk of gas explosion. This increase in explosion risk can be analyzed and explained from restricted space and the triple desk theory of the boundary layer. Furthermore, the presence of liquid also affects the distribution of peak overpressure along the pipeline. Based on the peak overpressure, considering overpressure ratio and distance, a model for predicting the energy of explosion wave is presented.