Effect of unilateral opening blockage ratio variation on bidirectional explosion characteristics of CH4/Air/CO2

Gas explosions pose recurrent hazards in coal mining operations and industrial facilities, and carbon dioxide (CO2) is known to mitigate the risk of such explosions. However, due to the variable nature of ventilation areas and the unclear relationship between CO2 explosion suppression performance, this experiment analyzed the bidirectional flame explosion characteristics in premixed gases with varying volume fractions of CO2 (ХCO2) within ducts featuring different opening blockage ratios (φ). The findings reveal that when the right side is not completely sealed, an increase in φ and ХCO2 leads to more oscillations of the left flame front (LFF) before the right flame front (RFF) exits the pipe. This influences the formation frequency of the distorted tulip flame (DTF), extends the generation time of flat flames, and results in the reemergence of tulip flames after they have disappeared. Moreover, distorted cusps appear on the flame tongue at full closure on the right side, which diminish as ХCO2 increases. At a constant ХCO2, an increase in φ enhances the explosion overpressure and the time it takes for the flame to rush out, yet the propagation rate and the amplitude of the overpressure oscillations are reduced. Compared to φ, ХCO2 has a less significant impact on the oscillations. This paper offers valuable data support for the safe utilization of natural gas and the strategic placement of pressure relief devices.