Experimental study on the effect of N2/CO2 on the wave evolution process and flame development of methane deflagration flow field

Abstract

To mitigate the hazards of natural gas explosions to neighboring buildings, this research focuses on gas-based flame-suppressant technologies, aiming to reduce the accident incidence. A circular pipeline with a diameter of 90 mm and a length of 12 m was built to simulate the building environment. It employed a biaxially oriented polypropylene (BOPP) film to simulate doors and windows, effectively isolating the 9.5 % methane-air mixture from the external gas. By changing the downstream gas composition to air, N₂, or CO₂, and varying the CO₂ pressures to 0.12, 0.14, and 0.16 MPa, the suppression effects of different gases and pressures on the pressure wave and flame of methane explosion are investigated, and their specific impacts on adjacent structures are elucidated. The main findings show that: (1) In a closed space, the propagation of explosion energy does not decrease uniformly with increasing distance. Instead, the unconsumed gas after membrane rupture propagates downstream to sustain combustion, triggering a local pressure surge far from the explosion epicenter; (2) In both N₂ and CO₂ gas environments, the maximum pressure peaks generated by the explosion are significantly lower than those in the air environment. In terms of flame propagation characteristics, CO₂ exhibits a more obvious inhibitory effect. The maximum flame propagation speed in CO₂ (170.721 m/s) is much lower than that in N₂ (389.484 m/s), and the maximum flame duration in CO₂ is 5.4 ms shorter than that in N₂; (3) As the CO₂ pressure in the pipeline increases, the peak explosion pressure decreases significantly. It is worth noting that at 0.16 MPa, the flame activity completely stops.