Study of Methane Explosion Suppression Characteristics of N2 and CO2 in Variable Cross-Section Ducts

To investigate the effect of concentration of N-2 and CO2 (0, 10, 20, 30, 40, and 50%) on the flame propagation characteristics of CH4/air premixed gases with stoichiometric ratios in variable cross-section ducts, experiments were conducted in four combinations of ducts at initial conditions of 298 K and 1 atm. The results show that the flame propagation velocity, propagation time, and overpressure are greater in the suddenly contracted duct than in the suddenly expanded duct if the dimensions of the ducts are kept constant. However, an increase in inert gas concentration leads to a decrease in flame propagation speed, an increase in flame propagation time, and changes in flame structure and pressure. "Tulip" flames appeared when a duct with a cross section of 100 mm x 100 mm was combined with a duct with a cross section of 70 mm x 70 mm, whether N-2 or CO2 was added or what its concentration was. However, when a duct with a cross section of 140 mm x 140 mm was combined with a 70 mm x 70 mm duct, a "tulip" flame is formed only at a CO2 concentration of 50%. As the concentration of inert gas increases, the explosion pressure first decreases and then stabilizes, while the rate of pressure increase showed a monotonically decreasing trend. The explosion pressure is minimized when the concentration of CO2 and N-2 is 30 and 40%, respectively.