Impact of Ammonia Content on Explosion of Methane‒Air Premixed Gas Duct with Varying Equivalence Ratios

In this study, a duct explosion experiment with an ammonia-methane-air mixture was conducted using a custom-built stainless steel flame acceleration duct (D = 120 mm, L/D = 45.8). The effects of varying ammonia concentrations (φ = 0%, 10%, 20%, 30%) and equivalence ratios (Φ = 0.9, 1.0, 1.1) on flame behavior were examined. The key aspects analyzed included the evolution of the explosion overpressure within the duct and the average propagation velocity of the deflagration flames. The results show that ammonia reduces the brightness of methane-air deflagration flames and that this reduction becomes more pronounced as the ammonia concentration (φ) increases, and the pressure‒time histories inside the duct have a three-peak structure (P_b, P_out, and P_ext), which is caused by the burst of the vent cover, venting of burned mixtures, and counterflow flame generated by the external explosion, Additionally, rarefaction waves in the duct following discharge can lead to oscillatory combustion, and a "backfire" phenomenon is observed in all experiments. This study provides fundamental theoretical support for the promotion and application of ammonia fuel.