Investigation on the explosion characteristics and mechanisms of methane blended with hydrogen/ammonia

In recent years, CH₄/NH₃ and CH₄/H₂ blended fuels have received extensive attention for their carbon emission reduction advantages. However, compared with pure methane, introducing NH₃ and H₂ not only alters the explosion characteristics of blended fuels and gives rise to potential process safety risks, but also poses considerable challenges to further clarifying their explosion mechanisms. In this study, the explosion behavior and micro-reaction regulation mechanism of CH₄/NH₃ and CH₄/H₂ mixtures were systematically investigated via a three-level framework: "macroscopic experiment - microscopic simulation - energy analysis". Experiments indicate that at the same blending ratio, the explosion intensity of CH₄/H₂ exceeds that of pure methane, which in turn exceeds that of CH₄/NH₃. The reactive force-field (ReaxFF) results indicate that with increasing hydrogen blending ratio, both the appearance time and peak time of ·CH₃ and CH₂O advance gradually, and at high hydrogen blending ratios, ·OH radicals dominate CH₄ oxidation, accompanied by intensified free radical oscillation and enhanced explosive reactivity. The initial reaction of NH₃ is faster than that of CH₄; however, in subsequent reactions, the nitrogen-hydrogen compounds derived therefrom collectively weaken the deflagration characteristics of the blended fuel through dual effects at the kinetic and energetic levels. At the kinetic level, the introduction of NH₃ enhances chain initiation of the chain reaction, while subsequent nitrogen-hydrogen species (NH₃, ·NH₂) dominate the competition for reaction sites with hydrocarbon active species, prematurely terminating chain propagation and termination. At the energetic level, density functional theory (DFT) calculations demonstrate that the typical elementary reactions involving nitrogen atom bonding not only need to overcome high energy barriers but also are accompanied by significant heat absorption. This characteristic further inhibits the overall energy release of the system, ultimately leading to a reduction in the deflagration intensity of the blended fuel.