Effect of H₂ in fuel-rich NH₃/H₂/air mixtures: Explosion venting experiments and molecular dynamics simulations

Ammonia (NH₃) is an important component of low-carbon energy systems, which are often blended with hydrogen (H₂) to optimize energy utilization efficiency and operated under fuel-rich conditions to reduce nitrogen oxide (NO_x) generation. However, the potential explosion safety risks of NH₃/H₂/air cannot be ignored. In this study, the explosion process of NH₃/H₂/air premixed gases under fuel-rich conditions is investigated, with a focus on H₂ volume fractions of 5%, 10%, 15%, and 20%. The variations in pressure and venting flame characteristics during the process of explosion are analyzed. Moreover, the reaction mechanism of the fuel-rich NH₃/H₂/air system is analyzed from a microscopic perspective through the use of the reactive force field molecular dynamics method. The results indicate that with increasing proportion of H₂ in the fuel-rich mixture, the maximum explosion pressure (p_max) and the maximum rate of pressure rise ((dp/dt)_max) decrease. At 5%, p_max and (dp/dt)_max are 0.22 MPa and 8.10 MPa·s⁻¹, respectively. The first venting flame lengthens at first and then shortens, whereas the length and velocity of the second venting flame increase. On a microscopic level, the addition of H₂ reduces the decomposition rate of NH₃, increases the generation frequency of •OH and •H in the system, and significantly decreases the amount of NO_x produced. Through the analysis of explosion venting and molecular dynamics reaction mechanisms, this study provides strong support for the safe and efficient practical application of fuel-rich NH₃/H₂/air mixtures in the energy sector.