Numerical investigation on the propagation process of ammonia diffusion flame ignited by hydrogen jet flame in a chamber with piston bowl

Hydrogen jet flame ignition technology, based on active pre-chamber, is an effective approach to improve the combustion inertness of ammonia. Revealing the transition mechanism of ammonia diffusion flame ignited by hydrogen jet flame, driven by the coupling of chemical reactions and mass transfer, is of great significance for developing advanced combustion strategies. This paper offers a comprehensive analytical perspective on the development process of ammonia–hydrogen ignition and combustion. The results show that, compared with the pre-chamber structure, the jet direction has a more significant impact on the turbulence kinetic energy of the mixture. The slender throat structure intensifies the turbulent thermal dissipation effect, which is detrimental to the formation and propagation of the initial flame. The process of ammonia combustion ignited by hydrogen jet flame can be divided into four stages. The hydrogen squeezed into the main chamber during the pre-chamber mixture ignition stage significantly impacts the propagation speed of the jet flame. During the transition from jet flame to diffusion flame, the combustion of the mixture shifts its dominant factor from the mass transfer rate of hydrogen to the chemical reaction rate. The combustion process of ammonia initially focuses on the thin reaction zone, followed by the flame front becoming corrugated under the influence of turbulent vortices and the reaction rate. The study provides an important theoretical basis for developing advanced combustion strategies, especially in the context of ammonia and hydrogen as the main power sources for zero-carbon marine vessels.