Combustion and emission characteristics of an ammonia engine applying hydrogen turbulent jet ignition and ammonia direct-injection

Ammonia and hydrogen, as zero-carbon fuels, are ideal fuels for internal combustion engines to achieve carbon neutrality and zero carbon emissions. Due to higher flame propagation speed of hydrogen, hydrogen-assisted combustion offers a promising solution to improve the ammonia engine performance. A new combustion concept for hydrogen turbulent jet ignition of ammonia diffusion combustion was proposed in this study, conducting a comprehensive analysis of the impact of jet flames on ammonia diffusion combustion and the formation of unburned ammonia by the numerical simulation. The results show that compared to dual-direct injection combustion mode, the jet ignition mode effectively enhances combustion efficiency. However, this mode also leads to a notable increase in unburned ammonia and N2O emissions. These emissions can be effectively reduced by optimizing the direction of ammonia injection. The high vaporization latent heat of liquid ammonia necessitates a critical jet flame temperature for the ignition of ammonia sprays. This temperature is substantially influenced by the mixing state of hydrogen in the pre-chamber. Uniform mixing and rapid heat release can lower the jet flame temperature, hindering the ignition of ammonia. In contrast, inhomogeneous blends prolong the ignition delay in the pre-chamber, resulting in unstable jet ignition. Under counter-swirl injection conditions, the ammonia flame ascends along the ammonia spray toward the nozzle, ensuring complete combustion of the ammonia and effectively reducing unburned ammonia. This also lowers the oxygen content in the ammonia mixture, which in turn suppresses the formation of N2O and NOx.