Effect of combustion chamber geometry on performance and emissions of direct injection hydrogen engines

Using hydrogen in internal combustion engines (ICEs) not only reduces CO₂ emissions but also leverages the high technological maturity of ICEs for rapid popularization, making it a very promising method. However, hydrogen ICEs face the challenge of high NO_X emissions. Optimizing the combustion chamber geometry can significantly improve the mixing quality of the fuel–air mixture, thereby increasing combustion stability and reducing original NO_X emissions. This paper discusses in detail the effects of five different chamber geometries on performance and emissions in a direct-injection spark-ignition hydrogen engine under ultra-lean conditions. The research results indicate that the nebular spiral arm structure of the nebular combustion chamber divides the large-scale vortex in the cylinder into several vortices, guiding the collision between different vortices or colliding with other walls of the combustion chamber. By enhancing the gas flow in the cylinder at the end of the compression stroke, the reasonable mixture concentration distribution and TKE distribution are achieved, thus showing the best combustion performance The eccentric hemispherical combustion chamber (EHCC), with its offset hemispherical structure, achieves stratified mixing and combustion effects with high concentration at the cylinder center and low concentration around the periphery. However, due to the weaker TKE of the mixture, the combustion performance of the EHCC is slightly inferior to that of the NECC. Compared to the initial combustion chamber (INCC), the NECC expands the excess air coefficient corresponding to the lean-burn limit from 2.52 to 2.91. Furthermore, at λ = 2.5, the NECC achieves both high thermal efficiency (46.2 %) and nearly zero emissions.