A Numerical Simulation of Mixture Formation in a Hydrogen Direct-Injection Internal Combustion Engine

Direct-injection technology applied in hydrogen internal combustion engines can effectively prevent backfire, thereby improving the engine performance. Nonetheless, optimizing the injection strategy is highly intricate, requiring a comprehensive understanding of the hydrogen–air mixture formation process inside the cylinder. In this study, a simulation of hydrogen–air mixture formation was systematically conducted in a hydrogen direct-injection internal combustion engine using three-dimensional computational fluid dynamics (CFD) software. Under rated conditions, the influence of the nozzle hole number, injection direction, injection timing, and combustion chamber geometry on the mixture formation was analyzed from the perspectives of flow state and mass transfer. The results indicate that more nozzle holes would lead to more significant non-uniformity of the mixture, mainly due to the Coanda effect. The normalized standard deviation (NSD) of a six-hole nozzle design is 0.3495, which is higher than the NSD of all the single-hole nozzle conditions. By changing the hydrogen injection timing from −144 °CA to −136 °CA, the non-uniformity coefficient of the mixture is little affected, while notable differences in the distribution of the mixture are observed. The appropriate injection directions and optimized combustion chamber geometries could also help to effectively organize the in-cylinder flow, significantly improving the uniformity of the in-cylinder mixture and reducing the likelihood of abnormal combustion events.