Effect of injection hole distribution on the mixture formation, combustion, and emission characteristics in a direct-injection hydrogen engine

The injection hole (IH) distribution of an injector plays a significant role in the mixture formation of a direct-injection H₂ engine with lean combustion technology. Therefore, the purpose of this study is to disclose the effect of IH distribution on the mixture formation to improve engine combustion and emission characteristics. To reach the goal, a three-dimensional model of an H₂ engine was initially constructed. Then the injection hole number (IHN) on an asymmetric multi-hole injector was increased from two to seven under the conditions with fixed spreading angle of 90° (SA90) and fixed interval angle of 22.5° (IA22.5), respectively. The results show that a lower IHN with SA90 can enhance the penetration ability of the H₂ jet, resulting in better mixture homogeneity. This contributes to better combustion of SA90-2IH and SA90-3IH. However, SA90-2IH shows a significantly lower NOx emission due to the low temperature combustion resulting from its higher homogeneity. Regarding fixed IA22.5 condition, increasing IHN can improve the mixture homogeneity, opposite to SA90 cases. Nonetheless, the combustion performance of the IA22.5-4IH case is most favorable, although it exhibits a low mixture homogeneity. This is caused by its higher equivalence ratio at the spark plug region, contributing to higher combustion temperature and the subsequent increased NOx emission. In addition, the SA90 case shows a higher IMEP compared to IA22.5.