Effects of relative position of injectors on the performance of ammonia/diesel two-stroke engines

A numerical study was conducted to investigate the impact of the relative position of injectors on the performance of ammonia/diesel two-stroke engines under typical marine operating conditions characterized by a 50 % load and a high ammonia energy ratio of 80 %. The results show that there are three combustion modes as the relative position of the diesel injectors changes. In the first combustion mode, the ammonia/diesel injectors are positioned adjacently, with the diesel injectors upstream. As the ammonia/diesel injectors are repositioned further apart, there is a slight reduction in indicated thermal efficiency and an increase in NOx emissions, accompanied by a slight rise in unburned ammonia and greenhouse gas emissions. In the second combustion mode, the ammonia/diesel injectors are spaced further apart. The fully developed diesel flame front end ignites its downstream ammonia spray, and its upstream ammonia spray is difficult to ignite, resulting in increased unburned ammonia and greenhouse gas emissions. In the third combustion mode, the ammonia/diesel injectors are positioned adjacently with the diesel injectors downstream. As the ammonia/diesel injectors are closer, the indicated thermal efficiency shows a significant decrease trend, with an increase in NOx emissions, while unburned ammonia and greenhouse gas emissions remain at lower levels. •Based on the impact of injector positioning, it is categorized classified into three combustion modes.•The diffusion, ignition and combustion processes of ammonia were described and compared.•The generation mechanisms of NO and N2O under three combustion modes were clarified.•Good performance was achieved in low emissions. Ammonia 0.36 g/W · h, NOx 3.62 g/W · h.