Study on Combustion and Emission Characteristics of Ammonia–Diesel Engine Under Diesel Pilot Injection Strategy

As a carbon-free fuel, ammonia can substantially reduce the carbon footprint of internal combustion engines. However, its slow flame propagation speed and high ignition temperature present combustion challenges. A dual-fuel engine combining ammonia with diesel can effectively address these issues and enhance combustion performance. This study investigates the effects of diesel split ratio (DSR), start of diesel pre-injection (SODI-pre), and start of diesel main-injection (SODI-main). The results indicate that, compared to single diesel injection, segmented diesel injection significantly improves mixture distribution and reactivity, leading to enhanced flame propagation. With a pre-injection ratio of 10% and SODI-pre advanced to −62 °CA, the indicated thermal efficiency increases from 45.35% to 47.61%. Meanwhile, NH3 emissions decrease from 1707 ppm to 689 ppm, and greenhouse gas N2O concentration drops from 370 ppm to 251 ppm. Nevertheless, elevated NOx emissions remain a significant challenge.