Parametric Investigation of Dual Direct-Injection Strategy for D/N/D Mode in Ammonia/Diesel Engines

While the split diesel bracketing ammonia (D/N/D) injection mode has shown high potential for performance enhancement in ammonia/diesel dual-fuel engines, its key operational parameters require systematic investigation. This study conducts a numerical investigation to systematically evaluate the D/N/D injection parameters. The effects of the start of diesel pre-injection (SODI-pre), start of diesel main injection (SODI-main), and diesel split ratio (DSR) on combustion and emission characteristics were systematically evaluated. Results indicate that at an SODI-pre of −15 °CA ATDC and an SODI-main of −5 °CA ATDC with a DSR of 15% minimizes equivalent indicated specific fuel consumption (EISFC: 156.7 g/kWh), NOx (8.6 g/kWh), and CO2 (192.5 g/kWh) but leads to relatively high knock index (KI: 1.15 MPa/°CA) and incomplete combustion emissions (CO, soot, unburned NH3, and HC). Retarding SODI-main to −1 °CA ATDC and raising the DSR to 30% substantially reduces the incomplete combustion emissions, with unburned NH3 and HC reaching 0.009 and 0.003 g/kWh, respectively, while offering a favorable overall trade-off among EISFC (157.9 g/kWh), KI (1.19 MPa/°CA), CO (0.067 g/kWh), soot (0.083 g/kWh), NO (9.7 g/kWh), and CO2 (194.0 g/kWh). Consequently, the selected injection strategy provides a favorable trade-off between thermal performance and multi-pollutant control.