Investigation of injector arrangements in a high-pressure direct-injection ammonia-biodiesel dual-fuel engine

Ammonia, as a carbon-free alternative fuel, has tremendous potential for global decarbonization, but its poor combustion characteristics present challenges for practical applications. Recently, the high-pressure direct-injection (HPDI) dual-fuel strategy has attracted considerable attention due to its flexible control and potential to reduce ammonia slip. While most previous studies on HPDI engines have focused on the two-injector design, research on the dual-fuel injector mode, enabling direct injection of both ammonia and diesel/biodiesel through a single injector, remains relatively limited. Moreover, the potential of injector design optimization for improving engine performance and comparisons between these two injector modes have not been adequately explored. In this work, after 3D-CFD models were validated against liquid ammonia spray data and experimental results from an HPDI ammonia-biodiesel engine with bore size of 86 mm, the effects of injector arrangements on combustion and emissions were analyzed for both injector modes. Results indicate that key injector design parameters, such as injection umbrella angle, injector position, and nozzle number, significantly influence engine performance and pollutant emissions, highlighting the importance of optimizing injector design. For example, optimized injector arrangements can reduce unburned NH3 emissions by up to 96 % compared to the base injector design, even at higher ammonia energy ratios. Furthermore, a comparison between two modes at 80 % ammonia energy ratio shows that the dual-fuel injector mode has the potential to achieve slightly higher indicated thermal efficiency and lower N2O emissions, while the two-injector mode provides lower NOx emissions. Overall, both injector modes achieve comparable engine performance, while the dual-fuel mode saves space but presents design challenges.