Analysis and Optimization of Diesel Injection Strategy to Minimize Unburned Hydrogen in a Hydrogen–Diesel Dual-Fuel Medium-Speed Marine Engine

Abstract To advance shipping decarbonization, hydrogen is increasingly recognized as a viable zero-carbon fuel. Currently, a hydrogen/diesel dual-fuel medium-speed engine represents an optimal prime mover for ships. However, challenges such as the large cylinder dimensions of marine medium-speed engines and the low temperatures at the combustion chamber walls can hinder efficient flame propagation, leading to the emission of unburnt hydrogen. This not only diminishes the engine’s mechanical output but also poses significant safety risks. To address these issues, this study employs computational fluid dynamics (CFD) modelling to explore optimal diesel injection strategies that minimize unburnt hydrogen emissions in such engines. Specifically, this research examines the impacts of the diesel injection start angle, spray tilt angle, and injection duration on hydrogen combustion efficiency. The findings reveal that fine-tuning injection parameters substantially lower the fraction of unburned hydrogen. Adjusting the injection timing from 9.5°CA BTDC to 49.5°CA BTDC decreases the unburnt hydrogen fraction from 50% to 3%. Furthermore, modifying the spray tilt angle from 75.5° to 55.5° further decreases it to 2%, while shortening the injection duration from 35°CA to 34°CA achieves the lowest unburnt hydrogen fraction at just 1%. These results underscore the effectiveness of diesel injection strategies in optimizing the combustion in hydrogen/diesel dual-fuel marine medium-speed engines, offering a pathway for similar applications in the sector.