Evaluation of hydrogen injection and oxygen enrichment strategies in an ammonia-hydrogen dual-fuel engine under high compression ratio.

[Display omitted] • Optimized injection strategies affect CA0-90 by varying NH 3 -H 2 premixing degree. • Multiple injection mode is more suitable for an ammonia-hydrogen dual-fuel engine. • Oxygen enrichment strategy improves the flame kernel formation and cyclic variation. • Oxygen-enriched levels of about 34.3% can elevate BMEP by more than 42%. • A hypothesis is proposed for the use of NH 3 -H 2 engines in hybrid power systems. Ammonia with low reactivity still faces some challenges as the main fuel for engines. Hydrogen and oxygen, as two combustion improvers, are expected to solve ammonia's reluctance to combust. To date, the application of oxygen enrichment strategies in ammonia-hydrogen dual-fuel engines is very rare, which motivates this study. The main objective of this investigation is to explore optimal hydrogen injection strategies and evaluate the effectiveness of oxygen enrichment strategies for the engine. Optimizing hydrogen injection parameters can vary the ammonia-hydrogen premixing degree, thus improving the flame kernel formation and flame propagation velocity. This is supported by the shortened CA0-90, lowered cyclic variation, and elevated thermal efficiency and power. Oxygen-enriched strategies enhance the heat release process and mitigate the negative effects of ammonia on the ignition process, which reduces cyclic variation and prominently increases power. However, the elevated oxygen concentration may increase the adiabatic flame temperature of the mixture and thus heat transfer loss, which decreases brake thermal efficiency. Moreover, a hypothesis that an ammonia-hydrogen engine may be employed in a hybrid power system in the future is proposed. The results of this work can be used as raw data for developing a hybrid power system. [ABSTRACT FROM AUTHOR]