Numerical investigation of multiple hydrogen injection in a jet ignition ammonia-hydrogen engine

Ammonia-hydrogen engines are promising for heavy-duty, long -distance transportation, while the lower hydrogen energy share (XH2) in ammonia-hydrogen fuels facilitates hydrogen storage and use. In this study, a numerical investigation of engine performance based on an engine with ammonia port injection and different hydrogen jet ignition strategies at a fixed XH2 of 3% was conducted. The results show that too-early hydrogen injection results in lower hydrogen concentration and weak ignition in the pre-chamber, while too-late injection results in less hydrogen entering the main chamber, making more ammonia not mix well with the hydrogen, both of which increase the combustion duration. Hydrogen injection at the bottom dead center before the compression stroke mixes the hydrogen with the ammonia preliminary and leads to the formation of a high-temperature, slightly lean-burn region during the combustion, which worsens NO emission but reduces N2O emission. Compared with hydrogen single injection, splitting the same mass into two equal-mass injections favors higher peak pressures, shorter combustion durations, and higher indicated thermal efficiency (ITE). Injections at 360 and 90 degrees CA before the top dead center, respectively, achieve at least 1% relatively higher ITE with similar NO, NH3, and N2O emission performance compared with the single injection.