To advance the application of zero-carbon ammonia fuel, this paper presents an
experimental investigation on the potential of ammonia substitution using a 2.0L
ammonia-hydrogen engine, where ammonia is injected into the intake port and
hydrogen is directly injected into the cylinder. The study examines the effects
of ammonia substitution rate under various load conditions on engine combustion
and emission performance. Results indicate that the maximum ammonia energy
substitution rate reached 98%, and within the stable combustion boundary, the
mass fraction of unburned ammonia was less than 3%. The ammonia energy
substitution ratio increased with load, and ammonia addition significantly
suppressed pre-ignition and knocking. As ammonia content increased, ignition
timing advanced, combustion duration extended, ignition delay prolonged, COV
increased, peak cylinder pressure, and pressure rise rate decreased, with a
corresponding decrease in peak heat release rate. Compared to a pure hydrogen
engine, the ammonia-hydrogen dual-fuel engine significantly improved brake
thermal efficiency (BTE), which continued to rise with increasing ammonia energy
substitution rate. At BMEP = 0.8 MPa, BTE reached a maximum of 41.1%. With
increased ammonia addition, unburned NH3 emissions in the exhaust gradually
increased, while NOx emissions decreased overall, but N2O emissions showed an
increasing trend.