Experimental Study on the Effects of Ammonia Energy Substitution Rate on Combustion and Emission Performance in a Hydrogen Engine

<div class="section abstract"><div class="htmlview paragraph">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.</div></div>