Experimental research on the effect of diesel post-injection conditions on the efficiency and global warming potential in a single-cylinder four-stroke marine engine fueled with ammonia and diesel

Ammonia is one of the most widely used carbon-neutral fuels; therefore, many efforts have been made to supply ammonia to dual fuel (DF) marine engines. Because ammonia is toxic, the amount of unburned ammonia in exhaust gas should be reduced. However, as ammonia does not easily combust, it is necessary to oxidize the unburned substances in the latter part of the main combustion process. Thus, diesel post-injection is required to oxidize the unburned emissions. In this study, the effects of diesel post-injection timing and amount on the combustion, emissions, and efficiency of ammonia-diesel DF four-stroke 12-L single-cylinder marine engine were experimentally evaluated under 900 rpm and 50 % load conditions. Post-injection timing varied from 35° to 95° after the start of a micro pilot (MP). The amount of post-injection was maintained at 25 % and 40 % of total injected diesel fuel. Consequently, conducting a diesel post-injection at a level of 40 % close to the MP injection enabled the reduction of unburned hydrocarbon by 18.9 %, unburned ammonia by 11.2 % and N₂O—a major greenhouse gas—by 19.4 % compared to conventional dual-fuel combustion while maintaining equivalent thermal efficiency.