Experimental study on combustion and emission characteristics of an ammonia-diesel dual-fuel engine under single and double injection strategies

Abstract

This study compares the effects of single and double diesel injection strategies on the combustion and emission characteristics of an ammonia-diesel dual-fuel engine at medium loads, as well as their potential for reducing greenhouse gas (GHG) emissions under different ammonia substitution ratios. At a 70% ammonia substitution ratio, single injection with early injection timing enhances the local mixture reactivity, shortens the ignition delay, and strengthens the diesel ignition, thereby improving ammonia combustion efficiency. Under the double injection strategy, the pilot injection of diesel forms a premixed charge with ammonia in the cylinder, accelerating the overall combustion speed and shortening the combustion duration compared to single injection, which benefits thermal efficiency. Overall, at a low ammonia substitution ratio (50%), the double injection strategy shows advantages in terms of indicated thermal efficiency (ITE) and GHG emissions. However, at a higher ammonia substitution ratio (70%), the ITE of both single and double injection strategies is nearly identical, but single injection results in lower emissions of GHG, N₂O, and unburned NH₃. At a 70% ammonia substitution ratio, the minimum GHG emissions of the single injection strategy reach 229.9 g/kW·h, representing a 61.5% reduction compared to the pure diesel mode. This demonstrates that the ammonia-diesel dual-fuel mode has significant potential for GHG reduction in internal combustion engines.