Experimental study of liquid ammonia injection timing in rapeseed methyl ester dual injection engine

Ammonia, a promising carbon-free fuel, offers practical advantages over hydrogen, such as liquid-phase storage, making it suitable for direct use in compression ignition engines. As a hydrogen carrier, ammonia has the potential to decarbonise internal combustion engines. However, its widespread adoption faces challenges, including high emissions of unburned ammonia and other pollutants. This study examines the effect of liquid injection timing of ammonia on the combustion, performance, and emissions of a rapeseed methyl ester (RME) dual-fuel compression ignition engine. Experiments were carried out on a single-cylinder diesel engine equipped with dual high-pressure injectors to evaluate ammonia injection timings between −25 and −7 CAD bTDC using a GDI injector. The results show that overlapping ammonia injection with RME significantly enhanced engine performance, with the optimal SOI of −17 CAD for both fuels achieving the highest indicated efficiency of 37.8 %. Moreover, injecting ammonia a few CADs after the RME effectively minimised emissions. Therefore, the lowest NH3 emission of 453 ppm was recorded at SOI of −14 CAD. However, delaying the SOI of ammonia further to −7 CAD led to a rise in CO, N2O, and PM emissions due to incomplete combustion of RME caused by liquid ammonia injection.