On ammonia/diesel dual-fuel combustion in optical engine

Abstract

Ammonia-diesel dual-fuel combustion mode is one of the potential ways to achieve lower carbon emissions in compression ignition engines. In this work, the effects of ammonia addition on diesel combustion characteristics were experimentally investigated in an optical CI engine. The gaseous ammonia is introduced to the engine through a port injection while diesel is directly injection into the cylinder. A color high-speed camera was utilized to detect and differentiate between diffusion burning and lean-premixed ammonia combustion. Additionally, computational models were conducted and the findings were coupled with the experimental data. According to optical investigations, the lift-off distance is created during the diesel spray and progressively grows as the ammonia energy ratio (AER) rises. The findings indicate that, in comparison to pure diesel combustion mode, combustion in an ammonia environment exhibits prolonged ignition delay duration and lesser flame luminosity. Secondly, a multi-injection strategy for diesel fuel was used where the diesel pre-injection timing (SOPI) values adjusted from −30 °CA ATDC to −60 °CA ATDC). Advancing SOPI is an effective approach to suppress diesel diffusion flame and reduce soot production in the cylinder. For advanced SOPI, findings reveal that rich pockets have decreased drastically as the combustion progresses. With the advancement of SOPI, there is a notable a connection between the flame speed and the peak heat release rate, where a high flame speed correlates to a greater heat release rate peak. Finally, the ratio of pre-injection of diesel fuel (ROPI) varied from 0 to 100% as a mean to improve flame propagation. There is a crucial threshold of pre-injection (ROPI) mass ratio of 45%, at which the initial flame features alter considerably. As the ROPI exceeds 45%, the flame kernel appears as a visible flame near to the main injection timing (SOMI), indicating that the ignition delay duration is decreasing.