Work

Analysis and visualization of micro-pilot diesel injection timing in a high-pressure direct injection Ammonia-Diesel dual-fuel marine engine

Year: 2025

Type: article

Abstract: This study investigates the effect of diesel injection timing on ammonia combustion performance in a single-cylinder, 12.5-liter-class, medium-speed, high-pressure direct-injection dual-fuel marine engine. Ammonia and diesel were directly injected into the cylinder through separate injectors, ammonia via a centrally mounted, mechanically controlled injector and diesel via a side-mounted, electronically controlled common-rail injector. Diesel served as the ignition source and was injected earlier than ammonia to promote favorable conditions for its combustion.Experiments were conducted under part-load conditions corresponding to 25% load. Diesel injection timing was varied from 31.5 to 11.5 crank angle degrees (CAD) before the ammonia injection timing at 5 CAD intervals, while the ammonia injection timing was fixed due to mechanical constraints and used as the reference point.Key performance indicators such as indicated thermal efficiency, ammonia combustion efficiency (η_(comb.NH3)), and emissions of NOX, N2O, and NH3 were analyzed. To understand the observed trends, the combustion process was divided into three stages based on the heat release rate: diesel premixed combustion, ammonia ignition delay, and ammonia main combustion. The energy contribution and timing of each stage were evaluated relative to diesel injection timing. Additionally, in-cylinder flame imaging was performed using an endoscope inserted through a side access port to capture high-speed images of ammonia flame development, which were used to analyze flame structure, location, and color.Results showed that excessively advanced (ref. –31.5 CAD) or delayed (ref. –11.5 CAD) diesel injection degraded overall performance, due to misalignment between premixed diesel combustion location and ammonia spray, and spray interference.

Source: Applied Thermal Engineering

DOI: 10.1016/j.applthermaleng.2025.129250