Study on energy-exergy-emission characteristics of an ammonia-diesel dual-fuel engine under the coupled effects of intake pressure and ammonia energy ratio

Amid growing concerns regarding energy security and environmental climate change, ammonia has attracted significant attention as a carbon-neutral fuel. This study investigated the combustion characteristics and energy-exergy-emission performance of an ammonia-diesel dual-fuel engine under the coupled effects of intake pressure (Pin) and ammonia energy ratio (RAE). A combined methodology of engine bench testing, numerical simulation, and exergy analysis was employed. Key findings reveal that Pin exerts a trade-off effect on the cooperative combustion. Elevated Pin enhances air-fuel mixing, thereby improving diesel combustion, but concurrently reduces flame speed of ammonia. The optimal synergy between ammonia and diesel combustion was achieved at 0.22 MPa Pin and 80 % RAE, yielding a peak indicated thermal efficiency of 47.7 %. Exergy analysis identified chemical reaction irreversibility as the primary source of exergy destruction. It is important to note that reducing exergy loss is not essential for enhancing exergy of work. The exergy of work is regulated by both exergy loss and the exergy-to-work conversion efficiency. With regard to emissions, increases in Pin and RAE resulted in elevated levels of unburned ammonia and NOx, whereas unburned hydrocarbons decreased. Notably, under the optimized condition of 0.22 MPa Pin and 80 % RAE, greenhouse gas emissions exhibited a substantial reduction of 76.2 % compared to conventional diesel operation.