Effects of Pre-Injection Strategy on Combustion Characteristics of Ammonia/Diesel Dual-Fuel Compression Ignition Mode

As a zero-carbon clean fuel, the use of ammonia in internal combustion engines is of great significance to achieve the "two-carbon" goal. This paper investigates the effect of the ammonia energy ratio and diesel injection timing on combustion and emissions. Based on Computational fluid dynamics (CFD) and the simulation analysis software, Converge, three-dimensional modeling is carried out for a direct injection diesel engine with a Compression Ignition (CI) mode. Under the initial full-load conditions of 1200 r/min, the engine simulation was calculated. The results show that the peak cylinder pressure increases and then decreases as the ammonia energy ratio increases, the ignition delay time increases, and the CO2 and N2O emissions decrease. With pre-injection, the peak cylinder pressure increases at the same energy ratio and the combustion stage advances, resulting in improved indicated thermal efficiency. In comparison to the pure diesel mode, the pre-injection strategy shows an obvious reduction in greenhouse gas (GHG) emissions with a decrease of 40.9% by adjusting the injection timing, while the single injection strategy shows a reduction of 36.5%. The soot emission peak occurs in the diesel-only mode with 98.13% and 99.6% reductions in emissions under single and pre-injection, respectively. The ammonia-diesel dual-fuel (ADDF) engine with an ammonia-to-energy ratio of 70% and optimized ammonia and diesel injection timing significantly reduces the NH3 emissions and GHG emissions by 69.34%.