Comparison of diesel single/double/triple injection strategies and early/late compression ignition regimes in an ammonia/diesel dual-fuel engine

The combustion and emission performance of ammonia/diesel dual-fuel (ADDF) engines is critically influenced by the diesel injection strategies and combustion regimes. However, there has been limited research performed on this topic. This paper has systematically compared the diesel single/double/triple injection strategies and the early/late compression ignition regimes, in terms of the heat release pattern, combustion performance, and pollutant emissions. The experiments are carried out on a 1.85 L PFI-DI single-cylinder ADDF engine. It's found that diesel pre-injection strategies can effectively improve the combustion and emission performance of an ADDF engine, whether in the ECI (early compression ignition) or the LCI (late compression ignition) combustion regime. From single to double and triple injection, ITE (indicated thermal efficiency) increases while PPRR (peak pressure rise rate) decreases, indicating smoother and more efficient combustion, and smoke opacity, THC, CO, uNH3 (unburned ammonia), NOx, and N2O emissions are all reduced. Compared to the LCI combustion regime, the ECI combustion regime produces a higher ITE, comparable PPRR, lower smoke opacity, THC, CO, and N2O emissions, and higher NOx emissions with the diesel double/triple injection strategies, but the result is reversed with the diesel single injection strategy. The experimental results indicate directions for the optimization of ADDF combustion.