The coupling effects of split diesel injection multi-variables on combustion and emission characteristics of an ammonia/diesel dual-fuel engine

Pre-injection is an effective means of improving combustion and thermal efficiency while reducing uNH 3 and N 2 O emissions in ammonia/diesel dual-fuel engines. However, the coupling effects of the multiple controlling variables such as PIR (pre-injection ratio), PIT (pre-injection timing), MIT (main injection timing), and diesel injection pressure on combustion and emissions remain to be investigated. To this end, experiments are conducted at 1200 r/min, IMEP 12 bar, and AEF (ammonia energy fraction) 50%, and the ammonia is injected into the intake manifold at -360 °CA ATDC. Results show that there are two ignition modes, called pre-injection-controlled ignition and main-injection-controlled ignition, depending on PIR and PIT. As PIR increases, ITE (indicated thermal efficiency) first increases and then decreases, and for different PIRs, delayed PIT is always good for ITE. When PIR is 60% and PIT is −50 °CA ATDC, ITE peaks at 50.7%. In terms of emissions, the pre-injected diesel mixes with the ammonia/air charge, increasing the chemical reactivity of the premixed gas and resulting in a significant reduction in uNH 3 and N 2 O emissions. However, due to the wall-wetting and dilution effect, the pre-injected diesel is difficult to burn completely, resulting in increased THC and CO emissions. The variation rule of ITE is identical to that of N 2 O and uNH 3 emissions, but opposite to that of NOx emissions.