Vol 77 No 4 77415

Abstract

To balance NO_X emissions and performance in ammonia-fueled marine engines, this study investigates exhaust gas recirculation (EGR) effects on combustion, performance, and emissions, and proposes a full-load EGR strategy. Based on a validated CFD model of a methanol/diesel dual-fuel engine and an ammonia spray model, an ammonia/diesel dual-fuel engine model was developed. Simulations at four typical loads were conducted with various EGR rates. Results show that higher EGR slows ammonia combustion, prolongs combustion duration, intensifies after-burning, and increases ammonia emissions. Heat release rate is load-dependent, with peaks regulated by EGR. Engine performance varies with load: the gross indicated mean effective pressure (IMEP_g) increases with EGR at low-to-medium loads, but first rises then decreases at high loads. EGR effectively reduces NO_X emissions at all loads, with maximum reduction ranging from 71.5 % to 90.2 %. Fuel NO_X shows higher sensitivity to EGR than thermal NO_X. However, EGR also increases ammonia and N₂O emissions—marginal at low loads but significant at medium-to-high loads, with a distinct surge threshold. Recommended EGR rates are 50 %, 40 %, 30 %, and 10 % at 25 %, 50 %, 75 %, and 100 % loads, respectively. This strategy enables compliance with IMO Tier III NO_X regulations, achieves low ammonia and N₂O emissions, and improves IMEP_g.