One-dimension modeling study on emissions control strategy for ammonia-diesel dual-fuel engines aftertreatment system

Ammonia-diesel dual-fuel engines have garnered increasing interests due to their potential for low-carbon emissions. However, under high ammonia energy ratio conditions, they face the challenge of elevated unburned ammonia (NH ₃ ) and nitrogen oxides (NO _x ) emissions. This study developed an “upstream selective catalytic reduction (SCR) + ammonia oxidation catalyst (AOC) + downstream SCR” aftertreatment system, which aimed at simultaneously mitigating both unburned ammonia and NO _x emissions. The upstream SCR primarily reduces NO _x formation, while AOC controls excessive NH ₃ . The downstream SCR is incorporated to further reduce NO _x generated by the AOC. The system was evaluated using a one-dimension transient model based on validated catalyst kinetics and measured engine-out conditions. The results indicate that the proposed strategy, featuring an upstream SCR stage, can reduce the required supplemental ammonia injection and decrease N ₂ O emissions. The one-stage configuration (SCR0 + AOC1 + SCR1) exhibited the most favorable overall emissions control performance. Parametric analyses showed that the 300°C temperature condition led to higher NH ₃ slip from SCR0 and higher predicted N ₂ O formation in AOC1. In addition, the mass flow rate mainly affects the transient response, and lower flow rates are more favorable for reducing residual NO _x and transient emission peaks.