The effects of traditional diesel aftertreatment systems on gaseous emission reductions from ammonia/diesel dual-fuel engine.

Ammonia used in existing diesel engines holds great decarbonization potential. However, determining whether ammonia can replace diesel requires considering its emissions (nitrous oxide (N2O), NH3, and water) and the compatibility and performance of aftertreatment systems. This study evaluates the impact of traditional diesel aftertreatment systems, specifically the combination of diesel oxidation catalyst (DOC) and selective catalytic reduction (SCR), on reducing complex gaseous emissions including nitrogen-based pollutants and greenhouse gases (GHGs) in ammonia/diesel dual-fuel engines, a topic that has been insufficiently addressed in existing studies but is essential for identifying key emission characteristics and guiding the design of specialized aftertreatment systems. Results show that DOC contributes to the oxidation of unburned hydrocarbons and carbon monoxide and, under elevated temperatures, can also facilitate partial removal of NH3, despite this not being its primary design function. In pure diesel operation, the DOC increases the ratio of nitrogen dioxide (NO2) to total nitrogen oxides (NOx), while in ammonia/diesel operation, DOC suppresses NO2 formation and promotes N2O generation due to interactions between NH3 and NO2. Furthermore, in dual-fuel mode, SCR achieves nearly complete NOx conversion and further reduces both NH3 and N2O emissions, suggesting that a specially tailored SCR could help reduce N2O emissions more effectively. These findings reveal critical emission behaviors and interactions, highlighting that while traditional DOC + SCR systems show partial adaptability to ammonia/diesel operation, further optimization, including unit-level improvements and system-level configuration adjustments, holds promise for meeting future emission standards. It is noteworthy that this study systematically investigates the influence mechanisms of DOC and SCR on pollutant emissions and conversion processes of ammonia/diesel dual-fuel engine under different speeds for the first time. The experimental results can provide fundamental data for the optimization of aftertreatment systems, thereby enabling ammonia fuel to fully exert its decarbonization potential in the field of internal combustion engines.