Abating secondary NH3 and N2O formation on the three-way catalysts: The role of steam

Abstract

Even though water injection has already been proven to reduce NOx formation within the combustion chamber, there is limited research on how this affects the formation of such emissions in three-way catalysts (TWCs). Considering this, the work presented here studies the effect of in-cylinder water injection on the performance of a TWC with respect to the formation of ammonia (NH₃) and nitrous oxide (N₂O). Experimental testing using a gasoline direct injection (GDI) engine fitted with an intake port water injection system was completed. These tests found a clear reduction in NH₃ formation over the TWC when in-cylinder water injection was implemented. The reduction in NH₃ formation, particularly pronounced at richer conditions, is attributed to lower engine-out NO concentrations, which in turn reduces secondary NH₃ formation over the TWC. Lean engine conditions did not produce any NH₃ with or without water injection, due to lower TWC NH₃ selectivity. There was minimal formation of N₂O during this work as the TWC temperature was greater than the typical N₂O formation window. This work highlights the synergistic benefits of reducing secondary emissions during the combustion process and the favourable effect on catalytic technologies through in-cylinder water enrichment.