Ammonia Generation over TWC with NOX Storage Component for Passive SCR NOX Control in Lean Gasoline Engines
Vitaly Prikhodko, Oak Ridge National Laboratory
Vitaly Y. Prikhodko, Josh A. Pihl, James E. Parks and Todd J. Toops
Fuels, Engines and Emissions Research Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (USA)
A prototype three-way catalyst (TWC) with NOX storage component was evaluated for ammonia (NH3) generation on a 2.0-liter BMW lean burn gasoline direct injection engine as a component in a passive ammonia selective catalytic reduction (SCR) system. The passive NH3 SCR system is a potential approach for controlling nitrogen oxides (NOX) emissions from lean burn gasoline engines. In this system, NH3 is generated over a close-coupled TWC during periodic slightly rich engine operation and subsequently stored on an underfloor SCR catalyst. Upon switching to lean, NOx passes through the TWC and is reduced by the stored NH3 on the SCR catalyst.
The TWC with a NOx storage component has shown some advantages compared to a PGM-only TWC. Specifically, adding a NOx storage component to a PGM-based TWC increases total NH3 yield as a result of the stored NOx to NH3 conversion, shortens rich times and decreases fuel consumption associated with NH3 generation. However, these benefits are primarily realized at low to moderate temperatures (300-500 °C) with little to no benefit at higher temperatures (>500 °C). This presentation will discuss engine parameters and control strategies affecting the NH3 generation over a TWC with NOx storage component.