Passive SCR for lean gasoline NO_X control: Engine-based strategies to minimize fuel penalty associated with catalytic NH₃ generation

Journal Article · Thu Feb 18 00:00:00 EST 2016 · Catalysis Today

DOI:https://doi.org/10.1016/j.cattod.2016.01.026· OSTI ID:1248774

Prikhodko, Vitaly Y. ^[1]; Parks, James E. ^[1]; Pihl, Josh A. ^[1]; Toops, Todd J. ^[1]

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1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Fuels, Engines, and Emissions Research Center

Lean gasoline engines offer greater fuel economy than common stoichiometric gasoline engines. However, excess oxygen prevents the use of the current three-way catalyst (TWC) to control nitrogen oxide (NO_X) emissions in lean exhaust. A passive SCR concept, introduced by General Motors Global R&D, makes use of a TWC that is already onboard to generate NH₃ under slightly rich conditions, which is stored on the downstream SCR. The stored NH₃ is then used to reduce NO_X emissions when the engine switches to lean operation. In this work, the effect of engine parameters, such as air-fuel equivalence ratio and spark timing, on NH₃ generation over a commercial Pd-only TWC with no dedicated oxygen storage component was evaluated on a 2.0-liter BMW lean burn gasoline direct injection engine. NO_X reduction, NH₃ formation, and reductant utilization processes were evaluated, and fuel efficiency was assessed and compared to the stoichiometric engine operation case. We found air-fuel equivalence ratio to be one of the most important parameters in controlling the NH₃ production; however, the rich operation necessary for NH₃ production results in a fuel consumption penalty. The fuel penalty can be minimized by adjusting spark timing to increase rich-phase engine out NO_X emissions and, thereby, NH₃ levels. Additionally, higher engine out NO_X during engine load increase to simulate acceleration resulted in additional fuel savings. Ultimately, a 10% fuel consumption benefit was achieved with the passive SCR approach by optimizing rich air-fuel equivalence ratio and spark timing while also utilizing acceleration load conditions.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Fuels, Engines and Emissions Research Center (FEERC); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). National Transportation Research Center (NTRC)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (EE-3V); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Transportation Office. Vehicle Technologies Office
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1248774
• Alternate ID(s): OSTI ID: 1358896
• Journal Information: Catalysis Today, Vol. 267, Issue C; ISSN 0920-5861
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
Passive SCR
TWC
Lean NOX reduction
NH₃ formation