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Control of N2O emissions is a significant challenge for manufacturers of HDD On-Road engines and vehicles due to requirements for NOx control and Green House Gas (GHG) Phases I & II requirements. OEMs continually strive to improve BSFE which often results in increased engine out NOx (EO NOx) emissions. Consequently, the necessity for higher NOx conversions results in increased N2O emissions over traditional SCR and SCR+ASC catalysts systems [1]. This study explores methods to improve NOx conversion while reducing the SCR contribution of N2O across the exhaust after treatment systems. For example, combinations of two traditional SCR catalysts, one Iron based and another Copper based, can be utilized at various proportions by volume to optimize their SCR efficiency while minimizing the N2O emissions. Results show that a proper combination of catalysts volume can significantly reduce N2O levels while simultaneously reaching the highest levels of NOx performance achieved in the study.

FTP emissions were measured on a 2009MY, 4 cylinder 2.4L Malibu PZEV vehicle with 3 and 33 ppm sulfur fuel. The exhaust system employed one close-coupled and one under floor converter. FTP evaluations with Phase-II certification fuel with 33 ppm sulfur exhibited increasing NOx emissions with subsequent FTP evaluations (NOx creep). In an effort to minimize NOx creep, FTP preparation cycles and low sulfur fuels were investigated. Results indicate that utilizing the US06 cycle in between subsequent FTP's can mitigate NOx creep. FTP evaluations with 3 ppm sulfur fuel exhibited no NOx creep regardless of FTP preparation cycle and yielded overall lower NOx emissions.