Effects of Fuel Type on Lean NOx Aftertreatment by Dual SCR (HC-SCR + NH3-SCR)

Galen  Fisher, University of Michigan

Galen B. Fisher*, Craig L. DiMaggio, Dan Trytko, Ken M. Rahmoeller,
and Mark Sellnau
Delphi Advanced Powertrain
Auburn Hills, MI 48326

Low-cost NOx aftertreatment is one of the main challenges facing high efficiency diesel engines and gasoline engines operating under lean conditions. In addition, the global demand for alternative fuels has sparked a renewed interest in catalyst systems that can effectively reduce NOx emissions from engines using a range of normal and bio-based HC fuels. Until recently, most approaches have relied on precious metals to either store NOx and subsequently release and reduce under rich conditions (lean NOx traps), or they use NH3-SCR catalysts with urea injection to reduce the NOx under lean conditions. However, we have introduced an aftertreatment system using Ag-based HC-SCR followed by NH3-SCR (Dual SCR) with testing done in a single-cylinder engine test cell with the Dual SCR aftertreatment system. A range of fuels, including E85 and diesel, with modest C/N ratios were used as reductants. This non-urea lean NOx reduction system has, at a fraction of the catalyst cost of a precious metal system, shown NOx reduction activity between 80% to 95% over a broad range of temperature and feed conditions, using several fossil and bio-based fuels injected into the exhaust. Although H2 is useful for enhancing this activity at low temperatures, relatively low concentrations of 0.1% have been used to improve the NOx activity of the catalyst system down to 150 C. Dual SCR technology could be a key enabler for low cost and efficient NOx reduction to help auto manufacturers meet Tier2/Bin5 and Tier2/Bin2 emissions standards.

* Chemical Engineering Department, University of Michigan, Ann Arbor, MI 48109; gbfisher@umich.edu