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Modeling Species Inhibition of NO Oxidation in Urea-SCR Catalysts for Diesel Engine NOx Control

[+] Author Affiliations
Maruthi Devarakonda, Russell Tonkyn, Diana Tran, Jong Lee, Darrell Herling

Pacific Northwest National Lab, Richland, WA

Paper No. ICEF2010-35054, pp. 491-498; 8 pages
  • ASME 2010 Internal Combustion Engine Division Fall Technical Conference
  • ASME 2010 Internal Combustion Engine Division Fall Technical Conference
  • San Antonio, Texas, USA, September 12–15, 2010
  • Conference Sponsors: Internal Combustion Engine Division
  • ISBN: 978-0-7918-4944-6 | eISBN: 978-0-7918-3882-2
  • Copyright © 2010 by ASME


Urea-selective catalytic reduction (SCR) catalysts are regarded as the leading NOx aftertreatment technology to meet the 2010 NOx emission standards for on-highway vehicles running on heavy-duty diesel engines. However, issues such as low NOx conversion at low temperature conditions still exist due to various factors, including incomplete urea thermolysis, inhibition of SCR reactions by hydrocarbons and H2 O. We have observed a noticeable reduction in the standard SCR reaction efficiency at low temperature with increasing water content. We observed a similar effect when hydrocarbons are present in the stream. This effect is absent under fast SCR conditions where NO ∼ NO2 in the feed gas. As a first step in understanding the effects of such inhibition on SCR reaction steps, kinetic models that predict the inhibition behavior of H2 O and hydrocarbons on NO oxidation are presented in the paper. A one-dimensional SCR model was developed based on conservation of species equations and was coded as a C-language S-function and implemented in Matlab/Simulink environment. NO oxidation and NO2 dissociation kinetics were defined as a function of the respective adsorbate’s storage in the SCR catalyst. The corresponding kinetic models were then validated on temperature ramp tests that showed good match with the test data.

Copyright © 2010 by ASME



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