A study on N2O formation mechanism and its reduction in a urea SCR system employed in a di diesel engine

Wataru Matsui, Tetsu Suzuki, Yasuo Ohta, Soichiro Ito, Yo Tanaka, Yutaka Kikuchi, Yasuhiro Daisho, Hisakazu Suzuki, Hajime Ishii

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1 Citation (Scopus)


N2O is known to have a significantly high global warming potential. We measured N2O emissions in engine-bench tests by changing the NO/NH3 ratio and exhaust gas temperature at the oxidation catalyst inlet in a heavy-duty diesel engine equipped with a urea SCR (selective catalytic reduction) system. The results showed that the peak N 2O production ratio occurred at an exhaust gas temperature of around 200°C and the maximum value was 84%. Moreover, the N2O production ratio increased with increasing NO/NH3. Thus, we concluded that N2O is produced via the NO branching reaction. Based on our results, two methods were proposed to decrease N2O formation. At low temperatures ∼200°C, NO should be reduced by controlling diesel combustion to lower the contribution of NO to N2O production. This is essential because the SCR system cannot reduce NOx at low temperatures. At temperatures higher than 200°C, it is necessary to reduce NH3 slip because N2O is produced via reactions involving NO generated by NH3 oxidation and NH3 slip. To investigate methods to reduce NH3 slip from the SCR catalyst, we conducted chemical kinetics simulations using Boost v5.1 by AVL. The main parameters governing NH 3 slip were the urea equivalence ratio (UER) and SCR catalyst volume. It is recommended that NH3 emitted from the tailpipe should be lower than 10 ppm. We identified the optimal UER and volume ratio (defined as SCR catalyst volume to engine displacement ratio) at different temperatures to ensure that catalyst outlet NH3 emissions were less than 10 ppm. At 200°C, the results showed that decreasing the UER was sufficient to reduce NH3 slip. At 400°C, we also considered a 90% NOx reduction efficiency. We demonstrated that an increase in the volume ratio was required to sufficiently reduce NH3 slip at high temperatures.

Original languageEnglish
Title of host publicationSAE Technical Papers
Publication statusPublished - 2012
EventSAE 2012 International Powertrains, Fuels and Lubricants Meeting, FFL 2012 - Malmo
Duration: 2012 Sep 182012 Sep 20


OtherSAE 2012 International Powertrains, Fuels and Lubricants Meeting, FFL 2012

ASJC Scopus subject areas

  • Automotive Engineering
  • Safety, Risk, Reliability and Quality
  • Pollution
  • Industrial and Manufacturing Engineering


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