Browse Publications Technical Papers 2007-01-0321

Diesel NO/NO2/NOX Emissions - New Experiences and Challenges 2007-01-0321

During the VERT *) testing of different DPF systems it was remarked, that the oxidation catalyst converts sometimes a big part of NO to NO2, producing on the one hand a more toxic composition of the exhaust gases and causing on the other hand measuring artefacts, which tend to underestimate of NO2 and NOx by the cold NOx - measurement.
The present work summarizes the experiences in this matter elaborated at the Laboratories for IC-Engines & Exhaust Emissions Control (AFHB) of the University of Applied Sciences Biel-Bienne, Switzerland, during several VERT activities and didactic projects on engine and chassis dynamometers in the years 2000-2006.
In general it can be stated:
  • With a strong oxidation catalyst in the exhaust system the hot NOx-measurement allows to recognize the NOx-values, which are in average of the investigated cases 27% higher, than with cold NOx-measurement,
  • A supplementary use of a Nafionpermeability sample dryer (still in case of a strong catalyst) enables to measure in average 5% higher NOx-values,
  • With a weak catalytic influence in the exhaust system the hot NOx-measurement yields higher values until
  • 3% and the use of Nafion dryer is not necessary,
  • The present configuration of Nafion dryer is not appropriate for transient measurements,
  • With a coated catalyst (Ox.Cat), or with catalytic surface filter (CSF) there is a maximum of NO2 / NOx-ratio typically in the exhaust gas temperature range of 300°C - 350°C,
  • With fuel borne catalyst (FBC), or with noncatalyzed DPF + FBC there is no NO - NO2 conversion, nevertheless FBC can affect (increase) the conversion activity of an Ox.Cat, or DPF in particulary due to the long term deposits,
  • The above tendencies were confirmed on different engines.


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