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.
