Browse Publications Technical Papers 2013-01-0526

NO 2 -Formation in Diesel Particle Filter Systems 2013-01-0526

NO₂ is much more toxic than NO. The average proportion of NO₂ in exhaust gases of vehicles increases significantly due to the use of oxidation catalysts and catalytic coatings in the exhaust gas systems during the last decades combined with generalization of using low sulfur fuels. Diesel oxidation catalysts (DOC) and Pt-containing DPF coatings are widely used to support the regeneration of particle filters, being a source of strongly increased production of NO₂.
The present work shows some examples and summarizes the experiences in this matter performed at the Laboratories for IC-Engines & Exhaust Emissions Control (AFHB) of the University of Applied Sciences Biel-Bienne, Switzerland, during some research activities on engine dynamometers in the years 2010-2012.
In general it can be stated: - there is a maximum of NO₂/NOx - ratio with Pt-coated catalyst (DOC), or with catalyzed soot filter (CSF), typically when the exhaust gas temperature range is around 350°C; there is even a higher potential for NO₂ formation with higher Pt-content in the coating, - lower NO₂ production appears with higher spatial velocity, higher S content in fuel and with used DOC/DPF and/or when these devices are loaded with soot, - in some cases of semi active regeneration systems (fuel injection upstream of DOC), or with the use of RME conditions with higher NO₂ rates can appear.


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