Conditions of NO2-production in catalyzed DPF-systems
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Publication date: 2012-09-01
Combustion Engines 2012,150(3)
NO2 is much more toxic than NO. Due to the use of oxidation catalysts and catalytic coatings in the exhaust gas systems in the last decades and due to the use of low sulphur fuels the average NO2-portion in exhaust gases of vehicles increases. Diesel oxidation catalysts (DOC) and Pt-containing DPF-coatings are generally used to support the regeneration of particle filters, which can be a source of strongly increased NO2-production. The present work shows some examples and 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 some research activities on engine dynamometers in the years 2010-2012. In general it can be stated: 1) with a Pt-coated catalyst (DOC), or with catalytic surface filter (CSF) there is a maximum of NO2/ NOx – ratio typically in the exhaust gas temperature range around 350 °C, 2) with higher Pt-content in the coating there is a higher potential for NO2-formation, 3) lower NO2-production appears with: higher spatial velocity, higher S-content in fuel and with DOC/DPF used and/or soot loaded, 4) in some cases of semi active regeneration systems, or with the use of RME conditions with higher NO2-rates can appear.