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Aging Effects of Catalytic Converters in Diesel Exhaust Gas Systems and Their Influence on Real Driving NO x Emissions for Urban Buses
Journal Article
02-11-03-0014
ISSN: 1946-391X, e-ISSN: 1946-3928
Sector:
Topic:
Citation:
Moeltner, L., Hohensinner, M., and Schallhart, V., "Aging Effects of Catalytic Converters in Diesel Exhaust Gas Systems and Their Influence on Real Driving NOx Emissions for Urban Buses," SAE Int. J. Commer. Veh. 11(3):171-190, 2018, https://doi.org/10.4271/02-11-03-0014.
Language:
English
Abstract:
The selective catalytic reduction (SCR) of nitrogen oxides seems to be the most
promising technique to meet prospective emission regulations of diesel-driven
commercial vehicles. In the case of developing cost-effective catalytic
converters with comparably high activity, selectivity, and resistance against
aging, ion-exchanged zeolites play a major role. This study presents, firstly, a
brief literature review and subsequently a discussion of an extensive conversion
analysis of exemplary Cu/ and Fe/zeolites, as well as a homogeneous admixture of
both. The aging stages of SCR catalysts deserve particular attention in this
study. In addition, the aging condition of the diesel oxidation catalyst (DOC)
was analyzed, which influences the nitrogen dioxide (NO2) formation,
because the NO2/nitrogen oxides (NOx) ratio upstream from
the SCR converter could be identified as a key factor for low temperature
NOx conversion. Furthermore, it could be proved that a surplus of
NO2 has the potential to suppress the overall efficiency in
NOx conversion. In the final step of this investigation, the data
gained during the conversion analysis were used as input parameters for a
numerical model. This previously published simulation model was applied to
predictively determine NOx emissions for one representative public
bus route, for all investigated configurations of SCR catalysts and DOCs in
different aging stages. It could be shown that an exhaust gas system in a
moderate aging stage has the potential to deliver lower NOx emissions
than its fresh equivalent. The reason for this could be a more favorable
NO2/NOx ratio caused by an aged DOC compared to a
fresh oxidation catalyst, which overcompensates for the losses in activity of
aged SCR converters, particularly at low temperatures.