A Comparative Study of Fresh and Aged Catalytic Converters in Diesel Exhaust Gas Systems and the Impact of NO₂ on the Overall NOₓ Conversion

Authors

V. Schallhart MSc, T. Steiner MSc, PD Dipl.-Ing. Dr.techn. L. Möltner, Management Center Innsbruck;
M. Hohensinner MSc, MSConsulting, Sistrans;
Dipl.-Ing. L. Flicker, Vienna University of Technology

Year

2020

Print Info

Fortschritt-Berichte VDI, Reihe 12, Nr. 813

Summary

The selective catalytic reduction of nitrogen oxide (NO_x) emissions is a promising technique to meet emission regulations of diesel-driven commercial vehicles. Due to the installation position of these catalytic converters downstream of both, the oxidation catalyst and the particulate filter, the relatively long light-off phase after engine startup limits the overall efficiency. Another concern is maintaining the light-off temperature while operation. In particular, the operation of busses with highly transient load profiles involves many phases of idling with low exhaust gas temperatures, which cool down the catalytic converters. This study deals with experimental and numerical investigations of thermal characteristics and NO_x conversion of catalysts for drive cycles of urban busses. The drive cycles were recorded during test rides and cover typical load spectra of regular city traffic, and bus routes with an increased proportion of semi-mountainous areas. A comparative screening of catalysts on an engine test bench delivers input parameters regarding NO_x conversion and properties of the exhaust gas. These data were implemented into a validated numerical model, which is capable of describing the progress of temperature in the exhaust gas system and NO_x conversion. The results demonstrate significant differences in NO_x emissions for the observed drive cycles and zeolite-based catalysts. Furthermore, the influence of the aging of catalysts was analyzed. In summary, the developed method delivers a tool to quickly assess real driving emissions of NO_x and allows the selection of the best-fitting catalyst with respect to the individual range of operation and to the installation order of catalytic converters.