To fullfill continually decreasing future emission standards, combined exhaust aftertreatment systems consisting of different catalyst technologies and particulate filter are necessary. Over the lifetime of such systems, catalytic performance of all individual components decreases due to thermal aging and poisoning effects. This has to be taken into account during system design as well as during the development of the operating and control strategies, to ensure long term system performance. Especially in commercial vehicle applications, this is an important issue because of long vehicle lifetimes in terms of mileage.
In combined aftertreatment systems, the thermal histories of the catalytic components are linked and influence each other. Especially in systems containing a diesel particulate filter, thermal aging of all components is mainly dominated by the active DPF regeneration strategy for the filter. During aftertreatment system development, temperature measurement data was gathered to investigate temperature profiles in different catalysts and filter during active DPF regeneration procedures, studying the influence of different regeneration strategies and operating conditions. This data was statistically evaluated and aging profiles for the different components were deduced. As thermal aging is largely dominated by the maximum temperatures inside the components, time reduced aging procedures could be developed focusing on the maximum temperature exposure.
During test bench investigations on combined aftertreatment systems, components were aged according to the developed procedures. The influence of thermal aging on catalytic conversion was investigated, on individual components and in combined systems.