Abstract
Keywords:
Diesel aftertreatment, SCR, NOx reduction, heat management
Abstract:
Compared to the NOx adsorber catalyst, the SCR technology has especially advantages with regard to high-temperature NOx-conversion and is less sensitive with regard to ageing and sulphur poisoning. On the other hand some specific challenges of the SCR technology have to be considered carefully for future applications. Most important within this context are the availability of a suitable reductant, the packaging in the vehicle, lowtemperature NOx conversion efficiency and the requirement for sophisticated control algorithms in order to achieve high NOx conversion rates while maintaining minimum ammonia slip. Within this paper the complex interacting processes of NOx conversion and ammonia storage on the SCR catalyst will be pointed out and appropriate approaches for control of a SCR system will be described. Furthermore the problem of lowtemperature activity, which is also closely related to the package boundary conditions, will be addressed and suitable countermeasures such as heating strategies will be described. Last but not least an alternative SCR system approach based on ammonia carbamate will be presented and the specific advantages of such a system concept especially for passenger car applications will be pointed out.