NOx-Particulate Filter (NPF) vs. NOx Storage Catalyst (NSC): Evaluation of an After-Treatment Concept to Meet Future Diesel Emission Standards

Simultaneous particulate and NOx reduction represent the next step in the reduction of diesel emissions. One of the most promising concepts to achieve this target involves the combination of two technologies already in use in the after-treatment technology: Diesel Particulate Filter and NOx Storage Catalyst. One of the most controversial points is the possibility to integrate these two functions in the same component, the so called NOx Particulate Filter (NPF). The first purpose of this project was to compare NOx Storage Catalysts (NSC) and NPF in terms of overall efficiency, especially in terms of changes of the NOx absorption efficiency over the cross section of the catalyst. The results showed a better behavior of the NPF. Theories concerning the reasons are provided, even if further investigations to fully explain this phenomenon are still necessary. As a second step, the NOx emissions for the NPF were analyzed during a test cycle with simple NOx regeneration (DeNOx) and combined soot and NOx regenerations (DeSoot- DeNOx), showing an overall NOx reduction capability of around 50%. Finally, different strategies to reduce temperature peaks and NOx slip were implemented. The timing of the rich spikes during DeSoot operation was optimized in order to reduce the NOx release.