Regeneration and NOx Conversion for DPF with an Integrated Vanadium SCR Catalyst
For trucks today, the diesel particulate filter (DPF) and SCR catalysts are combined in this sequential order in diesel exhaust systems with the drawback of insufficient temperature for the SCR catalyst during cold start and large volume. The problems can potentially be solved by integrating the SCR catalyst into the particulate filter as one multifunctional unit. For off-road and heavy-duty vehicles applications with fully managed passive NO2-soot regenerations, integration of V-based SCR formulations on the DPF (V-SCRonDPF) represents an attractive solution due to high sulfur resistance accompanied by low-temperature NOx conversion and improved fuel economy. Engine bench tests together with an NO2-active DOC show that it is possible to manage the NO2/NOx ratio so both a high NOx conversion and still a low soot balance point temperature is obtained. The soot balance point is almost unaffected by the fast SCR reaction when urea is introduced. For a full system, Engine → DOC → Urea(inj) → V-SCRonDPF → SCR → ASC → out on a MAN D 26 experimental engine, an NOx emission of 0.23 g/kWh well below the regulation was demonstrated for an off-road NRTC cycle, without any pressure drop increase over the VSCRonDPF and no soot accumulation measured by weight increase.