Meeting the EURO VI NOx Emission Legislation using a EURO IV Base Engine and a SCR/ASC/DOC/DPF Configuration in the World Harmonized Transient Cycle

To reach the very strict Euro VI regulations of PM and NOx for heavy-duty trucks, it will be necessary to apply integrated catalytic solutions for removal of both PM and NOx. The most cost-effective solution would be to base the Euro VI system on Euro IV/V base engines, without EGR, and apply a high efficiency aftertreatment system, able to reduce the NOx from the common 7-8 g/kWh down to the Euro VI level at 0.4 g/kWh. The described system consists of a catalytic configuration, where the SCR catalyst is placed directly downstream of the diesel engine followed by an ammonia slip catalyst (ASC) and diesel injection over an oxidation catalyst (DOC) and a catalyzed diesel particulate filter (cDPF). One of the advantages of this system configuration is that, in this way, the SCR catalyst is protected from high temperatures during filter regeneration, and that the SCR catalyst has the fastest heat-up required for good performance in the low-temperature biased test cycle used for testing the Euro VI compliance. Thus the SCR catalyst can be the commonly used vanadium-based type that is already proven technology for Euro IV and Euro V compliance in Europe. The system was tested on an engine test bed using a Euro IV 12-liter truck engine having high engine-out NOx emissions in order to demonstrate the NOx reducing potential of this system configuration. Experiments were performed with the proposed Euro VI testing cycle known as World Harmonized Transient Cycle (WHTC). Different urea dosing strategies were investigated as well as the effect of using different SCR catalyst volumes and thermal management. It was shown that Euro VI NOx emission limits can be achieved over the SCR catalyst on the WHTC cycle with NOx emissions being reduced from 11.5 g/kWh down to 0.4 g/kWh, the SCR catalyst thus achieved ≻95% NOx conversion with less than 10 ppm NH3 or N2O slip. This means that the system can be used on today's engines without applying EGR or other engine measures to reduce the NOx. The system will be the most cost-effective solution as well as having the lowest CO2 emissions among all the alternatives discussed for Euro VI.