NOx Reduction Potential of V-SCR Catalyst in SCR/DOC/DPF Configuration Targeting Euro VI Limits from High Engine NOx Levels

To reach the EPA ‘10 and Euro VI strict 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 described system consists of an alternative catalytic configuration where the SCR catalyst is placed downstream of the diesel engine followed by diesel injection over an oxidation catalyst (DOC) and a catalysed diesel particulate filter (cDPF). One of the advantages of this system configuration is that the SCR catalyst in this way is protected from high temperatures during filter regeneration and that the SCR catalyst has the fastest heat up required for good performance in cold test cycles. The SCR catalyst can therefore be of a standard V-based type that is already proven technology for Euro IV and Euro V compliance in Europe. Another advantage is that the DOC and cDPF act as clean-up catalysts for any possible ammonia slip from the SCR catalyst. The system was tested on an engine test bed using a Euro II 12-l truck engine having high engine-out NOx emissions in order to demonstrate the NOx reducing potential of this system configuration. Experiments were performed with transient cycles and various urea dosing strategies. It was shown that Euro VI NOx emission limits could be achieved over the SCR catalyst on the ETC cycle with NOx emissions being reduced from 10 g/kWh down to below 0.4 g/kWh, the SCR catalyst thus achieving >95% NOx conversion.