Since the implementation of Euro 6 in September 2014, diesel engines are facing another drastic reduction of NOx emission limits from 180 to only 80 mg/km during NEDC and real driving emissions (RDE) are going to be monitored until limit values are enforced from September 2017. Considering also long term CO2 targets of 95 g/km beyond 2020, diesel engines must become cleaner and more efficient. However, there is a tradeoff between NOx and CO2 and, naturally, engine developers choose lower CO2 because NOx can be reduced by additional devices such as EGR or a catalytic converter. Lower CO2 engine calibration, unfortunately, leads to lower exhaust gas temperatures, which delays the activation of the catalytic converter. In order to overcome both problems, higher NOx engine out emission and lower exhaust gas temperatures, new aftertreatment systems will incorporate close-coupled DeNOx systems. Since the majority of current diesel emission control systems feature a close-coupled DOC+DPF converter, it seems to be a natural evolutionary step for NOx emission reduction to integrate the SCR catalyst technology onto the DPF.
A high SCR catalyst loading will be required to have high conversion efficiency, however, higher loading amount causes high pressure drop for conventional DPF materials. Therefore a high porosity DPF design has been developed to overcome the tradeoff between high pressure drop, high washcoat loadings, and sufficient soot filtration efficiency. This paper will describe the advanced high porosity DPF for an integrated SCR concept including test results and future outlook.
