Potential of Advanced, Combined Aftertreatment Systems for Light-Duty Diesel Engines to Meet Upcoming EU and US Emission Regulation

The modern DI-diesel engine represents a valuable platform to achieve worldwide tightened CO₂ standards while meeting future strengthened emission regulations in the EU and the US. Due to the simultaneous, partially contrary legal demands, new integrated and combined systems are required to allow best overall performance within the upcoming legal frames concerning pollutant emission reduction and minimization of CO₂ output. As extended emission relevant areas in the engine map have to be respected in view of RDE and PEMS scenarios in EU, but also facing the LEVIII standards in the US, comprehensive and synchronized technical solutions have to be engineered. Based on furthermore optimized combustion systems with improved combustion efficiency, meaning also lowered exhaust gas temperatures, especially refined and tailored emission control systems are demanded. Besides possible realizations regarding integrated DPF and SCR (SDPF) functionalities on one substrate, also the combination with advanced LNT technology features beneficial aspects. To point out benefits and challenges of combined systems with relatively low complexity a simulative study was performed in this paper. For the European market conventional SCR as well as alternative SDPF concepts have been comparatively investigated for a 2.0L Diesel engine in WLTP cycle. It is shown that SDPF shows an improved thermal behaviour in comparison to the SCR based EAS layout. This is due to lower overall thermal mass within EAS, which leads to increased Nox conversion efficiency. However, a significant amount of required conversion efficiency can only be gained by catalyst heating measures. For the US market the application of a Passive NOx Adsorber (PNA) in combination with conventional SCR was studied for a 3.0L Diesel engine in FTP cycle. The simulation results point out that the PNA is in principle a valuable technology improving the NOx aftertreatment. However, the intended task of the PNA buffering NOx at cold start is only sufficient in case of low initial PNA NOx load at engine start. Therefore a somehow active operation of the PNA is required resulting in increased control logic algorithms and fuel economy penalty.