Concept Study for NOx Aftertreatment Systems for Europe 2009-01-0632
While the market share for diesel engines for LD vehicles in North America is still negligible, the market share in Europe has grown continuously in the past years and has reached a level of 50% in 2008. Until now, it has been possible to fulfill the limits for nitrogen oxides (NOx) in Europe without using an active NOx aftertreatment system. With the introduction of EU6, most new diesel applications will now require NOx aftertreatment.
One of the possible technologies for the reduction of nitrogen oxides in lean exhaust gas is the NOx storage catalyst (or lean NOx trap, LNT) which is utilized in the current Tier 2 Bin 5/8 diesel systems from Daimler and VW. For heavier applications urea SCR is the preferred technology to meet NOx legislation limits.
For EU5 most of the exhaust aftertreatment systems include a DOC-DPF system in order to meet targets for CO, HC and particles. For many EU 6 applications an active NOx aftertreatment system will be necessary and the fuel economy will be also in focus.
In this paper the two possible NOx-aftertreatment technologies, SCR and LNT will be discussed in terms of their differences and requirements for the Tier 2 and EU 6 legislation. On the bases of model gas and engine bench measurements the development in LNT technology will be presented and discussed. Regarding SCR the optimization of the DPF and SCR technology will be shown.