F2008-01-026
SCR System with Integrated Continuously Particle Reduction (SCRi(TM)): Next Generation of Nox Treatment and also Suitable for Retrofit
Due to the upcoming legislation for a further limitation of NOx emissions including the newly introduced air quality level for NO2 the automotive industry is developing new diesel engines with optimised exhaust gas recirculation and combustion processes. At the same time, continous reduction of PM-mass limit in combination with PM-number limitations will lead to combined aftertreatment systems of particle filters and SCR catalysts. The proposed exhaust systems consist usually of an oxidation catalyst, a DPF followed by the unit for Urea injection, a mixing device and the SCR catalyst itself. Todays Diesel Particulate Filters can only be thermally regenerated by increasing the exhaust temperature to above 600°C. This leads due to the exothermal reaction during the regeneration to an unnecessary high degree of aging of the following SCR catalyst, which can only be balanced by a new kind of washcoat development including more expensive coating materials. In addition, the need for 2 separate subsystems for NOx- and PM-reduction raises severe package constraints while the periodic pressure drop increase of the DPF in combination with the energy needed for the regeneration increases the fuel consumption and therefore the CO2-emission of the system. The herewith described integrated SCR system (SCRi (TM)) uses the continuously working PM Metalit (R), located not in front of the SCR part of the exhaust system, but integrated into it after the urea injection. At this position the filter not only oxidizes the particulate matters with the NO2 created by the DOC, but is also capable to mix the exhaust gas with the reduction agent due to his mixing structure. A thinly Hydrolysis coating supports the building of Ammonia and avoids any deposits on the surface. Since the particles are reduced continuously without any thermally induced process the SCR coating can be optimised for low temperature levels. The excellent efficiency of the SCRi (TM) system is supported by SCR catalysts which are designed with longitudinal and radial open structures to contribute to the design targets of such systems: efficiency, costs and packaging space. In this work the design of the system components and emission results are discussed. A special focus is drawn on the emission durability and the function of the PM Metalit (R) as hydrolysis catalyst.
Poster presentation: Mobility concepts