EU VI legislation for passenger cars and commercial vehicles proposes a reduction of particle number and mass, which has to be implemented in combination with a substantial NOx reduction. In modern engines the ratio between NOx and PM emissions can be modified, for example via EGR, allowing the application of a passively regenerating partial flow filter system in an SCRiR system and simultaneously reducing fuel consumption. This requires very effective compact catalysts that produce little backpressure. SCR in particular demands high activity rates. This paper systematically examined the effectiveness and backpressure potential of substrates with different structures at operating temperatures and established clear advantages for structured substrates: (1) LS structures show a significantly better mass transfer compared to standard substrates. They are more affected by channel flow speeds than any other type. (2) At not too high flow speeds LS structures produce significantly lower backpressure than standard substrates whose basic cell density is twice as high. (3) Maximum CPC, that is, the best ratio between effectiveness and backpressure, is achieved by the LS structures. This is made possible by a high β value at fairly low backpressure. Due to even lower backpressure smaller cell density offers particular advantages, whereas high conversion rates are more easily achieved by the application of higher cell density. The validity of these claims was checked and could be confirmed on an engine test bench using the SCR application. The SCR system had a smaller volume than standard ceramic systems. Using this system, which comprises passively regenerating PM-Metalit substrates of approx. 260 % of the engine capacity for soot aftertreatment and SCR catalysts of 200 % of the engine capacity for NOx aftertreatment, it was possible to demonstrate that EU IV limits could be met reliably. The dosing system was - regardless the 20 % increased dosage volume - not modified during the tests.
SCR and particle exhaust gas aftertreatment systems for heavy-duty EU VI and NRMM stage IV; the future is being scrutinized
SCR- und Partikel-Abgasnachbehandlungssysteme für Heavy Duty EU VI und NRMM Stufe IV; Die Zukunft auf dem Prüfstand
2010
25 Seiten, 13 Bilder, 4 Tabellen, 13 Quellen
Conference paper
English
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