Experimental Investigation of Combined LNT + SCR Diesel Exhaust Aftertreatment

• Published in: Emission control science and technology (Online) Vol. 1; no. 2; pp. 167 - 182
• Main Authors: Wittka, Thomas, Holderbaum, Bastian, Dittmann, Peter, Pischinger, Stefan
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.05.2015; Springer Nature B.V
• Subjects: Ammonia; Carbon dioxide; Carbon dioxide emissions; Catalysts; Chemical reduction; Conversion; Diesel engines; Diesel fuels; Earth and Environmental Science; Earth Sciences; Engine tests; Environmental Science and Engineering; Exhaust systems; Fuel consumption; Industrial Chemistry/Chemical Engineering; Nitrogen oxides; Reforming; Regeneration; Selective catalytic reduction; Steady state; Surfaces and Interfaces; Thin Films; Urea; NO; LNT; SCR; Diesel reformer; NH; formation; LNT + SCR
• ISSN: 2199-3629; 2199-3637
• DOI: 10.1007/s40825-015-0012-0

In the present work, an exhaust aftertreatment system combining lean NO X trap (LNT) plus exhaust bypass, passive selective catalytic reduction catalyst (SCR) and engine-independent LNT reductant supply by onboard exhaust fuel reforming was developed. Further, it was experimentally investigated in steady-state operation on an engine test bench and on road in a demonstrator vehicle. The intrinsic NH 3 formation during the LNT regeneration was intensively studied as one key function for passive SCR without active urea dosing. LNT regeneration duration and temperature are the most significant parameters for NH 3 emission. In steady-state operation, the passive SCR could be forced to a contribution to the total NO X conversion of up to 35 %. At 170 °C, 50 % steady-state total NO X conversion was achieved, and at 250 °C and a fuel consumption penalty of <2 %, complete NO X conversion could be demonstrated. Compared to conventional LNT operation with frequent engine enrichment, the engine-independent LNT regeneration with reformate gas is energetically more efficient and advantageous regarding CO 2 emissions. Additionally, by shifting NO X reduction from LNT to SCR, fuel consumption penalty due to LNT enrichment can be reduced. Finally, the combination system was demonstrated in transient test cycles and by real driving operation on road.