Development and Investigation of Diesel Fuel Reformer for LNT Regeneration

Abstract

In the present work, an exhaust after treatment system combining Lean NO X Trap (LNT) plus exhaust bypass, passive catalyst for selective catalytic reduction (SCR), and engine independent LNT reductant supply by on-board exhaust fuel reforming was developed. To demonstrate the mobile production of synthesis gas with focus on automotive application, an outline fuel reformer has been developed which is predominantly operated using engine exhaust gas. The reformer concept and design are described in detail. The reaction process is a variable superposition of exothermic catalyzed partial oxidation (CPOx) and endothermic steam (steam reforming (SR)) and CO 2 (dry reforming (DR)) reformation. This strong dependence of the reformer operation on the engine's exhaust gas composition was intensively studied by steady-state experiments on an engine test bench. Besides operating the reformer within thermal limits, the control strategy is designed in terms of low hydrocarbon emissions and high energetic efficiency. In comparison to pure CPOx, exhaust gas reforming showed favorable thermal behavior as well as efficiency benefits of up to 20 % due to the endothermic part of the reaction. The reformer could achieve a reductant yield of above 50 %, whereas only 10-25 % for medium engine load and up to 45 % for high engine load could be realized by engine-rich operation. For the investigated diesel engine-rich calibrations, the undesired HC emission reached a percentage share of the reductants of 15-55 %, whereas the reformer showed only up to 12 %.