Modem diesel engines have improved engine fuel economy and significantly reduced nitrogen oxides (NOx) and particulate matter (PM) emissions achieved by advances in both combustion and exhaust aftertreatment technologies. Recently, it has been shown that the vehicle emissions can be further improved by several catalytic systems including fuel reformers and aftertreatment systems, such as the Lean NOx Trap (LNT). This NOx removal system, called LNT, absorbs NOx under lean exhaust gas conditions and releases NOx under rich conditions. This technology can provide high NOx conversion efficiency, but the right amount of reducing agent should be supplied into the catalytic converter under appropriate conditions. In this work, plasma reformer was used to supply a hydrogen-enriched gas as a NOx reductant. The plasma reforming is one of the most promising on-board reforming technologies, which allows reformates containing H-2 and CO to feed for LNT catalyst efficiently. Partial oxidation is induced by plasma in the fuel reformer and diesel fuel is converted into a hydrogen-enriched gas. The supplying strategy was focused on the maximization of NOx reduction efficiency varying both the total amount of hydrogen-enriched reformate and the ratio of oxygen molecules to in the reformer air-fuel mixture prior to processing at a fixed engine operating condition. The effect of exhaust gas temperature was also studied, The NOx reduction efficiency is closely connected to the amount of supplied fuel to the plasma reformer and the ratio of fuel/air feed rate. The LNT can reduce NOx efficiently with only a 2.6% fuel penalty. Crown Copyright (c) 2009 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu. All rights reserved.