Reduction of nitrogen oxides (NO_x) in lean burn and diesel fueled Compression Ignition (CI) engines is one of the major challenges faced by automotive manufacturers. Lean NO_x Trap (LNT) and urea-based Selective Catalytic Reduction (SCR) exhaust after-treatment systems are well established technologies to reduce NO_x emissions. However, each of these technologies has associated advantages and disadvantages for use over a wide range of engine operating conditions. In order to meet future ultra-low NO_x emission norms, the use of both alternative fuels and advanced after-treatment technology may be required. The use of an alcohol fuel such as n-butanol or ethanol in a CI engine can reduce the engine-out NO_x and soot emissions. In CI engines using LNTs for NO_x reduction, the fuel such as diesel is utilized as a reductant for LNT regeneration. In the present work, a detailed evaluation of the performance of long breathing LNT (requiring fewer regenerations than conventional LNT) is carried out using ethanol and n-butanol as the reductants and are compared with diesel as the reductant. For this purpose, a long breathing LNT catalyst is examined on a flow bench under simulated exhaust conditions. The NO_x adsorption period is decoupled from regeneration, and reductant quantities are varied at 3% and 8.5% oxygen concentration. Ethanol and n-butanol are found to be more effective as reductants compared to diesel in terms of NO_x conversion and hydrogen yield during the LNT regeneration at the tested conditions. In order to further understand the impact of using ethanol and n-butanol, the formation of different hydrocarbon species due to reforming on the Diesel Oxidation Catalyst (DOC) and LNT catalyst has been studied as well.
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