Experimental Study of Urea SCR Catalyst for Diesel Engine NO_x Abatement

摘要

This paper comparatively describes the studies conducted and the experiments performed on CuZSM5-urea-SCR systems, with a view to lowering NO emissions of heavy-duty commercial diesel engines. The innovative outcome of this research is the finding of a relevant indicator forNO_x conversion, depending on the operation modes of the vehicles; this indicator, denominated weighted exhaust gas temperature (WET), predicts NO_x conversion in the SCR catalyst. A copper ion-exchanged ZSM5 zeolite was prepared, using an aqueous solution of Cu(CH3OO)2 which was deposed on a metallic support of the urea-SCR system. The SCR treatment applied to the exhaust gas emitted by 4-litre heavy-duty diesel engines experimentally revealed a NO_x reduction of 70%, at constant engine speeds and increasing loads, and of and 58.3%, in European Stationary Cycle. Following thorough analysis of the previous research on controlled feed gas reactors and diesel engines, with focus on the differences between NO conversions in terms of exhaust gas temperature, space velocity, water content, oxygen content, fuel sulphur content, an indicator of NO conversion was proposed, based on the average temperature of the emission test cycle. A practical result of the research work consisted in the compliance of NO_x emission from the tested diesel engine with the standard Euro IV.