Experimental Study of Urea SCR Catalyst for Diesel Engine NO x Abatement

This paper comparatively describes the studies conducted and the experiments performed on Diesel engines offer greater advantages than gasoline engines, such as higher efficiency, higher fuel economy and lower CO 2 emissions; however, as regards engine emissions, the abatement technique applied to the gasoline engine (three-way catalyst) is not effective in the case of the diesel engine, as it is difficult to remove the nitrogen oxides (NO x ) from the oxidizing diesel exhaust gas. Nitrogen oxides is considered a contradictory pollutant: on the one hand, in diesel-engines combustion process, higher values of the NO x emission generally indicate higher temperatures in the combustion chamber, which leads to increased thermodynamic efficiency and fuel economy; on the other hand, the global environmental problems related to NO x emissions are utterly challenging for humankind: generation of photo-chemical smog and acid rain, ozone layer depletion and global warming. Furthermore, the basic constituents of NO x (NO and NO 2 ) are considered to be toxic; hence a justified concern on air quality arose, which resulted in enforcement of ever more drastic regulations upon these emissions, leading to the introduction in Europe of catalytic reduction upon stationary sources and mobile sources Among the methods aiming at the removal of NO x Although extensive studies on CuZSM5-SCR systems have been conducted, the present paper describes the preparation of the catalyst and the achievement of experiments upon an urea-SCR system, which aims at lowering NO x emissions of a heavy-duty commercial dieselengine; the aforementioned purpose is underlain by the analysis of the influence exercised by different parameters reported in the literature. The main innovation of this research is the finding of a relevant indicator for the NO x conversion according to the operation modes of the vehicle; this indicator, called weighed exhaust gas temperature (WET) predicts the SCR catalyst NO x conversion to the driving cycles of the diesel engine. Experimental part The experiment included the measurement of the urea SCR activity within the exhaust gas from diesel engines, in real operation modes and not in reactors. The steps of the experiment were: catalyst preparation, construction of the SCR system and NO x engine testing