Experimental study of the selective catalytic reduction after-treatment for the exhaust emission of a diesel engine

In this experimental study, the after-treatment characteristics of urea-based selective catalytic reduction (urea-SCR) in a diesel engine was investigated at a low engine exhaust temperature (250 degrees C). This represented the idle state of diesel vehicles during road congestion. Detailed experimental work was performed on a heavy-duty diesel engine test bench under the World Harmonized Transient Cycle. The influence of the ammonia/nitrogen ratio was first investigated using vanadium-based SCR (V-SCR) catalyst. When the ammonia/nitrogen ratio was 1.0, the influences of space velocity on the after-treatment characteristics of two different configurations of V-SCR catalysts were investigated in terms of NOx emission, NH3 slip and NOx conversion efficiency. Small SV resulted in reduction of the NH3 slip and the coated-type catalyst indicated more NH3 slip than the extruded-type catalyst at equal catalyst dimensions. It was concluded that the extruded-type V-SCR catalyst showed better operating characteristics than did the coated-type V-SCR catalyst.