Performance evaluation of a urea-water selective catalytic reduction (SCR) for controlling the exhaust emissions from a diesel engine

An integrated performance analysis of a vanadium-based urea-SCR system used for the reduction of exhaust emissions from a diesel engine was carried out. The engine was run on an AC electrical dynamometer in accordance with an 8-mode steady-state cycle. The number-size distribution of particles and carbonyls was analyzed using an electrical low pressure impactor (ELPI) and high performance liquid chromatography (HPLC), respectively. It was found that conversion and/or reduction efficiency (RE) of the SCR were highly affected by the catalyst temperature and space velocity (SV). The NO_x pollutants were greatly reduced with the decrease in SV within the load modes of cyclic speeds. The SCR exhibited an RE of more than 50% for NO_x emissions at 321-435°C, while the maximum RE was 80.5%. Total hydrocarbon (HC) emissions were also increased with the decrease in load for both cyclic speeds, while the RE varied from 38.7% to 71.1%. Significant increases in upstream and downstream carbon monoxide (CO) emissions were noticed with the decrease in engine load. Reluctance to reduction or a negative RE, ranging from 1.5% to 72%, was observed for CO emissions with the SCR. In addition, nanoparticles were greatly reduced, whereas particles of the size range 57-255 nm showed less reduction. The number-size distribution of particles was shifted from smaller to larger sizes with the SCR retrofit. Furthermore, a substantial conversion of up to 55.3% was obtained in the case of carbonyl emissions. The maximum RE was 58%, 67%, 50%, and 64% for formaldehyde, acetaldehyde, acrolein and acetone, and propionaldehyde, respectively.