Plasma Enhanced Selective Catalytic Reduction of NOx in Diesel Exhaust: Test Bench Measurements

The potential of plasma enhanced selective catalytic reduction (PE-SCR) for Diesel-exhaust treatment at temperatures between 60 °C and 180 °C has been investigated in test bench measurements with a 1.9 liter 66 kW VW Passat TDI engine. Non-thermal plasmas were generated by pulsed electrical excitation of dielectric barrier discharge (DBD) modules each having a flow cross section of 9.5 cm² and an electrode length of 26 cm. Monolithic V₂O₅-WO₃/TiO₂-catalysts with cell densities of 150 cpsi and 200 cpsi were used for selective catalytic reduction.

First experiments were performed with a single DBD module and a catalyst volume of 3.5 liters. For temperatures between 100 °C and 160 °C and exhaust gas flow rates below 1200 liters (STP)/min NO_x-reduction rates up to 14 g/h were obtained with an energy cost of about 20 Wh/g NO_x. At larger gas flow rates NO_x-reduction rates decreased even at higher temperatures.

A reactor suitable for larger gas flow rates was obtained applying three DBD modules in parallel and a catalyst with a volume of 6 liters. NO_x-reduction rates of 21 g/h were obtained in a test cycle beginning with a cold start and ending with an exhaust temperature of 140 °C. Energy costs were reduced to about 6.3 Wh/g NO_x.