Influence of Exhaust Pipe Structure on Urea-Related Deposits in Diesel Engine SCR System

Abstract

To solve the problem of deposits formation in the exhaust pipe of a diesel engine SCR (selective catalytic reduction) system, the CFD (computational fluid dynamics) model of the exhaust pipe was established to research the influence of structural parameters on the wall film from the perspective of optimizing the flow field. The solid structure was simplified in the modeling without considering the flow fields inside the catalytic converter. The simulation conditions were obtained through bench tests and vehicle real road tests. The spray and temperature simulation results were verified via high-speed photographic and bench tests under three typical operating conditions. The conclusions are as follows: compared to the case with a step surface, wall film mass was reduced by 48.27~55.4% when the exhaust pipe had no step surface; compared to the case where the nozzle orifices were located 10 mm off center axis, wall film mass reduced by 2.83~6.38% when the nozzle orifices located in the center axis of exhaust pipe; compared to the case of 110 mm, wall film mass reduced by 21.3~24.72% when the exhaust pipe diameter was 100 mm. To eliminate the potential problem of deposit formation inside the catalytic converter, the nozzle should be arranged close to the engine turbine, and there should be no abrupt cross-section downstream of the exhaust pipe.