CFD simulation of particle deposition in exhaust gas treatment systems

Selective catalytic reduction (SCR) is an established technology for treatment of exhaust gases from combustion engines. However, a major drawback of typically used monolithic catalytic converters is their susceptibility regarding high particle loads. Clogging is a critical issue limiting space efficient design and operation time, particularly under high-dust operation from HFO fired large bore Diesel engines. In order to evaluate the clogging risk of exhaust gas treatment systems (EGTS) during the design process, a novel simulation approach for deposit formation has been developed and is presented in this paper. An Eulerian-Lagrangian treatment has been utilised for simulation of the particle-laden exhaust gas flow, where drag, gravitation, buoyancy, turbulent dispersion, Saffman’s lift force as well as Brownian motion are considered as governing particle transport mechanisms. For the modelling of the gas flow (CFD), the monolithic catalyst is represented by a porous media formulation. The grid used for the CFD is extended by a collision subgrid providing more detailed geometry data for particle-wall contact consideration. The sticking probability of an impacting particle is calculated based on an elastic-adhesive contact approach. The simulation procedure has been developed using ANSYS Fluent. The underlying subgrid as wells as the particle-wall contact model have been implemented to the flow solver via multiple User-Defined Functions (UDF). The model development has been accompanied by extensive experimental investigations on a test rig with a 4-stroke single cylinder research engine of type 1VDS18/15-CR. The simulation procedure achieved good agreement with respect to experimental data of particle capture efficiency as well as reduction of open frontal area (OFA).