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This paper describes the coupling of a 1D engine simulation code (Ricardo WAVE) to a 3D CFD code (STAR-CD) to study the flow behaviour inside a Close-Coupled Catalytic converter (CCC). A SI engine was modelled in WAVE and the CCC modelled in STAR-CD. The predictions of the stand-alone WAVE model were validated against engine bed tests before the coupled 1D/3D simulations were performed at 3000 RPM WOT for both motored and firing conditions. The predicted exhaust velocities downstream of the catalyst monolith in the coupled simulations matched fairly well with Laser Doppler Anemometry (LDA) measurements.

With the increasingly widespread use of catalytic converters for meeting exhaust emission regulations, considerable attention is currently being directed towards improving their performance. Experimental analysis is costly and time consuming. A desirable alternative would be a computational model based on established numerical techniques. To this end a transient three-dimensional model has been developed using a commercial CFD code. It simulates the fluid dynamics, chemical kinetics and heat and mass transfer that takes place in catalysts and their associated assembly. As a result the model can be used to predict important performance parameters such as conversion efficiency, incurred pressure drop and the thermal environment.

This paper investigates the flow maldistribution across the monolith of an axisymmetric catalyst assembly fitted to a pulsating flow test rig. Approximately sinusoidal inlet pulse shapes with relatively low peak/mean ratio were applied to the assembly with different amplitudes and frequencies. The inlet and outlet velocities were measured using Hot Wire Anemometry. Experimental results were compared with a previous study, which used inlet pulse shapes with relatively high peak/mean ratios. It is shown that (i) the flow is more maldistributed with increase in mass flow rate, (ii) the flow is in general more uniformly distributed with increase in pulsation frequency, and (iii) the degree of flow maldistribution is largely influenced by the different inlet velocity pulse shapes. Transient CFD simulations were also performed for the inlet pulse shapes used in both studies and simulations were compared with the experimental data.

Heat transfer in automotive exhaust catalyst systems with metallic substrates is modeled using a commercial Computational Fluid Dynamics (CFD) code. The substrate channels are modeled by approximating their geometry as both triangular and sinusoidal. The effect of the packing arrangement of adjacent channels is investigated. The effect of the angle of the flow entering ceramic substrate monoliths on the localised heat transfer is also studied and the related implications for catalyst aging and light off deduced.