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Flow maldistribution across automotive exhaust catalysts significantly affects their conversion efficiency. Flow behaviour can be predicted using computational fluid dynamics (CFD). This study investigates the application of CFD to modelling flow in a 2D system consisting of a catalyst monolith downstream of a wide-angled planar diffuser presented with steady flow. Two distinct approaches, porous medium and individual channels, are used to model monoliths of length 27 mm and 100 mm. Flow predictions are compared to particle image velocimetry (PIV) measurements made in the diffuser and hot wire anemometry (HWA) data taken downstream of the monolith. Both simulations compare favourably with PIV measurements, although the models underestimate the degree of mixing in the shear layer at the periphery of the emerging jet. Tangential velocities are predicted well in the central jet region but are overestimated elsewhere, especially at the closest measured distance, 2.5 mm from the monolith.

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.

In aftertreatment system design, flow uniformity is of paramount importance as it affects aftertreatment device conversion efficiency and durability. The major trend of downsizing engines using turbochargers means the effect of the turbine residual swirl on the flow needs to be considered. In this paper, this effect has been investigated experimentally and numerically. A swirling flow rig with a moving-block swirl generator was used to generate swirling flow in a sudden expansion diffuser with a wash-coated diesel oxidation catalyst (DOC) downstream. Hot-wire anemometry (HWA) was used to measure the axial and tangential velocities of the swirling flow upstream of the diffuser expansion and the axial velocity downstream the monolith. With no swirl, the flow in the catalyst monolith is highly non-uniform with maximum velocities near the diffuser axis. At high swirl levels, the flow is also highly nonuniform with the highest velocities near the diffuser wall.

Accumulation of phosphorus in an automotive catalyst is detrimental to catalyst performance, leading to partial or total deactivation. The deactivation model described in this paper utilises CFD to derive a one-dimensional mathematical solution to obtain phosphorus accumulation profiles down the length of a catalyst. The early work of Oh and Cavendish [1] is the basis for this study. A model output, θ, represents the fraction of catalytic surface area that is deactivated. This poisoned fraction is shown to build up locally depending on exposure time to phosphoric acid (H3PO4) in the exhaust flow. Having obtained the poisoned fraction from the model as a function of poison exposure time, θ is used to predict light off times and conversion efficiencies during the deactivation process through incorporation of a kinetic reaction scheme. The model provides a good representation of the phenomena noted in real catalysts; i.e. delayed light off times.

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.