Automotive catalytic converters are increasingly used to reduce emissions from internal combustion engines to comply with emission regulations. Maldistributed flow across the catalyst affects its warm up, light off time, ageing, and conversion efficiency. This thesis concerns flow distribution in automotive catalytic converters and methods to improve CFD predictions. Previous studies showed that modelling the monolith flow resistance using the Hagen- Poiseuille’s formulation under predicted flow maldistribution. The predictions were improved by incorporating an additional pressure loss term V2 2 1  , where V is transverse velocity just upstream of a monolith channel, for oblique entry of the flow into the monolith known as the entrance effect. Further improvement was obtained by incorporating the critical angle of attack method. However, there was no experimental evidence to support these oblique entry loss formulations. There also remained the possibility that under prediction of flow maldistribution might be due to the failure to predict flow in the diffuser accurately. A one-dimensional oblique angle flow rig was designed and built to measure the effect of oblique entry flow losses in monoliths. Experiments were performed at different angles of attack (α), using different lengths of substrate and a methodology was developed to obtain the oblique flow entrance losses. The results showed that the pressure loss attributed to the entrance effect increased with the angle of attack. The entrance effect was also found to be dependent on channel Reynolds number and substrate length. The theoretical assumption of V2 2 1  predicts accurately at low Reynolds number but looses its validity at high Reynolds number. From the experimental studies, an improved correlation for the entrance effect has been derived as a function of major controlling variables, i.e., angle of attack, length of the substrates and Reynolds number. A two-dimensional rig was designed to measure the flow field using PIV in a 2-D diffuser placed upstream of two different length substrates. The results showed that the flow in a wide angle diffuser consisted of a central core, free shear layer and recirculation regions. The near-field region was found similar to that of a plane jet. The flow field was found to be independent of Reynolds number. Increasing the substrate length resulted in a flattening of the axial profiles close to the substrate face. A CFD study was undertaken to predict maldistributed flow at the exit of the substrate for an axisymmetric catalyst model by incorporating the measured entrance effect correlation. A fixed critical angle of attack (αc,F) approach was used whereby the entrance effect is assumed constant for α>αc,F. Incorporating the entrance effect with αc,F= 810 improved the prediction of maldistribution in the flow profiles. A 2-D CFD study was undertaken to predict the flow distribution in the diffuser and downstream of the substrate. A comparison of the CFD predictions in the diffuser using different turbulence models showed that all the turbulence models used in this study over predicted the width of the central core region and the V2F turbulence model gave velocity predictions that compared best with PIV. Incorporating the entrance effect improved the predictions close to the diffuser-substrate interface and downstream of the substrate.

Automotive catalytic converters are used extensively in the automotive industry to reduce toxic pollutants from vehicle exhausts. The flow across automotive exhaust catalysts is distributed by a sudden expansion and has a significant effect on their conversion efficiency. The exhaust gas is pulsating and flow distribution is a function of engine operating condition, namely speed (frequency), load (flow rate) and pressure loss across the monolith. The aims of this study are to provide insight into the development of the pulsating flow field within the diffuser under isothermal conditions and to assess the steady-state computational fluid dynamics (CFD) predictions of flow maldistribution at high Reynolds numbers. Flow measurements were made across an automotive catalyst monolith situated downstream of a planar wide-angled diffuser in the presence of pulsating flow. Cycle-resolved Particle Image Velocimetry (PIV) measurements were made in the diffuser and hot wire anemometry (HWA) downstream of the monoliths. The ratio of pulse period to residence time within the diffuser (J factor) characterises the flow distribution. During acceleration the flow remained attached to the diffuser walls for some distance before separating near the diffuser inlet later in the cycle. Two cases with J ~ 3.5 resulted in very similar flow fields with the flow able to reattach downstream of the separation bubbles. With J = 6.8 separation occurred earlier with the flow field resembling, at the time of deceleration, the steady flow field. Increasing J from 3.5 to 6.8 resulted in greater flow maldistribution within the monoliths; steady flow producing the highest maldistribution in all cases for the same Re. The oblique entry pressure loss of monoliths were measured using a one-dimensional steady flow rig over a range of approach Reynolds number (200 < Rea < 4090) and angles of incidence (0o < α < 70o). Losses increased with α and Re at low mass flow rates but were independent of Re at high flow rates being 20% higher than the transverse dynamic pressure. The flow distribution across axisymmetric ceramic 400 cpsi and perforated 600 cpsi monoliths were modelled using CFD and the porous medium approach. This requires knowledge of the axial and transverse monolith resistances; the latter being only applicable to the radially open structure. The axial resistances were measured by presenting uniform flow to the front face of the monolith. The transverse resistances were deduced by best matching CFD predictions to measurements of the radial flow profiles obtained downstream of the monolith when presented with non-uniform flow at its front face. CFD predictions of the flow maldistibution were performed by adding the oblique entry pressure loss to the axial resistance to simulate the monolith losses. The critical angle approach was used to improve the predictions, i.e. the oblique entry loss was limited such that the losses were assumed constant above a fixed critical angle, αc. The result showed that the perforated 600 cpsi monolith requires the entrance effect to be restricted above αc = 81o, while the losses were assumed constant above αc = 85o for the ceramic 400 cpsi monolith. This might be due to the separation bubble at the monolith entrance being restricted by the smaller hydraulic diameter of the perforated monolith thus limiting the oblique entry loss at the lower incidence angle.

The distribution of platinum group elements and increase of thein emissions in the environment are mostly related to the use of automobile catalyst. The antropogenic emissions of these noble metals accumulate aloung the roads. The methods such as ICP-OES and XRD were used for determinativ of phase and elemental composition of these samples. The matrix of the gasoline catalyst is composed of Al, Ce oxides with Pt-Pd-Rh coatings. Matrix of diesel catalyst is composed of cordierite with Pt coatings. ICP-MS was used for determination Pt, Pd and Rh. Before the analysis was performed such as pre-concetration fire assay fusion into a NiS button. The leaching characterization of Pt, Pd and Rh was examined during kinetic batch experiments in sodium chloride (1g/l, NaCl), 20 mM Na2P4O7 (NaPyr), fulvic acid (FK, DOC 50 mg/L) and 20 mM citric acid . The results show, that the dissolution of Pt and Pd is the fastest in citric acid and sodium pyrophosphate. Sodium chloride in the concentrations employed, which could be derived from melt waters formed during winter road treatment, does not have a substantiv impal on the speciation and mobilization of Pt and Pd. Organic acid does not have significantly impct on the release of Pt and Pd to the solution. The calculated normalized bulk released NRi values in the range 0,16...

Le platine (Pt), le palladium (Pd) et le rhodium (Rh), font partie des Eléments du Groupe du Platine (EGP), utilisés dans les catalyseurs automobiles. En raison de leur émission dans l'environnement, ces éléments peuvent aujourd'hui être considérés comme des contaminants émergeants et traceurs de la contamination automobile. Cette étude porte sur la dispersion des EGP depuis leur source (monolithes et émission à l'échappement) jusqu'au champ proche (atmosphère, poussières de chaussées, eaux de ruissellement, sédiment,sol de bord de route). Leur mobilité à partir de monolithes a été étudiée en présence d'eau de ruissellement et de molécules organiques. Leur spéciation a été évaluée dans les poussières de chaussées et les sédiments. Les teneurs en EGP dans les monolithes étudiés montrent le remplacement de Pt par Pd dans les catalyseurs récents. L'abondance relative des EGP dans les échantillons environnementaux est Pd > Pt > Rh. Les expérimentations de mobilisation montrent que la mobilisation des EGP est plus significative au contact des molécules organiques, est dépendante du pH de la solution et augmente avec l'âge du monolithe. Rh est l'élément le plus mobilisable dans les monolithes. La spéciation montre que les EGP sont peu mobiles. Dans la part mobilisable, ils sont majoritairement liés à la fraction dite organique. / Platinum (Pt), palladium (Pd) and rhodium (Rh) (platinum-group elements; PGEs),are used in automotive catalytic converters to remove harmful emissions from exhaust gas. Nevertheless, nowadays, the PGEs are emerging as new environmental emission contaminators due to their increasing use. The goal of this research is to study the distribution of PGEs from the source (i.e. automotive catalytic converters and exhaust gas) to the environmental samples (i.e. atmospheric particles, road dust,storm water, pond sediments, and road-side soil). The mobility of PGEs from the converters in contact with run off water and natural complexing agents were studied. Also, the speciation of PGEs was investigated in road dust and pond sediments. Comparison of PGE contents in different catalysts confirms the replacement of Pt by Pd in more recent converters. Besides, the relative abundance of PGEs in environmental samples shows higher concentration of Pd compared toPt and Rh (i.e. Pd>Pt>Rh). The results of testing PGEs mobilization in catalytic converters demonstrate more significant mobilization by organic molecules as compared to run off water. Our results also show the dependency of PGEs mobilization on pH and on catalyst age. Among the PGEs, Rh was the most mobilized element in catalytic converters. More importantly, the speciation test shows that while PGEs are low mobile elements, in the mobilizable fraction, PGEs are in the organic fraction.