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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.

The increase in environmental levels of platinum can in part be attributed to the introduction of motor vehicle catalytic converters. Quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) has been evaluated as a analytical tool for the determination of platinum in environmental samples, such as vegetation, roadside dust, soil and sediment. Instrumental parameters were studied and a forward power of 1.4 kW and nebuliser flow rate of 0.95 1 min-1 were shown to give the optimum signal response for the 195Pt+ isotope. A detection limit of 0.12 ng ml-1 was achieved. Iridium was shown to be the most suitable choice for use as an internal standard with the 191Ir+ isotope being monitored. Various digestion methods were studied with aqua regia / hydrofluoric acid open vessel digestion being found to give good recovery for 2 certified reference materials, NIST 2556 (Used Autocatalyst, Pellets) and 2557 Used Autocatalyst, Monolith) with concentrations of 681 (38) mug g-1 and 1085 (32) mug g-1 respectively [certified values 697.4 (2.3) mug g-1 and 1131 (11) mug g-1]. Attention has been given to the problem of spectroscopic interference on 195Pt+ from hafnium oxide. Various correction methods were evaluated with a modification proposed to a previous method of mathematical correction being found to provide the best correction for the 179Hf16O+. An 'in-house' reference sample was prepared from a used catalytic converter and its platinum content of 3563 (176) ng g-1 established through inter-laboratory and inter-method procedures. Common rye grass (Lolium perenne) was shown to uptake platinum from both solid and liquid platinum-containing matrices. The methods developed were applied to a study of roadside dust samples taken from a busy section of the London M25 orbital motorway. The measured platinum levels of up to 194 ng g-1 agree with published literature from other European countries and represent a useful contribution to the knowledge concerning roadside platinum in the UK.

The research problem addressed in this study was to determine what the main factors are that contribute to the competitive advantage of the catalytic converter industry cluster in the Eastern Cape. To achieve this objective theoretical models of competitive advantage and literature of industry clustering were identified. For the models on competitive advantage, Porter’s diamond was used for national competitive advantage and Porter’s model on the competitive environment, which affects the competitive advantage of a region. Other theories on competitive advantage of cities and regions were identified, leading up to the theory on the cluster approach. The literature mentioned was broken down and analysed using literature, from knowledgeable people in the automotive industry in the Eastern Cape, identified during the study. A questionnaire was developed to test the degree to which the catalytic converter industry cluster in the Eastern Cape is in agreement with the literature study. The empirical study obtained a strong concurrence with the literature study on national competitive advantage and the theory of clusters. This resulted in a strategy for the catalytic converter industry cluster to sustain competitive advantage and remain globally competitive.

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.

In response to the increasingly widespread use of catalytic converters for meeting automotive exhaust emission regulations considerable attention is currently being directed towards improving their performance. Experimental analysis is costly and time consuming. A desirable alternative is computational modelling. This thesis describes the development of a fully integrated computational model for simulating monolith type automotive catalytic converters. Two commercial CFD codes, PHOENICS and STAR-CD, were utilised to implement established techniques for modelling the flow field in catalyst assemblies. To appraise the accuracy of the flow field predictions an isothermal steady flow rig was designed and developed. A selection of axisymmetric inlet diffusers and 180o expansions were tested, with the velocity profile across the monolith, the wall static pressure distribution along the inlet section and the total pressure drop across the assembly being measured. These datum sets were compared with predictions using a variety of turbulence models and solution algorithms. The closest agreement was achieved with a two-layer near wall approach, coupled to the fully turbulent version of the RNG k-ε model, and a nominally second order differencing scheme. Even with these approaches the predicted velocity profiles were too flat, the maximum velocity being as much as 17.5% too low. Agreement on pressure drops was better, the error being consistently less than 10%. These results illustrate that present modelling techniques are insufficiently reliable for accurate predictions. It is suggested that the major reason for the relatively poor performance of these techniques is the neglecting of channel entrance effects in the monolith pressure drop term. Despite these weaknesses it was possible to show that the model reproduces the correct trends, and magnitude of change, in pressure drop and velocity distributions as the catalyst geometry changes. The PHONETICS flow field model was extended to include the heat transfer, mass transfer and chemical reactions associated with catalysts. The methodology is based on an equivalent continuum approach. The result is a reacting model capable of simulating the three-dimensional distribution of solid and gas temperatures, species concentrations and flow field variables throughout the monolith mat and the effects that moisture has on the transient warm-up of the monolith. To assess the reacting model’s accuracy use was made of published light-off data from a catalyst connected to a test bed engine. Comparison with predicted results showed that the model was capable of reproducing the correct type, and time scales, of temperature and conversion efficiency behaviour during the warm-up cycle. From these predictions it was possible to show that the flow distribution across the monolith can significantly change during light-off. Following the identification, and subsequent modelling, of the condensation and evaporation of water during the warm-up process it was possible to show that, under the catalyst conditions tested, these moisture effects do not affect light-off times. Conditions under which moisture might affect light-off have been suggested. Although the general level of model accuracy may be acceptable for studying many catalyst phenomena, known deficiencies in the reaction kinetics used, errors in the flow field predictions, uncertainty over many of the physical constants and necessary model simplifications mean that accurate quantitative predictions are still lacking. Improving the level of accuracy will require a systematic experimental approach followed by model refinements.

Thesis (MBA (Business Management))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: South Africa has historically benefited from its mineral wealth, building one of the leading mining industries in the world. South Africa holds the worlds largest known PGM (or precious group metals) resource base (in a geological formation known as the Bushveld Igneous Complex), with an estimated life of 230 years (at current mining rates). This precious commodity is a precious source of both the direct as well as indirect contributions into the South African economy, as well as a leading source of employment in the South African mining industry. PGMs are predominantly used in auto catalysts, with an estimated 60% of global demand emanating from this application, where the commodity is used in breaking down noxious compounds in exhaust emissions. Given the strong correlation between automotive production and platinum sales, it seems viable to assume that platinum sales will continue to grow as more stringent legislation is introduced globally to reduce automotive emissions. This can currently only be down by increasing the platinum loads in auto catalysts, as alternative technologies are not widely accepted or developed at present. Given the influence (and positive correlation between) demand and prices, it appears that PGM prices will be driven upwards as demand continues to grow. This effect may be exacerbated by the fact that the expansion in demand is likely to outgrow the expansion in supply, given that few significant platinum operations have been started in recent years. Following the strong rally of commodity prices, specifically PGM prices in mid-2008 that saw platinum at a record high of USD2276/oz, major automotive producers have indicated that they are investigating alternatives to the application of precious metals in catalytic converters, in an attempt to curtail production costs. Although no viable substitute could be developed as yet, various alternatives (such as silver alloys) have been mentioned throughout the media. The purpose of this paper is to investigate the impact of such a substitution event on South African PGM producers and its resultant effect on the South African economy. The study will attempt to determine, at a high level, the direct impact of the event, as well as the indirect consequences of the proposed substitution event. / AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse ekonomie is histories op die mynbou- en landbousektore gebaseer, wat gelei het tot Suid-Afrika se wêreldklas mynbou industrie. Suid-Afrika beskik oor die wêreld se grootste PGM reserwes (in 'n geologiese formasie, ook bekend as die Bosveld Stollings Kompleks), met ‘n geskatte lewe van 230 jaar (teen huidige mynbou tempo's). Die komoditeite is verantwoordelik vir ‘n aansienlike hoeveelheid direkte en indirekte waardetoevoeging tot die Suid-Afrikaanse ekonomie. PGM’s word hoofsaaklik in katalisators in voertuie gebruik, met nagenoeg 60% van wêreldwye vraag wat uit die toepassing voortspring. PGMs word gebruik om uitlaatgasse op te breek en te verwerk in motorvoertuie. Gegewe die hoë mate van korrelasie tussen PGM en voertuigverkope, blyk dit voor die handliggend dat platinumverkope sal aanhou styg soos wat omgewingswetgeging in bepaling van toelaatbare uitlaatgasse in motorvoertuie strenger word. Die vermindering van uitlaatgasse is huidiglik slegs moontlik deur die verhoging van PGM ladings in katalisators, gegewe dat alternatiewe tegnologieë nog nie ver genoeg gevorder is om geimplementeer te word nie. Die hoë mate van korrelasie tussen PGM pryse en PGM vraag dui dat dit hoogs waarskynlik is dat die prys van edelmetaal sal aanhou styg soos wat vraag toeneem. Die verskynsel sal moontlik verder bou op die verwagting dat vraag vir die metaalaanbod oor die langtermyn sal oorskadu, siende dat geen wesenlike nuwe PGM myne onlangs oopgemaak is nie. Voertuigvervaardigers het aangedui dat hul alternatiewe tegnologieë opndersoek, nadat die platinumprys tot 'n rekord hoogtepunt van USD2276/ oz gestyg het in mid 2008. Die uitspraak is gelewer met die oog op koste kontrole in die vervaardiging van motorvoertuie. Alhoewel geen werkbare alternatief vir die edelmetale huidiglik bestaan nie, is verskeie moontlike materiale reeds in die media bespreek (byvoorbeeld verskeie silwer allooie). Die doel van die dokument is om die potensiële impak van so ‘n vervangings senario op die Suid-Afrikaanse ekonomie te ondersoek. Die studie sal poog om op ‘n hoë vlak die direkte en indirekte gevolge van die gebeurtenis te bepaal.

Considerable research is being carried out into the parameters that affect catalyst performance in order to meet the latest emission regulations. The conversion efficiency and the durability of automotive catalytic converters are significantly dependent on catalyst flow performance. Related investigations are commonly conducted using CFD techniques which represent an inexpensive and fast alternative to experimental methods. This thesis focuses on the flow performance of automotive catalytic converters using both experimental and computational techniques. The work describes the effects of inlet flow conditions on catalyst performance, the application of radial vanes to catalyst systems and the refinement of the CFD flow model which increases the accuracy of the predicted catalyst flow performance. the effects of inlet flow conditions on the flow maldistribution across the catalyst face and the total pressure loss through the system were assessed using a steady air flow rig. Tests were conducted over a range of Reynolds numbers typically encountered in automotive catalytic converters using a uniform and a fully-developed inlet flow condition. The results showed that the flow maldistribution significantly increases with Reynolds number notably in wide-angled diffusers. The catalyst flow performance is considerably improved when the inlet flow is uniform rather than fully-developed, the non-dimensional total pressure loss is reduced by 8% at Re=60000 and the flow maldistribution across the catalyst face is decreased by 12.5% and 15% respective Reynolds numbers of 30000 and 60000 when using a 60 degree diffuser. The total pressure loss through the system was found to be mostly associated with the monolith brick resistance. When the flow maldistribution is approximately 2, the pressure loss across the monolith brick represents 80% of the system pressure loss. The flow maldistribution across the catalyst face was improved by locating a system of radial splitters in the diffuser. The optimum flow performance was found to be a complex function of the vane design. A maximum improvement in the flow maldistrution indices M and Mi of 25% and 50% respectively was achieved at the expense of an increase in total pressure loss of 13.5% at Re = 60000. Both CFD and flow visualisation techniques were used as an aid to interpreting the flow field in the diffuser. Although a qualitative agreement was obtained using CFD, the flow maldistribution across the catalyst face was underpredected by up to 20%. The accuracy of the flow predictions was significantly improved by investigating the flow field in the monolith channels. Flow recirculation occurs in the channel entry length when the flow approaches the monolith channels at an angle which induces an additional implemented into four models of the flow through axisymmetric catalyst assemblies using various diffuser geometries and inlet flow conditions. By including the flow entrance effects in the porous media approach, the flow maldistribution was predicted within 8% instead of 15% when these effects are neglected. Further investigation of the flow in the monolith channels will be required to accurately model three-dimentional flows (racetrack catalysts) and to include various channel geometries and system flow rates.