An experimental and predictive study of the flow field in axisymmetric automotive exhaust catalyst systems

An experimental and theoretical investigation has been performed on the flow and pressure loss in axisymmetric catalytic converters and isolated monoliths under steady, isothermal flow conditions. Monolith resistance has been measured with a uniform, low turbulence, incident flow field. It has been found that the pressure loss expression for fully developed laminar flow is a good approximation to observations for x+ greater than 0.2. However, for x+ less than 0.2 the additional pressure loss due to developing flow is no longer negligible and a better approach is to use the correlation proposed by Shah. From experimental studies on the axisymmetric catalytic converters non-dimensional power law relationships have been derived relating maldistribution and pressure drop to expansion length, Re, and monolith length. These expressions are shown to generally fit the data well within ±5%. CFD predictions of the flow for a wide range of geometric configurations and flow conditions have shown that generally the system non-dimensional pressure loss can be predicted to within about 10% but that the maldistribution index is underpredicted within a range of 9-17.5%. It is believed that the pressure loss expression derived from 1-D flow studies is too simplistic. CFD predictions do, however, show the same pattern of change as observed experimentally and hence their performance in prediction trends is quite encouraging. Publisher statement: Copyright © 1996 SAE International. This paper is posted on this site with permission from SAE International and is for viewing only. It may not be stored on any additional repositories or retrieval systems. Further use or distribution is not permitted without permission from SAE

An experimental and predictive study of the tumbling generating characteristics of four-value cylinder heads under steady flow conditions

An experimental and predictive study has been conducted on the tumbling generating characteristics of a four-valve cylinder head under steady flow conditions. This was conducted on an idealised cylinder head with a disc combustion chamber and two straight axisymmetric intake ports equipped with shrouded valves. The tumbling generating characteristics of each intake configuration were evaluated using a steady flow rig which converted tumble into swirl. Experimental measurements of the swirl and axial velocity distributions for various valve lifts were obtained using laser Doppler anemometry. Theoretical predictions were performed using a commercial computational fluid dynamics (CFD) code. Comparisons have been made between the experimental results and theoretical predictions

Theoretical and experimental investigation of the flow in catalytic converters

In response to the increasing use of catalytic converters for meeting exhaust emission regulations, considerable attention is being directed towards improving their performance. One of the main factors affecting catalyst performance is the velocity distribution of the exhaust gases entering the reactor substrate. Thus optimisation of catalyst performance will require a detailed understanding of the flow fields that exist in catalyst assemblies. The cost and time advantages of computational modelling over experimental analysis has meant that CFD is increasingly being utilised as a design tool. Although validation against experimental data has been claimed by several authors, few systematic validation programmes have been carried out. The present paper includes such a programme for axisymmetric catalyst geometries. Experimental results are compared with CFD predictions, produced using approaches commonly adopted within industry. Significant discrepancies between experimental and predicted results are reported

Severe early onset preeclampsia: short and long term clinical, psychosocial and biochemical aspects

Preeclampsia is a pregnancy specific disorder commonly defined as de novo hypertension and proteinuria after 20 weeks gestational age. It occurs in approximately 3-5% of pregnancies and it is still a major cause of both foetal and maternal morbidity and mortality worldwide1. As extensive research has not yet elucidated the aetiology of preeclampsia, there are no rational preventive or therapeutic interventions available. The only rational treatment is delivery, which benefits the mother but is not in the interest of the foetus, if remote from term. Early onset preeclampsia (<32 weeks’ gestational age) occurs in less than 1% of pregnancies. It is, however often associated with maternal morbidity as the risk of progression to severe maternal disease is inversely related with gestational age at onset2. Resulting prematurity is therefore the main cause of neonatal mortality and morbidity in patients with severe preeclampsia3. Although the discussion is ongoing, perinatal survival is suggested to be increased in patients with preterm preeclampsia by expectant, non-interventional management. This temporising treatment option to lengthen pregnancy includes the use of antihypertensive medication to control hypertension, magnesium sulphate to prevent eclampsia and corticosteroids to enhance foetal lung maturity4. With optimal maternal haemodynamic status and reassuring foetal condition this results on average in an extension of 2 weeks. Prolongation of these pregnancies is a great challenge for clinicians to balance between potential maternal risks on one the eve hand and possible foetal benefits on the other. Clinical controversies regarding prolongation of preterm preeclamptic pregnancies still exist – also taking into account that preeclampsia is the leading cause of maternal mortality in the Netherlands5 - a debate which is even more pronounced in very preterm pregnancies with questionable foetal viability6-9. Do maternal risks of prolongation of these very early pregnancies outweigh the chances of neonatal survival? Counselling of women with very early onset preeclampsia not only comprises of knowledge of the outcome of those particular pregnancies, but also knowledge of outcomes of future pregnancies of these women is of major clinical importance. This thesis opens with a review of the literature on identifiable risk factors of preeclampsia