Ahmad Kamal Mat Yamin, Stephen F. Benjamin, Carol Ann Roberts (Coventry University) Steven Pierson (Jaguar Land Rover)
• Introduction • Methodology • CFD prediction • Results • Conclusion • Future work outline introduction methodology CFD predictions results conclusion future work references
INTRODUCTION Automotive catalysts? • Catalysts are substances capable of accelerating certain chemical reactions. In automotive exhaust systems, the chemical reactions convert poisonous gases to harmless gases. Factors affecting the conversion efficiency: • Flow uniformity • Mass transfer • Flow rate Metallic perforated brick: -2 layer of foils, i.e. one flat and one corrugated are perforated before winding them together outline introduction methodology CFD predictions results conclusion future work references
Typical Metallic Catalyst Brick Flat foil Corrugated foil Straight-line exhaust flow in a traditional metallic catalyst brick outline introduction methodology CFD predictions results conclusion future work references
Perforated Metallic Catalyst Brick Perforated flat foil Perforated corrugated foil Radial flow between adjacent channels resulting from the perforated foils outline introduction methodology CFD predictions results conclusion future work references
Laminar catalyst vs. turbulent catalyst The radial flow caused by perforated foils No cross channel flow • enhances flow uniformity Poor flow uniformity • improves mixing of gas species within and between Laminar catalyst channels • results in improved Increased conversion efficiency mass transfer Improved flow uniformity Turbulent catalyst outline introduction methodology CFD predictions results conclusion future work references
Aim : To develop an axisymmetric CFD model of a perforated brick with the aid of experimental measurements. Objectives : -To determine the axial resistance coefficients from measurement under uniform inlet flow conditions -To measure radial flow profiles and pressure drop under non-uniform inlet flow -To find the transverse resistance coefficients by best matching CFD predictions to measurements outline introduction methodology CFD predictions results conclusion future work references
METHODOLOGY OF CFD MODELLING 1. The perforated brick was modelled as a porous medium P 2 α U β U i s,i i s,i ξ i ( The pressure drop ( δ P) as a function of resistance coefficients ( α i and ß i ) and superficial velocity in the three mutually perpendicular directions) 2. Preliminary measurements showed the flow distribution downstream of the perforated brick was axi-symmetric 3. The axial alpha and axial beta were determined from pressure drop measurements under uniform inlet flow conditions 4. The radial flow profiles and axial pressure drop were measured under non- uniform inlet flow conditions 5. Determine the axial and transverse alpha values by best matching CFD predictions to measurements ( Assumption: transverse beta is zero) outline introduction methodology CFD predictions results conclusion future work references
Methodology flow diagram START Initial values of axial alpha and transverse alpha Run CFD predictions No Change transverse Compare P alpha Yes No Change Compare radial axial alpha velocity profile Yes FINISH outline introduction methodology CFD predictions results conclusion future work references
y Schematics of the flow behaviour inside the channels of two-type of catalysts, i.e. standard and x perforated catalysts (a) Laminar catalyst y Wake x (b) Turbulent catalyst under uniform flow inlet y x (c) Turbulent catalyst under non-uniform flow inlet outline introduction methodology CFD predictions results conclusion future work references
Rig set-up for pressure drop measurement under uniform inlet flow ΔP Pressure drop measurement across the perforated brick with flow DIFFUSER OUTLET straightener SLEEVE CYLINDRICAL FLOW PERFORATED NOZZLE PLENUM STRAIGHTENER BRICK 4 Velocity (m/s) Wall to wall velocity profile downstream 2 of the perforated brick with flow straightener 0 0 52.5 105 Wall to wall distance (mm) outline introduction methodology CFD predictions results conclusion future work references
Rig set-up for pressure drop and radial velocity profiles measurement under non-uniform inlet flow ΔP Pressure drop and radial velocity profiles measurement under non-uniform inlet flow AIR CATALYST NOZZLE CYLINDRICAL ASSEMBLY PLENUM Photograph of the rig outline introduction methodology CFD predictions results conclusion future work references
CFD PREDICTIONS • Simulation tool: Star-CD • Modelled as a 5-degree wedge and consisted of 5672 cells Inlet Porous Matrix Pressure Outlet X Z Y CFD model of the perforated brick outline introduction methodology CFD predictions results conclusion future work references
Turbulence model V2F – requires y+ < 1 for cells adjacent to the walls Differencing schemes: • MARS – U, V & W momentum • Upwind – turbulence kinetic energy and dissipation Grid independence study • Several built meshes showed consistency in pressure drop outline introduction methodology CFD predictions results conclusion future work references
RESULTS Pressure loss across the perforated brick for uniform flow compared with that deduced from non-uniform CFD flow study ----- outline introduction methodology CFD predictions results conclusion future work references
Pressure loss characteristic across the perforated brick under non-uniform inlet flow outline introduction methodology CFD predictions results conclusion future work references
15 10 Velocity (m/s) 5 0 0 52.5 105 Wall to wall distance (mm) Velocity distribution across the Perforated Brick under non-uniform inlet velocity various flow rates outline introduction methodology CFD predictions results conclusion future work references
1 (Max. velocity) (Local velocity)/ (Mean velocity) 0.5 0 0 52.5 105 Wall to wall distance (mm) Normalised velocity distribution across the Perforated Brick under non-uniform inlet velocity outline introduction methodology CFD predictions results conclusion future work references
Velocity distribution across the Perforated Brick under non-uniform inlet velocity- CFD (Solid lines ) vs measurement outline introduction methodology CFD predictions results conclusion future work references
CONCLUSION: • The perforated brick can be modelled as an axisymmetric model as the flow profiles across the brick under non-uniform inlet flow appeared to be approximately axi-symmetric • The axial alpha and transverse alpha were deduced by best-matching CFD predictions to the pressure drop and velocity profile measurement under non-uniform inlet flow. • The axial alpha and transverse alpha were 25 and 30,000 respectively. The axial alpha was 55% smaller than determined from the least square method of the measurement for uniform flow due to the presence of cross flow. • The alpha and beta values obtained are subject to confirmation in future work outline introduction methodology CFD predictions results conclusion future work references
FUTURE WORK: 1. Establish the generality of the method for obtaining resistance coefficients by investigating higher flow rates and geometrically different flow assemblies 2. Include flow simulation in the diffuser upstream of the catalyst. 3. Heat and mass transfer simulation throughout the perforated brick outline introduction methodology CFD predictions results conclusion future work references
REFERENCES: 1. Benjamin, S., Clarkson, R. J., Haimad, N. and Girgis, N. S. (1996) An Experimental and Prediction Study of the Flow Field in Axisymmetric Automotive Exhaust Catalyst Systems , SAE Paper 961208 2. Bollig, M., Liebl, J., Zimmer, R., Kraum, M., Seel, O., Siemund, S., Bruck, R., Diringer, J. and Maus, W. (2004) Next Generation Catalysts are Turbulent: Development of Support and Coating , SAE Paper 2004-01-1488 3. Kaiser, R., Stadler, F., Pace, L., and Presti, M. (2007) Simulation Model of Three-Way Catalysts with Perforated Foils , http://www.atzonline.com/. 4. Lotti, C., Rossi, V., Poggio, L., Holzinger, M., Pace, L., and Presti, M. (2005) Backpressure-Optimized, Close-Coupled Catalyst~First Application on a Maserati Powertrain , SAE Paper 2005-01-1105. outline introduction methodology CFD predictions results conclusion future work references
THANK YOU outline introduction measurements CFD predictions results conclusion future work references
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