(Coventry University) Steven Pierson (Jaguar Land Rover) - - PowerPoint PPT Presentation

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
• utline

introduction methodology CFD predictions results conclusion future work references

• utline

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

Typical Metallic Catalyst Brick

• utline

introduction methodology CFD predictions results conclusion future work references

Flat foil Corrugated foil

Straight-line exhaust flow in a traditional metallic catalyst brick

Perforated Metallic Catalyst Brick

• utline

introduction methodology CFD predictions results conclusion future work references

Perforated flat foil Perforated corrugated foil

Radial flow between adjacent channels resulting from the perforated foils

• utline

introduction methodology CFD predictions results conclusion future work references

Laminar catalyst vs. turbulent catalyst The radial flow caused by perforated foils

• enhances flow uniformity
• improves

mixing

• f

gas species within and between channels

• results in improved

conversion efficiency

Laminar catalyst Turbulent catalyst

No cross channel flow Increased mass transfer Poor flow uniformity Improved flow uniformity

• utline

introduction methodology CFD predictions results conclusion future work references

Aim: To develop an axisymmetric CFD model of a perforated brick with the aid

• f 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

METHODOLOGY OF CFD MODELLING

• 1. The perforated brick was modelled as a porous medium

(The pressure drop (δP) as a function of resistance coefficients (αi and ßi) 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)

• utline

introduction methodology CFD predictions results conclusion future work references

s,i i 2 s,i i i

U β U α ξ P

• utline

introduction methodology CFD predictions results conclusion future work references

START

Initial values of axial alpha and transverse alpha Run CFD predictions

FINISH

Compare P Change transverse alpha Yes No Compare radial velocity profile Yes No Change axial alpha

Methodology flow diagram

• utline

introduction methodology CFD predictions results conclusion future work references

Schematics of the flow behaviour inside the channels of two-type of catalysts, i.e. standard and perforated catalysts

x y

(a) Laminar catalyst

x y

(c) Turbulent catalyst under non-uniform flow inlet

x y

(b) Turbulent catalyst under uniform flow inlet

Wake

• utline

introduction methodology CFD predictions results conclusion future work references

Rig set-up for pressure drop measurement under uniform inlet flow

Wall to wall velocity profile downstream

• f the perforated brick

with flow straightener

Pressure drop measurement across the perforated brick with flow straightener

CYLINDRICAL PLENUM NOZZLE PERFORATED BRICK FLOW STRAIGHTENER OUTLET SLEEVE DIFFUSER

ΔP

2 4 52.5 105

Wall to wall distance (mm) Velocity (m/s)

• utline

introduction methodology CFD predictions results conclusion future work references

NOZZLE CATALYST ASSEMBLY

Rig set-up for pressure drop and radial velocity profiles measurement under non-uniform inlet flow

Pressure drop and radial velocity profiles measurement under non-uniform inlet flow Photograph of the rig

CYLINDRICAL PLENUM AIR

ΔP

• utline

introduction methodology CFD predictions results conclusion future work references

Pressure Outlet

Porous Matrix

Inlet

X Z Y

CFD PREDICTIONS

• Simulation tool: Star-CD
• Modelled as a 5-degree wedge and consisted of 5672 cells

CFD model of the perforated brick

• utline

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

• utline

introduction methodology CFD predictions results conclusion future work references

Pressure loss across the perforated brick for uniform flow compared with that deduced from non-uniform CFD flow study -----

RESULTS

• utline

introduction methodology CFD predictions results conclusion future work references

Pressure loss characteristic across the perforated brick under non-uniform inlet flow

• utline

introduction methodology CFD predictions results conclusion future work references

Velocity distribution across the Perforated Brick under non-uniform inlet velocity various flow rates

5 10 15 52.5 105

Wall to wall distance (mm) Velocity (m/s)

• utline

introduction methodology CFD predictions results conclusion future work references

Normalised velocity distribution across the Perforated Brick under non-uniform inlet velocity

0.5 1 52.5 105

Wall to wall distance (mm) (Local velocity)/ (Mean velocity)

(Max. velocity)

• utline

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

• utline

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

• utline

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

• utline

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.

• utline

introduction measurements CFD predictions results conclusion future work references

THANK YOU