1. STAR Global Conference 2017 Durability Analysis of Fouled EGR Cooler
Berlin, March 6th 2017
Raimund Vedder, Jawor Seidel – Atlanting GmbH
Dr. Jiansheng Yin – BENTELER Automotive

2. Contents
Motivation
Efficiency improvement of design process
FE analysis in STAR-CCM+
Summary

3. Motivation

4. Motivation EGR cooler durability
Lifetime durability of EGR coolers is challenging development task
Cooling → high local temperature gradients
Transient operation → high temporal gradients of temperature and pressure
Extended requirements with new emission legislations
Extended driving cycles / RDE + lower NOx limits require use of EGR cooler under all real driving conditions (RDC)
High load operating conditions → high temperature loads
Increase of temporal gradients in highly transient RDC operation
Extended development tasks and technical specifications
Supplier: Design of cooler must be more robust
OEM: Definition of extended requirements for EGR cooler

5. Motivation Global supplier of EGR coolers – BENTELER
Challenges for EGR cooler development
Extended use in the field –
Robust and efficient design required
NOx emission legislation [mg/km]
~60
~50
~30
~40
max. EGR Rate [%] 40
NOx limit [mg/km]
New driving cycles / RDE
Extension of map range with EGR use
Fins
Costs
Package
Performance
Durability

6. Testing of EGR cooler durability (Example: 4 EGR coolers parallel)
Motivation Durability testing for product approval at BENTELER
Testing of EGR cooler durability (Example: 4 EGR coolers parallel)
Extensive technical specifications from customers
Several thousand test cycles
Varying cycle conditions
Different specifications from different customers
Regularly adjusted to extended requirements
Approach: Increase of design maturity by extending CAE
Relief of test bench capacities
Consideration of real conditions
Real transient load / fouling

7. EGR cooler – inlet / outlet of cooled cassette
Motivation Operation under long term conditions
EGR cooler – inlet / outlet of cooled cassette
Fouling negatively impacts EGR cooler
Increase of pressure drop
Raise of EGR temperature
Risk of component failure
Consideration of fouling under real driving conditions
Different engine applications
Different driving cycles
Different fuels
Fouling also effects thermal durability
Extended boundary condition
Outlet
Inlet
EGR cooler valve

8. Efficiency improvement of
design process

9. Efficiency improvement of design process Product development EGR cooler
Cooling performance, pressure drop
Long-term performance / fouling
Driving cycles / load collectives
Durability
Different customer requirements
Approve of functionality (also long-term)
Testing and/or CAE – very complex and time consuming
Thermo shock cycles
Fouling cycles
Further efficiency improvement of development process necessary to maintain extended requirements of RDC

10. Efficiency improvement of design process 1st step – Definition of critical condition (done)
Downsized and approved design variant development
CAE work flow
CFD fouling analysis – STAR-CCM+
Transient CFD CHT analysis – STAR-CCM+
Non-linear FE analysis – Abaqus / Ansys / Nastran
Thermal loads
Fouling cycle
Fouling factors
Thermo shock cycle
Durability analysis – FE-Design / FEMFAT …
Stresses & strains
CFD fouling analysis – STAR-CCM+
Fouling factors
Evaluation in most critical operating condition
Steady state CFD CHT analysis – STAR-CCM+
Non-linear FE analysis – Abaqus / Ansys / Nastran
Thermal loads

11. Downsized and approved --- ------design variant development
Efficiency improvement of design process 2nd step – Enable FE analysis within ccm+
Downsized and approved design variant development
Currently transfer of thermal loads from STAR-CCM+ to FEA software required
Risk of failure + higher effort
Alternative: STAR-CCM+ also for FEA
Strength: Fouling + CHT + FEA in one software
High quality in data transfer
Automation / robustness
Quality assurance
Risks: Current limitations of FEA capabilities in STAR-CCM+ (11.06)
Linear / elastic FE analysis
Isotropic material properties
CFD fouling analysis – STAR-CCM+
Fouling factors
Evaluation in most critical operating condition
Steady state CFD CHT analysis – STAR-CCM+
Non-linear FE analysis – Abaqus / Ansys / Nastran
Thermal loads

12. FE analysis
in STAR-CCM+

13. (view on gas side of cooled cassette)
FE analysis in STAR-CCM+ Approach – Deposit properties from fouling analysis
Fouling in different driving cycles
(view on gas side of cooled cassette)
Fouling depends on long term engine use → Analysis in driving cycle(s)
Critical: City, low loads
Detailed approach presented last year – “CFD Analysis of EGR Cooler Fouling under Real Driving Conditions”
Local fouling properties are input to CHT analysis of most critical operating condition for stresses
Critical: High load
Cycle 1
Gas flow
Cycle 2
Gas flow
Cycle 3
Gas flow

14. Fouling analysis + CHT + FEA in one STAR-CCM+ model
FE analysis in STAR-CCM+ Approach – FE analysis of fouled conditions in STAR-CCM+
Fouling analysis + CHT + FEA in one STAR-CCM+ model
Fouling analysis
CHT analysis
FE analysis
Calculation of deposits
Driving cycle
Fouling factors – Thermal resistance of deposits
Fouling factors → Thermal contact resistance
Calculate CHT
No FEA solver
Map temperatures to FEA mesh
Use mapped temperatures as thermal load
Calculate solid stresses
FEA solver only

15. FE analysis in STAR-CCM+ Implementation – Mesh requirements
Result of mesh matrix for accuracy and performance → 2 separate meshes
CHT/Fouling – polyhedral cells
FEA – TET10 cells (tetrahedrons with mid nodes)
CHT: Exhaust gas, coolant and solids
Requirements for mesh quality (y+, aspect ratio) and 5 / 3 wall layers → 20 – 100 million cells
FEA: Solids
Requirements for resolution of stress gradients → million vertices
Gas flow
Section through CHT mesh
Exhaust gas
Coolant
Fins
Cooler sheets
FEA mesh, fins

16. FE analysis in STAR-CCM+ Implementation – Setup of solid stress model
Model settings
Boundary conditions
Steady state simulation
Temperature dependent material data – Field functions
Young’s modulus
Poisson’s ratio
Thermal expansion coefficient
Solver (Sparse direct solver)
“Out of core” calculation – High memory requirements
540 GB for 8 million vertices
All soldering joints are modeled as ideal connections
Thermal load: Temperature field
Mapped solid temperatures from CHT simulation
Surface loads: Pressure
Mapped absolute pressure on coolant and on gas side
Constraints: 3 points
Located at exhaust flange

17. FE analysis in STAR-CCM+ Results – Solid stress analysis in STAR-CCM+
FEA model of EGR cooler (STAR-CCM+)
EGR cooler at test bench
Temperature
Solid stress –
von Mises
High temperature gradients at inlet housing connection to cooled cassettes
Highest stresses at top 2 corners of connections
Also identified by tests as high stressed points

18. Solid stresses – von Mises (STAR-CCM+)
FE analysis in STAR-CCM+ Results – FEA, comparison of fouled / clean cooler
Solid stresses – von Mises (STAR-CCM+) 2 1
Clean cooler 3 4 2
Limit for elastic strains 1
Fouled cooler 3 4
In this example stresses at high loaded corners are slightly higher in clean cooler
Use of fouled conditions precises stresses – Trend depends on specific deposits
Deposits isolate → Lower sheet temperatures
Deposits can be very inhomogeneous → Increase of temperature gradients

19. FE analysis in STAR-CCM+ Evaluation of solid stress analysis in STAR-CCM+
Pro
Contra
Qualitatively very good results
Sufficient for design optimization
Smart work flow with FEA in STAR-CCM+
Full automation → Efficient
Easy to control → High quality
Comfortable post processing
High accuracy in transfer of loads
CHT and FEA in one model
No additional geometry preparation for 3rd party software
Only linear solver → No plastic deformations
Stresses are locally far above yield strength of used material
Quantitatively too high stresses
Only isotropic material properties → No composites / other anisotropic materials possible
High memory requirements
Same memory request as other solvers for non-linear computation

20. Summary

21. Summary Capabilities of solid stress analysis in STAR-CCM+
Suitable capabilities for design development / matrix of variants
Qualitatively very good results of solid stress analysis
All evaluation steps in one software → Smart and efficient work flow
Fouling analysis / CHT analysis / FE analysis
High grade of automation → Excellent quality assurance
No additional 3rd party FEA software required
Further potential for efficiency improvement of durability analysis
Development of STAR-CCM+ to handle non-linear FE analysis
Evaluation of work flow based on linear STAR-CCM+ analysis and life-time prediction with FEMFAT + Plast → Consideration of plastic deformations via post processing
Possible if stresses not exceed linear range too much

22. Summ ary– Interdisciplinary variant analysis
Parametric models
Drawings
Bill of materials
Design
Simulation
Flow, heat, kinetics
Durability / life-time
Progressive techniques
Materials
Tolerances
Processes
Production
Component tests
Testing instructions
Knowledge transfer
Testing
The demonstrated increase of process efficiency is part of the permanent improvement of Atlantings matrix processes
The matrix processes are the enabler to develop designs with 50% less costs & time

23. Thank you! Copyright Contact: Raimund Vedder (rvr@atlanting.de)
Reproduction and transmission of this document and any information and data from it is prohibited, unless this is explicitly allowed. Any offense will be punished. All rights reserved.
Thank you!
Contact:
Raimund Vedder
Dr. Jiansheng Yin