star global conference 2016 cfd analysis of egr cooler

© Atlanting GmbH / BENTELER Automotive |

STAR Global Conference 2016 – EGR Cooler Fouling

Raimund Vedder, Jawor Seidel – Atlanting GmbHDr. Jiansheng Yin – BENTELER Automotive

STAR Global Conference 2016

CFD Analysis of EGR Cooler Foulingunder Real Driving Conditions

Prague, March 7, 2016



Contents

Motivation

Approach

Implementation

Results and evaluation

Summary



Motivation



MotivationFouled EGR cooler (20'000 km, passenger car, 2015)

OutletInlet



MotivationSupport for OEM and supplier

Fouling depends on interaction between COOLER DESIGN and OPERATING CONDITIONS

Consideration of extended requirements from technical specifications Consideration of different conditions → load configuration, driving

cycle Specification of exhaust gas composition, depending on engine

application and/or fuel quality (sulfur content, cetane number → market restrictions)

Coordination of test bench investigations and CAE analysis Analysis of critical operating conditions Exact benchmarking of cooler variants / cooler concepts

Additional development target for cooler design Consideration of local conditions enables goal-oriented optimization Evaluation of long term performance



MotivationGlobal supplier of EGR coolers – BENTELER

Demands from customers /emission regulations

New driving cycles / RDE

➔ Extension of map range with EGR use

NOx emission legislation [mg/km]

Challenges for EGR coolerdevelopment

Fins

Costs Package

Performance Durability

250 18080 40

~30

~60

~40 max. EGR Rate [%]~50

NOx limit [mg/km]



MotivationComprehensive fouling investigations of BENTELER

Smooth Tube

Fin Type

Dented Tube

Fundamental gasoline studyFundamental Diesel study

Test engine 2.0l turbo

t=1.5 h t=3.0 h t=4.5 h

t=6.0 h t=7.5 h

10h fouling test

BENTELER 84.3%

BENTELER 41.8%



Approach



Full coupled CHT CFD simulation

Detailed geometry of heat transferring elements

Approach3D CHT analysis necessary for fouling process

3D resolved Temperature

Deposit mechanisms

3D resolved species concentrations

Condensation: Deposit formation and deposit consistency

3D resolved flow field / turbulence

Removal of deposits from wall

Temperature Deposit Thickness



BENTELER + Michigan University USA

Test bench investigations of different cooler designs

Diesel + gasoline engines

FVV project 966 and 1048 – “Fouling of EGR coolers I and II”

Test bench investigations of deposition formation

Impact of boundary conditions on deposit mechanisms and consistency

EU project „IPSY“ – „Innovative Particle trap System for future DI combustion concepts“

Soot characterization

Soot filtration mechanisms

ApproachTest bench results from research projects



ApproachFundamental mechanisms and influencing factors

Particle transport to the wall

Particles on the wall

Thermophoresis

Diffusiophoresis

Impaction

Diffusion

TGas>TWall

Ci,Gas>Ci,Wall

Governing parameters(operation point + cooler

geometry) Exhaust gas composition

Particle concentration and size distribution

HC concentration and spectrum

SO2 concentration

Gas temperature

Wall temperature (surface)

Gas / Coolant flow

Cooler design

FLFD

FV

Lift off from the wall Buoyancy and

drag forces Stick on the wall Van-der-Waals forces



ApproachDevelopment of incremental layer formation

Exhaustgas

Wall

Particles

1

TWall Wall

Particles Conden-sate

Conden-sate

TWall

Wall

Particles Removal

TWall

2

3

Exhaustgas

Exhaustgas

Wall

Particles Removal

TWall

4

Exhaustgas

1.) Start: Deposition rates in clean EGR cooler

2.) Wall layer formation

Thermal resistance ↑

TWall ↑ → deposit ↓

3.) Removal starts

Removing forces > sticking forces

4.) Equilibrium

Deposit = Removal

Layer formation takes place in each wall cell of the 3D model

Local deposit composition

Layer thicknessT_coolantT_surface

Time [h]

Laye

r thi

ckne

ss [m

m]

Tem

pera

ture

[°C

]



ApproachEnabler for an efficient CFD development process

State of equilibrium The local deposition layer thickness results from the equilibrium

between formation and the removal of depositions Enables the use of steady state flow simulations

to consider all geometrical detailsDriving cycle / load configuration Same EGR cooler shows different degree of fouling

in different applications Simulations in different engine operating points and

under different warm-up conditions Weighting based on deposition rate and duration/

frequency in the driving cycle → long term cooler performance



ApproachProcess overview

Parameters

Interdisciplinary CFD model

Deposit Removal Drag forces Lift forces Thermal forces Van-der-Waals forces

Operating conditions

Optimization

Temperatures Mass flow rates Particles HC, H2O, SO2

Design

EGR cooler design

Engine setup Combustion Cooling

management

Thermophoresis Diffusiophoresis Impaction Diffusion

Flow guiding Cooling Material Wall thickness

AutomatedCFD procedure Full CHT EGR

cooler Deposition rate +

layers Weighting in driving

cycle



Implementation



Exhaustgas

Coolant

Fins

Coolersheets

ImplementationGeometry and mesh requirements

Full CHT of exhaust gas flow, coolant flow, temperature distribution in walls

All structures are necessary

Mesh quality for reliable heat transfer

Prism layers (5, 3)

Y+ values, aspect ratios

20 – 100 Million cells



Field functions

ImplementationMechanisms and convergence criteria

STAR-CCM+ ®

Field Functions

Mechanisms

Incremental layer formation

Convergence criteria

Heat transfer, flow

Deposit, layers

Pressure drop

Porosity coefficients

Convergence criteria

Pressure drop

Porosity at inlet

Porosity at outlet



Boundary conditions

ImplementationBoundary conditions, automation

Boundary conditions

Geometry

Material properties

Thermodynamical conditions

Exhaust gas composition

Automation, macros

Meshing

Material properties

Solver settings

Flow parameters / convergence criteria

Fouling parameters / convergence criteria

Post processing

Automation

Run Script

CHT and foulingsimulation

Ai_foul_setup.java

Pre-ProcessingAi_setup.java

Post-ProcessingSingle operating points

Ai_foul_run.java

Ai_foul_Post_single_point.java

Averaging /Driving cycle

Post-ProcessingLong term fouling

Ai_foul_Post_weighted_results.java

Ai_foul_map_results.java



Results and evaluation



CFD results (constant operating condition)

Measured data (constant operating condition)

Results and evaluationExample – Fouling of U-flow EGR cooler

0 100 200 300 400 500 600 700 800 9000

10

20

30

40

50

60

70

80

90

6.0

6.2

6.4

6.6

6.8

7.0

7.2

7.4

Time [minutes]

Pres

sure

Dro

p [m

bar]

Coo

ling

Perf

orm

ance

[kW

]

Pressure dropCleancooler:

Fouledcooler:

Deposit thickness

Foulingfactor

Measurement CFD0

1

2

3

4

5

6

7

8

Loss

in C

oolin

g P

erfo

rman

ce [%

]

Measurement CFD0

10

20

30

40

50

60

Rai

se in

Pre

ssur

e D

rop

[mba

r]



Results and evaluationMethod exchange between test bench and CAE

CAE methodTest bench measurement

Local conditions are decisive for heat transfer Temperatures, flow, fouling – local and integral differences Usage of mean fouling factor instead of local distributed fouling factors

can lead to very different cooling performance

Gasinlet

Coolantoutlet

Measurements only at inlet and outlet

Integral examination (clean, fouled) → mean fouling factor

Local distribution of fouling factors

Problem analysis / evaluation

Detailed heat exchange

Fouling Factor

GasoutletCoolantinlet

Walls in contact withexhaust gas



Definition of driving cycle / load collective

Fouling - real driving conditions

Real driving conditions

Results and evaluationEvaluation of fouling under real driving conditions

Engine speed

Eng

ine

load

Hot engineIntermediate coolant temperatureCold engine

Engine map

0.0

0.2

0.4

0.6

0.8

1.0

Fouling factorLayer thickness

Mean values:Fouling factor: 0.0044 m²K/WDeposit thickness: 0.6327 mm

Single operating conditions

Fouling Factor [m²K/W]



Summary



SummaryCapabilities of the method

The presented CAE approach enables the exact analysis of fouling All mechanisms are considered in detail First key approach is the calculation of the state of equilibrium

No transient simulations necessary → efficient approach Formation of deposit layers with varying consistencies is

simulated → exact approach Second key approach is the analysis of driving cycles / load

collectives: several operating conditions are considered → real driving conditions Identification of critical operating points Influence of different fuel qualities

Test bench investigations and CAE analysis can be closely co-ordinated Exact benchmarking



Summary

RK-combustion

Knocking analysis

The TecUP „Fouling“ is another important element for exact engine analysis with CAE methods

Experiences from test bench as well as description of physical and chemical processes are included

Atlanting develops and integrates such extensions of methods

Flow acoustics

Fouling DPF/GPF

SCR deposits

Oil coking

Surge limit



Copyright

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 ([email protected])Dr. Jiansheng Yin ([email protected])

star global conference 2016 cfd analysis of egr cooler

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