EGR Systems Evaluation in Turbocharged Engines · EGR Systems Evaluation in Turbocharged Engines ... bypass system to mass through intake system ... turbine bypass system to mass

1 GT CONFERENCE 2013

© 2013 Chrysler Group LLC. All rights reserved

EGR Systems Evaluation in Turbocharged Engines

Lurun Zhong, Marc Musial, Ronald Reese and Gregg Black

Chrysler Group LLC

11/04/2013

CHRYSLER GROUP LLC

PTV: L.Zhong et al. Presentation

GT CONFERENCE 2013


2

Introduction

Turbocharger balance conditions

EGR system descriptions

EGR systems comparison

Influence of turbocharger efficiency

Dual-loop EGR system

Concept validation ◦ 1D GT-Power modeling

◦ Dynamometer test

Discussion

Conclusions

Acknowledgement

Contents

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EGR systems are widely applied in diesel engine and SI engines ◦ High pressure loop (HPL) EGR ◦ Low pressure loop (LPL) EGR ◦ Combination of above two EGR systems

The advantages of cooled EGR are as follows: ◦ Reduction of in-cylinder compression temperature and knocking event ◦ Reduction in pre-catalyst exhaust temperature and the need for fuel

enrichment ◦ Increased possibility of raising spark ignition (SI) engine compression

ratio for improved fuel economy.

Disadvantages of cooled EGR on the other hand are as follows: ◦ EGR degrades combustion ◦ The addition of EGR reduces engine Vol. efficiency and engine power

output.

To evaluate EGR systems to maximize its benefits in

turbocharged engines

Introduction

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Turbocharger Balance Conditions

Comp Turb

T s , M s

T T1 , M T

ε c , T s

Π T , T T2

T cb , M cb

T tb , M tb

Compressor speed equals turbine speed

Power balance

Mass balance

TcT

ss

t

c

T

TT

11

)1()1(1

1

21

α: the ratio of mass through the compressor bypass system to mass through intake system

β: the ratio of mass flowing through the turbine bypass system to mass flowing out of the engine

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Comp Turb

EGR

T s1 , M s

T T1 , M T

T EGR , M EGR

ε c , T s2

Π T , T T2

T cb , M cb

T tb , M tb

Comp Turb

EGR

T s1 , M s

T T1 , M T

T EGR , M EGR

ε c , T s2

Π T , T T2

T cb , M cb

T tb , M tb

EGR Systems Description

Comp Turb

EGR

T s1 , M s

T T1 , M T

T EGR , M EGR

ε c , T s2

Π T , T T2

T cb , M cb

T tb , M tb

LPL HPL MPL

TcT

sEGRs

t

c

TEGR

TTEGRTEGR

11

)1(1)1(

)1(1

1

21

TcT

sEGRs

t

c

TEGR

TTEGRTEGR

11

)1()1()1(

)1(1

1

21

TcT

ss

t

c

T

TT

11

)1()1(1

1

21

LPL

HPL

MPL

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EGR Systems Comparison Turbine expansion ratio is applied for EGR systems evaluation

◦ The lower turbine expansion ratio, the smaller engine PMEP

HPL has lowest turbine expansion ratio

MPL has highest turbine expansion ratio

At EGR <30%, the difference in turbine expansion between HPL and LPL is very small

Parameters Unit Value

Ts1 K 298

Ts2 K 398

Ps2/Ps1 - 1.6

α - 0

β - 0

ηtc - 0.45

Φ - 0.0688

TT K 780

TEGR K 320 1.5

2.0

2.5

3.0

3.5

4.0

4.5

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

External EGR (-, Base)

Tu

rbin

e E

xp

an

sio

n R

ati

o (

-)

Low-Base

High-Base

Mixed

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Influence of Turbocharger Efficiency Parametric study is focused on

◦ Turbine and compressor bypass percentage

◦ EGR temperature

◦ Turbocharger efficiency

◦ Combination of above parameters

Increase turbocharger efficiency from 45% (base) to 48%, turbine expansion ratio drops with both HPL and LPL EGR systems

1.6

1.8

2.0

2.2

2.4

2.6

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

External EGR (-, turbocharger efficiency)

Tu

rbin

e E

xp

an

sio

n R

ati

o (

-)

Low-Base

High-Base

Low-48%

High-48%

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Dual-Loop EGR System Dual-loop EGR system

◦ LPL EGR loop is utilized at lower engine speed

◦ HPL EGR loop is applied at higher engine speed

By selecting correct turbocharger, most of the full load points run at higher efficiency zone

Volumetric Flow Rate (m3/s)

Pre

ssu

re R

ati

o (

-)

Volumetric Flow Rate (m3/s)

Pre

ssu

re R

ati

o (

-)

Switch from LPL EGR loop to HPL EGR loop

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Concept Validation in Modeling A predictive combustion model with knock event prediction is applied

in this validation (1D GT-Power model)

Higher Engine Speed (rpm, at step 100rpm)

Tu

rbin

e e

xp

an

sio

n r

ati

o (

-)

HPL

LPL

0.2 at each grid


PM

EP

(b

ar)

HPL

LPL

0.2 at each grid

Negative PMEP


PM

EP

(b

ar)

HPL

LPL

0.2 at each grid

Negative PMEP


To

tal

turb

och

arg

er

eff

icie

ncy (

-)

HPL

LPL

0.05 at each grid

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Dynamometer Setup

Turbocharged engine with dual-loop CEGR system Dynamometer setup in Chrysler test cell

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Concept Validation in Dyno

The difference between compression pressure ratio and turbine expansion ratio with LPL EGR system is higher than that with HPL EGR system

PMEP is reduced significantly and engine power is improved more than 7%

External EGR (%,)

Pre

ssu

re R

ati

o (

-)

Compression Ratio (HPL) Expansion Ratio (HPL)

Compression Ratio (LPL) Expansion Ratio (LPL)

0.2 at each grid

2% at each grid

External EGR (%)

PM

EP

(K

Pa)

HPL LPL

10KPa at each grid 2% at each grid

4.0

5.0

6.0

7.0

8.0

9.0

10.0

External EGR (%)

Po

wer

Imp

rovem

en

t (%

)

2% at each grid

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Discussion

High O2 concentration was found in both Dynamometer test and 1D GT-Power modeling with HPL EGR System

-90 -30 30 90 150 210 270 330 390 450 510 570 630

Crank Angle Degree (º CA)

Pre

ssu

re (

bar)

Intake

Exhaust

0.2 bar at each grid

-0.12

-0.08

-0.04

0.00

0.04

0.08

0.12

-90 -30 30 90 150 210 270 330 390 450 510 570 630

Crank Angle Degree (º CA)

EG

R m

ass f

low

rate

(kg

/s)

Cycle-based pressure wave

Mixture passing through EGR valve

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Conclusions

A HPL EGR system gives the lowest expansion ratio, i.e. lowest PMEP, but it creates other issues as well: a) lower exhaust energy to drive the turbine at lower engine speeds; and b) inadequate EGR percentage because of fresh air discharged into the exhaust system with high efficiency turbochargers.

A LPL EGR system overcomes the issues of the HPL EGR system discussed above and can be an alternate choice; however expansion ratio has a slight increase with the increase of EGR percentage and goes up significantly at higher engine speeds because of lower turbocharger efficiency.

With a LPL EGR system, at lower engine speeds, slight opening of the compressor bypass valve or raising of EGR temperature may be beneficial for expansion ratio reduction at fixed load.

A new concept is put forward to completely and efficiently utilize a given turbocharger: A LPL EGR system at lower engine speeds and a HPL EGR system at higher engine speeds, which greatly extend usage of high efficiency zones of both the turbine and compressor.

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Acknowledgement

The authors are grateful to Chrysler Group LLC management teams for permission to publish this presentation

EGR Systems Evaluation in Turbocharged Engines · EGR Systems Evaluation in Turbocharged Engines ... bypass system to mass through intake system ... turbine bypass system to mass

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