egr systems evaluation in turbocharged engines · egr systems evaluation in turbocharged engines...
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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
© 2013 Chrysler Group LLC. All rights reserved
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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PTV: L.Zhong et al. Presentation
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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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PTV: L.Zhong et al. Presentation
GT CONFERENCE 2013
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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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PTV: L.Zhong et al. Presentation
GT CONFERENCE 2013
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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
CHRYSLER GROUP LLC
PTV: L.Zhong et al. Presentation
GT CONFERENCE 2013
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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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PTV: L.Zhong et al. Presentation
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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%
CHRYSLER GROUP LLC
PTV: L.Zhong et al. Presentation
GT CONFERENCE 2013
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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
CHRYSLER GROUP LLC
PTV: L.Zhong et al. Presentation
GT CONFERENCE 2013
© 2013 Chrysler Group LLC. All rights reserved
9
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
Higher Engine Speed (rpm, at step 100rpm)
PM
EP
(b
ar)
HPL
LPL
0.2 at each grid
Negative PMEP
Higher Engine Speed (rpm, at step 100rpm)
PM
EP
(b
ar)
HPL
LPL
0.2 at each grid
Negative PMEP
Higher Engine Speed (rpm, at step 100rpm)
To
tal
turb
och
arg
er
eff
icie
ncy (
-)
HPL
LPL
0.05 at each grid
CHRYSLER GROUP LLC
PTV: L.Zhong et al. Presentation
GT CONFERENCE 2013
© 2013 Chrysler Group LLC. All rights reserved
10
Dynamometer Setup
Turbocharged engine with dual-loop CEGR system Dynamometer setup in Chrysler test cell
CHRYSLER GROUP LLC
PTV: L.Zhong et al. Presentation
GT CONFERENCE 2013
© 2013 Chrysler Group LLC. All rights reserved
11
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
CHRYSLER GROUP LLC
PTV: L.Zhong et al. Presentation
GT CONFERENCE 2013
© 2013 Chrysler Group LLC. All rights reserved
12
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
CHRYSLER GROUP LLC
PTV: L.Zhong et al. Presentation
GT CONFERENCE 2013
© 2013 Chrysler Group LLC. All rights reserved
13
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.
CHRYSLER GROUP LLC
PTV: L.Zhong et al. Presentation
GT CONFERENCE 2013
© 2013 Chrysler Group LLC. All rights reserved
14
Acknowledgement
The authors are grateful to Chrysler Group LLC management teams for permission to publish this presentation