Control Strategy for a Dual Loop EGR System to Meet Euro 6 and Beyond
John Shutty and Robert Czarnowski
2009 Directions in Engine-Efficiency and Emissions Reduction Research (DEER) ConferenceAugust 3-6, 2009, Dearborn, Michigan.
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Contents
BackgroundSystem DescriptionThermodynamic Analysis
Control System OverviewStructureFeaturesControl Optimization
NEDC Results
On Engine Application
Conclusions
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Motivation
Reduce the cost and lower emissions of diesel engines in an ever tightening regulatory world
Focus on EGR and Boost Systems
NOx Emissions Regulation (g/km)
KoreaEuro III 2005
Euro IV 2010
China
Euro 3 2007
Euro 4 2010
EuropeEuro 3 2000
Euro 4 2005Euro 5 2009
United States
Tier II Bin 5 2007
Japa
nJa
pan
2005
Japa
n 20
09
0.4
0.6
0.8
1.0Indi
aB
hara
t II 2
005
Bha
rat I
II 20
10
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Exhaust Throttle
Charge Air Cooler
LP-EGR Valve
DPFHP-EGR Valve
Intake throttle
LP-
EGR Cooler
EGR Mixer
HP-
EGR Cooler
VTGI4 diesel engine, common rail
EGR & Turbo Charging System Architecture Base “Dual Loop” EGR system Layout
Base engine HW: 2L Inline 4 EURO4
Adjusted Parameters: EGR-rate, Boost pressure
Combustion system: standard Diesel (diffusive)
EGR-system: cooled HP-EGR, cooled LP- EGR
Boosting system:1-stage VTG
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Last year conclusions
A Dual Loop EGR System offers significant advantages to reduce emissions and fuel consumption and can meet future emission requirements
Mostly due to improved turbocharger operating efficiency
Charge Air Temperature ReducedUp to 4% improvement in BSFC in steady stateMore EGR can be driven without performance
sacrificeDynamic engine performance can be improved with a dual loop EGR systemTransient controls need to be developed and improved (focus of today's presentation)
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n = 2500 1/minBMEP = 12 barEGR = 30%
38%
75%
55%
n = 2500 1/minBMEP = 12 barEGR = 30%
38%
75%
55%
Specific fuel consumption at different HP/LP-EGR-splits
Thermodynamic Analysis HP&LP Loop
Low fuel consumptionBetter use of the exhaust energy and higher efficiencies of the compressor and turbine
100% HP
VTG Open
VTG Closed
100% LP
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Development Process
Modeling of Production BaselineFull GT-Power ModelReal time capable mean value model (MVM)
Development of controller in SimulinkController Verification and calibration with GT-Power MVM in SimulinkDynamometer testing and final calibration using same Simulink codeVerification on Dyno simulating NEDC Cycle
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Previous Controller Options
Separate EGR and Boost ControllersStability achieved by maintaining open loop or slow dynamic controls
Decoupled EGR and Boost ControllersLoop interference reduced but slow response and overshoots still an issue
In both cases, NOx and PM control compromised during transients
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Load
Speed HP EGR set point
LP EGR set point
EGR-Boost optimization
HP EGR Control
Map
LP EGR Control
Map
HPLSplit
LPLSplit
Total EGR frac
estimator
Feedback Controller
EGR TOTAL set-point
Sensor(s)
HP EGR Valve
Intake Throttle
LP EGR & Exhaust Throttle Module
Temperature
Δ
ΔBoost Pressure Set Point
Boost Controller
Turbo VTGSensor(s)
Engine State
Engine State
Air Controller System ArchitectureHigh Pressure Loop Controls
Turbo Controls
Low Pressure Loop Controls
Feed Forward Loops
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BW Coordinated Controller FeaturesNegative coupling is eliminated and positive coordination is added to improve response and control
Dual Loops and VTG help each other to achieve higher efficiency
Static EGR Estimation ImprovementAchieves requested EGR rate more accurately
EGR Boost Optimization BlockDetermines EGR loop splitCalculated dynamically for best efficiency
Utilization of EGR path which is most capable and efficient of achieving the set-point
statically (actuator saturation (virtual or actual))dynamically (slower loop dynamics)
Improved Dynamic ControlCoordinated EGR and boost system to adjust on the fly with closed loop control
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Coordinated Controller ResultsStatic EGR Estimation Improvement
Better fuel economy achieved at same NOx levelEGR Boost Optimization Block
Fuel economy improved by higher Turbo Efficiency and lower NOx achieved by increasing EGR
Dynamic feedback control of EGR mass flow, both EGR loops and VTG
Improved Dynamic ControlDecoupling of VTG and EGR allows control of each during transientsLess NOx and PM spikes
Easy to implement in production ECULow memory and CPU usageNo extra I/O
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HPL/LPL Split Strategy
Maximize Efficiency of Turbocharger
Minimize pumping losses
Improve dynamic Performance
Control Charge air temperature
Minimize Condensation in LPL
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0/100
LP / HP EGR Split Strategy Steady State Map
Torq
ue
Engine speed
%HP EGR / %LP EGR
100/0 Combustion temperature
20/80
40/60
High pumping loss with LP EGR
Increase oxygen content
75/2540/60 Optimizing
VTG position
40/60
Fast reaction time
75/25
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EGR
Rat
e (%
)
0
10
20
30
40
50
200 230 260 290 320 350 380 410 440 470 500
EGR rate setpoint EGR rate actual
EGR
Rat
e (%
)
0
10
20
30
40
50
200 230 260 290 320 350 380 410 440 470 500
EGR rate setpoint EGR rate actual
Production ECU Control
BorgWarner Control
Static and Dynamic Improvements – Relative to Baseline
EGR valve shut-
off to decouple
EGR Rate above requested rate
Maintains requested rate during cycle
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EUD Cycle - On Engine NOx Control
Vehi
cle
spee
d [k
m/h
]
0
40
80
120
NO
x co
ncen
trat
ion
[ppm
]
0
50
100
150
200
250
Cycle time [s]780 880 980 1080 1180
Base HP EGR calibration / Daimler ECU controller HP+LP EGR V0 calibration / BWES controller HP+LP EGR V5 calibration / BWES controller
HP EGR V0 / ECU Control HP/LP EGR V0 / BW Controller HP/LP EGR V5 / BW Controller
BW Dual Loop 35%
BW Dual Loop 20%
Production ECU – HPL 25%
NOx Peaks reduced
Significant NOx reduction
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25% Prod ECU HP EGR
35% Dual Loop EGR
25% Dual Loop EGR
Km/hr
Charge temperatures reduced with dual Loop EGR
•Temp reduced over 30C
•HPL & LPL have same size coolers
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Cumulative NOx and CO2 on NEDC Test
•
24% Reduction in NOx
• Constant PM
•
6% less fuel consumption
Production ECU Control HPL vs. BW Control Dual Loop EGR
BW Dual Loop EGR 20%
Prod ECU HP EGR 25%
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NO
x mg/km
Seconds
Km / hr
Increased EGR rate to Maximize NOx ReductionProduction ECU vs
BorgWarner Coordinated Controls
BW Dual Loop EGR 35%
Prod ECU HP EGR 25%
-72%
•72% Reduction in NOx
•Increased EGR to Obtain Equivalent Fuel Consumption & PM
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System SummarySystem EGR System Fuel
Consumption reduction (%)
NOxReduction (%)
Baseline High Pressure loop w/ cooler25%
NA NA
BorgWarner coordinated controls
High Pressure loop w/ cooler20%
8 0
BorgWarner coordinated controls
Dual Loop EGR w/ coolers20%
6 24
BorgWarner coordinated controls w/ increased EGR
Dual Loop EGR w/ coolers35%
0 72
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Summary Map: CO2 vs
NOx Relative Contributions to Emissions Reduction
NOx Reduction Contributions
155
160
165
170
175
180
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45
NOx g/km
CO
2 g/
km
+ BW Controls
+ 15 EGR
+ 15% EGR
ECU ControlHP EGR
+ LP EGR
+BorgWarner Air Path Controls
Theoretical Line +15% EGR
+15% EGR Actual
+15% EGR Actual
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ConclusionsDual Loop EGR offers significant advantages to reduce emissions and fuel consumption to meet future emission requirements
A coordinated control system has been developed to optimize the EGR and air boost system
Significantly reduces fuel consumption and / or NOx
Improves dynamic performance of turbocharger
Potential for NOx aftertreatment system cost reduction
Future work includes two stage boosting systems together with dual loop EGR allows further enhanced performance while utilizing down speeding to achieve CO2 targets.
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Thank You For Your Attention
For Further Information Contact:
Bob Czarnowski