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.
2DEER Conference 2009
Contents
Background System Description Thermodynamic Analysis
Control System Overview Structure Features Control Optimization
NEDC Results On Engine Application
Conclusions
3DEER Conference 2009
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 2
007
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4DEER Conference 2009
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
5DEER Conference 2009
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 Reduced Up to 4% improvement in BSFC in steady state More EGR can be driven without performance sacrifice
Dynamic engine performance can be improved with a dual loop EGR system Transient controls need to be developed and improved
(focus of today's presentation)
6DEER Conference 2009
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
7DEER Conference 2009
Development Process
Modeling of Production Baseline Full GT-Power Model Real time capable mean value model (MVM)
Development of controller in Simulink Controller Verification and calibration
with GT-Power MVM in Simulink Dynamometer testing and final
calibration using same Simulink code Verification on Dyno simulating NEDC
Cycle
8DEER Conference 2009
Previous Controller Options
Separate EGR and Boost Controllers Stability achieved by maintaining open loop or slow
dynamic controls
Decoupled EGR and Boost Controllers Loop interference reduced but slow response and
overshoots still an issue
In both cases, NOx and PM control compromised during transients
9DEER Conference 2009
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
Boost 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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DEER Conference 2009
BW Coordinated Controller Features Negative 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 Improvement Achieves requested EGR rate more accurately
EGR Boost Optimization Block Determines EGR loop split Calculated 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 Control Coordinated EGR and boost system to adjust on the fly with
closed loop control
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DEER Conference 2009
Coordinated Controller Results Static EGR Estimation Improvement Better fuel economy achieved at same NOx level
EGR 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 Control Decoupling of VTG and EGR allows control of each during
transients Less NOx and PM spikes
Easy to implement in production ECU Low memory and CPU usage No 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
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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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200 230 260 290 320 350 380 410 440 470 500
EGR rate setpoint EGR rate actual
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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
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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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DEER Conference 2009
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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DEER Conference 2009
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
BWDualLoopEGR20%
ProdECUHPEGR25%
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N
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Increased EGR rate to Maximize NOx ReductionProduction ECU vs
BorgWarner Coordinated Controls
BWDualLoopEGR35%
ProdECUHPEGR25%
-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
C
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+ 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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DEER Conference 2009
Conclusions Dual 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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DEER Conference 2009
Thank You For Your Attention
For Further Information Contact:
Bob Czarnowski
Slide Number 1ContentsMotivationSlide Number 4Slide Number 5Slide Number 6Development Process Previous Controller OptionsAir Controller System Architecture BW Coordinated Controller FeaturesCoordinated Controller ResultsHPL/LPL Split StrategyLP / HP EGR Split Strategy Steady State MapStatic and Dynamic Improvements Relative to Baseline EUD Cycle - On Engine NOx ControlSlide Number 16Cumulative NOx and CO2 on NEDC TestSlide Number 18System SummarySummary Map: CO2 vs NOx Relative Contributions to Emissions ReductionSlide Number 21Slide Number 22