control strategy for a dual loop egr system to meet … strategy for a dual loop egr system to meet...

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.

2

DEER Conference 2009

Contents

BackgroundSystem DescriptionThermodynamic Analysis

Control System OverviewStructureFeaturesControl Optimization

NEDC Results

On Engine Application

Conclusions

3


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

4


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

5


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)

6


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

7


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

8


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

[email protected]

control strategy for a dual loop egr system to meet … strategy for a dual loop egr system to meet...

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