can future emissions limits be met with a hybrid egr...

Can Future Emissions Limits be Met with a Hybrid EGR System Alone?

Robert Czarnowski, Volker Joergl, Olaf Weber, John Shutty,

Phil Keller

BorgWarner, Inc.

2008 Diesel Engine-Efficiency and Emissions Research (DEER) ConferenceAugust 4-7, 2008, Dearborn, Michigan.

2

DEER Conference 2008

Contents

IntroductionHybrid EGR System

Low Pressure and High Pressure EGR

Thermodynamic AnalysisTransient Behavior and ControlsApplication SolutionsConclusions

3


Introduction

Global tightening of vehicle emissions regulationsIncreasing cost of both diesel engines and aftertreatmentImprovements in efficiency of spark ignition engines and hybridization

Unless costs are controlled, diesel engines in light duty vehicles could become uncompetitive

4


Introduction Trends in engine out emission reduction…

4

2007

Ricardo announces

Tier 2 Bin 5 possible without NOx aftertreatment

2008

Daimler announces

future Diesel engines

with significant down speeding

Ricardo, DEER 2007

Diamler, Vienna 2008

5


Introduction What exactly is “Hybrid”

EGR?

5

Two or more EGR loops used in synergy to minimizeEngine out NOx emissions through highest possible EGR ratesFuel consumption through reduced turbo charger pumping work

While providingHighest flexibility for the engine’s combustion calibrationDrivability improvements through optimized EGR / boosting controlsCost effectiveness through simplified components

6


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 “Hybrid”

EGR system Layout

7


EGR-Turbo Mapping @ 2500RPM, 12bar BMEP, 30%EGR

Thermodynamic Analysis HP&LP Loop

VTG Open

VTG Closed

100% LP-EGR

100% HP-EGR

Cooling

8


n = 2500 1/minBMEP = 12 barEGR = 30%

38%

75%

55%

n = 2500 1/minBMEP = 12 barEGR = 30%

38%

75%

55%

Pumping losses at different HP/LP-EGR-splits


High pumping lossesdue to high mass flow through closed VTG and compressor condition near choke limit

9


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


Low fuel consumptionBetter use of the exhaust energy and higher efficiencies of the compressor and turbine

10


BSFC improvement for LPL in most operating conditions

Moderate LP-EGR Rates (identical to HP-EGR Euro 4/5 Baseline)

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

1500/2 2000/4 3000/5 2500/6 2000/10 2500/12

Engine speed (rpm) / load (BMEP)

% c

hang

e in

BS

FC (H

P-LP

) BSFC of HP EGR lower

BSFC of LP EGR lower

“Hybrid”

EGR system performance Low Pressure vs

High pressure Loop Fuel Economy

11


“Hybrid”

EGR system performance emissions tradeoff -

HP-EGR versus LP-EGR

MY2007 CR engine 0.5L/Cyl

production fuel injection system

** IAV, Tietze, CTI 2006

AVL, Weissbaeck, SIA 2008 *1700 kg vehicle, 2L class engine, engineering target specific for operating point

Steady state tests applying an optimal LP-EGR system to EURO5 engine HW show approximately 30% benefit in BSNOx at constant EGR, BSSoot and BSFC.

Improved A/F capability of two stage turbo charging (R2S™) will allow further increased EGR rates without suffering fuel economy penalties through higher pumping work.

2000 RPM / 7 BMEP

12


0

0.05

0.1

0.15

0.2

0.25

0.3

0 100 200 300 400 500 600 700 800 900 1000 1100 1200NEDC test time (s)

cum

ulat

ed N

Ox

(g/k

m)

0

20

40

60

80

100

120

140

vehi

cle

spee

d (k

m/h

)

EURO 4

EURO 5

EURO 6 proposal

12

“Hybrid”

EGR system performance NEDC Test cycle

0

5

10

15

20

25

1000 1500 2000 2500 3000 3500 4000 4500 5000engine speed (rpm)

BM

EP (b

ar)

HP-EGR cooled

LP-EGR cooled

Switching

point

use of HP-EGR for good FE in ECE, LP-EGR for NOx potential in EUDCSwitching between HP-EGR and LP-EGR to avoid condensation<0.1 g/km NOx achieved with standard VTG (55kW/L) and w/o fuel economy hit!

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

ECE EUDC

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Dynamic performance: HP vs. LP EGR

Influence on load step performance•

LP EGR ⇒ enhanced dynamic performance

•

influence of turbo charger

speed dominant

Load (Bar bmep) Air/Fuel ratio

Percent EGR Turbo charger VTG position

Low pressure EGR

High pressure EGR

1500 rpm / 2 bmep / 70% EGR

Turbo charger speed

Clo

sed

open

λ=1

1500 rpm / 9 bmep / 25% EGR

14


Dynamic controllability-

influence of EGR on turbo

30000

35000

40000

45000

50000

55000

60000

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40

Time (s)

TC-s

peed

(rpm

)

-230

-180

-130

-80

-30

20

70

Valv

e po

sitio

n (%

)

tc speed with LP-EGR tc speed with HP-EGRLP-EGR-valve position HP-EGR-valve position

0

20

40

60

80

100

120

140

160

180

200

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40Time (s)

Bac

k pr

essu

re b

efor

e TC

(mba

r)

-230

-180

-130

-80

-30

20

70

120

Valv

e po

sitio

n (%

)

P3 with LP-EGR P3 with HP-EGRLP-EGR-valve position HP-EGR-valve position

Influence of EGR on turbo charger boundary conditions •

Ex Man pressure and turbo charger speed are nearly constant with

and w/o LP-

EGR . •

the higher the EGR-rate, the bigger the difference between LP-

and HP-EGR becomes•

decoupling the EGR-rate from TC performance greatly improves transient controllability

2000 rpm / 2 bmep / 30% EGR

15


LP EGR vs. HP EGR: Transient behavior

Load step performance at low speed (1500rpm): Initial delay time

HP-EGR version show a faster BMEP increase at the beginning, but LP-EGR version keeps up and reaches the target BMEP faster

Low pressure EGR works optimally with closely packaged indirect charge air cooling.

Using hybrid EGR, the HP-EGR fraction can be optimized for each speed/load point.

1.0 1.2 1.4 1.6 1.8 2.0

2

4

6

8

10

time [s]

BM

EP

[bar

]

Δt

to 6 bar BMEP = +0.062s

Δt

to 9 bar BMEP = -0.9s

9bar BMEP, 25%

EGR

2bar BMEP, 70%

EGR

Low pressure EGR

High pressure EGR

16


0/100

LP / HP EGR Split Strategy

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

17


Air Controller System Architecture

Air FlowOptimization

Block

LP EGR OpenLoop Controller

EGR Closed Loop

Controller

HP EGR OpenLoop Controller

HP-EGRValve

IntakeThrottle

LP EGRValve

ExhaustThrottle

VTG

Total EGR %

-+

Boost PressureClosed Loop

Controller

++

++

++

Total EGR %Set-point

Boost PressureSet-point

HP EGR %Set-Point

LP EGR %Set-Point

Boost Pressure-

+

Boost PressureOpen Loop Controller

BoostSet-Point

BoostSet-Point

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New componentsLow pressure EGR valveLow pressure EGR coolerExhaust throttle valveMixerAir Flow Optimization Controls

Changes to present componentsEGR resistant compressor wheelCondensate resistant charge air coolerLarger TC possible, LP-EGR avoids surging with low compressor flow

LP EGR Application Development

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Conclusions

Hybrid EGR offers significant advantages to reduce emissions and fuel consumption and can meet future emission requirements

Aftertreatment system cost can be reduced with a hybrid EGR system

Two stage boosting systems together with hybrid EGR allow further enhanced performance while utilizing down speeding to achieve CO2 targets.

Dynamic performance can be improved with a hybrid EGR system

System and component development are production ready

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Thank You For Your Attention

can future emissions limits be met with a hybrid egr...

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