Late Intake Valve Closing and Exhaust Rebreathing in a V8 ... · Late Intake Valve Closing and...

1Advanced Diesel DEER Conference 2010

DEER Conference 2010

Late Intake Valve Closing and Exhaust Rebreathing in a V8 Diesel Engine for

High Efficiency Clean Combustion

High-Efficiency Clean Combustion Engine Designs for Compression Ignition Engines

GM-DOE AGREEMENT No. DE-FC26-05NT42415

Manuel A. Gonzalez D.General Motors Powertrain. Advanced Diesel

September 29, 2010


Outline

● Objectives

● Technical Approach & Hardware

● Discussion of Variable Compression Ratio - Late Intake Valve Closing & Two Stage Turbo Charging

● Discussion of Internal EGR - Exhaust Rebreathing

● Estimated overall driving cycle impacts

● Summary

● Acknowledgements


Objectives● Investigate the use of variable valve actuation (VVA) as a means to

improve the efficiency of a light duty diesel engine approaching and exceeding Tier 2 Bin 5 NOx emission levelsMulti-cylinder engine testing using a “simple mechanism” VVA system –

steady state engine-out emission targets combined with aftertreatment technology for beyond Tier 2 Bin 5 tailpipe targets and enhanced fuel economy─ Late Intake Valve Closing (LIVC) Study─ Exhaust Rebreating Study

● Barriers addressedTo operate at Low Temperature Combustion (LTC) conditions using “VVA

simple mechanisms” for control of effective compression ratio and internal EGR (IEGR)

Expand the useful range of the Early Premixed Charge Compression Ignition (PCCI) LTC mode in order to reduce fuel consumption

To reduce engine out emissionsTo minimize the fuel energy required to raise exhaust gas temperature for

catalyst efficiency and regeneration


0 100 200 300 400 500 600 700

PISTON / VALVE APPROACH DIAGRAM

PISTON MOTIONINTAKE VALVEEXHAUST VALVE

Strategy Valve profiles Observations

Late Intake Valve Closing (both valves)

• Too limiting for engine breathing reducing volumetric efficiency and torque

Late Intake Valve Closing (one valve)

• Effective compression ratio control• Reduces volumetric efficiency• LIVC with extended duration, same

expansion ratio with reduced compression ratio (improved efficiency)

Intake Re-breathing(Intake valve re-opening during exhaust stroke)

• Higher heat losses than exhaust re-breathing

• More difficult to open than exhaust valve

Exhaust Re-breathing (Exhaust valve re-opening during intake stroke)

• Only one exhaust valve lift profile need to be changed

• Multiple profiles possible and combined with intake - exhaust pressure control

• Easier to be opened than intake valve

• Less heat losses than intake re-breathing

VVA Strategies


Technical Approach - HardwareMulti Cylinder Engine – VVA Study• Late Intake Valve Closing (phasing of one valve per cylinder)• Exhaust Rebreathing (re-opening of one valve per cylinder) with single and two stage turbocharging

BaseEngine Testbed

Concentric Camshafts and phaser

Secondary exhaust opening profileTwo-stage turbocharging

Configuration/Displacement V8 4.5 liters

Compression Ratio 16.0:1

Bore x stroke 88 mm x 92 mm

Valve Train DOHC - 4v

Intake Configuration Outboard intake with integrated cam cover intake manifold

EGR System Cooled external

Exhaust System In Vee exhaust with manifold integrated into head

Emissions System DOC, Urea SCR and DPF


VVA - Late Intake Valve Closing

Two stage system, concentric camshaft and phaser in multi-cylinder engine head

LIVC phasing capability up to 90 ca degrees

Effective compression ratio in LIVC operating range

Engine operating map for LIVC study

Valv

e Li

ft

Crank angle

Exhaust

Intake

Intake phasing

BDC Intake14

14.5

15

15.5

16

16.5

17

0 70

Effe

ctiv

e Co

mpr

essi

on ra

tio

LIVC (crankangle degrees)

TDC

effectiveeffective V

VCR =


1-D Modeling for LMK 4.5L V8 Diesel Engine

Turbocharging for LIVC

Target:70 ca deg

phasing of one intake valve

matching AFR and EGR

Exh

Two stage charging selected

Base VGT LIVC0Base VGT LIVC70Base VGT Closed LIVC70

HP FG and LP FG LIVC70HP VGT and LP FG LIVC70HP FG and LP VGT LIVC70

Int


Charging

● Modeling air handling 1-D modeling base

engine and VVA system

Charging hardware selection

BSFC (g/Kw-h)

220.0

230.0

240.0

250.0

260.0

270.0

280.0

Single VGT Baseline

Single VGT 70 deg LIVC

Single VGT 70 deg

LIVC; VGT Closed

HP 2-stage 70 deg LIVC

1200/2.8 rpm/bar BMEP



AFR matching only reached when using a High Pressure VGT not using VNT closing which have detrimental BSFC performance

Experimental work also have shown emissions benefits with a controlled reduction in AFRP

ress

ure

ratio

Corrected Flow

0.465

0.48

0.495

0.51

0.525

0.54

0.555

57 0.57585 0.5850

6

0.6

615

0.6150.63

0.63

0.63

645

0.645

0.66

0.675

0.69

0.705

0.72

0.735

0.75

0.765

0.78

0.465

0.48

0.4950.510.525

0.540.555

0.570.5850.6

0.615

0.63 0.63

0.645 0.

645

0.66 0.

66

0.66

0.675 0.675

0.69 0.69

0.705

0.72

0.735

0.75

0.75

0.765

0.78


1600 rpm/4.8 bar BMEPNormal combustionCoolant @ 88C, Bypass OFFConstant NOx 1.2 g/kgCa50 12 atdc fix

Effective Compression Ratio on Cylinder Pressure

Peak cylinder pressure reduction resulted by LIVC implementation for lower effective compression ratio

Start of injection can be advanced for constant combustion phasing to compensate for longer ignition delay Coef of Variation of combustion phasing increases

with LIVC, cam phasing control stability and impact of changing flow dynamics of individual cylinders

SCE 1600 rpm x 4.2 bar LIVC60 EINOx 0.3 g/kg-fEarly PCCI (blue color, LIVC70) and late PCCI

-40 -20 0 20 40 60 800

0.5

1

Inj C

urr

-10

5

20

35

50

65

80

Cyl

Pre

ss (b

ar)

-10

5

20

35

50

65

80

AH

RR

(J/c

ad)

-40 -20 0 20 40 60 800

0.5

1

Inj C

urr

-10

5

20

35

50

65

80

Cyl

Pre

ss (b

ar)

-10

5

20

35

50

65

80

AH

RR

(J/c

ad)


LIVC0 LIVC40 LIVC50 LIVC60 LIVC70LIVCdegrees [-]

EGR

[%]

32

34

36

38

AIR

FU

EL R

ATI

O [-

]

16

18

20

DEL

TA M

AIN

INJE

CTI

ON

[°C

A

0

5

10

AIR

_FLO

W [k

g/h]

120

128

136

144

1600 rpm/4.8 bar BMEPNormal combustion

Coolant @ 88C, Bypass OFF< 1.2 g/kg EINOxCa50 12 atdc fix

Fix 70% VNT position

Variation of main engine parameters at different LIVC phasing and constant NOx

Advancing SOI for constant phasing

Flow to intake manifold

Less EGR at constant NOx

AFR drops with less efficient charging


1600 rpm/4.8 bar BMEPNormal combustion

Coolant @ 88C, Bypass OFF< 1.2 g/kg EINOxCa50 12 atdc fix

Fix 70% VNT position

Variation of main engine parameters at different LIVC phasing and constant NOx

LIVC0 LIVC40 LIVC50 LIVC60 LIVC70LIVC degrees [-]

SMO

KE

[FSN

]

0

1

2

3

BSF

C [g

/kW

h]

243

246

249

252

255

HYD

RO

CA

RB

ON

S [g

/kg]

1.8

2.1

2.4

2.7

Optimum BSFC determined by Phasing, Heat transfer, Friction

Higher oxygen accesibility by lower effective compression ratio and variable swirl

Lower temperature profile for higher HCs

SMO

KE

RAT

IO

1

0


0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0 3.3 3.6 3.9EINOX [g/kg]

Smok

e [F

SN]

0.0

0.3

0.6

0.9 EITH

C [g

/kg]

5.2

5.6

6.0BSF

C [g

/kW

h]

250

252

254

AFR

[-]

21

24

27

Base and LIVC 50 ca degreees1200 rpm/3.9 bar BMEP

Normal combustionCoolant @ 88C, Bypass OFF

Ca50 9 atdc fixFix 72% VNT position

30-42% EGR sweep

AFR, BSFC, HC, Smoke with LIVC Phasing

Consistent trends are

observed at different

keypoints

LIVC 0LIVC 50


1600 rpm/4.8 bar BMEPCoolant @ 88C, Bypass OFF

Two stage HP TC. Ca50 12 atdc fixFix 50% VNT position

High % EGR sweepNOx << 1 g/kg fuel

Smoke vs AFR at Low NOx with LIVC Phasing for PCCI Combustion Modes

Early PCCI encounters either high smoke or high noise if using a conventional valve lift profile.

For LIVC, a single injection strategy could achieve good overall engine performance.

By using LIVC, the combustion phasing can be advanced for better fuel economy.

The AFR can be reduced because smoke emissions are lower due to longer ignition delay.

The combustion noise is controlled within the noise limits by adjusting the injection timing.16 17 18 19 20 21 22 23 24 25

Air Fuel Ratio [-]

SMO

KE

[FSN

]

0.0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3.0

SMK_FSN_NOSMK_FSN_NOSMK_FSN_NO

LIVC 0LIVC 50LIVC 60

SMO

KE

RAT

IO

1

0.5

0


LIVC 50 ca delay - Overall Effects

Impact FTP CycleBSFC ~ -0.5%PM ~ -25%, > 50%

at keypointsHC > +17%

Operating region defined by trade-offs of fuel efficiency and

emissions (boundaries: HCs at light loads; loss of

ignition delay advantage for mixing at higher loads and

AFR drop)


Internal EGRExhaust rebreathing events

● Keypoints operating area selected by HC contribution to cold start FTP cycle

● High/Low Lift and duration profiles

● Valvetrain exhaust implementations opposite to intake helical and tangential ports RPM

Valv

e Li

ft

Camshaft Angle

High Lift - Duration

Low Lift - Duration

Baseline Exhaust


Internal EGR approach

Exhaust Valve Flows1600 rpm/6.8 bar

Exhaust Valve Flows650 rpm/2.2 bar

Fixed cams for switching profiles options

Representative IEGR profiles Modeling of HC and NOx contributing keypoints

Valv

e lif

t


0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

800/105 1000/112 1200/90 1400/190 1600/150 1600/191 1800/263 2000/333

Exte

rnal

(Byp

ass

) EG

R (%

)

Base

Reb cam

43 30 15

2614

4124

41

0

100

200

300

400

500

600

700

800/105 1000/112 1200/90 1400/190 1600/150 1600/191 1800/263 2000/333

Turb

ine

Inle

t Te

mpe

ratu

re (

C)

Base Temp Turbine Inlet Temp increase

Internal EGR relative to Baseline

• Turbine In temperature can be increased along all the operating range

• Can induce light-off for the DOC catalyst

• Varies with heat transfer, AFR by substitution of External (Bypass) EGR (%)

• Internal EGR amount by model based approach

Fix RPM/BMEP keypointsIn 200 sec warm-up phase

Coolant @ 40C, Bypass ONNOx ≤ target

RPM/TORQUE


Internal EGR relative to Baseline

Post DOC performance, (as HC % of reduction) is favored by less engine out emissions plus faster light-off and higher conversion by higher operating temperature

-90.0

-80.0

-70.0

-60.0

-50.0

-40.0

-30.0

-20.0

-10.0

0.0

800/105 1000/112 1200/90 1400/190 1600/150 1600/191 1800/263 2000/333

Post

DO

C H

C (%

)

Fix RPM/BMEP keypointsIn 200 sec warm-up phase


DOC inlet and Post DOC temperature can be further increased by HC/CO additional conversion (also changes in turbine operating point efficiency)

RPM/TORQUE


Impact of IEGRFix RPM/BMEP keypoints

In 200 sec warm-up phaseCoolant @ 40C, Bypass ON

NOx ≤ target

First 200 sec in the warmup phase FTP Cycle – Estimate by weighting

factors Test vehicle weight 7000 lbs. Exhaust Gas temperature Management at low coolant temperature

>20 % of the fuel consumed in FTP cycle

Smoke impact constrains for maximum applied engine bmeps

Whole FTP Cycle

Fuel consumption ~ +0.3%

Tailpipe Hydrocarbons ~ -20% (-50% first 200 sec of

FTP cycle)


Comparing exhaust heating strategies Fix RPM/BMEP keypointsIn 200 sec warm-up phase


• For matching exhaust temperature, IEGR by exhaust rebreathing shows promising results for a competitive strategy to retarded timing at idle

• Sources of sensitivity to port location to be subject of detailed investigation

200

220

240

260

280

300Tu

rbin

e In

tem

pera

ture

(C)

270

280

290

300

310

320

800 rpm / 105 N-m

BSFC

(g/k

W-h

)

Baseline

Baseline w/retarded injection

Low Lift - Duration Helical Port

Low Lift - Duration Tangential Port


IEGR Strategy / Aftertreatment modeling

Vehicle TVW 7000 lbs

● Phase 1 with highest contribution to HC and NOx overall tail-pipe emission for FTP

● Increasing exhaust temperature by 40 degrees

Overall emission for FTP can be reduced by 25% (HC) and 17%(NOx)

Total HC reduction Engine-out plus higher conversion 35%

0

50

100

150

200

250

300

350

400

450

500

0 20 40 60 80 100 120 140 160 180 200

Tem

p [C

]

Time [sec]

TemperaturesExh manifold

Pre DOC T

SCR_Tavg


The application of switching roller finger followers on the exhaust valvetrain of multi-cylinder diesel engines for selectively producing the re-opening of exhaust valves for internal EGR control

Patent application - Diesel engine with switching roller finger followers for

internal EGR control

1-D SimulationIdle

Internal EGR replacing external EGR

Ways to apply the system:

• Single Exhaust valve per cylinder - allows one discrete rebreathing profile to be used, switchable

• Both exhaust valves per cylinder - single actuator, allows a higher amount of EGR to be introduced based on a single actuator

• Both exhaust valves per cylinder - dual actuator circuit, allow combinations of internal EGR rate to be achieved (zero, low and high)

• Both Exhaust valves per cylinder - dual actuator circuit, dual lift profiles, flexible control with 3 levels of internal EGR possible (additional control achieved with back pressure regulation)

EGR Level Exh Valve #1 Exh Valve #2

0 Off Off

1 On Off

2 Off On

3 On On


Summary● Late Intake Valve Closing for Changing Effective Compression Ratio and Exhaust Rebreathing for

Internal EGR have been investigated with promising results

● Operating envelope LIVC operation at part loads for emissions and FE of hot FTP cycle, constrained by charging system capability IEGR operation from idle to part loads for warm-up and emissions of cold FTP cycle. Max BMEP determined by smoke limitations

VVA Major impacts Benefits / Limitations

Strategies

Intake

Exhaust

Profiles FTP75 cycle fuel

cons.

FTP75 cycle emissions. NOx PM HC CO Comb

noiseExhaust

temp

LIVC 1% * reduction

50% PM reduction + ++ - - + O

Internal EGR

0.3-0.5%increase

**

~20% HC reduction O - + + O +

Key:+ improvedo neutral- worse

*: Depending on charging capability**: Compensation by warm-up strategy and aftertreatment impact

Higher FE potentialimprovement for LIVC including the benefit for increased DPF regen interval


Summary

● Variabe valvetrain techniques have significant impacts on fuel efficiency and emissions with packaging and control challenges for implementation with different alternative valvetrain mechanisms in new engine designs

● Late intake valve closing and exhaust rebreathing provide further optimization opportunities for fuel efficiency and emissions

● Experimental impacts and estimations for the assessment of application are highly dependent on engine architecture and engine performance and emissions targets

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