Towards High Efficiency Engine –

THE Engine

Bengt Johansson

Div. of Combustion Engines

Director of KCFP,

Lund University,

Sweden

What is a high efficiency?

Any text book on ICE:

• Ideal cycle with heat addition at

constant volume:

• With a compression ratio, Rc, of 60:1

and γ=1.4 we get an efficiency of

80,6%

• Why then do engines of today have

an efficiency of 20-40%???2

Outline

• What is high efficiency?

• Combustion, thermodynamic, gas exchange

and mechanical efficiencies. All four must

be high.

• Combustion to enable high efficiency

• HCCI

• Partially Premixed Combustion

• Can we do something about engine

design?

• Conclusions

Energy flow in an IC engine

FuelMEP

QhrMEP

IMEPgross

lMEPnet

BMEP

QemisMEP

QlossMEP

QhtMEP

QexhMEP

PMEP

FMEP

Combustion efficiency

Thermodynamic efficiency

Gas exchange efficiency

Mechanical efficiency

Net Indicated efficiency

Brake efficiency

Gross Indicated efficiency

FuelMEP

QhrMEP

IMEPgross

lMEPnet

BMEP

QemisMEP

QlossMEP

QhtMEP

QexhMEP

PMEP

FMEP

Combustion efficiency

Thermodynamic efficiency

Gas exchange efficiency

Mechanical efficiency

Net Indicated efficiency

Brake efficiency

Gross Indicated efficiency

MechanicaleGasExchangmicThermodynaCombustionBrake

***

Outline

• What is high efficiency?

• Combustion, thermodynamic, gas exchange

and mechanical efficiencies. All four must

be high.

• Combustion to enable high efficiency

• HCCI

• Partially Premixed Combustion

• Can we do something about engine

design?

• Conclusions

6

HCCI -Thermodynamic efficiency

Saab SVC variable compression ratio, VCR, HCCI, Rc=10:1-30:1;

General Motors L850 “World engine”, HCCI, Rc=18:1, SI, Rc=18:1, SI, Rc=9.5:1

Scania D12 Heavy duty diesel engine, HCCI, Rc=18:1;

Fuel: US regular Gasoline

SAE2006-01-0205

All four efficiencies

7

SAE keynote Kyoto 2007

Net indicated efficiency= ηC ηT ηGE

SI std

SI high

HCCI

VCR

Scania

+100%

Brake efficiency

SI std

SI high

HCCI

VCR

Scania

Net indicated efficiency= ηC ηT ηGE

SI std

SI high

HCCI

VCR

Scania

47%

Outline

• What is high efficiency?

• Combustion, thermodynamic, gas exchange

and mechanical efficiencies. All four must

be high.

• Combustion to enable high efficiency

• HCCI

• Partially Premixed Combustion

• Can we do something about engine

design?

• Conclusions

PPC - Diesel engine running on gasoline

0 2 4 6 8 10 12 1420

25

30

35

40

45

50

55

60

Gross IMEP [bar]

Gro

ss In

dic

ate

d E

ffic

ien

cy [%

]

Group 3, 1300 [rpm]

FR47333CVX

FR47334CVX

FR47336CVX

HCCI: ηi=47% => PPC: η

i=57%

12

Partially Premixed Combustion, PPC

13

-180 -160 -140 -120 -100 -80 -60 -40 -20

1000

2000

3000

4000

5000

6000Spridare 8x0.12x90 & 8x0.12x150, Iso-oktan, CR-tryck 750 bar, Duration 0,6 ms = 3.6 CAD

HC

[ppm

]

SOI [ATDC]-180 -160 -140 -120 -100 -80 -60 -40 -20

200

400

600

800

1000

1200

NO

x [

ppm

]

Def: region between truly homogeneous combustion, HCCI,

and diffusion controlled combustion, diesel

HCCI

PPC

CI

SAE 2004-01-2990

14

Experimental setup, Scania D12

Bosch Common Rail

Prailmax 1600 [bar]

Orifices 8 [-]

Orifice Diameter 0.18 [mm]

Umbrella Angle 120 [deg]

Engine / Dyno Spec

BMEPmax 15 [bar]

Vd 1951 [cm3]

Swirl ratio 2.9 [-]

Fuel: Gasoline or Ethanol

SAE 2009-01-2668

15

Efficiencies 17.1:1

4 5 6 7 8 9 10 11 12 1350

55

60

65

70

75

80

85

90

95

100

Gross IMEP [bar]

[%] Combustion Efficiency

Thermal Efficiency

Gas Exchange Efficiency

Mechanical Efficiency

SAE 2009-01-2668

16

4 6 8 10 12 14 16 18

50

55

60

65

70

75

80

85

90

95

100

Gross IMEP [bar]

[%

] Combustion Efficiency

Thermal Efficiency

Gas Exchange Efficiency

Mechanical Efficiency

Efficiencies 14.3:1

SAE 2010-01-0871

1717

4 6 8 10 12 14 16 180

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Sm

oke

[F

SN

]

Gross IMEP [bar]

2 4 6 8 10 12 14 16 180

0.1

0.2

0.3

0.4

0.5

0.6

Gross IMEP [bar]

NO

x [g

/kW

h]

Gross

Net

Brake

EU VI

US 10

2 4 6 8 10 12 14 16 180

1

2

3

4

5

6

7

8

9

10

Gross IMEP [bar]

CO

[g

/kW

h]

Gross

Net

Brake

EU VI

US 10

2 4 6 8 10 12 14 16 180

0.3

0.6

0.9

1.2

1.5

Gross IMEP [bar]

HC

[g

/kW

h]

Gross

Net

Brake

EU VI

US 10

Emissions

18

Emissions – different fuels

2 4 6 8 10 12 14 16 18 200

0.5

1

1.5

2

2.5

Gross IMEP [bar]

So

ot [F

SN

]

Ethanol

FR47330CVX

FR47331CVX

FR47333CVX

FR47334CVX

FR47335CVX

FR47336CVX

FR47338CVX

2 4 6 8 10 12 14 16 18 200

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Gross IMEP [bar]

NO

x [g

/kW

h]

Ethanol

FR47330CVX

FR47331CVX

FR47333CVX

FR47334CVX

FR47335CVX

FR47336CVX

FR47338CVX

2 4 6 8 10 12 14 16 18 200

2

4

6

8

10

12

Gross IMEP [bar]

CO

[g

/kW

h]

Ethanol

FR47330CVX

FR47331CVX

FR47333CVX

FR47334CVX

FR47335CVX

FR47336CVX

FR47338CVX

2 4 6 8 10 12 14 16 18 200

1

2

3

4

5

6

7

8

9

10

Gross IMEP [bar]

HC

[g

/kW

h]

Ethanol

FR47330CVX

FR47331CVX

FR47333CVX

FR47334CVX

FR47335CVX

FR47336CVX

FR47338CVX

SAE 2010-01-0871

19

Efficiency with Diesel or Gasoline

5 10 15 20 25 3034

36

38

40

42

44

46

48

50

52

Gross IMEP [bar]

Bra

ke

Effic

ien

cy [%

]D13 Gasoline

D13 Diesel

D13 Diesel was calibrated by Scania to meet EU V

legislation.

Average improvement of 16.6% points at high load by replacing

diesel fuel with gasoline!

1.5 2 2.5 3 3.544

46

48

50

52

54

56

58G

ross In

dic

ate

d E

ffic

ien

cy [%

]

Abs Inlet Pressure [bar]

FR47338CVX

FR47335CVX

FR47334CVX

High dilution is needed

for high indicated efficiency

SAE paper 2010-01-1471

10%!

21

idealturbinemechanicalturbinecompressoridealcompressor WW __

4 6 8 10 12 14 16 180

5

10

15

20

25

30

35

40

45

50

55

Min

imu

m T

urb

o G

lob

al E

ffic

ien

cy [%

]

Gross IMEP [bar]

global

Turbo System Efficiency Requirement

Outline

• What is high efficiency?

• Combustion, thermodynamic, gas exchange

and mechanical efficiencies. All four must

be high.

• Combustion to enable high efficiency

• HCCI

• Partially Premixed Combustion

• Can we do something about engine

design?

• Conclusions

ICE research in Lund vs. time

1990 1995 2000 2005 2010 2015

23

CCV=Cycle to

Cycle

Variations in

Spark Ignition

Engines

GDI= Gasoline

Direct

Injection

2-S= Two Stroke

engine

VVT=Variable

Valve Timing

HCCI=Homogeneo

us Charge

Compression

Ignition

SACI=Spark

Assisted

Compression

Ignition

PPC= Partially

Premixed

Combustion

High efficiency thermodynamics:

Simulation results from GT-power

• Indicated efficiency 65,2%

• Brake efficiency 60.5%

Is 65% possible?

Any text book on ICE:

• Ideal cycle with heat addition at constant

volume:

• With a compression ratio of 60:1 and γ=1.4 we

get an efficiency of 80,6%

25

0 10 20 30 40 50 60 700

100

200

300

400

500

600

700

800

900

1000Peak cylinder pressure as function of compression ratio

Peak c

ylin

der

pre

ssure

[bar]

Compression ratio

Lambda = 1.2

Lambda = 3.0

There are a few drawbacks…

– Engine structure must be very

robust (if at all possible)

– Very high friction and hence

lower mechanical efficiency

26

There are a few drawbacks…

270 10 20 30 40 50 60 70

20

30

40

50

60

70

80

90Thermodynamic efficiency as function of compression ratio

Compression ratio

Therm

odynam

ic e

ffic

iency [%

]

No heat transfer losses

With heat transfer losses (Woschni)

How then make 60:1 usable?

• Swedish proverb: ”Den late förtar sig

hellre än går två gånger”

• Which according to google translate

means: ”The lazy man rather breaks

his back than walk twice”

28

Take it in steps!

How about

𝟔𝟎 = 𝟕. 𝟕𝟓If we divide the compression in two equal

stages the total pressure (and temperature)

ratio will be the product of the two

7.75:1 x 7.75:1=60:1

With a peak pressure of 300 bar the

pressure expansion ratio is 300:1 and hence

300^(1/1.4)=58.8.1 in volume ratio

(gamma=1.25 during expansion gives 96:1)

29

Split cycles from the past

30

From history: Compound Engine

Divide the expansion in

three cylinders with

same force, F, on each

piston.

The smaller cylinder

has higher pressure but

also smaller area

F=p*A

31

32

Split cycles from the present

33

Three step compression in production

• To run a smaller engine at

higher load turbocharging is

used. The engine is using two or

three shafts of which only one

can generate power

• High BMEP (up to 30 bar) results

with two-stage turbo

• Peak pressure 200 bar

34F. Steinparzer, W. Stütz, H. Kratochwill, W. Mattes: „Der neue BMW-Sechzylinder-Dieselmotor mit Stufenaufladung“, MTZ, 5,2005

Design criteria of engines today

Non-turbo SI engines

Load range 0-12 bar BMEP

Peak pressure during the

cycle 65-70 bar

Friction FMEP 0.25-0.5 bar

Highly turbocharged engines

Load range 0-30 bar BMEP

Peak pressure during the cycle

180-230 bar

Friction FMEP 1.2-2 bar

35

Divide the process into two cylinders

Low pressure cycle

• Use large naturally

aspirated engine designed

for 30 bar peak pressure

– Load range 0-5 bar BMEP

– Peak pressure during the

cycle 30 bar

• Friction FMEP 0.05-0.1 bar

High pressure cycle

• Use small engine with 300

bar peak pressure feed by

the large engine

– Load range 35-80 bar BMEP

– Peak pressure during the

cycle 250-300 bar

• Friction FMEP 1.2-2.2 bar

36

Principle layout

2 stroke- 4 stroke- 2 stroke

37

Operating cycle 2+4+2 stroke

38

Inlet

Inlet

Inlet

Compression Expansion

Compression

Compression

Expansion

Expansion

Exhaust

Exhaust

Exhaust

TDC TDCTDC

TDC

TDC

TDC TDC

TDC

TDCTDC BDCBDC

BDC BDC

BDCBDC

BDCBDC

1

1

3

3

2

2

4

4

Inlet

Compression

Expansion

Exhaust

Pre

ssure

Combustion

Principle layout

4 stroke + 4 stroke

39

Operating cycle 4 + 4 stroke

40

Inlet

Inlet

Inlet

Inlet

Compression Expansion

Compression

Compression

Compression Expansion

Expansion

Expansion

Exhaust

Exhaust

Exhaust

Exhaust

TDC TDCTDC

TDC

TDC

TDC TDC

TDC

TDCTDC BDCBDC

BDC BDC

BDCBDC

BDCBDC

1

1

3

3

2

2

4

4

Pre

ssure

Combustion

DOUBLE COMPRESSION EXPANSION ENGINE CONCEPTS: A PATH TO HIGH

EFFICIENCY

Nhut Lam, Martin Tunér, Per Tunestål, Bengt

Johansson, Lund University

Arne Andersson, Staffan Lundgren, Volvo Group

SAE 2015-01-1260

Conceptual design 4-4

42

SAE 2015-01-1260

SAE 2015-01-1260

43

Simulation setup, DCEE concept

- 2 models

Unit DCEE λ=1.2 DCEE λ=3.0

Bore, HP cylinder mm 95

Stroke, HP cylinder mm 100

HP-cylinder displacement dm3 0.71

CR, HP cylinder - 11.5:1

Bore, LP cylinder mm 317 249

Stroke, LP cylinder mm 100

LP-cylinder displacement dm3 7.9 4.9

CR, LP cylinder - 100:1

EGR % 0

CAC temperature K 350No

intercooling

Simulation engine speed rpm 1900

High Pressure cylinder

44

SAE 2015-01-1260

Low Pressure cylinder

45

SAE 2015-01-1260

Combined

46

SAE 2015-01-1260

Heat Transfer

• To reduce heat transfer:

– Reduce heat transfer coeff., h

– Reduce surface area, A

– Reduce gas temperature

– Increase wall temperature

47

Wall surface area

48

0 1 2 3 4 5 6 7 8 90

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Cylinder volume [dm3]

Are

a [m

2]

Wall surface area as function of cylinder volume

DCEE, lambda 1.2

DCEE, lambda 3.0

CI, lambda 1.2

CI, lambda 3.0

SAE 2015-01-1260

Area/volume-ratio

49

0 1 2 3 4 5 6 7 8 90

200

400

600

800

1000

1200

Cylinder volume [dm3]

Are

a/V

olu

me [m

2/m

3]

Wall surface area per volume as function of cylinder volume

DCEE, lambda 1.2

DCEE, lambda 3.0

CI, lambda 1.2

CI, lambda 3.0

SAE 2015-01-1260

Heat transfer losses

50

SAE 2015-01-1260

51

Estimation of friction mean effective

pressure, FMEP

0 50 100 150 200 250 3000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8FMEP as function of PCP

FM

EP

[bar]

PCP [bar]Designed engine peak cylinder pressure

Naturally aspirated SI-engine @

2300 rpm

Traditional heavy duty

turbocharged CI engine

HP cylinder,

DCEE-concept

LP cylinder,

DCEE-concept

•Friction is assumed to scale with

Peak Cylinder Pressure, Pmax

•FMEP assumed to be 1.2 bar @200 bar Pmax

SAE 2015-01-1260

52

Mechanical losses

UnitDCEE,

λ=1.2

DCEE,

λ=3.0

Conventional,

λ=1.2

Conventional,

λ=3.0

Peak cylinder pressure

-LP cylinder bar 36 16

-HP cylinder bar 300

FMEP

-LP cylinder bar 0.21 0.09

-HP cylinder bar 1.8

Total FMEP bar 0.34 0.31 1.8

Net indicated work,

IMEPn

bar 8.8 4.3 12.9 6.3

Mechanical efficiency % 96.1 92.8 86.0 71.6

Resulting Efficiencies

53

SAE 2015-01-1260

Summary

• HCCI has shown high efficiency

– Up to 100% improvement in indicated efficiency vs. standard

SI combustion

– Modest combustion efficiency

– HCCI peaks at 47% indicated efficiency at around 6 bar

BMEP

• PPC has shown higher fuel efficiency

– Indicated efficiency of 57% at 8 bar IMEP

– Indicated efficiency of 55% from 5-18 bar IMEP

– With 70 RON fuel we can operate all the way from idle to 26

bar IMEP

• With an effective compression/expansion ratio

of 60:1 the split cycle concept shows 62%

indicated/ 56% brake efficiency potential

54

hT =1-1

Rc

g-1

High Efficiency Combustion

Engines – What is the limit?

“It all starts at 40 and ends at 60”(% engine efficiency that is, not life)

Prof. Bengt Johansson

Lund University

Thank you!

56

Towards High Efficiency Engine –

THE Engine

Bengt Johansson

Div. of Combustion Engines

Director of KCFP,

Lund University,

Sweden