thermodynamic advantages of low temperature combustion ... · pdf filethermodynamic advantages...

t

TEMPERATURE COMBUSTION (LTC) ENGINES

J ld A C

g y ( )

THERMODYNAMIC ADVANTAGES OF LOW TEMPERATURE COMBUSTION (LTC) ENGINES

INCLUDING THE USE OF LOW HEAT REJECTION (LHR) CONCEPTSREJECTION (LHR) CONCEPTS

Jerald A. Caton Texas A&M University College Station, TX

for

Directions in Engine-Efficiency and Emissions Research (DEER)

2010 Conference

Detroit Marriott at the Renaissance Center

1

Detroit, MI 27 September 2010

( )

THERMODYNAMIC ADVANTAGES OF LOW TEMPERATURE COMBUSTION (LTC) ENGINESTEMPERATURE COMBUSTION (LTC) ENGINES

INCLUDING THE USE OF LOW HEAT REJECTION (LHR) CONCEPTS

• INTRODUCTION AND BACKGROUND

• DESCRIPTION OF THE CYCLE SIMULATION

• RESULTS AND DISCUSSION

9Engine and Operating Conditions9Engine and Operating Conditions

9Overall Results – Efficiencies

9Parametric Evaluations

9Nitric Oxide Results

• SUMMARY AND CONCLUSIONS

2

or

use

t t

INTRODUCTION AND BACKGROUND

• LTC engines have demonstrated low emissions and high efficiencies

These engines combinations of high CR high• These engines use combinations of high CR, high EGR, lean mixtures, fast burn rates, high boost and

other features • What is the contribution to the high efficiencies by each of these features? • What are the best combinations of these features? • Does including LHR concepts make sense?

Wh h not?Why or why not? • What does the second law say?

Wh i th i it i id i i ? 3

• What is the impact on nitric oxide emissions?

THERMODYNAMIC ENGINE CYCLE SIMULATION

Features/Considerations: 1. One common pressure 2. Three gas temperatures 3 Three volumes and masses

4

3. Three volumes and masses 4. Separate heat transfer

PROCEDURES FOR SOLUTIONS • ORDINARY DIFFERENTIAL EQUATIONS • NUMERICAL TECHNIQUES: EULERS• NUMERICAL TECHNIQUES: EULERS • INITIAL CONDITIONS: T1, p1, Residual Fraction • BOUNDARY CONDITIONS: INLET & EXHAUST • SPECIFY SUBMODEL PARAMETERS:

- Thermodynamic properties - Heat transfer coefficient - Fuel mass rates - Flow rate parameters

Nitric oxide kinetics - Nitric oxide kinetics - Other

5

6

SPECIFICATIONS FOR THE ENGINESPECIFICATIONS FOR THE ENGINE

PARAMETER VALUE Engine Automotive, V-8 Bore/Stroke 102/88 mm (4.0/3.5 in) Displacement 5.7 liter (350 in3) bmep 900 kPa Engine speed 2000 rpm C b i i iCombustion timing MBTMBT Geometric compression ratio from 8:1 to 20:1 Valve arrangement Valve arrangement OHV 2 valves/cylinderOHV, 2 valves/cylinder

t

= = = = =

Add f i ti l f hi

DESCRIPTION OF CASES -- STRATEGY –

Add features in a sequential fashion:

2 CR = 20 BD = 60o φ= 1 0 EGR = 0% T = 450 K 2 CR = 20; BD = 60o; φ= 1.0; EGR = 0%; Tw = 450 K 3 CR = 20; BD = 30o; φ= 1.0; EGR = 0%; Tw = 450 K 4 CR = 20; BD = 30o; φ= 0 7; EGR = 0%; T = 450 K 4 CR 20; BD 30o; φ 0.7; EGR 0%; Tw 450 K 5 CR = 20; BD = 30o; φ= 0.7; EGR = 50%; Tw = 450 K 6 CR = 20; BD = 30o; φ= 0.7; EGR = 50%; Tw = 550 K

7

6 CR 20; BD 30 ; φ 0.7; EGR 50%; Tw 550 K

CASECASE DESCRIPTION 1 CR = 8; BD = 60o; φ= 1.0; EGR = 0%; Tw = 450 K

RESULTSRESULTS � Thermal Efficiencies

� Cylinder Conditions

� Heat Transfer/Exhaust Energy

� Parameter Optimization

� Nitric Oxides� Nitric Oxides

� Low Heat Rejection (LHR) 8

Low Heat Rejection (LHR)

THERMAL EFFICIENCIES ¾ Base Case

%)

50 bmep = 900 kPa

2000 rpm MBT Timing

Effic

ienc

y (% 45

Net Indicated Efficiency

Gross Indicated Efficiency

d an

d B

rake 40

Brake Efficiency

Indi

cate 35

SE = 20 30

o

0.7

R =

50%

l = 5

50 K

Efficiency

Case

1 2 3 4 5 6

30 BAS

CR

=

θ b =

φ =

0

EGR

T wal

l

10

THERMAL EFFICIENCIES 50

bmep = 900 kPa 2000 rpm

MBT Timing

¾ High compression ratio

ffici

ency

(%)

45



and

Bra

ke E

40

y

Indi

cate

d

35

E 20 0 o 7 = 50

%

= 55

0 KBrake

Efficiency

Case

1 2 3 4 5 6

30 BAS

E

CR

=

θ b = 3

φ =

0.

EGR

=

T wal

l =

11

Case

Case

THERMAL EFFICIENCIES ¾ High compression ratio

¾ Short burn duration

)

50 bmep = 900 kPa

2000 rpm MBT Timing

Effic

ienc

y (% 45



d an

d B

rake

E

40

Indi

cate

d

35

E = 20 30

o

0.7

R =

50%

= 55

0 KBrake

Efficiency

Case

1 2 3 4 5 6

30 BAS

E

CR

=

θ b =

3

φ =

0

EGR

T wal

l

12

¾ L i t



)

50 bmep = 900 kPa

2000 rpm MBT Timing

¾ Lean mixture

Effic

ienc

y (%

)

45



and

Bra

ke E

40

Brake

Indi

cate

d

35

E 20 30 o

.7 = 50

%

= 55

0 K

Brake Efficiency

Case

1 2 3 4 5 6

30 BAS

E

CR

=

θ b = 3

φ =

0.

EGR

T wal

l =

13

Case

¾ L i t


¾ Short burn duration 50


MBT Timing ¾ Lean mixture

¾ High EGR

ffici

ency

(%)

45

g



and

Bra

ke E

f

40

Efficiency

Indi

cate

d a

35

20 0 o 7 = 50

%

550

K

Brake Efficiency

1 2 3 4 5 6

30 BAS

E

CR

= 2

θ b = 3

0

φ =

0.7

EGR

=

T wal

l =

14

Case

Case

¾ L i t

w emp



)

50 bmep = 900 kPa

2000 rpm MBT Timing

¾ Lean mixture

¾ High EGR

¾ High cylinder all t Effic

ienc

y (% 45



¾ High cylinder wall temp

d an

d B

rake

E

40

Brake

Indi

cate

d

35

E = 20 30

o

0.7

R =

50%

= 55

0 K

Efficiency

Case

1 2 3 4 5 6

30 BAS

E

CR

=

θ b =

3

φ =

0

EGR

T wal

l

15

=

C 1

50

THERMAL EFFICIENCIES %

)

50 bmep = 900 kPa

2000 rpm MBT Timing

Pumping Losses

RESULTS Case 6:

ffici

ency

(% 45


Gross Indicated Efficiency Mechanical

Friction ηind,g = 49.5% η = 48 2%

nd B

rake

Ef

40

Efficiency

Brake Efficiency

ηind,n 48.2% ηbrk = 41.6%

ndic

ated

an

35

0% 0 K

Case 1: ηInd,g = 36.1%

In

30 BAS

E

CR

= 2

0

θ b = 3

0 o

φ =

0.7

EGR

= 5

0

T wal

l = 5

50

ηind,n = 35.6% ηbrk = 32.7%

16 Case

1 2 3 4 5 6

t

COMPARISON TO THE LITERATURE

Fuels Gasoline/Diesel Isooctane Inlet Pressure (kPa) 200 227 G i CR 16 1 20Geometric CR 16.1 20 EGR (%) 45.5 50 Equivalence Ratio 0.77 0.7 Speed (rpm) 1300 2000 RESULTS: IMEPNET (kPa) 1100 1047IMEPNET (kPa) 1100 1047 Net Ind Efficiency (%) 50 48.2 Peak Pressure (MPa) 12 13.9 Nitric Oxide (g/kW-h) 0.01 0

ITEM REFERENCE (Kokjohn et al.)

THIS WORK (Case 6)

Bore/Stroke (mm) 137/165 102/88Bore/Stroke (mm) 137/165 102/88

15000

CYLINDER PRESSURES 15000


"MBT" Timing

Case = 6

Case = 5

a) 10000

ress

ure

(kPa

Case = 3

Case = 4

Pr

5000 Case = 2

Case = 1

19CRANK ANGLE

-90 -60 -30 0 30 60 90 0

CYLINDER TEMPERATURES

3000 bmep = 900 kPa

2000 rpm "MBT" Timing

C 2Case = 3

re (K

)

2000

2500

Case = 1

Case = 2

Case = 4

Tem

pera

tur

1500

Case = 6

One

-Zon

e

1000

Case = 5

500

20CRANK ANGLE

-90 -60 -30 0 30 60 90 0

50

HEAT TRANSFER AND EXHAUST ENERGY

45


MBT Timing

Exhaust Energy (%)

ener

gy)

35

40 y

(% o

f fue

l e

30 Relative

Heat Transfer (%) Le2

3

Ener

gy

20

25

Higher CR

Shorter

Lean Burn High EGR 1

2

4

5

10

15

Shorter Burn

Duration

Higher Wall

Temp 6

22Net Indicated Efficiency (%)

35 40 45 50 10

Note: from Otto

n a

1.35

b 900 kP

Average “gamma” for Expansion Stroke ke

)


MBT Timing

5 Note: from simple “Otto”

nsio

n st

rok

1.30

5 6

simple cycle considerations –

a “0.01” increase of gamma results i about 1%

ama

(exp

an

3

4 results in about a 1% efficiency gain

This implies that about one-

Aver

age

Ga

1.25

1

2 half to two thirds of the efficiency increases are due to the increase of gamma.

1 20

23Net Indicated Efficiency (%)

35 40 45 50 1.20

EFFECTS OF COMPRESSION RATIO

48

50 Case 6

(%) 44

46 Net Indicated Efficiency

l Effi

cien

cy

40

42 Case 6

Ther

mal

36

38

32

34 bmep = 900 kPa φ = 0.7, EGR = 50% 2000 rpm, θb = 30o

MBT Timing

Brake Efficiency

25Compression Ratio

0 5 10 15 20 25 30 30

g

EFFECTS OF BURN DURATION

48

50

C 6

(%)

46

Case 6

Net Indicated Efficiency l E

ffici

ency

42

44

C 6

Ther

ma

38

40

Case 6

Brake Efficiency

36 bmep = 900 kPa φ = 0.7, EGR = 50% 2000 rpm, cr = 20

MBT Timing

26Burn Duration, θb(oCA)

0 20 40 60 80 100 120 140 34

EFFECTS OF EGR

49

50

51

bmep = 900 kPa φ = 0.7, θb = 30o

2000 rpm, Twall = 550 K MBT Ti i 20

y (%

)

47

48

49 MBT Timing, cr = 20 Case 6

Net Indicated

al E

ffici

ency

45

46


Ther

m

43

44

40

41

42 Case 6 Brake

Efficiency

27EGR (%)

0 10 20 30 40 50 60 70 40

NITRIC OXIDES FOR EACH CASE 2020


MBT Timing 1

3

kW-h

) 15

2

3

4

ic O

xide

(g/k

10 2

Nitr

i

5

35 40 45 50

0 5 6

29

Net Indicated Efficiency (%)

35 40 45 50

LOW HEAT REJECTION (LHR)

%)

50 bmep = 900 kPa

2000 rpm MBT Timing

Pumping Losses

ffici

ency

(%

45


Gross Indicated Efficiency Mechanical

Friction

nd B

rake

Ef

40

Efficiency

Brake Efficiency

Indi

cate

d an

35

0%

50 K

0 K

I

30 BAS

E

CR

= 2

0

θ b = 3

0 o

φ =

0.7

EGR

= 5

0

T wal

l = 5

5

T wal

l = 8

80

31 Case

1 2 3 4 5 6 7

LOW HEAT REJECTION (LHR) 5555


MBT Timing LTC Engine

es (%

) 50

Net Indicated

e 6

LTC Engine

Cas

e 7

l Effi

cien

cie 45

Brake

Cas

e

Ther

ma 40

Conventional Engine Net Indicated

35 Brake

32Wall Temperature (K)

400 500 600 700 800 900 30

Oth C ditiOther Conditions

• Other operating conditions exhibit similar improvements

• For different “order” of features – same final result, but incremental gains slightly different

• For reduced heat transfer without higher wall temperatures, even higher gains are possible

33

thermal

d th i t d h i l f i ti i

CONCLUSIONS (1/2)CONCLUSIONS (1/2)

� High CR, high EGR, lean mixtures and other features can combine to yield ~50% net indicated thermal efficiencyefficiency

� Features of most importance: CR, EGR, lean mixtures

� The major reasons for the higher efficiencies include the lower heat transfer, the higher “gamma,” and the high CR

� To maintain load, higher cylinder pressures result

34

and the associated mechanical friction increases

c

CONCLUSIONS (2/2)CONCLUSIONS (2/2)

� The lower exhaust gas energy may cause the application of turbochargers to be problematic

� Low heat rejection (LHR) concepts are more compatible with LTC engines than with conventional enginesengines

� Predicted nitric oxides are “zero” for the LTC modes

� Exergy destruction during ombustion increases � Exergy destruction during combustion increases largely due to the lower temperatures – this is an acceptable trade-off for the higher efficiencies

35

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