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ANALYSIS OF POTENTIAL INCREASES IN ENERGY EFFICIENCY FOR PISTON COMBUSTION

MACHINES WITH UNCONVENTIONAL GEOMETRY

ICSAT conference

Dr.-Ing. Andreas Gotter, gofficient, Kaarst

Dr. Boris Schapiro, RKM, Berlin

26.02.2010

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The RKM engine principle

RKM (Rollkolbenmotor) engine has different geometry

than other IC engines

Principle:

Rolling piston instead

of oscillating piston

Different variants possible:

Inner piston

Outer piston

For more details, have a look at

the geometry presentations

of RKM engines

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Objective

Target: Analysis of the potential of the RKM engine

How can that be estimated ?

a) Simulation of a final designed RKM engine and compare to start of the art IC engine

- not possible due to to many uncleared parameters yet- would achieve only weak answer for potential (more for the individual design)

b) Identification of boundaries of conventional IC engines, which can be shiftedand simulation of benefit of shifting that boundaries- simulation can be done independent from individual design parameters- gives an good overview of thermodynamic potential

Method of choice

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Thermodynamics

Short excurse to basic thermodynamics of Combustion engines

Overall process efficiency is limited to

basic thermodynamic lawa and depends mainly on- Compression ratio- Isentropic coefficient of process medium

Limitations

Compression ratio is limited by knock

behaviour, if gasoline engine is used

Isentropic coefficient depends on exhaust gas

and drops with raising temperature

Limiting effects in real engine- Non-ideal combustion- Wall heat losses- Friction- Backpressure by exhaust components not perfect valve timing- etc

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,80

2 4 6 8 10 12 14 16 18 20

Lambda 0,8

Lambda 1,0

Lambda 1,7

Lambda 3,0

Lambda 100

η = 1 – ε1 – κ

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Boundary conditions

Which boundary conditions

a) Limit current IC engine efficiency

b) Could be moved by other engine concepts such as RKM ?

These parameters were identified:

Parameter Current limitation Investigation of up to…

Maximum peak pressure ~120 bar (Otto) 400 bar

~200 bar (Diesel)

Compression ratio ~20 (Diesel) 50

Break mean effective pressure ~25 bar 100 bar (a.m.a.p)

Friction mean effective pressure ~0.5 bar 0.1 bar

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Simulation software SimEngine

The used simulation software is SimEngine

- A product of gofficient- Has capability of complex thermodynamic simulation of all kinds of

- internal combustion engines- water/steam processes

- Is the unique simulation software for integrated simulation of different processes

Features

- Simulates real gas behaviour and has database for many fluids and gases- Stationary and transient calculation of fluid dynamics- Great component library for internal combustion engines- Lots of special analysis functions- Integration of calibration and control database (currently in development)

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Some screenshots of SimEngine

Component library

drawing area

data input

Analysis windows

Simulation software SimEngine

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Results

Variation of Injection timing

Test : Movement of WOT injection timing to earlier comustion angles

Effects : Rising max. pressure,small efficiency improvement with optimum ~6°CA earlier

41.0%

42.0%

43.0%

44.0%

45.0%

46.0%

0 2 4 6 8 10 12

injection timing (°CA rel. to Basis)

effi

cien

cy [

%]

ETA i

ETA e

120

160

200

240

280

320

0 2 4 6 8 10 12

injection timing (°CA rel. to Basis)

max

. p

ress

ure

[b

ar]

16

18

20

22

24

26

28

30

32

34

36

pmax

pmi

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Results

Variation of Compression ratio

Test : Raising compression ratio to extreme values

Effects : Strong rising max. pressure,efficiency improvement of ~2%-points

raising friction

optimum (eta e) ~ 28, optimum (eta i) ~ 32

41.0%

42.0%

43.0%

44.0%

45.0%

46.0%

15 20 25 30 35

compression ratio

effi

cien

cy [

%]

ETA i

ETA e 120

160

200

240

280

320

15 20 25 30 35

compression ratio

max

. p

ressu

re [

bar

]

16

18

20

22

24

26

28

30

32

34

36

imep

[b

ar]

pmax

pmi

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Results

Variation of A/F ratio

Test : Variation of A/F ratio at WOT conditions at const imep (variaton of charge air pressure for compensation)

Effects : slowly rising max. pressure with lean mixtureefficiency improvement of > 2%-points

41,0%

42,0%

43,0%

44,0%

45,0%

46,0%

47,0%

1 1,2 1,4 1,6 1,8 2 2,2 2,4rel. A/F ratio

effi

cien

cy [

%]

ETA i

ETA e

120

160

200

240

280

320

1 1,2 1,4 1,6 1,8 2 2,2 2,4rel. A/F ratio

max

. p

ress

ure

[b

ar]

16

20

24

28

32

36

imep

[b

ar]

pmax

pmi

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Results

Charge Air pressure

Test : Raising charge air pressure ratio to extreme values at constant compression ration of 19.5

Effects : Strong rising max. pressure & imepefficiency improvement of up to 2%-points

41.0%

42.0%

43.0%

44.0%

45.0%

46.0%

1.5 2 2.5 3 3.5 4 4.5 5

charge air pressure [bar]

effi

cien

cy [

%]

ETA i

ETA e 120

160

200

240

280

320

360

400

440

1.5 2 2.5 3 3.5 4 4.5 5

charge air pressure [bar]

max

. p

ress

ure

[b

ar]

16

20

24

28

32

36

40

44

48

imep

[b

ar]

pmax

pmi

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Results

Charge Air pressure

Test : Raising charge air pressure ratio to extreme values at constant compression ration of 26

Effects : Strong rising max. pressure & imepefficiency improvement of up to 2%-points

42.0%

43.0%

44.0%

45.0%

46.0%

47.0%

1.5 2 2.5 3 3.5 4 4.5 5

charge air pressure [bar]

effi

cien

cy [

%]

ETA i

ETA e

120

160

200

240

280

320

360

400

440

1.5 2 2.5 3 3.5 4 4.5 5

charge air pressure [bar]

max

. p

ress

ure

[b

ar]

16

20

24

28

32

36

40

44

48

imep

[b

ar]

pmax

pmi

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Results

Charge Air pressure

Test : Raising charge air pressure ratio to extreme values at constant compression ration of 26 and lean A/F ratio of 1.6

Effects : Strong rising max. pressure,further efficiency improvement, but also raising frictionefficiency @400bar pmax: 47.1% indicated and 45.3% effective

43.0%

44.0%

45.0%

46.0%

47.0%

48.0%

1.5 2 2.5 3 3.5 4 4.5 5

charge air pressure [bar]

effi

cien

cy [

%]

ETA i

ETA e

120

160

200

240

280

320

360

400

440

1.5 2 2.5 3 3.5 4 4.5 5

charge air pressure [bar]

max

. p

ress

ure

[b

ar]

16

20

24

28

32

36

40

44

48

imep

[b

ar]

pmax

pmi

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Conclusion

Friction

The assumption for friction have been calculated with similarity to conventional engines

If fmep could be reduced, the indicated efficiency is the upper efficiency limit

Conclusion

- By exceeding the current boundaries of mechanical engines, there

could an efficiency increasement potential of 7% (=3%-points) be achieved (if other paramters would stay constant)

- Imep and bmep can be increased to values of ~50bar,while engine speed will probably be lower

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Outlook

Outlook

Alternative engine designs such as RKM engines may be an

alternative for special applications with highest demands

Due to high possible pressure ratio and various speed, RKM engines

can also be used as compressors or expanders, e.g. for steam processes

Simulation is an important tool to discover potentials and application

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Thank youfor the attention