1 © Wärtsilä

Investigation of the lubrication conditions in bearings of large two-stroke diesel engines

GT-SUITE ConferenceFrankfurt, 09.11.2009

François Terrettaz, Dr. Wilfried SchifferWärtsilä Corporation

2 © Wärtsilä

Content

1. Introduction / purpose of investigation

2. Wärtsilä two-stroke diesel engines

3. Lubrication, crosshead and crank pin bearings

4. Model and simulation requirements

5. Simulation of previous generation engines

6. Simulation of new generation engines

7. Summary

8. Next steps

3 © Wärtsilä

1. Introduction / purpose of investigation

Purpose

• simulation of the unsteady lubrication conditions for crosshead and crank pin bearings of large two-stroke engines with GT-SUITE

To be considered• acceleration of oil due to movement of knee lever and ConRod• crank angle based resolution of crosshead and crank pin bearings solution

using appropriate boundary conditions in oil grooves and pockets

• fast motion of crosshead pin

• pressure pulsation in pipes and bores of oil circuit

-> interaction between oil circuit and bearings(crosshead and crank pin)

4 © Wärtsilä

1. Introduction / purpose of investigation

Simulation results

• oil consumption of crosshead and crank pin bearings• oil pressure at entry of crosshead and crank pin bearing over one revolution

-> to be used as boundary conditions for EHD-calculations• risk of cavitation in oil pipes and bores• efficiency of different supply systems (-> telescopic pipe or knee lever)

5 © Wärtsilä

2. Wärtsilä two-stroke diesel engines

• Crosshead engine

• Welded crank casing

• Semi-build crankshaft

• Power range 5’800 to 80’080 kW

• Speed range 61 to 137 rpm

• Number of cylinders 5 to 14 (in-line)

• Bore range 0.48 to 0.96 m

• Stroke range 1.8 to 3.375 m

• Stroke-to-bore ratio 2.60 to 4.17

• Weight range 171 to 2’300 tons

6 © Wärtsilä

2. Wärtsilä two-stroke diesel engines

Output [kW]Output [bhp]

100’000

80’000

60’000

40’000

20’000

10’000

8’000

6’0004’000

6’000

8’000

20’000

80’000

60’000

50’000

30’000

10’000

40’000

60 70 80 90 100 120 140

Engine speed [rpm]

RTA68T-B

RTA84T-D

RTA84C

RTA58T-B

RTA48T-B

RTA72U-B

RT-flex60CRTA62U-B

RTA52U-B

RTA96CContainer vessels

RTA84T-DTanker vessels

RTA84T-D

RTA48T-B

Bulk carrier vesselsRTA48T-B

7 © Wärtsilä

2. Wärtsilä two-stroke diesel engines

7RTA48T-B

power 10185 kWmass 225 tlength 7.6 mwidth 4.8 mheight 9.0 m

10RTA96C

power 57200 kWmass 1760 tlength 20.6 mwidth 7.5 mheight 13.5 m

8 © Wärtsilä

2. Wärtsilä two-stroke diesel engines

9 © Wärtsilä

pump

supply pipe

main gallery

knee lever

crosshead

connecting rod

crank pin bearing

crosshead bearing

3. Lubrication, crosshead and crank pin bearings

main gallery

knee lever(2 articulated pipes)

crosshead bearing

crank pin bearing

10 © Wärtsilä

4. Model and simulation requirements

Crosshead bearing

Crank angle based resolution ofbearing solution using Mobility method

• accurate bearing forces, including forces generated by pressure in large oil pockets

• accurate crosshead pin displacement

• oil flow rate according to Martin equation

11 © Wärtsilä

4. Model and simulation requirements

Crank pin bearing

Crank angle based resolution ofbearing solution using Mobility method

• accurate bearing forces, including force generated by pressure in oil grooves

• accurate crank pin displacement

• oil flow rate according to Modified Martin equation (s=0.6)

12 © Wärtsilä

4. Model and simulation requirements

Knee lever (at engine full speed)

acceleration: ± 300 m/s2

Acceleration Pressure

pressure: ± 1.7 bar

-2.0

-1.0

0.0

1.0

2.0

3.0

0 90 180 270 360

Crank Angle [deg]Pr

essu

re [

bar]

-400

-300

-200

-100

0

100

200

300

0 90 180 270 360

Crank Angle [deg]

Acc

eler

atio

n [m

/s2 ]

Centre of 1st. pipe of knee lever

Centre of 2nd. pipe of knee lever

Oil Acceleration

13 © Wärtsilä

4. Model and simulation requirements

ConRod bore (at engine full speed)

-200

-150

-100

-50

0

50

100

150

0 90 180 270 360

Crank Angle [deg]

Acc

eler

atio

n [m

/s2 ]

Oil Acceleration (at Centre)

acceleration: ± 150 m/s2

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

0 90 180 270 360

Crank Angle [deg]Pr

essu

re [

bar]

Acceleration Pressure

pressure: ± 2.5 bar

14 © Wärtsilä

4. Model and simulation requirements

Coupling: pin movement oil pressure

DATAFIL211 07. Jan 99 11:10low oil pressure

0

1

2

3

4

5

6

7

8

9

10

0 30 60 90 120 150 180 210 240 270 300 330 360crank angle [deg]

oil s

upp

ly p

ress

ure

[bar

]

X-head pressure before leverX-head pressure after lever

Speed: 100 %Power: 10 %

Displacement of crosshead pin:

• fast motion in vertical direction

• engine load (= speed) dependant

• huge influence on oil flow rate

• influence on instantaneous pressurein oil bores close to crosshead andcrank pin bearings and reciprocal

prediction of orbital path and oil flow rate as accurate as possible

Pressure at Entry ofCrosshead Bearing (meas.)

-0.3

-0.2

-0.1

0.0

0.1

0.2

0 30 60 90 120 150 180 210 240 270 300 330 360

Crank Angle [deg]

Vert

ical

Dis

pl. [

mm

]

Pin Displacement (simul.)

Crank Angle [deg]

Oil

Pres

sure

[ba

r]

15 © Wärtsilä

5. Simulation of previous generation engines

to Crankpin Bearing

low pressure main gallery

high pressure main gallery

• separate oil system for crosshead and crank pin bearing

• 10 12 bar bar feed pressure

• small volume for main gallery

• pressure in main gallery influenced by each crosshead

-> pressure not constant

-> oil circuit must be fully modelled

16 © Wärtsilä

5. Simulation of previous generation engines

Results for 50% loadCrosshead pressurebefore lever

Crosshead pressureafter lever

GT-SUITE Simulation

0

2

4

6

8

10

12

14

16

18

Oil

pres

sure

[ba

r]

Crosshead pressure before lever

Crosshead pressure after lever

DATAFIL 123 0 7 Dec 1 998 15:05high oil pre ss u re

0

2

4

6

8

10

12

14

16

18

0 30 60 90 120 150 18 0 210 240 270 3 00 330 360

crank angle [de g]

oil s

upp

ly p

ress

ure

[ba

r]

o il p ressure be fo re ma in bearingX-head pres sure be fo re leverX-head pres sure a fte r leverp is ton c oo l . press. a fte r lev er

Speed: 100 %Pow er: 50 %Measurement

Crank angle [deg]

Oil

pres

sure

[ba

r]

17 © Wärtsilä

5. Simulation of previous generation engines

Oil consumption crosshead + crank pin bearing

0.0

1.0

2.0

3.0

4.0

5.0

0 10 20 30 40 50 60 70 80 90 100Engine Load [%]

Lub.

Oil

Con

sum

ptio

n [m

3 /h/c

yl] Measurement

GT-SUITE Prediction

18 © Wärtsilä

6. Simulation of new generation engines

to Crankpin Bearing

main gallery

• single oil circuit for almost all engine components

• 5 bar feed pressure

• big volume of main gallery, many sub-volumes connected

• constant pressure

• pressure pulsations fully damped

19 © Wärtsilä

6. Simulation of new generation engines

Oil pressure (at full load)

Crosshead pressurebefore lever

Crosshead pressureafter lever

GT-SUITE Simulation

0

1

2

3

4

5

6

7

8

9

10

Oil

pres

sure

[ba

r]

Crosshead pressure before lever

Crosshead pressure after lever

DATAFIL186 05. Jan 99 10:44low oil pressure

0

1

2

3

4

5

6

7

8

9

10

0 30 60 90 120 150 180 210 240 270 300 330 360

crank angle [ deg]

oil s

uppl

y pr

essu

re [b

ar]

X-head pressure before leverX-head pressure after lever

Speed: 97 %Pow er: 90 %

Measurement

Crank angle [deg]

Oil

pres

sure

[ba

r]

20 © Wärtsilä

6. Simulation of new generation engines

0.0

1.0

2.0

3.0

4.0

5.0

0 10 20 30 40 50 60 70 80 90 100Engine Load [%]

Lub.

Oil

Con

sum

ptio

n [m

3 /h/c

yl] Measurement

GT-SUITE Prediction

Oil consumption crosshead + crank pin bearing

21 © Wärtsilä

6. Simulation of new generation engines

Comparison oil consumption at full load with result for previousengines

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Lub.

Oil

Con

sum

ptio

n [m

3 / h

/ Cyl

]

Measurements

GT-SUITE Prediction

5 bar Feed Pressure 12 bar Feed Pressure

22 © Wärtsilä

7. Summary

Oil flow rate prediction• at full load good compliance between simulation and measurement• at part load correct trend• below 40% load oil flow rate prediction is less accurate• Martin equation used for crosshead bearing• modified Martin equation (s=0.6) used for crank pin bearing

Pressure at entry and exit of knee lever• new generation engines (-> constant pressure in main gallery):

- calculated pressure in line with measurement- oil acceleration in knee lever and ConRod is correctly taken into account- crosshead / crank pin bearing behaviour accurate

• previous generation engines (-> fluctuating pressure in main gallery):

- agreement between calculation and measurement less good

23 © Wärtsilä

8. Next steps

• simulation of lubrication conditions using a telescopic pipe instead of knee lever

• prediction of cavitation risk in crosshead and crank pin bearing

• simulation of other engines components-> axial damper at free end of crankshaft

• implement oil lubrication pressure as result from GT-SUITE simulation for EHD calculations of crosshead and crank pin bearings

24 © Wärtsilä

The end

Thank you for your kind attention

Thanks to GAMMA Technologies and in particular

to Jon Harrison for excellent support !!