MEL 417 Lubrication Lec 170311

1

Lubrication features of a large diesel engine

• In some engines such as long and superlong stroke engines, the piston is not directly connected to the crank pin via a connecting rod.

• The piston has a piston rod extending from the bottom of the piston.

• The piston rod is then connected to the connecting rod at the crosshead bearing.

• The crosshead bearing has a to and fro motion and therefore a continuous hydrodynamic film cannot form.

• Therefore oil has to be pumped to the crosshead bearing at a predetermined pressure in order to take the loads of compression and combustion.

• The crosshead is connected to the crank pin via a connecting rod.

2

Piston

Piston rod

Crank pin, bottom end bearing (rotatory motion) Journal, journal bearing

(rotatory motion)

Crosshead, crosshead bearing (reciprocating)

Connecting rod

Piston rings

Oil pumped at a certain pressure

Ref: http://www.marinediesels.info/2_stroke_engine_parts/crosshead.htm

Web

Piston skirt

Stuffing box

Platform separating cylinder from crank case

3

Cylinder liner lubrication• In some engines, lubricating oil in the cylinder is different from the oil

supplied to the other bearings.

• The cylinder oil contains additives to withstand the high temperatures and contaminants from combustion products.

• The oil is slightly basic in nature to counter the acids formed from combustion.

• Scraper rings spread the oil over the liner surface.

• Lub. oil is usually injected between the two scraper rings.

• Oil is injected at a predetermined period during the downward stroke.

• Before starting, oil is pumped into the liner by manual priming methods.

• After starting, the oil pump is driven by the engine through a cam shaft.

4

Compression rings

Scraper rings

Cylinder liner

Oil injection passage

Injection pointsCylinder oil pump/lubricator

Handle

Camshaft

Piston

5

Trunk type engine (no piston rod)-Splash type lubrication

Piston rings

Web

Crank pin, bottom end bearing (rotatory motion)

Connecting rod

Gudgeon pin

Cylinder liner

Journal, journal bearing (rotatory motion)

Web extension

Oil

Oil is picked up by the webs while rotating, and splashed onto the piston and liner

6

Telescopic pipes (one moves inside the other)

Piston rod

Movement of crosshead

Movement of bearing

Connecting rodStationary pipe

Oil supply

CROSSHEAD LUBRICATION

Crosshead bearing

7

Journal bearing

Journal

Bearing

The journal bearing may undergo hydrodynamic lubrication or a combination of hydrodynamic and hydrostatic (externally pressurized) lubrication.

The oil supply may be from any one or number of positions, depending on the design.

Oil supply

8

Oil passage between bearings in a unit

Web

Journal

Crank pin

Oil passage (drilled)

Connecting rod

Gudgeon pin

TRUNK TYPE ENGINE

99

Lubrication system• TG- Temperature gauge• PG- Pressure gauge

ENGINE Shaft

Cooler

Storage tank PumpFilter

Bearings

PG

PG

TG PG

TG

10

Storage tank/sump

Engine sump

ENGINE Shaft Bearing

• The storage tank usually forms the bottom-most compartment of the engine.

• It is also sometimes known as the sump.

• Oil from the sump is usually transported to the bearings by an engine driven pump or an independently electric motor driven pump that transports the oil to the journal bearings.

• Through passages drilled in the crank shaft and webs, it is transported to the crank pin.

• Usually a strainer is provided on the suction side of the pump to prevent large contaminant particles from damaging the pump and bearings.

Pump

Connection for filling the tank

strainer

11

Oil cooler- tube and shell typeOil in

Oil out

Water in Water out

TG TG

TG

TG

•In this case, cooling water flows through the tubes.

•Oil flows in the shell around the tubes and passes the heat to the water.

•The in/out temperatures of the oil and water are to be monitored.

•Oil pressure is always kept above water pressure to prevent water contamination of oil

•However, if there is a leak oil is lost and the sump level is therefore to be monitored regularly

PG PGPG

PG

1212

Engine lubrication system

• TG- Temperature gauge• PG- Pressure gauge

ENGINE Shaft

Cooler

Storage tank PumpFilter

Bearings

PG

PG

TG PG

TG

Some adverse situations:

•Oil inlet pressure to engine LOW

•Oil outlet temperature from engine HIGH

•Oil outlet temperature from cooler HIGH

13

Adverse situations and reasonsAll pressure and temperature values in a lubrication system have to be constantly monitored •Oil inlet pressure to engine LOW

– Filter may be choked blocking flow.– Pump defective.

•Oil outlet temperature from engine HIGH– Bearing maybe running hot due to excessive friction.– Leakage of gas from combustion space past piston rings.

•Oil outlet temperature from cooler HIGH– Water flow may be restricted due to choked tubes.– Surface of tubes maybe coated with dirt.

•Temperature of oil outlet from cooler too LOW (excess viscosity)

– Water temperature may be too low- restrict water flow by partially shutting valve.

14

Other maintenance and problem issues

With engine is shut down– Oil filters should be cleaned regularly– Cooler tubes to be cleaned

Oil level in the sump is to be monitored regularlyLow level is indicative of oil leakage somewhere in the system– Can be at the cooler (oil flowing into water side)– At the pump– At the valves– Check constantly around the engine spaces for

accumulation of oil

15

Lubricating oil pumps

Lubrication pumps are positive displacement pumps- – They supply a definite amount of fluid for each cycle of

rotation regardless of resistance which may oppose the transfer.

– They do not need any initial priming

Different types are:•Reciprocating– Piston, plunger

•Rotary– Vane, piston, screw, gear, lobe and screw

16

Reciprocating piston pump

• In a reciprocating pump, a volume of liquid is drawn into the cylinder through the suction valve on the intake stroke and is discharged under positive pressure through the outlet valves on the discharge stroke.

• The discharge from a reciprocating pump is pulsating and changes only when the speed of the pump is changed.

• Often an air chamber is connected on the discharge side of the pump to provide a more even flow by evening out the pressure surges. Reciprocating pumps are often used for sludge and slurry.

Ref: http://www.lcresources.com/resources/getstart/pump.gif

17

Gear pump• Consists of two meshing gear wheels housed in a tight

fit casing.• The gears rotate in opposite directions and the

vacuum created due to this, draws the fluid into the inlet side of the pump.

• The fluid is trapped in the spaces between the teeth and casing to be carried round from the suction to the delivery side

• Fluid is displaced when gear teeth mesh• Therefore there is a continuous transfer of liquid from

suction to delivery side• The theoretical volume displacement is given by

• do = outside diameter• dr = root diameter• N = rps w = depth of gear perpendicular to the screen

)dd(wN4

Q 2r

2ot