Power Plant Engineering

8.10 LUBRICATION SYSTEM OF DIESEL POWER PLANT
Since frictional forces causes wear and tear of rubbing parts of the engine and thereby the life of
the engine is reduced. So the rubbing part requires that some substance should be introduced between

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the rubbing surfaces in order to decrease the frictional force between them. Such substance is called
lubricant. The lubricant forms a thin film between the rubbing surfaces. And lubricant prevents metal-
to-metal contact. So we can say “Lubrication is the admission of oil between two surface having relative
motion”.
The main function of lubricant is to,
1. To reduce friction and wear between the parts having relative motion by minimizing the force
of friction and ensures smooth running of parts.
2. To seal a space adjoining the surfaces such as piston rings and cylinder liner.
3. To clean the surface by carrying away the carbon and metal particles caused by wear.
4. To absorb shock between bearings and other parts and consequently reduce noise.
5. To cool the surfaces by carrying away heat generated due to friction.
6. It helps the piston ring to seal the gases in the cylinder.
7. It removes the heat generated due to friction and keeps the parts cool.
The various parts of an engine requiring lubrication are;
1. Cylinder walls and pistons.
2. Main crankshaft bearings.
3. Piston rings and cylinder walls.
4. Big end bearing and crank pins.
5. Small end bearing and gudgeon pin bearings.
6. Main bearing cams and bearing valve tappet and guides
7. Timing gears etc.
8. Camshaft and cam shaft bearings.
9. Valve mechanism and rocker arms.
A good lubricant should possess the following properties:
1. It should not change its state with change in temperature.
2. It should maintain a continuous film between the rubbing surfaces.
3. It should have high specific heat so that it can remove maximum amount of heat.
4. It should be free from corrosive acids.
5. The lubricant should be purified before it enters the engine.
6. It should be free from dust, moisture, metallic chips, etc.
7. The lubricating oil consumed is nearly 1% of fuel consumption.
8. The lubricating oil gets heated because of friction of moving parts and should be cooled
before recirculation.
The cooling water used in the engine may be used for cooling the lubricant. Nearly 2.5% of heat
of fuel is dissipated as heat, which is removed by the lubricating oil.
The various lubricants used in engines are of three types:
1. Liquid Lubricants or Wet sump lubrication system.
2. Solid Lubricants or Dry sump lubrication system.
3. Semi-solid Lubricants or Mist lubrication system.

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POWER PLANT ENGINEERING
Liquid oils lubricants are most commonly used. Liquid lubricants are of two types:
(a) Mineral oils
(b) Fatty oils.
Graphite, white lead and mica are the solid lubricants.
Semi solid lubricants or greases as they are often called are made from mineral oils and fatty-oils.