1. Engine Lubrication And Cooling
Thermal Engineering I
III year I semester
Mechanical Engineering
By Mr. Ali Ahmed
Assistant Professor

2. Engine Lubrication And Cooling
Principles of Engine Lubrication
Primary purpose is to reduce friction between moving parts.
Liquid lubricants (oil) are used universally in aircraft.
No metal to metal contact occurs.
Friction and wear held to a minimum.

3. Engine Lubrication And Cooling
Principles of Engine Lubrication
Oil film acts as a cushion between metal parts.
Crankshaft and connecting rods
Shock-loading parts

4. Engine Lubrication And Cooling
Principles of Engine Lubrication
Absorbs heat from the parts.
Pistons and cylinder walls.
Forms a seal between the piston and the cylinder wall.
Reduce abrasive wear.
Picks up foreign particles and carries them to the filter.

5. Engine Lubrication And Cooling
Principles of Engine Lubrication
Reduces friction
Cushions
Absorbs heat
Cooling
Forms a seal
Reduces abrasive wear
Cleans

6. Engine Lubrication And Cooling
Requirements & Characteristics Of Lubricants
The Most important characteristic is its viscosity.
The resistance of an oil to flow.
High viscosity is oil that flows slow.
Low viscosity is oil that flows freely.

7. Engine Lubrication And Cooling
How does temperature affect the viscosity of oil?

8. Engine Lubrication And Cooling
Some Grades of oil become practically solid in cold weather.
Increases drag
Makes circulation difficult.
Others become so thin at high temperatures that the oil film is broken.
Rapid wear of moving parts.

9. Engine Lubrication And Cooling
Flash Point And Fire Point
Flash Point is the temperature at which a liquid will begin to give off ignitable vapors.
Fire Point is the temperature at which there are sufficient vapors to support a flame.

10. Engine Lubrication And Cooling
Cloud Point, Pour Point And Specific Gravity
Cloud Point is the temperature at which its wax content, normally held in solution, begins to solidify and separate in to tiny crystals.
Pour Point is the lowest temperature at which it will flow or can be poured.
Specific Gravity is a comparison of the weight of the substance to the weight of an equal volume of distilled water.

11. Engine Lubrication And Cooling
Aviation oils are classified numerically according to an approximation of their viscosity.
Classified under an SAE (Society of Automotive Engineers) system.
SAE divides all oils into seven groups according to viscosity at either 130° or 210° F.
SAE 10 to 70 (SAE 20W)
“W” indicates that the oil is satisfactory oil for winter use in cold climates.

12. Engine Lubrication And Cooling
Lubricating Oil Types
Straight Mineral Oil
Ashless Dispersant
Synthetic

13. Engine Lubrication And Cooling
Straight Mineral oil
Used in engines after overhaul or when new to facilitate wear-in or seating of piston rings.
Often forms sludge when exposed to temperatures higher than normal.

14. Engine Lubrication And Cooling
Ashless Dispersant (AD)
Replaces mineral oil after the piston rings have seated.
Less tendency to oxidize to carbon, or form ash deposits.
Particles don’t clump together, forming sludge.
Better lubricating properties than mineral oils.

15. Engine Lubrication And Cooling
Oil Compatibility
Can different brands and grades of the same oil type be mixed?

16. Engine Lubrication And Cooling
Oil Compatibility
If necessary in order to have proper operating oil levels, brands of the same type can be mixed.

17. Engine Lubrication And Cooling
Internal Lubrication Of Reciprocating Engines
Three Methods used
Pressure
Splash
Combination Splash-And-Pressure

18. Engine Lubrication And Cooling
Pressure-Lubrication
A mechanical pump supplies oil under pressure to the bearings throughout the engine.
Splash-Lubrication
Used in addition to pressure lubrication on aircraft engines.

19. Engine Lubrication And Cooling
Advantages of pressure lubrication system
Positive introduction of oil to the bearings.
Cooling effect caused by the large quantities of oil which can be circulated through a bearing.
Satisfactory lubrication in various attitudes of flight.

20. From Reservoir
To Filter

21. Engine Lubrication And Cooling
Lubrication Systems
Wet-Sump System
Dry-Sump System

22. Engine Lubrication And Cooling
Wet-Sump
System consist of a sump or pan, in which the oil supply is contained.
The sump or pan is attached to the bottom of the engine case.

23. Engine Lubrication And Cooling
Wet-Sump
What are some of the disadvantages and advantages of the wet-sump system?

24. Engine Lubrication And Cooling
Wet-Sump
Disadvantages
Oil supply limited by sump.
Cooling is difficult.
Higher operating temperatures.
Not adaptable to inverted flying
Advantages
Requires no external parts and fittings to complicate installation.
No second (scavenge pump) required.
Can be operated in much cooler temperatures.

25. Engine Lubrication And Cooling
Dry-Sump
Oil supply is carried in a separate tank.
Scavenger pumps used to return the oil to the tank.
Used in radial engines and engines capable of sustained inverted flight.

26. Dry-Sump

27. Engine Lubrication And Cooling
System

28. Engine Lubrication And Cooling
Engine Cooling Systems
Why is excessive heat undesirable in internal combustion engines?

29. Engine Lubrication And Cooling
Affects the behavior of the combustion of the fuel/air charge.
It weakens and shortens the life of engine parts.
It impairs lubrication.

30. Engine Lubrication And Cooling
Engine Cooling Systems
About one-fourth of the heat released in an engine is changed into useful power.
Half of the heat goes out the exhaust, and the other is absorbed by the engine.
Oil picks up some heat and transfers it to the airstream.
The engine cooling system takes care of the rest.

31. Engine Lubrication And Cooling
Cooling Fins
Cooling fins increase the surface of a cylinder.
This arrangement increases the heat transfer by radiation (from a jug to a barrel).
Cylinders are normally replaced when a specified number of square inches of fins are missing.

32. Engine Lubrication And Cooling
Cylinder Head Temperature Indicating System
Consists of and indicator, electrical wiring, and a thermocouple.
Thermocouple consists of two dissimilar metals connected by wiring to an indicating system. A voltage is produced when the temperature of the junction is different from the temperature where the dissimilar metals are connected.

33. Engine Lubrication And Cooling
Thermal Shock
Occurs when engine parts that are operating at high temperatures are quickly cooled.
Idle power, high airspeed, cool or cold air.
Some parts are cooled much more rapidly then others. These parts shrink in size faster then the warmer, surrounding metals.

34. Thank You