Lesson 5 Engine Lubrication And Cooling Engine Lubrication

Lesson 5: Engine Lubrication And Cooling

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.

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

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.

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

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.

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

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.

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.

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.

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 20 W) • “W” indicates that the oil is satisfactory oil for winter use in cold climates.

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

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.

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.

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

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

Engine Lubrication And Cooling • Internal Lubrication Of Reciprocating Engines • Three Methods used – Pressure – Splash – Combination Splash-And-Pressure

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.

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.

From Reservoir To Filter

Engine Lubrication And Cooling • Lubrication Systems • Wet-Sump System • Dry-Sump System

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.

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

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.

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.

Dry-Sump

Engine Lubrication And Cooling • Lubrication System

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

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.

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.

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.

Engine Lubrication And Cooling • Cowling and baffles • Designed to force air over the cylinder cooling fins. • Direct the air close around the cylinders and prevent it from forming hot pools. • Blast tubes direct jets of cooling air onto the bottom spark plug elbows.

Engine Lubrication And Cooling

Engine Lubrication And Cooling • Temperature Controls • Controls the air circulation over the engine. • Keeps the engine from overheating on take off and getting too cold in high-speed low-power letdowns. • Cowl Flaps, Augmenters

Engine Lubrication And Cooling • Cowl Flaps

Engine Lubrication And Cooling • Augmenters

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.

Engine Lubrication And Cooling • Pilot Responsibility • Cowl Flaps? • Power Settings? • Airspeed? • Fuel Mixture?

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.