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Transcript
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 20W)
• “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 proper operating 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.