JET ENGINE PROPULSION

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JET ENGINE PROPULSION
Chapter 5
Oil System
Distribution and Lubrication
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TYPICAL OIL SYSTEM
In a jet engine there are many moving parts which
come into contact with each other.
Therefore with metal touching metal some sort of
lubricating system is required.
To achieve this jet engines have a pressure feed
oil system which puts oil between the moving
parts to lubricate them and stop wear and damage.
Oil comes in various guises and if the wrong type
is used it can damage the engine oil seals.
Also oil has different qualities which have to be
taken into consideration when designing a system.
One quality is viscosity The viscosity of
a fluid is a measure of its resistance to
gradual deformation.
Low viscosity is where the fluid moves easily.
i.e. cooking oil. Thinner consistency.
High viscosity is where the fluid is hard to
move. i.e. grease. Thicker consistency.
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TYPICAL OIL SYSTEM
Early jet engines were total loss system
Engine Bearing Chamber
Filter
Pump
Tank
Jet engines are now a DRY-SUMP -
RE-CIRCULATING Oil systems
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TYPICAL OIL SYSTEM
Bearing Chambers
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TYPICAL OIL SYSTEM
Notional oil system
MCD Magnetic Chip Detector.
OIL PUMP ASSEMBLY
OIL TANK
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TYPICAL OIL SYSTEM
MCD Magnetic Chip Detector.
This is a magnet which sits in the oil system
feed and scavenge pipework.
Any slivers or chips of metal from the bearings
or other moving parts will be carried around the
oil system and attach to the magnets.
The magnets are housed in a self sealing unit
with a bayonet type catch, which allows them to
be removed periodically for inspection.
On removal they taken to a laboratory where the
slivers or chips are removed and analysed.
The type of metal can be identified and therefore
so can the location it came from.
By looking at the size and location it can be
decided whether there is a danger of failure or
whether it can be left for a further period.
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TYPICAL OIL SYSTEM
Notional oil system
MCD Magnetic Chip Detector.
OIL PUMP ASSEMBLY
OIL TANK
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TYPICAL OIL SYSTEM
Bearing Support Structure
Shaft
Bearing Oil Supply and Scavenge
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TYPICAL OIL SYSTEM
Bearing Support Structure static part
Higher pressure air forced into the Bearing
Chamber prevents oil loss
This air seal is known as a Labyrinth Seal.
Shaft rotating part
Oil Jet
Air/Oil scavenged away to tank
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TYPICAL OIL SYSTEM
Notional oil system
with Air Sealing
OIL PUMP ASSEMBLY
SCAVENGE
OIL TANK
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TYPICAL OIL SYSTEM
Notional oil system
with Air Sealing
The air used to seal the bearing areas is
compressor air and in the bearing area it
collects some particles of oil.
The air is constantly fed to the bearing area so
it must be exhausted.
If it was just dumped overboard it would use more
oil and contaminate the atmosphere.
Therefore to stop this the air/oil mixture is fed
to a centrifugal breather.
This device is driven by the engine and has an
impeller which when the air is fed in at the
centre, the oil gets separated and thrown to the
outside of the impeller casing.
The clean air can now be dumped overboard.
The oil in the breather is fed back to the oil
tank to be reused.
Air from the top of the oil tank is also fed to
the breather to extract the oil.
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TYPICAL OIL SYSTEM
Notional oil system
with Air Sealing
OIL PUMP ASSEMBLY
SCAVENGE
OIL TANK
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TYPICAL OIL SYSTEM
Any Questions?