1. Distribution and Lubrication
JET ENGINE PROPULSION
Chapter 5
Oil System
Distribution and Lubrication

2. 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.

3. TYPICAL OIL SYSTEM Early jet engines were total loss system
Engine Bearing Chamber
Pump
Filter
SUMP
Scavenge Pump
Tank
Jet engines are now a
‘DRY-SUMP - RE-CIRCULATING’
Oil systems
i.e. oil was lost in the gas stream

4. TYPICAL OIL SYSTEM Bearing Chambers Centre Bearing Chamber
Front Bearing Chamber
Rear Bearing Chamber
Roller Bearing
Ball Bearing (Location Bearing)
Roller Bearing

5. TYPICAL OIL SYSTEM Notional oil system MCD – Magnetic Chip Detector.
SCAVENGE
OIL COOLER
MCD
MASTER MCD
MCD – Magnetic Chip
Detector.
OIL PUMP ASSEMBLY
PRESSURE
OIL TANK

6. 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.

7. Let’s take a closer look at what happens here
TYPICAL OIL SYSTEM
Notional oil system
Let’s take a closer look at what happens here
SCAVENGE
OIL COOLER
MCD
MASTER MCD
MCD – Magnetic Chip
Detector.
OIL PUMP ASSEMBLY
PRESSURE
OIL TANK

8. TYPICAL OIL SYSTEM Bearing Support Structure Shaft Oil Jet Scavenge
Oil Supply
Scavenge
Bearing Oil Supply and Scavenge

9. TYPICAL OIL SYSTEM Bearing Support Structure = static part
Pressurised air from compressors
Higher pressure air forced into the Bearing Chamber prevents oil loss
This air seal is known
as a Labyrinth Seal.
Shaft = rotating part
Oil Supply
Oil Jet
Air/Oil scavenged away to tank

10. TYPICAL OIL SYSTEM Notional oil system with Air Sealing OIL COOLER
PRESSURE
OIL COOLER
MCD
MASTER MCD
OIL PUMP ASSEMBLY
SCAVENGE
OIL TANK
Scavenge Oil passes through Air/Oil Separator in Oil Tank

11. 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.

12. TYPICAL OIL SYSTEM Notional oil system with Air Sealing OIL COOLER
PRESSURE
OIL COOLER
Clean(?) Air Overboard
MCD
MASTER MCD
OIL PUMP ASSEMBLY
SCAVENGE
Gearbox Drive
Centrifugal Breather
OIL TANK
Scavenge Oil passes through Air/Oil Separator in Oil Tank

13. TYPICAL OIL SYSTEM
Any Questions?