1. JET PROPULSION
Part 5
Jet Engine Operation
Oil Systems

2. Introduction ‘Dry Sump, Recirculating System’
Early jet engines had a ‘Total Loss’ oil system,
that is oil was taken from the tank,
used for lubrication and was then lost overboard.
Now, jet engines have what is known as
‘Dry Sump, Recirculating System’
In jet engines oil is sucked (scavenged) out of the sump and returned to a separate tank.
The scavenge pumps have a greater capacity than is required to make sure that all the oil is actually taken out of the sump, hence the term ‘dry’ sump.

3. Engine Bearing Chamber
Dry Sump Recirculating System
Early jet engines were a total loss system
Engine Bearing Chamber
Pump
Filter
Tank
SUMP
Scavenge Pump
Scavenge pumps make sure all the oil
is actually taken out of the sump,
hence the term ‘DRY-SUMP’.
i.e. oil was lost
in the gas stream

4. Engine Bearing Chamber
Dry Sump Recirculating System
Early jet engines were a total loss system
Engine Bearing Chamber
Pump
Filter
Tank
SUMP
Scavenge Pump
Oil scavenged from the engine,
is replaced in the tank
ready to be used again,
hence the term ‘RECIRCULATING’.

5. Oil Systems Typical Oil System
SUPPORT BEARINGS
As we know, location bearings support the engine rotor,
which have to be lubricated to maintain smooth operation.
These bearings are contained within bearing chambers;
the number of bearings inside a chamber can vary
with different designs of jet engines.

6. Oil Systems Typical Oil System
OIL COOLER
OIL PUMP ASSEMBLY
PRESSURE
OIL TANK
Oil is sucked out of the tank by the pressure pump,
which then forces it through an oil cooler.
Coolers are placed before the tank, a ‘Cool Tank system’
or after, a ‘Hot Tank system’.

7. Oil Systems Typical Oil System
OIL COOLER
OIL PUMP ASSEMBLY
PRESSURE
OIL TANK
Oil flows via individual pipes, to the bearing chambers.
Oil distribution is set to the correct flow because bearings
near hotter engine parts require the greater oil flow
for cooling as well as lubrication.

8. Oil Systems Typical Oil System
SCAVENGE
OIL COOLER
OIL PUMP ASSEMBLY
PRESSURE
OIL TANK
Each chamber is scavenged by its own pump
ensuring no oil rests in the bearing chamber sump.
The outlet from the scavenge pumps is combined to a
single return flow back to the oil tank.

9. Oil Systems Typical Oil System
SCAVENGE
OIL COOLER
MCD
MASTER MCD
OIL PUMP ASSEMBLY
PRESSURE
OIL TANK
If a bearing starts to disintegrate, it generates particles.
As bearings are made from magnetic metals,
magnets are fitted into the scavenge system called
Magnetic Chip Detectors (MCD’s).

10. The Bearing Chamber Bearing Oil Supply and Scavenge
Let’s take a closer look at what happens here

11. The Bearing Chamber Bearing Oil Supply and Scavenge Shaft
Oil Jet
The oil is delivered under pressure to a jet.
Once the oil has passed through the jet, its pressure
becomes the same as the bearing chamber pressure.

12. The Bearing Chamber Bearing Oil Supply and Scavenge Shaft
Oil Jet
The jet is directed to a rotating reservoir,
filling by centrifugal force when the engine is running.
The oil evens out providing a feed through internal drillings
to all areas of the bearings.

13. The Bearing Chamber Bearing Oil Supply and Scavenge Shaft
Oil Jet
Scavenge Oil to tank
After the oil has lubricated the bearing,
it drops to the bottom of the bearing chamber sump,
and is taken away by the scavenge pumps
and returned to the oil tank.

14. The Bearing Chamber Bearing Oil Supply and Scavenge Shaft
Oil Jet
Scavenge Oil to tank
In order to prevent the loss of oil,
the bearing chambers need to be sealed,
allowing the oil to be continuously recirculated
through the system.

15. The Bearing Chamber Bearing Oil Supply and Scavenge Shaft
Oil Jet
Scavenge Oil to tank
As the bearings are situated between
the rotating and static parts of the engine,
the seals cannot be of contact type,
so air sealing vents are added.

16. The Bearing Chamber Bearing Oil Supply and Scavenge Shaft
Pressurised air from compressors
Higher pressure air forced into the
Bearing Chamber prevents oil loss
Shaft
Oil Supply
Oil Jet
Scavenge Oil to tank
The seals basically comprise of a small gap
between the rotating and static part of the engine,
to which an air pressure is applied from the outside.

17. Oil Systems Oil System with Air Sealing
SCAVENGE
PRESSURE
OIL PUMP ASSEMBLY
MCD
MASTER MCD
OIL COOLER
OIL TANK
Scavenge Oil
passes through
Air/Oil Separator
Returning oil passes through an air/oil separator :-
A Settlement tray allows air to bubble to the oil surface
A Vortex separator which squeezes the air to the centre
and then to the top of the tank.

18. Oil Systems Oil System with Air Sealing
SCAVENGE
PRESSURE
OIL PUMP ASSEMBLY
MCD
MASTER MCD
OIL COOLER
OIL TANK
Clean(?) Air Overboard
Gearbox Drive
Centrifugal Breather
Scavenge Oil
passes through
Air/Oil Separator
The air in the tank passes to a Centrifugal Breather,
with a vent line from each bearing chamber.
Driven by the engine gearbox, the air is throws out
and the oil returned to the tank.

19. Oil Systems Oil System with Air Sealing
SCAVENGE
PRESSURE
OIL PUMP ASSEMBLY
MCD
MASTER MCD
OIL COOLER
OIL TANK
Clean(?) Air Overboard
Gearbox Drive
Centrifugal Breather
Scavenge Oil
passes through
Air/Oil Separator
Centrifugal Breathers are never 100% effective,
and oil loss can be visible as a blue-ish smoke.
Too much smoke shows over filling of oil or other problems
like bearing chamber seal failure.

20. Check of Understanding
What type of oil system
do modern jet engines have?
Sealed Sump Redirecting System
Dry Sump Recirculating System
Sealed Sump Centrifugal System
Dry Sump Scavenger System

21. Check of Understanding
What is fitted into a scavenge system
to check if bearings are disintegrating?
Magnetised Coil Detectors
Magnetised Chip Detectors
Magnetic Coil detectors
Magnetic Chip Detectors

22. Check of Understanding
In the bearing oil supply, the oil is delivered
under pressure to a jet.
Once the oil has passed through the jet,
which of the following applies?
Its pressure becomes the same
as the bearing chamber pressure
Its pressure becomes less than
the bearing chamber pressure
Its pressure becomes more than
the bearing chamber pressure
Its pressure remains the same

23. Check of Understanding
In the bearing oil supply,
why do the bearing chambers
need to be sealed?
To prevent the loss of oil
To maintain the oil pressure
To maintain oil temperature
To withstand outside air pressure

24. Check of Understanding
In the bearing system,
air sealing vents are added,
contact seals cannot be applied because
The oil and air pressure is too high
The bearings are situated between
rotating and static parts of the engine
The oil and air temperatures are too high
The bearings would be inoperative
if contact seals were used

25. Check of Understanding
If blue-ish smoke is exiting an engine,
which of the following could apply?
Damage to the centrifugal breather
Too little oil in the system
Bearing chamber seal failure
Bearing particles in the system

26. JET PROPULSION
End of Presentation