JET ENGINE PROPULSION Chapter 5

Oil SystemDistribution and Lubrication

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 betweenthe 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.

TYPICAL OIL SYSTEM

Engine Bearing Chamber

Pump Filter

Tank

Early jet engines were total loss system

i.e. oil was lost in the gas stream

SUMP

Scavenge Pump

Jet engines are now a

‘DRY-SUMP - RE-CIRCULATING’

Oil systems

TYPICAL OIL SYSTEM

Front Bearing

Chamber

Centre Bearing

Chamber

Rear Bearing

Chamber

Bearing Chambers

Roller Bearing

Ball Bearing (Location Bearing)

Roller Bearing

TYPICAL OIL SYSTEM

OIL PUMP ASSEMBLY

SCAVENGEPRESSURE

OIL COOLER

MCDMCDMCD

MASTER MCD

OIL TANK

Notional oil system

MCD – Magnetic ChipDetector.

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.

TYPICAL OIL SYSTEM

OIL PUMP ASSEMBLY

SCAVENGEPRESSURE

OIL COOLER

MCDMCDMCD

MASTER MCD

Let’s take a closer look at what

happens here

OIL TANK

Notional oil system

MCD – Magnetic ChipDetector.

TYPICAL OIL SYSTEM Bearing Support Structure

Shaft

Oil Jet

Oil Supply Bearing Oil Supply and Scavenge

Scavenge

TYPICAL OIL SYSTEM Bearing Support Structure = static part

Shaft = rotating partShaft = rotating part

Oil Jet

Oil Jet

Oil Supply

Pressurised air from

compressors

Higher pressure air forced into the Bearing Chamber prevents oil loss

Air/Oil scavenged away to tank

This air seal is known as a Labyrinth Seal.

TYPICAL OIL SYSTEM Notional oil system

OIL PUMP ASSEMBLY

SCAVENGEPRESSURE

OIL COOLER

OIL TANK

with Air Sealing

Scavenge Oil passes through Air/Oil Separator in Oil Tank

MCDMCDMCD

MASTER MCD

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.

TYPICAL OIL SYSTEM Notional oil system

OIL PUMP ASSEMBLY

SCAVENGEPRESSURE

OIL COOLER

OIL TANK

with Air Sealing

Scavenge Oil passes through Air/Oil Separator in Oil Tank

Centrifugal Breather

Gearbox Drive

Clean(?) Air Overboard

MCDMCDMCD

MASTER MCD

Any Questions?

TYPICAL OIL SYSTEM