aircraft jet engines oil 5994772

8/11/2019 Aircraft Jet Engines Oil 5994772

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Lubrication Systems


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Table of Contents

1. Introduction

2. Wet Sump System

3. Dry Sump

4. Oil Tanks

5. Oil Pumps

6. Oil Filters

7. Bearing Chamber (may be deleted)

8. Oil System Valves

9. Other Oil Components

10.Spectrometric Oil Analysis Program (SOAP)

11.Trouble Shooting & Maintenance


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1- Introduction

The primary function of a lubricationsystem is to provide oil to the various partsof the engine which are subject to friction

loads from engine rotation and heat loadsfrom the gas path.

The lubrication system can be divided intotwo sections:

The Pressure side

The Scavenge side.


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There are two basic classifications of gas

turbine lubrication systems:

Wet Sump

Dry Sump


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2-Wet Sump System

A wet sump lubrication system was used on early gasturbine engines and is now more often found on smallerengines or APU's.

A wet sump system is a lubrication system where the oilsupply is carried within the engine itself or accessorygearbox.

Pressurized oil is used to lubricate the main enginebearings but the accessory gearbox is splash lubricatedby oil carried in the gearbox housing that also acts as aoil reservoir


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3-Dry Sump

A dry sump lubrication system carries its

oil supply in a tank separate from the

engine.

This now the most common type of

lubrication system in modern gas turbine

engines.


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Dry sump cont

Dry sump lubrication systems are divided

into two categories;

hot-tank system and

the cold-tank systems.


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-Hot-Tank Lubrication System

Has the oil cooler placed in the pressure

side of the system, and the oil is returned

'hot' to the oil tank.

An advantage of this type of system is that

a maximum heat exchange occurs

because the oil has less entrained air in

the pressure side of the system and thisallows a smaller oil-cooler to be used.


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Cold-Tank Lubrication System

A cold tank system is essentially the sameas the hot-tank system except that the oil

cooler is located in the scavenge sideofthe lubrication system and the oil is cooledbefore being returned to the oil tank.

In engines that have higher oiltemperatures this is an advantage, as highoil temperatures affect oil service life.


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5-Oil Tanks

A gas turbine engine oil reservoir is

usually mounted on the engine or nearby

airframe.

They are usually constructed of aluminum

or stainless steel and are designed to

provide a constant supply of oil to the

lubrication system.


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Oil tanks cont

Federal Aviation Regulations (FAR's) require that thetanks have an oil tight filler cap and an expansion spaceof 10%.

The expansion space is to make allowance for an

increase in oil volume due to thermal expansion andentrapped air when the engine is operating.

Most tanks are pressurized to approximately 4 psi, thishas two purposes:

Positive flow of oil

Suppresses foaming and pump cavitations.


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Oil tanks cont

The tanks can contain:

A venting system

Filler cap and strainer

De-aerator to remove air

Oil pick up

Dip stick

Sight gauge Oil quantity transmitter


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Oil Pumps

Vane Pump

Vane pumps are a constant displacement

pump more often found in the scavengeside of the lubrication system as they are

more tolerant of debris and have a high

volume and relatively low pressure.


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Gerotor Pump

Gerotor pumps are a constant

displacement pump and are used in boththe pressure side and the scavenge side

of the engine.


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Oil pumps cont

Gear Pump

Gear pumps are the most commonly used

constant displacement pump and can befound in the either the scavenge side or

the pressure side.


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6- Oil Filters

It is extremely important that the oil used in a gas turbineengine is free from foreign particles as these particlescan cause severe bearing damage.

To keep the oil clean filters are used as the oil leaves the

pressure pump and again in what are called the 'lastchance' filters just before the oil is sprayed from the oil

jet nozzle.

There are three common types of filter used in gas

turbine engines:


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Woven Wire Mesh Filter

Easy to clean, but can generally only

remove particles larger than 40 microns.


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Disk-type / Wafer Type Filter

Made up of a series of screen type filters

with spacers in between each screen to

form a chamber which is ported to the

central collection tube.

This type of filter is easily cleaned and

provides better filtration than a wire mesh

filter.


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Pleated Fiber Filter

Can remove particles as small as 15

microns. Can be cleanable or disposable


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Bearing Chambers


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8-Oil System Valves

Relief Valve

Relief valves are designed to maintain a constantpressure in the lubrication system and prevent over

pressurization and damage. The relief valves are situated on the discharge side of

the pump, when the oil pressure exceeds the valvesetting the valve opens and ports oil to the inlet side ofthe pump.

Some valve pressure settings can be adjusted by ascrew.


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Bypass valves

normally found in oil system components

and are designed to allow oil to bypass a

component should the component fail and

oil is prevented flowing through it.


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Check Valve

A one-way valve that ensures that oil flows

in one direction only


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9-Other Oil Components

Chip Detectors

Magnetic chip detectors are installed inscavenge side of the lubrication system

used to determine the level of metallic wearoccurring in the engine.

Some chip detectors are easily removed forvisual inspections while other may include an

electrical circuit that illuminates a warning light inthe flight deck when enough metal chips haveaccumulated to close the gap in the detector.


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Heat exchanger

The oil in a gas turbine engine gathers a

great deal of heat from the main bearings

and this heat maybe transferred to eitherfuel or air.

Most modern gas turbine engines transfer

the heat to the fuel to prevent theformation of ice crystals.


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Air-Oil Separator

The oil that is picked up by the scavenge pumpcontains a lot of air.

Oil tanks contain dwell chambers which allowthe air to separate and the air-free oil to enter

the tank. Some engines also utilize a gear driven

centrifugal air-oil separator.

As oil laden air enters the rotating slinger

chamber, centrifugal action throws the oiloutwards to collect on the walls and drain downinto the tank


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Breather system

The breather system is used to keep the

air in the oil tank at the same pressure as

the air in the bearing housing.

This ensures that there is a positive flow of

oil to the inlet of the main pump and

prevents cavitations.


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After lubricating the bearing the oil drains down into the sump and iscollected by the scavenge pump and returned to the oil tank.

The scavenge pump not only collects all the oil, but also collectssome air as well.

This air is transferred to the tank and is separated from the oil by thedeaerator and is used to pressurize the tank.

The bearing chamber is vented to the oil tank by the vent line and acheck valve.

The oil tank is also vented to ambient air through the pressurizingvalve which maintains the tank at approximately 3-4 psi.

If the scavenge pump lowers the pressure in the bearing chamber,the vacuum valve opens and allows air to enter the chamber


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10-Spectrometric Oil Analysis

Program (SOAP)

Oil sampling should be done at regular

intervals just after an engine has been run.

The contaminants in the oil provide an

indication of engine wear.


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Oil samples taken are passed through a

spectrometer which precisely burns the oil

and measures the wavelength of the

emitted light to determine the type andquantity of contaminates in the oil.

The spectrometer can detect contaminants

at 2-3 parts per million of oil


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The contents of the filters can be

examined for evidence of metal particles,

but by the time particles large enough to

be visible are discovered serious enginedamage has already occurred


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