Jet Aircraft Maintenance Fundamentals ATA 79

Beijing Ameco Aviation College Page 6... The oil is stored in the oil tank and pumped by the supply pump through the supply lines to the oil nozzles in the engine bearing compartments an

ATA 79 Lubrication System

Book No: JAMF ATA 79 ALL

Lufthansa Lufthansa Base

Issue: July 2000 For Training Purposes Only Lufthansa 1995 ã

Technical Training GmbH

Training Manual Fundamentals

JAR-66

Jet Aircraft Maintenance Fundamentals

Beijing Ameco

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For training purpose and internal use only.

Copyright by Lufthansa Technical Training GmbH All rights reserved No parts of this training

manual may be sold or reproduced in any form without permission of:

Lufthansa Technical Training GmbH

Lufthansa Base Frankfurt

D-60546 Frankfurt/Main

Tel +49 69 / 696 41 78

Fax +49 69 / 696 63 84

Lufthansa Base Hamburg

Weg beim Jäger 193

D-22335 Hamburg

Tel +49 40 / 5070 24 13

Fax +49 40 / 5070 47 46

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OIL GENERAL

TASK OF ENGINE OIL

In this segment you will learn about the main tasks of engine oil and the

different characteristics of oils First let us look at the main tasks of oil on

modern jet engines, include:

lubricating,

cooling,

cleaning

and corrosion protection

Generally, lubrication is needed to reduce friction between metal surfaces that

move against each other

You can see here, in this example, that the contact surfaces look very smooth

but when you look more closely at them through a microscope, you can see

that they are very rough

When the surfaces move against each other they can cause very high friction

and wear So the oil is needed to form a protective film This prevents the

contact between the metal surfaces

task of engine oil cont.

Cooling is another task of the engine oil All the heat in the lubricating areas

caused by the operating engine must be removed

The heat of the materials is transferred to the oil when it is in contact with the

task of engine oil cont.

Oil is used to clean the system from contamination These contaminations can

be caused by abrasions from the gears or bearings or by foreign objects like

sand or dust particles

The oil carries these particles until they are caught in an oil filter Sometimes,

the particles are very small so that they are not caught by the filter These very

small particles, which also indicate some internal wear can only be found by a

special analysis in a laboratory

Another important task of the oil is to protect the metal surfaces from corrosion

You will find that many materials in the engine are not resistant to corrosion As

you can see in this video, if oil is not used corrosion can occur

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TYPES OF OIL

There are two groups of engine oils, mineral oils and synthetic oils

Mineral oils are generally not as capable as synthetic oils They are only used

on piston type engines

Synthetic oils are used on jet engines They are designed specially to meet the

needs of the engine

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MINERAL OIL

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Figure 4 Mineral and Synthetic Oil

Hay dung`: 2 loai oil

goc' tu nhien

goc tong hop (tot hon)

oil VN airline: Mobile Jet Oil II Exxon 2380 ( thinh thoang moi dung`)

Oil A/C phai dung` dung loai

neu khong thi` phai suc' rua

sach truoc khi thay loai oil

moi vao`

types of oil cont.

You can find three different types of synthetic oils These are Type 1, 2 and 3

Type 1 oil is a first generation synthetic oil It is now only used on some older

gas turbine engines

Type 2 oil is mostly used on modern gas turbine engines

Type 3 oil has a higher thermal stability and viscosity at high temperatures than

the Type 2 oils You will find that this type of oil is only used on special aircraft,

for example, Concorde

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types of oil cont.

The advantages of synthetic oils are that they have better viscosity, better

thermal stability and a high pressure resistance

One disadvantage of synthetic oils is that they have a high price They are also

harmful to the skin but the most critical disadvantage of synthetic oils is that

they cannot be mixed with synthetic oils from other manufacturers even if they

are of the same type

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ADVANTAGE DISADVANTAGE

THERMALSTABILITYPRESSURERESITSTANCE

PRICESKINIRRATIONNON-MIXABLE

and thermal stability.

The viscosity is the most important characteristic of engine oil It is the internal

resistance of a fluid against deformation

If you let a metal ball fall into a glass of oil, you can see that the ball takes time

to reach the bottom

If the ball falls slowly, this shows that the viscosity of the oil is high

If the ball falls quickly, this shows that the viscosity of the oil is low

The viscosity of the oil depends on the temperature of the oil It is high at low

temperatures and it is low at high temperatures

This means, that warm oil with a low viscosity has a low internal resistance A

low internal resistance is an advantage, but if the viscosity gets too low, the

load carrying capability of the oil decreases and the oil film can no longer

separate the moving surfaces

You will find that the viscosity is usually measured in centistokes (cS) The

viscosity of Type 2 oils must be higher than 5 centistokes at 99° C and lower

than 13,000 centistokes at a temperature of 40° C

Let us now look at the next characteristic of engine oil You reach the pour

point of the oil, if you cool it down more and more At this temperature the oil

becomes so thick that it stops flowing

Note that Type 2 oils for jet engines have a pour point of 57° C So if the

temperature is lower than this, the oil stops flowing

Now let’s have a look at the flash point of engine oils It should be as high as

possible to avoid fire in the oil system So, type 2 oils have a flashpoint which is

FLASHPOINT250° CPRESSURE RESISTANCEOXIDATION RESISTANCE

oil specification cont.

The pressure resistance capability of the oil is an important factor for the oil film

between the moving components

We will explain this process with this example Here you can see oil film on an

engine bearing This film resists the loads on the bearing and prevents contact

between the moving surfaces

If the loads are higher than the pressure resistance capability of the oil, the

metal bearing surfaces come into contact and heavy material wear occurs

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FLASHPOINT250° CPRESSURE RESISTANCEOXIDATION RESISTANCE

THERMAL STABILITY

BEARINGINNER RACE

BEARINGINNER RACEOIL FILM

oil specification cont.

Oxidation is the reaction between oil and oxygen When the oil reacts with

oxygen it gets thicker and increases its viscosity

The oil starts to react with oxygen when the oil temperature increases above a

certain level

Therefore the oxidation resistance is an important characteristic of oil because

it increases the durability of the oil

Type 2 oils are resistant to oxidation at oil temperatures up to 220° C

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FLASHPOINT250° CPRESSURE RESISTANCE

OXIDATION RESISTANCE

UP TO 220° CTHERMAL STABILITY

oil specification cont.

The term thermal stability describes the oil resistance to decomposition of the

oil compounds at high temperatures The oil molecules are made of several

individual compounds

At high temperatures these molecules can break apart and the chemical

composition and the lubrication capability of the oil changes

This decomposition usually occurs at very high temperatures, far above the

normal operating temperatures of the engine oil Type 2 oils can resist chemical

FLASHPOINT250° CPRESSURE RESISTANCE

BASIC LUBRICATION SYSTEM

INTRODUCTION

The lubrication system distributes oil to the engine bearing compartments and

the gearboxes

Most gas turbine engines use a self contained dry sump lubrication system

The oil is recirculated through this system by pumps The system keeps the oil

in a fit condition to perform its tasks

The basic lubrication system has four subsystems

an oil reservoir and supply system

OIL SUPPLY TOBEARINGCOMPARTMENTS

OIL RESERVOIR AND SUPPLY

SYSTEMSCAVANGE SYSTEMVENT SYSTEMMONITORING SYSTEM

OIL RESERVOIR AND SUPPLY SYSTEM

The oil reservoir and supply system is also called the pressure oil system

The main components of this system are:

the oil tank

the supply lines

the supply pump

and the supply filter

The oil is stored in the oil tank and pumped by the supply pump through the

supply lines to the oil nozzles in the engine bearing compartments and the

gearboxes

The oil is filtered before it reaches the oil nozzles The supply filter is located

downstream of the supply pump The filter removes any foreign particles from

the oil before it reaches the oil nozzles This prevents blockage of the nozzles

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SUPPLYPUMP

SUPPLYLINES

AGB

FWD BEARINGCOMPARTMENT

TGB

AFT BEARINGCOMPARTMENT

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Figure 12 Pressure Oil System Schematic

bom duoc gan vao gear box

BEARING COMPARTMENTS WITH LABYRINTH SEALS

Here you can see the bearing surrounded by the bearing compartment walls

The walls prevent any leakage of oil from the bearing compartment In this

example the oil is sprayed on the bearing by an oil nozzle

The oil drips off the bearing to the bottom of the bearing compartment and

leaves the bearing compartment via the scavenge oil line As you can see the

scavenge oil line is connected to the bottom of the bearing compartment

Seals are used where the shaft passes through the bearing compartment walls

These can be labyrinth type seals as you see here or carbon seals which you

will see later

The labyrinth type seals have knife edges which rotate with the shaft and the

seal land which is made from a soft abradable material

The cavities outside the bearing compartments are pressurized with air This is

necessary for sealing The inner seals prevent air escaping from the bearing

compartment They are called oil seals

The outer seals minimize the air escaping from the cavities They are called air

seals The cavity drains normally release air during engine operation

They can also release any oil that leaks into the cavities if the oil seals are not

AFT BEARING COMPARTMENT

OILTANK

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Figure 13 Bearing Compartment with Labyrinth Seals

de chong oil tran ra khoi o bi

BEARING COMPARTMENTS WITH CARBON SEALS

Carbon seals are also used to seal the gap between the bearing compartment

walls and the engine shaft

The main components of a carbon seal are

the carbon ring

the seal seat

the seal support

springs

and the seal ring

The carbon ring is a static ring of carbon which rubs against the seal seat The

carbon ring is supported in the seal support The gap between the carbon ring

and the bearing compartment wall is sealed by a seal ring

The seal seat is a rotating collar on the engine shaft The contact face of the

seal seat with the carbon ring has a polished surface Springs are used to

maintain the contact between the seal seat and the carbon ring

Seal wear or, for example, vibrations can give an airflow across the carbon

seals into the bearing compartment Because of this the bearing compartments

must be vented

The contact surface of the seal seat is lubricated when the engine is running

The lubrication of the carbon seals has a number of benefits It reduces seal

wear leading to a longer service life the oil removes the heat caused by friction

and the sealing is improved

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SEALRING

SEALSUPPORT

SPRING

OIL PASSAGE

TO CONTROLSURFACE

POLISHEDSURFACE

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Figure 14 Bearing Compartment with Carbon Seal

SCAVENGE SYSTEM

The scavenge system is part of every dry sump lubrication system It returns

the oil from the bearing compartments and the gearboxes to the oil tank

This prevents the accumulation of lubrication oil in the bearing compartments

and the gearboxes

The lubrication oil is returned to the oil tank via

the individual scavenge lines

the scavenge pumps

the common scavenge lines

the scavenge oil filter

and the oil cooler

There is a scavenge pump installed in each of the individual scavenge lines

The scavenge pumps remove the lubrication oil at a faster rate than it is

delivered via the oil nozzles This prevents the accumulation of oil in the

bearing compartments and the gearbox sumps Now you know where the term

dry sump comes from

Because of their high capacity the scavenge pumps remove air as well as oil

and therefore send an air/oil foam back to the oil tank

The scavenge oil filter in the common scavenge line has a very fine filter

element to remove any foreign matter from the scavenge oil

The oil cooler is installed downstream of the filter The oil cooler removes the

heat from the oil

The oil is ready to be recirculated after it passes through the filter and the

cooler to the tank

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SUPPLYPUMP

AGB

FWD BEARINGCOMPARTMENT

TGB

AFT BEARINGCOMPARTMENT

INDIVIDUALSCAVENGELINE

SCAVENGEPUMPS

SCAVENGEOIL FILTER COMMON

SCAVENGE LINE

OILCOOLER

pump hut' ve`

(hut ve nhanh hon bom di)

VENT SYSTEM

The vent system releases air from the lubrication system to the atmosphere

Some systems have vent lines in the engine shaft and some systems have

separate external vent lines

The vent air leaves the shaft at the rear of the engine The oil tank is

con-nected to this vent system via a vent line to the forward bearing compartment

It is necessary to remove the air which is pumped into the oil tank with the

scavenge oil

The vent system also supplies air from the forward bearing compartment to the

gearboxes via the radial drive shaft housing This air is used to replace the air

which is pumped out of the gearboxes with the scavenge oil

The second type of vent system has external vent lines from the bearing

compartments The oil tank is connected to this vent system and air is supplied

from the forward bearing compartment to the gearboxes

A de oiler is connected to the end of the vent line The de oiler is a centrifugal

air/oil separator driven by the gearbox

The vent air goes through the de oiler before it is released to the atmosphere

The oil which is taken out of the vent air leaves via the de oiler scavenge line

As you can see the de oiler scavenge line has its own scavenge pump

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AGB TGB

VENTLINE

RADIALDRIVESHAFT

DE-OILERSCAVENGEPUMPDE-OILER

SCAVENGELINE

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Figure 16 Vent System

de tranh hien tuong bom

nhot vao nhieu qua' lam

qua ap' =>nhot khong vao

duoc nua Nguoi ta dung

de-oiler de thong thoang cac

pump voi khi ngoai troi`

(dung luc ly tam de thu nhot'

lai, con khi' thi` xa ra ngoai`)

OIL SYSTEM MONITORING

The indicating subsystem measures and indicates oil quantity oil pressure and

oil temperature

The indicating system provides a flight crew warning if the oil pressure drops

below the minimum level or if the scavenge filter becomes clogged

The indicating system needs several sensors to detect this information

The sensors are:

the oil quantity sensor

the oil pressure sensor

the oil temperature sensor

the low oil pressure switch

and the filter clogging switch

Mechanical clogging indicators are used to indicate a clogged filter when the

engine is stopped They are also called pop out indicators

The contamination in the oil can indicate the condition of the lubricated engine

parts The contamination can be checked by inspecting the filters and by using

magnetic chip detectors

Magnetic chip detectors are small magnets which are in contact with the

scavenge oil They collect particles of magnetic metal which are passing

through the oil

They are usually installed in the individual scavenge lines of each sump This

makes it easy to isolate the source of the contamination

The detectors are easily removed for inspection You will learn more about

magnetic chip detectors in the lesson on maintenance practice

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FWD BEARING COMPARTMENT

TGB

AFT BEARING COMPARTMENT

INDIVIDUALSCAVENGE LINES

OIL TEMPERATURESENSORFILTER

OILPRESSURESENSOR

LOW OILPRESSURESWITCH

OIL QUANTITYSENSOR

CLOGGINGINDICATORMAGNETIC

CHIPDETECTOR

FILTER

OIL FILTERCLOGGINGSWITCH

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Figure 17 Oil Indicating System

chi co sensor nay khong di qua ECU

OIL SUPPLY SYSTEM

FULL FLOW

The full flow system is the simplest type of oil supply system This system has

no way of regulating the oil pressure

The oil pressure changes with changes in N2 rotor speeds, changes in oil

temperature and changes in the flow areas downstream of the supply pump

The supply pump is driven by the N2 rotor system via the gearbox At higher

N2 rotor speeds the supply pump produces a higher flow of oil through the

supply lines This higher flow leads to a higher oil pressure because the supply

lines have a given flow area If the N2 rotor speed decreases the oil pressure

also decreases

Oil pressure is also influenced by oil temperature An increase in oil

temperature leads to lower viscosity of the oil

If we assume a constant N2 speed then a lower viscosity gives lower flow

resistance and lower oil pressure In the same way a decrease in oil

temperature leads to higher oil pressure With low oil temperatures the oil

pressure is near the upper line of the operating range and with high oil

temperatures the oil pressure is near the lower line of the operating range

You can see that you can have different oil pressures for a given N2

A third reason for changes in oil pressure is changes in the total flow area

downstream of the supply pump A clogged oil nozzle, for example, can reduce

the total flow area downstream of the supply pump This leads to an increase in

the oil pressure

A leakage in the oil system leads to an increase in the total flow area

downstream of the supply pump This leads to a decrease in the oil pressure

Normally when we have an external leakage the decrease in oil pressure

comes with a decrease in oil quantity

We can also have a special type of leakage which is hard to identify With this

leakage there is a decrease in oil pressure but no change in oil quantity

The oil pressure can become too high for the system components A common

example is when we have very low oil temperature combined with high N2 rotor

speeds

A pressure relief valve is installed between the delivery side and the suction

side of the supply pump to prevent oil pressure becoming too high

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FWD BEARING COMPARTMENT

TGBAGB

OILTANK

AFT BEARING COMPARTMENT

WARM OIL

OPERATING RANGE COLD OIL

CONSTANT PREESURE

Sometimes the constant pressure system is called the regulated pressure

system

The system has a pressure regulating valve

The pressure regulating valve holds the oil pressure to a given design value at

all N2 rotor speeds from idle to maximum You can see this relationship on the

graph at the top of the screen

Changes in oil temperature also have no effect on oil pressure

The control parameters are the oil pressure in the supply line and the vent

pressure The difference between the supply pressure and the vent pressure

controls the position of the valve piston against the valve spring

The position of the piston controls the spill flow of the supply pump from the

delivery side to the suction side A change in the flow area has the same effect

on pressure as a leak in the full flow system

The pressure regulating system holds the pressure difference between the oil

pressure and the vent pressure constant This ensures that we have the same

flow at all engine speeds

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