Fuel System

Issue:

Author:

For Training Purposes Only

LTT 2006

Gas Turbine Engine/Fuel System

ATA 73

EJAMF_M15.11_A_E

eJAMF

Fundamentals

SwD

EASA Part-66

A

Module 15.1121.10.2008

Training Manual

For training purposes and internal use only.

Copyright by Lufthansa Technical Training (LTT).

LTT is the owner of all rights to training documents and trainingsoftware.

Any use outside the training measures, especially reproductionand/or copying of training documents and software also extractsthere of in any format all (photocopying, using electronic systemsor with the aid of other methods) is prohibited.

Passing on training material and training software to third partiesfor the purpose of reproduction and/or copying is prohibited withoutthe express written consent of LTT.

Copyright endorsements, trademarks or brands may not beremoved.

A tape or video recording of training courses or similar services isonly permissible with the written consent of LTT.

In other respects, legal requirements, especially under copyrightand criminal law, apply.

Lufthansa Technical Training

Dept HAM USLufthansa Base HamburgWeg beim Jger 19322335 HamburgGermany

Tel: +49 (0)40 5070 2520

Fax: +49 (0)40 5070 4746

E-Mail: [email protected]

www.Lufthansa-Technical-Training.com

Revision Identification:

The date given in the column Issue on the face of this cover is binding for the complete Training Manual.

Dates and authors ID, which may be given at the base of the individual pages, are for information about the latest revision of that page(s) only.

The LTT production process ensures that the Training Manual contains a complete set of all necessary pages in the latest finalized revision.

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!

Page 1ATA DOC

M15 GAS TURBINE ENGINE eJAMFGas Turbine Engine

MODULE 15

HAM US/F SwD APR 15, 2008

M15.11 FUEL SYSTEM

Lufthansa T

echnic

al T

rain

ing

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!

Page 201|Intro/A/B1

M15.11 FUEL SYSTEMS (ATA 73)ENGINE FUEL DISTRIBUTION

eJAMFGas Turbine Engine

MODULE 15


ENGINE FUEL DISTRIBUTION

INTRODUCTION

On an aircraft we distinguish between the primary fuel system, which stores thefuel and the secondary fuel system, which is on the engine. Here we will onlytalk about the secondary fuel system.

One purpose of this system is to supply the fuel to the combustion chamber,and the other main purpose is to control the quantity of fuel necessary for alloperating conditions of the engine.

The engine fuel system can be split into 2 subsystems: the fuel distributionsubsystem and the fuel control subsystem.

The engine fuel distribution subsystem has 3 main tasks:

First it has to safely supply the fuel from the aircraft fuel system to thecombustion chamber.

The second task is to pressurize the fuel sufficiently so that it can bevaporized in the combustion chamber.

The third task of the distribution system is to heat the fuel. This makes surethat fuel flow to the fuel nozzles is not blocked by ice buildup.

Lufthansa T

echnic

al T

rain

ing

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!

Page 301|Intro/A/B1

M15.11 FUEL SYSTEMS (ATA 73)ENGINE FUEL DISTRIBUTION


MODULE 15


Lufthansa T

echnic

al T

rain

ing

Figure 1 Fuel Distribution System Purpose

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!

Page 402|Distribution Layout/A/B1

FUEL SYSTEMSENGINE FUEL DISTRIBUTION


MODULE 15


DISTRIBUTION LAYOUT

Here you can see a simplified engine fuel distribution system.

This system usually starts directly behind the low pressure fuel shut-offvalve. This valve feeds the fuel into the main fuel supply line, which runsfrom the wing to the engine accessory gearbox where you can find the nextcomponent of this system.

This is the low pressure fuel pump. The low pressure fuel pump increasesthe fuel pressure that comes from the tank boost pumps.

The fuel from the low pressure pump then enters the oil cooler. Thiscomponent has a dual function. The cold fuel cools the oil of the enginelubrication system and by this process the fuel is heated to a temperatureabove the freezing point of water. This prevents ice particles coming from thefuel tanks and blocking the fuel filter.

So this is the reason why the fuel filter is located downstream of the oil cooler.It is needed to protect the following components in the engine fuel system.

The next component behind the fuel filter is the high pressure fuel pump.This pump increases the fuel pressure to the high level needed for proper fuelvaporization in the combustion chamber. It is always equipped with a pressurerelief valve, which protects the components in the high pressure fuel systemagainst overpressure.

The fuel from the high pressure fuel pump then enters the fuel control unit.The fuel control unit meters the fuel that is needed for combustion. It is alsoresponsible for supply and shut-off of fuel to the fuel nozzles at the combustionchamber.

The fuel control unit needs some of the high pressure fuel as servo pressure tooperate the internal control mechanisms. To be sure that this servo fuel isabsolutely free of ice, some engines have an additional servo fuel heater.

Lufthansa T

echnic

al T

rain

ing

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Fuel Nozzles

Lufthansa T

echnic

al T

rain

ing

Figure 2 Fuel Distribution System

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Distribution Layout cont.

When the fuel leaves the fuel control unit, it has to pass through the fuel flowtransmitter. The fuel flow transmitter measures the actual fuel flow andtransmits signals to the cockpit for the fuel flow and fuel used indication.

Note, that all the components of the fuel distribution system, from the LP fuelpump to the fuel flow transmitter, are in the area of the accessory gearbox atthe engine.

From the fuel flow transmitter the fuel is then routed to the fuel manifold,which distributes the fuel to the individual fuel nozzles on the combustionchamber.

Lufthansa T

echnic

al T

rain

ing

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Fuel Nozzles

Lufthansa T

echnic

al T

rain

ing

Figure 3 Fuel Distribution System

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Distribution Layout cont.

Some engines have the oil cooler downstream of the high pressure pump, asshown in this example.

This arrangement has the advantage that it requires less external fuel lines,because the low pressure pump and the high pressure pump are usually in onehousing, but the danger of fuel leaks in the oil cooler is much higher than in alow pressure system.

Lufthansa T

echnic

al T

rain

ing

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Lufthansa T

echnic

al T

rain

ing

Figure 4 Oil Cooler in High Pressure System

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!

Page 1005|Distribution Operation/A/B1



MODULE 15


DISTRIBUTION OPERATION

When the fuel boost pumps in the tanks are on and the LP fuel shut-off valve isopen, the fuel flows from the tank to the low pressure stage of the engine fuelpump.

This low pressure fuel pump increases the fuel pressure from the tanks up toapproximately 175 psi and supplies the fuel across the oil cooler and fuel filterto the high pressure stage of the fuel pump.

The pressure increase by the low pressure fuel pump is necessary so that thehigh pressure stage does not have to draw the fuel from the tank by suction.

The low pressure fuel pump is needed to prevent cavitation at the inlet of thehigh pressure fuel pump.

At maximum engine speed the high pressure fuel pump increases the fuelpressure to approx. 900 psi. At this pump an overpressure relief valve isneeded to prevent damage to the following fuel system components.

The overpressure relief valve usually opens when, at a malfunction, thepressure reaches approx. 1250 psi. At this point it releases some fuel back tothe inlet port of the high pressure fuel pump.

Fuel from the high pressure fuel pump then flows to the metering section of thefuel control unit.

Note, that the pump always supplies more fuel than is needed for combustion.The metering section lets only the metered fuel pass to the fuel nozzles. Thefuel that is not needed returns to the fuel pump by the bypass return line.

Lufthansa T

echnic

al T

rain

ing

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Fuel Nozzles

Lufthansa T

echnic

al T

rain

ing

Figure 5 Distribution System Operation

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Distribution operation cont.

On some engines you find that this bypass fuel is used to cool the IDG oilcooler, as shown in this example. When the bypass fuel passes through theIDG oil cooler, it takes the heat from the IDG oil.

In low engine power conditions the hot bypass return fuel heats up the fuelfrom the low pressure pump too much, so that the engine oil can not be cooledsufficiently.

In this situation the bypass return fuel is fed back to the fuel tank by the fuelrecirculation system.

Some cold fuel from the low pressure stage is added to the hot bypass fuel sothat the fuel that enters the tank is not too hot.

Lufthansa T

echnic

al T

rain

ing

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Fuel Nozzles

Lufthansa T

echnic

al T

rain

ing

Figure 6 Fuel Recirculation

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!

Page 1401|Introduction/A/B1

FUEL SYSTEMSHYDROMECHANICAL FUEL CONTROLS


MODULE 15


HYDROMECHANICAL FUEL CONTROLS

INTRODUCTION

The fuel control unit of an engine is usually mounted to the engine fuel pumpon the accessory gearbox. On most turbofan engines the fuel control unit is ahydromechanical component.

In a hydromechanical fuel control unit all the control functions are done by fluidpressures and mechanical components.

The engine manufacturers use many different names for their fuel control unitsto point out special tasks and capabilities of these components.

You can find names like main engine control (MEC) or fuel flow regulator, but toavoid confusion the name fuel control unit is used throughout this lesson.

Lufthansa T

echnic

al T

rain

ing

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Lufthansa T

echnic

al T

rain

ing

Figure 7 Fuel Control Units

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Introduction cont.

There are 2 different types of fuel control units:

speed governed fuel control units, which you usually find on older enginetypes, or

constant thrust fuel control units used on more modern turbofan engines.

Speed governed fuel control units mainly use the N2 demand signal and the N2speed feedback signal for steady state fuel metering.

Constant thrust fuel control units use similar signals like the speed governedfuel control units, and they additionally use thrust feedback signals like N1speed, ambient pressure, and temperature signals.

Lufthansa T

echnic

al T

rain

ing

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Lufthansa T

echnic

al T

rain

ing

Figure 8 Types of Fuel Control Units

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Introduction cont.

You can see that this fuel control unit has many pipes and push-pull cablesconnected to it. Some of them are needed to transmit the throttle demandsignal, the temperature signal, the pressure signal, and the speed feedbacksignals for fuel metering, and others are needed to control the enginecompressor.

The thrust lever signal is usually a mechanical deflection of a small power leverat the fuel control unit. This is either done by a rack and pinion transmission orby rods and levers. The N2 speed feedback signal is usually transmitted via amechanical driveshaft from the main fuel pump.

Some fuel control units even get N1 speed feedback signals. This signal is afuel pressure signal which comes from a hydromechanical N1 speed sensor.

The temperature signals like CIT or fan inlet temperature come fromhydromechanical temperature sensors. These temperature sensors convert theair temperatures to fuel pressure signals.

The fuel control unit receives pressure signals like CDP or ambient pressurevia air sense lines. Pressure sensors in the fuel control unit convert thepressure signals into mechanical signals.

So in summary hydromechanical fuel control units use hydraulic, mechanical,and pneumatic signals for their operation.

Lufthansa T

echnic

al T

rain

ing

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Lufthansa T

echnic

al T

rain

ing

Figure 9 Signals for the Fuel Control Unit

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!

Page 2004|Fuel Control UnitOrganization/A/B1



MODULE 15


FUEL CONTROL UNIT ORGANIZATION

To help you to understand the operation of a fuel control unit we can split it into2 major sections:

the fuel metering section, and

the computing section.

The computing section can be further split into

a governing section, and

a limiting section.

These 3 main sections of course are not individual chambers inside thehousing of the fuel control unit. They represent the main tasks of a fuel controlunit. These are:

fuel metering,

power control, and

engine protection.

The metering section makes sure that the necessary fuel gets to the fuelnozzles and all the fuel, that is not needed for combustion, returns to the fuelpump.

The governing section makes sure that the selected power is controlled.

The limiting section of the fuel control unit monitors the governing section andmakes sure that the engine always operates within safe limits.

Lufthansa T

echnic

al T

rain

ing

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!

Page 2104|Fuel Control UnitOrganization/A/B1



MODULE 15


Lufthansa T

echnic

al T

rain

ing

Figure 10 Fuel Control Unit Organization

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!

Page 2201|Introduction/ALL

FUEL SYSTEMSFADEC SYSTEM


MODULE 15


FADEC SYSTEM

INTRODUCTION

The term FADEC is an abbreviation for Full Authority Digital Engine Control.

As the name indicates, in a FADEC system a digital computer has full authorityover the engine control functions. The digital computer is the heart of theFADEC system.

It is usually named the electronic control unit (ECU) or on other engines it isnamed the electronic engine control (EEC). To avoid confusion, we use theterm ECU throughout this segment.

The second main component of the FADEC system is the fuel metering unit(FMU). This component is also named the hydromechanical unit, or HMU onother engines. To avoid confusion, we use the term FMU throughout thissegment.

The terms FMU and HMU do not have a letter C. This indicates that the FMUcannot control. It only receives orders from the ECU to move the fuel meteringvalve.

Engines with a FADEC system do not have a hydromechanical fuel control unitinstalled.

You usually find the electronic control unit on the fan stator case of the engine.The fuel metering unit is at the same location as the fuel control unit on olderengines.

To operate correctly the electronic control unit needs the demand signal fromthe thrust lever in the cockpit.

It also needs to know the engine speeds and all important air temperatures andair pressures in the engine, and it certainly needs electrical power supply for itsoperation.

This power supply either comes from the aircraft, or it can also come from asmall permanent magnet alternator on the engine accessory gearbox.

The ECU also needs a feedback signal about the opening condition of the fuelmetering valve.

Lufthansa T

echnic

al T

rain

ing

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Lufthansa T

echnic

al T

rain

ing

Figure 11 ECU & FMU Location

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Introduction cont.

The ECU can fulfil many tasks in addition to fuel metering and engine limitprotection.

It performs full power management and gives optimum thrust control for alloperating conditions. It also controls other engine subsystems like

the compressor stall protection system,

the turbine and compressor clearance control system,

the thrust reverser system,

the engine starting system, and

the engine indication system.

With all the data that the ECU receives, it permanently monitors the engineoperation and the important system components and gives fault messages tothe centralized aircraft maintenance computer to indicate faulty components.

On some aircraft there are so-called engine interface units installed. TheseEIUs transmit the data between the FADEC system and the aircraft. They alsocontrol the power supply from the aircraft to the ECU.

A typical FADEC system has

an electronic control unit,

a fuel metering unit,

many electrical sensors on the engine

and many control possibilities for other engine sub systems.

The FADEC system is a centralized computer with all necessary sensors whichcontrols the engine and all its important sub systems.

Lufthansa T

echnic

al T

rain

ing

F

OR

TR

AIN

ING

PU

RP

OS

ES

ON

LY

!




MODULE 15


Lufthansa T

echnic

al T

rain

ing

Figure 12 FADEC System

TABLE OF CONTENTS

EJAMF M15.11 A E

Page i

M15.11 FUEL SYSTEM 1. . . . . . . . . . . . . . . . . . . . . .

ENGINE FUEL DISTRIBUTION 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

INTRODUCTION 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DISTRIBUTION LAYOUT 4. . . . . . . . . . . . . . . . . . . . . . . . . .

DISTRIBUTION OPERATION 10. . . . . . . . . . . . . . . . . . . . . .

HYDROMECHANICAL FUEL CONTROLS 14. . . . . . . . . . . . . . . . . . . . . .

INTRODUCTION 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FUEL CONTROL UNIT ORGANIZATION 20. . . . . . . . . . . .

FADEC SYSTEM 22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

INTRODUCTION 22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TABLE OF CONTENTS

Page ii

TABLE OF FIGURES

EJAMF M15.11 A E

Page i

Figure 1 Fuel Distribution System Purpose 3. . . . . . . . . . . . . . . . . . . . . . . .

Figure 2 Fuel Distribution System 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 3 Fuel Distribution System 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 4 Oil Cooler in High Pressure System 9. . . . . . . . . . . . . . . . . . . . . .

Figure 5 Distribution System Operation 11. . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 6 Fuel Recirculation 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 7 Fuel Control Units 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 8 Types of Fuel Control Units 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 9 Signals for the Fuel Control Unit 19. . . . . . . . . . . . . . . . . . . . . . . . .

Figure 10 Fuel Control Unit Organization 21. . . . . . . . . . . . . . . . . . . . . . . . .

Figure 11 ECU & FMU Location 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 12 FADEC System 25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TABLE OF FIGURES

Page ii

TABLE OF FIGURES

Page iii

TABLE OF FIGURES

Page iv

Documents

Fuel System