Mohd  Ashraf  Mohd  Ismail    

Laboratory  Experiment  8  

Name : Mohammed Ashraf Bin Mohammed Ismail

Student No: N0806406

Contact No: 98225529

Date Submitted:

Lab. :  Turbine  Fuel  System

Course Instructor: Mr Roger Chua

   

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Table of Contents

ABSTRACT .................................................................................................................. 3

INTRODUCTION ......................................................................................................... 4

OBJECTIVES................................................................................................................ 5

EXPIREMENT PROCEDURE ..................................................................................... 6

DISCUSSION OF RESULT.......................................................................................... 7

Aircraft Fuel Systems ................................................................................................ 7 Engine Fuel Systems.................................................................................................. 9 Fuel Inerting............................................................................................................. 11

 

REFERENCE .............................................................................................................. 12

APPENDIX.................................................................................................................. 13

Introduction  to  Aerospace  Engineering  Lab  8  

 

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Abstract

This lab work is concerned with the fuel systems that are commonly found on most

turbine engine system.

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Introduction

The airplane fuel system store and distributes fuel for use by engines and the auxiliary

power units. The system must have a means of safely holding the fuel, allowing

filling and draining of the tanks, preventing unwanted pressure buildups, protect from

contamination and assure a steady supply of fuel to the engines. Many portions of the

fuel system are operated automatically by a fuel management system that monitors

fuel quantities, fuel distribution in the tanks and component status. Fuel system can be

displayed on the Engine Indicating and Crew Alerting System (EICAS) by selecting

the fuel synoptic. The fuel system can signal fuel system flight conditions and/or

faults to the flight crew through EICAS and can record flight condition and faults in

the Central Maintenance Computer Systems (CMCS) for aid in maintenance.

The Fuel system is composed of four major subsystems:

• Storage – The storage subsystem consists of fuel tank ventilation systems, and

means to transfer fuel from tank to tank within the airplane.

• Distribution- The distribution subsystem consists of components (fuel pumps,

boots pumps, fuel filters) and tubing necessary to deliver fuel to the engine

and auxiliary power unit.

• Jettison – The Jettison subsystem consists of the components and fuel tubing

necessary to jettison (dump) fuel overboard through nozzles on the wingtips.

• Indicating – The Indicating subsystem contains components to provide fuel

quantity indication by electronics or mechanical means. Quantity

measurements determined by the indicating subsystem are used to

automatically control fuel feed, transfer, refueling, and jettison operations.

Indicating subsystem also contains components for indicating low fuel

pressure in the fuel feed and jettison subsystem pumps.

All these capabilities must be carried out without compromising the safety of

the aircraft or it’s occupants.

Introduction  to  Aerospace  Engineering  Lab  8  

 

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Objectives

From the experiment we were able to :

I. To  familiarize  students  with  the  functions  of  a  typical  turbine  aircraft  fuel  system.

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Experimental Procedure

Procedure:

1.  Turn  master  switch  to  the  "on"  position.  2.  Fill  wing  tank  by  turning  the  "refill"  switch  to  the  "on"  position.  3.  Turn  refill  switch  off  when  fuel  quantity  reaches  the  top  of  the  fuel  tank  window.  4.  Turn  Transfer  pump  switch  to  the  "on"  position.  Note  the  fuel  transferring  from  the  wing  tank  to  the  main  tank.  The  fuel  will  continue  to  fill  the  main  tank  until  the  level  reaches  the  high  level  switch  of  the  fuel  level  transmitter.  5.  Turn  boost  pump  to  the  "on"  position.  6.  Open  the  firewall  shutoff  valve  by  moving  the  switch  to  the  "open"  position.  Note  the  indicated  fuel  pressure.  7.  Move  the  power  lever  to  the  increase  position.  Notice  the  fuel  flow  gauge  increase  and  the  fuel  flowing  into  the  "Turbine  Engine  Combustion  Area".  8.  The  fuel  is  now  flowing  from  the  Main  tank  to  the  Combustion  area  and  then  draining  into  the  holding  tank.  Allow  the  fuel  to  continue  flowing,  noting  the  fuel  level  of  the  main  tank.  When  the  level  reaches  the  refill  mark,  the  transfer  pump  will  automatically  cut  on  and  refill  the  main  tank.  9.  With  the  transfer  pump  switch  in  the  “ON”  position,  the  transfer  pump  is  in  on  automatic  mode,  refilling  the  main  tank  when  needed.  If  the  wing  tank  is  allowed  to  run  dry  with  the  transfer  switch  on,  after  approximately  30  -­‐  40  seconds  the  "no  transfer  light"  should  illuminate  and  the  transfer  pump  will  shut  down.  10.  Refill  the  wing  tank  from  the  holding  tank  as  needed.  This  system  is  a  closed  loop  and  the  fluid  from  the  "Combustion  Area"  drains  back  into  the  holding  tank,  and  then  can  be  pumped  into  the  wing  tank  by  the  refill  pump.    SHUT  DOWN  PROCEDURE  1.  Transfer  all  fuel  to  the  holding  tank  located  at  the  rear  of  the  trainer.  This  is  accomplished  by  operating  the  trainer  and  moving  all  of  the  fuel  out  of  the  wing  and  main  fuel  tanks  to  the  combustion  chamber.  The  fuel  will  gravity  drain  from  the  "Turbine  Engine  Combustion  

1) Area"  back  into  the  holding  tank.

2) Make  sure  all  switches  on  the  front  panel  are  in  the  "down/off'  position

3) .  Disconnect  AC  power  cord.

(NOTE:  Storing  fuel  in  the  wing  or  main  tank  for  an  extended  period  of  time  will  cause  staining  and  discoloration  of  the  clear  tank  walls)  

Introduction  to  Aerospace  Engineering  Lab  8  

 

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Discussion of Result

REPORT  (1)  Draw  a  schematic  diagram  of  an  aircraft  (any  aircraft  type)  fuel  system.  Explain  the  function  of  the  various  components  used  in  the  system.  

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The schematic diagram previous page is from the aircraft Boeing 777-200/300 The fuel is distributed in 4 main tanks, two outboard reserve tank and a center-wing tank. A fuel vent systems provides positive venting to the atmosphere of all fuel tanks, fuel cells, thereby preventing excessive internal or external pressure. The engine fuel-feed systems consists of fuel lines, pumps and valves which distribute the fuel to the engines. This system includes all the tanks are interconnected by a fuel manifold such that fuel from any of the tanks can be delivered to any the engines Main fuel pumps deliver a continuous supply of fuel at the proper pressure during operation of the aircraft engine. Engine-driven fuel pumps must be able to deliver the maximum flow needed at high pressure to obtain satisfactory nozzle spray and accurate fuel regulation. The fuel-feed line from each tank is pressurisied by boost pumps. The distribution of fuel to the engines is controlled by electric motor driven slide valve in the fuel lines. Fuel Filters All gas turbine engines have several fuel filters at various points along the system. It is common practice to install at least one filter before the fuel pump and one on the high-pressure side of the pump. In most cases the filter will incorporate a relief valve set to open at a specified pressure differential to provide a bypass for fuel when filter contamination becomes excessive. Pressurizing and Drain (Dump) Valves The pressurizing and drain valve prevents flow to the fuel nozzles until sufficient pressure is reached in the main fuel control. Once pressure is attained, the servo assemblies compute the fuel-flow schedules. It also drains the fuel manifold at engine shutdown to prevent post-shutdown fires Fuel Shutoff Valves The engine fuel shutoff valve is installed in the main fuel supply line or tank outlet to the engine. It is controlled from the pilot's compartment. A fuel shutoff valve is usually installed between the fuel control unit and the fuel nozzles. When the throttle is placed in the closed position, this ensures positive shutoff of fuel to the engine. Fuel Heater

Fuel heater operates as a heat exchanger to warm the fuel. The heater can use engine bleed air, an air-to-liquid exchanger, or an engine lubricating oil, a liquid-to-liquid exchanger, as a source of heat. Fuel deicing systems are designed to be used intermittently

   

Introduction  to  Aerospace  Engineering  Lab  8  

 

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(2)  Draw  a  schematic  diagram  of  an  engine  (any  engine  type)  fuel  system.  Explain  the  function  of  the  various  components  used  in  the  system.  

   

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Introduction  to  Aerospace  Engineering  Lab  8  

 

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The main fuel systems is composed of several components, mounted in the airframe and on the engine. The common airframe components are the fuel tanks, fuel boot pump, fuel shutoff valve and the low-pressure fuel filter. The engine mounted components are main fuel pump, fuel filter, main engine control, fuel /oil heat exchanger, flow divider and fuel nozzles. The fuel system is can be divided into Low- and high pressure systems. The low pressure systems must supply the fuel to the engine at a suitable pressure, constant rate of flow and temperature to ensure satisfactory engine performance.

The fuel pump receives fuel from the Aircraft and pressurises it sufficiently.

Fuel Oil Heat Exchanger (FOHE) transfers the heat from the engine oil to the fuel to prevent ice formation in the fuel. Heat is transferred from the oil to the fuel in the core of the FOHE. It then proceeds to the IDG fuel/oil heat exchanger to warm the fuel further.

LP Fuel Filter removes contaminants from the fuel before passing the fuel flow meter.

Metering of fuel to the engine and basic engine control computations are performed in the hydromechanical control unit .The electrical and hydromechanical control units compute the fuel quantity to satisfy power requirements of the engine. from electrical inputs received from the following:

• EEC

• Overspeed Protection System (OPS)

• Cockpit engine master switch

Fuel Flow meter provides a signal of fuel flow to the EEC for onward transmission to the cockpit for display. It also provide information for calculation of fuel usage. The fuel flow metering system controls fuel flow to the engine

After the fuel control meter the fuel, the fuel then flow through the fuel flow transmitter before entering the engine oil cooler. The engine oil cooler use the fuel entering the engine to cool the oil and warms the fuel.

After exiting the oil cooler, fuel pass through the pressurizing and dump valve and into the fuel manifold where the high pressure fuel is brought to the fuel spray nozzles (FSNs). It is an assembly of flexible hoses at equal distances around the combustion outer case. The manifold distributes the fuel to the 20 FSNs that provide the necessary atomisation of fuel into the combustion chamber and is ignite and burn efficiently.

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3)  As  a  result  of  the  TWA  800  crash,  what  is  the  current  FAA  rule  on  fuel  tank  inerting?  Explain  the  operation  of  a  system  in  use  for  fuel  tank  inerting.

Significant emphasis has been placed on fuel tank safety since the TWA flight 800

accident in July 1996. NTSB determined that the "probable cause of the TWA flight

800 accident was an explosion of the center wing fuel tank (CWT), resulting from

ignition of the flammable fuel/air mixture in the tank.

Fuel tank inerting is the process of replacing potentially flammable gas space above

the fuel tank (ullage) with a non-flammable atmosphere. 2 main types of fuel inerting

1) Fuel scrubbing - Air, and particularly oxygen, readily dissolves in fuel. When a

commercial transport airplane takes off after fueling, the resulting change in altitude

causes a decrease in atmospheric pressure in the fuel tank. This decrease in pressure

allows for some of the air to escape solution and enter the ullage space of the fuel

tank. Fuel scrubbing is a process by which most of the oxygen dissolved in the fuel is

displaced with nitrogen. Fuel and nitrogen are combined through a series of nozzles in

a large container with the resulting combination having a very small amount of

oxygen in solution.

2) Ullage washing - Is a process that requires displacing the air in the fuel tank empty

space, also known as ullage, with nitrogen gas or nitrogen enriched air (NEA). Ullage

washing would be accomplished by providing the nitrogen or NEA to a supply line

that feeds a simple fuel tank gas supply manifold.

Under much contention this working group published a final report (2001 ARAC

Report) which recommended that no rule making actions be taken at this time and

stated that additional research and development was needed

Introduction  to  Aerospace  Engineering  Lab  8  

 

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Reference

1) Fuel Tank Protection. Federal Aviation Administration

<http://www.fire.tc.faa.gov/systems/fueltank/intro.stm.> 6th October

2008.

2) Micheael J. Kroes, Willism A. Watkins, Frank Delp. “Aircraft

Maintenance & Repair”. Sixth Edition. Macmillan/McGrraw-

HillSchool Publishing Company, 1993.

3) Micheael J. Kroes, Thomas W. Wild, “Aircraft Powerplant” Seventh

Edition Macmillan/McGrraw-HillSchool Publishing Company, 1994.

4)

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Appendix

Right Side (From Front View)

Introduction  to  Aerospace  Engineering  Lab  8  

 

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Fuel Tank Protection Significant emphasis has been placed on fuel tank safety since the TWA flight 800 accident in July 1996. After the accident, the NTSB determined that the "probable cause of the TWA flight 800 accident was an explosion of the center wing fuel tank (CWT), resulting from ignition of the flammable fuel/air mixture in the tank (NTSB Report). The NTSB further concluded that contributing factors to the accident were that the design and certification of the aircraft required only the preclusion of all potential ignition sources in order to prevent a fuel tank explosion. Following the accident, the Federal Aviation Administration (FAA) has issued numerous Airworthiness Directives and has enacted a comprehensive regulation to correct potential ignition sources (SFAR 88) in fuel tanks as well as conducting research into methods that could eliminate or significantly reduce the exposure of transport airplanes to flammable vapors. The latter has been in response to a new FAA policy that strives to eliminate or reduce the presence or consequences of flammable fuel tank vapors. This has included fuel tank inerting, which is commonly used by the military. Fuel tank inerting is the process of replacing potentially flammable gas space above the fuel tank (ullage) with a non-flammable atmosphere. However, the systems weight, resource requirements, and relatively low dispatch reliability have indicated that military fuel tank inerting systems would not be practical for application to transport airplanes. A fuel tank inerting working group was formed by the Aviation Rulemaking Advisory Committee (ARAC) in response to a task assigned by the FAA to evaluate a proposed rule that would require a reduction in flammability of some or all commercial transport fuel tanks. A previous ARAC working group (1998 ARAC Report) has stated that a potentially cost-effective method of fuel tank flammability reduction was ground-based inerting (GBI). The new working group was charged with examining fuel tank inerting methods to reduce or eliminate the flammability of all or some fuel tanks in the commercial transport fleet while developing regulatory text as well as determining the cost and benefit of the proposed rule change. Under much contention this working group published a final report (2001 ARAC Report) which recommended that no rule making actions be taken at this time and stated that additional reserach and development was needed. Since the inception of the 2001 ARAC WG the FAA has performed extensive research into the lower oxygen concentration (LOC) required to render a fuel tank ullage inert as well as the equipment and methods needed to develop a fuel tank inerting system. The Fuel Tank Protection Task has two research areas working closely together in an attempt to find practical solutions to this problem. The Fuel Flammability Research examines and defines the effects of various parameters on the flammable vapors existing within a fuel tank ullage, while the Fuel Tank Inerting Research is aimed at the validation of inerting requirements and the design of an economical and practical method of rendering inert the CWT of a commercial transport airplane. Fuel Tank Inerting The FAA has focused research to support two primary methods of fuel tank protection, both involving fuel tank inerting. Ground-based fuel tank inerting would involve some combination of fuel scrubbing and ullage washing with Nitrogen Enriched Air (NEA) while the airplane is on the

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ground. On-board fuel tank inerting would involve ullage washing during some or all aircraft operations with a system that generates NEA on the aircraft with the APU and/or engine bleed air. FAA research has evaluated Hollow Fiber Membrane (HFM) gas separation technology. HFM technology could be used to develop on-board inerting systems that are much lighter with greatly improved dispatch reliability than current military aircraft systems. Thus there is an interest in ground-based fuel tank inerting, with either airport supplied or on-board generated NEA, and also in an on-board inert gas generating system (OBIGGS) with the capability of providing NEA, as required throughout the ground/flight profile. OBIGGS also has the potential to improve commercial transport airplane fire safety as NEA generated on-board the aircraft could be used in an emergency for fire suppression in other parts of the aircraft. Ullage Washing and Fuel Scrubbing Ullage Washing Ullage washing is a process that requires displacing the air in the fuel tank empty space, also known as ullage, with nitrogen gas or nitrogen enriched air (NEA). NEA is a term used to describe low purity nitrogen (90-98% pure), generally generated via a gas separation process. Ullage washing would be accomplished by providing the nitrogen or NEA to a supply line that feeds a simple fuel tank gas supply manifold. Fuel Scrubbing Air, and particularly oxygen, readily dissolves in fuel. When a commercial transport airplane takes off after fueling, the resulting change in altitude causes a decrease in atmospheric pressure in the fuel tank. This decrease in pressure allows for some of the air to escape solution and enter the ullage space of the fuel tank. Since oxygen dissolves more readily than nitrogen, this can increase the oxygen concentration of the fuel tank ullage above ambient, although the total amount of gas evolving from the fuel is small. This can have a profound effect on the fuel tank oxygen concentration for both inert fuel tanks as well as fuel tanks with ambient air in the ullage space. Fuel scrubbing is a process by which most of the oxygen dissolved in the fuel is displaced with nitrogen. Fuel and nitrogen are combined through a series of nozzles in a large container with the resulting combination having a very small amount of oxygen in solution. The military has used fuel scrubbing to allow for fuel tank inerting systems to operate more effectively and to increase survivability to ballistic impact in combat.