20068641 aircraft fuel systems

8/6/2019 20068641 Aircraft Fuel Systems

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Aircraft Fuel

Reciprocating engine fuels

Turbine engine fuels

Jet A – which is Kerosene Jet B – a blend of kerosene and

gasoline

Jet A-1 – used for operation at

extremely low temperatures• Jet A and Jet B are the most common

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Abha-Saudi Arabia



Fuel System Contamination

The higher the viscosity of the fuel, the greaterit’s ability to hold contaminants in suspension

This is why jet fuels, which have a higherviscosity than av-gas, are also more susceptibleto contamination than av-gas

The main contaminants that reduce the qualityof fuel are: Other petroleum products

Water

Rust

Scale

Dirt


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Water Contamination

Water contamination in fuel can be in twoforms: Dissolved in the fuel

Entrained or suspended in the fuel Water in fuel can cause icing in the

aircraft fuel system, usually in: Boost pump screens

Low pressure filters Large amounts of water can cause engine

stoppage


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Microbial Growth

Microbial Growth is produced by variousforms of micro-organisms that live andmultiply in water which is in jet fuel

These micro-organisms form slime thatcan be red, brown, green, or black

The organisms feed on hydrocarbons inthe fuel but require water to multiply

This buildup can: Interfere with fuel flow and quantity

indications

Start electrolytic corrosive action


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Contamination Detection

Coarse fuel contamination can bedetected visually

Uncontaminated fuel should be: Clean

Bright

Contain no perceptible free water


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Contamination Detection(cont.)

Clean means the absence of any readilyvisible sediment or entrained water

Bright refers to the shiny appearance of

clean, dry fuel

Free water is indicated by a cloud, haze,or water slug

Water saturated in fuel is not always visible Perfectly clear water can contain as much as

three times the acceptable limit


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Engr Salman Ali S ed



Contamination Detection(cont.)

There is no accurate method of detectingfuel entrained water when it is frozen

For this reason, it is important that fuel is

checked when the water is in a liquidstate This should not be done following a flight at

altitude when the fuel would be below 32degrees F

It is more effective to drain the fuel after thefuel has set undisturbed for a period of time,allowing the water to precipitate and settle tothe drain point


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Engr Salman Ali Syed



Fuel Systems

The purpose of an aircraft fuel system isto store and deliver the proper amount of clean fuel at the correct pressure to the

engine Fuel systems should provide positive and

reliable fuel flow through all phases of flight including:

Changes in altitude Violent maneuvers

Sudden acceleration and deceleration


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Fuel Systems (cont.)

Fuel systems should alsocontinuously monitor systemoperation such as:

Fuel pressure

Fuel flow

Warning signals

Tank quantity


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Types of Fuel Systems

Fuel systems can be classified in twobroad categories:

Gravity-Feed Systems Pressure-Feed Systems


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Gravity-Feed Systems

Gravity-Feed Systems use only theforce of gravity to push fuel to theengine fuel-control mechanism

The bottom of the fuel tank must behigh enough to provide adequatepressure to the fuel-controlcomponent This type of system is often used in

high-wing light aircraft


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Pressure-Feed Systems

Pressure-Feed Systems require the use of a fuelpump to provide fuel-pressure to the engine’sfuel-control component

There are two main reasons these systems are

necessary: The fuel tanks are too low to provide enough pressure

from gravity

The fuel tanks are a great distance from the engine

Also, most large aircraft with higher powered

engines require a pressure system regardless of the fuel tank location because of the largevolume of fuel used by the engines


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Fuel System Components

Pumps

Tanks

Lines

Valves

Fuel Flow-meters

Filters and

Strainers

Quantity Indicators

WarningComponents

Fuel Drains

Heaters


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Engr. Salman Ali Syed



Fuel Pumps

Fuel pumps are used to move fuelthrough the system then gravity feed isinsufficient

There are three main functions of fuelpumps, they are to move fuel from:

The tanks to the engines

One tank to another

The engine back to the tanks


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Fuel-Pump Requirements

Engine fuel systems require mainpumps and in some systemsemergency pumps

These requirements depend on thetype of engines installed on theaircraft


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Reciprocating-Engine Fuel-Pump Requirements

Reciprocating-engines which are notgravity-fed require:

At least one main pump for each engine These pumps must be engine-driven

The pump capacity must capable of providing enough fuel flow for all

operations


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Turbine-Engine Fuel-PumpRequirements

Turbine-Engines require:

At least one main pump for each engine

Main pump power supply must beindependent of all other main pumppower supplies

Each positive-displacement main pump

must be able to be bypassed

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Turbine-Engine Fuel-PumpRequirements (cont.)

Turbine-engines also require emergencypumps The emergency pump must be immediately

available to supply fuel to the engine in theevent of a main pump failure

Emergency pump power supplies must beindependent of that of the corresponding mainpump

If both the emergency and main pumpsoperate continuously, there must be somemeans of alerting the flight crew of a failure of either pump

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Fuel Pump Classification

One way to classify fuel pumps isaccording to the pump’s function

These classifications are: Boost Pump

Scavenge Pump

Cross-feed Pumps


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Fuel Pump Classification

Another way to classify fuel pumpsis by their method of operation

These pumps are: Vane-type

• Variable-volume

Centrifugal

Ejector


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Vane-Type Pumps

Vane-type fuel pumps are the mostcommon

They use a rotor which turns vanesin a cylinder, the vanes act to pushthe fuel through the system

Vane-type pumps can have fromtwo to six vanes and they may bevariable volume also


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Centrifugal Pumps

Centrifugal pumps are used to movefuel from one tank to another orfrom the fuel tank to the engine

They are electrically driven andsome may operate at differentspeeds

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Ejector Pumps

An ejector pump is normally used toscavenge fuel from remote areas

These pumps have no moving partsthey rely on return fuel from theengine to pump the fuel

Ejector pumps work on the venturiprinciple





Fuel Tanks

Fuel systems on different aircraftmay use several types of fuel tanks

The three basic types of fuel tanksused on aircraft are:

Integral

Rigid Removable

Bladder





Integral Fuel Tanks

Integral Fuel Tanks are commonly located in theaircraft’s wings or fuselage

These tanks are ones that are built into thestructure of the aircraft and generally can not be

removed Integral Fuel Tanks are formed by the actual

structure of the aircraft

The seams are sealed, usually with syntheticrubber, to produce an area inside the aircraftstructure which will contain the fuel

This type of tank is used in some light high-performance aircraft and turbine-poweredtransports





Rigid Removable Fuel Tanks

Rigid removable fuel tanks are oftenmade of aluminum components that arewelded together

These tanks are installed incompartments specifically made for thetank

The tanks may be held in place with

padded straps This type of tank is often found on more

expensive light aircraft and reciprocating-engine-powered transports





Bladder Type Fuel Tanks

Bladder type fuel tanks are basically areinforced rubberized bag

These tanks are installed in

compartments which support the weightof the fuel

The tank is held in place with buttons orsnaps on the bottom and sides of the

tank This type of tank is usually found on light

aircraft and some turboprop and turbine-powered aircraft





Fuel Lines

Fuel lines on aircraft are either made of rigid metal tubing or flexible hose

Most of the fuel lines are the rigid type

which are usually made of aluminumalloys

The flexible hose fuel lines are eithermade of synthetic rubber or Teflon

The diameter of tubing used is decided bythe engine’s fuel requirements





Valves

Fuel selector valves are used inaircraft fuel systems to:

Shut off fuel flow

Cross-feed

Transfer fuel

Selector valves may be operated

manually or electrically dependingon the installation





Filters and Strainers

Fuel is usually strained at three points inthe system

Through a finger or bootstrap strainer in

the bottom of the fuel tank Through a master strainer which is

usually located at the lowest point in thesystem

Through a third strainer near the fuelcontrol unit





Quantity Indicators

Mechanical

Inverted float gauge

Rotating dial gauge

Upright float gauge

Sight-glass gauge

Resistance

Capacitance

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Fuel Subsystems

Some aircraft fuel subsystems allowfor fuel:

Jettison Heating

Cross-Feeding





Fuel Jettison

The fuel jettison system comprises acombination of fuel lines, valves,and pumps provided to dump fueloverboard during an in-flightemergency

This will reduce the weight of the

aircraft so an emergency landing ispossible





Fuel Heating

Fuel heating is necessary for turbineengines to thaw ice particles in thefuel that would otherwise clog the

filters Fuel is routed through a heat

exchanger that uses either engineoil or compressor bleed air to bringthe fuel up to an acceptabletemperature

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Cross Feeding

Cross feed systems allow the flow of fuel from any of the tanks to any of the engines

Some reasons that this systemmight be used are: Engine failure

Problem with one or more fuel tanks Redistribute fuel for weight and balance

purposes

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20068641 aircraft fuel systems

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