Post on 27-Nov-2014
transcript
Aircraft Fuel Systems
By: Gitau
•Information in this section was taken from:
Aircraft Maintenance and Repair p.467-504
Transport Category Aircraft Systems p.6-1 through 6-28
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
Fuel System Contamination The higher the viscosity of the fuel, the greater
it’s ability to hold contaminants in suspension This is why jet fuels, which have a higher
viscosity than av-gas, are also more susceptible to contamination than av-gas
The main contaminants that reduce the quality of fuel are: Other petroleum products Water Rust Scale Dirt
Water Contamination Water contamination in fuel can be in two
forms: 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
Microbial Growth Microbial Growth is produced by various
forms of micro-organisms that live and multiply in water which is in jet fuel
These micro-organisms form slime that can be red, brown, green, or black
The organisms feed on hydrocarbons in the fuel but require water to multiply
This buildup can: Interfere with fuel flow and quantity indications Start electrolytic corrosive action
Contamination Detection Coarse fuel contamination can be
detected visually Uncontaminated fuel should be:
Clean Bright Contain no perceptible free water
Contamination Detection (cont.) Clean means the absence of any readily
visible 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
Contamination Detection (cont.) There is no accurate method of detecting
fuel entrained water when it is frozen For this reason, it is important that fuel is
checked when the water is in a liquid state This should not be done following a flight at
altitude when the fuel would be below 32 degrees F
It is more effective to drain the fuel after the fuel has set undisturbed for a period of time, allowing the water to precipitate and settle to the drain point
Fuel Systems The purpose of an aircraft fuel system is
to 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
Fuel Systems (cont.) Fuel systems should also
continuously monitor system operation such as: Fuel pressure Fuel flow Warning signals Tank quantity
Types of Fuel Systems Fuel systems can be classified in two
broad categories: Gravity-Feed Systems Pressure-Feed Systems
Gravity-Feed Systems Gravity-Feed Systems use only the
force of gravity to push fuel to the engine fuel-control mechanism
The bottom of the fuel tank must be high enough to provide adequate pressure to the fuel-control component This type of system is often used in
high-wing light aircraft
Pressure-Feed Systems Pressure-Feed Systems require the use of a fuel
pump to provide fuel-pressure to the engine’s fuel-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 large volume of fuel used by the engines
Fuel System Components Pumps Tanks Lines Valves Fuel Flow-meters Filters and
Strainers
Quantity Indicators Warning
Components Fuel Drains Heaters
Fuel Pumps Fuel pumps are used to move fuel
through the system then gravity feed is insufficient
There are three main functions of fuel pumps, they are to move fuel from: The tanks to the engines One tank to another The engine back to the tanks
Fuel-Pump Requirements Engine fuel systems require main
pumps and in some systems emergency pumps
These requirements depend on the type of engines installed on the aircraft
Reciprocating-Engine Fuel-Pump Requirements Reciprocating-engines which are not
gravity-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
Turbine-Engine Fuel-Pump Requirements Turbine-Engines require:
At least one main pump for each engine Main pump power supply must be
independent of all other main pump power supplies
Each positive-displacement main pump must be able to be bypassed
Turbine-Engine Fuel-Pump Requirements (cont.) Turbine-engines also require emergency
pumps The emergency pump must be immediately
available to supply fuel to the engine in the event of a main pump failure
Emergency pump power supplies must be independent of that of the corresponding main pump
If both the emergency and main pumps operate continuously, there must be some means of alerting the flight crew of a failure of either pump
Fuel Pump Classification One way to classify fuel pumps is
according to the pump’s function These classifications are:
Boost Pump Scavenge Pump Cross-feed Pumps
Fuel Pump Classification Another way to classify fuel pumps
is by their method of operation These pumps are:
Vane-type• Variable-volume
Centrifugal Ejector
Vane-Type Pumps Vane-type fuel pumps are the most
common They use a rotor which turns vanes
in a cylinder, the vanes act to push the fuel through the system
Vane-type pumps can have from two to six vanes and they may be variable volume also
Centrifugal Pumps Centrifugal pumps are used to move
fuel from one tank to another or from the fuel tank to the engine
They are electrically driven and some may operate at different speeds
Ejector Pumps An ejector pump is normally used to
scavenge fuel from remote areas These pumps have no moving parts
they rely on return fuel from the engine to pump the fuel
Ejector pumps work on the venturi principle
Fuel Tanks Fuel systems on different aircraft
may use several types of fuel tanks The three basic types of fuel tanks
used on aircraft are: Integral Rigid Removable Bladder
Integral Fuel Tanks Integral Fuel Tanks are commonly located in the
aircraft’s wings or fuselage These tanks are ones that are built into the structure
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 synthetic rubber,
to produce an area inside the aircraft structure which will contain the fuel
This type of tank is used in some light high-performance aircraft and turbine-powered transports
Rigid Removable Fuel Tanks Rigid removable fuel tanks are often
made of aluminum components that are welded together
These tanks are installed in compartments specifically made for the tank
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 a
reinforced rubberized bag These tanks are installed in
compartments which support the weight of the fuel
The tank is held in place with buttons or snaps 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 aluminum alloys
The flexible hose fuel lines are either made of synthetic rubber or Teflon
The diameter of tubing used is decided by the engine’s fuel requirements
Valves Fuel selector valves are used in
aircraft fuel systems to: Shut off fuel flow Cross-feed Transfer fuel
Selector valves may be operated manually or electrically depending on the installation
Filters and Strainers Fuel is usually strained at three points in
the 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 the system Through a third strainer near the fuel
control unit
Quantity Indicators Mechanical
Inverted float gauge Rotating dial gauge Upright float gauge Sight-glass gauge
Resistance Capacitance
Fuel Subsystems
Some aircraft fuel subsystems allow for fuel:
Jettison Heating Cross-Feeding
Fuel Jettison The fuel jettison system comprises a
combination of fuel lines, valves, and pumps provided to dump fuel overboard during an in-flight emergency
This will reduce the weight of the aircraft so an emergency landing is possible
Fuel Heating Fuel heating is necessary for turbine
engines to thaw ice particles in the fuel that would otherwise clog the filters
Fuel is routed through a heat exchanger that uses either engine oil or compressor bleed air to bring the fuel up to an acceptable temperature
Cross Feeding Cross feed systems allow the flow of
fuel from any of the tanks to any of the engines
Some reasons that this system might be used are: Engine failure Problem with one or more fuel tanks Redistribute fuel for weight and balance
purposes