Full Authority Digital
Engine Control (FADEC) System Description & Operation
FADEC Fuel Control Systems
A full authority digital
electronic control (FADEC) is a most advance system to control fuel flow on modern
turbine engine models. For the majority of current turbine engine models, a
full authority digital electronic control (FADEC) system has been incorporated
to regulate fuel flow. A hydromechanical fuel control backup system is absent
from a real FADEC system. The system makes use of electronic sensors to supply
the EEC with data about engine parameters. The EEC collects the data required
to calculate the fuel flow rate and sends it to a fuel metering valve. The
gasoline metering valve only responds to the EEC's directives. The fuel
delivery system's computational component, the EEC, is a computer, and the
metering valve measures the fuel flow. Many different types of turbine engines,
ranging from APUs to the largest propulsion engines, utilise FADEC systems.
FADEC Function
True full authority
digital engine controls don't offer any kind of manual override, giving the
computer entire control over the engine's operational parameters. The engine fails
in the event of a complete FADEC failure. If the engine is digitally and
electronically controlled yet has a human override feature, it is only referred
to as an EEC or ECU. Despite being a part of a FADEC, an EEC is not a FADEC in
and of itself. Until the pilot requests to take over, the EEC makes all
decisions when operating alone.
The air density, throttle
position, engine temperatures, engine pressures, and a variety of other factors
are all input variables that FADEC uses to operate. The EEC receives the inputs
and processes them up to 70 times per second. These data are used to compute
and then apply engine operating parameters including fuel flow, stator vane
position, air bleed valve position, and others. Engine starting and restarting
are likewise under FADEC's supervision. The FADEC's primary goal is to deliver
the best engine performance under a certain set of flight conditions.
The manufacturer may
programme engine restrictions, get engine health and maintenance reports, and
ensure that engines are operated efficiently thanks to FADEC. For instance, the
FADEC can be set up to automatically conduct the necessary actions without the
pilot's input to prevent exceeding a specific engine temperature.
FADEC Fuel Control Turbine Engine
Large high-bypass
turbofan engines frequently employ fuel control systems of the FADEC type. The
main element of the FADEC engine fuel control system is the EEC. The EEC is a
computer that manages how the engine runs. The internal physical separation of
the two computers within the EEC housing's two electronic channels allows for
natural convection cooling. Typically, the EEC is situated in a section of the
engine nacelle that stays cool while the engine is running. Shock mounts are
used to secure it to the lower-left fan casing.
To control engine
operation, the EEC computer uses input from numerous engine sensors and
aircraft systems. To control engine power or thrust, it receives electrical
signals from the flight deck. The throttle lever angle resolver sends a signal
to the EEC proportional to the location of the thrust lever. Most engine parts
are under the supervision of the EEC, which also gets input from them. For
engine operation, the EEC receives data from numerous components.
The aircraft electrical
system or the permanent magnet alternator provide power for the EEC (PMA). The
PMA directly feeds power to the EEC when the engine is operating. Every aspect
of engine function is managed by the two-channel EEC computer. Each channel,
which is a separate computer, has full control over how the engine runs. The
processor performs all control calculations and provides all the information
needed to create the control signals for the solenoids and torque motors. In
order to determine which EEC channel will best control the output driver for a
torque motor or solenoid bank, the cross-talk logic examines data from channels
A and B. Each output driver is under the control of the principal channel. If
the cross-talk logic determines that the other channel is superior for
controlling a particular bank, the EEC switches that bank's control to the
alternative channel. The EEC has output driver banks that provide the engine
parts with the control signals. Control signals are provided to the driver
banks through each EEC channel. For storing performance and maintenance data,
the EEC features both volatile and nonvolatile memory.
By using a mode selection
switch, the EEC can manage the engine thrust in two different ways. Engine
thrust is controlled by EPR in the standard mode and by N1 in the alternative
mode. The EEC resets when the fuel control switch is switched from run to
cutoff. All fault information is saved in the nonvolatile memory during this
reset. To supply fuel flow for combustion, the fuel metering unit's metering
valve is controlled by the EEC. The gasoline metering device is fixed to the
front of the fuel pump and located on the front face of the gearbox. In order
to start or stop the flow of fuel, the fuel metering unit's minimum pressure
and shutdown valve receives a signal from the EEC.
Thermocouples, rotary
differential transformers, and linear variable differential transformers are
used by the EEC to obtain position feedback for various engine parts. These
sensors transmit data on engine parameters to the EEC from various systems. The
high-pressure fuel shutoff valve that regulates fuel flow is controlled by the
fuel control run cutoff switch. The fuel outlet line on the back of the
fuel/oil cooler is where the fuel temperature sensor thermocouple attaches. It
communicates this information to the EEC.
The gasoline metering
unit's metering valve is moved by the EEC using a torque motor driver. The
other FMU operations are managed by the EEC via solenoid drivers. Through
torque motors and solenoids, the EEC also regulates a number of additional
engine subsystems, including the fuel and air oil coolers, bleed valves,
variable stator vanes, turbine cooling air valves, the turbine case cooling and
other system.
Three on each side and
one on the bottom make up the seven electrical connections that each EEC
channel has. The inputs of the two connections on top of the EEC are shared by
both channels. These are the test connector and the programming plug. The
programming plug chooses the appropriate EEC software based on the engine's
thrust rating. A lanyard is used to fasten the plug to the engine fan case. The
plug stays with the engine when the EEC is taken out. On the bottom of the EEC,
there are three pneumatic connectors for each channel. A signal proportional to
the pressure is provided to the associated and opposing EEC channels via
transducers inside the EEC. The ambient pressure, burner pressure, LPC exit
pressure, and fan inlet pressure are the pressures that the EEC measures. The
cable colour that links the EEC to each channel's sensors is unique. While
channel B sensor signals are green, channel A wiring is blue. The thermocouple
indications are yellow, while the non-EEC circuit wire is grey.
Fuel System Operation
The fuel system of the
aeroplane supplies fuel to the fuel pump. The fuel is pressurized and sent to
the fuel/oil cooler via the pump's low-pressure boost stage (FOC). Fuel travels
from the FOC to the high-pressure main stage of the pump after passing through
the fuel pump filter element. Fuel pressure is raised by the high-pressure main
stage and sent to the fuel metering unit (FMU). Additionally, it provides servo
fuel to the engine parts, including the servo fuel heater. The distribution
valve receives fuel for combustion (metered fuel) through the fuel flow
transmitter.
The fuel supply manifolds receive metered fuel from the fuel distribution valve. The fuel supply manifolds feed the metered fuel to the fuel injectors, which then dispense it into the engine for burning. A disposable fuel filter element is located within the fuel pump housing. The EEC receives a signal from the fuel filter differential pressure switch informing it that the filter is virtually blocked. If the filter element clogs, unfiltered fuel can then get through.
Safety Concern
Safety is a major problem
because the engines' operation depends so significantly on automation. Two or
more independent but identical digital channels serve as redundancy. Any engine
function may be provided by any channel without limitations. In order to
provide fault-tolerant engine management, FADEC also keeps an eye on a range of
data from the aircraft's linked systems and the engine subsystems.
A 2015 Airbus A400M
catastrophe in Seville, Spain, has been linked to engine management issues that
caused up to three engines to lose thrust at the same time. On May 29, Airbus
Chief Strategy Officer Marwan Lahoud declared that the deadly crash was the
result of improperly installed engine control software. There are no structural
flaws in the aeroplane, however the final assembly is seriously lacking in
quality.
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