RE: FADEC - Full Authority Digital Engine Control.
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Turbine engines provide the propulsive force for a significant percentage of modern transportation systems and are especially important as the engine for a wide variety of aircraft. Although often viewed as a mature technology, a substantial amount of resources are expended to improve these Systems because of the large impact they have on society. The NASA program in Fundamental Aeronautics  describes one such research effort and is aimed at reducing emissions, fuel burn, and noise. Separately, the Department of Defense’s Versatile Affordable Advanced Turbine Engines (VAATE) Program  describes similar goals regarding fuel burn reduction with perhaps more emphasis on overall performance and reducing cost. A multitude of fundamental technologies are involved in realizing these improvements, however, many of them are only enabled or reach full potential through the use of supporting controls technology.
The control system is not generally considered to be the limiting factor in the performance of an engine. Controls do have a direct impact on performance by how well they enable the engine system to operate within its design envelope. Yet the control system negatively affects performance indirectly because it has physical mass and volume. It also uses electric power and dissipates heat which ultimately impacts weight and volume. More control capability through sensing and actuation could feasibly enable better engine performance; however this is constrained because the impact outweighs the gain. The control architecture can be a tool to reduce the negative impact of an existing control capability or provide additional performance capability with the same impact.
FADEC – Full Authority Digital Engine Control
The newest version of a jet engine fuel control is called a FADEC - Full Authority Digital Electronic Control. The original fuel controls on early jet engines of the late 1940's and early 1950's were simply constructed and resembled a common gate valve connected to a throttle lever, Engines and controls became more sophisticated through the 1950's and 1960's, Better performance, more reliability, and increased safety became driving forces, the new electronic fuel controls will be even smarter, more precise, more accurate and more reliable than present day fuel controls and they will be with us for many years.
Full Authority Digital Engine Control (FADEC) is a system consisting of a digital computer, called an electronic engine controller (EEC) or engine control unit (EEU), and its related accessories that control all aspects of aircraft engine performance. FADECs have been produced for both piston engines and jet engines.
FADEC is a system consisting of a digital computer and ancillary components that control an aircraft’s engine and propeller. First used in turbine-powered aircraft, and referred to as full authority digital electronic control, these sophisticated control systems are increasingly being used in piston powered aircraft.
Developed in the early 1970s for military aircraft, electronic flight and engine-control system have found increasing application in commercial fleets of the world. The goal of any engine control system is to allow the engine to perform at maximum efficiency for a given condition. The complexity of this task is proportional to the complexity of the engine. Originally, engine control systems consisted of simple mechanical linkages controlled by the pilot, but then evolved and became the responsibility of the third pilot-certified crew member, the flight engineer. By moving throttle levers directly connected to the engine, the pilot or the flight engineer could control fuel flow, power output, and many other engine parameters.
Following mechanical means of engine control came the introduction of analog electronic engine control. Analog electronic control varies an electrical signal to communicate the desired engine settings. The system was an evident improvement over mechanical control but had its drawbacks, including common electronic noise interference and reliability issues.
Full authority analogue control was used in the 1960s and introduced as a component of the Rolls Royce Olympus 593 engine of the supersonic transport aircraft Concorde. However, the more critical inlet control was digital on the production aircraft.
Following analog electronic control, the logical progression was to digital electronic control systems. Later in the 1970s, NASA and Pratt and Whitney experimented with the first experimental FADEC, first flown on an F-111 fitted with a highly modified Pratt & Whitney TF30 left engine. The experiments led to Pratt & Whitney F100 and Pratt & Whitney PW2000 being the first military and civil engines, respectively, fitted with FADEC, and later the Pratt & Whitney PW4000 as the first commercial "dual FADEC" engine. The first FADEC in service was developed for the Harrier II Pegasus engine by Dowty & Smiths Industries Controls.
Today, each FADEC is unique and therefore expensive to develop, produce, maintain and upgrade for its particular application.
Full Authority Digital Engine (or Electronics) Control (FADEC) is a system consisting of a digital computer, called an electronic engine controller (EEC) or engine control unit (ECU), and its related accessories that control all aspects of aircraft engine performance. FADECs have been produced for both piston engines and jet engines.
ENGINE CONTROL UNIT
An engine control unit (ECU) is a type of electronic control unit that controls a series of actuators on an internal combustion engine to ensure the optimum running. It does this by reading values from a multitude of sensors within the engine bay, interpreting the data using multidimensional performance maps (called Look-up tables), and adjusting the engine actuators accordingly.
Before ECU's, air/fuel mixture, ignition timing, and idle speed were mechanically set and dynamically controlled by mechanical and pneumatic means. One of the earliest attempts to use such a unitized and automated device to manage multiple engine control functions simultaneously was the "Kommandogerät" created by BMW in 1939, for their 801 14-cylinder aviation radial engine.
Working Of ECU
Control of ignition timing
A spark ignition enigine requires a spark to initiate combustion in the combustion chamber. An ECU can adjust the exact timing of the spark (called ignition timing) to provide better power and economy. If the ECU detects knock, a condition which is potentially destructive to engines, and "judges" it to be the result of the ignition timing being too early in the compression stroke, it will delay (retard) the timing of the spark to prevent this. Since knock tends to occur more easily at lower rpm, the ECU controlling an automatic transmission will often downshift into a lower gear as a first attempt to alleviate knock.
Control of Air/Fuel ratio
For an engine with fuel injection, an engine control unit (ECU) will determine the quantity of fuel to inject based on a number of parameters. If the Throttle position sensor is showing the throttle peddle is pressed further down, the Mass flow sensor will measure the amount of additional air being sucked into the engine and the ECU will inject more fuel into the engine. If the Engine coolant temperature sensor is showing the engine has not warmed up yet, more fuel will be injected (causing the engine to run slightly 'rich' until the engine warms up). Mixture control on computer controlled carburetors works similarly but with a mixture control solenoid or stepper motor incorporated in the float bowl of the carburetor.
Control of idle speed
Most engine systems have idle speed control built into the ECU. The engine RPM is monitored by the crankshaft position sensor which plays a primary role in the engine timing functions for fuel injection, spark events, and valve timing. Idle speed is controlled by a programmable throttle stop or an idle air bypass control stepper motor. Early carburetor-based systems used a programmable throttle stop using a bidirectional DC motor. Early TBI systems used an idle air control stepper motor . Effective idle speed control must anticipate the engine load at idle. Changes in this idle load may come from HVAC systems, power steering systems, power brake systems, and electrical charging and supply systems. Engine temperature and transmission status, and lift and duration of camshaft also may change the engine load and/or the idle speed value desired.