Powerplant Systems & Components: Fuel Metering Systems π Flashcards
Where are the fuel spray nozzles located in a turbine engine?
They are located either externally or internally on the combustion chamber in such a way that the fuel can be sprayed into the combustion area.
Name the heat sources for the operation of fuel heaters used in turbine engines.
Turbine engines use heat exchangers to heat fuel and prevent the possibility of ice crystal formations. Fuel lines are routed through the fuel heater, which uses a heat source, either bleed air or engine lubricating oil. If bleed air is used as a heat source it is called an air-to-liquid heat exchanger. When oil is used, it is a liquid-to-liquid heat exchanger.
What engine variables are sensed by a hydro mechanical fuel control?
The fuel control senses power level position, rpm, compressor inlet pressure temperature, burner pressure, or compressor discharge pressure, and EGT or TIT.
What are the two most commonly used carburetors in small reciprocating engines?
They are the float-type carburetor and pressure-type carburetor
What type of fuel control unit is used in a turbine engine?
Both hydro mechanical and electronic fuel control units are in use today. The most common is hydro mechanical
What is meant by trimming a turbine engine?
Adjusting the fuel control for the proper specific gravity of the fuel and for the proper idle and full throttle RPM.
When should a turbine engine be trimmed?
Whenever there is a loss in engine power or the manufacturer specifies
What specifications are used to trim a turbine engine?
The data plate on the engine typically contains the trimming specifications
What are two types of electronic fuel controls for turbine engines?
Supervisory EEC (Electronic Engine Control) and FADEC (Full-Authority Digital Electronic Control)
What is a FADEC?
Full-Authority Digital Electronic Control is a high precision digital electronic fuel control that utilizes an electronic engine control and the flight management computer to measure the fuel nozzles that prevent over-speed and over-temperature conditions. The FADEC also sends information to indication systems for the aircraft crew.
Does a turbine engine controlled by a FADEC require manual trimming?
No, it is self-trimming
What is the purpose of a mixture control in a float type carburetor?
It is to control the fuel-air mixture as air density changes with altitude changes
What is the purpose of an accelerating system on a float type carburetor?
When the throttle is opened rapidly, the fuel-air mixture will lean out momentarily. To overcome this tendency, a charge of fuel from the accelerating pump will temporarily enrich the mixture in the venturi.
Describe the purpose and operation of a venturi.
In a carburetor it is an example of Bernoulliβs Principle which states βas the velocity of a gas or liquid increases, the pressure decreasesβ. The venturi proportions the fuel-air mixture, lowers the pressure at the discharge nozzle, and limits airflow at full throttle. The principle operation of the carburetor depends on the differential between the atmospheric pressure and the decreased pressure offered by the venturi.
What is the function of a metering jet?
Its purpose is to limit the fuel flow when the throttle valve is wide open. The main metering jet is placed in the fuel passage between the float chamber and the discharge nozzle.