Powerplant Systems & Components: Fuel Metering Systems πŸ”Š Flashcards

1
Q

Where are the fuel spray nozzles located in a turbine engine?

A

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.

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2
Q

Name the heat sources for the operation of fuel heaters used in turbine engines.

A

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.

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3
Q

What engine variables are sensed by a hydro mechanical fuel control?

A

The fuel control senses power level position, rpm, compressor inlet pressure temperature, burner pressure, or compressor discharge pressure, and EGT or TIT.

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4
Q

What are the two most commonly used carburetors in small reciprocating engines?

A

They are the float-type carburetor and pressure-type carburetor

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5
Q

What type of fuel control unit is used in a turbine engine?

A

Both hydro mechanical and electronic fuel control units are in use today. The most common is hydro mechanical

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6
Q

What is meant by trimming a turbine engine?

A

Adjusting the fuel control for the proper specific gravity of the fuel and for the proper idle and full throttle RPM.

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7
Q

When should a turbine engine be trimmed?

A

Whenever there is a loss in engine power or the manufacturer specifies

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8
Q

What specifications are used to trim a turbine engine?

A

The data plate on the engine typically contains the trimming specifications

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9
Q

What are two types of electronic fuel controls for turbine engines?

A

Supervisory EEC (Electronic Engine Control) and FADEC (Full-Authority Digital Electronic Control)

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10
Q

What is a FADEC?

A

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.

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11
Q

Does a turbine engine controlled by a FADEC require manual trimming?

A

No, it is self-trimming

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12
Q

What is the purpose of a mixture control in a float type carburetor?

A

It is to control the fuel-air mixture as air density changes with altitude changes

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13
Q

What is the purpose of an accelerating system on a float type carburetor?

A

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.

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14
Q

Describe the purpose and operation of a venturi.

A

In a carburetor it is an example of Bernoulli’s Principle which states β€œas the velocity of a gas or liquid increases, the pressure decreases”. 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.

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15
Q

What is the function of a metering jet?

A

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.

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16
Q

What is the fuel metering force in a float type carburetor?

A

It is differential pressure between the pressure in the float chamber and at the nozzle.

17
Q

What will be the result of using excessively rich idle mixtures?

A

Carbon fouling of the spark plug

18
Q

What is the purpose of the economizer system in a float carburetor?

A

It is essentially a valve which is closed at throttle settings below 60-70% of rated power, but provides additional fuel for cooling the engine to prevent detonation at higher throttle settings above 60-70%.

19
Q

Where does a pressure injection carburetor obtain fuel pressure?

A

It obtains fuel pressure from the boost pump for starting and from the engine driven fuel pump for normal operations

20
Q

What operated an automatic mixture control (AMC) on a pressure carburetor?

A

The AMC contains sealed bellows that expand or contract with changes in atmospheric pressure. The movement of the bellow operates a tapered needle that controls the impact air pressure into the β€œA” chamber of the carburetor.

21
Q

In what position do you place the mixture control of a pressure injection carburetor to stop the engine?

A

In the idle cutoff position

22
Q

What RPM indication should result when the mixture control is placed in the idle cutoff position when the idle mixture is set correctly?

A

There should be a slight increase in RPM, followed by a rapid drop of RPM to zero

23
Q

What is the purpose of filling a pressure injection carburetor full of fuel and allowing it to soak for a period of about eight hours prior to installation?

A

To soften the diaphragms and make them as pliable as they were when the carburetor was originally calibrated.

24
Q

What are three types of carburetor icing?

A

Throttle icing, impact icing, and fuel evaporation icing.

25
Q

What is the typical fuel pressure in a float type carburetor?

A

3-5 PSI