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Powerplant Oral > 7 Engine Fuel And Fuel Metering > Flashcards

7 Engine Fuel And Fuel Metering Flashcards

1
Q
  1. What are some of the sources used to heat the fuel in a turbine engine fuel system?
A

Bleed air and engine lubricating oil.

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2
Q
  1. What are the most common types of fuel metering systems used on small reciprocating engines?
A

Float type carburetor, pressure injection carburetor, and direct fuel injection systems.

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3
Q
  1. What function does the mixture control perform?
A

Controls the fuel/air mixture.

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4
Q
  1. What generally causes spark plug fouling?
A

Operating the engine with an excessively rich mixture at idle.

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5
Q
  1. What is the purpose of an accelerating system?
A

It provides an immediate but brief increase in fuel flow in the venturi to enrich the mixture.

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6
Q
  1. What is a carburetor economizer system?
A

It is a power enrichment system that provides a richer mixture at high power settings, where the excess fuel aids in engine cooling. This system functions at throttle settings above cruise power settings.

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7
Q
  1. When the mixture is placed in the idle cutoff position, a slight rise in RPM is noted prior to the engine decelerating. What does this indicate?
A

The idle mixture is set correctly.

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8
Q
  1. Why should engine RPM be accelerated periodically when making carburetor adjustments?
A

To clear the engine.

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9
Q
  1. What maintains the fuel pressure in a pressure injection carburetor?
A

An engine driven fuel pump.

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10
Q
  1. What happens if the manual mixture control of a pressure injection carburetor is moved to the idle cutoff position?
A

The engine stops.

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11
Q
  1. How does an automatic mixture control function?
A

A sealed brass bellows connected to the fuel metering system, expands, and contracts with changes in pressure and temp, adjusting the mixture accordingly.

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12
Q
  1. What are some of the advantages of fuel injection systems over carburetor systems?
A

Less danger of induction icing, better acceleration, better fuel distribution, better fuel economy, reduced overheating of individual cylinders.

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13
Q
  1. What purpose do turbine engine fuel control units serve?
A

They automatically meter fuel to the engine.

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14
Q
  1. What are the 2 basic types of turbine engine fuel control units?
A

Hydromechanical and electronic.

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15
Q
  1. What are the engine variables detected by the fuel control unit?
A

Power level position, engine RPM, compressor inlet temp, compressor inlet pressure, compressor discharge pressure, burner pressure.

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16
Q
  1. What are the 2 major components of a supervisory electronics engine control?
A

ECU and hyrdromechanical fuel control.

17
Q
  1. What are some of the advantages of a full authority digital engine control FADEC over a hydromechanical fuel control?
A

Better fuel economy, improved starts, requires no engine trimming, provides engine limit protection, provides constant idel speeds regardless of atmospheric conditions or bleed air requirements, fully modulated the active clearance control, and allows more repeatable engine transients.

18
Q
  1. What do turbine engine fuel spray nozzles do?
A

They inject fuel into the combustion area.

19
Q
  1. What are the different engine indications used for trimming a turbine engine?
A

Either EPR or RPM is used depending on the particular engine.

20
Q
  1. What maintenance adjustments are normally allowed on an installed hydromechanical fuel control?
A

Specific gravity for fuel, idle RPM, and max RPM.

21
Q
  1. What type of pump can vary the amount of fuel discharged regardless of speed?
A

A variable displacement pump.

22
Q
  1. What is used to keep water, sediment, and foreign matter out of the carburetor?
A

The main fuel strainer.

23
Q
  1. What is the purpose of a pressure relief valve in a constant displacement pump?
A

It returns excess fuel that isn’t required by the engine to the inlet side of the pump.

24
Q
  1. What type of engine driven fuel pump is widely used other than gear or piston pumps?
A

A rotary vane type.

25
Q
  1. What function do fuel boost pumps perform?
A

They supply pressurized fuel to the fuel pump, which helps prevent vapor lock and cavitation.

26
Q
  1. What is a commonly used type of fuel boost pump?
A

The centrifugal type.

27
Q
  1. What causes vapor lock and why is it of concern?
A

Vapor lock is caused by insufficient fuel pressure, high fuel temps, and excessive fuel turbulence, which may completely block any fuel flow resulting in engine failure.

28
Q
  1. What function does the engine driven pump on a turbine engine perform?
A

It provides a continuous supply of fuel at the proper pressure while the engine is running.

29
Q
  1. Name the 2 categories of turbine engine pumps.
A

Constant and variable displacement.

30
Q
  1. What category is a gear type pump classified in?
A

Constant displacement.

31
Q
  1. When performing an external inspection of an engine driven fuel pump, what should you look for?
A

Leaks and security of mounting.

32
Q
  1. What is the purpose of a shear section of the driveshaft in a duel element constant displacement pump?
A

If one element seizes, a portion of the driveshaft seizes, allowing the other element to continue to operate.

33
Q
  1. Where in a turbine engine fuel system is ice formation likely to occur and how is it prevented?
A

The fuel filter is most susceptible to ice formation, so a fuel heater is used that consists of a heat exchanger using either engine oil or bleed air to warm the fuel.

34
Q
  1. What is the purpose of a bypass valve in an engine fuel system micron filter?
A

It is a safety feature that allows fuel to flow to the engine if the filter becomes blocked.

35
Q
  1. What is the purpose of a duplex fuel nozzle?
A

Discharges 2 different spray patterns. The spray pattern is wider during start up and acceleration and narrows when engine speed increases above idle.

36
Q
  1. What are the functions of the pressurizing and dump portions of a pressurizing and dump valve?
A

The pressurizing portion provides primary and secondary fuel flow to dual line duplex fuel nozzles, and the dump portion allows fuel to drain from the manifolds after engine shutdown.

37
Q
  1. What purpose do fuel selector valves serve?
A

They allow tank and engine selection, and provide a means for shutting off fuel flow.

Powerplant Oral (13 decks)

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