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Powerplant O&P > Engine Fuel and Fuel Metering Systems > Flashcards

Engine Fuel and Fuel Metering Systems Flashcards

1
Q

Why do aircraft fuel metering systems for reciprocating engines have mixture controls?

A

The air density decreases as the aircraft ascends, causing the mixture to become richer. The mixture control allows the fuel to be decreased to maintain a fuel-air mixture ratio that produces the desired power

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2
Q

What does an air-fuel mixture ratio of 12:1 represent?

A

This represents an air-to-fuel ratio mixture of 12 pounds of air and 1 pound of fuel

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3
Q

What is the function of a float carburetor?

A

The float carburetor measures airflow through the engine induction system and dispenses the appropriate amount of gasoline into the airflow for all engine operating parameters.

The float carburetor’s function is the measure of airflow through the engine induction system and dispense the appropriate amount of gasoline into the airflow for all engine operating perimeters and conditions. It must also provide the fuel in a state that is as vaporized as possible by the time ignition occurs in the engine cylinders

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4
Q

What two things are adjusted when setting the idling conditions on a float carburetor?

A
  1. Idling RPM by adjusting the throttle stop
  2. Idling mixture by adjusting idle needle valve
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5
Q

What would likely cause a reciprocating engine equipped with a float carburetor to hesitate momentarily when the throttle is rapidly advanced from idle to full power?

A

A malfunctioning accelerator pump

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6
Q

What are the two types of fuel injection systems used on modern reciprocating aircraft engines?

A
  1. Teledyne Continental (TCM)
  2. Precision Airmotive (Bendix) system
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7
Q

What is used in the TCM fuel injection system to control the amount of fuel sent to the nozzles?

A

The engine speed determines the injector pump output pressure. The relief valve determines the fuel for low-speed operation, and the adjustable orifice determines the fuel for high-speed operation

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8
Q

What is used in the precision airmotive system to control the amount of fuel sent to the nozzles?

A

The mass of the air entering the engine acts on an air diaphragm that controls a servo ball valve in the line between the regulator and the flow divider

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9
Q

What are some sources used to heat the fuel in a turbine engine fuel system?

A

Bleed air and engine lubricating oil.

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10
Q

What are most common types of fuel metering systems used on small reciprocating engines?

A
  1. Float type carburetors
  2. Pressure injection carburetors
  3. Direct fuel injection systems
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11
Q

What function does the mixture control perform?

A

Fuel/Air mixture

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12
Q

What generally causes spark plug fouling.

A

Operating the engine with an excessively rich mixture at idle.

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13
Q

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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14
Q

What is the 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. The system functions at throttle settings above cruise power settings.

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15
Q

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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16
Q

Why should engine RPM be accelerated periodically when making carburetor adjustments?

A

To clear the engine.

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17
Q

What maintains the fuel pressure in a pressure injection carburetor?

A

Engine driven fuel pump.

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18
Q

What happens if the manual mixture control of a pressure injection carburetor is moved to the idle cut off position?

A

The engine stops.

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19
Q

How does an automatic mixture control (AMC) function?

A

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

20
Q

What are some of the advantages of fuel injection systems over carburetor systems?

A
  1. Less danger of induction icing
  2. better acceleration
  3. better fuel distribution
  4. better fuel economy
  5. reduced overheating of individual cylinders
21
Q

What purpose do turbine engine fuel control units serve?

A

They automatically meter fuel to the engine.

22
Q

What are the two basic types of turbine engine fuel control units?

A
  1. Hydromechanical
  2. Electronic
23
Q

What are the engine variables detected by the fuel control unit?

A
  1. Power level position
  2. Engine RPM
  3. Compressor inlet temperature
  4. Compressor inlet pressure
  5. Compressor discharge pressure
  6. Burner pressure
24
Q

What are two major components of supervisory electronics engine control?

A
  1. The electronic control unit
  2. hydromechanical fuel control
25
Q

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 idle speeds regardless of atmospheric conditions or bleed air requirements, fully modulates the active clearance control, and allows more repeatable engine transients.

26
Q

What do turbine engine fuel spray nozzles do?

A

They inject fuel into the combustion area.

27
Q

What are the different engine indications used for trimming a turbine engine?

A

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

28
Q

What maintenance adjustments are normally allowed on an installed hydromechanical fuel control?

A
  1. Specific gravity for fuel
  2. idle RPM
  3. maximum RPM
29
Q

What type of pump can vary the amount of fuel discharged regardless of speed?

A

A variable displacement pump.

30
Q

What is used to keep water, sediment, and foreign matter out of the carburetor

A

Main fuel strainer

31
Q

What is the purpose of a pressure relief valve in a constant displacement pump?

A

It return excess fuel to the inlet side of the pump

It returns excess fuel that is not require by the engine to the inlet side of the pump.

32
Q

What type of engine driven fuel pump is widely used other than gear or piston pump?

A

Rotary vane type.

33
Q

What function do fuel boost pumps perform?

A

Supply pressurized fuel to the fuel pump which prevents vapor lock and cavitation.

34
Q

What is a commonly used type of fuel boost pump?

A

Centrifugal type

35
Q

What causes vapor lock and why is it of concern?

A

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

36
Q

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.

37
Q

Name the two categories of turbine engine pumps.

A
  1. Constant
  2. Variable displacement
38
Q

What category is a gear type pump classified in?

A

Constant displacement

39
Q

When performing an external inspection of an engine driven fuel pump, what should you look for?

A

Leaks and security of mounting.

40
Q

What is the purpose of a shear section driveshaft in a dual element constant displacement pump?

A

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

41
Q

Where in a turbine engine fuel system is ice formation likely to occur and how is it prevented?

A

The fuel filter. A fuel heater is used that consists of a heat exchanger using either engine oil or bleed air to warm the fuel.

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.

42
Q

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.

43
Q

What is the purpose of a duplex fuel nozzle?

A

A duplex fuel nozzle discharges two different spray patterns. The pattern is wider during start up and acceleration and narrows when engine speed increases above idle.

44
Q

What are the functions of the pressurizing and dump portions of a pressurizing and dump valve?

Delete

A
  1. The pressurizing portion provides primary and secondary fuel flow to dual line duplex fuel nozzles
  2. The dump portion allows fuel to drain from the manifolds after engine shutdown.
45
Q

What purpose do fuel selector valves serves?

A

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

Powerplant O&P (11 decks)

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