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NIFE > NIFE Engines 3-2-1 Gas turbine Engines > Flashcards

NIFE Engines 3-2-1 Gas turbine Engines Flashcards

1
Q

Describe inlet ducts

A

Provides proper high pressure, turbulent free airflow, steady and uniform to 1st stage of compressor

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2
Q

Describe compressor function

A

Primary function is to supply enough air to satisfy the requirements of the combustion section.

Improves Burner efficiency

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3
Q

List types of compressors

A
  1. Centrifugal flow
  2. Axial flow
  3. Axial-centrifugal flow
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4
Q

Centrifugal flow compressor

A

Have divergent passages in the diffuser to convert the high velocity airflow to high pressure

Impeller accelerates air and increases pressure. Diffuser reduces velocity and increases pressure. Manifold directs airflow to the combustion chamber

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5
Q

Centrifugal Compressor Advantages and Disadvantages

A

Advantages

  • Rugged
  • Low cost
  • Good power output over a wide range of RPMs
  • Highest pressure increase per stage

Disadvantages

  • Large frontal area required
  • Impractical for multiple stages
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6
Q

Axial-flow compressor

A

Uses multiple stages of rotors and stators
The efficient use of multiple stages can produce very high overall compression ratios

Dual Spool: also referred to as twin or split spool. Creates greater flexibility and power

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7
Q

Axial flow compressor advantages and disadvantages

A

Advantages
High peak efficiencies, small frontal area, straight through-flow for high ram efficiency, better combustion efficiency, greater starting flexibility and improved high-altitude performance

Disadvantages

  • Could stall at low speeds
  • High compressor inlet temps cause low compression ratios and will reduce the air supply to the rear of the compressor
  • Good efficiencies only possible over a narrow rotational speed
  • Expensive
  • High starting power requirements
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8
Q

Axial-centrifugal flow compressor

A

combines axial and centrifugal flow compressors; axial section allows for ‘straight through’ ram efficiency and multiple stages for high pressure; the centrifugal section significantly increases that pressure through its one stage

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9
Q

Describe the burner section of a gas turbine engine

A

The burner section provides the means for proper mixing of the fuel and air to assure good combustion

Contains the combustion chamber

Must deliver the combustion gases to the turbine section at a temperature that will not exceed the allowable limit of the turbine blades

Combustion chamber must add sufficient heat energy to the gases passing through the engine to accelerate their mass and produce the desired thrust for the engine and power of the turbines

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10
Q

List types of combustion chambers

A
  1. Can
  2. Annular
  3. Can-annular
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11
Q

Can Combustion Chamber

A

Airflow is ducted to individual combustion cans that are arranged around the circumference of the burner section (each burner contains its own fuel nozzle, burner liner, and casing)

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12
Q

Can combustion advantages

A

strength, durability, ease of maintenance

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13
Q

Can combustion disadvantages

A

Poor use of space
Greater pressure loss
Uneven heat distribution
Malfunction of one can lead to turbine damage

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14
Q

Annular Combustion Chamber

A

Consists of a continuous circular, inner and outer shroud around the outside of the compressor drive shaft - fuel is introduced through a series of nozzles where it is mixed and ignited with the incoming air (used on small aircraft/helicopters)

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15
Q

Annular combustion advantages and disadvantages

A

uniform heat distribution
better mixing fuel and air
better use of space

disadvantages
maintenance

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16
Q

Annular combustion disadvantages

A

unit cannot be removed without major overhaul

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17
Q

Can-annular Combustion Chamber

A

(used on large, high performance aircraft) combines ease of maintenance w/ excellent thermodynamics of the annular type - consists of cans at the front where the fuel and air are mixed and burned. But it is expensive

18
Q

Describe the turbine section of a gas turbine engine

A

Comprised of stators and rotors

Turbine section drives the compressor and the accessories, designed to increase velocity
Unlike compressor, designed to increase airflow velocity

Turbines rotor converts the heat energy of the hot expanding gases from the burner chamber into mechanical energy
75% of the total pressure energy from the exhaust gases is converted to power compressor and accessories
25% is used for thrust

19
Q

Describe the phenomenon of creep

A

When turbine blades undergo elongation as they are heated. Could result in permanent blade deformation if under excessive temps for long periods of time.

20
Q

Describe the exhaust section

A

Must direct the flow of hot gases rearward to cause a high exit velocity to the gases while preventing turbulence

21
Q

Describe the after burner

A

Used in turbojets and turbofans for a short period of time

Increases max thrust available from an engine by 50% or more

22
Q

Describe a basic civilian reciprocating engine

A

Basic components are the crankcase, crankshaft, pistons, rods, valves, spark plugs, and cylinders

23
Q

What is the purpose on an engine inlet?

A

To provide proper amount of high pressure, turbulent free air that is ready and uniform to the first stage of the compressor

24
Q

What is the shape of a subsonic inlet duct? Why?

A

Divergent.

25
Q

What is the shape of a supersonic inlet duct? Why?

A

Convergent / Divergent

Act as subsonic until supersonic speeds. Convergent: Decrease pressure, increase velocity

26
Q

What is the purpose of a variable geometry inlet duct?

A

To be able to fly through all flight regimes (adjusting for sub-sonic and supersonic speeds)

27
Q

What do inlet and exit guide vanes do?

A

Inlet:

  • Impart swirling motion to air entering compressor
  • Directs airflow to the first stage rotor
  • Reduces aerodynamic drag

Exit:
- Reduces turbulence

28
Q

What is the function of the diffuser?

A

Prepare air for entry into the burner section by decreasing velocity and increase pressure

29
Q

Describe a dual spool axial flow compressor. Why is it used?

A

Two separate compressors driven by its own turbine to obtain higher compressor ratios. OHIO.

30
Q

What are the criteria for a good burner section?

A
  1. Minimum pressure loss
  2. High combustion efficiency
  3. Flame must not blow out
  4. Contain the total combustion process
31
Q

What is the purpose of the exhaust duct?

A

Direct the flow of hot gases rearward

32
Q

How much of the energy produced is used to turn the compressor and accessories?

A

75%

33
Q

What type of exhaust nozzle is used on an afterburner equipped aircraft?

A

Variable exhaust nozzle

34
Q

How does subsonic airflow react through a convergent opening? A divergent opening?

A

Airflow velocity will increase and pressure will decrease. Airflow pressure will increase and volcity will decrease

35
Q

What are the components of a reciprocating engine?

A

Crankcase, cylinders, pistons, connecting rods, valves, valve operating mechanism, and the crankshaft

36
Q

Describe a subsonic and supersonic exhaust duct and how each operates.

A

Subsonic - convergent

Supersonic - convergent/divergent

37
Q

Describe the four parts of an afterburner.

A

Spray Bars introduce fuel
Flameholders create turbulent eddies and ensure air and fuel are mixed
Screech Liner reduce pressure and vibrations
Variable Exhaust Nozzle opens to allow gases to expand

38
Q

Describe how an afterburner operates.

A

Secondary air from burner section is mixed with fuel and ignited in the afterburner duct to augment thrust

39
Q

What controls the amount of thrust augmentation an afterburner will produce?

A

Fuel. More fuel = more thrust

40
Q

What is a screech liner and how does it operate?

A

reduce pressure and vibration (shock absorber)

NIFE (24 decks)

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