NIFE Engines 3-2-1 Gas turbine Engines Flashcards
Describe inlet ducts
Provides proper high pressure, turbulent free airflow, steady and uniform to 1st stage of compressor
Describe compressor function
Primary function is to supply enough air to satisfy the requirements of the combustion section.
Improves Burner efficiency
List types of compressors
- Centrifugal flow
- Axial flow
- Axial-centrifugal flow
Centrifugal flow compressor
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
Centrifugal Compressor Advantages and Disadvantages
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
Axial-flow compressor
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
Axial flow compressor advantages and disadvantages
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
Axial-centrifugal flow compressor
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
Describe the burner section of a gas turbine engine
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
List types of combustion chambers
- Can
- Annular
- Can-annular
Can Combustion Chamber
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)
Can combustion advantages
strength, durability, ease of maintenance
Can combustion disadvantages
Poor use of space
Greater pressure loss
Uneven heat distribution
Malfunction of one can lead to turbine damage
Annular Combustion Chamber
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)
Annular combustion advantages and disadvantages
uniform heat distribution
better mixing fuel and air
better use of space
disadvantages
maintenance
Annular combustion disadvantages
unit cannot be removed without major overhaul
Can-annular Combustion Chamber
(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
Describe the turbine section of a gas turbine engine
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
Describe the phenomenon of creep
When turbine blades undergo elongation as they are heated. Could result in permanent blade deformation if under excessive temps for long periods of time.
Describe the exhaust section
Must direct the flow of hot gases rearward to cause a high exit velocity to the gases while preventing turbulence
Describe the after burner
Used in turbojets and turbofans for a short period of time
Increases max thrust available from an engine by 50% or more
Describe a basic civilian reciprocating engine
Basic components are the crankcase, crankshaft, pistons, rods, valves, spark plugs, and cylinders
What is the purpose on an engine inlet?
To provide proper amount of high pressure, turbulent free air that is ready and uniform to the first stage of the compressor
What is the shape of a subsonic inlet duct? Why?
Divergent.
