Turbine Engine Systems Flashcards
What are Gas Turbine Engines?
- Heat engines that continually create expanding gases (in the Gas Generator) who’s energy is converted into propulsive force to move an aircraft
- Nozzles are used to Accelerate the high energy gases that are exiting the Gas Generator and route them through it’s smaller exhaust opening
- This produces increased Thrust!
What is the role of Compressors in a GTE?
• Compress Intake Air, and force air into the Combustor/Combustion Chamber where fuel is ignited, creating exhaust gases
What is the role of Turbines in a GTE?
- Driven by exhaust gases that pass thru (from the Compressors)
- As the Turbines rotate, they provide drive force to the common Shaft, which will continue to rotate and drive the Compressors (self-sustaining)
How does a Centrifugal Flow Compressor work?
- Air intake is directed through an Impeller, which centrifugally slings it outwards into a chamber, or “diffuser”
- here the velocity of the out-slung air is slowed to increase air pressure before it enters the combustion chamber
How does an Axial Flow Compressor work?
- Intake air is directed into the first set of Rotor Blades and through stationary Stater Vanes
- Airflow remains parallel to the longitudinal axis of the Engine, Stater Vanes help maintain linear airflow
- Air pressure increases more and more after passing through each “Compressor Stage”
What does a Compressor Stage refer to
Consists of 1 row of Rotor Blades and the following row of Stater Vanes
What is the Low Pressure Spool?
- The forward most compressor
- N1 Shaft driven by the Rearmost Turbine
- Rotational speed of this Low Pressure Compressor is N1
What is the High Pressure Spool?
- The 2nd compressor
- Its hollow N2 Shaft is driven by its own high pressure Turbine
- Counter rotates over the N1 Shaft
- Rotational Speed of this High Pressure Compressor is N2
Every Turbine Engine is built around the same core, which consists of:
Compressor
Combustor
Turbine Section
What is the difference between the design of a Turbofan Engine vs a Turbojet Engine?
What affect does the design have on thrust/efficiency?
Turbofan has a Shrouded Fan at the front of the engine that’s driven by the engine’s turbine section!
- This accelerates large amounts of air, routing some through the core and some “bypass air” around the outside of the core.
- Bypass Air increases THRUST thanks to turbofan blade design, and at lower altitudes 80% of a high-bypass ratio engine’s thrust comes from the Shrouded Fan, resulting in increased Efficiency!
What is the significance of a Fan Driven Gear System (FDGS) reducing fan speed to 1/3 N1?
- Enables the low pressure turbine to run at a higher speed than the fan so both fan and turbine achieve peak efficiency
In a Geared Turbofan Engine (GTF) the reduction gear box:
- Slows the fan section rotation
- Prevents blades from going supersonic/shockwave/drag/noise
What does the FCU (fuel control unit) in a turbine aircraft do?
The FCU determines how quickly to reposition the fuel-valve, depending on various internal engine pressures that it senses based off the Pilot’s thrust lever “request”
(Hydromechanical) Electronic Engine Control (EEC)
vs
Fully Authority Digital Engine Control (FADEC)
EEC:
- All mechanical linkage (throttle vale, flyweights, speeder spring)
- Powered independently of the a/c’s electrical system by a permanent-magnet alternator, driven by the engine’s accessory section. Hydromechanical backup.
FADEC:
- NO mechanical linkage (electronically connected by wire)
- Powered independently. No backup so if FADEC loses power the engine will shut down.
What indications are most commonly used to set thrust on a turbine engine?
N1 - low pressure shaft RPM
EPR - Engine Pressure Ratio
