Basic Gas Turbine Flashcards
TGT stands for what?
Turbine Gas Temperature
Measured in the turbine exhaust
How many ignitiors are present on most typical turbine engines?
Two
When starting a modern turbine engine, what is introduced last?
Fuel
What are the cons of an Axial Flow compressor system?
More complex design, engineering maintenance & costly
Vulnerable to Foreign Object Damage
What factors will reduce the thrust available from a turbine engine?
- High humidity
- High temperature
- Low pressure
The purpose of rotor blades in a turbine engine is to…..?
Increase the kinetic energy of the air
Symptoms of a compressor stall includes what?
- Rapidly rising turbine temp
- Fluctuating fuel flow
How does the temp, density, pressure & velocity of a gas flow vary through a convergent duct at subsonic speed?
Temp, density & pressure reduce.
Velocity increases.
What is the purpose of a turbine shaft?
To attach the turbine disc to the drive compressor
What is the function of an oil relief valve?
To maintain oil supply to the engine if the oil filter or cooler gets blocked
What is the function of nozzle guide vanes?
To accelerate the velocity of combustion gas flow & present it to the first stage turbine at the correct angle of attack.
Turbine starters, otherwise known as nozzle guide vanes do what?
Sit prior to the turbine disc & increase the velocity of the combustion gas & reduce pressure
Divergent shape in the exhaust cone before convergence does what?
Slows air down to reduce energy losses to skin friction
The difference in temp, pressure, & velocity of air before it enters the compressor vs after does what?
Temp & pressure increase
Velocity slightly decreases
An advantage of a centrifugal compressor over an axial flow
Lighter
What are the advantages of a centrifugal compressor over an axial flow compressor?
- Cheaper & easier to manufacture
- More robust
- Better handling of FOD
- Relatively lower in weight
What are disadvantages of using compressor bleed valves to prevent stalls & surges at low RPM?
- Decreased mass airflow through engine.
- Decreased thrust for a given setting.
- Raises EGT due to less cooling air flowing through combustion chamber.
The starter motor can be discontinued when?
Once self sustaining RPM is reached
What are the cons of a centrifugal compressor?
- Large frontal area = more drag.
- Cannot have more than 2 stages due to energy losses between stages.
- Poor acceleration leading to surging, stalling & choking.
In an axial flow compressor, one purpose of the stator vanes in compressor are?
- Decrease velocity
- Prevent swirling
- Boost pressure
- Straighten airflow
Turbine assemblies increase in diameter towards the rear of the engine, why?
To increase the torque from the assemblies.
During the start sequence of a turbine engine, if there was insufficient fuel flow, what sort of abnormal start is most likely to occur?
Hung start
Bleeding air is taken from where & what functions does it supply?
- Pressurisation of cabin
- Anti + de-icing
- Heating of fuel
- Sealing
- Cooling
The compressor ratio of an Axial Flow compressor is a function of what?
Number of compressor stages
Axial flow compressor are designed to do what?
So that the pressure rises in both the rotor & stator blades
What instrument is sued to set power on a turbo-prop aircraft?
Torque gauge
What are the pros of an Axial Flow compressor?
- Smaller frontal area = less drag.
- Can provide a high compression ratio without large losses of efficiency.
- Quick acceleration.
- More stages can be added together to obtain a higher compression ratio.
What is Specific Fuel Consumption?
Measure of the efficiency of an engine.
Fuel flow
/
Thrust
What is a stage?
5 stage compressor
A paring of a rotor & stator.
5 rotors + 5 stators
How does tenp, density, pressure & velocity of a gas flow vary through a divergent duct at subsonic speeds?
Temp, density & pressure increase.
Velocity decreases.
Fluctuating core RPM & fluctuating fuel flow could be indications of what?
Compressor stall
