15.15 Power Augmentation Flashcards
What is power augmentation used for?
To restore or boost power for improved performance
What are the three ways to compensate for a loss in power if Max takeoff weight cannot be reduced?
Increase engine speed
Increase fuel flow
Increase air density
How is an increase in air density achieved?
By cooling the air that passes through the engine
What is the efficient way of cooling the air passing through the engine?
By spraying water into air intake or front of combustion chamber
What type of aircraft are these methods used for respectively?
Water methanol
Water injection
After burner standard
Water methanol for turbo prop and turbo shaft
Water injection for turbo jet
After burner standard on military aircraft only
What is the ratio of water and methanol by volume in water methanol method?
60% water and 40% methanol
What is compressor inlet injection?
Water/methanol used to prevent water from freezing. This method is more suited to centrifugal flow compressors.
What does spraying water/methanol into a compressor inlet do?
What happens if you just spray water?
Reduces temperature and increases air density and thrust
Only reduces turbine inlet temp
What type of compressor is combustion chamber injection suited for?
Axial flow compressors
How is the injection of the mixture delivered in a combustion chamber injection?
Through small holes in fuel nozzles
Which increased mass flow through turbine relative to compressor
This reduces pressure and temperature across turbine which results in greater pressure within jet pipe = more thrust
What is wet thrust?
Using water injection for Max takeoff thrust on older low bypass engines
The water is injected into compressor inlet or diffuser to increase takeoff thrust on warmer days where density is lower
It is not used on high bypass turbo fan engines
Why is water methanol used?
Water methanol used to prevent freezing of water and methanol burns in combustion chamber adding to thrust
What temperatures can afterburners increase the engine to?
1700°C +
What type of propelling nozzle after Berner jet pipe use?
Two position or variable area
Simple explanation for afterburners
Fuel is introduced and burnt between turbine and exhaust nozzle utilising unburnt O2 and exhaust gas
Nozzle opens up when afterburning to allow for increase in volume of gas stream prevent preventing any increase in pressure
How do the fuel nozzles distribute evenly over flame area?
Via burners
What is the basic construction of the burners?
Several circular fuel manifold supplied by fuel lines in support struts for jet pipe
Flame stabilisers are blunt nosed V section annular rings downstream of the burners
What is the jet pipe usually made from in afterburners?
Heat resistant nickel alloy which requires more insulation than standard jet pipe
How are the movable eyelids operated in a two position propelling nozzle?
Actuators or pneumatic rounds to open and close them
What is the construction of the Jet pipe skin in afterburners?
An outer skin (flight loads)
An inner skin (thermal loads)
Layer of cooling air between both skins
