Introduction Flashcards
What is the basic operation of a jet engine?
Compressor is driven by the turbine - they are on the same driveshaft
How is thrust created?
Simple case of Newton’s laws of motion
Rate of change of momentum of the working fluid
Engine needs to accelerate the working fluid
Results in exhaust just having high kinetic energy
What do rocket engines carry in tanks?
Fuel AND oxidant (both injected into combustion chamber)
What accelerates the combustion products to supersonic speeds in rocket engines?
Enthalpy release
How do liquid fuelled engines work?
A turbine drives pumps that pump fuel and oxidant into the combustion chamber at high pressures and high volume flow rates
Fuel and oxidant is atomised (sprayed) in the entrance to the combustion chamber and so thoroughly mixed before combustion takes place
In most engines, the fuel or oxidant is used to cool the rocket engine nozzle
How do solid propellant rocket motors work?
Propellant is stored directly in the combustion chamber of the motor
The propellant grain actually forms the shape of the chamber
Once ignited they cannot be throttled not shut down
Propellant burns radially outwards and gases flow axially down the engine towards the nozzle
Relatively simple design so cheaper to develop than liquid engine
Used for booster stages extensively and also for some orbital manoeuvers
What is the purpose of the inlet?
They guide the flow into the engine and aim to provide the fan with a uniform flow so it can operate efficiently
What do the rotor and stator do in axial compressors?
Rotor blades rotate and accelerate the flow
Stator blades are stationary and decelerate the flow
When are centrifugal compressors used?
Used where a single stage is required to produce a large pressure rise
Used for lower mass flow applications
How do centrifugal compressors work?
Flow enters the rotor ‘eye’ and is accelerated as it flows rapidly outward to the tip
Flow decelerates once out of the rotor and gains a further pressure rise
Work done on the flow by turning and accelerating the flow rapidly
What is the purpose of the combustor?
To raise the enthalpy of the working fluid by burning fuel in the compressed air delivered from the compressor
The high temperature and pressure combustion products turn the turbine and eventually generate thrust
What is the purpose of the turbine?
Extract energy from the high enthalpy working fluid and so drive the compressor at the correct rotational speed
What do the rotor and stator do in the turbine?
Rotor blades rotate
Stator blades are stationary and accelerate the flow
What is the bypass ratio?
Ratio of the air that goes around to the air that goes through the core
How do twin spool turbofans work?
Two compressors driven by two turbines through concentric drive shafts at different speeds
