The fan sucks and compresses a high volume of air at the front of the engine. A significant volume of this air bypasses the engine core and exits the cold exhaust nozzle, contributing the largest proportion of the engine's thrust.

A large fan is better for propulsive efficiency and noise but introduces challenges such as weight and drag.

The compressors deliver high pressure air to the combustor. The more the air is compressed the more power can be extracted inside the turbines. Some of this compressed air is used for secondary tasks such as cooling hot components.

The challenge is to maximise the compression ratio and efficiency without increasing the weight and complexity of the engine.

The combustor burns fuel with air fed from the compressor.

The combustor must generate a large amount of energy in order to drive the turbines. The challenge is to generate the maximum amount of heat from the smallest amount of fuel with the lowest emissions.

The turbine extracts energy from the hot gas stream delivered by the combustor.

This power is used to drive the fan and compressors. The challenge for the turbine blades is to operate in an extremely hostile environment of high temperatures and large centrifugal loads.

Topic: Forces

The fan provides the force to push the aircraft through the air by pushing air out of the back of the engine. By pushing the air backwards an equal and opposite force pushes the engine and therefore aeroplane forward. This is like blowing up a balloon and letting it go – the air pushed out of the back of the balloon pushes the balloon in the opposite direction making it fly round the room.

Theory:

Newton’s Third Law – Every action has an equal and opposite reaction, or whenever an object pushes with a force on a second object, the second object pushes with an equal force in the opposite direction on the first object.

Topic: Combined gas law

The compressor takes the air entering the engine and compresses, or squashes it, which increases its pressure and temperature. The air is compressed to decrease the volume it takes up so that more oxygen is available in the combustor.

Theory:

Gas law:
P1V1 = P2V2
  T1      T2


This states that the ratio of Pressure x Volume and Temperature stays the same for a fixed mass of gas. (Pressure should be in Pa, Volume in m3 and Temperature in K)

e.g. If 1m3 of air enters the compressors at a pressure of ... and temperature of .... and leaves at a pressure of .... and temperature of .... we can calculate the volume of air by:

Air entering the compressor: P1 = 68950 Pa, V1 = 1m3, T1 = 298 K
Air leaving the compressor: P2 = 413700 Pa , V2 = ?, T2 = 533 K

P1V1 = P2V2
  T1      T2

68950 x 1 = 413700 x V2
 298                 533

V2 = 68950 x 1 x 533 = 0.30 m3 (Rounded figure)
        298 x 413700

Topic: Efficiency

Fuel is burnt in the combustor to release energy as heat, sound and light. The heat energy makes the gas in the combustor expand and push its way out of the back of the engine with kinetic energy. The more kinetic energy produced for each litre of fuel the more efficient the engine is.

Theory:

Efficiency is a measurement of how good something is at transforming energy from one type to another. A 100% efficient engine would change all the chemical energy in fuel to kinetic energy. In real life this is not possible as some energy is always wasted as heat and sound.
Efficiency = (Energy in – useful energy out)/Energy in x 100
Efficiency of the engine = (Chemical energy – kinetic energy)/Chemical energy x 100

Topic: Energy transformations

Words:
The turbine blades take the kinetic energy from the gases moving through them and use that energy to turn the fan and compressors blades.

Theory:

Energy cannot be created or destroyed only changed from one type to another.

E.g. In the combustor fuel is burnt and to release kinetic energy but this also releases heat, sound and light:

chemical energy heat + sound + light + kinetic energy