1. JET PROPULSION
Part 1
The Compressor

2. Introduction The principle of jet propulsion
was demonstrated by Hero of Alexandria
as long ago as the first century AD.
However, the jet engine, as we know it,
did not become a practical possibility
until 1930 when Sir Frank Whittle patented
the design of his first reaction motor
suitable for aircraft propulsion.

3. Introduction The gas turbine engine,
commonly referred to as the ‘jet’ engine,
is an internal combustion engine which
produces power by the controlled burning of fuel.
In both the gas turbine and the motor car engine
air is compressed,
fuel is mixed with it, and the mixture is burnt.
The heat which results produces
a rapid expansion of the gas
and this is used to do work.

4. The Compressor The compressor, situated at the front of the engine,
is driven by the turbine,
and performs two functions -
it draws air into the engine
and it compresses it
before delivering it
into the combustion chamber.
COMBUSTION
CHAMBER
COMPRESSOR
TURBINE

5. The Compressor Whenever air is forced into a smaller space,
two things happen –
The Pressure of the trapped air Increases,
The Temperature of the trapped air Increases.
A jet engine compressor
is a constant flow of air,
constantly being compressed.

6. Compressor Operations
The Compressing Action consists of
taking a quantity of air,
and forcing it into a smaller space.
This square represents
a quantity of air
This square represents the same quantity of air
but squeezed into a smaller volume
LET’S SEE HOW THIS IS DONE

7. Compressor Operations
The Compressing Action consists of
taking a quantity of air,
and forcing it into a smaller space.
SQUEEZE
SQUEEZE
SQUEEZE
SQUEEZE
PUSH BACK
PUSH BACK
PUSH BACK
PUSH BACK
The air is pushed and squeezed
into ever smaller spaces.

8. Compressor Operations
The Compressing Action consists of
taking a quantity of air,
and forcing it into a smaller space.
SQUEEZE
SQUEEZE
SQUEEZE
SQUEEZE
BIG AT FRONT
SMALL AT REAR
PUSH BACK
PUSH BACK
PUSH BACK
PUSH BACK
This is why compressors are shaped
the way they are

9. Compressor Operations
Compressors have a series of ‘stages’,
each stage giving a small pressure rise
over the previous stage.
BIG AT FRONT
SMALL AT REAR

10. Compressor Operations
Each stage consists of
a Rotor Blade to the front
and a Stator Vane
to the rear.
FIRST
STAGE
SECOND
STAGE
THIRD
STAGE
FOURTH
STAGE
FIFTH
STAGE
ROTOR
STATOR
ROTOR
STATOR
ROTOR
STATOR
ROTOR
STATOR
ROTOR
STATOR
FRONT
REAR

11. Compressor Operations
Compressor Rotor Blades
are aerofoil sections producing lift,
while rotating like propellers.
As the blades rotate they force air to the rear,
they do the ‘pushing’ back.
ROTOR
STATOR
ROTOR
STATOR
ROTOR
STATOR
ROTOR
STATOR
ROTOR
STATOR
FRONT
REAR

12. Compressor Operations
The Stator Vanes
are fixed to the engine casing,
in clusters, or a complete ring.
The vanes do the ‘squeezing’ or compressing
of the forced back air.
ROTOR
STATOR
ROTOR
STATOR
ROTOR
STATOR
ROTOR
STATOR
ROTOR
STATOR
FRONT
REAR

13. Compressor Operations
Each stage produces a small pressure rise
which factored for the number of stages,
would produce an overall pressure rise,
known as the ‘Pressure Ratio’.
Pressure ratios around 26:1 are common.
(meaning pressure is 26 times ambient)
FIRST
STAGE
SECOND
STAGE
THIRD
STAGE
FOURTH
STAGE
FIFTH
STAGE
ROTOR
STATOR
ROTOR
STATOR
ROTOR
STATOR
ROTOR
STATOR
ROTOR
STATOR
FRONT
REAR

14. The Compressor Due to the operating nature of the compressor,
the airflow does not travel straight through it.
The rotor blades push the air around the engine,
whereas the stator vanes straighten it out.
COMPRESSOR
ROTO BLADE
COMPRESSOR
ROTO BLADE
STATOR VANE
CLUSTER
STATOR VANE
CLUSTER

15. The Compressor Many modern engines have more than one compressor,
because a high degree of compression
requires a large number of compressor rows
or ‘stages’.
Each stage has an optimum speed
for best efficiency –
the smaller the blades
the higher the speed.

16. The Compressor If all the stages are on the same shaft,
only a few of them will be
operating at their optimum speed.
This is overcome by dividing the compressor
into 2 or 3 parts,
each rotating at its optimum speed.
By this means,
compression ratios up to 30:1 can be achieved,
resulting in extremely high efficiency
and very low specific fuel consumption.

17. Check of Understanding
When air is forced into a smaller space,
what two things happen?
Pressure Increases
Temperature Decreases
Pressure Increases
Temperature Increases
Pressure Decreases
Temperature Decreases
Pressure Decreases
Temperature Increases

18. Check of Understanding
What does each stage of a compressor
consist of?
Rotor vanes and Compressor blades
Rotor blades and Stator vanes
Rotor blades and Compressor vanes
Rotor vanes and Stator blades

19. Check of Understanding
Which of the following statements is not true?
Stator vanes are like aerofoils
Rotor blades
force air backwards
Stator vanes are fixed
to the engine casing
Rotor blades rotate

20. Check of Understanding
A compressor produces
an overall pressure rise,
What is this known as?
Pressure angle
Pressure increase ratio
Pressure ratio
Pressure increment

21. Check of Understanding
What is the result of
a high Pressure Ratio?
High thrust to weight ratio
Low fuel temperatures
High combustion ratio
Low specific fuel consumption

22. Check of Understanding
Each stage of a compressor
has an optimum speed for best efficiency.
Which of the following applies?
The smaller the blade
the higher the speed
The smaller the blade
the lower the pressure
The smaller the vane
the higher the pressure
The smaller the vane
the slower the speed

23. JET PROPULSION
End of Presentation