JET PROPULSION Part 1 The Compressor. The principle of jet propulsion was demonstrated by Hero of Alexandria as long ago as the first century AD. However,

JET PROPULSION

Part 1

The Compressor

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.

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.

Introduction

COMPRESSOR TURBINE

COMBUSTION

CHAMBER

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.

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.

The Compressor

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 airbut squeezed into a smaller volume

LET’S SEE HOW THIS IS DONE

Compressor Operations




PUSH BACK

SQUEEZE

PUSH BACK PUSH BACK PUSH BACK

SQUEEZE

SQUEEZESQUEEZE

The air is pushed and squeezed into ever smaller spaces.



This is why compressors are shaped the way they are


PUSH BACK PUSH BACK PUSH BACK PUSH BACKBIG AT FRONT SMALL AT REAR

SQUEEZESQUEEZE

SQUEEZESQUEEZE

BIG AT FRONT SMALL AT REAR


Compressors have a series of ‘stages’,

each stage giving a small pressure rise over the previous stage.

Compressor OperationsEach stage consists of

a Rotor Blade to the front

and a Stator Vaneto the rear.

FRONT REAR

FIRSTSTAGE

SECONDSTAGE THIRD

STAGE FOURTHSTAGE FIFTH

STAGE

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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.


FRONT REAR

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FRONT REAR

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.

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FRONT REAR

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)

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FIRSTSTAGE SECOND

STAGE THIRDSTAGE FOURTH

STAGE FIFTHSTAGE

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.

COMPRESSORROTO BLADE

COMPRESSORROTO BLADE

STATOR VANECLUSTER

STATOR VANECLUSTER

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.

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 efficiencyand very low specific fuel consumption.

The Compressor

Check of Understanding

When air is forced into a smaller space,what two things happen?

Pressure DecreasesTemperature Increases

Pressure IncreasesTemperature Decreases

Pressure DecreasesTemperature Decreases

Pressure IncreasesTemperature Increases

What does each stage of a compressorconsist of?

Rotor vanes and Stator blades

Rotor vanes and Compressor blades

Rotor blades and Compressor vanes

Rotor blades and Stator vanes


Which of the following statements is not true?

Rotor blades rotate

Stator vanes are like aerofoils

Stator vanes are fixed to the engine casing

Rotor blades force air backwards


A compressor produces an overall pressure rise,What is this known as?

Pressure increment

Pressure angle

Pressure ratio

Pressure increase ratio


What is the result of a high Pressure Ratio?

Low specific fuel consumption

High thrust to weight ratio

High combustion ratio

Low fuel temperatures


Each stage of a compressor has an optimum speed for best efficiency.

Which of the following applies?

The smaller the vane the slower the speed

The smaller the blade the higher the speed

The smaller the vane the higher the pressure

The smaller the blade the lower the pressure


JET PROPULSION

End of Presentation

Documents

JET PROPULSION Part 1 The Compressor. The principle of jet propulsion was demonstrated by Hero of Alexandria as long ago as the first century AD. However,