2 Introduction The principle of jet propulsion was demonstrated by Hero of Alexandriaas long ago as the first century AD.However, the jet engine, as we know it,did not become a practical possibilityuntil 1930 when Sir Frank Whittle patentedthe design of his first reaction motorsuitable for aircraft propulsion.
3 Introduction The gas turbine engine, commonly referred to as the ‘jet’ engine,is an internal combustion engine whichproduces power by the controlled burning of fuel.In both the gas turbine and the motor car engineair is compressed,fuel is mixed with it, and the mixture is burnt.The heat which results producesa rapid expansion of the gasand 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 engineand it compresses itbefore delivering itinto the combustion chamber.COMBUSTIONCHAMBERCOMPRESSORTURBINE
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 compressoris a constant flow of air,constantly being compressed.
6 Compressor Operations The Compressing Action consists oftaking a quantity of air,and forcing it into a smaller space.This square representsa quantity of airThis square represents the same quantity of airbut squeezed into a smaller volumeLET’S SEE HOW THIS IS DONE
7 Compressor Operations The Compressing Action consists oftaking a quantity of air,and forcing it into a smaller space.SQUEEZESQUEEZESQUEEZESQUEEZEPUSH BACKPUSH BACKPUSH BACKPUSH BACKThe air is pushed and squeezedinto ever smaller spaces.
8 Compressor Operations The Compressing Action consists oftaking a quantity of air,and forcing it into a smaller space.SQUEEZESQUEEZESQUEEZESQUEEZEBIG AT FRONTSMALL AT REARPUSH BACKPUSH BACKPUSH BACKPUSH BACKThis is why compressors are shapedthe way they are
9 Compressor Operations Compressors have a series of ‘stages’,each stage giving a small pressure riseover the previous stage.BIG AT FRONTSMALL AT REAR
10 Compressor Operations Each stage consists ofa Rotor Blade to the frontand a Stator Vaneto the rear.FIRSTSTAGESECONDSTAGETHIRDSTAGEFOURTHSTAGEFIFTHSTAGEROTORSTATORROTORSTATORROTORSTATORROTORSTATORROTORSTATORFRONTREAR
11 Compressor Operations Compressor Rotor Bladesare aerofoil sections producing lift,while rotating like propellers.As the blades rotate they force air to the rear,they do the ‘pushing’ back.ROTORSTATORROTORSTATORROTORSTATORROTORSTATORROTORSTATORFRONTREAR
12 Compressor Operations The Stator Vanesare fixed to the engine casing,in clusters, or a complete ring.The vanes do the ‘squeezing’ or compressingof the forced back air.ROTORSTATORROTORSTATORROTORSTATORROTORSTATORROTORSTATORFRONTREAR
13 Compressor Operations Each stage produces a small pressure risewhich 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)FIRSTSTAGESECONDSTAGETHIRDSTAGEFOURTHSTAGEFIFTHSTAGEROTORSTATORROTORSTATORROTORSTATORROTORSTATORROTORSTATORFRONTREAR
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.COMPRESSORROTO BLADECOMPRESSORROTO BLADESTATOR VANECLUSTERSTATOR VANECLUSTER
15 The Compressor Many modern engines have more than one compressor, because a high degree of compressionrequires a large number of compressor rowsor ‘stages’.Each stage has an optimum speedfor best efficiency –the smaller the bladesthe higher the speed.
16 The Compressor If all the stages are on the same shaft, only a few of them will beoperating at their optimum speed.This is overcome by dividing the compressorinto 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.
17 Check of Understanding When air is forced into a smaller space,what two things happen?Pressure IncreasesTemperature DecreasesPressure IncreasesTemperature IncreasesPressure DecreasesTemperature DecreasesPressure DecreasesTemperature Increases
18 Check of Understanding What does each stage of a compressorconsist of?Rotor vanes and Compressor bladesRotor blades and Stator vanesRotor blades and Compressor vanesRotor vanes and Stator blades
19 Check of Understanding Which of the following statements is not true?Stator vanes are like aerofoilsRotor bladesforce air backwardsStator vanes are fixedto the engine casingRotor blades rotate
20 Check of Understanding A compressor producesan overall pressure rise,What is this known as?Pressure anglePressure increase ratioPressure ratioPressure increment
21 Check of Understanding What is the result ofa high Pressure Ratio?High thrust to weight ratioLow fuel temperaturesHigh combustion ratioLow specific fuel consumption
22 Check of Understanding Each stage of a compressorhas an optimum speed for best efficiency.Which of the following applies?The smaller the bladethe higher the speedThe smaller the bladethe lower the pressureThe smaller the vanethe higher the pressureThe smaller the vanethe slower the speed