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AIRCRAFT AND JET PROPULSION SYSTEMSBy: Ratan kumar rout Regd no.:-1221225081 Mechanical Engg. College:-BCET

ContentsHistory of Jet EnginesIntroductionParts Of Jet EngineHow A Jet Engine worksTypes Of Jet Engine 5.1 Ramjet 5.2 Turbojet 5.3 Turbofan 5.4 Turboprop 5.5 Turboshaft

Continued . . .Jet Engine Vs RocketsScramjetsSuggestion For ImprovementMerits And DemeritsConclusionFuture VisionBibliography

1.History Of Jet Engines

The first jet engine was built by Egyptian scientists during 100 B.C.

The device was known as Aeolipile and used steam power directed through two nozzles to cause a sphere to spin rapidly on its axis

It was not used for supplying mechanical power and was simply considered a curiosity

Dr. Hans von Ohain and Sir Frank Whittle were the pioneers behind todays jet engines.

2.IntroductionThe term jet engine loosely refers to an Internal Combustion Air Breathing Jet Engine (a duct engine). These typically consist of an engine with a rotary (rotating) air compressor powered by a turbine ("Brayton cycle"), with the leftover power providing thrust via a propelling nozzle.

Jet engine is nothing but a Gas turbine.

It works under the principle of Newtons third law which states that For every acting force there is an equal and opposite force.

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BRAYTON CYCLE1-2 Isentropic compression (in a compressor) 2-3 Constant pressure heat addition

3-4 Isentropic expansion (in a turbine)

4-1 Constant pressure heat rejection

3.Parts Of Jet Engine

FANCOMPRESSORCOMBUSTORTURBINEMIXERNOZZLE

4.How A Jet Engine Works ?

Jet engines propels an aircraft forward with a great force which is produced by a tremendous thrust from them, hence allowing the plane to fly.

Continued . . .Air Intake

sucked in by the compressor

Compressor

series of vanes and stators. The vanes rotate, while the stator remains stationary. compressor speed and temperature increases gradually

Fuel Burner

Fuel is mixed with the air, and electric sparks light the mixture causing it to combust.

Combustion Chamber

The air is burnt along with fuel.Hence increasing the temperature and pressure of the air inside the engine.

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Continued..Turbine

Works like a windmillThe blades gain energy from the hot gases moving past them. This movement is used to power the compressor.

Jet Pipe and Propelling Nozzle

The hot air rushes out of the nozzle. high pressureHot air rushes out at very high speed

5. Types Of Jet EnginesRamjet TurbojetTurbofanTurbopropTurbo shaft

5.1 RamjetIt has no moving parts.

Its compression ratio depends on forward speed.

They consist of three sections; an inlet to compressed oncoming air, a combustor to inject and combust fuel, and a nozzle

Require a relatively high speed to efficiently compress the oncoming air.

They are most efficient at supersonic speeds, It has no static thrust

guided-missile systems, Space vehicles use this type of jet

5.2 TurbojetThe turbojet engine is a reaction engine.

A turbojet engine works by compressing air with an inlet and a compressor, mixing fuel with the compressed air, burning the mixture in the combustor, and then passing the hot, high pressure air through a turbine and a nozzle

Substantial increases in thrust can be obtained by employing an afterburner

Used in fighter planes, and were used in the Concorde.

Recent Turbojet EngineThe Rolls-Royce/Snecma Olympus 593 was a reheated (afterburning) turbojet which powered the supersonic airliner Concorde.General characteristicsType: TurbojetLength: 4039 mm (159 in) Diameter: 1212 mm (47.75 in) Dry weight: 3175 kg (7,000 lb)

5.3 Turbofan

A turbofan engine is a gas turbine engine that is very similar to a turbojet. Turbofans differ from turbojets as they have an additional component, a fan

The objective of this sort of bypass system is to increase thrust without increasing fuel consumption.

It achieves this by increasing the total air-mass flow and reducing the velocity within the same total energy supply.

ANIMATION OF AIR FLOW IN TURBOFAN ENGINE

5.4 Turboprop

A turboprop engine is a jet engine attached to a propeller.

Majority of their thrust is from the propeller, though hot-jet exhaust is an important design point, and maximum thrust is obtained by matching thrust contributions of the propeller to the hot jet.

Modern turboprop engines are equipped with propellers that have a smaller diameter but a larger number of blades for efficient operation at much higher flight speeds

5.5 TurboshaftTurboshaft engines are very similar to turboprops, differing in that nearly all energy in the exhaust is extracted to spin the rotating shaft.

They therefore generate little to no jet thrust.

It does not drive a propeller and provides power for a helicopter rotor.

It permits the rotor speed to be kept constant even when the speed of the generator is varied .

6. Jet Engines Vs RocketsJet Engine RocketsOxygen from atmosphere for combustionCarry their own oxygen for combustionWork only in atmosphereWork in vacuum and atmosphereLiquid fuel liquid or solid fuelHigh Specific Impulse Low Specific Impulse

Complex Structure Simple StructureHigh EfficiencyLow Efficiency

7.Scramjets

A scramjet (supersonic combustion ramjet) is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow.The scramjet is composed of three basic components: a converging inlet, where incoming air is compressed and decelerated; a combustor, where gaseous fuel is burned with atmospheric oxygen to produce heat; and a diverging nozzle, where the heated air is accelerated to produce thrust.

8. Suggestion For ImprovementEmploy active cooling

Designing better materials and alloys which retain their strength at high temperatures

Smart structures Structure and material which change their shapes and properties in flight.

Design engines which switch from scramjets to ramjets.

9. Merits And DemeritsMerits of Jet Engine over IC Engine

Mechanical efficiency of jet engine is high as compared to IC engine.

Weight and speed of jet engine per HP developed is higher than IC engine.

Ignition and lubricating systems are much simpler in jet engine than IC engine.

Thermal efficiency of Jet engine is low compared to IC engine

Difficult to start

Turbine blades need a special cooling system due high temperatureDemerits Of Jet Engines Over IC engine

10. ConclusionNormal type of jet engine is used for domestic purpose i.e. Traveling, carrying goods etc.

Ram and scram type of jet engines used in only in Defence sector. Because it travels at supersonic speed and generally high level of training is required.

Since it travels at such a speed it is can not used for traveling and hence turbofan engines are used.Lot of improvement and scope exists to maximize efficiency of the engines.

11. Future Vision

Decreased gross lift off weight> Smaller facilities & easier handlingLeading to higher safetyFlights can be aborted, whiles the vehicle glides back to earthMissions can be more flexibleWider range of emergency landing sites for intact abortAircraft with:

12. Bibliography

Books referredElements of Propulsion , Gas turbines and rockets- Jack.D.MattinglyAircraft propulsion and gas turbine engines- Ahmed F.El sayedBasic and applied thermodynamics-P.K.NagInternal combustion engines- Mathur and SharmaUltimate visual dictionary D.K. publications

Internet linkshttp://science.howstuffworks.com/transport/flight/modern/turbine.htmhttp://en.wikipedia.org/wiki/Jet_enginehttp:// www.google.comhttp:// www.boeing.comhttp:// www.jet engine.comhttp://www.nasa.gov