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Jet Propulsion

Lecture-1

Ujjwal K Saha, Ph.D.Department of Mechanical Engineering

Indian Institute of Technology Guwahati

Prepared underQIP-CD Cell Project

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Propulsion : From PROPEL

to move forward/onwardAct of change of motion of a body.

Reaction principle (Newton’s law)From the jet (Stream of fluid forced out of an opening)

What is propulsion? The word is derived from two Latin words: promeaning before or forwards and pellere meaning to drive. Propulsionmeans to push forward or drive an object forward. A propulsion system is a machine that produces thrust to push an object forward.

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Example:Example:

Each force vector is opposed by an equal and opposite vector, so there is no tendency for the balloon to move.

When the forces acting toward the east are allowed to escape, the remaining forces acting on the balloon will propel it toward the west.

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Turbine EngineTurbine Engine

The balloon with machinery at the front to keep it full as air escapes out at the back for continuous thrust

The turbine engine has a cylinder of turbomachinery with unbalanced forces pushing forward

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Thrust: Force that moves a body forward.Devices Propulsive device

PropulsorJet propelled engineThruster

Air breathing engines (ABE)Non air breathing engines (NABE)

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ABE Uses the atmospheric air as the main fluid.Operation is limited within earth’s atmosphere.e.g., Aircraft engines.

NABE Uses its own propulsive agent (liquid/ solid)

Capable to operate beyond earth’s atmosphere.e.g., Rocket engines.

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Aircraft Engine/ Propulsion

Piston engineby a propeller

Thrust Gas turbine engineby the jet of gas turbine engine

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Propeller gives a smaller acceleration to a larger weight of air.

Jet engine gives a larger acceleration to a smaller weight of air.

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Propeller/Jet

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Characteristics (Piston Engine):

Power/ weight ratio is lowComplex system/ designReciprocating parts Balancing problemLow ηm due to reciprocating partsCombustion problem (knocking/ pre-ignition)Frequent maintenance/ service problem.

Gas turbines are widely used to power aircraft because they are light and compact, and have a

high power-to-weight ratio.

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In both the gas turbine (aircraft engine) and the piston engine (motor car engine), air is compressed, fuel is added and the mixture is ignited. The resulting hot gas expands rapidly and is used to produce the power. In the motor car engine, the burning is intermittent and the expanding gas moves a piston and crank to produce rotary or shaft power which is transmitted to the road wheels.

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The advantages are that the gas turbine engine has a very high power to weight ratio compared to other engines. Also for its power the gas turbine engine is much smaller than other engines.

The main disadvantage of the gas turbine is that compared to engines of similar size they are very expensive. As they spin at extremely fast speeds and have extremely high working temperatures, the manufacture and design of the gas turbine is a hard concept in the fields of engineering and materials. Gas turbines also tend to use more fuel when stationary and work more efficiently when there is a constant load instead of a fluctuating load, hence they are not used in cars but instead in aircrafts and power plants.

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Piston engines : Early development.Gas Turbine engines : World war II.

PushpakSmall Trainer Aircraft

Cessna

Thrust : 7 kN (1600 lb)Present times : 440 kN (100,000 lb)

Von-ohain (1939)Frank Whittle (1941)

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EvolutionEvolution: : Turbojet :Turbojet : MIG 27 , ConcordeMIG 27 , Concorde

100% thrust from jet100% thrust from jet

Military application

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TurbopropTurboprop: Dornier, Jetstream, Fokker, ATR: Dornier, Jetstream, Fokker, ATR

Propeller thrust 80% ; Jet thrust 20%Propeller thrust 80% ; Jet thrust 20%Medium range transport / passenger aircraftMedium range transport / passenger aircraft

PW100

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TurbofanTurbofan : Boeing , Airbus, DC: Boeing , Airbus, DC--1010

Fan thrust =75Fan thrust =75--80%; Engine thrust =2580%; Engine thrust =25--20%20%

Medium / long range Transport / Passenger AircraftMedium / long range Transport / Passenger Aircraft

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Turboshaft : Similar to Turboprop.

drive the compressor FreeTwo Turbines Turbine

drive the rotor shaft

Used in helicopters / choppers

Single Turbine both compressor Fixedand rotor shaft

PT6T Engine PW200

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RamjetRamjet::

No rotary components.No rotary components.No thrust : Static conditionNo thrust : Static condition

(motion is required)(motion is required)Additional powerAdditional power--plant in an Aircraftplant in an Aircraft

Fuel Burner Combustion Chamber

Air Intake Propelling Nozzle

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Can run on static conditionIntermittent CombustionUsed in helicopters

o Emergency powerplant for small aircraft and gliders

o High fuel consumption makes it unsuitable

Shutter Valve

Air Intake

FuelSupply

Combustion Chamber

Jet Pipr andProelling Nozzle

Charging(Shutter Valve Open)

Firing(Shutter Valve Closed)

PulsejetPulsejet::

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Turbofan adaptation /Turboprop derivative of Turboshaft Turbojet.

FanPropellerRotor

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Schematic diagram of a turbojet with afterburner

General Electric J79 turbojet with afterburner

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Property variations through the General Electric J79 AB turbojet engine

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SummarySummary

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SummarySummary

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SummarySummary

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References1. Hill, P.G., and Peterson, C.R., (1992), Mechanics and

Thermodynamics of Propulsion, Addison Wesley.2. Saravanamuttoo, H.I.H, Rogers, G.F.C, and. Cohen, H, (2001), Gas

Turbine Theory, Pearson Education.3. Oates, G.C., (1988), Aerothermodynamics of Gas Turbine and Rocket

Propulsion, AIAA, New York.4. Mattingly, J.D., (1996), Elements of Gas Turbine Propulsion, McGraw

Hill.5. Cumpsty, N.A., (2000), Jet Propulsion, Cambridge University Press.6. Bathie, W.W., (1996), Fundamentals of Gas Turbines, John Wiley.7. Treager, I.E., (1997), Aircraft Gas Turbine Engine Technology, Tata

McGraw Hill. 8. Anderson, J. D. Jr., (2000), Introduction to Flight, 4th Edition, McGraw

Hill. 9. M.J.L.Turner, (2000), Rocket and Spacecraft Propulsion, Springer.10. Sutton, G.P. and Biblarz, O., (2001), Rocket Propulsion Elements,

John Wiley & Sons.11. Zucrow, M.J., (1958), Aircraft and Missile Propulsion, Vol. II, John

Wiley.12. Barrere, M., Jaumotte, A., Veubeke, B., and Vandenkerckhove, J.,

(1960), Rocket Propulsion, Elsevier.

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