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Jet Propulsion

Lecture - 21

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

Indian Institute of Technology Guwahati

Prepared underQIP-CD Cell Project

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Reaction Propulsion• Development of Thrust in a Rocket Motor:

Pressure is BalancedPressure is Balanced Burning Propellant along the insideBurning Propellant along the insideof the casing exerts pressure in allof the casing exerts pressure in alldirections at once, until a nozzle isdirections at once, until a nozzle isfitted a one end.fitted a one end.

Pressure is UnPressure is Un--BalancedBalancedForward VelocityForward Velocity

ThrustThrust

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Thrust: Produced by ejecting propellant products.

Propellant: Fuel+Oxidizer

Properties:

Carries its own propulsive agentsDoes not have moving parts (in general)Gives high thrust for short-duration.

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A rocket is called a launch vehicle when it is used to launch a satellite or other payload into space.

A rocket becomes a missile when the payload is a warhead and it is used as a weapon.

Launch Vehicle / MissileLaunch Vehicle / Missile

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Rocket Principles

• High pressure/temperature/velocity exhaust gases provided through combustion and expansion through nozzle of suitable fuel and oxidiser mixture.

• A rocket carries both the fuel and oxidiser onboard the vehicle whereas an air-breather engine (e.g. turbojet or turbofan) takes in its oxygen supply from the atmosphere.

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History of Rockets

• First military use of proper rockets was by Chinese in 1232 in Battle of Kai-Keng v Mongols.

• Used gunpowder (saltpeter, sulphur, charcoal mixture) to fill capped bamboo tubes attached to arrows - known as fire arrows.

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History of Rockets (Cont.)• Mongols then produced rockets of their own and

use spread across Europe via Arabs.• In England, Roger Bacon improved gunpowder

mixture to greatly increase range.• In France, Jean Froissant improved flight

accuracy by tube-launching (forerunner of bazooka).

• In Italy, Joanes de Fontanadesigned surface-running torpedo to attack ships.

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History of Rockets (Cont.)

• By 16th century, rockets were only used for fireworks, though one breakthrough was made by German Johann Schmidlap.

• He was the first to use staging - a firework with a large sky rocket (1st stage) jettisoned after burn-out with a smaller 2nd stage going to a higher altitude.

• Basis behind all of today’s space rockets.

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History of Rockets (Cont.)

• By late 17th century, Newton’s laws were being applied to rockets.

• German and Russian rocket experimenters built powerful rockets with masses above 45 kg.

• Military use again by Indian army in 1792 & 1799 against British.

• Led to British use, designs by Col William Congreve used by British ships v Fort McHenry in war of 1814 (“rocket’s red glare” in Star-Spangled Banner).

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History of Rockets (Cont.)

• Rocket inaccuracy continued to be a big bugbear but was significantly improved due to England’s William Hale’s discovery of spin stabilisation - using the exhaust gas to strike small vanes and give the rocket spin.

• Advances in breech-loaded cannon with rifled barrels and exploding warheads (e.g. by Prussians v Austrians) led to another demise in military rocket use.

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Modern Rocketry• Probably began with Russia’s Konstantin

Tsiolkovsky (1857-1935) who proposed idea of space exploration by rockets in 1903!

• Suggested use of liquid propellants for increased range and stated that speed and range were limited only by jet velocity of escaping gas.

• Also came up with mathematical range equations.

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Modern Rocketry (Cont.)• Next major pioneering work done by Robert

Goddard (1882-1945) in USA, conducting practical rocket experiments.

• Began with solid propellant rockets in 1915 but then produced world’s first liquid propellant rocket in 1926 (liquid oxygen and gasoline).

• Later improvements: gyroscope for flight control, payload compartment and parachute recovery.

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Modern Rocketry (Cont.)

• Followed by Herman Oberth (1894-1989) in Transylvania.

• Published an important book on the use of rockets for space travel in 1923.

• His work led to further military development of the rocket in the form of the infamous German V-2 (known as A-4 in Germany), used against London in WW2.

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V-2• Programme directed by Wernher Von Braun.• Burnt mixture of liquid oxygen and alcohol at rate

of 130 kg/s for about a 70 s to develop maximum thrust of about 725 kN - ballistic coast to target.

• Introduced too late to change outcome of war but led to swift development of ICBM’s.

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V-2 (Cont.)• Maximum speed - approx 1340 m/s.• Impact velocity - approx 1100 m/s (> Mach 3).• Typical range/altitude of 350/90 km respectively.• Carried 1 ton explosive warhead.• Launch mass about 13000 kg, impact mass about

4040 kg.• Length 14 m• Diameter 1.65 m

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Performance:

Specific Impulse, ( S e c )s pFI

W•

=

Energy SourcesChemical combustion Chemical Rockets

Non-chemical combustionNuclearElectrical

Non Chemical Rockets

Developed, used and found practical

Technically feasible, yet to be developed.

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Classifications(1) Type of energy sources

(2) Functions/ Applications

Satellite launchers (Booster/Sustainer)Aircraft for assisted take offSounding RocketsSpace vehiclesMissiles (Guided/Unguided)Auxiliary motors for guidance and

control of vehicles

Guided Missiles: Flight path is controlled by radio signals.

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Strap-on-Rockets

Pay load

3rd stage

2nd stage

1st stage

(3) No.of stages/units

Single stageTwo stage Multi stage

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Chemical Propulsion

Energy Propellant CombustionGas Temperature = 2800 – 4400 KExhaust Velocity = 1800 - 4300 m/s

Physical State

Solid Rocket MotorsLiquid Rocket EnginesHybrid Rocket Engines

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Solid Rocket Motor Igniter Grain

CC

Thrust chamber

N

# Simplicity.# No feed system.# Control of thrust becomes difficult.# Small motor size due to high density.# Not used in space propulsion.# No sloshing# Specific Impulse, 200-300 secs.

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Liquid Rocket Engines

( )250 450 secsspI −

Relatively Complex Feed System (Gas Pump/Turbo Pump) Easier Control Start-stop-restart capabilities High

Remark: Historically, the word engine is used for a liquid propellant rocket propulsion system, and the word motoris used for a solid propellant rocket propulsion system. They were developed by different groups.

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MMHUDMHN2H4CH4

HNO3H2O2

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Hybrid Rocket Engines

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Hybrid Rocket Engines

Grain manufacturing is easier and hence low cost Safety during storage and operation

(because they are separate)

Start-stop- restart capabilitiesis higher than solid motors. s pI

Chemical Rockets have relatively low values of specific impulse, relatively light machinery (low weight), a very high thrust capability, and therefore high acceleration and high specific power (Pjet/mo).

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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