AEROSPACE PROPULSION SYSTEM

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AEROSPACE PROPULSION SYSTEM

• PROF. SEUNG WOOK BAEK
• DIV. OF AEROSPACE ENGINEERING, KAIST, IN KOREA
• ROOM Bldg. N7-2 3304
• TELEPHONE 3714
• http//procom.kaist.ac.kr
• swbaek_at_kaist.ac.kr

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Propulsion devices
devices which produce thrust for acceleration and
overcome external drag by generating rearward
momentum in one or more streams of gas
Airbreathing engine (propeller, turpoprop,
turbojet, turbofan, ramjet, scramjet) fluid
stream entering and leaving the propulsion
device Rocket engine (liquid and solid) ejection
of stored mass (fueloxidizer)
PROPULSION AND COMBUSTION LABORATORY
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Airbreathing engines

• release internal chemical energy combined with
  external oxidizer
• chemical -gt thermal -gt kinetic energy
• Engine components inlet, compressor (and fan),
• combustor, turbine, afterburner and nozzle
• Common performance measures
• a compromise among specific thrust, specific
  impulse, thrust specific fuel consumption

PROPULSION AND COMBUSTION LABORATORY
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Airbreathing engines

• Thermal efficiency a ratio of the rate of
  kinetic energy generation to the rate of thermal
  (chemical) energy input
• Propulsive efficiency a ratio of the useful
  power transmitted to the flight vehicle to the
  rate of kinetic energy generation
• Afterburning increases the specific thrust at
  the high performance condition and allows use of
  a more fuel-efficient system for subsonic
  cruise.

PROPULSION AND COMBUSTION LABORATORY
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Chemical rockets

• release internal chemical energy combined with
  internal oxidizer
• Solid propellant rockets
• -relative simplicity
• -weapon or strap-on booster rocket to very
• large orbiting rockets
• -increased propellant density with heavily
  aluminized solid propellant-very small cross
  section and reduced drag for low altitude

PROPULSION AND COMBUSTION LABORATORY
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Chemical rockets

• Solid propellant rockets
• Design problem
• -thrust level variation and rapid thrust
  termination
• -screaming acoustic instability resilient
  propellant material-optimal cross-sectinal
  shapes that reduce wave reflection

PROPULSION AND COMBUSTION LABORATORY
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Solid propellant rockets

• Double-base propellants
• -homogeneous propellant grain
• -nitrocellulose type of gunpowder dissolved in
  nitroglycerin
• -major ingredients are explosives and
  contribute to the functions of fuel, oxidizer
  and binder

PROPULSION AND COMBUSTION LABORATORY
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Solid propellant rockets

• Composite propellants
• -heterogeneous propellant grain
• -oxidizer crystals and powdered fuel
  (usually aluminum) held together in a matrix
  of synthetic rubber binder
• -less hazardous to manufacture and handle
  than double-base propellants

PROPULSION AND COMBUSTION LABORATORY
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Solid propellant rockets

• Composite double-base propellants
• -a combination of double-base and composite
  propellants
• -usually crystalline oxidizer (ammonium
  perchlorate) and powdered aluminum fuel
  held together in a matrix of nitrocellulose- nitro
  glycerin

PROPULSION AND COMBUSTION LABORATORY
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Chemical rockets

• Liquid propellant rockets
• -highly energetic liquid fuels and oxidizers in
  low pressure tanks
• -variable thrust level capability
• -pumps and associated piping lead to an
  increase in size and overall mass of the
  vehicle
• Boiling points O2 -183 0C
• H2 -253 0C
• N2 -196 0C

PROPULSION AND COMBUSTION LABORATORY
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Chemical rockets

• Liquid propellant rockets
• Design problem
• -turbo pumps to supply the necessary
  fuel/oxidizer ratio
• -variable nozzle to provide the maximum
  possible thrust for each altitude(maximum
  possible thrust occurs when the nozzle
  exhaust pressure is very near the ambient
  pressure
• -base heating

PROPULSION AND COMBUSTION LABORATORY
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Chemical rockets

• Liquid propellant rockets
• Design problem
• Instabilities
• -chugging-relatively low-frequency oscillation
  when combustion chamber pressure variations
  couple with the liquid fuel and oxidizer
  supply system-raising the fuel and oxidizer
  supply pressures-heavy piping and pump
  equipment

PROPULSION AND COMBUSTION LABORATORY
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Chemical rockets

• Liquid propellant rockets
• Design problem
• Instabilities
• -screaming-acoustic instability indentified with
  the increase in the thermal output of fuel-
  oxidizer
• -increase in pressure and temperature in the
  two phase region close to injector heads
• -amplified to extreme levels by reflection form
  chamber walls-acoustic tiling

PROPULSION AND COMBUSTION LABORATORY
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Non-chemical rockets

• -required for very high energy missions for which
  the vehicle velocity change is very large
• -energy supplied to a propellant through the
  thermal energy or radiative energy from a nuclear
  reactor and solar concentrator
• -nuclear heated rocket, electrical rocket and
  etc.

PROPULSION AND COMBUSTION LABORATORY
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Overall performance

• Thrust reaction to the net force that the engine
  exerts on the fluid passing through it
• Separate engine performance from effects of
  enclosure or airframe
• Fthrust which would be produced by the thrust
  generator if the external flow are isentropic

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Overall performance

• Determine F in terms of engine parameters
• Propulsive flow flow of the working fluid
• External flow flow of fluid surrounding the
  thrust generator in a frame of reference fixed to
  the thrust generator

PROPULSION AND COMBUSTION LABORATORY