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Characteristic velocity

From Wikipedia, the free encyclopedia

Characteristic velocity or , or C-star is a measure of the combustion performance of a rocket engine independent of nozzle performance, and is used to compare different propellants and propulsion systems. c* should not be confused with c, which is the effective exhaust velocity related to the specific impulse by: . Specific impulse and effective exhaust velocity are dependent on the nozzle design unlike the characteristic velocity, explaining why C-star is an important value when comparing different propulsion system efficiencies. c* can be useful when comparing actual combustion performance to theoretical performance in order to determine how completely chemical energy release occurred. This is known as c*-efficiency.

Formula

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  • is the characteristic velocity (m/s, ft/s)
  • is the chamber pressure (Pa, psi)
  • is the area of the throat (m2, in2)
  • is the mass flow rate of the engine (kg/s, slug/s)

  • is the specific impulse (s)
  • is the gravitational acceleration at sea-level (m/s2)
  • is the thrust coefficient
  • is the effective exhaust velocity (m/s)
  • is the specific heat ratio for the exhaust gases
  • is the gas constant per unit weight (J/kg-K)
  • is the chamber temperature (K)


References

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  • Rocket Propulsion Elements, 7th Edition by George P. Sutton, Oscar Biblarz
  • Rocket Propulsion Elements, 9th Edition by George P. Sutton, Oscar Biblarz