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