Characteristic velocity
Characteristic velocity,, or C-star is a measure of the combustion performance of a rocket engine independent of Rocket [engine nozzle|nozzle] performance, and is used to compare different propellants and propulsion systems. It is independent of the nozzle, making it a useful metric for evaluating propellant combustion alone. 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, or the combustion efficiency. This is known as c*-efficiency, or , and is calculated by dividing with. Standard values for '' range from 0.85 to 1.03.''
Formula
- is the characteristic velocity.
- is the chamber pressure.
- is the area of the throat.
- is the mass flow rate of the engine.
- is the specific impulse.
- is the gravitational acceleration at sea-level.
- is the thrust coefficient.
- is the effective exhaust velocity.
- is the specific heat ratio for the exhaust gases.
- is the gas constant per unit weight.
- is the chamber temperature.