Characteristic velocity

Characteristic velocity or ${\displaystyle c^{*}}$, 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. 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: ${\displaystyle I_{s}={\frac {c}{g_{0}}}}$. 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 ${\displaystyle n_{v}}$, and is calculated by dividing ${\displaystyle c_{Actual}^{*}}$ with ${\displaystyle c_{Theoretical}^{*}}$. Standard values for ${\displaystyle n_{v}}$ range from 0.85 to 1.03.