Characteristic velocity or [math]\displaystyle{ c^* }[/math], 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: [math]\displaystyle{ I_s = \frac{c}{g_0} }[/math]. 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.
[math]\displaystyle{ c^* = \frac{p_c A_t }{\dot{m}} }[/math]
[math]\displaystyle{ c^* = \frac{I_{sp} g_0}{C_F} = \frac{c}{C_F} =\sqrt{\frac{RT_c}{\gamma} \Bigl(\frac{\gamma+1}{2}\Bigr)^{\frac{\gamma+1}{\gamma-1}}} }[/math]
Original source: https://en.wikipedia.org/wiki/Characteristic velocity.
Read more |