The propulsive efficiency () of a liquid propellant rocket engine is a measure of how effectively the chemical energy stored in the liquid propellants is converted into kinetic energy of the exhaust gases, resulting in thrust. The efficiency is typically expressed in terms of the specific impulse (), which is related to the exhaust velocity.
The propulsive efficiency is a crucial parameter in evaluating the performance of a rocket engine, indicating how well it converts propellant energy into useful thrust. Practical rocket engines often have propulsive efficiencies less than 100% due to factors like incomplete combustion, heat losses, and other inefficiencies in the propulsion system.
The propulsive efficiency () is defined by the following formula:
where,
- is the propulsive efficiency,
- is the thrust produced by the rocket engine,
- is the effective exhaust velocity of the rocket,
- ṁ is the mass flow rate of the propellants,
- is the specific impulse of the rocket engine,
- g0 is the acceleration due to gravity (approximately 9.81 m/s²).