The propulsive efficiency of a chemical rocket engine is a measure of how effectively the engine converts the chemical energy stored in its propellants into kinetic energy of the exhaust gases, ultimately producing thrust. The propulsive efficiency is typically expressed in terms of the effective exhaust velocity and the specific impulse.
The specific impulse is a key parameter that characterizes the efficiency of a rocket engine. It represents the thrust produced per unit mass flow rate of propellant. The effective exhaust velocity is the velocity that a rocket would achieve in a vacuum, neglecting atmospheric effects and other losses.
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).