Hybrid rockets are a type of rocket propulsion system that combines features of both solid rocket engines and liquid rocket engines. In a hybrid rocket, one of the propellants is in solid form, typically a solid fuel, while the other propellant is in liquid or gaseous form, acting as the oxidizer.
The propulsive efficiency of a hybrid rocket engine can be expressed in terms of the effective exhaust velocity and the specific impulse, similar to other rocket engines. Hybrid rocket engines use a combination of liquid or gaseous oxidizer and a solid fuel, typically a rubbery substance, to generate thrust.
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).