A hybrid-propellant rocket is a rocket with a rocket motor that uses rocket propellants in two different phases: one solid and the other either gas or liquid.
In a hybrid rocket engine, the combustion process typically involves a liquid oxidizer and a solid fuel. The combustion occurs at the interface between the liquid oxidizer and the solid fuel grain. While there may be a combustion chamber, there is often no traditional nozzle for the expansion of exhaust gases as in liquid or solid rocket engines.
Instead, the thrust in a hybrid rocket engine is generated by the combustion of the liquid oxidizer and solid fuel, and the resulting hot gases are expelled through the aft end of the combustion chamber. The specific energy terms used for hybrid rockets may include parameters related to combustion efficiency, specific impulse, and thrust.
The total energy () at the nozzle Inlet can be expressed as:
where,
- E is the Total Energy, i.e sum of kinetic and potential energy
- is the Static Enthalpy at nozzle Inlet,
- is the velocity of the incoming air relative to the reference frame of the engine