Rocket engine nozzle
![Nozzles can be (top to bottom):underexpanded,ambient,overexpanded,grossly overexpanded.If a nozzle is under- or overexpanded, then loss of efficiency occurs relative to an ideal nozzle.
Grossly overexpanded nozzles have improved efficiency relative to an overexpanded nozzle (though are still less efficient than a nozzle with the ideal expansion ratio), however the exhaust jet is unstable.[7]](/uploads/202502/16/Rocket_nozzle_expansion.svg4557.png)
A rocket engine nozzle is a propelling nozzle (usually of the de Laval type) used in a rocket engine to expand and accelerate the combustion gases produced by burning propellants so that the exhaust gases exit the nozzle at hypersonic velocities.