Rocket engine nozzle
![Figure 1: A de Laval nozzle, showing approximate flow velocity increasing from green to red in the direction of flow](/Images/godic/202502/16/De_laval_nozzle.svg4557.png")
![Nozzle on the first stage of an RSA-3 rocket](/Images/godic/202502/16/Nozzle_RSA-3-0014557.jpg")
![Diagram of a de Laval nozzle, showing flow velocity (v) increasing in the direction of flow, with decreases in temperature (t) and pressure (p). The Mach number (M) increases from subsonic, to sonic at the throat, to supersonic.](/Images/godic/202502/16/Nozzle_de_Laval_diagram.svg4557.png")
![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]](/Images/godic/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.