Editing Engine cycle

The '''engine cycle''' of a [[rocket engine]] describes the primary method chosen to transport [[Propellant|propellants]] into the [[Combustion chamber|combustion chamber]]. Real rocket engines can have multiple different engine cycles active during their operation in sequence, for optimal performance at different thrust levels or during ignition and cut-off. 

The goals of an engine cycle are, to deliver the right amount of propellants to the combustion chamber and do that at the right pressure for the [[Injector|injector]]. If the maximum pressure of the propellants at the injector is lower than the [[Chamber pressure|chamber pressure]], the propellant cannot be injected into the chamber and combustion stalls. 

==Pressure-feed==
The simplest engine cycle is the pressure-feed. It relies on the [[Ullage pressure|ullage pressure]] of the tanks to push the propellants into the [[Combustion chamber|combustion chamber]]. It is very robust and such an engine can easily be started and cut-off, which makes this cycle preferred for [[RCS]] and restartable main engines.

==Gas-generator cycle==
''See also: [[Gas-generator cycle]]''
The gas-generator cycles uses a gas generator and a turbine to drive a pump, which transports the fuel into the [[Combustion Chamber|combustion chamber]]. The exhaust of the gas generator is vented outboards, contributing only little thrust. The gas-generator cycle has an upper limit for chamber pressure, as a higher chamber pressure requires more power for the pump, which means more fuel has to be burned inside the gas generator without producing thrust.

==Staged combustion cycle==
The propellants get partially combusted in one or more preburners and the exhaust products are routed through one or more [[Turbine|turbines]] and into the main combustion chamber, where they are finally combusted. This cycle allows high chamber pressures and this very high [[Specific impulse|specific impulse]].