Gas-generator cycle

Propellant is burned in a gas generator (or "preburner") and the resulting hot gas is used to power the propellant pumps before being exhausted overboard and lost.

Because of this loss, this type of engine is termed open cycle.

The gas generator cycle exhaust products pass over the turbine first.

The major disadvantage is that this propellant contributes little to no thrust because they are not injected into the combustion chamber.

The major advantage of the cycle is reduced engineering complexity compared to the staged combustion (closed) cycle.

Gas-generator rocket cycle. Some of the fuel and oxidizer is burned separately to power the pumps and then discarded. Most gas-generator engines use the fuel for nozzle cooling.