Physics:Gas-generator 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.

The gas-generator cycle, also called open cycle, is one of the most commonly used power cycles in bipropellant liquid rocket engines. Part of the unburned 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. Then they are expelled overboard. They can be expelled directly from the turbine, or are sometimes expelled into the nozzle (downstream from the throat) for a small gain in efficiency.

The main combustion chamber does not use these products. This explains the name of the open cycle. 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 combustion engines include:

• Vulcain, HM7B
• Merlin
• RS-68
• RS-27A
• J-2X
• F-1
• RD-107
• CE-20

Rocket launch systems that use gas-generator combustion engines include:

• Ariane 5
• Falcon 9,
• Falcon Heavy
• Delta IV
• Saturn V
• Soyuz
• GSLV
• LVM III
• Long March 3B, Long March 2F
• Miura 5

See also

• Combustion tap-off cycle
• Expander cycle
• Pressure-fed engine
• Rocket engine
• Staged combustion cycle
• Turbopump

External links

• Rocket power cycles
• Rocket-Engine Cooling at NASA