Gas-generator cycle (rocket)

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 is a power cycle of a bipropellant rocket engine. Some of the propellant is burned in a gas-generator and the resulting hot gas is used to power the engine's pumps. The gas is then exhausted. Because something is "thrown away" this type of engine is also known as open cycle.

There are several advantages to the gas generator cycle over its counterpart, the staged combustion cycle. The gas generator turbine does not need to deal with the counter pressure of injecting the exhaust into the combustion chamber. This simplifies plumbing and turbine design, and results in a less expensive and lighter engine.

The main disadvantage is lost efficiency due to discarded propellant. Gas generator cycles tend to have lower specific impulse than staged combustion cycles.^{[citation needed]}

As in most cryogenic rocket engines, some of the fuel in a gas-generator cycle is used to cool the nozzle and combustion chamber. Current construction materials cannot stand extreme temperatures of rocket combustion processes by themselves. Cooling permits the use of rocket engines for relatively longer periods of time with today’s material technology. Without rocket combustion chamber and nozzle cooling, the engine would fail catastrophically.

Examples of gas-generator engines are the Merlin rocket engine, the Vulcain engine of Snecma Moteurs used on the ESA Ariane 5 rocket, and the more recent J-2X engine to be used on NASA's future Space Launch System rockets. ISRO is developing the first Indian cryogenic engine CE-20, at its Liquid Propulsion Systems Centre to power the upper stage of the Geosynchronous Satellite Launch Vehicle III.

See also

• Expander cycle
• Pressure-fed cycle
• Rocket engine
• Staged combustion cycle

External links

• Rocket power cycles
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