A gas generator usually refers to a device, often similar to a solid rocket or a liquid rocket that burns to produce large volumes of relatively cool gas, instead of maximizing the temperature and specific impulse. The low temperature allows the gas to be put to use more easily in many applications, particularly to drive turbines. Gas generators are used to power turbopumps in rocket motors, to deploy airbags, and in other cases where large volumes of gas are needed, and storing it as a pressurized gas is undesirable or impractical.
A gas-generator cycle can also specifically refer to a way of designing a turbopump-fed liquid rocket engine, where some of the propellant is burned to drive the turbopump, and the exhaust is dumped overboard (usually through a nozzle) instead of being fed into the main combustion chamber. Many liquid rockets are designed this way, for example the Saturn V F-1 and SpaceX Merlin engines. Usually, the propellants are burned in a highly fuel-rich mix to keep flame temperatures low — O:F ratios below 0.5 are common.
Another good example is the V-2 rocket, which used hydrogen peroxide decomposed by a liquid sodium permanganate catalyst solution as a gas generator. This was used to drive the main turbopump to pressurize the LOX-ethanol propellants.
A common use for gas generators is in automobile air bags. A small pyrotechnic charge is usually used to open a valve, which begins the gas generation process. A typical charge might be a pound of sodium azide.
Another common gas generator is the chemical oxygen generator.
Gas generators have also been used to power torpedoes. Hydrogen peroxide is frequently used in such applications.
Gas generators can be also used for powering of auxiliary power units and emergency power units. Hydrazine is often used as a fuel.
Famous quotes containing the words gas and/or generator:
“one pale woman all alone,
The daylight kissing her wan hair,
Loitered beneath the gas lamps’ flare,
With lips of flame and heart of stone.”
—Oscar Wilde (1854–1900)
“He admired the terrible recreative power of his memory. It was only with the weakening of this generator whose fecundity diminishes with age that he could hope for his torture to be appeased. But it appeared that the power to make him suffer of one of Odette’s statements seemed exhausted, then one of these statements on which Swann’s spirit had until then not dwelled, an almost new word relayed the others and struck him with new vigor.”
—Marcel Proust (1871–1922)