A gas generator usually refers to a
propellantmixture, often similar to a solid rocketpropellant, that burns to produce large volumes of gas. It is similar to a rocketpropellant, but is usually designed to produce large volumes of cool gas, instead of maximizing the energy available. The low temperature allows the gas to be put to use more easily in many applications. 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 rocketengine, 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 VF-1 and SpaceXMerlin 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 peroxidedecomposed by a liquid sodium permanganate catalystsolution as a gas generator. This was used to drive the main turbopumpto pressurize the LOX- ethanolpropellants.
A common use for gas generators is in the car
air bags. A small pyrotechnic charge is usually used there.
Another common gas generator is the
chemical oxygen generator.
Gas generators have also been used to power
torpedoes. Hydrogen peroxideis frequently used in such applications.
Gas generators can be also used for powering of
auxiliary power units and emergency power units. Hydrazineis often used as a fuel.
Common fuels and reactions used
Hydrogen peroxidedecomposes to oxygen and water. As a high test peroxideit is used to power torpedoes and in some rocket engines.: 2 H2O2 → 2 H2O + O2
Hydrazinedecomposes to nitrogen and hydrogen. The reaction is strongly exothermic and produces high volume of hot gas from small volume of liquid. It is used in some small rocket engines, and some auxiliary power units, e.g. in the Space Shuttle, and emergency power units, e.g. in the F-16aircraft.
#3 N2H4 → 4 NH3 + N2
#N2H4 → N2 + 2 H2
#4 NH3 + N2H4 → 3 N2 + 8 H2
Chlorates and perchlorates
Sodium, potassium, and lithium
chlorates and perchlorates are used for production of oxygen in chemical oxygen generators.
Sodium azidedecomposes exothermically to sodium and nitrogen. The reaction is employed in some early designs of air bags.: 2 NaN3 -> 2 Na + 3 N2The resulting sodium is hazardous, so other materials are added, e.g. potassium nitrate and silica, to convert it to e.g. a silicate glass.
olid rocket propellants
Many solid rocket propellant compositions can be used as gas generators.
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