Gas generator
Encyclopedia
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 turbopump
s 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..
Another common gas generator is the chemical oxygen generator
.
Gas generators have also been used to power torpedo
es. Hydrogen peroxide
is frequently used in such applications.
Gas generators can be also used for powering of auxiliary power unit
s and emergency power unit
s. Hydrazine
is often used as a fuel.
decomposes to oxygen and water. As a high test peroxide
it is used to power torpedoes and in some rocket engines.
decomposes 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-16 aircraft.
s and perchlorates are used for production of oxygen in chemical oxygen generator
s.
decomposes exothermically to sodium and nitrogen. The reaction is employed in some early designs of air bags.
The resulting sodium is hazardous, so other materials are added, e.g. potassium nitrate and silica, to convert it to a silicate glass.
Solid rocket
A solid rocket or a solid-fuel rocket is a rocket engine that uses solid propellants . The earliest rockets were solid-fuel rockets powered by gunpowder; they were used by the Chinese in warfare as early as the 13th century and later by the Mongols, Arabs, and Indians.All rockets used some form of...
or a liquid rocket
Liquid rocket
A liquid-propellant rocket or a liquid rocket is a rocket engine that uses propellants in liquid form. Liquids are desirable because their reasonably high density allows the volume of the propellant tanks to be relatively low, and it is possible to use lightweight pumps to pump the propellant from...
that burns to produce large volumes of relatively cool gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
, 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 turbopump
Turbopump
A turbopump is a gas turbine that comprises basically two main components: a rotodynamic pump and a driving turbine, usually both mounted on the same shaft, or sometimes geared together...
s 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
Gas-generator cycle (rocket)
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...
can also specifically refer to a way of designing a turbopump-fed liquid rocket
Liquid rocket
A liquid-propellant rocket or a liquid rocket is a rocket engine that uses propellants in liquid form. Liquids are desirable because their reasonably high density allows the volume of the propellant tanks to be relatively low, and it is possible to use lightweight pumps to pump the propellant from...
engine, where some of the propellant is burned to drive the turbopump, and the exhaust is dumped overboard (usually through a nozzle
Nozzle
A nozzle is a device designed to control the direction or characteristics of a fluid flow as it exits an enclosed chamber or pipe via an orifice....
) instead of being fed into the main combustion chamber
Combustion chamber
A combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber...
. Many liquid rockets are designed this way, for example the Saturn V
Saturn V
The Saturn V was an American human-rated expendable rocket used by NASA's Apollo and Skylab programs from 1967 until 1973. A multistage liquid-fueled launch vehicle, NASA launched 13 Saturn Vs from the Kennedy Space Center, Florida with no loss of crew or payload...
F-1
F-1 (rocket engine)
The F-1 is a rocket engine developed by Rocketdyne and used in the Saturn V. Five F-1 engines were used in the S-IC first stage of each Saturn V, which served as the main launch vehicle in the Apollo program. The F-1 is still the most powerful single-chamber liquid-fueled rocket engine ever...
and SpaceX
SpaceX
Space Exploration Technologies Corporation, or more popularly and informally known as SpaceX, is an American space transport company that operates out of Hawthorne, California...
Merlin
Merlin (rocket engine)
Merlin is a rocket engine developed by SpaceX for use on its Falcon 1 and Falcon 9 rockets. Merlin uses RP-1 and liquid oxygen as propellants in a gas-generator power cycle...
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
V-2 rocket
The V-2 rocket , technical name Aggregat-4 , was a ballistic missile that was developed at the beginning of the Second World War in Germany, specifically targeted at London and later Antwerp. The liquid-propellant rocket was the world's first long-range combat-ballistic missile and first known...
, which used hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
decomposed by a liquid sodium permanganate
Sodium permanganate
Sodium permanganate is the inorganic compound with the formula NaMnO4. It is closely related to the more commonly encountered potassium permanganate, but it is generally less desirable, because it is more expensive, absorbs water from the atmosphere, and has a low melting point...
catalyst solution as a gas generator. This was used to drive the main turbopump
Turbopump
A turbopump is a gas turbine that comprises basically two main components: a rotodynamic pump and a driving turbine, usually both mounted on the same shaft, or sometimes geared together...
to pressurize the LOX
Lox
Lox is salmon fillet that has been cured. In its most popular form, it is thinly sliced—less than in thickness—and, typically, served on a bagel, often with cream cheese, onion, tomato, cucumber and capers...
-ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
propellants.
A common use for gas generators is in automobile air bags. A small pyrotechnic charge
Squib (explosive)
A squib is a miniature explosive device used in a wide range of industries, from special effects to military applications. It resembles a tiny stick of dynamite, both in appearance and construction, although with considerably less explosive power...
is usually used to open a valve, which begins the gas generation process..
Another common gas generator is the chemical oxygen generator
Chemical oxygen generator
A chemical oxygen generator is a device releasing oxygen created by a chemical reaction. The oxygen source is usually an inorganic superoxide, chlorate, or perchlorate. A promising group of oxygen sources are ozonides. The generators are usually ignited mechanically, by a firing pin, and the...
.
Gas generators have also been used to power torpedo
Torpedo
The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...
es. Hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
is frequently used in such applications.
Gas generators can be also used for powering of auxiliary power unit
Auxiliary power unit
An auxiliary power unit is a device on a vehicle that provides energy for functions other than propulsion. They are commonly found on large aircraft, as well as some large land vehicles.-Function:...
s and emergency power unit
Emergency power unit
An emergency power unit , also called an emergency power supply unit , is a device for energy production in case of failure of the primary systems....
s. Hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
is often used as a fuel.
Hydrogen peroxide
Hydrogen peroxideHydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
decomposes to oxygen and water. As a high test peroxide
High test peroxide
High-test peroxide or HTP is a high -concentration solution of hydrogen peroxide, with the remainder predominantly made up of water. In contact with a catalyst, it decomposes into a high-temperature mixture of steam and oxygen, with no remaining liquid water...
it is used to power torpedoes and in some rocket engines.
- 2 H2O2 → 2 H2O + O2
Hydrazine
HydrazineHydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
decomposes 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
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
, and emergency power units, e.g. in the F-16 aircraft.
- 3 N2H4 → 4 NH3 + N2
- N2H4 → N2 + 2 H2
- 4 NH3 + N2H4 → 3 N2 + 8 H2
Chlorates and perchlorates
Sodium, potassium, and lithium chlorateChlorate
The chlorate anion has the formula ClO. In this case, the chlorine atom is in the +5 oxidation state. "Chlorate" can also refer to chemical compounds containing this anion; chlorates are the salts of chloric acid. "Chlorate", when followed by a roman numeral in parentheses, e.g...
s and perchlorates are used for production of oxygen in chemical oxygen generator
Chemical oxygen generator
A chemical oxygen generator is a device releasing oxygen created by a chemical reaction. The oxygen source is usually an inorganic superoxide, chlorate, or perchlorate. A promising group of oxygen sources are ozonides. The generators are usually ignited mechanically, by a firing pin, and the...
s.
Sodium azide
Sodium azideSodium azide
Sodium azide is the inorganic compound with the formula NaN3. This colourless azide salt is the gas-forming component in many car airbag systems. It is used for the preparation of other azide compounds. It is an ionic substance and is highly soluble in water. It is extremely...
decomposes exothermically to sodium and nitrogen. The reaction is employed in some early designs of air bags.
- 2 NaN3 -> 2 Na + 3 N2
The resulting sodium is hazardous, so other materials are added, e.g. potassium nitrate and silica, to convert it to a silicate glass.