Gas generator

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A gas generator is a device for generating gas. A gas generator may create gas by a chemical reaction or from a solid or liquid source, when storing a pressurized gas is undesirable or impractical.

Contents

The term often refers to a device that uses a rocket propellant to generate large quantities of gas. The gas is typically used to drive a turbine rather than to provide thrust as in a rocket engine. Gas generators of this type are used to power turbopumps in rocket engines, in a gas-generator cycle.

It is also used by some auxiliary power units to power electric generators and hydraulic pumps.

Another common use of the term is in the industrial gases industry, where gas generators are used to produce gaseous chemicals for sale. For example, the chemical oxygen generator, which delivers breathable oxygen at a controlled rate over a prolonged period. During World War II, portable gas generators that converted coke to producer gas were used to power vehicles as a way of alleviating petrol shortages.

Other types include the gas generator in an automobile airbag, which is designed to rapidly produce a specific quantity of inert gas.

Common applications

As a power source

The V-2 rocket used hydrogen peroxide decomposed by a liquid sodium permanganate catalyst solution as a gas generator. This was used to drive a turbopump to pressurize the main LOX-ethanol propellants. [1] In the Saturn V F-1 [2] [3] and Space Shuttle main engine, [4] some of the main propellant was burned to drive the turbopump (see gas-generator cycle and staged combustion cycle). The gas generator in these designs uses a highly fuel-rich mix to keep flame temperatures relatively low.

The Space Shuttle auxiliary power unit [5] and the F-16 emergency power unit (EPU) [6] [7] use hydrazine as a fuel. The gas drives a turbine which drives hydraulic pumps. In the F-16 EPU it also drives an electric generator.

Gas generators have also been used to power torpedoes. For example, the US Navy Mark 16 torpedo was powered by hydrogen peroxide. [8]

A concentrated solution of hydrogen peroxide is known as high-test peroxide and decomposes to produce oxygen and water (steam).

Hydrazine decomposes to nitrogen and hydrogen. The reaction is strongly exothermic and produces high volume of hot gas from small volume of liquid.

Many solid rocket propellant compositions can be used as gas generators. [9]

Inflation and fire suppression

Many automobile airbags use sodium azide for inflation (as of 2003). [10] A small pyrotechnic charge triggers its decomposition, producing nitrogen gas, which inflates the airbag in around 30 milliseconds. A typical airbag in the US might contain 130 grams of sodium azide. [11]

Similar gas generators are used for fire suppression. [12]

Sodium azide decomposes exothermically to sodium and nitrogen.

The resulting sodium is hazardous, so other materials are added, e.g. potassium nitrate and silica, to convert it to a silicate glass.

Oxygen generation

A chemical oxygen generator delivers breathable oxygen at a controlled rate over a prolonged period. Sodium, potassium, and lithium chlorates and perchlorates are used.

Generation of fuel gas

A device that converts coke or other carbonaceous material into producer gas may be used as a source of fuel gas for industrial use. Portable gas generators of this type were used during World War II to power vehicles as a way of alleviating petrol shortages. [13]

See also

Related Research Articles

<span class="mw-page-title-main">Hydrogen peroxide</span> Chemical compound

Hydrogen peroxide is a chemical compound with the formula H2O2. In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution in water for consumer use, and in higher concentrations for industrial use. Concentrated hydrogen peroxide, or "high-test peroxide", decomposes explosively when heated and has been used both as a monopropellant and an oxidizer in rocketry.

<span class="mw-page-title-main">Nitrogen</span> Chemical element, symbol N and atomic number 7

Nitrogen is a chemical element; it has symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh in total abundance in the Milky Way and the Solar System. At standard temperature and pressure, two atoms of the element bond to form N2, a colorless and odorless diatomic gas. N2 forms about 78% of Earth's atmosphere, making it the most abundant uncombined element in air. Because of the volatility of nitrogen compounds, nitrogen is relatively rare in the solid parts of the Earth.

<span class="mw-page-title-main">Turbopump</span> Pump driven by a gas turbine

A turbopump is a propellant pump with two main components: a rotodynamic pump and a driving gas turbine, usually both mounted on the same shaft, or sometimes geared together. They were initially developed in Germany in the early 1940s. The purpose of a turbopump is to produce a high-pressure fluid for feeding a combustion chamber or other use. While other use cases exist, they are most commonly found in liquid rocket engines.

<span class="mw-page-title-main">Hybrid-propellant rocket</span> Rocket engine that uses both liquid / gaseous and solid fuel

A hybrid-propellant rocket is a rocket with a rocket motor that uses rocket propellants in two different phases: one solid and the other either gas or liquid. The hybrid rocket concept can be traced back to the early 1930s.

<span class="mw-page-title-main">Hydrazine</span> Colorless flammable liquid with an ammonia-like odor

Hydrazine is an inorganic compound with the chemical formula N2H4. It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine hydrate.

<span class="mw-page-title-main">Hypergolic propellant</span> Type of rocket engine fuel

A hypergolic propellant is a rocket propellant combination used in a rocket engine, whose components spontaneously ignite when they come into contact with each other.

In chemistry, azide is a linear, polyatomic anion with the formula N−3 and structure N=N+=N. It is the conjugate base of hydrazoic acid HN3. Organic azides are organic compounds with the formula RN3, containing the azide functional group. The dominant application of azides is as a propellant in air bags.

T-Stoff (; 'substance T') was a stabilised high test peroxide used in Germany during World War II. T-Stoff was specified to contain 80% (occasionally 85%) hydrogen peroxide (H2O2), remainder water, with traces (<0.1%) of stabilisers. Stabilisers used included 0.0025% phosphoric acid, a mixture of phosphoric acid, sodium phosphate and 8-oxyquinoline, and sodium stannate.

<span class="mw-page-title-main">Liquid-propellant rocket</span> Rocket engine that uses liquid fuels and oxidizers

A liquid-propellant rocket or liquid rocket utilizes a rocket engine that uses liquid propellants. Gaseous propellants may also be used but are not common because of their low density and difficulty with common pumping methods. Liquids are desirable because they have a reasonably high density and high specific impulse (Isp). This allows the volume of the propellant tanks to be relatively low. The rocket propellants are usually pumped into the combustion chamber with a lightweight centrifugal turbopump, although some aerospace companies have found ways to use electric pumps with batteries, allowing the propellants to be kept under low pressure. This permits the use of low-mass propellant tanks that do not need to resist the high pressures needed to store significant amounts of gasses, resulting in a low mass ratio for the rocket.

<span class="mw-page-title-main">Rocketdyne J-2</span> Rocket engine

The J-2, commonly known as Rocketdyne J-2, was a liquid-fuel cryogenic rocket engine used on NASA's Saturn IB and Saturn V launch vehicles. Built in the United States by Rocketdyne, the J-2 burned cryogenic liquid hydrogen (LH2) and liquid oxygen (LOX) propellants, with each engine producing 1,033.1 kN (232,250 lbf) of thrust in vacuum. The engine's preliminary design dates back to recommendations of the 1959 Silverstein Committee. Rocketdyne won approval to develop the J-2 in June 1960 and the first flight, AS-201, occurred on 26 February 1966. The J-2 underwent several minor upgrades over its operational history to improve the engine's performance, with two major upgrade programs, the de Laval nozzle-type J-2S and aerospike-type J-2T, which were cancelled after the conclusion of the Apollo program.

High-test peroxide (HTP) is a highly concentrated solution of hydrogen peroxide, with the remainder consisting predominantly of water. In contact with a catalyst, it decomposes into a high-temperature mixture of steam and oxygen, with no remaining liquid water. It was used as a propellant of HTP rockets and torpedoes, and has been used for high-performance vernier engines.

The highest specific impulse chemical rockets use liquid propellants. They can consist of a single chemical or a mix of two chemicals, called bipropellants. Bipropellants can further be divided into two categories; hypergolic propellants, which ignite when the fuel and oxidizer make contact, and non-hypergolic propellants which require an ignition source.

<span class="mw-page-title-main">Sodium azide</span> Chemical compound

Sodium azide is an inorganic compound with the formula NaN3. This colorless salt is the gas-forming component in some car airbag systems. It is used for the preparation of other azide compounds. It is an ionic substance, is highly soluble in water, and is very acutely poisonous.

<span class="mw-page-title-main">Staged combustion cycle</span> Rocket engine operation method

The staged combustion cycle is a power cycle of a bipropellant rocket engine. In the staged combustion cycle, propellant flows through multiple combustion chambers, and is thus combusted in stages. The main advantage relative to other rocket engine power cycles is high fuel efficiency, measured through specific impulse, while its main disadvantage is engineering complexity.

Chemical decomposition, or chemical breakdown, is the process or effect of simplifying a single chemical entity into two or more fragments. Chemical decomposition is usually regarded and defined as the exact opposite of chemical synthesis. In short, the chemical reaction in which two or more products are formed from a single reactant is called a decomposition reaction.

<span class="mw-page-title-main">Hydrazoic acid</span> Unstable and toxic chemical compound

Hydrazoic acid, also known as hydrogen azide, azic acid or azoimide, is a compound with the chemical formula HN3. It is a colorless, volatile, and explosive liquid at room temperature and pressure. It is a compound of nitrogen and hydrogen, and is therefore a pnictogen hydride. The oxidation state of the nitrogen atoms in hydrazoic acid is fractional and is -1/3. It was first isolated in 1890 by Theodor Curtius. The acid has few applications, but its conjugate base, the azide ion, is useful in specialized processes.

<span class="mw-page-title-main">Guanidine nitrate</span> Chemical compound

Guanidine nitrate is the chemical compound with the formula [C(NH2)3]NO3. It is a colorless, water-soluble salt. It is produced on a large scale and finds use as precursor for nitroguanidine, fuel in pyrotechnics and gas generators. Its correct name is guanidinium nitrate, but the colloquial term guanidine nitrate is widely used.

The chemical element nitrogen is one of the most abundant elements in the universe and can form many compounds. It can take several oxidation states; but the most common oxidation states are -3 and +3. Nitrogen can form nitride and nitrate ions. It also forms a part of nitric acid and nitrate salts. Nitrogen compounds also have an important role in organic chemistry, as nitrogen is part of proteins, amino acids and adenosine triphosphate.

Fastrac was a turbo pump-fed, liquid rocket engine. The engine was designed by NASA as part of the low cost X-34 Reusable Launch Vehicle (RLV) and as part of the Low Cost Booster Technology project. This engine was later known as the MC-1 engine when it was merged into the X-34 project.

<span class="mw-page-title-main">Rocket propellant</span> Chemical or mixture used as fuel for a rocket engine

Rocket propellant is the reaction mass of a rocket. This reaction mass is ejected at the highest achievable velocity from a rocket engine to produce thrust. The energy required can either come from the propellants themselves, as with a chemical rocket, or from an external source, as with ion engines.

References

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  2. Sutton, George P. (1992). Rocket Propulsion Elements (6th ed.). Wiley. pp. 212–213. ISBN   0-471-52938-9.
  3. "F-1 Engine Fact Sheet" (PDF). NASA. Archived from the original (PDF) on 2016-04-13.
  4. "Main Propulsion System (MPS)" (PDF). Shuttle Press Kit.com. Boeing, NASA & United Space Alliance. October 6, 1998. Archived from the original (PDF) on 2012-02-04. Retrieved December 7, 2011.
  5. "Auxiliary Power Units". Human Space Flight - The Shuttle. Archived from the original on 2001-05-04. Retrieved 2016-09-26.
  6. Suggs; Luskus; Kilian; Mokry (1979). Exhaust Gas Composition of the F-16 Emergency Power Unit (Report). USAF school of aerospace medicine. SAM-TR-79. Archived from the original on June 3, 2018.
  7. "F-16 chemical leak sends 6 airmen to hospital". Air Force Times. Associated press. August 26, 2016. Retrieved 2016-09-23.
  8. Jolie, E.W. (1978). A Brief History of U.S. Navy Torpedo Development (Report). Naval Underwater Systems Center, Newport. p. 83 via Maritime.Org.
  9. Sutton 1992 , pp. 441–443
  10. Betterton, Eric A. (2003). "Environmental Fate of Sodium Azide Derived from Automobile Airbags (Abstract)". Critical Reviews in Environmental Science and Technology. 33 (4): 423–458. doi:10.1080/10643380390245002. S2CID   96404307.
  11. "How do air bags work?". Scientific American. Retrieved 2016-09-22.
  12. Yang, Jiann C.; Grosshandler, William L. (28 June 1995). Solid Propellant Gas Generators: An Overview and Their Application to Fire Suppression (Report). NIST. NISTIR 5766.
  13. Lord Barnby (1941-07-16). "PRODUCER GAS FOR TRANSPORT. (Hansard, 16 July 1941)". Parliamentary Debates (Hansard) . Retrieved 2014-05-26.