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. The term often refers to a device that uses a

rocket propellant Rocket propellant is the reaction mass of a rocket. This reaction mass is ejected at the highest achievable velocity from a rocket engine A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propuls ...

to generate large quantities of gas. The gas is typically used to drive a turbine rather than to provide

thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that syst ...

as in a

rocket engine A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propulsive jet of fluid, usually high-temperature gas. Rocket engines are reaction engines, producing thrust by ejecting mass rearward, in accordanc ...

. Gas generators of this type are used to power

turbopump 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 purpo ...

s in rocket engines, in a

gas-generator cycle The gas-generator cycle is a power cycle of a pumped liquid bipropellant rocket engine. Part of the unburned propellant is burned in a gas generator (or preburner) and the resulting hot gas is used to power the propellant pumps before being exh ...

. It is also used by some

auxiliary power unit An auxiliary power unit (APU) is a device on a vehicle that provides energy for functions other than propulsion. They are commonly found on large aircraft and naval ships as well as some large land vehicles. Aircraft APUs generally produce 115& ...

s to power

electric generator In electricity generation, a generator is a device that converts motive power (mechanical energy) or fuel-based power (chemical energy) into electric power for use in an external circuit. Sources of mechanical energy include steam turbines, gas ...

s 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 A chemical oxygen generator is a device that releases oxygen via a chemical reaction. The oxygen source is usually an inorganic superoxide, chlorate, or perchlorate; ozonides are a promising group of oxygen sources. The generators are usually ig ...

, which delivers breathable oxygen at a controlled rate over a prolonged period. During

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

, portable gas generators that converted coke to producer gas were used to power vehicles as a way of alleviating

petrol Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic co ...

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 The V-2 (german: Vergeltungswaffe 2, lit=Retaliation Weapon 2), with the technical name ''Aggregat 4'' (A-4), was the world’s first long-range guided ballistic missile. The missile, powered by a liquid-propellant rocket engine, was develop ...

used

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . 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 (3%� ...

decomposed by a liquid

sodium permanganate Sodium permanganate is the inorganic compound with the formula Na MnO4. It is closely related to the more commonly encountered potassium permanganate, but it is generally less desirable, because it is more expensive to produce. It is mainly avai ...

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

solution as a gas generator. This was used to drive a

to pressurize the main

LOX Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries—is the liquid form of molecular oxygen. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an appli ...

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...

propellants. In the

Saturn V Saturn V is a retired American super heavy-lift launch vehicle developed by NASA under the Apollo program for human exploration of the Moon. The rocket was human-rated, with multistage rocket, three stages, and powered with liquid-propellant r ...

F-1 and

Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...

main engine, some of the main propellant was burned to drive the turbopump (see

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

and the

F-16 The General Dynamics F-16 Fighting Falcon is a single-engine Multirole combat aircraft, multirole fighter aircraft originally developed by General Dynamics for the United States Air Force (USAF). Designed as an air superiority day fighter, it ...

emergency power unit (EPU) use

hydrazine Hydrazine is an inorganic compound with the chemical formula . 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 ...

as a fuel. The gas drives a turbine which drives hydraulic pumps. In the F-16 EPU it also drives an

. Gas generators have also been used to power

torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, and with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, su ...

es. For example, the US Navy Mark 16 torpedo was powered by

. A concentrated solution of

is known as

high-test peroxide High-test peroxide (HTP) is a highly concentrated (85 to 98%) 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 n ...

and decomposes to produce oxygen and water (steam). : 2 H2O2 -> 2 H2O + O2

Hydrazine Hydrazine is an inorganic compound with the chemical formula . 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 ...

decomposes to nitrogen and hydrogen. The reaction is strongly exothermic and produces high volume of hot gas from small volume of liquid. # 3 N2H4 -> 4 NH3 + N2 # N2H4 -> N2 + 2 H2 # 4 NH3 + N2H4 -> 3 N2 + 8 H2 Many

solid rocket propellant 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 ...

compositions can be used as gas generators.

Inflation and fire suppression

Many automobile airbags use sodium azide for inflation (). A small pyrotechnic charge triggers its decomposition, producing

nitrogen Nitrogen is the chemical element with the 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 se ...

gas, which inflates the airbag in around 30 milliseconds. A typical airbag in the US might contain 130 grams of sodium azide. Similar gas generators are used for fire suppression. Sodium azide decomposes exothermically to sodium and nitrogen. : 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.

Oxygen generation

delivers breathable oxygen at a controlled rate over a prolonged period. Sodium, potassium, and lithium

chlorate The chlorate anion has the formula ClO3-. 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 ...

s and

perchlorate A perchlorate is a chemical compound containing the perchlorate ion, . The majority of perchlorates are commercially produced salts. They are mainly used as oxidizers for pyrotechnic devices and to control static electricity in food packaging. Per ...

s 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

to power vehicles as a way of alleviating

shortages.

References