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 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 In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can al ...

as in a

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

. 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 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 World War II by country, vast majority of the world's countries—including all of the great power ...

, 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 c ...

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 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 Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a h ...

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 three stages, and powered with liquid fuel. It was flown from 1 ...

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 gas-generator cycle and

staged combustion cycle The staged combustion cycle (sometimes known as topping cycle, preburner cycle, or closed cycle) is a power cycle of a bipropellant rocket engine. In the staged combustion cycle, propellant flows through multiple combustion chambers, and is ...

). The gas generator in these designs uses a highly fuel-rich mix to keep flame temperatures relatively low. The Space Shuttle auxiliary power unit and the

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

emergency 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&n ...

(EPU) 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

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, s ...

es. For example, the US Navy

Mark 16 torpedo The Mark 16 torpedo was a redesign of the United States Navy's standard Mark 14 torpedo in use during World War II. It incorporated war-tested improvements into a weapon designed to be used in unmodified United States fleet submarines. Due to high ...

was powered by hydrogen peroxide. A concentrated solution of hydrogen peroxide is known as high-test peroxide and decomposes to produce oxygen and water (steam). : 2 H2O2 -> 2 H2O + O2 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 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 seve ...

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

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

to power vehicles as a way of alleviating

shortages.

References