A propellant is a material that produces pressurized gas that:
Common chemical propellants are energetic materials and consist of a fuel; like gasoline, jet fuel, rocket fuel, and an oxidizer. Chemical propellants are burned or otherwise decomposed to produce the propellant gas. Other propellants are simply liquids that can readily be vaporized into the desired pressurized gas. Such propellants include the nitrous oxide that is dissolved in the butterfat canned whipped cream, and the dimethyl ether or low-boiling alkane used in hairspray.
Propellants are used in pressurised dispensing systems, such as aerosol sprays, to force a material through a nozzle.
In rockets, the propellant produces an exhaust and the exhausted material is usually expelled under pressure through a nozzle. The pressure may be from a compressed gas, or a gas produced by a chemical reaction. The exhaust material may be a gas, liquid, plasma, or, before the chemical reaction, a solid, liquid or gelled.
In aircraft, the propellant is usually a fuel and is combusted to generate energy to power the aircraft's flight.
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In aerosol spray cans, the propellant is simply a pressurized gas in equilibrium with its liquid (at its saturated vapour pressure). As some gas escapes to expel the payload, more liquid evaporates, maintaining an even pressure. (See aerosol spray propellant for more information.)
Technically, the word propellant is the general name for chemicals used to create thrust. For vehicles, the term propellant refers only to chemicals that are stored within the vehicle prior to use, and excludes atmospheric gas or other material that may be collected in operation.
Amongst the English-speaking laymen, used to having fuels propel vehicles on Earth, the word fuel is inappropriately used. In Germany, the word Treibstoff—literally "drive-stuff"—is used; in France, the word ergols is used; it has the same Greek roots as hypergolic, a term used in English for propellants which combine spontaneously and do not have to be set ablaze by auxiliary ignition system.
In rockets, the most common combinations are bipropellants, which use two chemicals, a fuel and an oxidiser. There is the possibility of a tripropellant combination, which takes advantage of the ability of substances with smaller atoms to attain a greater exhaust velocity, and hence propulsive efficiency, at a given temperature.
Although not used in practice, the most developed tripropellant systems involves adding a third propellant tank containing liquid hydrogen to do this.
In ballistics and pyrotechnics, a propellant is a generic name for chemicals used for propelling projectiles from guns and other firearms.
Propellants are usually made from low explosive materials, but may include high explosive chemical ingredients that are diluted and burned in a controlled way (deflagration) rather than detonation. The controlled burning of the propellant composition usually produces thrust by gas pressure and can accelerate a projectile, rocket, or other vehicle. In this sense, common or well known propellants include, for firearms, artillery and solid propellant rockets:
Propellants that explode in operation are of little practical use currently, although there have been experiments with Pulse Detonation Engines.
Propellants are used in forms called grains. A grain is any individual particle of propellant regardless of the size or shape. The shape and size of a propellant grain determines the burn time, amount of gas and rate produced from the burning propellant and consequently thrust vs time profile.
There are three types of burns that can be achieved with different grains.
There are four different types of solid propellant compositions:
Common propellant combinations used for liquid propellant rockets include:
Common monopropellant used for liquid rocket engines include:
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