A propellant is a material that is used to move ("propel") an object. This will often involve a chemical reaction. It may be a
gas, liquid, plasma, or, before the chemical reaction, a solid.
Common chemical propellants consist of a fuel, like
gasoline, jet fueland rocket fuel, and an oxidizer.
aerosol spraycans, 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.)
Solid propellant rockets and projectiles
ballisticsand pyrotechnics, a propellant is a generic name for chemicals used for propelling projectiles from guns and other firearms.
Propellants are nearly always chemically different from
high explosives as used in shells and mines to produce a blasting effect. However, some explosive substances can be used both as propellants and as bursters, as for example gunpowder, and some of the ingredients of a propellant may be similar, though differently proportioned and combined, to those of an explosive.
A very typical propellant burns rapidly but controllably and "non" explosively, to produce
thrustby gas pressureand thus accelerates a projectileor rocket. In this sense, common or well known propellants include, for firearms, artilleryand solid propellant rockets:
*Gun propellants, such as:
Composite propellants made from a solid oxidizersuch as ammonium perchlorateor ammonium nitrate, a rubber such as HTPBor PBAN, and usually a powdered metal fuelsuch as aluminum.
*Some amateur propellants use
potassium nitrate, combined with sugar, epoxy, or other fuels / binder compounds.
Potassium perchloratehas been used as an oxidizer, paired with asphalt, epoxy, and other binders.
Propellants that explode in operation are of little practical use currently, although there have been experiments with
Pulse Detonation Engines.
Aircraft and rockets
Technically, the word propellant is the general name for chemicals used to create thrust. 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 lay public, 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.
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.
Common propellant combinations used for liquid propellant rockets include:
RFNAand keroseneor RP-1
Dinitrogen tetroxideand UDMH, MMHand/or Hydrazine
Liquid oxygenand keroseneor RP-1
Liquid oxygenand liquid hydrogen
Hydrogen Peroxideand alcoholor RP-1
Chlorine pentafluoride& Hydrazine
ources and references
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