Propellant
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 fuel and rocket fuel, and an oxidizer.
Aerosol sprays
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.)
Solid propellant rockets and projectiles
In ballistics and pyrotechnics, a propellant is a generic name for chemicals used for propelling projectiles from guns and other firearms.
Propellants may include high explosive chemical ingredients, but if so, the explosive compounds are diluted and burned in a controlled way to release their energy, rather than detonated or destructively blasted as in shells and mines. 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:
- Gun propellants, such as:
- Gunpowder (black powder)
- Nitrocellulose-based powders
- Cordite
- Ballistite
- Smokeless powders
- Composite propellants made from a solid oxidizer such as ammonium perchlorate or ammonium nitrate, a rubber such as HTPB, or PBAN (may be replaced by energetic polymers such as polyglycidyl nitrate or polyvinyl nitrate for extra energy) , optional high explosive fuels (again, for extra energy) such as RDX or nitroglycerin, and usually a powdered metal fuel such as aluminum.
- Some amateur propellants use potassium nitrate, combined with sugar, epoxy, or other fuels / binder compounds.
- Potassium perchlorate has 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.
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.
Common propellant combinations used for liquid propellant rockets include:
- RFNA and kerosene or RP-1
- RFNA and UDMH
- Dinitrogen tetroxide and UDMH, MMH and/or Hydrazine
- Liquid oxygen and kerosene or RP-1
- Liquid oxygen and liquid hydrogen
- Hydrogen Peroxide and alcohol or RP-1
- Chlorine pentafluoride & Hydrazine
Sources and references
(incomplete)
- This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press.
{{cite encyclopedia}}: Missing or empty|title=(help) - Clark, John D. (1972). Ignition! An Informal History of Liquid Rocket Propellants. Rutgers University Press. p. 214. ISBN 0813507251.
