Monopropellant
Encyclopedia
Monopropellants are propellants composed of chemicals or mixtures of chemicals which can be stored in a single container with some degree of safety. While stable under defined storage conditions, they react very rapidly under certain other conditions to produce a large volume of energetic (hot) gases for the performance of mechanical work. Although solid deflagrants such as nitrocellulose
, the most commonly used propellant in firearms, and ammonium perchlorate
/aluminum/synthetic rubber
, widely used in military and spacecraft boosters, could be thought of as monopropellants, the term is usually reserved for liquids in engineering literature. These can either be a single chemical that can be made to decompose exothermically, or a mixture of chemicals (generally a fuel
and an oxidizer) that can be made to react with one another to release energy.
http://www.aerojet.com/capabilities/spacecraft.php which is generally decomposed by exposure to an iridium
http://www.aerojet.com/news2.php?action=fullnews&id=153 catalyst bed (Hydrazine is pre-heated to keep reactant liquid) to produce the desired jet of hot gas and thus thrust
. Hydrogen peroxidehttp://www.hq.nasa.gov/pao/History/conghand/propulsn.htm has been used for main thrusters and as power source for propellant tank pumps in rockets like the German WWII V-2
(same as US Redstone rocket), ch. 7.. The hydrogen peroxide
is passed through a platinum
catalyst meshhttp://www.hq.nasa.gov/pao/History/conghand/propulsn.htm, or comes in contact with manganese dioxide impregnated ceramic beads, or Z-Stoff
permanganate
solution is co-injected, which causes hydrogen peroxide to decompose into hot steam and oxygen.
Monopropellants are also used in some air-independent propulsion
systems (AIP) to "fuel" reciprocating or turbine
engines in environments where free oxygen is unavailable. Weapons intended primarily for combat between nuclear powered submarines generally fall into this category. The most commonly used propellant in this case is stabilized propylene glycol dinitrate
(PGDN), often referred to as "Otto fuel
". A potential future use for monopropellants not directly related to propulsion is in compact, high-intensity powerplants for aquatic or exoatmosperic environments.
Many partially nitrated alcohol esters are suitable for use as monopropellants. "Trimethylene glycol dinitrate" or 1,3-propanediol
dinitrate is isomer
ic with PGDN, and produced as a fractional byproduct in all but the most exacting laboratory conditions; the marginally lower specific gravity
(and thus energy density
) of this compound argues against its use, but the minor differences in chemistry may prove useful in the future.
The related "dinitrodiglycol", more properly termed diethylene glycol dinitrate
in modern notation, was widely used in World War 2 Germany, both alone as a liquid monopropellant and colloidal with nitrocellulose
as a solid propellant. The otherwise desirable characteristics of this compound; it is quite stable, easy to manufacture, and has a very high energy density; are marred by a high freeze point (-11.5 deg. C) and pronounced thermal expansion, both being problematic in spacecraft. "Dinitrochlorohydrin" and "tetranitrodiglycerin" are also likely candidates, though no current use is known. The polynitrates of long chain and aromatic hydrocarbons are invariably room temperature solids, but many are soluble in simple alcohols or ethers in high proportion, and may be useful in this state.
Hydrazine
http://cs.astrium.eads.net/sp/SpacecraftPropulsion/MonopropellantThrusters.html, ethylene oxide
http://www.rocketmotorparts.com/resources/ethylene_oxide.pdf, hydrogen peroxide
http://www.rocketmotorparts.com/resources/h2o2.pdf, and nitromethane
http://www.rocketmotorparts.com/resources/nitromethane.pdf are common rocket monopropellants. As noted the specific impulse of monopropellants is lowerhttp://www.hq.nasa.gov/pao/History/conghand/propelnt.htm, p. 36 than bipropellants and can be found with the Air Force Chemical Equilibrium Specific Impulse Code tool.http://www.rocketmotorparts.com/pdfs/AFCESIC.exe
Newer monopropellants include nitrous oxide fuel blend
s. Nitrous oxide
may be blended with a range of different fuels and emulsifiers and used as a rocket monopropellant.
Nitrous oxide monopropellants decompose into oxygen-rich air, and they require no separate supply of oxidizer such as the liquid oxygen
used in many high performance rocket engines today.
Nitrocellulose
Nitrocellulose is a highly flammable compound formed by nitrating cellulose through exposure to nitric acid or another powerful nitrating agent. When used as a propellant or low-order explosive, it is also known as guncotton...
, the most commonly used propellant in firearms, and ammonium perchlorate
Ammonium perchlorate
Ammonium perchlorate is an inorganic compound with the formula NH4ClO4. It is the salt of perchloric acid and ammonia. It is a powerful oxidizer, which is why its main use is in solid propellants...
/aluminum/synthetic rubber
Synthetic rubber
Synthetic rubber is is any type of artificial elastomer, invariably a polymer. An elastomer is a material with the mechanical property that it can undergo much more elastic deformation under stress than most materials and still return to its previous size without permanent deformation...
, widely used in military and spacecraft boosters, could be thought of as monopropellants, the term is usually reserved for liquids in engineering literature. These can either be a single chemical that can be made to decompose exothermically, or a mixture of chemicals (generally a fuel
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...
and an oxidizer) that can be made to react with one another to release energy.
Uses
The most common use of monopropellantshttp://www.hq.nasa.gov/pao/History/conghand/propelnt.htm is in low-impulse rocket motorshttp://www.rocketmotorparts.com/resources.html, such as reaction control thrusters, the usual propellant being hydrazineHydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
http://www.aerojet.com/capabilities/spacecraft.php which is generally decomposed by exposure to an iridium
Iridium
Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...
http://www.aerojet.com/news2.php?action=fullnews&id=153 catalyst bed (Hydrazine is pre-heated to keep reactant liquid) to produce the desired jet of hot gas and thus thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
. Hydrogen peroxidehttp://www.hq.nasa.gov/pao/History/conghand/propulsn.htm has been used for main thrusters and as power source for propellant tank pumps in rockets like the German WWII V-2
V-2 rocket
The V-2 rocket , technical name Aggregat-4 , was a ballistic missile that was developed at the beginning of the Second World War in Germany, specifically targeted at London and later Antwerp. The liquid-propellant rocket was the world's first long-range combat-ballistic missile and first known...
(same as US Redstone rocket), ch. 7.. The hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
is passed through a platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
catalyst meshhttp://www.hq.nasa.gov/pao/History/conghand/propulsn.htm, or comes in contact with manganese dioxide impregnated ceramic beads, or Z-Stoff
Z-Stoff
Z-Stoff was a name for calcium permanganate or potassium permanganate mixed in water. It was normally used as a catalyst for T-Stoff in military rocket programs by Nazi Germany during World War II....
permanganate
Permanganate
A permanganate is the general name for a chemical compound containing the manganate ion, . Because manganese is in the +7 oxidation state, the permanganate ion is a strong oxidizing agent. The ion has tetrahedral geometry...
solution is co-injected, which causes hydrogen peroxide to decompose into hot steam and oxygen.
Monopropellants are also used in some air-independent propulsion
Air-independent propulsion
Air-independent propulsion is a term that encompasses technologies which allow a submarine to operate without the need to surface or use a snorkel to access atmospheric oxygen. The term usually excludes the use of nuclear power, and describes augmenting or replacing the diesel-electric propulsion...
systems (AIP) to "fuel" reciprocating or turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...
engines in environments where free oxygen is unavailable. Weapons intended primarily for combat between nuclear powered submarines generally fall into this category. The most commonly used propellant in this case is stabilized propylene glycol dinitrate
Propylene glycol dinitrate
Propylene glycol dinitrate is an organic chemical, an ester of nitric acid and propylene glycol. It is structurally similar to nitroglycerin, except that it has one fewer -O-NO2 group...
(PGDN), often referred to as "Otto fuel
Otto fuel II
Otto fuel II is a monopropellant used to drive torpedoes and other weapon systems. It is not related to the Otto cycle.-Properties:This distinct-smelling, reddish-orange, oily liquid is a mixture of three synthetic substances: propylene glycol dinitrate , 2-nitrodiphenylamine, and dibutyl...
". A potential future use for monopropellants not directly related to propulsion is in compact, high-intensity powerplants for aquatic or exoatmosperic environments.
Research in brief
Much work was done in the US in the 1950s and 1960s to attempt to find better and more energetic monopropellants. For the most part, researchers came to the conclusion that any single substance that contained enough energy to compete with bipropellants would be too unstable to handle safely under practical conditions. With new materials, control systems and requirements for high-performance thrusters, engineers are currently re-examining this assumption.Many partially nitrated alcohol esters are suitable for use as monopropellants. "Trimethylene glycol dinitrate" or 1,3-propanediol
1,3-Propanediol
1,3-Propanediol is the organic compound with the formula CH22. This three-carbon diol is a colorless viscous liquid that is miscible with water.-Products:...
dinitrate is isomer
Isomer
In chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...
ic with PGDN, and produced as a fractional byproduct in all but the most exacting laboratory conditions; the marginally lower specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...
(and thus energy density
Energy density
Energy density is a term used for the amount of energy stored in a given system or region of space per unit volume. Often only the useful or extractable energy is quantified, which is to say that chemically inaccessible energy such as rest mass energy is ignored...
) of this compound argues against its use, but the minor differences in chemistry may prove useful in the future.
The related "dinitrodiglycol", more properly termed diethylene glycol dinitrate
Diethylene glycol dinitrate
Diethylene glycol dinitrate is a nitrated alcohol ester produced by the action of concentrated nitric acid, normally admixed with an excess of strong sulfuric acid as a dehydrating agent, upon diethylene glycol....
in modern notation, was widely used in World War 2 Germany, both alone as a liquid monopropellant and colloidal with nitrocellulose
Nitrocellulose
Nitrocellulose is a highly flammable compound formed by nitrating cellulose through exposure to nitric acid or another powerful nitrating agent. When used as a propellant or low-order explosive, it is also known as guncotton...
as a solid propellant. The otherwise desirable characteristics of this compound; it is quite stable, easy to manufacture, and has a very high energy density; are marred by a high freeze point (-11.5 deg. C) and pronounced thermal expansion, both being problematic in spacecraft. "Dinitrochlorohydrin" and "tetranitrodiglycerin" are also likely candidates, though no current use is known. The polynitrates of long chain and aromatic hydrocarbons are invariably room temperature solids, but many are soluble in simple alcohols or ethers in high proportion, and may be useful in this state.
Hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
http://cs.astrium.eads.net/sp/SpacecraftPropulsion/MonopropellantThrusters.html, ethylene oxide
Ethylene oxide
Ethylene oxide, also called oxirane, is the organic compound with the formula . It is a cyclic ether. This means that it is composed of two alkyl groups attached to an oxygen atom in a cyclic shape . This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered...
http://www.rocketmotorparts.com/resources/ethylene_oxide.pdf, hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
http://www.rocketmotorparts.com/resources/h2o2.pdf, and nitromethane
Nitromethane
Nitromethane is an organic compound with the chemical formula . It is the simplest organic nitro compound. It is a slightly viscous, highly polar liquid commonly used as a solvent in a variety of industrial applications such as in extractions, as a reaction medium, and as a cleaning solvent...
http://www.rocketmotorparts.com/resources/nitromethane.pdf are common rocket monopropellants. As noted the specific impulse of monopropellants is lowerhttp://www.hq.nasa.gov/pao/History/conghand/propelnt.htm, p. 36 than bipropellants and can be found with the Air Force Chemical Equilibrium Specific Impulse Code tool.http://www.rocketmotorparts.com/pdfs/AFCESIC.exe
Newer monopropellants include nitrous oxide fuel blend
Nitrous oxide fuel blend
Nitrous Oxide Fuel Blend propellants are a class of liquid rocket propellants. The fuel and oxidizer are blended and stored, and are sometimes referred to as 'mixed monopropellants'. Upon use, the propellant is heated or passed over a catalyst bed and the Nitrous oxide decompose into oxygen-rich...
s. Nitrous oxide
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
may be blended with a range of different fuels and emulsifiers and used as a rocket monopropellant.
Nitrous oxide monopropellants decompose into oxygen-rich air, and they require no separate supply of oxidizer such as the liquid oxygen
Liquid oxygen
Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...
used in many high performance rocket engines today.