Monopropellants are
propellants
A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the e ...
consisting of chemicals that release energy through exothermic chemical decomposition. The molecular bond energy of the monopropellant is released usually through use of a catalyst. This can be contrasted with bipropellants that release energy through the chemical reaction between an oxidizer and a fuel. While stable under defined storage conditions, monopropellants decompose very rapidly under certain other conditions to produce a large volume of its own energetic (hot) gases for the performance of mechanical work. Although solid
deflagrants such as
nitrocellulose
Nitrocellulose (also known as cellulose nitrate, flash paper, flash cotton, guncotton, pyroxylin and flash string, depending on form) is a highly flammable compound formed by nitrating cellulose through exposure to a mixture of nitric acid and ...
, the most commonly used propellant in firearms, could be thought of as monopropellants, the term is usually reserved for liquids in engineering literature.
Uses
The most common use of monopropellants
is in low-impulse
monopropellant
Monopropellants are propellants consisting of chemicals that release energy through exothermic chemical decomposition. The molecular bond energy of the monopropellant is released usually through use of a catalyst. This can be contrasted with bipro ...
rocket motor
A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propulsive jet of fluid, usually high-temperature gas. Rocket engines are reaction engines, producing thrust by ejecting mass rearward, in accordan ...
s, such as
reaction control thrusters, the usual propellant being
hydrazine
Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
[, p. 230] which is generally decomposed by exposure to an
iridium
Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density of ...
[, pp. 307—309] catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
bed (the hydrazine is pre-heated to keep the reactant liquid). This decomposition produces the desired jet of hot gas and thus
thrust
Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that syst ...
.
Hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%†...
has been used as a power source for propellant tank pumps in rockets like the German WWII
V-2
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 develope ...
and the American
Redstone. The
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%†...
is passed through a
platinum
Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver".
Platinu ...
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
mesh,
or comes in contact with
manganese dioxide impregnated ceramic beads, or
Z-Stoff
Z-Stoff (, "substance Z") was a name for calcium permanganate or sodium permanganate mixed in water. It was normally used as a catalyst for T-Stoff ( high-test peroxide) in military rocket programs by Nazi Germany during World War II.
Z-Stoff was ...
permanganate
A permanganate () is a chemical compound containing the manganate(VII) ion, , the conjugate base of permanganic acid. Because the manganese atom is in the +7 oxidation state, the permanganate(VII) ion is a strong oxidizing agent. The ion is a tra ...
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
A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating ...
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 (PGDN, ttup 1,2-propylene glycol dinitrate, or 1,2-propanediol 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 n ...
(
PGDN
Propylene glycol dinitrate (PGDN, ttup 1,2-propylene glycol dinitrate, or 1,2-propanediol 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 n ...
), 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 exoatmospheric 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 dinitrate is
isomer
In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers.
Iso ...
ic with
PGDN
Propylene glycol dinitrate (PGDN, ttup 1,2-propylene glycol dinitrate, or 1,2-propanediol 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 n ...
, and produced as a fractional byproduct in all but the most exacting laboratory conditions; the marginally lower
specific gravity
Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water (molecule), wa ...
(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
Diethylene glycol dinitrate (DEGDN) is an explosive nitration, nitrated Alcohol (chemistry), alcohol ester with the formula C4H8N2O7. While chemically similar to numerous other high explosives, pure diethylene glycol dinitrate is difficult to ig ...
in modern notation, was widely used in World War 2 Germany, both alone as a liquid monopropellant and
colloidal
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend ...
with
nitrocellulose
Nitrocellulose (also known as cellulose nitrate, flash paper, flash cotton, guncotton, pyroxylin and flash string, depending on form) is a highly flammable compound formed by nitrating cellulose through exposure to a mixture of nitric acid and ...
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
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends ...
(-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
Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past groupin ...
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 is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
,
ethylene oxide
Ethylene oxide is an organic compound with the chemical formula, formula . It is a cyclic ether and the simplest epoxide: a three-membered Ring (chemistry), ring consisting of one oxygen atom and two carbon atoms. Ethylene oxide is a colorless a ...
,
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%†...
(especially in its German World War II form as ''
T-Stoff
T-Stoff (; 'substance T') was a stabilised high test peroxide used in Germany during World War II. T-Stoff was specified to contain 80% (occasionally 85%) hydrogen peroxide (H2O2), remainder water, with traces (<0.1%) of stabilisers. Stabilisers ...
''), and
nitromethane
Nitromethane, sometimes shortened to simply "nitro", is an organic compound with the chemical formula . It is the simplest organic nitro compound. It is a polar liquid commonly used as a solvent in a variety of industrial applications such as in ...
are common rocket monopropellants. As noted the specific impulse of monopropellants is lower
than bipropellants and can be found with the Air Force Chemical Equilibrium Specific Impulse Code tool.
One newer monopropellant under development is
nitrous oxide
Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or nos, is a chemical compound, an oxide of nitrogen with the formula . At room temperature, it is a colourless non-flammable gas, and has a ...
, both neat and in the form of
nitrous oxide fuel blend
Nitrous oxide fuel blend propellants are a class of liquid rocket propellants that were intended in the early 2010s to be able to replace hydrazine as the standard storable rocket propellent in some applications.
In nitrous-oxide fuel blends, ...
s. Nitrous oxide offers the advantages of being self-pressurizing and of being relatively non-toxic, with a specific impulse intermediate between hydrogen peroxide and hydrazine.
Nitrous oxide
Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or nos, is a chemical compound, an oxide of nitrogen with the formula . At room temperature, it is a colourless non-flammable gas, and has a ...
generates oxygen upon decomposition, and it is possible to blend it with fuels to form a monopropellant mixture with a specific impulse up to 325 s, comparable to
hypergolic bipropellants.
Direct comparison of physical properties, performance, cost, storability, toxicity, storage requirements and accidental release measures for hydrogen peroxide,
hydroxylammonium nitrate
Hydroxylammonium nitrate or hydroxylamine nitrate (HAN) is an inorganic compound with the chemical formula H3OHNO3]. It is a salt derived from hydroxylamine and nitric acid. In its pure form, it is a colourless hygroscopic solid. It has potent ...
(HAN), hydrazine and various cold gas monopropellants shows that hydrazine is the highest performing in terms of specific impulse. However, hydrazine is also the most expensive and toxic. In addition HAN and hydrogen peroxide have the highest density impulse (total impulse per given unit volume).
See also
*
Monopropellant rocket
A monopropellant rocket (or "monochemical rocket") is a rocket that uses a single chemical as its propellant.
Chemical-reaction monopropellant rockets
For monopropellant rockets that depend on a chemical reaction, the power for the propulsive re ...
*
Nitrous oxide fuel blend
Nitrous oxide fuel blend propellants are a class of liquid rocket propellants that were intended in the early 2010s to be able to replace hydrazine as the standard storable rocket propellent in some applications.
In nitrous-oxide fuel blends, ...
*
Green Propellant Infusion Mission
The Green Propellant Infusion Mission (GPIM) was a NASA technology demonstrator project that tested a less toxic and higher specific impulse, performance/efficiency chemical propellant for next-generation launch vehicles and CubeSat spacecraft. ...
References
External links
*
* There is an entire chapter on the history of monopropellant development in the autobiography
* The book "Germany's Secret Weapons In World War Two" by Roger Ford ({{ISBN, 0-7603-0847-0 c.2000) contains some useful information on the surprising diversity of fuels and propellants employed by wartime Germany.
* "
The Chemistry Of Powder And Explosives" by
Tenney L. Davis is an outstanding, if outdated, source of information on a great many aspects of high enthalpy compounds. (This work originally published by MIT Press, 1943, as a textbook. Subsidy republication as late as 1995 by Pyrotek Inc., an amateur rocketry supply house. No catalog data given in this edition. Current publication status unknown.).
1999 Conference Paper on Historical Rocket Grade Hydrogen Peroxide Uses including monopropellant applications
Rocket propellants