Otto fuel II is a

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 biprop ...

mixture of chiefly

propylene glycol dinitrate Propylene glycol dinitrate (PGDN, 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 nitrat ...

(an

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

and

propylene glycol Propylene glycol ( IUPAC name: propane-1,2-diol) is a viscous, colorless liquid. It is almost odorless and has a faintly sweet taste. Its chemical formula is CH3CH(OH)CH2OH. As it contains two alcohol groups, it is classified as a diol. An al ...

, and structurally similar to

nitroglycerin Nitroglycerin (NG) (alternative spelling nitroglycerine), also known as trinitroglycerol (TNG), nitro, glyceryl trinitrate (GTN), or 1,2,3-trinitroxypropane, is a dense, colorless or pale yellow, oily, explosive liquid most commonly produced by ...

) that is used to drive

torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, such ...

es and other weapon systems. It was invented by Otto Reitlinger in 1963 (although tests with the substance had taken place before, for example in 1960). Otto fuel II, sometimes known simply as Otto fuel, is not related to the

Otto cycle An Otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical spark ignition piston engine. It is the thermodynamic cycle most commonly found in automobile engines. The Otto cycle is a description of what happ ...

; it is named after Reitlinger and for being the second iteration of the fuel. It was developed by the US Navy and the first torpedo to use it was the

Mark 48 torpedo The Mark 48 and its improved Advanced Capability (ADCAP) variant are American heavyweight submarine-launched torpedoes. They were designed to sink deep-diving nuclear-powered submarines and high-performance surface ships. History The Mark 48 wa ...

in the 1960s.

Properties

Otto fuel II is a distinct-smelling (described by submariners as being similar in smell to wintergreen oil; i.e. sweet, fruity and minty), reddish-orange, oily liquid that is a mixture of three synthetic substances:

(the major component), 2-nitrodiphenylamine, and

dibutyl sebacate Dibutyl sebacate (DBS) is an organic chemical, a di butyl ester of sebacic acid. Its main use is as a plasticizer in production of plastics, namely cellulose acetate butyrate, cellulose acetate propionate, ethyl cellulose, polyvinyl butyr ...

. It does not need exposure to any

oxidant An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or "Electron acceptor, accepts"/"receives" an electron from a (called the , , or ''electr ...

to ignite and release energy, as its three components will react among themselves whenever vaporised and heated. Needing no oxidants and being a stable substance makes Otto fuel II ideal for use in the constrained environment of a submarine. Although the fuel can be made to explode, this requires such extreme conditions that it can be regarded as practically stable. The

vapour pressure Vapor pressure or equilibrium vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indicat ...

of the fuel is low (i.e., it is not volatile), minimizing toxic hazards. Finally, the fuel's

energy density In physics, energy density is the quotient between the amount of energy stored in a given system or contained in a given region of space and the volume of the system or region considered. Often only the ''useful'' or extractable energy is measure ...

far surpasses the capacity of the

electric battery An electric battery is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices. When a battery is supplying power, its positive Terminal (electronics), terminal is the ...

used in other torpedoes, maximizing range.

Major ingredients

Named after its inventor, Otto Reitlinger, Otto fuel II consists of the nitrated

explosive

propellant A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or another motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicle ...

(PGDN), to which a desensitizer (

) and a stabilizer ( 2-nitrodiphenylamine) have been added. The chief component, propylene glycol dinitrate, accounts for approximately 76% of the mixture, while dibutyl sebacate and 2-nitrodiphenylamine account for approximately 22.5% and 1.5% (by weight), respectively. The principal current use of propylene glycol dinitrate is as a propellant in Otto fuel II.

Nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...

s of polyhydric alcohols such as this have been used in medicine for the treatment of

angina pectoris Angina, also known as angina pectoris, is chest pain or pressure, usually caused by insufficient blood flow to the heart muscle (myocardium). It is most commonly a symptom of coronary artery disease. Angina is typically the result of part ...

, and as

explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An ex ...

s since the mid-nineteenth century. In addition to its use by the

United States Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...

as a stabilizer in the manufacture of Otto fuel II, 2-nitrodiphenylamine is employed for similar purposes by the

United States Army The United States Army (USA) is the primary Land warfare, land service branch of the United States Department of Defense. It is designated as the Army of the United States in the United States Constitution.Article II, section 2, clause 1 of th ...

in the manufacture of double base solid propellants. It also has civilian applications as a solvent dye. Dibutyl sebacate is a desensitizer in Otto fuel II. However, its major use is as a

plasticizer A plasticizer ( UK: plasticiser) is a substance that is added to a material to make it softer and more flexible, to increase its plasticity, to decrease its viscosity, and/or to decrease friction during its handling in manufacture. Plasticizer ...

in production of plastics, namely

cellulose acetate butyrate Cellulose acetate butyrate (CAB) is a mixed ester thermoplastic derivative of cellulose acetate that contains both acetate and butyrate functional groups. It has improved weathering resistance and lower moisture absorption compared to cellulose a ...

cellulose acetate propionate Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important s ...

polyvinyl butyral Polyvinyl butyral (or PVB) is a resin mostly used for applications that require strong binding, optical clarity, adhesion to many surfaces, toughness and flexibility. It is prepared from polyvinyl alcohol by reaction with butyraldehyde. The m ...

polystyrene Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It i ...

, and many

synthetic rubber A synthetic rubber is an artificial elastomer. They are polymers synthesized from petroleum byproducts. About of rubber is produced annually in the United States, and of that amount two thirds are synthetic. Synthetic rubber, just like natural ru ...

s. It can be used for plastics in use in the food

packaging Packaging is the science, art and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of designing, evaluating, and producing packages. Packaging can be described as a coo ...

industry. It is also used as a lubricating ingredient in shaving lotions, and a flavoring additive in

non-alcoholic beverage An alcohol-free or non-alcoholic drink, also known as a temperance drink, is a version of an alcoholic drink made without Alcohol (drug), alcohol, or with the alcohol removed or reduced to almost zero. These may take the form of a non-alcoholic mi ...

ice cream Ice cream is a frozen dessert typically made from milk or cream that has been flavoured with a sweetener, either sugar or an alternative, and a spice, such as Chocolate, cocoa or vanilla, or with fruit, such as strawberries or peaches. Food ...

, ices, candy, and baked goods.

Toxicity

Otto fuel II is a toxic substance found in EPA

National Priorities List The National Priorities List (NPL) is the priority list of hazardous waste sites in the United States eligible for long-term remedial investigation and remedial action (cleanup) financed under the federal Superfund program. Environmental Protec ...

. Ingestion of contaminated food or direct exposure at worksites can cause headaches, poor eye–hand coordination, eye irritation, congested noses, nausea, dizziness, and difficulty breathing. An MSA Demand Mask is mandatory for cleanup/mitigation efforts.

Used in

Mark 37 torpedo The Mark 37 torpedo is a torpedo with electrical propulsion, developed for the US Navy after World War II. It entered service with the US Navy in the early 1950s, with over 3,300 produced. It was phased out of service with the US Navy during the ...

(With speed-up kit) *

Mark 46 torpedo The Mark 46 torpedo is the backbone of the United States Navy's lightweight anti-submarine warfare torpedo inventory and is the NATO standard. These aerial torpedoes are designed to attack high-performance submarines. In 1989, an improvement p ...

* Mark 54 torpedo *

Spearfish torpedo The Spearfish torpedo (formally Naval Staff Target 7525) is the heavy torpedo used by the submarines of the Royal Navy. It can be guided by Torpedo#Radio and wire guidance, wire or by acoustic homing, autonomous active or passive sonar, and pro ...

(with oxidizer) * Yu-6 torpedo *

Futlyar ''Futlyar'' (''Fizik-2'') is a Russian deep-water homing torpedo tested by the Russian Navy in 2017; it entered service in the same year. Developed by the Saint Petersburg Research Institute of Marine Engineering and produced by the Dagdizel Mac ...

References

External links