EP2620422B1 - N2O-based, ionic monopropellants for space propulsion - Google Patents

Description

The chemical propulsion of the satellites is generally ensured by the decomposition or the combustion of propellants thus producing gases with very high temperature and very high pressure. The propellants may be monergols or bergols.

Biergol propulsion is undoubtedly one of the two technologies most used today, especially on satellites. Its large volume of use is mainly due to its adoption on telecommunications satellites (large market), high masses, where the thrusts involved are higher range (10N to 400N). Their high performance (specific impulse (Isp) = 320s for an expansion ε of 330, real) are also a parameter of choice that reduces the amount of embedded propellant for long transfer operations in geostationary orbit. In contrast, biogas require the storage of two chemical compounds (an oxidant and a fuel) in separate tanks, and therefore involve a complex architecture. Biergol Nitrogen Peroxide (NTO) / Monomethylhydrazine (MMH) is currently the oxidant / reducer combination of choice.

Monergol propulsion is the second most widely used satellite technology. Its most common form is to use a metastable propellant that can decompose in the passage of a catalytic bed exothermically, which has the effect of converting propellant into gaseous products at high temperature and low molar mass. Propulsion monergol in its generality is for small outbreaks (1 N to 10N) and shows fairly average performance. Hydrazine (N ₂ H ₄ ) is the most common monergol and displays an Isp of the order of 210s at ε = 80 (real). Its major advantage is to rely on a fairly simple architecture due to the presence of a unique propellant. However, the use of hydrazine and its methylated derivatives (MMH or UDMH) poses significant risks in terms of manufacturing, handling and operations because of their sensitivity to impurities and, to a lesser extent, to temperature and their extreme toxicity. . These constraints generate cumbersome operating procedures and high implementation costs. In addition, hydrazine is currently on the list of compounds listed by REACh (European Chemical Regulation), because of its dangerousness (carcinogenic substance, mutagenic or toxic, persistent, biaccumulable or toxic). In fact, a potential progressive ban on hydrazine and its derivatives is to be expected and its substitution may be necessary in the near future.

Many studies are currently being conducted to identify alternatives labeled "green" because of their reduced toxicity compared to that of hydrazine. The "green propellants" sought, complying with the REACh regulations, will also have to comply with specific requirements in the space field, particularly in terms of long-term storage, thermal and mechanical stability (with respect to shocks, detonation, adiabatic compression). , etc.), broad compatibility with propulsion system materials (tanks, pipes, valves, etc.), compatibility with spatial constraints (melting / boiling points, vapor pressure, etc.), impact control systems (bulk / mass, assembly, integration and tests) while presenting high performances (Isp, density).

Among the alternatives studied were monergols based on DNA (ammonium dinitramide), HAN (hydroxylammonium nitrate) or HNF (hydrazinium nitroformate). Their implementation is identical to that of hydrazine but, unlike the latter, these ionic monergols have the particularity to enter into combustion after their catalytic decomposition due to the presence of oxidizing and reducing species conducive to oxidation. reduction. This makes it possible to achieve, under the effect of the temperature, Isp slightly higher than that of hydrazine (Isp = 230s at ε = 50, real). The patent application WO0050363 discloses a formulation based on the dinitramide anion (N (NO ₂ ) ₂ ^- ) associated with an energetic cation - preferably ammonium (NH ₄ ⁺ ), hydrazinium (N ₂ H ₅ ⁺ ) or hydroxylammonium (OHNH ₃ ⁺ ), ammonium being preferred - the salt formed being dissolved in an aqueous reducing solution or not. The liquid reductant can thus serve as a solvent or be in equilibrium with a water fraction so as to form a liquid ionic energy solution. The reducing agent may in particular be chosen from alcohols, amines, aldehydes or ketones, a large polarity being sought in order to promote the solubility of the energetic salt. Increasing the polarity of the reducer then makes it possible to reduce the water content and thus increase the Isp of the mixture. The theoretical Isp are between 245s to 280s (chamber pressure of 20 bar and ε = 50). One formulation received particular attention for its thermal storage stability: LMP-103S (60-65% DNA, 15-20% methanol, 3-6% ammonia and water supplement), demonstrating a theoretical Isp of 252s. However, despite theoretical performance superior to those of hydrazine, such monergols have a major disadvantage related to their implementation in the propellant: these propellants are indeed decomposed by catalysis and their decomposition products are in combustion due to the cohabitation of oxidizing and reducing agents and a decomposition temperature above the autoignition threshold. Therefore, the flame temperatures reached are higher (1800 ° C) than in the case of monergol hydrazine (900 ° C) and generate intense thermal stress for the catalyst bed. Among the problems related to this thermal stress can be mentioned: deactivation of the catalyst by oxidation, erosion of the active phase or sintering of the support particles. This loss of activity results in a gradual decrease in performance and a limitation of the life of the propellant: despite a level higher than that of hydrazine in "early life", the Isp can strongly decrease in the course of mission to finally generate much lower overall performance. It appears then that the use of a catalytic device, historically used in propulsion monergol, seems unsuitable if one tends towards compounds with high energy density. An alternative implementation of the decomposition / reaction of propellant in which the activation energy would be achieved by a non-catalytic process would then open the door to compounds much more energetic than hydrazine and even DNA.

Other avenues have been pursued in terms of both alternative "green" monergols and the implementation of their reaction. Patent applications WO01 / 51433 and WO2009 / 062183 teach as liquid monolols mixtures of nitrous oxide (N ₂ O) as an oxidant and hydrocarbon fuel, such as propane (C ₃ H ₈ ) or ethane (C ₂ H) ₆ ), ethylene (C ₂ H ₄ ), acetylene (C ₂ H ₂ ). By way of example, NOFB34 is a mixture of N ₂ O and acetylene in a ratio ^O / _F = 4. The choice of nitrous oxide as oxidant is motivated by its very good oxidizing power and by its volatile nature offering the possibility of a self-pressurization of the tank. In contrast, the hydrocarbons used, very volatile, lead in the range of use temperature to a gas phase containing both nitrous oxide and hydrocarbon. This gaseous mixture is sensitive and has high detonation risks in response to thermal or mechanical stimuli. In this respect, mention can be made of work on the study of the detonability of N ₂ O / hydrocarbon mixtures, Mr. Kaneshige et al. (Hydrocarbon-Air-NitrousOxideDetonations, Western States Section / The Combustion Institute, Spring Meeting, Sandia National Laboratories, Livermore, CA, April 14 and 15 1997 ). In addition, the binary N ₂ O / hydrocarbon formed mixture has a high saturation vapor pressure (38 bar at 10 ° C for the monergol NOFB34) and very sensitive to the temperature (48 bar at 20 ° C for the same monergol), which, on the one hand, requires qualified equipment for a higher operating pressure than those currently encountered and, on the other hand, makes its thermal control continuously delicate. In addition, the energy density of these mixtures remains to be improved in particular because of their density sometimes less than 700 kg.m ^-3 .

The subject of the present invention is therefore a monergol based on nitrous oxide which does not have the disadvantages stated above, and in particular instability. In the first place, the problem related to the sensitivity of the mixture has been solved by generating a monergol in which the fuel is, in its isolated form, an energetic salt. Its dissolution in the nitrous oxide generates an ionic liquid phase. Due to its reduced saturated vapor pressure, the fuel is fixed in the liquid phase, so that the vapor phase coexisting with the liquid contains only nitrous oxide. Secondly, the density of monergols thus formed is high thanks to the contribution of salt, thus guaranteeing a high energy density. The salts used have enthalpies of formation and structures such that their association with nitrous oxide provides theoretical Isp between 300s and 350s depending on the candidates.

• du protoxyde d'azote (N₂O) à titre d'oxydant au moins partiellement sous forme liquide, et
• un combustible sous forme de sel dans la phase liquide du N₂O.

According to a first object, the present invention thus relates to a monergol formed by a mixture comprising:

• nitrous oxide (N ₂ O) as an oxidant at least partially in liquid form, and
• a fuel in the form of salt in the liquid phase of N ₂ O.

Nitrous oxide N ₂ O, molar mass 44.013 kg mol ^-1 , is also called nitrous oxide, nitrous oxide, nitrogen oxide, nitrous oxide. Its critical point is at P _c = 72.51 bar and T _c = 36.42 ° C. Its saturation vapor pressure (the pressure at which the gas phase is in equilibrium with its liquid phase) varies in the range [0 +20] ° C between 31.3 bar and 50.6 bar. Over the same interval, the density of its liquid phase increases from 907.4 kg.m ^-3 to 786.6 kg.m ^-3 , while that of its gas phase increases from 84.9 kg.m ^-3 to 158.1 kg.m ^-3 . Nitrous oxide is therefore a highly volatile compound. Depending on the temperature and pressure conditions, N ₂ O can exist in diphasic form (thermodynamic liquid / gas equilibrium) or monophasic beyond its critical point. Under normal temperature and pressure conditions, nitrous oxide is in liquid / gas equilibrium.

According to the invention, the nitrous oxide is in liquid form. It can be partially in the form of gas.

The presence of N ₂ O in liquid form is particularly advantageous in that it solubilizes the fuel and thus act as a solvent. The nitrous oxide is then in solution with the liquid phase of fuel.

The liquid phase of N ₂ O is then mixed with the fuel. In fact, the oxidizing and combustible species are in the same phase.

The presence of a gaseous phase consisting of N ₂ O equilibrium in the monergol is also interesting in that the gaseous N ₂ O plays the role of pressurizing gas.

"Pressurizing gas" is a neutral gas - that is, not intended to participate in the chemical reaction - used in reservoirs to pressurize the monergols and allow them to flow back into the fluidic lines in the direction of flow. thrusters. The system associated with this mode of operation is then called "positive expulsion". Helium (He) and dinitrogen (N ₂ ) are the most common pressurizing gases. The use of an additional gas induces certain disadvantages such as the loss of effective volume in the reservoir and the presence of traces of gas in the monergol by absorption.

According to the invention, the fuel is an ionic compound introduced into the liquid phase of the monergol.

1. 1) du combustible sous forme de sel solide lorsque isolé à température ambiante et solubilisé dans le N₂O au moins partiellement présent sous forme liquide, ou
2. 2) du sel fondu du combustible en mélange binaire avec le N₂O au moins partiellement présent sous forme liquide, ou
3. 3) d'une solution ionique du combustible dissous dans un solvant énergétique organique ou ionique, en mélange binaire avec le N₂O au moins présent sous forme liquide. Si un solvant ionique est utilisé, il s'agit d'un sel fondu.

The liquid phase can consist of:

1. 1) fuel in solid salt form when isolated at room temperature and solubilized in N ₂ O at least partially present in liquid form, or
2. 2) molten salt of the fuel in a binary mixture with N ₂ O at least partially present in liquid form, or
3. 3) an ionic solution of the fuel dissolved in an organic or ionic energy solvent, in a binary mixture with the N ₂ O at least present in liquid form. If an ionic solvent is used, it is a molten salt.

An ionic solution is a liquid containing ions among the solvent.

According to embodiment 1), the salt is generally polar, is solid under standard temperature conditions, and is soluble in N ₂ O.

By way of illustration, mention may be made of 1,5-diamino-4-methyl-tetrazolium azide.

According to Embodiment 2), the salt is generally present as a pure liquid at room temperature (RTIL: Room Temperature Lonic Liquid), has a melting temperature below -20 ° C, and forms a binary mixture with N ₂ O.

By way of illustration, mention may be made of 3-azido-1,2,4-triazolium-5-nitro-tetrazolate.

According to Embodiment 3), the salt, solid in the standard state, is dissolved in a solvent to form an ionic solution itself in admixture with N ₂ O present in liquid form. The solvent is advantageously an energy solvent, such as methanol, for example.

By way of illustration, mention may be made of 1,5-diamino-4-methyl-tetrazolium dinitramide mixed in methanol.

When the N ₂ O is at least partially present in liquid form, the liquid phase contains this part of N ₂ O in solution.

The fuel in liquid form makes it possible to guarantee an advanced stability of the monergol in the face of thermomechanical stimuli, in particular of detonation (shocks, adiabatic compression, etc.) and electrostatic stimuli.

The fuel is such that it is compatible with N ₂ O and of reduced volatility by its ionic nature. In particular, under the monergol storage conditions, the fuel can be considered as non-volatile.

• soluble ou miscible et apte à former des mélanges binaires solide-liquide ou liquide-liquide respectivement avec le N₂O liquide ;
• donne lieu à un mélange thermodynamiquement stable avec le N₂O liquide dans les conditions standard.

The term "compatible" here means that the fuel is, according to its phase under the standard conditions:

• soluble or miscible and capable of forming solid-liquid or liquid-liquid binary mixtures respectively with liquid N ₂ O;
• gives rise to a thermodynamically stable mixture with liquid N ₂ O under standard conditions.

The fuel must be an N ₂ O reducing species but may optionally include certain oxidizing groups.

To meet the energy density requirements necessary for space propulsion, the fuel is selected from the salts of the energetic compounds.

élevé, gage d'impulsion spécifique élevée.Energetic compounds are molecules or combinations of molecules with high energy density and high material density. This results in a standard enthalpy of positive and high formation, which may reach several thousand kJ.kg ^-1 - typically 2000 to 3000 kJ.kg ^-1 - and a high density, generally greater than 1000 kg.m ^-3. . This is called HEDM (High Energy Density Materials). Some HEDMs demonstrate outstanding performance but have limitations of use because of their instability (uncontrolled release of energy) and are classified in the category of explosive materials. This is particularly the case of derivatives of pentazole. In addition, an additional feature specific to space propulsion concerns the molar mass of the products resulting from the combustion of these energetic compounds. The latter must be as low as possible - generally less than 30 gmol ^-1 - in order to guarantee a flame temperature to molar mass ratio. $\left(\frac{T_{\mathit{ad}}}{M}\right)$

high, pledge of high specific impulse.

According to the invention, the fuel (also called "reducing agent") is any combination of a linear or heterocyclic cation and a linear or heterocyclic anion meeting the criteria presented above. The anion and / or the cation generally comprise one or more nitrogenous and / or unsaturated energetic groups such as amino, azido, cyano, propargyl, tripropargyl and guanidyl.

The fuel is usually a nitrogen derivative, in the form of salt. Thus, the anion and / or the cation of said salt may contain one or more nitrogen atoms.

Said cation may be chosen from nitrogen derivatives such as aliphatic, cyclic or aromatic, quaternary amines.

• les cations linéaires, tels que les ions ammonium, hydroxylammonium, hydrazinium, et leurs dérivés ;
• les cations hétérocycliques saturés tels que pipéridinium, pipérazinium, et leurs dérivés ; et
• les cations hétérocycliques aromatiques ou non, tels que les azinium, azolium, diazolium, triazolium et tétrazolium, notamment pyridinium, pyrrolium, isoxazolium, pyrazolium, oxazolium, pyrazolium, imidazolium, oxadiazolium, triazolium, oxatriazolium, tétrazolium, pyrrolidium, triazinium, pyridazinium, pyrimidinium, pyrazinium, pipéridinium, 1,2,3- ou 1,2,4-triazolium, 1,4,5- ou 2,4,5- tétrazolium, ainsi que leurs analogues -inium et -idinium, et leurs dérivés.

Said cation may especially be chosen from:

• linear cations, such as ammonium, hydroxylammonium, hydrazinium, and their derivatives;
• saturated heterocyclic cations such as piperidinium, piperazinium, and their derivatives; and
• aromatic or non-aromatic heterocyclic cations, such as azinium, azolium, diazolium, triazolium and tetrazolium, in particular pyridinium, pyrrolium, isoxazolium, pyrazolium, oxazolium, pyrazolium, imidazolium, oxadiazolium, triazolium, oxatriazolium, tetrazolium, pyrrolidium, triazinium, pyridazinium, pyrimidinium , pyrazinium, piperidinium, 1,2,3- or 1,2,4-triazolium, 1,4,5- or 2,4,5-tetrazolium, as well as their analogues -inium and -idinium, and their derivatives.

More particularly, said cation may be chosen from ammonium, imidazolium, triazolium and tetrazolium ions and their derivatives.

The term "ion derivatives" refers to compounds having a nitrogen atom in the form of said ion.

The analogues -inium and -idinium of the above unsaturated heterocyclic compounds refer to the corresponding partially saturated (-inium) and saturated (-idinium) analogues resulting from a partial or complete partial hydrogenation, such as, for example, pyrrolinium as an analogue. partially unsaturated and pyrrolidinium as a saturated analogue of pyrrolium.

Examples of ammonium derivatives that may be mentioned are substituted ammonium compounds, such as ethylenediammonium, ethanolammonium, propylammonium, monopropargylammonium, tripropargylammonium, tetraethylammonium, N-tributyl-N-methylammonium, N-trimethylammonium, N-butylammonium, N-trimethyl-N-hexylammonium, N-trimethyl-N-propylammonium.

Examples of pyrrolium derivatives that may be mentioned are substituted pyrroliums, in particular with an alkyl group, such as N-methylpyrrolium.

As imidazolium derivatives, mention may be made of substituted imidazoliums, in particular with one or more alkyl groups, and / or hydroxyalkyls, such as 1-butyl-2,3-dimethylamidazolium or 1-butyl-3-methylimidazolium, 1,3-dimethylimidazolium, 1-ethanol-3-methylimidazolium, 1-ethyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, methylimidazolium, 1-octyl-3-methylimidazolium, 1-propyl-2 3-dimethylimidazolium, 1-propyl-2,3-dimethylimidazolium.

By way of pyrrolidinium derivatives, mention may be made of substituted pyrrolidiniums, in particular with one or more alkyl groups, such as 1-butyl-1-methylpyrrolidinium, 1-ethyl-1-methylpyrrolidinium and N-propyl-N-methylpyrrolidinium. .

As piperidinium derivatives, mention may be made of piperidinium substituted with one or more alkyl groups, such as 1-methyl-1-propylpiperidinium.

As triazolium derivatives, there may be mentioned 1-methyl-1,2,4-triazolium, 3-azido-1,2,4-triazolium, 1-methyl-3-azido-1,2,4 -triazolium, 4-amino-1,2,4-triazolium.

As derivatives of tetrazolium, there may be mentioned 1-amino-4,5-dimethyltetrazolium, 2-amino-4,5-dimethyltetrazolium, 1,5-diamino-4-methyltetrazolium.

Azinium (6 atomes) Pyridinium

Azolium Pyrrolium

Diazolium Pyrazolium

Imidazolium

Triazolium 1,2,3-Triazolium (à g.)

1,2,4-Triazolium (à d.) Tétrazolium 1,4,5-Tétrazolium (à g.)

2,4,5-Tétrazolium (à d.) où chacun des R1, R2, R3, R4, R5 et R6, identiques ou différents, représentent indépendamment un atome d'hydrogène, ou un groupe alkyle ; CN ; alkyle substitué par CN ; NRR' ; azido-(-N₃) ; nitro ; propargyl ; tripropargyl et guanidyl ; où RR' représente indépendamment un atome d'hydrogène ou un groupe alkyle...By way of illustration, mention may be made of the following families of cations: Family Compound Generic structure Ammonium

Azinium (6 atoms) pyridinium

azolium pyrrolium

Diazolium pyrazolium

imidazolium

triazolium 1,2,3-Triazolium (left)

1,2,4-Triazolium (right) tetrazolium 1,4,5-Tetrazolium (left)

2,4,5-Tetrazolium (right) wherein each of R1, R2, R3, R4, R5 and R6, which are the same or different, independently represent a hydrogen atom, or an alkyl group; CN; alkyl substituted with CN; NRR '; azido - (- N ₃ ); nitro; propargyl; tripropargyl and guanidyl; where RR 'independently represents a hydrogen atom or an alkyl group ...

• les anions linéaires tels que les ions azoture, nitrate, nitramide, nitroformiate, dinitramide, nitrite, acétate, cyanamide, dicyanamide, phosphate, méthylphosphonate, éthylphosphonate ; et
• les anions hétérocycliques insaturés tels que les azolates (tels que pyrrolate), diazolate (tel que pyrazolate, imidazolate), triazolate (1,2,3- et 1,2,4-triazolate) et tétrazolate (tel que nitrotétrazolate),

et leurs dérivés, tels que le 4,5-dinitroimidazolate, le 5-nitrotétrazolate.The counter-ion (anion) of the fuel can be any anion with a negative charge, nitrogen or not. It can be chosen from

• linear anions such as azide, nitrate, nitramide, nitroformate, dinitramide, nitrite, acetate, cyanamide, dicyanamide, phosphate, methylphosphonate, ethylphosphonate; and
• unsaturated heterocyclic anions such as azolates (such as pyrrolate), diazolate (such as pyrazolate, imidazolate), triazolate (1,2,3- and 1,2,4-triazolate) and tetrazolate (such as nitrotetrazolate),

and their derivatives, such as 4,5-dinitroimidazolate, 5-nitrotetrazolate.

Nitramide Nitramide

Dinitramide

Azoture N=N=N Cyanamide Cyanamide HN-C≡N Dicyanamide N≡C-N-C≡N Azolate Pyrrolate

Diazolate Pyrazolate

Imidazolate

Triazolate 1,2,3-Triazolate (à g.)

1,2,4-Triazolate (à d.) Tétrazolate 3-Tétrazolate (à g.)

2-Tétrazolate (à d.) où chacun des R1, R2, R3, R4, R5 et R6, identiques ou différents représentent indépendamment un atome d'hydrogène, ou un groupe alkyle ; CN ; alkyle substitué par CN ; NRR' ; azido-(-N₃) ; nitro ; propargyl ; tripropargyl et guanidyl ; où RR' représentent indépendamment un atome d'hydrogène ou un groupe alkyle.By way of illustration, the following families of anions can be mentioned: Family Compound Genetic structure Nitrate

nitramide nitramide

dinitramide

azide N = N = N cyanamid cyanamid HN-C≡N dicyanamide N≡CNC≡N Azolate Pyrrolate

Diazolate pyrazolate

imidazolate

triazolate 1,2,3-Triazolate (left)

1,2,4-Triazolate (right) Tétrazolate 3-Tetrazolate (left)

2-Tetrazolate (right) wherein each of R1, R2, R3, R4, R5 and R6, which are the same or different, independently represent a hydrogen atom, or an alkyl group; CN; alkyl substituted with CN; NRR '; azido - (- N ₃ ); nitro; propargyl; tripropargyl and guanidyl; where RR 'independently represent a hydrogen atom or an alkyl group.

By alkyl group is meant saturated hydrocarbon radicals, straight or branched chain, of 1 to 20 carbon atoms, preferably 1 to 5 carbon atoms. Mention may in particular be made, when they are linear, the methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, nonyl, decyl, dodecyl, hexadecyl and octadecyl radicals. When they are branched or substituted by one or more alkyl radicals, mention may be made especially of the isopropyl, tert-butyl, 2-ethylhexyl, 2-methylbutyl, 2-methylpentyl, 1-methylpentyl and 3-methylheptyl radicals.

The counterion (anion) is especially chosen from azide, nitrate, dinitramide, dicyanamide, imidazolate and tetrazolate ions and their derivatives.

• l'azoture d'ammonium (AA),
• l'azoture de tétrabutylammonium,
• le nitrotétrazolate de triazolium,
• le nitrotétrazolate d'azidotriazolium,
• le dinitramide d'ammonium (ADN),
• l'azoture d'hydroxylammonium (HAA),
• l'azoture d'hydrazinium (HA),
• le nitrate d'hydroxylammonium (HAN),
• le dinitramide d'ammonium (ADN),
• le nitroformiate d'hydrazinium (HNF),
• le nitrate d'ammonium (AN),
• le nitrate d'hydrazinium (HN),
• le nitrate de triéthanolammonium (TEAN),
• le dinitramide d'hydroxylammonium (HADN),
• les sels d'azoture, d'acétate, de nitrate, de dinitramide, de dicyanamide, de méthylphosphonate, de 4,5-dinitroimidazolate, de 5-nitro-tétrazolate et d'éthylphosphonate

d'ammonium, éthylènediammonium, éthanolammonium, propylammonium, monopropargylammonium, tripropargylammonium, tétrabutylammonium, tétraéthylammonium, N-tributyl-N-méthylammonium, N-triméthyl-N-butylammonium, N-triméthyl-N-hexylammonium, N-triméthyl-N-propylammonium, pyrrolinium, N-méthylpyrrolinium, imidazolium, 1-butyl-2,3-diméthylamidazolium, 1-butyl-3-méthylimidazolium, 1,3-diméthylimidazolium, 1-éthanol-3-méthylimidazolium, 1-éthyl-3méthylimidazolium, 1-héxyl-3-méthylimidazolium, méthylimidazolium, 1-octyl-3-méthylimidazolium, 1-propyl-2,3-diméthylimidazolium, 1-propyl-2,3-diméthylimidazolium, 1-(2-butynyl)-3-méthyl-imidazolium, pyrrolidinium, 1-butyl-1-méthylpyrrolidinium, 1-éthyl-1-méthylpyrrolidinium, N-propyl-N-méthyl-pyrrolidinium, pipéridinium et 1-méthyl-1-propylpipéridinium, de 1,2,4-triazolium, de 1-méthyl-1,2,4-triazolium, de 3-azido-1,2,4-triazolium, de 1-méthyl-3-azido-1,2,4-triazolium, de 4-amino-1,2,4-triazolium, de 1-amino-4,5-diméthyl-tétrazolium, de 2-amino-4,5-diméthyl-tétrazolium, de 1,5-diamino-4-méthyl-tétrazolium.More particularly, the following compounds may be mentioned as fuel:

• ammonium azide (AA),
• tetrabutylammonium azide,
• triazolium nitrotetrazolate,
• azidotriazolium nitrotetrazolate,
• ammonium dinitramide (DNA),
• hydroxylammonium azide (HAA),
• hydrazinium azide (HA),
• hydroxylammonium nitrate (HAN),
• ammonium dinitramide (DNA),
• hydrazinium nitroformate (HNF),
• ammonium nitrate (AN),
• hydrazinium nitrate (HN),
• triethanolammonium nitrate (TEAN),
• hydroxylammonium dinitramide (HADN),
• the salts of azide, acetate, nitrate, dinitramide, dicyanamide, methylphosphonate, 4,5-dinitroimidazolate, 5-nitro-tetrazolate and ethylphosphonate

ammonium, ethylenediammonium, ethanolammonium, propylammonium, monopropargylammonium, tripropargylammonium, tetrabutylammonium, tetraethylammonium, N-tributyl-N-methylammonium, N-trimethyl-N-butylammonium, N-trimethyl-N-hexylammonium, N-trimethyl-N-propylammonium, pyrrolinium, N-methylpyrrolinium, imidazolium, 1-butyl-2,3-dimethylamidazolium, 1-butyl-3-methylimidazolium, 1,3-dimethylimidazolium, 1-ethanol-3-methylimidazolium, 1-ethyl-3-methylimidazolium, 1-hexyl- 3-methylimidazolium, methylimidazolium, 1-octyl-3-methylimidazolium, 1-propyl-2,3-dimethylimidazolium, 1-propyl-2,3-dimethylimidazolium, 1- (2-butynyl) -3-methylimidazolium, pyrrolidinium, 1-butyl-1-methylpyrrolidinium, 1-ethyl-1-methylpyrrolidinium, N-propyl-N-methyl-pyrrolidinium, piperidinium and 1-methyl-1-propylpiperidinium, 1,2,4-triazolium, 1-methyl- 1,2,4-Triazolium, 3-azido-1,2,4-triazolium, 1-methyl-3-azido-1,2,4-triazolium, 4-amino-1,2,4-triazolium , 1-amino-4,5-dimet hyl-tetrazolium, 2-amino-4,5-dimethyl-tetrazolium, 1,5-diamino-4-methyl-tetrazolium.

• l'azoture d'ammonium (AA),
• l'azoture de tétrabutylammonium,
• le nitrotétrazolate de triazolium,
• le nitrotétrazolate d'azidotriazolium,
• le dinitramide d'ammonium (ADN),
• l'azoture d'hydroxylammonium (HAA),
• l'azoture d'hydrazinium (HA),
• l'azoture de 1-(2-butynyl)-3-méthyl-imidazolium
• le nitrate d'hydroxylammonium (HAN),
• le dinitramide d'ammonium (ADN),
• le nitroformiate d'hydrazinium (HNF),
• le nitrate d'ammonium (AN),
• le nitrate d'hydrazinium (HN),
• le nitrate de triéthanolammonium (TEAN),
• le dinitramide d'hydroxylammonium (HADN),
• le dicyanamide d'ammonium,
• le dicyanamide d'imidazolium,
• le dicyanamide de 1-butyl-3-méthylimidazolium,
• l'acétate de 1-butyl-2,3-diméthylamidazolium,
• l'acétate, le dicyanamide, de 1-butyl-1-méthylpyrrolidinium,
• le méthylphosphonate de 1,3-diméthylimidazolium,
• le dicyanamide de 1-éthanol-3-méthylimidazolium,
• l'éthylphosphonate, le méthylphosphonate, de 1-éthyl-3-méthylimidazolium,
• le dicyanamide de N-tributyl-N-méthylammonium,
• le dicyanamide d'ammonium,
• l'azoture d'ammonium,
• le dicyanamide de 1-butyl-3-méthyl-imidazolium,
• 4,5-dinitro imidazolate de 1,2,4-triazolium
• 4,5-dinitro imidazolate de 1-méthyl-1,2,4-triazolium,
• 4,5-dinitro imidazolate de 3-azido-1,2,4-triazolium,
• 4,5-dinitro imidazolate de 1-méthyl-3-azido-1,2,4-triazolium,
• 4,5-dinitro imidazolate de 4-amino-1,2,4-triazolium,
• 5-nitro tétrazolate de 1,2,4-triazolium,
• 5-nitro tétrazolate de 1-méthyl-1,2,4-triazolium,
• 5-nitro tétrazolate de 3-azido-1,2,4-triazolium,
• 5-nitro tétrazolate de 1-méthyl-3-azido-1,2,4-triazolium,
• 5-nitro tétrazolate de 4-amino-1,2,4-triazolium,
• Nitrate de 1-amino-4,5-diméthyltétrazolium
• Nitrate de 2-amino-4,5-diméthyltétrazolium
• Nitrate de 1,5-diamino-4-méthyltétrazolium
• Dinitramide de 1,5-diamino-4-méthyltétrazolium
• Azoture de 1,5-diamino-4-méthyltétrazolium
• le dinitramide de 1,5-diamino-4-méthyl-tétrazolium.

As an illustration, we can mention:

• ammonium azide (AA),
• tetrabutylammonium azide,
• triazolium nitrotetrazolate,
• azidotriazolium nitrotetrazolate,
• ammonium dinitramide (DNA),
• hydroxylammonium azide (HAA),
• hydrazinium azide (HA),
• 1- (2-butynyl) -3-methyl-imidazolium azide
• hydroxylammonium nitrate (HAN),
• ammonium dinitramide (DNA),
• hydrazinium nitroformate (HNF),
• ammonium nitrate (AN),
• hydrazinium nitrate (HN),
• triethanolammonium nitrate (TEAN),
• hydroxylammonium dinitramide (HADN),
• ammonium dicyanamide,
• imidazolium dicyanamide,
• 1-butyl-3-methylimidazolium dicyanamide,
• 1-butyl-2,3-dimethylamidazolium acetate,
• acetate, dicyanamide, 1-butyl-1-methylpyrrolidinium,
• 1,3-dimethylimidazolium methylphosphonate,
• 1-ethanol-3-methylimidazolium dicyanamide,
• ethylphosphonate, methylphosphonate, 1-ethyl-3-methylimidazolium,
• N-tributyl-N-methylammonium dicyanamide,
• ammonium dicyanamide,
• ammonium azide,
• 1-butyl-3-methylimidazolium dicyanamide,
• 4,5-dinitro-1,2,4-triazolium imidazolate
• 4,5-dinitro imidazolate of 1-methyl-1,2,4-triazolium,
• 4,5-dinitro imidazolate of 3-azido-1,2,4-triazolium,
• 4,5-dinitro imidazolate of 1-methyl-3-azido-1,2,4-triazolium,
• 4,5-dinitroimidazolate of 4-amino-1,2,4-triazolium,
• 1,2,4-triazolium 5-nitro tetrazolate,
• 1-methyl-1,2,4-triazolium 5-nitro tetrazolate,
• 3-azido-1,2,4-triazolium 5-nitro tetrazolate,
• 1-methyl-3-azido-1,2,4-triazolium 5-nitro tetrazolate,
• 4-amino-1,2,4-triazolium 5-nitro tetrazolate,
• 1-amino-4,5-dimethyltetrazolium nitrate
• 2-amino-4,5-dimethyltetrazolium nitrate
• 1,5-Diamino-4-methyltetrazolium nitrate
• Dinitramide of 1,5-diamino-4-methyltetrazolium
• Azide of 1,5-diamino-4-methyltetrazolium
• 1,5-diamino-4-methyl-tetrazolium dinitramide.

These salts are usually commercially available. Thus, AA, HAA, HA, triazolium nitrotetrazolate, azidotriazolium nitrotetrazolate and ammonium dinitramide (DNA) are sold in particular by EURENCO Bofors (Sweden).

The other salts listed above may for example be marketed by Solvionic.

The salts according to the invention, if they are not available commercially, can be obtained by application or adaptation of known methods, in particular according to the methods described by Keskin et al., J. of Supercritical Fluids 43 (2007) 150-180 , in particular by coupling of its constituents, by metathesis or by acid-base reaction. Thus, in particular, the desired salt can be prepared from the compound in neutral form by salification, for example by addition of the acid containing the desired anion; or from another ionic compound by ion exchange, for example on a column, or by transsalification in the presence of an acid containing the desired anion, or by metathesis. Alternatively, it is possible to regenerate the fuel in free form in a basic medium and to generate a new ion by salification. It is also possible to generate a quaternary ion from the corresponding base by protonation or substitution (eg alkylation), for example. The nitrate, dinitramide and azide salts can be advantageously prepared by metathesis in the presence of the silver salts of nitrate, dinitramide and azide from the corresponding halides.

We can thus cite the methods described in US8,034,202 ; Asikkala et al. (Application of ionic liquids and micron activation in the organic reaction, Acta Univ., A 502, 2008 ; Singh et al. Bond Structure 2007, 125: 35-83 ; Schneider et al. Inorganic Chemistry 2008, 47 (9), 3617-3624 .

It is understood that other salts can be used. Thus, depending on the commercially available anions and cations and the optimization thereof (depending on the energy performances, and / or compatibility properties with N ₂ O, stability, toxicity, etc., desired), it may be advantageous to vary their structure. Different counter ions can be obtained with a given cation or anion.

The monergols according to the invention are such that the ratio N ₂ O / fuel (by mass), known as the mixing ratio and often noted ^O / _F or OF (for Oxidizer / Fuel ratio) is generally between 0, 1 and 10, preferably between 1 and 6.

où C* , g ₀ , γ, P_e et P_c représentent respectivement la vitesse caractéristique des gaz éjectés par la tuyère, la pesanteur à l'altitude considérée, le coefficient isentropique moyen des gaz ejectés, la pression d'éjection et la pression au sein de la chambre.One way to quantify the performance of a propellant is the specific impulse, often referred to as Isp. The specific impulse represents the duration during which the engine provides a thrust equal to the weight of the consumed propellant. It is thus an indicator of the "sobriety" and therefore of the energy performance of an ergol. The Isp be expressed as follows: $$\mathit{Isp}=\frac{{\mathrm{VS}}^{*}}{{\mathrm{<figure-callout\; id="0"\; label="boy\; Wut"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">boy\; Wut</figure-callout>}}_0}\mathrm{.}\gamma \mathrm{.}\sqrt{\left(\frac{2}{\gamma -1}\right)\mathrm{.}{\left(\frac{2}{\gamma +1}\right)}^{\frac{\gamma +1}{\gamma -1}}\cdot \left[1-{\left(\frac{P_e}{P_{\mathrm{vs}}}\right)}^{\frac{\gamma -1}{\gamma }}\right]}$$

where C *, g ₀ , γ, P _e and P _c respectively represent the characteristic velocity of the gases ejected by the nozzle, the gravity at the altitude considered, the average isentropic coefficient of the ejected gases, the ejection pressure and the pressure in the room.

avec la célérité du son : $a_0=\sqrt{\frac{\gamma \mathrm{.}R\mathrm{.}{T}_{\mathit{ad}}}{M}}$

où R , T_ad et M sont respectivement la constante universelle des gaz parfaits, la température adiabatique au sein de la chambre (dite « de flamme » si présence de combustion) et la masse molaire moyenne des gaz éjectés.The characteristic speed of ejected gases is related to the speed of sound according to: ${\mathrm{VS}}^{*}=\frac{{\mathrm{at}}_0}{{\mathrm{\Gamma }}^{\text{'}}}=\frac{{\mathrm{at}}_0}{\gamma \mathrm{.}{\left(\frac{2}{\gamma +1}\right)}^{\frac{\gamma +1}{2\left(\gamma -1\right)}}}$

with the speed of sound: ${\mathrm{at}}_0=\sqrt{\frac{\gamma \mathrm{.}R\mathrm{.}{T}_{\mathit{ad}}}{M}}$

where R, T _ad and M are respectively the universal constant of the ideal gases, the adiabatic temperature within the chamber (so-called "flame" if presence of combustion) and the average molar mass of the ejected gases.

où M_e est le nombre de Mach de l'écoulement dans la section d'éjection de la tuyère et peut être obtenu par la relation implicite suivante faisant intervenir le rapport d'expansion de la tuyère : $$\epsilon =\frac{A_e}{A_{\mathit{col}}}=\frac{1}{M_e}\mathrm{.}{\left[\left(\frac{2}{\gamma +1}\right)\mathrm{.}\left(1+\frac{\gamma -1}{2}\mathrm{.}{M_e}^2\right)\right]}^{\frac{\gamma +1}{2\left(\gamma -1\right)}}$$

avec ε le rapport d'expansion tuyère égal au rapport entre les sections d'éjection (A_e ) et du col sonique (A_col ).The ratio of the ejection and chamber pressures involved in the expression of the Isp depends on the nature of the ejected gases but also on the geometrical characteristics of the nozzle: $$\frac{P_e}{P_{\mathrm{vs}}}={\left(1+\frac{\gamma -1}{2}\mathrm{.}{{\mathrm{<figure-callout\; id="2"\; label="M\; e"\; filenames="imgf0001.png"\; state="\{\{state\}\}">M\; </figure-callout>}}_e}^2\right)}^{\frac{\gamma }{1-\gamma }}$$

where M _e is the Mach number of the flow in the ejection section of the nozzle and can be obtained by the following implicit relationship involving the nozzle expansion ratio: $$\epsilon =\frac{{\mathrm{AT}}_e}{{\mathrm{AT}}_{\mathit{collar}}}=\frac{1}{M_e}\mathrm{.}{\left[\left(\frac{2}{\gamma +1}\right)\mathrm{.}\left(1+\frac{\gamma -1}{2}\mathrm{.}{{\mathrm{<figure-callout\; id="2"\; label="M\; e"\; filenames="imgf0001.png"\; state="\{\{state\}\}">M\; </figure-callout>}}_e}^2\right)\right]}^{\frac{\gamma +1}{2\left(\gamma -1\right)}}$$

with ε the nozzle expansion ratio equal to the ratio between the ejection sections ( A _e ) and the sonic neck ( A _neck ).

The monergols according to the invention generally have a theoretical Isp of between 300s and 350s when calculated under the following conditions: pressure in the combustion chamber of 10 bar, nozzle expansion ratio of ε = 100 and expansion at equilibrium in the nozzle.

According to another object, the present invention also relates to the process for preparing the monergol according to the invention. Thus, said process comprises the step of mixing the fuel and N ₂ O. This mixture can be carried out at room temperature, but in the case where a solid salt in the standard state is used, the maximum solubility should be considered at room temperature. the minimum storage temperature of the monergol orbit to overcome any risk of saturation and recrystallization in flight. It is therefore necessary, during the synthesis of the monergol, to respect this threshold. The minimum operating temperature of the monolgy in orbit is typically 0 ° C.

The monolif according to the invention can be stored taking care not to exceed the maximum permissible storage temperature so as not to exceed a certain saturation vapor pressure level, the MEOP (Maximum Expected Operating Pressure, maximum pressure expected in operation) being between 10 and 50 bar, typically between 20 and 40 bar. The maximum storage temperature is generally between 0 ° and 50 ° C. The monoling stone must have sufficient stability to be stored in orbit for a period of several years - typically 5 years, but possibly up to 15 years. The stability must be reflected in particular by the absence of phase separation (demixing, settling, etc.).

According to another object, the present invention also relates to a method of spatial propulsion using the monergol according to the invention. Spatial propulsion is the propulsion of spacecraft such as launchers and satellites.

Advantageously, the monergol according to the invention is suitable for combustion operation. Combustion makes it possible to dispense with a catalytic bed and consequently with a complex propellant structure. In addition, the life of the propellant may be extended insofar as the catalyst currently constitutes the limiting element due to phenomena such as catalyst deactivation by erosion, oxidation, sintering, etc.

The method according to the invention therefore comprises the combustion of the monergol according to the invention.

The combustion is generally carried out by controlled ignition. This can be done according to the usual technologies, in particular by means of a high energy candle. The spark plug is generally positioned in the injection head, at the arrival of the monergol in the combustion chamber, the gases burned and evacuated by a nozzle placed at the opposite end of the combustion chamber.

The method according to the invention may also comprise the means for pressurizing the monergol in the tank. Generally, the present propellant systems known as "catalytic monergols" with hydrazine operate for pressures in the tank of the order of 20 bar at the beginning of life (initial pressure) and 5 bar at the end of life. This pressure decreases during the draining of the monergol due to the relaxation of the pressurizing gas in the volume released by the propellant. Some systems provide for tank pressure regulation to keep it constant over a certain part of the satellite's mission (performance optimization). This is the case on a telecommunication platform, but this introduces a complex and expensive equipment.

In the case of the present invention, it can be envisaged to operate at an upper reservoir pressure - typically between 25 and 40 bar at the beginning of life - in order to take into account the saturation vapor pressure of the N ₂ O-based mixture. The pressurization can be advantageously carried out by the N ₂ O solution itself because of its volatile nature, so that the use of an additional inert gas is no longer necessary. This results in a gain on the filling rate of the reservoir as well as on the apparent density of the liquid-gas torque.

As long as the liquid and vapor phases coexist (equilibrium between phases), the pressure remains constant (at constant temperature imposed) due to the vaporization of the liquid whose effect is to generate a volume of gas compensating the emptying of the reservoir. In this case, the pressurizing means can be ensured only by filling the monergol in the tank. In reality, the return to equilibrium between the liquid and vapor phases by vaporization of a liquid N ₂ O fraction is accompanied by a slight drop in temperature (endothermic phenomenon), so that a slight decrease in pressure will be observed. This phenomenon can be counterbalanced by the exercise of a reheating of the tank via a thermal control (thermistors). This phenomenon of self-pressurization "represents a major advantage since, similarly to pressure regulators on biliquid engines, it allows the thrusters to operate near their optimum performance.

As soon as the liquid phase is depleted, the phase balance is no longer feasible. The tank then operates in a conventional "blow down" manner similar to an inert gas pressurization.

The method according to the invention may also include the previous step of loading the monolgy into the tank of the spacecraft.

figures

• The figures 1-3 represent the specific impulse (Isp) as a function of the mixing ratio for two expansion ratios ( ε = 80 and ε = 330) for each of the monergols of Examples 1, 2 and 3 respectively.
• The figure 4 illustrates the solubility stress with respect to optimal performance in the case of a monergol involving a solid salt in the standard state (Example 1 or 3).

The following examples are given by way of non-limiting illustration of the present invention.

Examples 1- Choice of the energy salt

The following tables give some examples of energetic salts among the ammonium, diazolium, triazolium and tetrazolium cations, some of which are provided with alkyl, azido or amino substituent groups. Associated anions are taken from dicyanamide, azide, imidazolate, tetrazolate, nitrate or dinitramide, substituted or not by the nitro group. The atomic composition and some of their properties are specified (melting point, thermal decomposition threshold, density of salt in standard state, standard enthalpy of formation).
■ Based on ammonium cation: Denomination Atomic composition T _FUS T _DECOMP ρ ΔH _f ° VS NOT H O [° C] [° C] [Kg / m3] [KJ / kg] Ammonium dicyanamide 2 4 4 0 - - - 505.8 Ammonium azide 0 4 4 0 160 > 796 1346 1889.4
■ Based on cation diazolium (imidazolium): Denomination Atomic composition T _FUS T _DECOMP ρ ΔH _f ° (1) VS NOT H O [° C] [° C] [Kg / m3] [KJ / kg] 1-butyl-3-methyl-imidazolium dicyanamide 10 5 15 0 -6 - 1060 1004.6 (1) after Emel'yanenko et al JACS 2007, 129, 3930/3937.

1-Butyl-3-methyl-imidazolium dicyanamide can be prepared using the methodology described by Asikkala et al (Application of Ionic Liquids and Microactivation in Selected Organic Reactions, Acta Univ Oul. A 502, 2008, p. 134) by transsalification from 1-butyl-3-methyl-imidazolium chloride in the presence of sodium dicyanamide, the chloride being prepared by reaction between 1-chlorobutane and 1-methylimidazole.

Alternatively, the dicyanamide of 1-butyl-3-methyl-imidazolium can be prepared by metathesis as described in particular in US8,034,202 from 1-butyl-3-methylimidazolium bromide in the presence of silver dicyanamide.
■ Based on triazolium cation: Denomination Atomic composition T _FUS T _DECOMP ρ ΔH _f ° VS NOT H O [° C] [° C] [Kg / m3] [KJ / kg] 1,2,4-triazolium 4,5-dinitroimidazolate 5 7 5 4 156 165 1730 1022.5 4,5-dinitroimidazolate of 1-methyl-1,2,4-triazolium 6 7 7 4 102 150 1660 831.1 3-azido-1,2,4-triazolium 4,5-dinitro-im idazoate 5 10 4 4 92 158 1700 2214.6 4,5-dinitroimidazolate of 1-methyl-3-azido-1,2,4-triazolium 6 10 6 4 80 145 1600 1987.6 4,5-dinitroimidazolate of 4-amino-1,2,4-triazolium 5 8 6 4 137 149 1650 1440.9 1,2,4-triazolium 5-nitro-tetrazolate 3 8 4 2 137 183 1530 2370.7 1-methyl-1,2,4-triazolium 5-nitro-tetrazolate 4 8 6 2 62 163 1520 2033.8 3-azido-1,2,4-triazolium 5-nitro-tetrazolate 3 11 3 2 -35 161 1530 3559.6 1-methyl-3-azido-1,2,4-triazolium 5-nitro-tetrazolate 4 11 5 2 -38 141 1450 3215.5 4-amino-1,2,4-triazolium 5-nitro-tetrazolate 3 9 5 2 102 190 1580 2739.7
■ Based on tetrazolium cation Denomination Atomic composition T _FUS T _DECOMP ρ ΔH _f ° VS NOT H O [° C] [° C] [Kg / m3] [KJ / kg] 1-amino-4,5-dimethyltetrazolium nitrate 3 6 8 3 -59 170 1500 801.7 2-amino-4,5-dimethyltetrazolium nitrate 3 6 8 3 94 173 1550 750.0 1,5-Diamino-4-methyl-tetrazolium nitrate 2 7 7 3 121 181 1510 986.4 Dinitramide of 1,5-diamino-4-methyl-tetrazolium 2 9 7 4 85 184 1720 1744.8 Azide of 1,5-diamino-4-methyl-tetrazolium 2 9 7 0 135 137 1420 4309.6

The above salts can be prepared according to Singh et al Structure Bond 2007, 125: 35-83.

2- Theoretical performances

• Exemple 1 : monergol formé par un sel « cristal » dissous dans le N₂O liquide ;
• Exemple 2 : sel liquide en mélange binaire avec le N₂O liquide ;
• Exemple 3 : solution formée d'un sel « cristal » dissous dans un solvant énergétique organique ou ionique, elle-même en équilibre binaire avec le N₂O liquide :

The theoretical performances of certain cation / anion pairs in mixture with N ₂ O are given here on the basis of formation enthalpies found in the literature. The tables and figures below show the evolution of the specific impulse (Isp) in the vacuum of the monergol as a function of the mixing ratio ( ^O / _F ). The calculations are made for a pressure in the combustion chamber of 10 bar, a nozzle expansion ratio of ε = 100 and an equilibrium expansion in the nozzle. Tables and curves are given for values around the maximum of Isp and the corresponding optimal mixing ratio. The examples given below involve energetic salts dissolved in each of the three methods described earlier, namely:

• Example 1: monergol formed by a "crystal" salt dissolved in liquid N ₂ O;
• Example 2: liquid salt in a binary mixture with liquid N ₂ O;
• Example 3: solution formed of a "crystal" salt dissolved in an organic or ionic energy solvent, itself in binary equilibrium with liquid N ₂ O:

Example 1: the first case can be illustrated by the use of the azide of 1- (2-butynyl) -3-methyl-imidazolium, noted [ByMIM] [N ₃ ^- ]. This compound can be prepared from bromide of 1- (2-butynyl) -3-methyl-imidazolium on azide exchange resin according to Schneider et al Inorganic Chemistry 2008, 47 (9), 3617-3624 . It can be dissolved by direct dissolution in N ₂ O. The following figure gives the structure of [ByMIM] [N ₃ ^- ]:

The table below and the Figure 1 provide the theoretical values of Isp for a chamber pressure of 10 bar and for two expansion ratios: ε = 80 and ε = 330. Maximum Isp values of approximately 311s and 329s are respectively found for an optimal mixing ratio of ^O / _F = 5. This corresponds to the solution of 200 g of [ByMIM] [N ₃ ^- ] per kg of N ₂ O. Parameter Unit Value O / C [-] 1.0 2.0 3.0 4.0 5.0 6.0 , 0 8.0 9.0 Isp empty ( ε = 80) [S] 274.8 289.0 302.9 309.7 311.3 304.6 296.0 288.1 282.1 Isp empty ( ε = 330) [S] 291.3 305.1 318.5 325.6 329.2 322.0 311.8 303.1 295.6

Example 2: the second case can be represented by the liquid-liquid binary mixture between 1-butyl-3-methyl-imidazolium dicyanamide, denoted [BMIM] [N (CN) ₂ ^- ] (marketed by Solvionic), and the N ₂ O. The following figure gives the structure of [BMIM] [N (CN) ₂ ^- ]:

The variation of the Isp with the mixing ratio is described in the table below and the Figure 2 under the same conditions as those specified in Example 1. The maxima of Isp are obtained for an optimum mixing ratio of ^O / _F = 6 and are respectively 304.6s and 322.3s respectively for ε = 80 and ε = 330. Parameter Unit Value O / C [-] 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 Isp empty ( ε = 80) [S] 246.5 267.3 287.1 298.8 304.2 304.6 296.3 289.0 282.6 Isp empty ( ε = 330) [S] 263.0 284.0 301.9 314.5 320.4 322.3 312.3 303.7 296.3

Example 3: the third case can be illustrated by the ternary equilibrium between 1,5-diamino-4-methyl-tetrazolium dinitramide, noted [DAMT] [N (NO ₂ ) ₂ ] synthesized according to Singh et al Structure Bond 2007, 125: 35-83 ,, pyrrolidine and N ₂ O. The structure of [DAMT] [N (NO ₂ ) ₂ ] is as follows:

As it is a ternary mixture, the notion of mixing ratio ^O / _F is no longer used here. Instead, we study the ternary Isp diagram where the mass fractions of the three compounds are scanned. The table below and the Figure 3 provide the maximum Isp values and the corresponding optimal blending ratios for different mass fractions of salt in the energy solvent. The calculations are carried out under the same conditions as those of Examples 1 and 2. Parameter Unit Value Mass fraction of salt in the solvent [%] 0 10 20 30 40 50 O / F optimal * [-] 0.5 1.2 2.0 2.7 3.4 4.0 Maximum vacuum isp ( ε = 80) [S] 316.2 313.2 311.6 310.6 310.0 309.4 Maximum vacuum isp ( ε = 330) [S] 333.1 330.3 329.3 328.3 327.6 326.8 * Calculated as the ratio of the masses N ₂ O on solution of {salt + energetic solvent}

3- Salt preparation

• par quaternarisation par alkylation selon Singh et al., Structure bond 2007, 125 :35-83 ; US 8,034,202 ; Asikkala et al. (Application of ionic liquids and microwave activation in selected organic reaction, Acta Univ. Oul. A 502, 2008
• par métathèse en présence des sels d'argent de nitrate, dinitramide, azoture à partir des halogénures correspondants selon Singh et al Structure bond 2007, 125 :35-83 ; US 8,034,202 ;
• à partir d'un autre composé ionique par échange d'ions selon Asikkala et al (Application of ionic liquids and microwave activation in selected organic reaction, Acta Univ Oul. A 502, 2008 ; sur colonne : Schneider et al Inorganic Chemistry 2008, 47(9), 3617-3624 .

The salts according to the invention can be prepared in particular:

• by quaternization by alkylation according to Singh et al., Structure Bond 2007, 125: 35-83 ; US8,034,202 ; Asikkala et al. (Application of ionic liquids and micron activation in the organic reaction, Acta Univ., A 502, 2008
• by metathesis in the presence of the silver salts of nitrate, dinitramide, azide from the corresponding halides according to Singh et al Structure Bond 2007, 125: 35-83 ; US8,034,202 ;
• from another ionic compound by ion exchange according to Asikkala et al (Application of ionic liquids and micron activation in selected organic reactions, Acta Univ Oul. A 502, 2008 ; on column: Schneider et al Inorganic Chemistry 2008, 47 (9), 3617-3624 .

4- Optimization of the salt

The specific impulse generated by monergol combustion is closely dependent on the ^O / _F mixture ratio between N ₂ O and the fuel (dissolved "crystalline" salt or liquid salt). A curve can then be described by plotting the evolution of the Isp as a function of ^O / _F , any other parameter being kept constant (chamber pressure, initial temperature, expansion ratio ε ). A maximum of Isp can then be identified as well as the corresponding optimal ^O / _F. Ideally, the monergol must be synthesized respecting this mixing ratio in order to provide the best propulsive performance.

However, in the case of a crystalline salt (ie solid under standard conditions), the solubility of the salt in N ₂ O or in the N ₂ O combined solution limits the range of ^O / _F available. Indeed, the mixing ratio must be greater than a threshold value dictated by the solubility of the salt at the minimum use temperature (typically T _min = 0 ° C.). It clearly appears that, given the given ratio, it is preferable for the optimum mixing ratio to be in a zone of feasible solubility so as to be able to reach the maximum of Isp: $${\left({}^O{/}_F\right)}_{\mathit{Opt}}>{\left({}^O{/}_F\right)}_{\min }=\frac{1}{S\left(T_{\min }\right)}$$

This is illustrated on the Figure 4 .

soit démonter un optimum d'Isp à rapport de mélange élevé (typiquement 4≤ ^O / _F ≤10).The crystalline salts of interest must therefore either have a high solubility at the specified minimum temperature (typically $S\left(T_{\min }\right)>100\mathrm{boy\; Wut}\mathrm{.}k{\mathrm{boy\; Wut}}_{{\mathrm{NOT}}_{2}O}^{-1}$

or to disassemble a high mixing ratio Isp optimum (typically 4 ^{O O} / _F ≤ 10).

de sel. Cette valeur est bien au-delà de la solubilité maximale de [DAMT][N(NO₂)₂] à 0°C. Le recours au solvant énergétique permet de rehausser le rapport de mélange optimal, de diminuer la quantité de sel nécessaire et donc de respecter le plafond de solubilité. Ainsi, pour une fraction massique de sel de 40% dans la solution de pyrrolidine, un rapport de mélange optimale de 3.4 est trouvé, ce qui permet d'abaisser la masse de sel nécessaire à $117\mathit{g}\mathrm{.}k{g}_{N_{2}O}^{-1}\mathrm{.}$

Toutefois, cette approche altère l'Isp maximale (ici, -6s environ), ce qui montre toute l'importane de la densité énergétique du solvant utilisé.Example 3 given above illustrates this problem: without the use of solvents, the maximum Isp is found for ( ^O / _F ) _opt = 0.5, which corresponds to a dissolution of $2\mathit{kg}\mathrm{.}k{\mathrm{boy\; Wut}}_{{\mathrm{NOT}}_{2}O}^{-1}$

salt. This value is well above the maximum solubility of [DAMT] [N (NO ₂ ) ₂ ] at 0 ° C. The use of energetic solvent makes it possible to enhance the optimal mixing ratio, to reduce the amount of salt required and thus to respect the solubility ceiling. Thus, for a mass fraction of salt of 40% in the pyrrolidine solution, an optimal mixing ratio of 3.4 is found, which makes it possible to lower the mass of salt necessary for $117\mathit{boy\; Wut}\mathrm{.}k{\mathrm{boy\; Wut}}_{{\mathrm{NOT}}_{2}O}^{-1}\mathrm{.}$

However, this approach alters the maximum Isp (here, about -6s), which shows all the importance of the energy density of the solvent used.

The respect of the condition on the minimum mixing ratio ( ^O / _F ) _min must be valid regardless of the progress of the emptying of the tank. However, the phase change of the N ₂ O during the emptying, due to the monitoring of the saturation curve of the mixture, will induce an increase in the content of the liquid phase salt. The mixing ratio will gradually decrease during the withdrawal of the liquid phase. It must be ensured that the increase in salt concentration does not lead to the solubility being exceeded, at the risk of recrystallizing the solubility. The choice of the initial mixture ratio of the monergol must then take into account its state at the end of emptying. This is why in some cases, especially if ( ^O / _F ) _opt is very close to ( ^O / F ) _min , it is necessary to move to an initial mixing ratio higher than the optimum. In an adverse case, the maximum Isp is in an area beyond saturation. The accessible Isp will be less than the maximum value and chosen in an area up to the maximum of solubility.

5- Preparation of the monergol

1. 1) Introduction dans l'enceinte du sel sous forme cristalline ou liquide, selon une masse respectant le critère d'optimisation présenté ci-avant ;
2. 2) Le cas échéant, injection du solvant énergétique dans les proportions requises ;
3. 3) Mise sous vide de l'enceinte (pression résiduelle typiquement de 10³ Pa);
4. 4) Injection dans l'enceinte du protoxyde d'azote avec contrôle de la masse introduite par pesée continue de l'enceinte d'arrivée ou pesée continue du contenant de départ du N₂O;
5. 5) Agitation du mélange ;
6. 6) Stockage avec contrôle des conditions pression-température de l'enceinte - ou « fût de stockage » - afin de respecter l'intervalle de température spécifié.

The volatile nature of the nitrous oxide involves a specific mode of preparation of the monergol, during which the mixture salt and / or solvent and N ₂ O can not to be realized in the open air, but on the contrary in a closed enclosure. An illustrative procedure is as follows, starting from a clean and decontaminated enclosure:

1. 1) Introduction into the chamber of the salt in crystalline or liquid form, according to a mass respecting the optimization criterion presented above;
2. 2) If necessary, injection of the energy solvent in the required proportions;
3. 3) evacuation of the chamber (residual pressure typically 10 ³ Pa);
4. 4) Injection into the nitrogen oxide enclosure with control of the mass introduced by continuous weighing of the inlet enclosure or continuous weighing of the N ₂ O starting container;
5. 5) Agitation of the mixture;
6. 6) Storage with pressure-temperature control of the enclosure - or "storage drum" - to maintain the specified temperature range.

6- Filling on satellite

The filling of the satellite tank can then be carried out by placing the storage tank and the propulsion module tank in communication and withdrawing the liquid phase. The driving force for the transfer of monoling from the drum to the reservoir is directly ensured by the self-pressurization of the monergol. The use of an additional neutral gas may be considered to expel the monolgy from the storage drum.

7- Operating conditions & combustion

The monol {N ₂ O + ionic fuel} stored in the pressurized tank is injected into the propellant via a usual fluid line including in particular a flow control valve called "motor valve". The monergol is withdrawn at the reservoir by its liquid phase insofar as only this phase comprises both the oxidant and the fuel. A bleeding technique well adapted to the present invention is the capillary network system (also known as the surface tension tank), well known to those skilled in the art. The expulsion of the monergol through the fluidic line supplying the thrusters is ensured by the pressure generated by the N ₂ O gas in equilibrium with the liquid solution. Only the liquid phase is then expelled.

The value of the mass flow rate of the monergol injected into the propellant (s) is dictated by the total pressure drop in the fluid lines of the reservoir to the engine (s), in particular by the singular pressure drop of the injector (dictated by its design). As long as the monergol has not crossed the injection head, it remains in liquid phase as long as it exists in this state in the tank.

When the monergol goes through the injector located at the engine head (called "front end"), the latter undergoes a relaxation. It then enters the upstream part of the combustion chamber and is caused to undergo a phase change. The cause of the phase change differs according to the state of the combustion chamber, more precisely its pressure and temperature level. If it is an ignition, it can be assumed that the monergol enters a "fresh" environment and empty or near vacuum (so-called rarefied medium) to the extent that the room communicates with the vacuum space via the nozzle. The monolol will volatilize rapidly since its saturation vapor pressure will be significantly higher than the residual pressure within the combustion chamber. This phenomenon will be exacerbated if the monolayer or the walls of the thruster are at a higher temperature.

The ignition phase consists in synchronizing the triggering of the spark plug with the arrival of the flow of the monergol in order to generate a "soft" ignition (contrary to the "hard start" involving a peak of transient pressure and violent damage to the system) . The assurance of a quality ignition can also be achieved by the realization of a train of triggers of the candle (bursts of electric arcs) with relatively constant frequency (period of the order of a few tens of milliseconds to hundreds of milliseconds). The arcing stream can also be fired in a slight phase advance over the injection to act as a local preheat. The optimization of the ignition thus relies on the conjunction of a geometric design and an optimized sequence of trips.

In the case where the monergol penetrates into a "hot" chamber, which corresponds for example to several successive firing interspersed with relatively close inactive phases (short cycles), the ignition is facilitated because the monergol receives a supply of energy extra before the stimuli of the candle. These problems are well known to those skilled in the art, especially in the field of ignition of turbojet engines at high altitude or cryocyclic liquid propellants.

Advantageously, the combustion is maintained after ignition as long as the monergol flow is maintained (open motor valve) and therefore does not require additional spark plugs. The energy released by the combustion of the monergol is sufficient to maintain the reaction of the fresh species injected. Combustion consists of a reaction between the main oxidant, namely N ₂ O, and the ionic fuel optionally comprising oxidizing groups (eg nitramides). The reaction produces hot gases at high pressure. The combustion chamber is dimensioned such that the thermodynamic equilibrium is reached before ejection of the flue gas so as to achieve maximum efficiency. The gases are ejected through a nozzle provided with a convergent, sonic and divergent neck to initiate and accelerate the flow to generate an optimal thrust force.

Claims (14)

1. A monopropellant comprising a mixture comprising:

   - nitrous oxide (N₂O) as an oxidizer, at least partly in liquid form, and

   - a fuel in the form of a salt in the liquid N₂O phase.
2. The monopropellant according to claim 1, such that said nitrous oxide is partly in the form of a gas.
3. The monopropellant according to anyone of the preceding claims, such that its liquid phase is constituted by:

   (i) fuel in the form of a solid salt when it is isolated at room temperature and solubilized in said N₂O at least partly present in liquid form, or

   (ii) a molten salt of the fuel in a binary mixture with said N₂O at least partly present in liquid form, or

   (iii) an ionic solution of the fuel dissolved in an organic or ionic energetic solvent, in a binary mixture with said N₂O at least present in liquid form.
4. The monopropellant according to anyone of the preceding claims, such that the fuel is a salt of an energetic organic compound.
5. The monopropellant according anyone of the preceding claims, such that the fuel is a salt of a nitrogen-containing derivative.
6. The monopropellant according to anyone of the preceding claims, such that the cation of said salt is selected from:

   - linear cations, such as ammonium, hydroxyl ammonium, hydrazinium ions and their derivatives;

   - saturated heterocyclic cations such as piperidinium, piperazinium cations and their derivatives; and

   - heterocyclic cations, either aromatic or not, such as azinium, azolium, diazolium, triazolium and tetrazolium, notably pyridinium, pyrrolium, isoxazolium, pyrazolium, oxazolium, pyrazolium, imidazolium, oxadiazolium, triazolium, oxatriazolium, tetrazolium, pyrrolidium, triazinium, pyridazinium, pyrimidinium, pyrazinium, piperidinium, 1,2,3- or 1,2,4- triazolium, 1,4,5- or 2,4,5-tetrazolium, as well as their -inium and -idinium analogues, and their derivatives.
7. The monopropellant according to claim 6 such that the cation is selected from ammonium, imidazolium, triazolium, tetrazolium ions and their derivatives.
8. The monopropellant according to anyone of the preceding claims such that the anion of said salt is selected from:

   - linear anions such as azide, nitrate, nitramide, dinitramide, nitroformate, nitrite, acetate, cyanamide, dicyanamide ions; and

   - unsaturated heterocyclic anions such as azolates such as pyrrolate, diazolate such as pyrazolate, imidazolate, triazolate such as 1,2,3- and 1,2,4-triazolate and tetrazolate such as nitrotetrazolate, and their derivatives.
9. The monopropellant according to claim 8, such that the counter-ion (anion) is selected from azide, nitrate, dinitramide, dicyanamide, imidazolate and tetrazolate ions and their derivatives.
10. The monopropellant according to claim 1 such that the fuel is selected from:

    - ammonium azide (AA),

    - tetrabutylammonium azide,

    - triazolium nitrotetrazolate,

    - azidotriazolium nitrotetrazolate,

    - ammonium dinitramide (ADN),

    - hydroxylammonium azide (HAA),

    - hydrazinium azide(HA),

    - 1-(2-butynyl)-3-methyl-imidazolium azide

    - hydroxylammonium nitrate (HAN),

    - hydrazinium nitroformate (HNF),

    - ammonium nitrate (AN),

    - hydrazinium nitrate (HN),

    - triethanolammonium nitrate (TEAN),

    - hydroxylammonium dinitramide (HADN),

    - ammonium dicyanamide,

    - imidazolium dicyanamide,

    - 1-butyl-3-methylimidazolium dicyanamide,

    - 1-butyl-2,3-dimethylamidazolium acetate,

    - 1-butyl-1-methylpyrrolidinium acetate, dicyanamide,

    - 1-ethanol-3-methylimidazolium dicyanamide,

    - N-tributyl-N-methylammonium dicyanamide,

    - 1-butyl-3-methyl-imidazolium dicyanamide,

    - 1,2,4-triazolium 4,5-dinitro-imidazolate

    - 1-methyl-1,2,4-triazolium 4,5-dinitro-imidazolate,

    - 3-azido-1,2,4-triazolium 4,5-dinitro-imidazolate ,

    - 1-methyl-3-azido-1,2,4-triazolium 4,5-dinitro-imidazolate,

    - 4-amino-1,2,4-triazolium 4,5-dinitro-imidazolate,

    - 1,2,4-triazolium 5-nitro-tetrazolate,

    - 1-methyl-1,2,4-triazolium 5-nitro-tetrazolate,

    - 3-azido-1,2,4-triazolium 5-nitro-tetrazolate,

    - 1-methyl-3-azido-1,2,4-triazolium 5-nitro-tetrazolate,

    - 4-amino-1,2,4-triazolium 5-nitro-tetrazolate,

    - 1-amino-4,5-dimethyltetrazolium nitrate

    - 2-amino-4,5-dimethyltetrazolium nitrate

    - 1,5-diamino-4-methyltetrazolium nitrate

    - 1,5-diamino-4-methyltetrazolium dinitramide

    - 1,5-diamino-4-methyltetrazolium azide

    - 1,5-diamino-4-methyi-tetrazolium dinitramide.
11. The method for preparing a monopropellant according to anyone of the preceding claims comprising the step of mixing the fuel and N₂O in a closed enclosure.
12. A space propulsion method using a monopropellant according to anyone of the preceding claims.
13. The propulsion method according to claim 12, comprising the combustion of the monopropellant by controlled ignition.
14. The method according to claim 12 or 13, comprising the means for pressurizing the monopropellant in the tank.

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