DE102023101308A1 - FUEL FOR SPACECRAFT AND/OR AIRCRAFT - Google Patents

Abstract

The invention relates to a nitromethane fuel for spacecraft and/or missiles, wherein the fuel comprises at least one additive in the form of a metallocene and/or an inhibitor.

Description

State of the art

The invention relates to a fuel for spacecraft and/or missiles.

Liquid Monergol fuels are often used to control the orbit and attitude of satellites and missiles. Since only one tank and one set of components for fuel delivery is required, very simple and inexpensive systems can be implemented in this way.

Up to now, hydrazine has been used as a fuel in such systems. The decomposition of this substance, which is necessary for ignition and for the operation of such an engine, can be achieved very easily with the help of iridium-platinum-based catalysts. The decomposition gases, i.e. the reactive support mass that is created during decomposition, have a relatively low temperature of around 800 K, which allows for simple construction without the use of expensive high-temperature materials. Despite this, a relatively high propulsion power can be achieved: the theoretical specific impulse is 1979 m/s. The disadvantages of using hydrazine, however, are the high costs involved in handling this substance. This is due to the high toxicity and carcinogenicity of this substance.

To meet this challenge, a number of alternative propellants have been researched, developed and tested. One approach to realising such so-called "green propellants" is to prepare solutions of solid explosive oxidizers such as hydroxyl ammonium nitrate (HAN) and ammonium dinitramide (ADN) in water and then add a fuel component such as methanol or ammonia to create a premixed reactive mixture or explosive substance that is nevertheless insensitive enough to be used as a propellant. Such propellants typically have a higher volume and mass specific impulse than hydrazine.

However, HAN and ADN-based fuels have high production costs. In addition, these fuels also have significantly higher burn-off temperatures than hydrazine, which has so far been a challenge for the construction materials of such engines. In addition, fuels based on solutions of energetic materials in water are difficult to ignite because the water must first be evaporated from the solution for successful combustion.

Another approach is the use of natural, i.e. non-premixed, monergols. In this case, the use of highly concentrated hydrogen peroxide solutions (90-98% by weight in water) is particularly important. This relatively non-toxic substance can be easily catalytically decomposed, just like hydrazine. The biggest disadvantage of hydrogen peroxide solutions is their low performance compared to other comparable fuels, as well as their low stability, which limits their storage over long periods of time.

The use of nitromethane also represents a potential green propellant. This substance is a cheap and widely used laboratory solvent, but has properties that make its use as an aerospace fuel significantly more difficult. The substance shows no or unstable combustion at low combustion chamber pressures. It is poorly flammable. The substance is very sensitive to impact and is considered explosive.

The EP 2 662 350 B1 discloses a gel-like, monergolic fuel in which the high combustion temperature is reduced by adding an additive to the fuel which oxidises the carbon to carbon monoxide during combustion of the fuel and does not provide oxygen for the oxidation of hydrogen to water and of carbon monoxide to carbon dioxide.

The EP 2 607 337 B1 discloses a gel-like, injectable single-component fuel which consists of a mixture of at least one monergolic base fuel, namely a hydrocarbon containing at least one nitro group, and at least one gelling agent consisting of carbon particles or carbon nanotubes and at least one solid oxidizer with an average particle size of at most 0.4 millimeters.

Disclosure of the invention

The object of the invention is to create a fuel with improved properties for spacecraft and/or missiles

The objects are achieved by the features of the independent claim. Favorable embodiments and advantages of the invention emerge from the further claims, the description and the drawing.

The features listed individually in the patent claims can be combined with one another in a technologically meaningful manner and can be supplemented by explanatory facts from the description and by details from the figures, whereby further embodiments of the invention are shown.

According to one aspect of the invention, a nitromethane fuel for spacecraft and/or missiles is proposed, wherein the fuel comprises at least one additive in the form of a metallocene and/or an inhibitor.

Additives such as metallocenes significantly improve the ignitability of nitromethane fuel compared to pure nitromethane and advantageously enable combustion at low combustion chamber pressures.

The addition of an inhibitor, also known as a phlegmatizing agent, can make the combustion of the fuel significantly more stable. In addition, the possible deterioration in the impact sensitivity of the fuel that may accompany the addition of metallocenes can be counteracted by adding an inhibitor.

Depending on the fuel design, the proportion of metallocene can be 0.5 wt.% to 5 wt.%. Alternatively or additionally, the proportion of inhibitor can be 5 wt.% to 25 wt.%. These proportions of metallocenes can advantageously improve the ignitability of a fuel made of nitromethane and promote combustion at low combustion chamber pressures. The proportions of inhibitors can advantageously reduce the impact sensitivity of the fuel.

According to a favorable design of the fuel, the metallocene can be at least one from the group chromocene and related substances, nickelocene and related substances, ferrocene and related substances, in particular ethylferrocene, butylferrocene, catocene.

An addition of, for example, 0.5 wt.% to 5 wt.% of ferrocene and related substances such as ethylferrocene, butylferrocene, catocene, as well as chromocene and related substances, as well as nickelocene and related substances can greatly improve the ignitability of liquid and gelatinous nitromethane fuels under an inert gas atmosphere. In addition, combustion can advantageously be enabled in the low pressure range up to 12.5 bar.

Depending on the fuel design, the inhibitor can be dimethyl sulfoxide.

The use of the inhibitor dimethyl sulfoxide (DMSO) is particularly advantageous. An addition of more than 6% by weight of pure nitromethane can already bring about a significant improvement in the impact sensitivity. The addition of 12% by weight makes the mixture almost insensitive to impact.

The addition of DMSO to nitromethane can have a beneficial catalytic effect at elevated pressures and temperatures. Compared to the addition of n-butanol or pure nitromethane, the decomposition takes place at lower temperatures. This behavior is particularly pronounced when ferrocene is added to a nitromethane-DMSO mixture. The exothermic reaction is now located at a significantly lower temperature.

For example, a mixture containing 85% by weight of nitromethane, 13% by weight of DMSO, 2% by weight of ferrocene or a similar mixture can be used advantageously as a low-cost, non-toxic and safe "green" missile or satellite fuel with high performance compared to hydrazine and ADN and HAN fuels. In addition, this fuel does not contain water and is therefore more easily ignited than fuels based on aqueous solutions of ADN or HAN.

According to a favorable embodiment of the fuel, the inhibitor can be at least one of n-butanol, in particular with a proportion of 3 wt.% to 10 wt.%, nitroethane, in particular with a proportion of 10 wt.% to 30 wt.%.

The addition of 3 wt.% to 10 wt.% n-butanol or 10 wt.% to 30 wt.% nitroethane can bring about a beneficial improvement in impact sensitivity to values greater than 10 J.

According to a favorable design of the fuel, the inhibitor can be an ionic liquid. In particular, the inhibitor can be ethyl ammonium nitrate (EAN), in particular in a proportion of 4 wt.% to 30 wt.%.

Mixtures of 4 wt.% to 12 wt.% EAN with 1 wt.% to 2 wt.% ferrocene or ethylferrocene and nitromethane can be advantageously used as insensitive liquid Monergol fuels.

According to a favorable embodiment, the fuel can contain at least one organic gelling agent, in particular in a proportion of 1% to 10% by weight. An organic gelling agent can also advantageously act as an inhibitor to improve the impact sensitivity.

The addition of 1% to 4% by weight of organic gelling agent, in particular a low molecular weight gelling agent (LMOG; for example N-alkyl gluconamides, 12-hydroxystearic acids and salts, (oligo)ureas, alkoxybenzoic acids, N-(oligo-hydroxyalkyl) alkoxybenzamides, alkoxybenzhydrazines and hydrazides, alkoxybenzoyl semicarbazides and alkoxybenzoic sulfonic acids) has proven to be particularly beneficial for improving the impact sensitivity of nitromethane fuel.

According to a favorable design of the fuel, the organic gelling agent can be at least one of a fumed silica, an organic gelling agent with a low molecular weight, carbon particles, carbon nanotubes. Such a gelling agent has proven to be particularly favorable for improving the impact sensitivity of the nitromethane fuel.

Depending on the fuel design, the proportion of additives can be between 10% and 20% by weight. This allows the desired properties of the nitromethane fuel, such as good ignitability, combustion at low combustion chamber pressures and low impact sensitivity, to be developed.

drawing

Further advantages emerge from the following description of the drawing. The drawing shows embodiments of the invention. The drawing, the description and the claims contain numerous features in combination. The person skilled in the art will also expediently consider the features individually and combine them into further useful combinations.

• 1 Ergebnisse von Messungen zur dynamischen Differenzkalorimetrie im geschlossenen Tiegel an verschiedenen Treibstoffen aus Nitromethan für Raumfahrzeuge und/oder Flugkörper nach Ausführungsbeispielen der Erfindung.

It shows, for example:

• 1 Results of closed crucible dynamic differential scanning calorimetry measurements on various nitromethane fuels for spacecraft and/or missiles according to embodiments of the invention.

Embodiments of the invention

The figure shows only examples and is not to be understood as limiting.

Before the invention is described in detail, it should be noted that it is not limited to the particular components of the device and the particular method steps, since these components and methods may vary. The terms used herein are intended only to describe particular embodiments and are not used in a limiting sense. In addition, when the singular or indefinite articles are used in the description or in the claims, this also refers to the plural of these elements, unless the overall context clearly indicates otherwise.

Directional terminology used below with terms such as "left", "right", "top", "bottom", "before", "behind", "after" and the like is intended only to facilitate understanding of the figure and is in no way intended to limit the scope. The components and elements shown, their design and use may vary in accordance with the considerations of a person skilled in the art and may be adapted to the respective applications.

The proposed nitromethane fuel for spacecraft and/or missiles can advantageously contain at least one additive of a metallocene and/or an inhibitor in order to improve the properties of the fuel with regard to ignitability, burn-up at low combustion chamber pressures and impact sensitivity. Advantageously, the proportion of a metallocene can be 0.5 wt.% to 5 wt.% and/or the proportion of an inhibitor can be 5 wt.% to 20 wt.%. The metallocene can be at least one from the group chromocene and related substances, nickelocene and related substances, ferrocene and related substances, in particular ethylferrocene, butylferrocene, catocene.

The total amount of additives may advantageously be between 10% and 20% by weight.

The fuel can advantageously contain at least one inhibitor to reduce the impact sensitivity. The inhibitor can advantageously be, for example, dimethyl sulfoxide (DMSO). The inhibitor can also be at least one of n-butanol, in particular with a proportion of 3% by weight to 10% by weight, nitroethane, in particular with a proportion of 10% by weight to 30% by weight. The inhibitor can also be an ionic liquid. In particular, the inhibitor can be ethyl ammonium nitrate, in particular with a proportion of 4% by weight to 30% by weight.

Advantageously, the fuel can comprise at least one organic gelling agent, in particular in a proportion of 1% to 10% by weight. The organic gelling agent can be, for example, at least one of a pyrogenic silica, an organic gelling agent with a low molecular weight, carbon particles, carbon nanotubes.

Table 1 shows the measured drop hammer impact sensitivities S _i for nitromethane fuels with various additives. Table 1: Results of drop hammer impact sensitivities for nitromethane fuels Addition in % by weight Shock sensitivity in J Nitromethane, pure S _i < 5 5% n-butanol 10 < S _i ≤ 15 6% n-butanol 15 < S _i ≤ 20 7% n-butanol 40 < S _i ≤ 50 8% n-butanol 40 < S _i ≤ 50 10% n-butanol S _i > 50 6% n-butanol + 2% ferrocene 10 < S _i ≤ 15 6% DMSO 10 < S _i ≤ 15 8% DMSO 20 < S _i ≤ 30 10% DMSO 15 < S _i ≤ 20 12% DMSO S _i > 50 10 % DMSO + 1 % Ferrocen 10 < S _i ≤ 15 13 % DMSO + 2 % Ferrocen 10 < S _i ≤ 15 25% nitroethane 5 < S _i ≤ 10 35 % Nitroethane 10 < S _i ≤ 15

Table 1 shows that the addition of an inhibitor such as n-butanol, nitroethane or DMSO shifts the shock sensitivity to higher values, i.e. improves it.

The addition of ferrocene worsens the impact sensitivity to a certain extent.

1 shows results of measurements on dynamic differential scanning calorimetry (DSC) in a closed crucible on various nitromethane fuels for spacecraft and/or missiles according to embodiments of the invention.

The signals 20 of the DSC measurement are plotted in units of µV/mg as a function of temperature 10 in °C. Curve 30 represents measurements for pure nitromethane. Curve 32 represents measurements for a nitromethane fuel with 6 wt.% n-butanol, curve 34 for a nitromethane fuel with 13 wt.% DMSO, curve 36 for a nitromethane fuel with 13 wt.% DMSO and 2 wt.% ferrocene.

Out of 1 , which shows the DSC measurement curves of some nitromethane-based fuels, it is clear that the addition of DMSO (here 13 wt. %) to nitromethane has a catalytic effect at increased pressures and temperatures. Compared to the addition of n-butanol or to pure nitromethane, the decomposition, recognizable by the increase and the peak of the exothermic reaction, takes place at lower temperatures.

This behavior is particularly pronounced when ferrocene is added to a nitromethane-DMSO mixture. The exothermic reaction is now located at a significantly lower temperature.

The pure nitromethane fuel (curve 30) shows the peak of the exotherm at about 380 °C. Nitromethane fuel with 6 wt% n-butanol (curve 32) shows the peak at about 390 °C. Nitromethane fuel with 13 wt% DMSO (curve 34) shows a broad peak at about 360 °C, while nitromethane fuel with 13 wt% DMSO and 2 wt% ferrocene (curve 36) shows the peak at about 280 °C.

This is consistent with combustion chamber tests and so-called strand burner tests. In strand burner tests, a mixture of 85% by weight nitromethane, 13% by weight DMSO and 2% by weight ferrocene could be made to burn at 12.5 bar inert gas pressure. In combustion chamber tests, stable combustion could be achieved with this mixture at 13 bar to 15 bar. With a comparable mixture, but with 6% n-butanol as an inhibitor, only a minimum combustion chamber pressure of 40 bar could be demonstrated.

Based on the measurement results presented, the following fuels made from nitromethane with additives prove to be suitable for various applications:

Fuels for spacecraft and missiles:

• 85 wt% nitromethane, 13 wt% DMSO, 2 wt% ferrocene;
• 92% by weight nitromethane, 6% by weight n-butanol, 2% by weight ferrocene;
• 92 wt.% nitromethane, 6 wt.% n-butanol, 2 wt.% metal salt (e.g. chromium (III) acetyl acetonate);
• 94 wt.% nitromethane, 6 wt.% dimethyl sulfoxide;
• 92% by weight nitromethane, 6% by weight n-butanol, 2% by weight ferrocene;
• 90% by weight nitromethane, 8% by weight EAN, 2% by weight ferrocene.

Gel fuels for missiles:

• 85 wt% nitromethane, 10 wt% DMSO, 4 wt% LMOG gelling agent, 1 wt% ethylferrocene;
• 88 wt% nitromethane, 7 wt% EAN, 4 wt% LMOG gelling agent, 1 wt% ethylferrocene.

Reference symbols

10

temperature

20

signal

30

Nitromethane, pure

32

Nitromethane + 6% by weight n-butanol

34

Nitromethane + 13 wt.% DMSO

36

Nitromethane + 13 wt% DMSO + 2 wt% ferrocene

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• EP 2662350 B1 [0008]
• EP 2607337 B1 [0009]

Claims (9)

Nitromethane fuel for spacecraft and/or missiles, wherein the fuel comprises at least one additive in the form of a metallocene and/or an inhibitor. Fuel to Claim 1 , wherein the proportion of a metallocene is 0.5 wt. % to 5 wt. % and/or wherein the proportion of an inhibitor is 5 wt. % to 25 wt. %. Fuel to Claim 1 or 2 , wherein the metallocene is at least one from the group chromocene and related substances, nickelocene and related substances, ferrocene and related substances, in particular ethylferrocene, butylferrocene, catocene. A fuel according to any preceding claim, wherein the inhibitor is dimethyl sulfoxide. Fuel according to one of the preceding claims, wherein the inhibitor is at least one of n-butanol, in particular in a proportion of 3 wt.% to 10 wt.%, nitroethane, in particular in a proportion of 10 wt.% to 30 wt.%. Fuel according to one of the preceding claims, wherein the inhibitor is an ionic liquid, in particular wherein the phlegmatizing agent is ethyl ammonium nitrate, in particular in a proportion of 4 wt.% to 30 wt.%. Fuel according to one of the preceding claims, wherein the fuel comprises at least one organic gelling agent, in particular in a proportion of 1 wt.% to 10 wt.%. Fuel to Claim 7 wherein the organic gelling agent is at least one of a fumed silica, a low molecular weight organic gelling agent, carbon particles, carbon nanotubes. Fuel according to one of the preceding claims, wherein the proportion of additives is between 10 wt.% and 20 wt.%.