Low-toxicity hypergolic bipropellant and method for producing same

Abstract

The low-toxicity hypergolic bipropellant according to the present invention is characterized in that hydrogen peroxide having a concentration of 95 wt% is used as an oxidizing agent in a hypergolic liquid fuel having 45.5 wt% of ethanol and 9 wt% of a tetrakisimidazolium monocyanoborohydride copper (II) catalyst mixed in 45.5 wt% of an ionic liquid mixture fuel.

Description

Low-toxicity contact-ignition binary propellant and method for producing the same

[0001] The present invention relates to a low-toxicity contact-ignition binary propellant for a liquid rocket engine, and more particularly, to a low-toxicity contact-ignition binary propellant using ethanol and a catalyst additive mixed with an ionic liquid fuel and hydrogen peroxide as an oxidizer.

[0002] A variety of small and large rocket engines generate thrust by igniting liquid propellants and releasing the high-temperature, high-pressure gases.

[0003] Hydrazine (N2H4), a propellant widely used in rocket engines, is a molecular compound with a relatively high vapor pressure and high toxicity, making it difficult to handle on the ground. Consequently, handling hydrazine incurs handling costs, such as the requirement to wear a Self-Contained Atmospheric Protective Ensemble (SCAPE) suit.

[0004] The European Chemicals Agency issued a hazard warning (H350 and H330) on hydrazine in 2011 and listed it as an SVHC (Substance of Very High Concern) on the REACH (Registration, Evaluation, Authorization & Restriction of Chemicals) candidate list.

[0005] To improve these problems, ionic liquid fuels, which are being studied as alternative propellants, have the advantages of lower vapor pressure and less toxicity than hydrazine, and are therefore being studied as alternative propellants that are easy to handle on the ground.

[0006] Ionic liquid fuels, unlike typical organic solvents, are liquid substances that exist in ionic form. Ionic liquid fuels are environmentally friendly chemicals because they have low vapor pressure, are non-toxic, and can be ignited by contact with oxidizers such as nitric acid or hydrogen peroxide.

[0007] However, ionic liquids have a problem in that their high viscosity makes it difficult to mix homogeneously with the oxidizer, which causes a decrease in performance.

[0008] The present invention aims to solve the above problems by providing a low-toxicity contact ignition binary propellant for a liquid rocket engine and a method for manufacturing the same.

[0009] The ionic liquid fuel according to the present invention for solving the above problem comprises a cyanoborohydride anion and an imidazolium-based heterocyclic cation.

[0010] In one embodiment, the ionic liquid mixed fuel is a mixture of the ionic liquid fuel and ethanol in an equal weight ratio to lower the viscosity of the ionic liquid fuel.

[0011] In one embodiment, the contact ignition liquid fuel is one in which tetrakisimidazolium monocyanoborohydride copper(II) is added as a catalyst to the ionic liquid mixed fuel.

[0012] In one embodiment, the contact ignition liquid fuel is a mixture of 45.5 wt% of ionic liquid mixed fuel, 45.5 wt% of ethanol, and 9 wt% of tetraximidazolium monocyanoborohydride copper(II) catalyst.

[0013] In one embodiment, a low-toxicity contact-ignition binary propellant uses hydrogen peroxide at a concentration of 95 wt% as an oxidizer in the contact-ignition liquid fuel.

[0014] In another embodiment of the present invention, a method for producing a contact-ignitable liquid fuel comprises the steps of synthesizing 1-ethyl-3-methylimidazolium bromide and dissolving the synthesized ethyl methylimidazolium bromide in dichloromethane to synthesize 1-ethyl-3-methylimidazolium cyanoborohydride.

[0015] In one embodiment, the method for producing the contact ignition liquid fuel further includes a step of mixing ethanol in an equal weight ratio to lower the viscosity of the ionic liquid fuel.

[0016] As an example, the method for manufacturing the contact ignition liquid fuel comprises: II Steps for synthesizing (H-imidazole)4Cl2 and the Cu II A further step of adding (H-imidazole)4Cl2 to an acetonitrile stirred solution containing sodium cyanoborohydrate is included.

[0017] The low-toxicity contact ignition binary propellant according to the present invention uses a low-toxicity contact ignition fuel (hereinafter referred to as 'ILethCu-01') containing a mixture of 1-ethyl-3-methylimidazolium cyanoborhydride (hereinafter referred to as 'EMIM BH3CN'), ethanol, and a catalyst additive (hereinafter referred to as 'Cu-P1') and 95 wt% hydrogen peroxide oxidizer.

[0018] In addition, EMIM BH3CN has excellent solubility in ethanol, creating a completely miscible fluid, and the additive Cu-P1 also dissolves well in the fluid of EMIM BH3CN dissolved in ethanol, enabling the production of a homogeneous liquid mixed fuel, which is environmentally friendly and has low toxicity, as well as reducing the cost.

[0019] In addition, ILethCu-01 according to the present invention exhibits low combustion instability of less than 5% when used with 95 wt% hydrogen peroxide oxidizer, making it an excellent fuel for a propulsion device.

[0020] Figure 1 is a chemical structural formula of 1-ethyl-3-methylimidazolium cyanoborohydride according to the present invention.

[0021] Figure 2 is a chemical structural formula of copper(II) tetraximidazolium monocyanoborohydride according to the present invention.

[0022] Figure 3 is a chemical structural formula of ethanol according to the present invention.

[0023] Figure 4 is a high-speed camera drop image of a drop test according to the present invention.

[0024] Figure 5 is a block diagram of a drop combustion experiment device according to the present invention.

[0025] Figure 6 is a perspective view of the injector and chamber of the thruster according to the present invention.

[0026] Figure 7 is a pressure graph with an oxidizer / fuel ratio of 3.5 according to the present invention.

[0027] Figure 8 is a pressure graph with an oxidizer / fuel ratio of 4.3 according to the present invention.

[0028] Figure 9 is a pressure graph with an oxidizer / fuel ratio of 5.0 according to the present invention.

[0029] Contact-ignition binary propellants are propellants that can be 'ignited' and 're-ignited' without an external ignition source, and ignite when the oxidizer comes into contact with the fuel.

[0030] Low-toxicity ionic liquids used as fuel have high viscosity, making it difficult to mix with oxidizers, which leads to reduced performance.

[0031] In the present invention, bioethanol was used to improve miscibility with an oxidizer in order to lower the viscosity of a low-toxicity ionic liquid, and a copper catalyst was used to improve contact ignition characteristics.

[0032] Bioethanol is a highly economical fuel derived from agricultural products. It uses cosolvents to lower the viscosity of ionic liquids, enabling them to effectively mix with oxidizers. Furthermore, the use of high-concentration hydrogen peroxide (95 wt%) in ionic liquid fuels reduces ignition performance, so catalysts are used to improve ignition delay. Hydrogen peroxide is an environmentally friendly oxidizer that decomposes into water and oxygen.

[0033] [Example 1] Synthesis of low-toxicity ionic liquid fuel

[0034] Figure 1 is a chemical structural formula of 1-ethyl-3-methylimidazolium cyanoborohydride (hereinafter referred to as 'EMIM BH3CN') according to the present invention, in which 1-ethyl-3-methylimidazolium bromide is prepared and then 1-ethyl-3-methylimidazolium cyanoborohydride is synthesized.

[0035] 1) Synthesis of ethyl methylimidazolium bromide

[0036] One equivalent of methylimidazole and 1.1 equivalents of ethyl bromide were dissolved in 500 ml of acetonitrile in a glass reactor. The reaction was carried out under reflux at 50–55°C for 24 hours, and then the acetonitrile was evaporated using a vacuum rotary evaporator. In addition, the oily product was washed with ethyl acetate to obtain a white solid crystallized product, which was then dried under vacuum at room temperature for 24 hours. The yield of ethyl methylimidazolium bromide was 95%.

[0037] 2) Synthesis of 1-ethyl-3-methylimidazolium cyanoborohydride

[0038] In a 500 mL reactor, 1 equivalent of 1-ethyl-3-methylimidazolium bromide was dissolved in the required amount of dichloromethane under a nitrogen atmosphere. Consequently, 1.1 equivalents of sodium cyanoborohydride were added to the reactor. The reaction mixture was stirred at room temperature for 36 hours. The white precipitate of sodium bromide was filtered through a 0.44-micron Whatman filter using a glass vacuum filtration device. The solvent was removed from the filtrate using a rotary vacuum evaporator. Finally, the ionic liquid was obtained and dried under vacuum at 70-80°C for 24 hours. The purity of the synthesized 1-ethyl-3-methylimidazolium cyanoborohydride was confirmed using nuclear magnetic resonance spectroscopy (NMR), and the yield was approximately 87%.

[0039] The synthesized 1-ethyl-3-methylimidazolium cyanoborohydride comprises at least one cyanoborohydride anion and an imidazolium-based heterocyclic cation.

[0040] [Example 2] Synthesis of catalyst additives

[0041] Figure 2 shows the chemical structure of the catalyst additive tetrakisimidazolium monocyanoborohydride copper (II) (hereinafter abbreviated as 'Cu-P1'), which was synthesized using the following method.

[0042] 1) Cu II Synthesis of (H-imidazole)4Cl2

[0043] 4 equivalents of imidazole and 1 equivalent of anhydrous copper chloride were placed in a round-bottom flask containing 30-40 ml of ethanol and stirred at room temperature for 1 hour. Diethyl ether was added to remove Cu II The precipitation of (H-imidazole)4Cl2 was induced. The precipitated compound was filtered and dried under vacuum for 24 h. Cu II The yield of (H-imidazole)4Cl2 compound was 95%.

[0044] 2) Cu II Synthesis of (H-imidazole)4BH3CN

[0045] Add Cu to 10-20 ml of acetonitrile stirred solution containing 2 equivalents of sodium cyanoborohydrate. II (H-imidazole)4Cl2 was added. The reaction mixture was stirred at 25-30°C for 24 hours, and sodium chloride was precipitated, followed by filtration through a 0.44 mm filter paper. The residual solvent was removed using a rotary vacuum evaporator. The synthesized compound was washed 3-4 times with pentane. The produced Cu II (H-imidazole)4BH3CN was blue and the yield was 90%.

[0046] [Example 3] Synthesis of contact ignition fuel (ILethCu-01)

[0047] A contact-ignitable liquid fuel (ILethCu-01) was prepared by mixing 45.5 wt% of the ionic liquid synthesized in Example 1, 45.5 wt% of ethanol, and 9 wt% of the Cu-P1 additive synthesized in Example 2. The homogeneous mixture was prepared at room temperature and stored in a sealed glass container. The physicochemical properties of ILethCu-01 are shown in Table 1.

[0048] [Table 1]

[0049]

[0050] [Example 4] Contact ignition drop test

[0051] Drop tests of the contact-ignitable liquid fuel ILethCu-01 were performed with 95 wt% hydrogen peroxide. Approximately 40 μL of 95 wt% hydrogen peroxide was dropped onto a 100 μL pool of ILethCu-01 fuel, and ignition images were captured using a high-speed camera (4000 fps). Three consecutive drop tests were performed, and the average ignition delay time (IDT) was 7.50 ms.

[0052] Contact ignition characteristics were measured in terms of ignition delay time (IDT). IDT is the time difference between the initial contact of the fuel and oxidizer and the first visible flame. To avoid hard starting of the engine, liquid rocket applications require an ignition delay time (IDT) of less than 50 ms, although less than 10 ms is more suitable. The ignition delay time drop test measurements for various fuel combinations using ILethCu-01 were performed using 95 wt% hydrogen peroxide. Three tests were conducted for each fuel combination, and the average ignition delay time was recorded based on images captured with a high-speed camera.

[0053] Figure 4 shows high-speed camera images of the ILethCu-01 drop test. Vapor formation was observed at 5.75 ms, flame ignition occurred at 7.25 ms, and the average propellant ignition delay time was 7.50 ms.

[0054] [Example 5] High-temperature combustion experiment of ILethCu-01 using hydrogen peroxide

[0055] The engine is designed with a chamber pressure of 10 bar and a thrust of 50 N, and the oxidizer-fuel-oxidizer (OFO) method was chosen over the triple injector to facilitate propellant preservation during propellant injection.

[0056] The combustion test apparatus, as shown in Figure 5, consists of a tank, piping, and a propulsion device and is made of stainless steel. Tables 2 and 3 present the theoretical design parameters of the rocket engine.

[0057] [Table 2]

[0058]

[0059] [Table 3]

[0060]

[0061] A 50N rocket engine was developed to study the performance of ILethCu-01, and the triple injector was designed with a 90° collision angle. Typically, a starting point for a liquid thruster is 20% of the chamber pressure, with an injector pressure drop recommended. Because ILethCu-01 has low viscosity, a pressure drop of approximately 5 bar was considered during the injector design. The characteristic length of the chamber was determined to be approximately 1.0 m, allowing sufficient space for the contact ignition reaction. Figure 6 is a perspective view of the injector and chamber of the thruster according to the present invention.

[0062] Considering fuel-rich and oxidizer-rich conditions, three different high-temperature combustion tests were performed at oxidizer-to-fuel ratios (O / F) of 3.5, 4.3, and 5.0, with a total combustion time of 2 seconds. A stable pressure curve was observed with an average chamber pressure of 8–10 bara (absolute pressure).

[0063] Figure 7 is a pressure graph with an oxidizer / fuel ratio of 3.5 according to the present invention.

[0064] Figure 8 is a pressure graph with an oxidizer / fuel ratio of 4.3 according to the present invention.

[0065] Figure 9 is a pressure graph with an oxidizer / fuel ratio of 5.0 according to the present invention.

[0066] A theoretical investigation of ILethCu-01 fuel using 95 wt% hydrogen peroxide at a chamber pressure of 10 bar and an area ratio of 100 was performed using the NASA CEA code. The optimal theoretical characteristic velocity (C-star) and specific impulse under vacuum were 1609 m / s and 317 s, respectively, at an oxidizer-to-fuel ratio (O / F) of 3.9. ILethCu-01 / 95 wt% hydrogen peroxide showed a 6% higher density specific impulse than monometallic hydrazine / dinitrogen tetroxide (MMH / N2O4). Interestingly, propellant performance can be improved when using higher concentrations of HTP, such as 95 wt% or higher. For example, ILethCu-01 / 98 wt% hydrogen peroxide provides a vacuum specific impulse of 320 s.

[0067] The average mass flow rates of the propellant were 20.7, 19.50, and 14.5 g / s at oxidizer-to-fuel (O / F) ratios of 3.5, 4.3, and 5.0, respectively. The pressure drops of the oxidizer and fuel were close to the design values. The combustion efficiency was approximately 85% at fuel-rich conditions with an oxidizer-to-fuel ratio of 3.5. Similarly, a lower combustion efficiency of 84% was observed at an oxidizer-rich condition with an oxidizer-to-fuel ratio of 5.0. However, the combustion efficiency improved to 96% at an oxidizer-to-fuel ratio of 4.3. An oxidizer-to-fuel (O / F) ratio of 4.3 was still an oxidizer-rich condition but close to the stoichiometric oxidizer-to-fuel ratio.

[0068] Combustion instability in rocket engines can arise from chamber pressure fluctuations during combustion. This complex and potentially uncertain phenomenon, if not properly managed, can lead to engine failure, resulting in structural damage or even catastrophic failure. Inconsistent fuel-oxidizer mixing and prolonged ignition delays can lead to localized hot spots, which can cause pressure fluctuations and unstable combustion. Improper design of thruster components can also contribute to combustion instability.

[0069] The combustion stability of the propellant was calculated by considering the root mean square of the steady-state chamber pressure (PcRMS) in the analysis window. Compared to the Stock2 / hydrogen peroxide (HTP) eco-friendly propellant, which reported combustion instability ranging from 5.3% to 6.2%, the ILethCu-01 / 95 wt% hydrogen peroxide propellant exhibited a low combustion instability of less than 5%. Overall, instability greater than 5% may not be suitable for small rocket engines.

[0070] The rise time (τp) was measured as the time required for the chamber mean pressure to rise from 10% (Pc10%) to 90% (Pc90%). This generally refers to the time required for the combustion process to reach maximum chamber pressure. The rise time of the contact-ignition propellant differed between the first pulse and subsequent second pulse combustion tests. Considering fuel-rich and oxidizer-rich conditions, the average rise time of the first combustion pulse occurred at approximately 100 ms. The overall rise time of the ILethCu-01 / 95 wt% hydrogen peroxide propellant was still higher than that of the HIP_11 and Stock2 / 95 wt% hydrogen peroxide propellants. However, this is within the acceptable range for normal operation of a liquid rocket engine (considering an ignition delay time (IDT) of <100 ms).

[0071] Table 4 shows the results of the high-temperature combustion test.

[0072] [Table 4]

[0073]

[0074] The present invention can be used as a propellant for a liquid rocket engine by mixing ethanol and a catalyst additive into an ionic liquid fuel and using hydrogen peroxide as an oxidizer and a low-toxicity contact ignition binary propellant.

Claims

1. An ionic liquid fuel comprising a cyanoborohydride anion and an imidazolium-based heterocyclic cation.

2. The ionic liquid fuel of paragraph 1 and An ionic liquid mixed fuel in which ethanol is mixed in an equal weight ratio to lower the viscosity of the above ionic liquid fuel.

3. The ionic liquid mixed fuel of paragraph 2 and A contact-ignitable liquid fuel containing tetrakisimidazolium monocyanoborohydride copper(II) as a catalyst.

4. In paragraph 3, A contact ignition liquid fuel characterized by mixing 45.5 wt% of the above ionic liquid mixed fuel with 45.5 wt% of ethanol and 9 wt% of a tetraximidazolium monocyanoborohydride copper (II) catalyst.

5. For the contact ignition liquid fuel of paragraph 3 A low-toxicity contact-ignition binary propellant characterized by using 95 wt% hydrogen peroxide as an oxidizer. Steps for synthesizing 6.1-ethyl-3-methylimidazolium bromide and A method for producing a contact-ignitable liquid fuel, characterized in that it comprises a step of dissolving the synthesized ethyl methylimidazolium bromide in dichloromethane to synthesize 1-ethyl-3-methylimidazolium cyanoborohydride.

7. In paragraph 6, A method for producing a contact ignition liquid fuel, characterized in that it further comprises a step of mixing ethanol in an equal weight ratio to lower the viscosity of the ionic liquid fuel.

8. In paragraph 7, Cu II Steps for synthesizing (H-imidazole)4Cl2 and The above Cu II A method for producing a contact-ignitable liquid fuel, characterized in that it further comprises the step of adding (H-imidazole)4Cl2 to an acetonitrile stirred solution containing sodium cyanoborohydrate.

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