Boron-containing fuel-rich propellant as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of fuel-rich propellants for solid fuel ramjet engines, and particularly relates to a boron-containing fuel-rich propellant as well as a preparation method and application of the boron-containing fuel-rich propellant. 20-28% of an oxidizing agent; 30-40% of boron powder with a core-shell structure; 16-25% of an auxiliary fuel; 0.1%-0.5% of a performance regulator; the core-shell structure boron powder is of a structure formed by taking boron powder as a core, taking iron oxide as a first coating agent to coat the boron powder and taking polymethyl methacrylate as a second coating agent to secondarily coat the iron oxide-coated boron powder, and in the propellant, a fluorine-containing plasticizer is adopted to replace an inert plasticizer; the content of the oxidant in the propellant is reduced under the condition that the process performance of the propellant is not influenced, and the propellant is ensured to have relatively high combustion efficiency under the condition of low oxidant content.

Description

Technical Field

[0001] This invention belongs to the technical field of fuel-rich propellants for solid fuel ramjet engines, specifically relating to a boron-containing fuel-rich propellant, its preparation method, and its application. Background Technology

[0002] Air-breathing aircraft can cruise with power throughout their flight, and have unique advantages such as fast response speed, strong penetration capability, ballistic maneuverability without excessive speed loss, and high terminal speed. They represent one of the disruptive development directions for future aircraft.

[0003] Scramjet engines are one of the bottleneck technologies restricting air-breathing cruise vehicles, and all major spacefaring nations in the world regard them as an important strategic development direction. Solid scramjet engines not only have advantages such as high specific impulse and high propulsion efficiency under hypersonic conditions, but also possess the inherent advantages of traditional solid rocket engines, such as simple structure, small size, low cost, high safety and reliability, and good storage and maintenance performance. They can meet the engineering application requirements of aircraft such as low cost, high reliability, strong environmental adaptability, and long-term all-weather operation.

[0004] In recent years, in order to improve artillery range, increase strike range, and enhance firepower suppression capabilities, Western countries have attempted to integrate ramjet engines into artillery to extend its range. Norway's Nammo and the US's Boeing have integrated a solid-fuel ramjet engine into a 155mm projectile, developing a new type of ramjet-powered extended-range projectile. In 2022, the Ramjet 155 ramjet-powered extended-range artillery was successfully test-fired, achieving an actual range of over 70km.

[0005] Solid-fuel ramjet engines have low oxidizer content (generally below 25%), and their combustion process mainly relies on the incoming air flow. The propellant burning rate is mostly regulated by methods such as airflow. Hydrocarbon propellants have excellent ignition and combustion performance, especially with extremely low oxidizer content, and can achieve high combustion efficiency. Therefore, most solid-fuel ramjet engines choose hydrocarbon propellants.

[0006] Currently, extended-range artillery systems in Europe and the United States, represented by the Ramjet 155, use hydrocarbon propellants as their power source. However, hydrocarbons have low density and low propellant energy performance, resulting in limited actual range increases.

[0007] Boron-rich propellants have a high calorific value, and their application in fuel-powered ramjet engines can further increase the range of projectiles. However, boron powder has a high melting and boiling point, making it difficult to melt and vaporize, and its ignition temperature is high (1900K). Furthermore, during the combustion process, boron powder produces highly viscous boron oxides (B2O3) that cover its surface, making ignition difficult and hindering complete combustion. This limits the application of boron-rich propellants in fuel-powered ramjet engines. Summary of the Invention

[0008] To address the problem of low combustion efficiency in fuel ramjet engines caused by the high ignition temperature and difficulty of boron powder, this invention provides a boron-rich fuel propellant, its preparation method, and its application. The propellant of this invention exhibits high ignition and combustion performance under low oxidizer content. This propellant uses core-shell structured boron powder (CBSFe) instead of ordinary boron powder. The core-shell structured boron powder has boron as its core, an iron oxide first coating layer, and a polymethyl methacrylate outer coating layer. The core-shell structured boron powder maintains the high calorific value of boron while possessing superior storage performance and excellent... Compared to conventional boron powder in current high-energy rich fuel propellants, this core-shell structured boron powder has numerous advantages, including superior ignition performance. It exhibits a lower ignition temperature, higher oxidation activity, higher combustion efficiency, and good compatibility with hydroxyl-terminated polybutadiene binders. This improves the combustion performance and energy efficiency of boron-based rich fuel propellants. The polymethyl methacrylate layer on the surface of the core-shell structured boron powder possesses high mechanical strength, ensuring that the core-shell structured boron powder maintains its structural integrity even in high-shear environments. The propellant of this invention exhibits significantly improved processability, combustion performance, and energy levels.

[0009] The technical solution adopted in this invention is as follows: This invention provides a boron-rich fuel propellant comprising the following components and their mass percentage content: binder system: 18-24%; oxidant: 20-28%; core-shell structured boron powder: 30-40%; auxiliary fuel: 16-25%; performance modifier: 0.1-0.5%; the core-shell structured boron powder is formed by a secondary coating process where boron powder is used as the core, iron oxide is used as the first coating agent to coat the boron powder, and polymethyl methacrylate is used as the second coating agent to coat the boron powder coated with iron oxide; the particle size of the core-shell structured boron powder is 1.2-2.0 μm.

[0010] Furthermore, the boron content in the aforementioned core-shell structured boron powder is 93%~96% by mass; the iron oxide content is 2%~5% by mass; and the polymethyl methacrylate content is 1%~3% by mass.

[0011] Furthermore, the aforementioned auxiliary fuels include auxiliary high-temperature combustion metal fuel, high-calorific-value fuel, and combustion promoter; wherein the auxiliary metal fuel is magnesium with a particle size of 1-5 μm and a mass percentage of 3-6% in the propellant; the high-calorific-value fuel is carborane propyl methyl ether with a particle size of 10-20 μm and a mass percentage of 12-18% in the propellant; and the combustion promoter is ferric polyacrylate with a mass percentage of 1-2% in the propellant.

[0012] Furthermore, the oxidant mentioned above is ammonium dinitramide, and the particle size of the oxidant includes one or more of the following three types: Class I (280~360μm), Class III (90~140μm), Class IV (5~15μm), and Class V (0.5~2μm).

[0013] Furthermore, the above-mentioned adhesive system includes an adhesive, a curing agent, and a plasticizer, wherein the plasticizer is diisooctyl perfluoroadipate, and its mass percentage in the propulsion process is 3%; the adhesive is hydroxyl-terminated polybutadiene, and the curing agent is isophorone diisocyanate.

[0014] Furthermore, the aforementioned performance modifier is one or more of lecithin, tris[1-(2-methyl)aziridinyl]phosphine oxide, N,N-diphenyl-p-phenylenediamine, N-phenyl-2-naphthylamine, and N-phenyl-N-cyclohexyl-p-phenylenediamine.

[0015] The second aspect of the present invention also provides a method for preparing the boron-containing rich fuel propellant of the first aspect of the present invention, comprising the following steps: S1. Preparation of core-shell structured boron powder; S2, Mix all materials; S3, Propellant casting and curing; The method for preparing core-shell structured boron powder using S1 is as follows: Step 1: Pretreatment of boron powder: Dissolve the polyol in a 50% (w / w) ethanol solution to prepare a 10% (w / w) polyol solution. Add the polyol solution and cyclohexane in a 3:1 mass ratio to a reactor equipped with a reflux device and a tail gas receiving device. Add boron powder while stirring, reflux at 100℃ for 3 hours, cool to room temperature, and filter to obtain pretreated boron powder. Step 2: Coating with iron oxide: Prepare a 10% (w / w) ferric chloride aqueous solution at room temperature and mix it with anhydrous ethanol at a mass ratio of 2:1. Add the mixture to a reactor equipped with a reflux device and a tail gas receiving device. Add the pretreated boron powder in proportion while stirring. Then add 10% (w / w) ammonia water dropwise to the system. After the addition is complete, continue stirring for 0.5 to 1 hour. Wash with deionized water. Finally, add 5 to 8 times the mass of the boron powder to ethylene glycol. React at 260 to 300°C for 3 hours. Cool naturally to room temperature, filter, wash with anhydrous ethanol, and dry to obtain boron powder coated with iron oxide. Step 3: Polymer Composite: Polymethyl methacrylate with a molecular weight of 450,000 to 600,000 is dissolved in methyl methacrylate to prepare a 5% (w / w) polymethyl methacrylate solution; the solvent is added to a reactor equipped with a reflux device and a tail gas receiving device, and iron oxide-coated boron powder is added to the solvent under stirring. The temperature is controlled at 30 to 40°C, and the polymethyl methacrylate solution is added dropwise. After the addition is complete, the solution is filtered, washed, and dried to obtain the core-shell structured boron powder.

[0016] Furthermore, in the preparation of core-shell structured boron powder using S1 above: The polyol in step one is a sugar, and its mass is 10% to 20% of the mass of the boron powder raw material. In step two, the mass of ferric chloride is 6% to 10% of the mass of boron powder raw material, the mass of ammonia water is 50% to 80% of the mass of boron powder raw material, and the ammonia water is added dropwise over 2 to 3 hours. In step three, the mass of polymethyl methacrylate (PMMA) is 2% to 5% of the mass of boron powder raw material, and the PMMA solution is added dropwise over a period of 6 to 10 hours. The solvent is an organic alkane and / or a cycloalkanes, and the amount of solvent used is 5 to 8 times the volume of the PMMA solution.

[0017] Furthermore, the above-mentioned S2 specifically includes the following steps: S21. Weighing and premixing of propellant: Weigh all components accurately in a dry environment, add oxidant and plasticizer quickly to binder and mix well, then add performance modifier and combustion promoter from auxiliary fuel in sequence, mix well to obtain premixed slurry. S21. Mixing: Add the core-shell structure boron powder, the auxiliary high-temperature metal fuel and the high-calorific-value fuel from the auxiliary fuel to the premixed slurry in sequence, mix evenly, then add the curing agent and continue mixing, control the mixing temperature to 30℃~50℃, and the mixing time to 70min~110min, and discharge the material after the system is completely mixed evenly. S23. Propellant casting and curing: Vacuum casting of the slurry and curing in a dry environment of 50℃~70℃ for 5~8 days to obtain the propellant product.

[0018] The third aspect of the invention also provides the application of the boron-containing rich fuel propellant of the first aspect of the invention in a solid fuel ramjet engine.

[0019] The technological advantage of this invention lies in: 1. The propellant of this invention uses core-shell structured boron powder, which improves the propellant's process performance: Because iron oxide in the core-shell structured boron powder is tightly covered on the surface of the boron powder, an aluminothermic reaction can occur at around 1100℃, greatly improving the ignition performance of the boron powder and effectively enhancing the combustion efficiency of the propellant; During combustion, the surface polymethyl methacrylate decomposes and burns, providing a high-temperature heat source for iron oxide and boron powder. Iron oxide and core boron powder undergo an aluminothermic reaction at high temperature, the boron powder burns while the iron oxide is reduced to elemental iron, and then the iron is re-oxidized by oxygen in the environment to generate iron oxide. Iron oxide acts as an oxygen carrier, promoting oxygen transfer and improving the combustion of boron powder, thus solving the problems of poor ignition performance and low combustion performance of boron powder in propellants for fuel ramjet engines with extremely low oxidizer content.

[0020] 2. This invention uses a combination of high-burning-temperature metal Mg, high-calorific-value fuel CPM, and high-efficiency combustion promoter FeAA as auxiliary fuel to compensate for heat loss caused by the decomposition of the propellant binder, improve the ignition performance of the propellant in a low-oxidizer environment, provide a high-temperature environment for the primary combustion of boron powder, promote the oxidation of boron powder, improve the combustion efficiency of the propellant, and maintain a relatively stable combustion rate with a low pressure index within the working pressure range. The combustion process of the propellant first involves the decomposition of the binder into small hydrocarbon fragments, followed by exothermic combustion. The decomposition of the binder is an endothermic process. However, the propellant used in fuel ramjet engines has a very low oxidizer content and more stringent requirements for the combustion environment. Therefore, it is necessary to add substances that can increase the primary combustion temperature of the propellant, ensure the temperature environment for boron powder oxidation, and promote the primary combustion of boron powder. Carborane propyl methyl ether increases the primary combustion temperature, ensuring the primary combustion of boron powder. The combustion process provides an excellent ignition environment, significantly improving the propellant's ignition and primary combustion performance. Mg has a high primary combustion temperature and excellent ignition performance; adding a small amount of Mg can compensate for heat loss caused by the decomposition of the propellant binder, resulting in more stable combustion. This invention uses carborane propyl methyl ether (CPM) as a high-calorific-value fuel, enabling rapid ignition of the propellant in a low-oxidizer environment and providing a high-temperature environment for the primary combustion of boron powder, improving the primary combustion efficiency of boron powder and providing a heat source for secondary combustion. CPM is a high-calorific-value fuel with excellent combustion performance, improving the propellant's ignition performance in a low-oxidizer environment, providing a high-temperature environment for the primary combustion of boron powder, promoting boron powder oxidation, improving the primary combustion efficiency of boron powder, and providing a heat source for secondary combustion. Ferric polyacrylate (FeAA) is used as a combustion promoter (oxygen transfer agent) to promote efficient oxidation of boron powder, effectively improving the propellant's energy level. Ferric polyacrylate (FeAA) is an ionomer-type combustion rate modifier that improves the combustion performance of boron powder through the redox reaction of iron ions. Solid-fuel ramjet engines have relatively small combustion chambers. According to the Clapeyron equation PV=nRT, pressure and temperature are directly proportional when volume remains constant; lower combustion chamber pressure means lower combustion temperature. Since the iron oxide content in core-shell boron powder is low, the aluminothermic reaction is limited at lower temperatures. Adding FeAA as a catalyst can further promote the aluminothermic reaction, and the ionization of iron ions acts as an oxygen transfer agent, further accelerating the oxidation of boron powder.

[0021] 3. This invention uses diisooctyl perfluoroadipate, which has very low fluorine segment reactivity and low electronegativity, to replace conventional plasticizers. The propellant will not agglomerate due to the electronegativity of the fluorinated segments, allowing for a reduction in the oxidizer content in the propellant without affecting its processing performance, thus ensuring high combustion efficiency at low oxidizer levels. The fluorinated plasticizer used acts as an oxidizer, reacting with boron during propellant combustion to form boron oxyfluoride (BOF) gas, which breaks down the boron oxide covering the boron powder surface, promoting the oxidation reaction of the boron powder and improving the propellant's combustion efficiency. Common fluorinated compounds have strong electronegativity and exhibit strong interactions with the propellant system, causing agglomeration of binders and fillers, leading to deterioration of propellant processing performance. To prevent propellant performance deterioration due to agglomeration of fluorinated compounds, it is necessary to reduce the contact between the fluorinated segments and propellant components. The end-capping group of diisooctyl perfluoroadipate is alkyl, with the fluorinated structure located in the middle of the chain segment. The shorter length of the fluorinated segment reduces its flexibility and reactivity compared to a longer chain structure. The electronegativity of the fluorinated segment significantly reduces its impact on the propellant system, preventing agglomeration and accumulation due to the electronegativity of the fluorinated segment. Adding FAPE to the propellant does not degrade its processing performance. Using FAPE as a plasticizer allows for a reduction in the oxidizer content in the propellant without affecting its processing performance, ensuring high combustion efficiency even with low oxidizer levels. Diisooctyl perfluoroadipate ensures that the propellant's processing performance remains unaffected and maintains high combustion efficiency in low oxidizer environments: as an oxidizer, it reacts with boron during propellant combustion to form boron oxyfluoride gas, greatly improving combustion efficiency.

[0022] 4. In the propellant preparation method of the present invention, ADN is an oxidant with excellent performance and high energy performance. However, ADN is extremely hygroscopic. Therefore, it must be weighed in a dry environment. In order to minimize the contact between ADN and air, it is quickly mixed with binder and plasticizer to prevent the propellant from deteriorating due to water absorption.

[0023] 5. In the propellant preparation method of this invention, especially in the preparation of core-shell structured boron powder, the surface of the boron powder is covered with a viscous and non-dense boron oxide layer, which seriously affects the combustion performance and process performance. This invention uses a polyol (such as ordinary white sugar) as a reactant to remove the boron oxide on its surface, and uses iron oxide as a surface layer to deposit and cover the boron surface, forming a compact core-shell structured boron powder. Polymethyl methacrylate is used for secondary coating, which completely isolates the air and gives the boron powder a certain mechanical strength and regular structure, so that the boron powder will not oxidize due to contact with air, nor will the iron oxide separate from the boron powder due to mechanical vibration, thus improving the storage performance and process performance of the boron powder. Detailed Implementation

[0024] The embodiments of this application will be described in further detail below. Obviously, the described embodiments are only a part of the embodiments of this application, and not an exhaustive list of all embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0025] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0026] Example 1 A boron-containing fuel-rich propellant, the composition and properties of which are shown in Table 1 and Table 2, respectively: Table 1 Propellant composition of Example 1 Table 2 Propellant performance of Example 1 Example 2 A boron-containing fuel-rich propellant, the composition and properties of which are shown in Tables 3 and 4, respectively: Table 3 Propellant composition of Example 2 Table 4 Propellant performance of Example 2 Example 3 A boron-containing fuel-rich propellant, the composition and properties of which are shown in Tables 5 and 6, respectively: Table 5 Propellant composition in Example 3 Table 6 Propellant performance in Example 3 Example 4 A boron-containing fuel-rich propellant, the composition and properties of which are shown in Tables 7 and 8, respectively: Table 8 Propellant composition in Example 4 Table 9 Propellant performance in Example 4 Example 5 A boron-containing fuel-rich propellant, the composition and properties of which are shown in Tables 9 and 10, respectively: Table 9 Propellant composition in Example 5 Table 10 Propellant performance in Example 5 Example 6 A boron-containing fuel-rich propellant, the composition and properties of which are shown in Tables 11 and 12, respectively: Table 11 Propellant composition in Example 6 Table 12 Propellant performance in Example 6 Comparative Example 1 A propellant, the composition and properties of which are shown in Table 13 below, corresponds to the composition in Example 3, but the fuel used is ordinary boron powder, for comparison.

[0027] Table 13 Propellant composition in Comparative Example 1 Propellant performance The propellant cannot form a uniform slurry during the mixing process, thus failing to produce a drug.

[0028] Comparative Example 2 Because the ordinary boron powder mixing process used in Comparative Example 1 was extremely poor, it was impossible to produce the propellant. To verify the effect of different auxiliary fuels on the propellant, composite boron powder was used for loading, providing the same formulation composition and performance as in Example 3, but with a different type of combustion modifier, as shown in Tables 14 and 15 for comparison.

[0029] Table 14 Propellant composition in Comparative Example 2 Table 15 Propellant performance in Comparative Example 2 As can be seen from Comparative Example 2, when iron oxide is used instead of FeAA, the propellant cannot be ignited below 3 MPa, resulting in reduced injection and combustion efficiency.

[0030] Comparative Example 3 To verify the effect of different plasticizers on propellants, conventional diisooctyl sebacate was used as a plasticizer to replace FAPE in Example 3 for propellant loading. The composition and performance of the resulting propellant formulation are shown in Tables 16 and 17 for comparison.

[0031] Table 16 Propellant composition in Comparative Example 3 Table 17 Propellant performance in Comparative Example 3 As can be seen from Comparative Example 3, when DOS is used instead of FAPE, the propellant cannot be ignited below 7MPa, resulting in reduced injection and combustion efficiency.

[0032] Comparative Example 4 To verify the effects of different high-calorific-value additives on propellants, hydrocarbon segment binders were used to replace the CPM and its content in the components of Example 3 for loading. The resulting propellant formulation composition and performance are shown in Tables 18 and 19 for comparison.

[0033] Table 18 Propellant composition in Comparative Example 4 Table 19 Propellant performance in Comparative Example 4 As can be seen from Comparative Example 4, when a hydrocarbon segment binder is used instead of CPM, the burning rate of the propellant at various pressure points is reduced, and both the theoretical and measured calorific values ​​of the propellant are reduced, resulting in decreased injection and combustion efficiency.

[0034] As can be seen from the examples, the propellant has excellent combustion performance in a low oxidizer environment and has a low pressure index.

[0035] As can be seen from the comparative examples, when boron powder is used to replace the core-shell structure boron powder, the propellant cannot be made into a drug.

[0036] When iron oxide is used instead of FeAA, the propellant cannot ignite below 3 MPa, resulting in reduced injection and combustion efficiency. This is because the amount of iron oxide coating the surface of boron powder is limited, and the amount of boron powder capable of undergoing aluminothermic reactions is small. Furthermore, there is no direct contact between the free iron oxide and the boron powder, and under low pressure, iron ions in the iron oxide are difficult to catalyze the oxidation of boron powder, resulting in limited catalytic effect.

[0037] When DOS is used to replace FAPE, the propellant cannot ignite below 7 MPa, resulting in reduced injection and combustion efficiency. This is because FAPE acts as an oxidizer, promoting the combustion of boron powder and enabling the propellant to have higher combustion efficiency even with low oxidizer content. The propellant contains CPM, which also contains a large amount of boron. Therefore, using DOS to replace FAPE when the oxidizer is insufficient will also lead to a decrease in combustion efficiency.

[0038] Replacing CPM with hydrocarbon segment binders reduces the burning rate of the propellant at various pressure points, lowers both the theoretical and measured calorific values ​​of the propellant, and reduces injection and combustion efficiency. This is because CPM is a high-calorific-value fuel that can provide a high-temperature heat source for the propellant, promoting the combustion of hydrocarbon fuels.

[0039] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A boron-containing fuel-rich propellant, characterized in that: It contains the following components and their percentage by mass: Adhesive system: 18-24%; Oxidizing agent: 20-28%; Core-shell structured boron powder: 30-40%; Auxiliary fuel: 16~25%; Performance modifier: 0.1–0.5%; The core-shell structured boron powder is formed by a secondary coating process, where boron powder is used as the core, iron oxide is used as the first coating agent to coat the boron powder, and polymethyl methacrylate is used as the second coating agent to coat the boron powder coated with iron oxide. The particle size of the core-shell structured boron powder is 1.2~2.0μm.

2. The boron-containing rich fuel propellant according to claim 1, characterized in that: The boron content in the core-shell structured boron powder is 93%~96% by mass; the iron oxide content is 2%~5% by mass; and the polymethyl methacrylate content is 1%~3% by mass.

3. The boron-containing rich fuel propellant according to claim 1, characterized in that: The auxiliary fuel includes an auxiliary high-temperature combustion metal fuel, a high-calorific-value fuel, and a combustion promoter; wherein the auxiliary high-temperature combustion metal fuel is magnesium with a particle size of 1-5 μm and a mass percentage of 3-6% in the boron-rich propellant; the high-calorific-value fuel is carborane propyl methyl ether with a particle size of 10-20 μm and a mass percentage of 12-18% in the boron-rich propellant; and the combustion promoter is ferric polyacrylate with a mass percentage of 1-2% in the boron-rich propellant.

4. The boron-containing rich fuel propellant according to claim 1, characterized in that: The oxidant is ammonium dinitramide, and the particle size of the oxidant includes one or more of the following three types: Class I (280~360μm), Class III (90~140μm), Class IV (5~15μm), and Class V (0.5~2μm).

5. The boron-containing rich fuel propellant according to claim 1, characterized in that: The adhesive system includes an adhesive, a curing agent, and a plasticizer. The plasticizer is diisooctyl perfluoroadipate, which has a mass percentage of 3% in the boron-rich fuel propellant. The adhesive is hydroxyl-terminated polybutadiene, and the curing agent is isophorone diisocyanate.

6. The boron-containing rich fuel propellant according to claim 1, characterized in that: The performance modifier is one or more of the following: lecithin, tris[1-(2-methyl)aziridinyl]phosphine oxide, N,N-diphenyl-p-phenylenediamine, N-phenyl-2-naphthylamine, and N-phenyl-N-cyclohexyl-p-phenylenediamine.

7. A method for preparing a boron-containing rich fuel propellant as described in any one of claims 1-6, characterized in that: Includes the following steps: S1. Preparation of core-shell structured boron powder; S2. The binder system, oxidant, core-shell boron powder, auxiliary fuel and performance modifier are mixed to obtain a slurry; the slurry is then poured and cured to obtain a boron-rich fuel propellant. The method for preparing core-shell structured boron powder using S1 is as follows: Step 1: Pretreatment of boron powder: Dissolve the polyol in a 50% (w / w) ethanol solution to prepare a 10% (w / w) polyol solution. Add the polyol solution and cyclohexane to the reactor at a mass ratio of 3:

1. Add the boron powder raw material while stirring. Reflux at 100℃ for 3 hours. Cool to room temperature and filter to obtain pretreated boron powder. Step 2: Coating with iron oxide: Prepare a 10% (w / w) ferric chloride aqueous solution at room temperature and mix it with anhydrous ethanol at a mass ratio of 2:

1. Add the mixture to the reactor and add the pretreated boron powder in proportion while stirring. Then add 10% (w / w) ammonia water dropwise to the system. After the addition is complete, continue stirring for 0.5 to 1 hour and wash with deionized water. Finally, add 5 to 8 times the mass of boron powder to ethylene glycol and react at 260 to 300°C for 3 hours. Cool naturally to room temperature, filter, wash with anhydrous ethanol, and dry to obtain boron powder coated with iron oxide. Step 3: Polymer Composite: Polymethyl methacrylate with a molecular weight of 450,000 to 600,000 is dissolved in methyl methacrylate to prepare a 5% (w / w) polymethyl methacrylate solution; solvent is added to a reactor, and the iron oxide-coated boron powder is added to the solvent under stirring, while controlling the temperature at 30 to 40°C. The polymethyl methacrylate solution is added dropwise, and after the addition is complete, it is filtered, washed, and dried to obtain the core-shell structured boron powder.

8. The method for preparing boron-containing rich fuel propellant according to claim 7, characterized in that: In the preparation of core-shell structured boron powder in S1: The polyol is a sugar, and its mass is 10% to 20% of the mass of the boron powder raw material. The ferric chloride aqueous solution contains 6% to 10% of the boron powder raw material by mass of ferric chloride and 50% to 80% of the boron powder raw material by mass of ammonia water, with the ammonia water added over a period of 2 to 3 hours. The mass of the polymethyl methacrylate is 2% to 5% of the mass of the boron powder raw material, and the polymethyl methacrylate solution is added dropwise over a period of 6 to 10 hours; the solvent is an organic alkane and / or a cycloalkanes, and the amount of solvent used is 5 to 8 times the volume of the polymethyl methacrylate solution.

9. The method for preparing boron-containing rich fuel propellant according to claim 7, characterized in that: S2 includes the following sub-steps: S21. Accurately weigh all components in a dry environment, add oxidant and plasticizer to the binder and mix well, then add performance modifier and combustion promoter from auxiliary fuel in sequence, mix well to obtain premixed slurry; S22. The core-shell structure boron powder, the auxiliary high-temperature metal fuel and the high-calorific-value fuel in the auxiliary fuel are added to the premixed slurry in sequence and mixed evenly. Then, the curing agent is added and mixing is continued. The mixing temperature is controlled at 30℃~50℃ and the mixing time is 70min~110min. The slurry is obtained after the system is completely mixed and evenly mixed. S23. Vacuum casting of the slurry and curing in a dry environment of 50℃~70℃ for 5~8 days to obtain boron-rich fuel propellant.

10. An application of the boron-containing rich fuel propellant as described in any one of claims 1-6, characterized in that, Used in solid fuel ramjet engines.

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