Grain for hybrid rocket and its manufacturing method

Abstract

To provide a grain for hybrid rockets that achieves an improved thrust during combustion while maintaining ease of production.SOLUTION: A grain for hybrid rockets 10 has a plural layers of solid fuel 11 laminated in a radial direction in a cross-sectional circle of the grain 10, and a combustible partition 12 for separating the layers of the solid fuel 11. The partition 12 is composed of a one-side sheet having a tabular sheet and a wavy sheet joined together at a contact point of both.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to grains (solid fuel products) for hybrid rockets and methods for producing the same. [Background technology]

[0002] Conventionally, three main types of rocket engines have been known: liquid fuel rockets, solid fuel rockets, and hybrid rockets. In order for a rocket to generate thrust in a space with low oxygen concentration, it needs fuel and an oxidizer to burn it. In a liquid fuel rocket, both the fuel and the oxidizer are liquid, in a solid fuel rocket, both the fuel and the oxidizer are solid, and in a hybrid rocket, the fuel is solid and the oxidizer is liquid. In this specification, all solid fuel products are referred to as "grain."

[0003] The grains for hybrid rockets have one or more combustion spaces formed. Hybrid rockets generate thrust by supplying a liquid oxidizer to the combustion space of the grains, burning the grains, and ejecting the gas generated by the combustion phenomenon from a nozzle. Hybrid rockets have advantages over liquid-fuel and solid-fuel rockets, such as easier manufacturing because the solid fuel and liquid oxidizer are structurally separated. Furthermore, hybrid rockets offer the advantages of high safety and easy combustion control due to the ease of managing the solid fuel and liquid oxidizer. On the other hand, hybrid rockets have the disadvantage of having a lower specific impulse (the impulse of thrust obtained using a unit weight of propellant) than, for example, liquid-fuel rockets, making it difficult to generate thrust. While hybrid rockets are easy to manufacture and have excellent safety and manageability, their low thrust often makes them popular as engines for sounding rockets that measure data during suborbital flight.

[0004] As mentioned above, hybrid rockets have the disadvantage of low thrust, but a known method of compensating for this is to spirally wind the solid fuel itself and form gaps between each layer, as disclosed in Patent Documents 1 and 2. In this way, by providing gaps between the layers of spirally wound solid fuel, it is believed that the combustion efficiency of the solid fuel can be increased, making it possible to generate a large thrust. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 55-144494 [Patent Document 2] Japanese Patent Application Publication No. 55-144495 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, the invention described in Patent Document 1 involves stacking a corrugated solid fuel sheet on one side of a flat solid fuel sheet, and winding the resulting integrated product into a spiral. However, it is difficult to process solid fuel, which has a certain thickness (for example, 1 mm), into a corrugated shape and integrate it with a flat plate, which poses a problem that the advantage of hybrid rockets, that is, ease of manufacture, is lost. For example, the contact points between the flat and corrugated sheets must be bonded with a low-temperature adhesive, but when such an adhesive is used, the corrugated sheet shape must be maintained until the adhesive completely solidifies, which poses a problem that it is difficult to efficiently and continuously produce grains in which flat and corrugated sheets are integrated.

[0007] In addition, the invention described in Patent Document 2 forms protruding spacers on one side of a flat solid fuel and then spirally winds the solid fuel, but there is a problem in that such protrusions do not ensure sufficient voids between each layer of the solid fuel. In fact, simply forming protruding spacers on the surface of the solid fuel as in Patent Document 2 does not allow for the maintenance of voids between each layer as in Patent Document 1. As a result, it is believed that the structure of Patent Document 2 has only a limited effect on improving combustion efficiency.

[0008] Therefore, the main object of the present invention is to improve the combustion efficiency of grains for hybrid rockets while maintaining ease of manufacturing, thereby improving the thrust during combustion. [Means for solving the problem]

[0009] The inventors of the present invention have intensively studied means for solving the problems of the conventional inventions, and have found that by forming partition walls using simple one-sided corrugated sheets formed by joining a flat sheet and a corrugated sheet, and by using these partition walls to form gaps between layers of solid fuel, it is possible to provide grains that are easy to manufacture and have high fuel efficiency. Based on this finding, the inventors have come to the conclusion that the problems of the conventional inventions can be solved, and have completed the present invention. Specifically, the present invention includes the following configurations or steps.

[0010] A first aspect of the present invention relates to a grain 10 for a hybrid rocket. The grain 10 according to the present invention includes a solid fuel 11 and a partition wall 12. The grain 10 is generally cylindrical, and one or more combustion spaces S are formed along its central axis A. The term "approximately cylindrical" refers to a cylindrical shape having a closed circular cross section (see FIG. 6) as well as a substantially cylindrical shape formed by spirally wound sheets (see FIG. 2, etc.). The solid fuel 11 is stacked in multiple layers in the radial direction R of the cross section of the grain. The solid fuel may be integrated or may be separated into multiple pieces. The partition wall 12 is combustible and separates each layer of the solid fuel 11 in the radial direction R of the grain 10. The partition wall 12 is composed of a single-column sheet formed by joining a flat sheet 13 and a corrugated sheet 14 at their contact points 15. The solid fuel 11 and the partition wall 12 may be made of different materials or the same material.

[0011] As described above, the grain 10 according to the present invention includes, in addition to the solid fuel 11, a combustible partition 12 made of a single-column sheet. In this respect, the grain 10 according to the present invention differs from the grain described in Patent Document 1, in which the solid fuel itself is made of only a single-column structure in which a flat plate and a corrugated plate are integrated. In the present invention, the partition 12 having a single-column structure has a gap V formed at the portion where the flat sheet 13 and the corrugated sheet 14 are separated. Inserting this partition 12 between the solid fuels 11 improves the combustion efficiency between the solid fuels 11. That is, to improve the thrust of the grain 10 during combustion, it is important to increase the rate at which the burning surface of the solid fuel 11 retreats from the center to the periphery of the grain 10. In this case, by disposing the partition 12 with the gap V formed by the single-column structure between the layers of the solid fuel 11, the retreat rate of the solid fuel 11 can be increased. Furthermore, the flat sheet 13 and the corrugated sheet 14 constituting the partition 12 do not need to be thick, and therefore can each be made into a relatively thin sheet. Therefore, the single-sided corrugated sheet formed by joining the flat sheet 13 and the corrugated sheet 14 can be easily processed and manufactured using, for example, a known corrugator for corrugated cardboard. Furthermore, the single-sided corrugated sheet that constitutes the partition wall 12 can be easily wound into a spiral shape or processed into various shapes such as a circular cross section, a rectangular cross section, or other polygonal cross sections. By forming the partition wall 12 that separates the solid fuel 11 using the single-sided corrugated sheet that is easy to manufacture and process, it is possible to improve the thrust during combustion while maintaining the ease of manufacturing the grains 10.

[0012] In the grain 10 according to the present invention, the partition 12 is preferably arranged so that the corrugated sheet 14 faces inward. The corrugated sheet 14 facing inward means that, of the flat sheet 13 and the corrugated sheet 14 that constitute the partition 12, the corrugated sheet 14 faces the center of the grain 10. By arranging the partition 12 with the corrugated sheet 14 facing inward, the corrugated sheet 14 can more easily hold the solid fuel 11. Furthermore, in this arrangement, the outer surface of the grain 10 becomes the flat sheet 13. This allows the outer surface of the grain 10 to more easily adhere to the inner surface of the motor case 20 (cylinder) of the rocket engine 100, allowing gas generated during combustion to efficiently pass through the grain 10. In particular, because the partition 12 has a single-stage structure, the compression recovery force of the structure itself allows the outer surface of the grain 10 to adhere to the inner surface of the motor case 20.

[0013] In the grain 10 according to the present invention, the partition walls 12 may be formed by spirally winding a single-corrugated sheet. This allows the partition walls 12 to be easily formed by preparing one single-corrugated sheet. Furthermore, the single-corrugated sheet can be easily wound into a spiral.

[0014] In the grain 10 according to the present invention, the partition walls 12 may be formed by arranging multiple layers of cylindrical single-sided corrugated sheets. That is, multiple cylindrical single-sided corrugated sheets with different diameters may be prepared and arranged so that the smaller diameter cylinder is enclosed within the larger diameter cylinder. This structure also makes it possible to easily form the partition walls 12.

[0015] The grain 10 according to the present invention may further include a combustible partition wall 16. The partition wall 16 is formed along the radial direction R of the grain 10 to partition a storage space for the solid fuel 11 in the circumferential direction C of the grain 10. Providing the partition wall 16 in this manner prevents the solid fuel 11 from shifting position. Providing the partition wall 16 also improves the strength of the grain 10. The partition wall 16 can be applied to both the embodiment in which the partition wall 12 is formed by spirally winding the aforementioned single-sided corrugated sheet and the embodiment in which the partition wall 12 is formed by arranging multiple layers of cylindrical single-sided corrugated sheets. The partition wall 16 may be a simple flat plate, or may be formed of a single-sided corrugated sheet (single-sided structure) like the partition wall 12. The partition wall 16 may also have a truss structure in which a corrugated sheet is sandwiched between two flat sheets and the contact points of the sheets are joined.

[0016] In the grain 10 according to the present invention, the solid fuel 11 may be filled between the partition walls 12. Filling refers to a state in which the solid fuel 11 is disposed between the corrugated sheet 14 of one partition wall 12 and the flat sheet 13 of another partition wall 12 facing it, with substantially no gaps. For example, the solid fuel 11 is placed on one side of a single-sided corrugated sheet, and then the single-sided corrugated sheet is rolled around while wrapping the solid fuel 11 to form the partition walls 12, thereby filling the solid fuel 11 between the partition walls 12. Alternatively, the single-sided corrugated sheet may be rolled to form the partition walls 12, and then a material for the solid fuel 11 may be poured between the partition walls 12 and solidified, thereby filling the solid fuel 11 between the partition walls 12. Even when the solid fuel 11 is filled between the partition walls 12 in this way, the partition walls 12 themselves have a single-sided corrugated structure containing the voids V, so that the solid fuel 11 can be burned efficiently.

[0017] In the grain 10 according to the present invention, the solid fuel 11 may be rod-shaped. Examples of rod-shaped shapes include a cylindrical shape, a quadrangular prism, a pentagonal prism, and other polygonal prism shapes. In this case, when the joint portions of the single-corrugated sheet between the flat sheet 13 and the corrugated sheet 14 are defined as valley portions 14a and the portions where the corrugated sheet 14 separates from the flat sheet 13 are defined as peak portions 14b, the solid fuel 11 is preferably inserted into the valley portions 14a between the two peak portions 14b. Note that the rod-shaped solid fuel 11 does not need to be inserted into all of the valley portions 14a of the single-corrugated sheet; there may be valley portions 14a where the solid fuel 11 is not inserted. For example, the solid fuel 11 may be placed in the valley portions 14a of the single-corrugated sheet, and then the single-corrugated sheet may be rolled up while wrapping around the solid fuel 11 to form the partition wall 12. Alternatively, after the partition walls 12 are formed by winding the single-sided corrugated sheet, the solid fuel 11 may be inserted between the valley portions 14a of the single-sided corrugated sheet. By inserting the rod-shaped solid fuel 11 between the valley portions 14a of the single-sided corrugated sheet in this way, the gap V between the solid fuels 11 can be maintained, allowing each solid fuel 11 to burn efficiently. Furthermore, even when the rod-shaped solid fuel 11 is inserted, it is possible to prevent the solid fuel 11 from shifting in position within the grain 10. Furthermore, by forming the solid fuel 11 into a rod shape, the surface area of ​​the entire solid fuel 11 increases, thereby making it possible to increase the burning speed of the solid fuel 11.

[0018] In the grain 10 according to the present invention, the layer of solid fuel 11 located on the outermost side of the grain 10 may have a higher oxygen content than the layer of solid fuel 11 located on the innermost side of the grain 10. As the combustion of the grain 10 progresses, there may be a shortage of oxidizer for the solid fuel 11, but this shortage of oxidizer can be compensated for by adjusting the oxygen content of the solid fuel 11 in the outer layer to be higher.

[0019] The grain 10 according to the present invention has one or more combustion spaces S formed so as to extend along its central axis A. When the grain 10 has one combustion space S, the combustion space S is preferably formed on the central axis A of the grain 10. On the other hand, when the grain 10 has multiple combustion spaces S, the combustion spaces S only need to be parallel to the central axis A of the grain 10, and do not necessarily have to be formed on the central axis A. In another embodiment, the combustion space S may be formed spirally within the grain 10.

[0020] A second aspect of the present invention relates to a method for manufacturing grains for hybrid rockets. In the manufacturing method according to the present invention, first, a combustible single-corrugated sheet is manufactured by joining a flat sheet 13 and a corrugated sheet 14 at their contact points 15 (first step). Next, the single-corrugated sheet is rolled up while wrapping the solid fuel 11 around it, or the solid fuel 11 is inserted into the layer formed by the single-corrugated sheet after rolling it up, thereby stacking the solid fuel 11 in multiple layers in the radial direction R of the grain 10 (second step). As a result, partition walls 12 made of the single-corrugated sheet are formed between the layers of solid fuel 11. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide grains for hybrid rockets that maintain ease of manufacturing while improving thrust during combustion. [Brief explanation of the drawings]

[0022] [Figure 1] Figure 1 shows a schematic diagram of the structure of a hybrid rocket equipped with grains. [Figure 2] FIG. 2 shows a cross-sectional structure of a grain according to the first embodiment of the present invention. [Figure 3] FIG. 3 shows a cross-sectional structure of the partition wall of the grain shown in FIG. [Figure 4] FIG. 4 shows a perspective view of the partition wall shown in FIG. [Figure 5]FIG. 5 shows a cross-sectional structure of a grain according to the second embodiment, in which a plurality of rod-shaped solid fuels are inserted into the partition walls shown in FIG. [Figure 6] FIG. 6 shows a cross-sectional structure of a grain partition wall according to a third embodiment of the present invention. [Figure 7] FIG. 7 shows a perspective view of a partition wall of a grain according to a fourth embodiment of the present invention. [Figure 8] FIG. 8 shows a cross-sectional structure of a grain partition wall according to a fifth embodiment of the present invention. [Figure 9] Figure 9 shows a schematic example of a combustion space that can be formed by the partition wall shown in Figure 8. Figure 9(a) shows an example in which two combustion spaces are formed linearly, and Figure 9(b) shows an example in which two combustion spaces are formed in a double spiral shape. [Figure 10] Figure 10 shows modified examples of grains. Figure 10(a) shows an example in which a solid propellant is layered on the inner surface of the grain, and Figure 10(b) shows an example in which the oxygen content of the solid fuel that makes up the grain is changed. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below, and includes appropriate modifications of the embodiments described below within the scope obvious to those skilled in the art.

[0024] FIG. 1 shows the main components of a hybrid rocket 100. As shown in FIG. 1, the hybrid rocket 100 includes a grain 10, a motor case 20, an oxidizer tank 30, an injection nozzle 40, and explosives 50. The grain 10 is generally cylindrical, and a combustion space S is formed therein. The motor case 20 is a container for housing the grain 10 and is designed to be strong enough to withstand the high-pressure gas generated when the grain 10 burns. The oxidizer tank 30 is a container filled with liquid oxidizer and is connected to the front end of the motor case 20. It supplies the liquid oxidizer to the combustion space S of the grain 10. Examples of liquid oxidizers include liquid oxygen and nitrous oxide. The injection nozzle 40 functions as an injection port for gas generated by the combustion of the grain 10 and is connected to the rear end of the motor case 20. The explosives 50 are disposed in the combustion space S of the grain 10.

[0025] When launching the hybrid rocket 100, the liquid oxidizer in the oxidizer tank 30 is supplied to the combustion space S of the grain 10, and the explosive 50 is ignited. This causes the grain 10 (combustible material) to start burning, using the explosive 50 as the initial heat source and the oxygen contained in the liquid oxidizer as the oxidizer. As the grain 10 burns, gas is generated in the motor case 20, and when the pressure inside the motor case 20 reaches a predetermined level, the combustion gas is ejected from the injection nozzle 40. This provides thrust to the hybrid rocket 100. The combustion of the grain 10 progresses from the center to the periphery so that the combustion space S gradually expands. The combustion of the grain 10 ends when all the grain 10 has burned or when the liquid oxidizer in the oxidizer tank 30 has run out. Note that the combustion of the grain 10 can also be stopped by stopping the supply of liquid oxidizer from the oxidizer tank 30 to the grain 10.

[0026] The present invention mainly relates to the grain 10 included in the hybrid rocket 100. However, the scope of the present invention can be expanded to the hybrid rocket 100 equipped with the grain 10. In that case, the motor case 20, oxidizer tank 30, liquid oxidizer, injection nozzle 40, and explosive 50 described above can be publicly known. The grain 10 will be described in detail below.

[0027] 2 to 4 show a grain 10 according to a first embodiment of the present invention. As shown in Fig. 2, the grain 10 includes a solid fuel 11 and a partition wall 12. As shown in Fig. 2 to 4, the grain 10 is formed in a substantially cylindrical shape, and a combustion space S is provided at the center thereof. In Fig. 4, the central axis of the cylindrical grain 10 is indicated by symbol A, the radial direction is indicated by symbol R, and the circumferential direction is indicated by symbol C.

[0028] The solid fuel 11 is stacked in multiple layers when viewed in the radial direction R of the grain 10. Partition walls 12 are provided to separate each layer of the solid fuel 11 in the radial direction R. The grain 10 according to the present invention has a basic configuration of a multi-layer structure of solid fuel 11 separated by such partition walls 12.

[0029] The material of the solid fuel 11 may be, for example, a hydrocarbon polymer commonly used in hybrid rockets. For example, polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers are preferably used as the solid fuel 11. Other examples of the solid fuel 11 include polybutadiene resins such as hydroxyl-terminated polybutadiene and carboxyl-terminated polybutadiene; polyurethane resins such as polyester-type polyurethane and polyether-type polyurethane; polyester resins such as polylactic acid and polyethylene terephthalate; polyacrylonitrile resins such as acrylonitrile homopolymer and acrylonitrile copolymer; polyvinyl chloride resin; poly(meth)acrylic acid ester resins such as polymethyl methacrylate; polyisobutylene; epoxy resin; and paraffin. Furthermore, a combination of oils and fats with an amino acid-based gelling agent, or a combination of ethanol and calcium acetate can also be used.

[0030] The thickness of each layer of the solid fuel 11 can be adjusted as appropriate, but is preferably thicker than the flat sheet 13 and the corrugated sheet 14 described below. For example, the thickness of each layer of the solid fuel 11 is preferably 0.1 mm or more, and may be 0.25 mm or more, 0.5 mm or more, or 1 mm or more. The upper limit of the thickness of each layer of the solid fuel 11 is preferably 200 mm or less, and may be 150 mm or less, 20 mm or less, 15 mm or less, 5 mm or less, or 3 mm or less. Specifically, the preferred thickness varies depending on the form of the solid fuel 11. For example, when the solid fuel 11 is sheet-shaped, the thickness of each layer is preferably 0.1 mm or more, and more preferably 0.25 mm or more. Furthermore, because the solid fuel 11 can be easily wound together with the single-sided corrugated sheet, the upper limit of the thickness of each layer of the solid fuel 11 is preferably 5 mm or less, and more preferably 3 mm or less. When the solid fuel 11 is rod-shaped, the thickness of each layer is preferably 0.5 mm or more, and more preferably 1 mm or more, because this eliminates the need to use a large number of extremely thin rod-shaped fuels. The upper limit of the thickness of each layer of solid fuel 11 is preferably 20 mm or less, and more preferably 15 mm or less. On the other hand, when a fluid material of solid fuel 11 is poured between partition walls 12 and then solidified for use, the thickness of each layer is preferably 0.1 mm or more, and more preferably 0.25 mm or more. The upper limit of the thickness of each layer of solid fuel 11 is preferably 200 mm or less, and more preferably 150 mm or less.

[0031] The structure of the partition wall 12 is shown in detail in Figure 3. The partition wall 12 is composed of a single-sided corrugated sheet. This single-sided corrugated sheet has a structure in which a flat sheet 13 and a corrugated sheet 14 are joined at a contact point 15 between them. At the contact point 15, the flat sheet 13 and the corrugated sheet 14 may be joined by applying an adhesive, or the flat sheet 13 and the corrugated sheet 14 may be joined by locally heating them using a heat sealing process to melt them.

[0032] In the single-sided corrugated sheet that constitutes the partition wall 12, the flat sheet 13 and the corrugated sheet 14 are joined at their contact points 15 but are separated in other areas. This results in a gap V being formed between the flat sheet 13 and the corrugated sheet 14. The corrugated sheet 14 is periodically undulating, and the flat sheet 13 is bonded to one side of the corrugated sheet 14. This results in valleys 14a being formed at the contact points 15 (joint portions) between the flat sheet 13 and the corrugated sheet 14, and peaks 14b being formed in the areas where the flat sheet 13 and the corrugated sheet 14 are separated.

[0033] In FIG. 3 , the thickness of the flat sheet 13 is indicated by the symbol T1, and the thickness of the corrugated sheet 14 is indicated by the symbol T2. Considering the need to provide the single-sided corrugated sheet with sufficient strength to maintain the gaps between the solid fuels 11, the thickness T1 of the flat sheet 13 and the thickness T2 of the corrugated sheet 14 are preferably, for example, 0.05 mm or more, 0.07 mm or more, 0.1 mm or more, 0.15 mm or more, 0.2 mm or more, or 0.25 mm or more. On the other hand, if the sheets 13 and 14 are too thick, processing and manufacturing the single-sided corrugated sheet becomes difficult. Therefore, the thicknesses T1 and T2 of the sheets 13 and 14 are preferably less than 1 mm, and more specifically, are preferably 0.9 mm or less, 0.8 mm or less, 0.7 mm or less, 0.6 mm or less, or 0.5 mm or less. The thicknesses of the flat sheet 13 and the corrugated sheet 14 may be the same or different.

[0034] In addition, in Figure 3, the distance between the contact points 15 (joint portions) of the corrugated sheet 14 and the flat sheet 13 is indicated by the symbol P. Since the corrugated sheet 14 is undulating at a constant cycle, the distance P is also basically constant. There are no particular restrictions on the distance P, and it may be adjusted appropriately depending on the size of the grain 10 and the hybrid rocket 100 carrying it. For example, the distance P may be 1 mm or more, 2 mm or more, or 3 mm or more, with the upper limit being 10 mm or less, 8 mm or less, or 6 mm or less.

[0035] 3, the height of the gap V formed between the corrugated sheet 14 and the flat sheet 13 is indicated by the symbol H. The height H of the gap V is also not particularly limited and may be adjusted appropriately depending on the size of the grain 10 and the hybrid rocket 100 carrying it. For example, the height H of the gap V may be 0.3 mm or more, 0.5 mm or more, or 1 mm or more, with the upper limit being 10 mm, 5 mm or less, or 3 mm or less.

[0036] The corrugated sheet 14 and the flat sheet 13 that make up the single-sided corrugated sheet are each made of a flammable material. The materials for the sheets 13, 14 can be, for example, flammable paper or thermoplastic resin. The raw materials for the paper can include wood, such as hardwoods and softwoods, recycled paper, and other plant fibers, such as hemp, paper mulberry, mitsumata, and bamboo. Similarly to the solid fuel 11 described above, the thermoplastic resin that makes up the sheets 13, 14 can be a hydrocarbon polymer, such as polyolefin resin, polybutadiene resin, polyurethane resin, polyester resin, polyacrylonitrile resin, polyvinyl chloride resin, poly(meth)acrylic ester resin, polyisobutylene, epoxy resin, or paraffin. The corrugated sheet 14 and the flat sheet 13 can be made of the same material or different materials. The single-sided corrugated sheet that makes up the partition wall 12 and the solid fuel 11 can be made of the same material, but they can also be made of different materials.

[0037] Such a single-sided corrugated sheet can be easily processed and manufactured using a known corrugated board corrugator (e.g., JP 58-153631 A). For example, if both the flat sheet 13 and the corrugated sheet 14 are made of a thermoplastic resin, a resin base plate is placed on a heated corrugating roll and thermoformed into a corrugated shape to obtain the corrugated sheet 14. The flat sheet 13 and the corrugated sheet 14 are then introduced between the heated corrugating roll and a flat press roll to thermocompress the two sheets 13, 14 together. This allows industrial production of a single-sided corrugated sheet in which the flat sheet 13 and the corrugated sheet 14 are bonded together without using an adhesive. However, it is also possible to use a method of bonding the flat sheet 13 and the corrugated sheet 14 together using an adhesive.

[0038] In the first embodiment shown in FIGS. 2 to 4, a spiral-shaped partition wall 12 is formed by winding a single-sided corrugated sheet. The partition wall 12 is arranged so that the corrugated sheet 14 faces inward and the flat sheet 13 faces outward. Solid fuel 11 is filled between the spiral-shaped partition walls 12. As a result, multiple layers of solid fuel 11 are formed in the radial direction R of the grain 10. In this embodiment, in each layer, the solid fuel 11 is in close contact with the flat sheet 13 of one partition wall 12 layer and the corrugated sheet 14 of the next partition wall 12 layer. However, due to the compressive recovery force in the height direction of the corrugated sheet 14 of the single-sided corrugated sheet, gaps between the layers of solid fuel 11 can be maintained, thereby improving the combustion efficiency of the solid fuel 11 and generating a large thrust during combustion.

[0039] 2, the solid fuel 11 has three or four layers, but the number of layers of the solid fuel 11 can be adjusted appropriately depending on the size of the grain 10 and the hybrid rocket 100 on which it is mounted. For example, there is no particular limit to the number of layers of the solid fuel 11, but it is preferable to have, for example, three or more layers.

[0040] The grain 10 according to this embodiment can be produced, for example, by placing solid fuel 11 on a single-corrugated sheet before rolling, and then spirally rolling the single-corrugated sheet while rolling up the solid fuel 11. As an alternative method, the grain 10 can also be produced by spirally rolling the single-corrugated sheet, pouring a fluid material for the solid fuel 11 between the partition walls 12 formed by the single-corrugated sheet, and then solidifying the material for the solid fuel 11.

[0041] 4, in the grain 10 according to this embodiment, the contact points 15 (joint portions) between the flat sheets 13 and the corrugated sheets 14 of the single-corrugated sheet that form the partition walls 12 are formed in a straight line extending parallel to the central axis A of the grain 10. In this way, making the contact points 15 parallel to the central axis A of the grain 10 is the easiest way to process the single-corrugated sheet into a spiral shape, given its structure.

[0042] Next, another embodiment of the grain 10 according to the present invention will be described. The description of this embodiment will focus on the differences from the first embodiment described above. In this embodiment, the same elements as those in the first embodiment described above will be assigned the same reference numerals, and details thereof will be omitted.

[0043] 5 shows a cross-sectional structure of a grain 10 according to a second embodiment of the present invention. The grain 10 according to the second embodiment has the same structure of the partition walls 12 as the first embodiment, but differs from the first embodiment in the layer structure of the solid fuel 11. That is, as shown in FIG. 2, the second embodiment employs a plurality of rod-shaped (particularly cylindrical) solid fuels 11. Such rod-shaped solid fuels 11 are inserted and arranged between the partition walls 12 to form a layer of the solid fuel 11.

[0044] More specifically, the rod-shaped solid fuel 11 is arranged in the valley portion 14a between two peak portions 14b of the single-sided corrugated sheet that forms the partition wall 12 (see FIG. 3). By inserting the solid fuel 11 into the valley portion 14a of the single-sided corrugated sheet in this manner, it is possible to prevent the position of the solid fuel 11 from shifting after the grain 10 is completed.

[0045] In the embodiment shown in Fig. 5, rod-shaped solid fuel 11 is disposed in almost all of the valley portions 14a of the single-coated sheet, but this is not necessarily the case. For example, valley portions 14a in which solid fuel 11 is disposed and valley portions 14a in which no solid fuel 11 is disposed may be arranged alternately. It is also possible to vary the proportion of valley portions 14a in which solid fuel 11 is disposed for each layer. For example, the proportion of valley portions 14a in which solid fuel 11 is disposed may be increased in layers closer to the center of the grain 10, and the proportion of valley portions 14a in which solid fuel 11 is disposed may be decreased in layers closer to the periphery of the grain 10.

[0046] Fig. 6 shows a cross-sectional structure of the partition walls 12 of the grain 10 according to the third embodiment of the present invention. Although the solid fuel 11 is not shown in Fig. 6, the third embodiment may employ either the method of filling the spaces between the partition walls 12 shown in Fig. 2 or the method of inserting a plurality of rod-shaped solid fuels 11 between the partition walls 12 shown in Fig. 5.

[0047] As shown in FIG. 6, in the third embodiment, instead of spirally winding the single-sided corrugated sheet, multiple cylinders made of the single-sided corrugated sheet are first prepared. The multiple cylinders have different diameters, with a smaller diameter cylinder placed inside a larger diameter cylinder. At this time, the multiple cylinders made of the single-sided corrugated sheet are arranged concentrically. In this way, a partition wall 12 spanning multiple layers can be formed using multiple cylindrical single-sided corrugated sheets.

[0048] Furthermore, in the third embodiment, combustible partition walls 16 are further provided along the radial direction R to partition the storage space for the solid fuel 11 in the circumferential direction C of the grain 10. By providing such partition walls 16, the spacing between the cylindrical partition walls 12 can also be maintained. In the example shown in FIG. 6, each partition wall 16 is formed in a simple flat plate shape. However, the partition walls 16 can also be formed from a single-sided corrugated sheet, similar to the partition walls 12. As the combustible material for the partition walls 16, for example, the same material as the flat sheet 13 or the corrugated sheet 14 forming the single-sided corrugated sheet may be used.

[0049] In the example shown in FIG. 6, four layers for storing solid fuel 11 are formed by five cylindrical single-column sheets (partition walls 12), and the partition walls 16 arranged in each layer are aligned in a straight line. However, the arrangement of the partition walls 16 in each layer is not limited to this; for example, the partition walls 16 may be arranged with a shift to the left or right for each layer. Also, in the example shown in FIG. 6, the number of partition walls 16 arranged in each layer is the same (specifically, 12), but the number of partition walls 16 in each layer may be different. For example, in order to standardize the size of the storage space for solid fuel 11, it is possible to reduce the number of partition walls 16 in the inner layer and increase the number of partition walls 16 in the outer layer.

[0050] Fig. 7 shows a perspective view of the partition walls 12 of the grain 10 according to the fourth embodiment of the present invention. Note that the solid fuel 11 is also omitted in Fig. 7, but in the fourth embodiment, either the method of filling the spaces between the partition walls 12 shown in Fig. 2 or the method of inserting a plurality of rod-shaped solid fuels 11 between the partition walls 12 shown in Fig. 5 can be employed.

[0051] As can be seen by comparing FIG. 7 with FIG. 4, the fourth embodiment shown in FIG. 7 differs from the first embodiment shown in FIG. 4 in that the contact points 15 (joint portions) between the flat sheet 13 and the corrugated sheet 14 of the single-sided corrugated sheet forming the partition wall 12 are inclined at a predetermined angle θ with respect to the central axis A of the grain 10. The angle θ at which the contact points 15 are inclined with respect to the central axis A is preferably 5 to 35 degrees. By inclining the contact points 15 in this manner, the gap V between the flat sheet 13 and the corrugated sheet 14 is also inclined parallel to the contact points 15. This allows a swirling flow of combustion gas to be generated in the combustion space S during combustion of the solid fuel 11, thereby enabling the solid fuel 11 to burn uniformly. Furthermore, swirling the combustion gas stabilizes the direction of combustion gas injection and the resulting thrust.

[0052] 7 , when a plurality of rod-shaped solid fuels 11 are inserted between the partition walls 12, the rod-shaped solid fuels 11 are preferably arranged along the contact points 15 between the flat sheet 13 and the corrugated sheet 14. That is, the rod-shaped solid fuels 11, together with the contact points 15, are inserted between the partition walls 12 in a state inclined at a predetermined angle θ with respect to the central axis A of the grain 10.

[0053] Fig. 8 shows a cross-sectional structure of the partition walls 12 of the grain 10 according to the fifth embodiment of the present invention. Although the solid fuel 11 is not shown in Fig. 8 either, in the fifth embodiment, it is possible to employ either the method of filling the spaces between the partition walls 12 shown in Fig. 2 or the method of inserting a plurality of rod-shaped solid fuels 11 between the partition walls 12 shown in Fig. 5.

[0054] As shown in FIG. 8, the partition wall 12 in the fifth embodiment is designed to form a first combustion space S1 and a second combustion space S2 in a substantially cylindrical grain 10. That is, in the example shown in FIG. 8, the partition wall 12 is composed of first to fifth single-corrugated sheets 12(a) to 12(e). The first single-corrugated sheet 12(a) is spirally wound to form the outer periphery of the grain 10. The second single-corrugated sheet 12(b) is disposed inside the first single-corrugated sheet 12(a) and spirally wound to form the first combustion space S1. The third single-corrugated sheet 12(c) is disposed inside the first single-corrugated sheet 12(a) and spirally wound to form the second combustion space S2. Note that, in the illustrated example, the first combustion space S1 and the second combustion space S2 have approximately the same diameter, but the diameters of these spaces S1 and S2 can also be different. The fourth and fifth single-side corrugated sheets 12(d) and 12(e) are arranged inside the first single-side corrugated sheet 12(a) and are bent or curved at appropriate locations so as to fill the gaps between the first single-side corrugated sheet 12(a) and the second and third single-side corrugated sheets 12(b) and 12(c). In this way, it is also possible to form the partition wall 12 using multiple single-side corrugated sheets 12(a) to 12(e).

[0055] Up to this point, we have described grains 10 that have improved combustion efficiency of the solid fuel 11 by using partition walls 12 with a single-column structure to form voids V between the layers of the solid fuel 11. However, depending on the solid fuel selected, it is possible to obtain grains with high combustion efficiency even though the voids V are filled with solid fuel. Specifically, the grains 10 are manufactured by impregnating a combination of a single-column sheet roll or a cylindrical object, as shown in Figures 3, 6, 7, and 8, with a fluid material for the solid fuel 11, and then solidifying the material for the solid fuel 11. In this case, the solid fuel is also filled in the region corresponding to the voids V shown in Figure 3.

[0056] Examples of fluid solid fuels include the solid fuel 11 described above, such as epoxy resin, paraffin (e.g., wax), a combination of fats and oils with an amino acid-based gelling agent, and a combination of ethanol and calcium acetate. Among these, paraffin (e.g., wax), a combination of fats and oils with an amino acid-based gelling agent, and a combination of ethanol and calcium acetate all have lower melting points than the materials described above for the corrugated sheet 14 and the flat sheet 13. For example, if a thermoplastic resin sheet is used as the single-corrugated sheet and a flammable material with a lower melting point than the single-corrugated sheet is used as the solid fuel 11, the single-corrugated sheet will melt during combustion of the grains 10, creating holes through which flammable gas, i.e., liquefied solid fuel 11, will be ejected into the combustion space, promoting combustion and increasing the recession rate. Furthermore, epoxy resin, a combination of fats and oils with an amino acid-based gelling agent, and a combination of ethanol and calcium acetate all have higher oxygen contents than the materials described above for the corrugated sheet 14 and the flat sheet 13. For example, if the oxygen content in the solid fuel 11 is higher than that in the one-side corrugated sheet, the amount of oxygen supplied to the grains 11 increases as combustion progresses, which is preferable because the regression rate increases. The oxygen content will be described later.

[0057] When the fluid material of solid fuel 11 is impregnated between partition walls 12 and then solidified for use, the thickness of the solid fuel 11 layer is preferably 0.1 mm or more, more preferably 0.25 mm or more. The upper limit of the thickness of each layer of solid fuel 11 is preferably 200 mm or less, more preferably 150 mm or less.

[0058] FIG. 9 schematically shows a grain 10 having two combustion spaces S1 and S2. In the example shown in FIG. 9(a), the two combustion spaces S1 and S2 each extend linearly parallel to the central axis of the grain 10. On the other hand, in the example shown in FIG. 9(b), the two combustion spaces S1 and S2 each extend spirally, forming a double helix. Note that FIG. 9(b) also shows the positional relationship of the combustion spaces S1 and S2 on the top and bottom surfaces of the grain 10, as well as the positional relationship of the combustion spaces S1 and S2 on two cross sections between them. As such, the combustion spaces S1 and S2 of the grain 10 are not limited to being linear, but may also be spiral. By making the combustion spaces S1 and S2 of the grain 10 spiral, a swirling flow of combustion gas can be generated.

[0059] Fig. 10 shows a modified example of the grain 10 according to the present invention. The modified example shown in Fig. 10 can be applied to any of the first to fifth embodiments. Fig. 10(a) and Fig. 10(b) show the cross-sectional structure of the grain 10.

[0060] In the modification shown in Figure 10(a), a solid propellant 60 is further laminated on the inner circumferential surface of the grain 10 (including the solid fuel 11 and the partition wall 12). As described above, the grain 10 burns using a liquid oxidizer as a combustion support, while the solid propellant 60 is a solid fuel and a solid oxidizer bound together by a binder and burns independently. The solid fuel, solid oxidizer, and binder that make up the solid propellant 60 may be any known material.

[0061] By stacking the solid propellant 60 on the inner circumferential surface of the substantially cylindrical grain 10 in this manner, the rocket can generate thrust in two stages. That is, in the first stage, the solid propellant 60 is burned alone to provide thrust to the rocket. When the solid propellant 60 finishes burning, the rocket temporarily loses thrust. Note that because the grain 10 does not burn alone, fire from the solid propellant 60 does not spread to the grain 10. Then, in the second stage, liquid fuel is supplied from the oxidizer tank 30 (see FIG. 1) to the combustion space S of the grain 10, and is ignited again in the combustion space S, causing the grain 10 to start burning. This allows thrust to be provided again to the rocket. Therefore, for example, the solid propellant 60 is burned during launch from the ground, and liquid oxidizer is supplied to burn the grain 10 during return from outer space or the atmosphere. This allows the rocket to switch fuels between its outbound and return journeys.

[0062] In the modified example shown in FIG. 10(b), the oxygen content of each layer of the solid fuel 11 in the aforementioned grain 10 gradually increases from the center of the grain 10 toward the periphery. In the example of FIG. 10(b), the grain 10 is divided into a first layer 10(a), a second layer 10(b), a third layer 10(c), and a fourth layer 10(d) in order from the center. In this case, the oxygen content of each layer increases in the order of the first layer 10(a), the second layer 10(b), the third layer 10(c), and the fourth layer 10(d). In a hybrid rocket, liquid oxidizer is supplied to the combustion space S at the center of the grain 10 to burn the solid fuel 11 constituting the grain 10, but the amount of liquid oxidizer supplied decreases toward the periphery of the grain 10. Therefore, by increasing the oxygen content toward the periphery of the grain 10, the shortage of liquid oxidizer can be compensated for.

[0063] The "oxygen content" referred to here refers to the percentage by mass of oxygen atoms contained in the material that makes up the fuel. Examples of materials that contain oxygen atoms include diglycidyl azide polymer, polyethylene glycol, polymethyl methacrylate, polyethylene terephthalate, epoxy resin, cellulose, ethanol, and oils. The oxygen content can be determined by elemental analysis. For example, a sample is burned at 1050°C in an oxygen-free helium carrier, and the amount of nitrogen monoxide generated is quantified.

[0064] In the above, in order to express the contents of the present invention, the present specification has described the embodiments of the present invention with reference to the drawings. However, the present invention is not limited to the above embodiments, and includes modifications and improvements that are obvious to those skilled in the art based on the matters described in the present specification. [Explanation of symbols]

[0065] 10...Grain 11...Solid fuel 12...Partition wall 13...Flat sheet 14...Wavy sheet 14a...Valve portion 14b...ridge 15...contact point 16...Partition wall 20...Motor case 30...oxidizer tank 40...spray nozzle 50... Gunpowder 100... Hybrid rocket S...Combustion space S1...First combustion space S2: Second combustion space V: Void

Claims

1. A grain for a hybrid rocket, a solid fuel layered in a plurality of layers in a radial direction of the cross-sectional circle of the grain; a combustible partition separating each layer of the solid fuel; The partition wall is made of a single-sided corrugated sheet in which a flat sheet and a corrugated sheet are joined at their contact points. Grain.

2. The partition wall is arranged so that the corrugated sheet faces inward. The grain according to claim 1 .

3. The partition wall is formed by winding the single-sided corrugated sheet. The grain according to claim 1 .

4. The partition wall is formed by arranging the cylindrical single-sided corrugated sheet in a plurality of layers. The grain according to claim 1 .

5. The solid fuel storage space may further include a combustible partition wall formed along the radial direction of the grain to partition the solid fuel storage space in the circumferential direction of the grain. The grain according to claim 1 .

6. The solid fuel is filled between the partition walls. The grain according to claim 1 .

7. the solid fuel is rod-shaped, In the single-sided corrugated sheet, when a joint portion between the flat sheet and the corrugated sheet is defined as a valley portion and a portion where the corrugated sheet deviates from the flat sheet is defined as a peak portion, the solid fuel is inserted into the valley portion between the two peak portions. The grain according to claim 1 .

8. The layer of the solid fuel located on the outermost side of the grain has a higher oxygen content than the layer of the solid fuel located on the innermost side of the grain. The grain according to claim 1 .

9. The grain has one or more combustion spaces formed therein extending along its central axis. The grain according to claim 1 .

10. A method for producing grain for a hybrid rocket, comprising: a step of producing a combustible single-corrugated sheet by joining a flat sheet and a corrugated sheet at their contact points; and a step of winding the single-layer corrugated sheet while winding the solid fuel therein, or winding the single-layer corrugated sheet and then inserting the solid fuel into the layer formed by the single-layer corrugated sheet, thereby laminating the solid fuel in a plurality of layers in the radial direction of the grain. Manufacturing method.

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