Ignition device and manufacturing method thereof, ignition method, and rocket combustion system

Abstract

An ignition device 30 is provided with a housing 31, a bulk fuel 40, and at least two lead wires 50 that serve as electrodes. The bulk fuel 40 is formed of a plastic material such as a polylactic acid (PLA) and an epoxy resin. The bulk fuel 40 contains a conductive substance in a powder form, the conductive substance being dispersed in the bulk fuel 40, thereby enabling the achievement of a conductive solid fuel. One end of each lead wire 50 is partially buried in the bulk fuel 40. The other end of each lead wire 50 is connected to a power supply (not shown in the drawing). Some of the bulk fuel 40 is gasified by having a current passed through the lead wires 50, and a gasified fuel 42 is combusted through a reaction with an oxidant OX. Due to this configuration, the present invention enables, with a simple structure, the achievement of ignition that is excellent in terms of reignition performance, safety management, heat management and reliability.

Description

[Technical Field]

[0001] The present invention relates to an electrically conductive solid fuel, an ignition device, a manufacturing method thereof, and an ignition method for igniting, for example, liquid fuel for liquid rockets, solid fuel for solid rockets, solid fuel for hybrid rocket motors, wood, charcoal, flammable gas, etc. The present invention also relates to a rocket combustion system for igniting liquid fuel for liquid rockets, solid fuel for solid rocket motors, and solid fuel for hybrid rocket motors, which are mounted on, for example, space rockets, artificial satellites, flying vehicles, etc. [Background technology]

[0002] In outer space, the kick motor (thruster) of a satellite intended for orbital transfer to an orbit without an intersection (such as Hohmann transfer), or orbital injection into an orbit around another celestial body, or landing on a gravitational celestial body, requires re-ignition capability.

[0003] Hybrid rockets are capable of "reignition," something that is impossible with solid propulsion systems, and several reignition devices have been developed around the world to take advantage of this advantage. Non-Patent Document 1 below attempts reignition using a simple ignition method in which fuel is gasified with a heating element and ignited by mixing it with an oxidizer. However, this method is not very energy efficient, and it requires the application of approximately 100 to 200 W of power for 15 seconds or more to gasify the fuel.

[0004] Non-Patent Document 2 proposes a method of igniting a mixture of oxygen and methane gases with a spark plug. This method allows for reliable re-ignition with controlled heat output, but the use of methane compromises the safety of hybrid rockets. Furthermore, a separate supply system for methane is required, which increases the weight and volume of the igniter relative to the overall rocket system.

[0005] In Non-Patent Document 3, an ignition device using a diode laser was developed with the aim of developing a re-ignition device that could be used with any combination of propellants. Re-ignition was successful at an output of 10.84 W under atmospheric pressure and 12 W under low-pressure conditions. However, the diode laser ignition device requires a copper heat sink to absorb heat, a lens to prevent scattering of the laser light, and ABS fuel to promote ignition, which increases the complexity, weight, and cost. Furthermore, because the laser ignition is too localized, the igniter's position cannot be freely determined.

[0006] In Non-Patent Document 4, it was discovered in 2015 that applying ultra-high voltage to ABS fuel causes an arc discharge, and they succeeded in re-igniting it with approximately 4 W of power under atmospheric pressure. However, this ignition method requires an ultra-high voltage of several hundred to several thousand volts, which necessitates a voltage amplifier. While this ignition method is excellent in terms of thermal efficiency, it complicates the electrical system and increases the weight and volume of the electrical system relative to the overall rocket system.

[0007] When considering the optimal rocket system, it is important to minimize the weight ratio of the ignition device to the overall system. In particular, it is essential to have a safe, low-cost, small, lightweight re-ignition device that does not compromise the safety of the hybrid rocket, yet can ignite in a short time. However, no re-ignition device that meets these requirements exists in the world. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] S. Hirai, K. Landon, H. Nagata, "Development of safe, low-cost, re-ignitable rocket ignition system", 2021 AIAA Propulsion and Energy forum, 2021. [Non-patent document 2] Flora S. Mechentel and Brian J. Cantwell, "Small-scale Gaseous Oxygen Hybrid Rocket Testing for Regression Rate and Combustion Efficiency Studies", 53rd AIAA / SAE / ASEE Joint Propulsion Conference, 2017. [Non-patent document 3] David M. Dyrda, Flora S. Mechentel, Brian J. Cantwell, Ashley C. Karp, Jason Rabinovitch and Elizabeth T. Jens, "Diode Laser Ignition of a Poly(Methyl Methacrylate) and Gaseous Oxygen Hybrid Motor", JOURNAL OF PROPULSION AND POWER, Volume 36, Number 5, 2020. [Non-patent document 4] Stephen A. Whitmore, Nathan R. Inkley, Daniel P. Merkley and Michael I. Judson, "Development of a Power-Efficient, Restart-Capable Arc Ignitor for Hybrid Rockets", JOURNAL OF PROPULSION AND POWER, Volume 31, Number 6, 2015. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to provide an electrically conductive solid fuel, an ignition device, a manufacturing method thereof, and an ignition method that are simple in structure and have excellent re-ignition performance, safety management, heat management, and reliability, as well as a rocket combustion system equipped with such an ignition device. [Means for solving the problem]

[0010] A first aspect of the present invention is a conductive solid fuel that is gasified by energization and ignited by reaction with an oxidizer, a bulk fuel formed of a plastic material; and a powdered conductive material dispersed in the bulk fuel.

[0011] An ignition device according to a second aspect of the present invention comprises the conductive solid fuel described above, an electrode partially embedded in the bulk fuel.

[0012] A third aspect of the present invention provides an ignition method, comprising the steps of: gasifying a portion of the bulk fuel using heat generated by energizing an electrode; and providing an oxidant to combust the gasified bulk fuel.

[0013] A rocket combustion system according to a fourth aspect of the present invention includes an oxidizer line for supplying an oxidizer; a flow valve for controlling the flow rate of the oxidant flowing through the oxidant line; a casing having an interior space to which the oxidant line is connected; a main fuel accommodated in the internal space; a nozzle for discharging combustion gas generated by the reaction between the main fuel and the oxidizer; and the above-mentioned ignition device, which is provided between the oxidizer line and the internal space and ignites the main fuel.

[0014] A method for manufacturing an ignition device according to a fifth aspect of the present invention includes: softening the conductive solid fuel by heating; pressing an electrode into the softened conductive solid fuel to partially embed the electrode; and fixing the electrode by hardening the conductive solid fuel. [Effects of the Invention]

[0015] According to the present invention, a rocket combustion system with a simple structure can be realized that is excellent in re-ignition performance, safety management, heat management, and reliability. Furthermore, the rocket combustion system according to the present invention can achieve stable re-ignition operation even in outer space. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a configuration diagram showing an example of a hybrid rocket to which the present invention can be applied. [Figure 2] 1 is a configuration diagram showing an example of a hybrid rocket combustion system according to the present invention. [Figure 3] 1 is a configuration diagram showing an example of an ignition device according to the present invention; [Figure 4] FIG. 10 is a configuration diagram showing another example of an ignition device according to the present invention. [Figure 5] FIG. 1 is a configuration diagram showing another example of a hybrid rocket to which the present invention can be applied. [Figure 6] FIG. 10 is a configuration diagram showing still another example of an ignition device according to the present invention. [Figure 7] FIG. 7(A) is a perspective half-sectional view showing an example of various shapes of bulk fuel, and FIG. 7(B) is a sectional view seen from the side thereof. [Figure 8] FIG. 8(A) is a perspective half-sectional view showing an example of various shapes of bulk fuel, and FIG. 8(B) is a sectional view seen from the side thereof. [Figure 9] FIG. 9(A) is a perspective half-sectional view showing an example of various shapes of bulk fuel, and FIG. 9(B) is a sectional view seen from the side thereof. [Figure 10] FIG. 10(A) is a perspective half-sectional view showing an example of various shapes of bulk fuel, and FIG. 10(B) is a sectional view seen from the side thereof. [Figure 11] FIG. 11(A) is a perspective half-sectional view showing an example of various shapes of bulk fuel, and FIG. 11(B) is a sectional view seen from the side thereof. [Figure 12]FIG. 12(A) is a perspective half-sectional view showing an example of various shapes of bulk fuel, and FIG. 12(B) is a sectional view seen from the side thereof. [Figure 13] FIG. 13(A) is a perspective half-sectional view showing an example of various shapes of bulk fuel, and FIG. 13(B) is a sectional view seen from the side thereof. [Figure 14] 1A to 1C are perspective views showing examples of various shapes of lead wires. [Figure 15] FIG. 15(A) is a perspective half-sectional view showing an example of various embedding modes of the lead wire, and FIG. 15(B) is a sectional view seen from the side thereof. [Figure 16] FIG. 16(A) is a perspective half-sectional view showing an example of various modes of embedding a lead wire, and FIG. 16(B) is a sectional view thereof as seen from the side. [Figure 17] FIG. 17(A) is a perspective half-sectional view showing an example of various embedding modes of the lead wire, and FIG. 17(B) is a sectional view seen from the side thereof. [Figure 18] FIG. 18(A) is a perspective half-sectional view showing an example of various embedding modes of the lead wire, and FIG. 18(B) is a sectional view seen from the side thereof. [Figure 19] FIG. 19(A) is a perspective half-sectional view showing an example of various modes of embedding a lead wire, and FIG. 19(B) is a sectional view thereof as seen from the side. [Figure 20] FIG. 20(A) is a perspective half-sectional view showing an example of various embedding modes of the lead wire, and FIG. 20(B) is a sectional view seen from the side thereof. [Figure 21] FIG. 21(A) is a perspective half-sectional view showing an example of various embedding modes of the lead wire, and FIG. 21(B) is a sectional view thereof as seen from above. [Figure 22] FIG. 22(A) is a perspective half-sectional view showing an example of various embedding modes of the lead wire, and FIG. 22(B) is a sectional view thereof as seen from above. [Figure 23] 1 is an explanatory diagram showing the operation of an example of a lead wire left and right insertion type ignition device. FIG. [Figure 24] 1 is an explanatory diagram showing the operation of an example of a lead wire left and right insertion type ignition device. FIG. [Figure 25]1 is an explanatory diagram showing the operation of an example of a lead wire vertical insertion type ignition device. FIG. [Figure 26] 1 is an explanatory diagram showing the operation of an example of a lead wire vertical insertion type ignition device. FIG. [Figure 27] Fig. 27(A) is a perspective half-sectional view showing another example of the shape of bulk fuel. Fig. 27(B) is a perspective half-sectional view showing an example of a manner in which lead wires are embedded in the bulk fuel shown in Fig. 27(A). Fig. 27(C) is a perspective half-sectional view showing another example of a manner in which lead wires are embedded in the bulk fuel shown in Fig. 27(A). [Figure 28] FIG. 10 is a configuration diagram showing still another example of an ignition device according to the present invention. [Figure 29] Fig. 29(A) is a perspective half-sectional view showing an example of the shape of the bulk fuel shown in Fig. 28. Fig. 29(B) is a perspective half-sectional view showing an example of how lead wires are embedded in the bulk fuel shown in Fig. 29(A). [Figure 30] Figure 30(A) is a perspective half-sectional view showing another example of the shape of the bulk fuel shown in Figure 28. Figure 30(B) is a perspective half-sectional view showing an example of how lead wires are embedded in the bulk fuel shown in Figure 30(A). [Figure 31] 30 is an explanatory diagram showing the operation of the example of the ignition device shown in FIG. 29. [Figure 32] 30 is an explanatory diagram showing the operation of the example of the ignition device shown in FIG. 29. [Figure 33] 31 is an explanatory diagram showing the operation of the example of the ignition device shown in FIG. 30. FIG. [Figure 34] 31 is an explanatory diagram showing the operation of the example of the ignition device shown in FIG. 30. FIG. [Figure 35] 1 is a graph showing the relationship between volume resistivity and graphite content of bulk fuel. [Figure 36] 1 is a graph showing the relationship between volume resistivity and carbon black content of bulk fuel. DETAILED DESCRIPTION OF THE INVENTION

[0017] Figure 1 is a structural diagram showing an example of a hybrid rocket to which the present invention can be applied. The hybrid rocket HR comprises a rocket motor RM carrying a main solid fuel, an oxidizer tank OT for storing oxidizer to be supplied to the rocket motor RM, a pressure pump P for supplying pressure to the oxidizer tank, an ignition device IG for igniting the main solid fuel, a payload PL for cargo, crew, experimental equipment, etc., and avionics AV including electronic devices for flight control. The present invention can be applied not only to the solid fuel of a hybrid rocket motor, but also to igniting liquid fuel of a liquid rocket, solid fuel of a solid rocket, wood, charcoal, flammable gas, etc.

[0018] Fig. 2 is a configuration diagram showing an example of a hybrid rocket combustion system 10 according to the present invention. Fig. 3 is a configuration diagram showing an example of an ignition device 30 according to the present invention. Referring to Figs. 2 and 3, the hybrid rocket combustion system 10 as a whole comprises an oxidizer supply pipe and a rocket motor RM carrying a main solid fuel.

[0019] The oxidizer supply line includes, for example, a main line 21, a main valve 22, a bypass line 25, a bypass valve 26, an ignition device 30 shown in FIG. 3, and a manifold 15. The main line 21 delivers the oxidizer OX stored in an oxidizer tank OT. Examples of the oxidizer OX that can be used include oxygen, hydrogen peroxide, nitric acid, nitrous oxide, dinitrogen tetroxide, ammonium perchlorate, ammonium nitrate, nitroglycerin, and nitrocellulose.

[0020] The main valve 22 controls the flow rate of the oxidant OX flowing through the main line 21 in accordance with commands from a controller (not shown). The oxidant OX, the flow rate of which is controlled by the main valve 22, is fed to the manifold 15.

[0021] The bypass line 25 is connected midway through the main line 21 and diverts a portion of the oxidizer OX flowing in the main line 21. The bypass valve 26 controls the flow rate of the oxidizer OX flowing in the bypass line in accordance with commands from the controller. The oxidizer OX, the flow rate of which is controlled by the bypass valve 26, is fed to an ignition device 30 incorporated inside the manifold 15. Combustion gas generated by the ignition device 30 is fed directly into the internal space of the rocket motor RM.

[0022] The rocket motor RM includes, for example, a casing 11, a heat insulating material 12, a main solid fuel 13, a nozzle 14, and the like.

[0023] The casing 11 has a cylindrical internal space and is connected to the manifold 15 so as to be in fluid communication with it. The heat insulating material 12 is provided over the entire or part of the inner wall of the casing 11 and has the function of suppressing the transfer of heat generated in the internal space to the casing 11. The main solid fuel 13 is housed in the internal space and is formed of a material selected from the group consisting of, for example, polyethylene, polyester, polyurethane, polyacrylonitrile, and polymethyl methacrylate (PMMA).

[0024] 3, the ignition device 30 includes, for example, a housing 31, bulk fuel 40, at least two lead wires 50 as electrodes, and an input port. The housing 31 has a cylindrical interior space and is connected to be in fluid communication with the input port. The input port is connected to the bypass valve 26 shown in FIG. 1. A bulge 34 having a small-diameter outlet 35 is provided on a lower surface 33 of the housing 31. This allows the pressure of the combustion gas to be efficiently concentrated toward the outlet 35 of the bulge 34. A flange 32 is provided on an upper surface of the housing 31.

[0025] The bulk fuel 40 is housed in the internal space and is made of a material selected from the group consisting of polylactic acid (PLA), epoxy resin, polyethylene, polyester, polyurethane, polyacrylonitrile, polymethyl methacrylate (PMMA), acrylonitrile-butadiene-styrene resin (ABS resin), and polyethylene terephthalate. The bulk fuel 40 preferably has a cylindrical outer shape similar to the internal space and has at least one through-hole 41 extending parallel to the longitudinal direction of the cylinder. The through-hole 41 may be provided at only one location along the center of the bulk fuel 40 and / or at multiple locations at predetermined radial positions from the center of the bulk fuel 40. The through-hole 41 may or may not be coaxial with the center of the bulk fuel 40. The presence of such through-hole 41 allows the bulk fuel 40 to burn stably in the axial direction.

[0026] The bulk fuel 40 contains a powdered conductive material dispersed therein, resulting in a conductive solid fuel. The conductive material may be, for example, a material selected from the group consisting of graphite, carbon black, metal, semiconductor, graphene, carbon fiber, and carbon nanotubes. The dispersion of the conductive material allows the bulk fuel 40 to have a predetermined volume resistivity. The volume resistivity of the bulk fuel 40 is preferably in the range of 0.763 to 10,000,000 [Ω·cm]. If the volume resistivity falls below the lower limit, the resistance of the bulk fuel 40 becomes too low, requiring a low-voltage, high-current power supply. If the volume resistivity exceeds the upper limit, the resistance of the bulk fuel 40 becomes too high, requiring a high-voltage power supply or shortening the distance of the lead wires 50.

[0027] The lead wire 50 is electrically connected to the bulk fuel 40 via the flange 32. One end of the lead wire 50 is partially buried in the bulk fuel 40. The other end of the lead wire 50 is connected to a power source (not shown). When power is supplied from the power source in accordance with a command from a controller (not shown), current flows along a path from the tip of the first lead wire 50 → the bulk fuel 40 → the tip of the second lead wire 50, and the bulk fuel 40 is heated and vaporized by Joule heat, generating gasified fuel 42 in the through-hole 41.

[0028] The gasified fuel 42 generates combustion gas 43 through a chemical reaction with the oxidizer OX, and the combustion gas 43 is discharged to the outside through the outlet 35, thereby igniting the main solid fuel 13 of the rocket motor RM. The input port, the through-hole 41, and the outlet 35 are preferably arranged coaxially along a predetermined reference line. This allows rotationally symmetric or asymmetric combustion around the reference line in the internal space of the housing 31.

[0029] Fig. 4 is a structural diagram showing another example of an ignition device 30 according to the present invention. This ignition device 30 has a similar structure to that shown in Fig. 3, but an electrically insulating layer 36 made of synthetic resin or the like is provided on the inner surface of the housing 31. This prevents current flowing between the lead wires 50 from leaking into the housing 31 when the housing 31 is made of a conductive material such as metal, thereby improving the heating efficiency of the bulk fuel 40.

[0030] Next, an example of a manufacturing method for the ignition device 30 will be described. First, the bulk fuel 40 containing the powdered conductive material described above is heated to soften it. Examples of heating methods that can be used include 1) electrically heating the bulk fuel 40 by applying a small amount of power to it, and 2) heating the bulk fuel 40 using an external heater or a heating furnace. Next, electrodes such as lead wires are press-fitted into the softened bulk fuel 40 to partially embed them. Next, the bulk fuel 40 is hardened by natural or forced cooling, thereby fixing the electrodes. This simple method enables the bulk fuel 40 to be connected to the electrodes.

[0031] Figure 5 is a structural diagram showing another example of a hybrid rocket to which the present invention can be applied. Figure 6 is a structural diagram showing yet another example of an ignition device 30 according to the present invention. This hybrid rocket HR has a similar structure to that shown in Figure 2, but the ignition device 30 is installed in the internal space of the rocket motor RM.

[0032] 6, the ignition device 30 includes bulk fuel 40 and at least two lead wires 50, and the housing is omitted. The bulk fuel 40 has a cylindrical outer shape similar to the internal space of the casing 11, and has at least one through-hole 41 extending parallel to the longitudinal direction of the cylinder. The bulk fuel 40 contains a powdered conductive material dispersed therein, similar to that shown in FIG. 3.

[0033] The lead wire 50 is electrically connected to the bulk fuel 40 via the casing 11. One end of the lead wire 50 is partially buried in the bulk fuel 40. The other end of the lead wire 50 is connected to a power source (not shown). When power is supplied from the power source in accordance with a command from a controller (not shown), current flows along a path from the tip of the first lead wire 50 → the bulk fuel 40 → the tip of the second lead wire 50, and the bulk fuel 40 is heated and vaporized by Joule heat, generating gasified fuel 42 in the through-hole 41.

[0034] The gasified fuel 42 generates combustion gas 43 through a chemical reaction with the oxidizer OX, and the combustion gas 43 is discharged toward the main solid fuel 13 of the rocket motor RM, thereby igniting the main solid fuel 13.

[0035] By using the conductive solid fuel as described above, it is possible to realize ignition with a simple structure that is excellent in re-ignition performance, safety management, heat management, and reliability.

[0036] 7(A) to 13(A) are perspective half-sectional views showing examples of various shapes of bulk fuel 40, and FIGS. 7(B) to 13(B) are cross-sectional views seen from the side. The bulk fuel 40 shown in FIG. 7 has a cylindrical outer shape and has a cylindrical through-hole 41 at its center. The bulk fuel 40 shown in FIG. 8 has a cylindrical outer shape that is flatter than that of FIG. 7 and has a cylindrical through-hole 41 at its center. The bulk fuel 40 shown in FIG. 9 has a cylindrical outer shape similar to that of FIG. 7 and has three through-holes 41 at its center and at approximately half the radius from the center.

[0037] The bulk fuel 40 shown in Figure 10 has a prismatic outer shape with a regular octagonal cross section and has a cylindrical through-hole 41 at its center. The bulk fuel 40 shown in Figure 11 has a cylindrical outer shape and has a rectangular tubular through-hole 41 at its center with a regular hexagonal cross-section. The bulk fuel 40 shown in Figure 12 has a prismatic outer shape with a square cross-section and has a cylindrical through-hole 41 at its center. The bulk fuel 40 shown in Figure 13 has a prismatic outer shape with a square cross-section and has a rectangular tubular through-hole 41 at its center with a square cross-section.

[0038] 14(A) to 14(D) are perspective views showing examples of various shapes of the lead wire 50. The lead wire 50 includes a conductive wire 51 made of copper, aluminum, or the like, and an electrically insulating film 52 that covers the entire lead wire except for the tip. An electrode terminal 53 is connected to the lead wire 50 as needed. The lead wire 50 shown in FIG. 14(A) does not include the electrode terminal 53, and the conductive wire 51 is embedded in the bulk fuel 40 as is. The lead wire 50 shown in FIG. 14(B) has a two-pronged electrode terminal 53 and is embedded in the bulk fuel 40 together with the conductive wire 51. The lead wire 50 shown in FIG. 14(C) has a six-pronged electrode terminal 53 and is embedded in the bulk fuel 40 together with the conductive wire 51. The lead wire 50 shown in FIG. 14(D) has a mesh-shaped electrode terminal 53 and is embedded in the bulk fuel 40 together with the conductive wire 51. The contact area between the lead wire 50 and the bulk fuel 40 can be controlled depending on the shape and size of the electrode terminal 53.

[0039] 15(A) to 22(A) are perspective half-sectional views showing examples of various embedding modes of the lead wire 50, FIGS. 15(B) to 20(B) are cross-sectional views as seen from the side, and FIGS. 21(B) to 22(B) are cross-sectional views as seen from above. Here, the use of the cylindrical bulk fuel 40 shown in FIG. 7 is illustrated, but the bulk fuel 40 shown in FIGS. 8 to 13 can also be used. In the bulk fuel 40 shown in FIG. 15, the tips of the conductive wires 510 shown in FIG. 14(A) are arranged opposite each other so as to sandwich the through-hole 41 from the left and right. In the bulk fuel 40 shown in FIG. 16, the tips of the electrode terminals 53 shown in FIG. 14(B) are arranged opposite each other so as to sandwich the through-hole 41 from the left and right. In the bulk fuel 40 shown in FIG. 17, two lead wires 50 shown in FIG. 14(A) are inserted from the left and right, and the tips of the electrode terminals 53 are arranged opposite each other so as to sandwich the through-hole 41 from the left and right. The bulk fuel 40 shown in FIG. 18 has two lead wires 50 shown in FIG. 14(B) inserted into it from the left and right, and the tips of the electrode terminals 53 are arranged opposite each other so as to sandwich the through-hole 41 from the left and right.

[0040] In the bulk fuel 40 shown in Fig. 19, the tips of the conductive wires 510 shown in Fig. 14(A) are inserted from above and below at the sides of the through-hole 41 and are arranged facing each other. In the bulk fuel 40 shown in Fig. 20, the tips of the electrode terminals 53 shown in Fig. 14(B) are inserted from above and below at the sides of the through-hole 41 and are arranged facing each other. In the bulk fuel 40 shown in Fig. 21, the tips of the electrode terminals 53 shown in Fig. 14(D) are arranged facing each other so as to sandwich the through-hole 41 from the left and right. In the bulk fuel 40 shown in Fig. 22, the tips of the electrode terminals 53 shown in Fig. 14(C) are arranged facing each other so as to sandwich the through-hole 41 from the left and right.

[0041] 23(A) to (D) and 24(A) to (D) are explanatory diagrams showing the operation of an example of left-right lead wire insertion type ignition device 30. Figures 25(A) to (D) and 26(A) to (D) are explanatory diagrams showing the operation of an example of top-bottom lead wire insertion type ignition device 30.

[0042] As shown in Figures 23(A) and 25(A), when power is supplied via the lead wire 50, an electric current path Q1 is formed that passes through the bulk fuel 40 between the tip of the first lead wire 50 and the tip of the second lead wire 50. Next, as shown in Figures 23(B) and 25(B), the bulk fuel 40 is heated and vaporized by the current, generating gasified fuel Q2 in the through-hole 41. Next, as shown in Figures 23(C) and 25(C), oxidizer Q3 is supplied into the through-hole 41. As shown in Figures 23(D) and 25(D), the gasified fuel Q2 and the oxidizer Q3 undergo a chemical reaction Q4 to generate combustion gas Q5. The combustion gas Q5 ignites the main solid fuel 13 of the rocket motor RM. Note that the bulk fuel 40 can be ignited even if an oxidizer is flowing before the current is applied.

[0043] The combustion of the main solid fuel 13 can be stopped by reducing the amount of oxidizer supplied to zero. As shown in Figures 24(A) and 26(A), after the main solid fuel 13 has burned, the gasified portion becomes hollow. To reignite the main solid fuel 13, as shown in Figures 24(B) and 26(B), when the lead wire 50 is energized again, a current path Q6 is formed between the lead wires 50. Next, as shown in Figures 24(C) and 26(C), the bulk fuel 40 is heated and vaporized, generating gasified fuel Q7 in the through-hole 41. Next, as shown in Figures 24(D) and 26(D), when oxidizer Q3 is supplied into the through-hole 41, the gasified fuel Q7 generates combustion gas Q10 through a chemical reaction Q9 with the oxidizer Q3. The combustion gas Q10 reignites the main solid fuel 13 of the rocket motor RM.

[0044] Fig. 27(A) is a perspective half-sectional view showing an example of another shape of bulk fuel 40. Fig. 27(B) is a perspective half-sectional view showing an example of a manner in which lead wires 50 are embedded in bulk fuel 40 shown in Fig. 27(A). Fig. 27(C) is a perspective half-sectional view showing another example of a manner in which lead wires 50 are embedded in bulk fuel 40 shown in Fig. 27(A).

[0045] The bulk fuel 40 shown in Figure 27(A) has a cylindrical outer shape and has a total of seven through-holes 41 at its center and at approximately half the radius from the center. In Figure 27(B), rod-shaped electrode terminals 53, each connected to a lead wire 50, are inserted into two of the seven through-holes 41. The two electrode terminals 53 are preferably arranged opposite each other so as to sandwich the central through-hole 41 from the left and right, which enables uniform electrical heating.

[0046] In Figure 27(C), a rod-shaped electrode terminal 53 connected to a lead wire 50 is inserted into the central through-hole 41. A cylindrical electrode terminal 54 connected to the lead wire 50 is attached to the side of the bulk fuel 40. This electrode arrangement allows current to flow along the radial direction of the bulk fuel 40, enabling uniform electrical heating.

[0047] Fig. 28 is a structural diagram showing yet another example of an ignition device 30 according to the present invention. This ignition device 30 has a similar structure to that shown in Fig. 4, but a rod-shaped electrode terminal 53 connected to a lead wire 50 is inserted into a central through-hole 41. A cylindrical electrode terminal 54 connected to the lead wire 50 is attached to the side of the bulk fuel 40. An electrical insulating layer 36 made of synthetic resin or the like is provided between the electrode terminal 54 and the housing 31. The oxidizer OX is supplied to the internal space via an input port 31a provided on the side of the housing 31, without passing through the flange 32.

[0048] In operation, when current begins to flow between lead wires 50, a current flows between electrode terminals 53 and 54, and gasification begins at the bottom end surface of bulk fuel 40, generating gasified fuel 42. The gasified fuel 42 chemically reacts with the oxidizer OX supplied from input port 31a to generate combustion gas 43, which is discharged to the outside through outlet 35. This ignites main solid fuel 13 of rocket motor RM. As gasification progresses, the bottom end surface of bulk fuel 40 retreats upstream.

[0049] Fig. 29(A) is a perspective half-section showing an example of the shape of the bulk fuel 40 shown in Fig. 28. Fig. 29(B) is a perspective half-section showing an example of how the lead wire 50 is embedded in the bulk fuel 40 shown in Fig. 29(A). The bulk fuel 40 shown in Fig. 29(A) has a cylindrical outer shape with a through-hole at its center, into which a rod-shaped electrode terminal 53 connected to the lead wire 50 is inserted. A cylindrical electrode terminal 54 connected to the lead wire 50 is attached to the side of the bulk fuel 40.

[0050] FIG. 30(A) is a perspective half-section showing another example of the shape of the bulk fuel 40 shown in FIG. 28. FIG. 30(B) is a perspective half-section showing an example of how the lead wire 50 is embedded in the bulk fuel 40 shown in FIG. 30(A). The bulk fuel 40 shown in FIG. 30(A) has a truncated cone-like outer shape with a lower end smaller than an upper end, and has a through-hole at its center into which a rod-shaped electrode terminal 53 connected to a lead wire 50 is inserted. A tapered cylindrical electrode terminal 54 connected to a lead wire 50 is attached to the side of the bulk fuel 40. When current is applied to this bulk fuel 40, the current density is higher near the lower end compared to the upper end, ensuring reliable gasification at the lower end.

[0051] Figures 31(A) to (D) and Figures 32(A) to (D) are explanatory diagrams showing the operation of one example of the ignition device shown in Figure 29. Figures 33(A) to (D) and Figures 34(A) to (D) are explanatory diagrams showing the operation of one example of the ignition device shown in Figure 30. These operations are similar to the operations explained in Figures 23 to 26, and redundant explanations will be omitted.

[0052] Next, a gasification test of the bulk fuel 40 will be described. A cylindrical bulk fuel sample (outer diameter d = 20 mm, length L = 20 mm) shown in Table 1 was produced using a 3D printer and a commercially available conductive filament (3DFS, Electrically Conductive Composite PLA). Next, ABS powder and carbon black powder were mixed to produce a cylindrical bulk fuel sample (outer diameter d = 48.4 mm, length L = 11.6 mm) shown in Table 2. Next, by passing current through the lead wire, tests were conducted to determine whether gasification occurred and whether ignition occurred using an oxidizer.

[0053] [Table 1]

[0054] [Table 2]

[0055] These test results showed that bulk fuel ignition occurs when the applied power is in the range of 18 to 250 W and the applied voltage is below 100 V, the same as a household power supply.

[0056] Next, we will explain the volume resistivity of bulk fuel. Powdered graphite C was mixed and uniformly dispersed in plastic material, and the volume resistivity of samples molded into various shapes was measured. The results are shown in Table 3. Samples 1 to 7 are rectangular, and sample 8 is cylindrical. PLA is polylactic acid. PPF is a pre-made product (Proto-Pasta Filament). "Not measurable" indicates that the resistance value exceeded the measurement range of the measuring instrument (resistance value of MΩ or more). Next, powdered carbon black CB was mixed and uniformly dispersed in plastic material (ABS), and the volume resistivity of samples molded into filaments was measured. The results are shown in Table 4.

[0057] [Table 3]

[0058] [Table 4]

[0059] Figure 35 is a graph showing the relationship between the volume resistivity y and the graphite content x of bulk fuel. It can be seen that the volume resistivity decreases exponentially as the graphite content increases. From the graph, it can be seen that the material behaves as an electrical insulator in the range of 0≦x≦approximately 34%, as an electrical conductor in the range of approximately 65%≦x≦approximately 100%, and as a heater with an appropriate electrical resistance in the range of approximately 34%≦x≦approximately 65%. Figure 36 is a graph showing the relationship between the volume resistivity y and the carbon black content x of bulk fuel. As with the graph in Figure 35, it can be seen that the volume resistivity decreases as the carbon black content increases. It can be seen that the volume resistivity becomes almost flat when the carbon content is in the range of 16.68% to 20%.

[0060] As such, it can be seen that the ignition device of the present invention has a simple structure and is excellent in re-ignition performance, safety management, heat management, and reliability. Note that while the application to a hybrid rocket combustion system has been exemplified here, the present invention can also be applied to igniting liquid fuel for liquid rockets, solid fuel for solid rockets, wood, charcoal, solid fuel, flammable gas, cigarettes, etc. [Industrial Applicability]

[0061] The present invention is extremely useful industrially in that it can provide an ignition device that has a simple structure and is excellent in various performances. [Explanation of symbols]

[0062] 10 Hybrid Rocket Combustion System 11 Casing 12. Insulation 13 Main Solid Fuel 14 nozzles 15 Manifold 21 Main Line 22 Main valve 25 Bypass Line 26 Bypass valve 30 Ignition system 31 Housing 36 Electrical insulating layer 40 Bulk Fuel 41 Through hole 50 lead wire 53,54 Electrode terminal OX oxidizing agent

Claims

1. a bulk fuel as a conductive solid fuel material, which includes a plastic material and a powdery conductive substance dispersed in the plastic material, and which is gasified by passing an electric current through it and ignites by reacting with an oxidizer supplied from the outside; at least two electrodes partially embedded in the bulk fuel; An ignition device in which the bulk fuel is gasified by Joule heat generated when an electric current flows from one electrode through the bulk fuel to the other electrode.

2. 2. The ignition device of claim 1, wherein the plastic material is formed from a material selected from the group consisting of polylactic acid, epoxy resin, polyethylene, polyester, polyurethane, polyacrylonitrile, polymethyl methacrylate, acrylonitrile butadiene styrene resin, and polyethylene terephthalate.

3. 10. The ignition device of claim 1, wherein the conductive material is formed of a material selected from the group consisting of graphite, carbon black, a metal, a semiconductor, graphene, carbon fiber, and carbon nanotubes.

4. The ignition device of claim 1 , wherein the bulk fuel has a cylindrical or prismatic shape extending along a longitudinal direction.

5. 2. The ignition device according to claim 1, wherein the bulk fuel has a volume resistivity in the range of 0.763 to 10,000,000 [Ω·cm].

6. 6. The ignition device according to claim 5, wherein a fork-shaped, mesh-shaped, rod-shaped or cylindrical electrode terminal is attached to a tip of the electrode.

7. An ignition method using the ignition device according to any one of claims 1 to 6, gasifying a portion of the bulk fuel using heat generated by energizing the electrodes; and providing an oxidizer to combust the gasified bulk fuel.

8. an oxidant line for delivering an oxidant; a flow valve for controlling the flow rate of the oxidant flowing through the oxidant line; a casing having an interior space to which the oxidant line is connected; a main fuel accommodated in the internal space; a nozzle for discharging combustion gas generated by the reaction between the main fuel and the oxidizer; 7. A rocket combustion system comprising: an ignition device according to claim 1, which is provided between the oxidizer line and the internal space and ignites the main fuel.

9. A method for manufacturing an ignition device according to any one of claims 1 to 6, A step of softening a bulk fuel as a conductive solid fuel including a plastic material and a powdered conductive substance dispersed in the plastic material by heating; Pressing an electrode into the softened conductive solid fuel bulk fuel to partially embed the electrode; and fixing the electrode by hardening the bulk fuel as the conductive solid fuel.

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