Hydrogen engine

Abstract

The invention relates to a hydrogen engine. The hydrogen engine has a combustion chamber for combusting a gas mixture of air and hydrogen gas, an injector for directly injecting the hydrogen gas into the combustion chamber, and an insertion hole communicating with the combustion chamber and into which the injector is inserted. The surface of the ejector in the insertion hole is provided with a film of a lubricant containing a composition having a molecular structure in which a side chain does not have an alkyl group.

Description

Technical Field

[0001] This invention relates to hydrogen engines. Background Technology

[0002] Regarding hydrogen engines, for example, Japanese Patent Application Publication No. 2024-76203 describes a liquid hydrogen system for supplying hydrogen to a hydrogen engine. Summary of the Invention

[0003] In a hydrogen engine, a direct injection (in-cylinder injection) injector injects hydrogen gas directly into the combustion chamber. The direct injection injector is inserted into an insertion hole located on the cylinder head of the hydrogen engine. During the manufacture of the hydrogen engine, a lubricant (insertion aid) is applied to the surface of the insertion site of the direct injection injector to facilitate insertion.

[0004] However, some lubricants exhibit high oxidizing reactivity and high ignition properties in a hydrogen-air mixture. If such a lubricant is used, it is possible that the lubricant will ignite whenever hydrogen is injected from the direct injection nozzle, resulting in premature ignition or other abnormal combustion.

[0005] Therefore, the present invention was made in view of the above-mentioned problems, and its object is to provide a hydrogen engine capable of suppressing abnormal combustion of hydrogen.

[0006] The hydrogen engine of the present invention has a combustion chamber for burning a mixture of air and hydrogen, an injector for directly injecting hydrogen into the combustion chamber, and an insertion hole communicating with the combustion chamber and for inserting the injector. A film of a lubricant containing a molecular structure with a side chain without alkyl groups is provided on the surface of the injector in the insertion hole.

[0007] In the aforementioned hydrogen engine, the injector may have a sealing member that seals the gap between itself and the inner wall of the insertion hole, and a film of the aforementioned lubricant may be provided on the surface of the sealing member.

[0008] In the aforementioned hydrogen engine, the composition may be a polydimethylsiloxane represented by the following chemical formula 1. In the following chemical formula 1, X is an integer of 2 or more.

[0009] (Chemical Formula 1)

[0010]

[0011] According to the present invention, abnormal combustion of hydrogen can be suppressed in a hydrogen engine. Attached Figure Description

[0012] Hereinafter, the features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described with reference to the accompanying drawings, wherein the same symbols denote the same elements.

[0013] Figure 1 This is a partial cross-sectional view that schematically illustrates an example of a hydrogen engine.

[0014] Figure 2 It is a top view that roughly shows the bottom surface of the cylinder head.

[0015] Figure 3 It is along Figure 2 A partial sectional view of the cylinder head along line III-III. Detailed Implementation

[0016] Figure 1 This is a partial cross-sectional view schematically showing an example of a hydrogen engine 1. The hydrogen engine 1 includes a cylinder block 2, a cylinder head 3, a piston 4, a connecting rod 5, and a direct injection injector (hereinafter referred to as an injector) 8. The hydrogen engine 1 is used as a power source in vehicles such as hydrogen fuel cell vehicles. It should be noted that... Figures 1-3 The X, Y, and Z directions are shown as being orthogonal to each other.

[0017] The cylinder head 3 is joined to the cylinder block 2 at the boundary surface P along the XY plane. A cylinder 6 is disposed inside the cylinder block 2 along the Z direction. The cylinder head 3 is configured to block one open end of the cylinder 6. The cylinder block 2 and cylinder head 3 are formed of metals such as aluminum alloy or cast iron.

[0018] Piston 4 reciprocates in the Z-direction within cylinder 6. Piston 4 is connected to connecting rod 5 via piston pin. Connecting rod 5 is connected to crankshaft (not shown) via crank pin. Connecting rod 5 functions to convert the reciprocating motion of piston 4 into the rotational motion of crankshaft. Furthermore, combustion chamber 7, where the air-hydrogen mixture is burned, is defined by the walls of cylinder 6 in cylinder block 2, cylinder head 3, and the upper surface of piston 4.

[0019] An intake port 11 for intake and an exhaust port 12 for exhaust are arranged adjacent to each other in the X direction on the cylinder head 3. The intake port 11 faces the combustion chamber 7 and communicates with the combustion chamber 7 via an intake opening 13 formed on the cylinder head 3. The exhaust port 12 faces the combustion chamber 7 and communicates with the combustion chamber 7 via an exhaust opening 14 formed on the cylinder head 3. In addition, the cylinder head 3 is provided with an intake valve 21 that opens and closes the intake opening 13, an exhaust valve 31 that opens and closes the exhaust opening 14, a spark plug 41 that ignites the air-fuel mixture in the combustion chamber 7, and an injector 8 that directly injects hydrogen into the combustion chamber 7.

[0020] Figure 2This is a top view schematically showing the bottom surface of the cylinder head 3. Two sets of intake openings 13 and exhaust openings 14 are provided in the combustion chamber 7. The two intake openings 13 are arranged side-by-side in the Y direction, and the two exhaust openings 14 are also arranged side-by-side in the Y direction. A spark plug 41 is arranged along the Z direction, located substantially at the center of the two intake openings 13 and the two exhaust openings 14. An injector 8 is inserted into an insertion hole 45 within the cylinder head 3, injecting hydrogen into the combustion chamber 7 via an injection hole 62 opening into the combustion chamber 7. The injector 8 is arranged such that its axis L is along the X direction and passes through the middle of the two intake openings 13 and the middle of the two exhaust openings 14 in the Y direction.

[0021] Figure 3 It is along Figure 2 A partial cross-sectional view of the cylinder head 3 along line III-III. An injector 8 is inserted into an insertion hole 45 within the cylinder head 3. The insertion hole 45 extends approximately towards the center of the combustion chamber 7 and is formed in accordance with the shape of the injector 8. The insertion hole 45 communicates with the combustion chamber 7 via an injection hole 62.

[0022] The injector 8 has a nearly cylindrical main body 80, an extension 81 extending from the main body 80, and a front end portion 810 disposed at the front end of the extension 81. The extension 81 has a nearly cylindrical shape with a diameter smaller than that of the main body 80 and tapers midway, and a nearly strip-shaped sealing member 82 is wound around the tapered portion. The sealing member 82 is formed, for example, of Teflon (registered trademark), and seals the gap between itself and the inner wall of the insertion hole 45. This maintains the airtightness of the combustion chamber 7. It should be noted that the sealing member 82 is not necessarily required as long as the airtightness of the combustion chamber 7 can be maintained.

[0023] The front end portion 810 has an annular shape that tapers towards the hydrogen injection direction, and is located in the insertion hole 45, adjacent to the inner wall 450 on the combustion chamber 7 side, which is adjacent to the edge of the opening of the injection hole 62. A gap 61, referred to as a bladder, is formed between the front end portion 810 and the inner wall 450. Inside the front end portion 810 and the extension portion 81, an outlet hole 811 for discharging hydrogen is provided along the axis L. Hydrogen enters the gap 61 from the outlet hole 811 and is injected into the combustion chamber 7 through the injection hole 62 as shown by arrow D. It should be noted that the extension direction of the injection hole 62 is inclined at only a predetermined angle relative to the axis L of the injector 8 so that the hydrogen is injected in an appropriate direction inside the combustion chamber 7.

[0024] The front end 810 of the injector 8 is separated from the combustion chamber 7 by a gap 61 between it and the inner wall 450 of the insertion hole 45. This reduces the temperature rise of the injector 8's needle (not shown) and other components compared to the absence of the gap 61. It should be noted that if the injector 8 has high temperature resistance, the gap 61 may not be necessary.

[0025] As indicated by symbol E, the insertion hole 45 has a stepped portion 451 formed in such a way as to abut against the front end side of the main body 80. The injector 8 is positioned relative to the insertion hole 45 by the contact between the main body 80 and the stepped portion 451.

[0026] During the manufacture of the hydrogen engine 1, the injector 8 is inserted into the insertion hole 45. At this time, a lubricant, which functions as an insertion aid, is applied to the surface of the injector 8 within the range indicated by the symbol R to facilitate insertion. The lubricant is applied to the surfaces of the front end 810 and the extension 81, as well as the outer surface of the sealing member 82. Even after the injector 8 is inserted into the insertion hole 45, the lubricant remains applied to the surface of the injector 8. In contrast, assuming the use of a port-type injector, it is not necessary to insert it into the insertion hole 45 like the injector 8, but rather it is mounted on the intake port 11 of the cylinder head 3.

[0027] The symbol M represents an enlarged schematic diagram of the vicinity of the sealing member 82. A thin film 9 of lubricant exists between the surfaces of the extension 81 and the sealing member 82 and the inner peripheral surface of the insertion hole 45. Thus, lubricant is applied not only to the surface of the extension 81 but also to the outer peripheral surface of the sealing member 82. Therefore, when the injector 8 is inserted, the friction between the portion of the extension 81 covered by the sealing member 82 and the inner peripheral surface of the insertion hole 45 is reduced, making insertion easier.

[0028] Additionally, the symbol N represents an enlarged schematic diagram of the area near the front end portion 810. A thin film 9 of lubricant exists between the surface of the front end portion 810 and the inner circumferential surface of the insertion hole 45. Thus, since lubricant is also applied to the front end portion 810, friction between the front end portion 810 and the inner circumferential surface of the insertion hole 45 is reduced when the injector 8 is inserted, making insertion easier. It should be noted that the thin film 9 is not necessarily formed continuously as shown by the symbols M and N; sometimes it is formed separately in multiple locations. It should be noted that the lubricant film 9 is an example of a lubricant membrane.

[0029] (Chemical Formula 2)

[0030]

[0031] Chemical Formula 2 represents the molecular structure of the composition contained in the comparative example lubricant. In Chemical Formula 2, X and Y are the repetition numbers of the structures within parentheses, which are integers greater than or equal to 2. Additionally, R represents an organic group such as an aryl group, Q1 represents an alkyl group, and Q2 represents an aralkyl group. The lubricant is an alkylaralkyl-modified silicone oil. In the molecular structure of the lubricant, silicon atoms (Si) bonded to three methyl groups (-CH3) and oxygen atoms (O) are bonded to other silicon atoms within the repeating structure (X) via oxygen atoms. The silicon atoms within the repeating structure are bonded to methyl groups, oxygen atoms, and alkyl groups.

[0032] The silicon atom within the repeating structure is bonded to silicon atoms in other repeating structures (Y) via oxygen atoms. Silicon atoms in other repeating structures are bonded to methyl groups, oxygen atoms, and aralkyl groups. This silicon atom is also bonded via oxygen atoms to other silicon atoms bonded with three methyl groups (-CH3).

[0033] Lubricants are polymers with a silicon-oxygen (Si-O) backbone, where methyl groups are bonded to silicon atoms, thus stabilizing the Si-O bond. Compared to other types of oils, silicone oils have a larger molecular weight and stronger intermolecular forces, resulting in lower volatility. Silicone oils are stable and heat-resistant over a wide temperature range, exhibiting excellent heat resistance and inhibiting decomposition and volatilization even at high temperatures. Furthermore, compared to typical intercarbon-bonded hydrocarbon chains, methyl groups are less flammable.

[0034] The oxidation of alkyl groups is exothermic, releasing a large amount of energy. Therefore, the lubricant in the comparative example can become an ignition source for the exothermic oxidation reaction that occurs in a mixture of hydrogen and air. The minimum ignition energy of hydrogen is 0.02 mJ, compared to 0.28 mJ for methane, for example. Therefore, when hydrogen is injected from the injector 8, the lubricant coated around the injector 8 undergoes an exothermic oxidation reaction and ignites, potentially leading to premature ignition or other abnormal combustion. In particular, the lubricant coated on the surface of the tip 810 is exposed to hydrogen present in the gap 61 between the tip and the inner wall 450 of the insertion hole 45, thus easily becoming an ignition source.

[0035] (Chemical Formula 1)

[0036]

[0037] Chemical Formula 1 represents the molecular structure of the composition contained in the lubricant of the embodiment. Polydimethylsiloxane can be cited as an example of this composition. In Chemical Formula 1, X is the number of repetitions of the structure in parentheses, which is an integer greater than or equal to 2. The lubricant of the embodiment is silicone oil. In the molecular structure of the lubricant, a silicon atom (Si) bonded to three methyl groups (-CH3) and an oxygen atom (O) is bonded to other silicon atoms within the repeating structure (X) via the oxygen atom. The silicon atom within the repeating structure is bonded to two methyl groups and an oxygen atom. This silicon atom is then bonded to other silicon atoms bonded to three methyl groups (-CH3) via the oxygen atom.

[0038] The lubricant in the embodiments is similar to that in the comparative examples, with methyl groups bonded to silicon atoms, thereby stabilizing the Si-O bonds. Furthermore, the lubricant in the embodiments is silicone oil, thus also possessing the advantages described above, such as the ability to suppress decomposition and volatilization even at high temperatures, and the non-flammability of methyl groups.

[0039] The lubricant of the embodiment does not have alkyl groups in its molecular structure side chains. Compared with lubricants with alkyl groups in their side chains, such as those in the comparative example, the lubricant of the embodiment is less prone to exothermic oxidation reactions in a hydrogen-air mixture. Therefore, even if the surface of the injector 8 is coated with the lubricant of the embodiment, the possibility of abnormal combustion such as premature ignition is reduced when hydrogen is injected from the injector 8 compared to the comparative example. It should be noted that silicone oil is listed as an example of a lubricant, but it is not limited to this; fluorinated oils and hydrocarbon oils can also be used. Here, fluorinated oils generally exhibit less viscosity change with temperature changes than other types of oils, thus demonstrating high stability in harsh environments with large temperature variations.

[0040] Thus, the hydrogen engine 1 of this embodiment is able to suppress abnormal combustion of hydrogen because the surface of the injector 8 is coated with a lubricant with a molecular structure in which the side chain does not have an alkyl group.

[0041] The above-described embodiments are preferred embodiments of the present invention. However, they are not limited thereto, and various modifications can be made without departing from the spirit of the present invention.

Claims

1. A hydrogen engine comprising a combustion chamber for burning a mixture of air and hydrogen, an injector for directly injecting the hydrogen into the combustion chamber, and an insertion port communicating with the combustion chamber and into which the injector is inserted. The surface of the injector within the insertion hole is provided with a film of a lubricant containing a molecular structure with a side chain that does not have alkyl groups.

2. The hydrogen engine according to claim 1, wherein, The injector has a sealing member that seals the gap between itself and the inner wall of the insertion hole. A film of the lubricant is provided on the surface of the sealing member.

3. The hydrogen engine according to claim 1 or 2, wherein, The composition is a polydimethylsiloxane represented by the following chemical formula 1, where X is an integer greater than or equal to 2. Chemical Formula 1

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