Hydrogen engine

Abstract

To provide a hydrogen engine that can suppress abnormal combustion of hydrogen gas. [Solution] The hydrogen engine has a combustion chamber for burning a 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 into which the injector is inserted. The surface of the injector inside the insertion hole is provided with a film of lubricant containing a composition with a molecular structure that does not have alkyl groups in its side chains.

Description

Technical Field

[0001] The present invention relates to a hydrogen engine.

Background Art

[0002] Regarding hydrogen engines, for example, Patent Document 1 describes a liquid hydrogen system that supplies hydrogen to a hydrogen engine.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A direct injection (DI) injector directly injects hydrogen gas into the combustion chamber of a hydrogen engine. The DI injector is inserted into an insertion hole provided in 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 DI injector to facilitate insertion.

[0005] However, there are types of lubricants with high ignition reactivity and high oxidation reactivity in an environment of a mixture of hydrogen gas and air. If this type of lubricant is used, there is a risk that the lubricant will catch fire every time hydrogen gas is injected from the DI injector, causing abnormal combustion such as pre-ignition.

[0006] Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a hydrogen engine capable of suppressing abnormal combustion of hydrogen gas.

Means for Solving the Problems

[0007] The hydrogen engine of the present invention comprises a combustion chamber for burning a 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 into which the injector is inserted. The surface of the injector within the insertion hole is provided with a film of lubricant containing a composition having a molecular structure that does not have alkyl groups in its side chains.

[0008] In the hydrogen engine described above, the injector has a sealing member that seals the gap between it and the inner wall of the insertion hole, and a film of the lubricant may be provided on the surface of the sealing member.

[0009] In the hydrogen engine described above, the composition may be a polydimethylsiloxane represented by the following formula 1 (wherein X is an integer of 2 or more). [ka] [Effects of the Invention]

[0010] According to the present invention, abnormal combustion of hydrogen gas can be suppressed in a hydrogen engine. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic partial cross-sectional view showing an example of a hydrogen engine. [Figure 2] Figure 2 is a schematic plan view showing the bottom surface of the cylinder head. [Figure 3] Figure 3 is a partial cross-sectional view of the cylinder head along line AA in Figure 2. [Modes for carrying out the invention]

[0012] Figure 1 is a schematic partial cross-sectional view showing an example of a hydrogen engine 1. The hydrogen engine 1 comprises a cylinder block 2, a cylinder head 3, a piston 4, a connecting rod 5, and a direct injection injector (hereinafter referred to as injector) 8. The hydrogen engine 1 is installed as a power source in vehicles such as hydrogen-powered cars. Figures 1 to 3 show the mutually orthogonal X, Y, and Z directions.

[0013] The cylinder head 3 is joined to the cylinder block 2 at an interface P along the XY plane. Inside the cylinder block 2, a cylinder 6 is provided, oriented in the Z direction. The cylinder head 3 is positioned to close one open end of the cylinder 6. The cylinder block 2 and cylinder head 3 are made of metal such as aluminum alloy or cast iron.

[0014] The piston 4 reciprocates within the cylinder 6 in the Z direction. The piston 4 is connected to the connecting rod 5 via a piston pin. The connecting rod 5 is connected to the crankshaft (not shown) via a crank pin. The connecting rod 5 acts to convert the reciprocating motion of the piston 4 into rotational motion of the crankshaft. In addition, the walls of the cylinder 6 in the cylinder block 2, the cylinder head 3, and the top surface of the piston 4 define a combustion chamber 7 where a mixture of air and hydrogen gas burns.

[0015] The cylinder head 3 is provided with an intake port 11 for intake and an exhaust port 12 for exhaust, adjacent to each other in the X direction. The intake port 11 faces the combustion chamber 7 and communicates with the combustion chamber 7 through an intake opening 13 formed in the cylinder head 3. The exhaust port 12 faces the combustion chamber 7 and communicates with the combustion chamber 7 through an exhaust opening 14 formed in the cylinder head 3. The cylinder head 3 is also provided with an intake valve 21 for opening and closing the intake opening 13, an exhaust valve 31 for opening and closing the exhaust opening 14, a spark plug 41 for igniting the air-fuel mixture in the combustion chamber 7, and an injector 8 for directly injecting hydrogen gas into the combustion chamber 7.

[0016] Figure 2 is a schematic plan view showing the bottom surface of the cylinder head 3. The combustion chamber 7 is provided with two sets of intake openings 13 and exhaust openings 14. 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. The spark plug 41 is positioned along the Z direction and is located substantially in the center of the two intake openings 13 and the two exhaust openings 14. The injector 8 is inserted into an insertion hole 45 in the cylinder head 3 and injects hydrogen gas into the combustion chamber 7 through an injection hole 62 that opens into the combustion chamber 7. The injector 8 is positioned such that its axis L is along the X direction and passes through the midpoint between the two intake openings 13 and the midpoint between the two exhaust openings 14 in the Y direction.

[0017] Figure 3 is a partial cross-sectional view of the cylinder head 3 along line AA in Figure 2. The injector 8 is inserted into an insertion hole 45 in the cylinder head 3. The insertion hole 45 extends toward approximately the center of the combustion chamber 7 and is formed according to the shape of the injector 8. The insertion hole 45 communicates with the combustion chamber 7 through an injection hole 62.

[0018] The injector 8 has a roughly cylindrical main body 80, an extension 81 extending from the main body 80, and a tip 810 provided at the tip of the extension 81. The extension 81 has a smaller diameter than the main body 80 and is roughly cylindrical with a constriction in the middle, and a roughly band-shaped sealing member 82 is wrapped around the constricted portion. The sealing member 82 is made of, for example, Teflon (registered trademark) and seals the gap between it and the inner wall of the insertion hole 45. This maintains the airtightness of the combustion chamber 7. However, if the airtightness of the combustion chamber 7 is maintained, it is not necessarily required to provide the sealing member 82.

[0019] The tip portion 810 has a tapered annular shape facing the injection direction of hydrogen gas, and in the insertion hole 45, it faces the inner wall 450 on the combustion chamber 7 side adjacent to the edge of the opening of the injection hole 62. A gap 61 called a sac is formed between the tip portion 810 and the inner wall 450. Inside the tip portion 810 and the extension portion 81, a delivery hole 811 through which hydrogen gas is delivered is provided along the axis L direction. The hydrogen gas enters the gap 61 from the delivery hole 811 and is injected into the combustion chamber 7 through the injection hole 62 as indicated by the arrow D. Note that the extending direction of the injection hole 62 is inclined by a predetermined angle with respect to the axis L of the injector 8 so that the hydrogen gas is injected in an appropriate direction inside the combustion chamber 7.

[0020] The tip portion 810 of the injector 8 is separated from the combustion chamber 7 by the gap 61 between it and the inner wall 450 of the insertion hole 45. Thereby, compared with the case where the gap 61 does not exist, the temperature rise of the needle (not shown) etc. of the injector 8 is suppressed. Note that if the temperature resistance of the injector 8 is high, the gap 61 may not be provided.

[0021] The insertion hole 45 has a stepped portion 451 formed so as to contact the surface on the tip end side of the main body portion 80 as indicated by the reference sign E. When the main body portion 80 and the stepped portion 451 contact each other, the injector 8 is positioned with respect to the insertion hole 45.

[0022] The injector 8 is inserted into the insertion hole 45 during the manufacture of the hydrogen engine 1. At this time, a lubricant that functions as an insertion aid is applied to the surface of the injector 8 in the range indicated by the reference sign R so as to facilitate insertion. The lubricant is applied to the surfaces of the tip portion 810 and the extension portion 81 and the outer surface of the seal member 82. The lubricant remains applied to the surface of the injector 8 even after the injector 8 is inserted into the insertion hole 45. On the other hand, if a port injection type injector is used, there is no need to insert it into the insertion hole 4 like the injector 8, and it is attached to the intake port 11 of the cylinder head 3.

[0023] The symbol M indicates a schematic diagram showing an enlarged view of the vicinity of the seal member 82. A thin film of lubricant 9 exists between the surfaces of the extended portion 81 and the seal member 82 and the inner circumferential surface of the insertion hole 45. In this way, since lubricant is applied not only to the surface of the extended portion 81 but also to the outer circumferential surface of the seal member 82, when the injector 8 is inserted, friction between the portion of the extended portion 81 covered by the seal member 82 and the inner circumferential surface of the insertion hole 45 is reduced, making insertion easier.

[0024] Furthermore, the symbol N indicates a schematic diagram showing an enlarged view of the vicinity of the tip portion 810. A thin film of lubricant 9 exists between the surface of the tip portion 810 and the inner circumferential surface of the insertion hole 45. In this way, since lubricant is also applied to the tip portion 810, even if the tip portion 810 and the inner circumferential surface of the insertion hole 45 come into contact during insertion of the injector 8, friction between them is reduced, making insertion easier. Note that the thin film 9 is not necessarily formed continuously as shown by the symbols M and N, but may be formed in multiple locations. The thin film of lubricant 9 is just one example of a lubricant film.

[0025] [ka]

[0026] Formula (1) shows the molecular structure of the composition contained in the lubricant of the comparative example. In formula (1), X and Y are integers of 2 or more, representing the number of repetitions of the structure in parentheses. 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 aralkyl-aralkyl modified silicone oil. The molecular structure of the lubricant consists of three methyl groups (-CH3) and silicon atoms (Si) bonded to oxygen atoms (O), which are bonded to other silicon atoms in the repeating structure (X) via the oxygen atoms. The silicon atoms in the repeating structure are bonded to methyl groups, oxygen atoms, and alkyl groups.

[0027] The silicon atoms in one repeating structure are bonded to silicon atoms in another repeating structure (Y) via oxygen atoms. The silicon atoms in the other repeating structure are bonded to a methyl group, an oxygen atom, and an aralkyl group. These silicon atoms are bonded to other silicon atoms, which are bonded to three methyl groups (-CH3), via oxygen atoms.

[0028] Lubricants are polymers with a silicon-oxygen (Si-O) backbone, where the Si-O bond is stabilized by the bonding of methyl groups to silicon atoms. Silicone oil has a relatively large molecular weight compared to other types of oils, and its intermolecular forces are strong, resulting in low volatility. Silicone oil is stable over a wide temperature range and is heat resistant, possessing excellent heat resistance, and its decomposition and volatilization are suppressed even in high-temperature environments. In addition, methyl groups are less flammable than hydrocarbon chains with typical carbon-carbon bonds.

[0029] The oxidation reaction of alkyl groups is exothermic, releasing a large amount of energy. Therefore, the lubricant in the comparative example can become an ignition source by undergoing an exothermic oxidation reaction in an environment of a mixture of hydrogen gas and air. The minimum ignition energy of hydrogen gas is 0.02 mJ, while the minimum ignition energy of methane, for example, is 0.28 mJ. Consequently, when hydrogen gas is injected from the injector 8, the lubricant applied around the injector 8 may undergo an exothermic oxidation reaction and ignite, potentially causing abnormal combustion such as pre-ignition. In particular, the lubricant applied to the surface of the tip portion 810 is exposed to hydrogen gas present in the gap 61 between it and the inner wall 450 of the insertion hole 45, making it particularly susceptible to becoming an ignition source.

[0030] [ka]

[0031] Formula (2) shows the molecular structure of the composition contained in the lubricant of the example. Here, polydimethylsiloxane is given as the composition. In formula (2), X is the number of repetitions of the structure in parentheses and is an integer of 2 or more. The lubricant of the example is a silicone oil. The molecular structure of the lubricant is such that silicon atoms (Si) bonded to three methyl groups (-CH3) and oxygen atoms (O) are bonded to other silicon atoms in the repeating structure (X) via the oxygen atoms. The silicon atoms in the repeating structure are bonded to two methyl groups and oxygen atoms. These silicon atoms are bonded to other silicon atoms bonded to three methyl groups (-CH3) via the oxygen atoms.

[0032] In the lubricant of the example, the Si-O bond is stabilized by the bonding of methyl groups to silicon atoms, similar to the comparative example. Furthermore, since the lubricant of the example is a silicon oil, as mentioned above, decomposition and volatilization are suppressed even in high-temperature environments, and it also has the advantage that the methyl groups are less flammable.

[0033] The lubricant in the example does not have alkyl groups in the side chains of its molecular structure. Compared to lubricants that have alkyl groups in the side chains, such as the comparative example, the lubricant in the example is less likely to undergo an exothermic oxidation reaction in an environment of a mixture of hydrogen gas and air. Therefore, even if the lubricant in the example is applied to the surface of the injector 8, the risk of abnormal combustion such as pre-ignition when hydrogen gas is injected from the injector 8 is reduced compared to the comparative example. Although silicone oil is given as an example of a lubricant, it is not limited to this, and fluorine-based oils or hydrocarbon-based oils may also be used. Here, fluorine oil generally exhibits less viscosity change with temperature changes than other types of oils, and therefore shows high stability in harsh environments with large temperature changes.

[0034] Thus, in this embodiment, the hydrogen engine 1 has a lubricant with a molecular structure that does not have alkyl groups in its side chains applied to the surface of the injector 8, which can suppress abnormal combustion of hydrogen gas.

[0035] The embodiments described above are preferred examples of the present invention. However, the invention is not limited thereto, and various modifications are possible without departing from the spirit of the invention. [Explanation of Symbols]

[0036] 1 Hydrogen engine, 7 Combustion chamber, 8 Direct injection injector (injector), 9 Thin film, 45 Insertion hole, 61 Gap, 82 Sealing member, 810 Tip

Claims

1. A combustion chamber for burning a mixture of air and hydrogen gas, An injector that directly injects the hydrogen gas into the combustion chamber, It has an insertion hole that communicates with the combustion chamber and into which the injector is inserted, A film of lubricant containing a composition having a molecular structure without alkyl groups in its side chains is provided on the surface of the injector within the insertion hole. Hydrogen engine.

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

3. The composition is a polydimethylsiloxane represented by the following formula 1 (wherein X is an integer of 2 or more). A hydrogen engine according to claim 1 or 2. 【Chemistry 1】

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