Ignition system

Abstract

An ignition system 200 comprises: a first auxiliary chamber 202 which communicates with a combustion chamber via at least one first communication hole; a second auxiliary chamber 204 in which an ignition device 206 is provided; and at least one second communication hole 204b which is bent and communicates the first auxiliary chamber 202 and the second auxiliary chamber.

Description

Ignition System

[0001] This disclosure relates to an ignition system. This application claims the benefit of priority based on Japanese Patent Application No. 2024-171105 filed on September 30, 2024, the content of which is incorporated herein by reference.

[0002] In a gas engine, a fuel having poor combustibility may be used. For example, as disclosed in Patent Document 1, a technique of using ammonia having poor combustibility as a fuel has been proposed. By using ammonia as a fuel, carbon dioxide emissions can be suppressed.

[0003] Japanese Patent Application Laid-Open No. 2020-148198

[0004] When a fuel having poor combustibility is used, if the promotion of combustion in the combustion chamber is insufficient, there is a risk that the in-cylinder pressure will become low. Therefore, it is desirable to promote combustion in the combustion chamber.

[0005] An object of this disclosure is to provide an ignition system capable of promoting combustion in a combustion chamber.

[0006] To solve the above problems, the ignition system of this disclosure includes a first sub-chamber communicating with a combustion chamber through at least one first communication hole, a second sub-chamber provided with an ignition device, and at least one second communication hole that connects the first sub-chamber and the second sub-chamber and is bent.

[0007] The second sub-chamber is formed in a cylindrical shape, and the inclination angle of the central axis of the first sub-chamber side of the second communication hole with respect to the central axis of the second sub-chamber and the inclination angle of the central axis of the second sub-chamber side of the second communication hole with respect to the central axis of the second sub-chamber may be different from each other.

[0008] The second sub-chamber is formed in a cylindrical shape, and when viewed in the central axis direction of the second sub-chamber, the central axis of the first sub-chamber side of the second communication hole and the central axis of the second sub-chamber side of the second communication hole may intersect each other.

[0009] The second sub-chamber is formed in a cylindrical shape, and the central axis of the first sub-chamber side of the second communication hole may be eccentric with respect to the central axis of the second sub-chamber.

[0010] The second subchamber is formed in a cylindrical shape, and the central axis of the second communication hole on the side of the second subchamber may be eccentric with respect to the central axis of the second subchamber.

[0011] According to this disclosure, combustion in the combustion chamber can be promoted.

[0012] Figure 1 is a diagram showing a schematic configuration of a gas engine according to an embodiment of the present disclosure. Figure 2 is a diagram showing a schematic configuration of an ignition system according to an embodiment of the present disclosure. Figure 3 is a diagram showing a schematic configuration of a second sub-chamber and ignition device in an ignition system according to an embodiment of the present disclosure. Figure 4 is a view from below of the second sub-chamber housing in an ignition system according to an embodiment of the present disclosure. Figure 5 is a diagram showing a schematic configuration of a second sub-chamber and ignition device in an ignition system according to a first modification of the present disclosure. Figure 6 is a diagram showing a schematic configuration of a second sub-chamber and ignition device in an ignition system according to a second modification of the present disclosure. Figure 7 is a diagram showing a schematic configuration of a second sub-chamber and ignition device in an ignition system according to a third modification of the present disclosure. Figure 8 is a cross-sectional view of the second sub-chamber housing in an ignition system according to a fourth modification of the present disclosure, viewed in the direction of the central axis of the second sub-chamber. Figure 9 is a cross-sectional view of the second sub-chamber housing in an ignition system according to a fifth modification of the present disclosure, viewed in the direction of the central axis of the second sub-chamber. Figure 10 is a cross-sectional view of the second sub-chamber housing in the ignition system according to the sixth modification of the present disclosure, viewed in the direction of the central axis of the second sub-chamber. Figure 11 is a cross-sectional view of the second sub-chamber housing in the ignition system according to the seventh modification of the present disclosure, viewed in the direction of the central axis of the second sub-chamber.

[0013] Embodiments of this disclosure will be described below with reference to the attached drawings. The dimensions, materials, and other specific numerical values ​​shown in the embodiments are merely examples for the purpose of facilitating understanding and do not limit this disclosure unless otherwise specified. In this specification and drawings, elements having substantially the same function or configuration are denoted by the same reference numerals to avoid redundant explanations, and elements not directly related to this disclosure are omitted from the illustrations.

[0014] Figure 1 shows a schematic configuration of the gas engine 100 according to this embodiment. As shown in Figure 1, the gas engine 100 comprises a cylinder block 102, a cylinder head 104, and a piston 106.

[0015] A cylinder 102a is formed in the cylinder block 102. The inner circumferential surface of the cylinder 102a may be formed by a cylinder liner that is press-fitted or cast into the interior of the cylinder block 102. A piston 106 is housed in the cylinder 102a. A combustion chamber 108 is formed inside the cylinder 102a. The combustion chamber 108 is partitioned by the cylinder 102a of the cylinder block 102, the cylinder head 104, and the crown surface 106a of the piston 106.

[0016] An intake port 104a and an exhaust port 104b are formed in the cylinder head 104. The intake port 104a and the exhaust port 104b open into the combustion chamber 108. The opening of the intake port 104a on the combustion chamber 108 side is opened and closed by an intake valve 110a. The opening of the exhaust port 104b on the combustion chamber 108 side is opened and closed by an exhaust valve 110b.

[0017] An ignition system 200 is provided in the cylinder head 104. The ignition system 200 is positioned, for example, on the central axis of the piston 106. The ignition system 200 comprises a first sub-chamber 202, a second sub-chamber 204, and an ignition device 206. Details of the ignition system 200 will be described later with reference to Figure 2, etc.

[0018] The gas engine 100 is, for example, a four-stroke engine. During the intake stroke, the intake valve 110a opens and the exhaust valve 110b closes, and the piston 106 moves toward bottom dead center. A mixture of fuel gas and air flows into the combustion chamber 108 from the intake port 104a. During the compression stroke, the intake valve 110a and the exhaust valve 110b close, and the piston 106 moves toward top dead center. The mixture compressed by the piston 106 is guided from the combustion chamber 108 through the first sub-chamber 202 to the second sub-chamber 204. The combustion gas produced by the ignition device 206 igniting the mixture is ejected into the combustion chamber 108 through the second sub-chamber 204 and the first sub-chamber 202. The mixture burns in the combustion chamber 108 due to the combustion gas. During the expansion stroke, the piston 106 is pushed toward bottom dead center. During the exhaust stroke, the intake valve 110a closes and the exhaust valve 110b opens, causing the piston 106 to move towards top dead center. The exhaust gas after combustion is discharged from the combustion chamber 108 through the exhaust port 104b.

[0019] The fuel gas used in the gas engine 100 is not particularly limited. However, in some cases, a flame-retardant fuel may be used in the gas engine 100. Examples of flame-retardant fuels include ammonia or dilute natural gas. When a flame-retardant fuel is used, if the combustion in the combustion chamber 108 is not sufficiently promoted, the cylinder pressure may become low. In this embodiment, combustion in the combustion chamber 108 is promoted by modifying the ignition system 200. The details of the ignition system 200 will be described below.

[0020] Hereafter, the axial, circumferential, and radial directions of the piston 106 will also be referred to simply as the axial, circumferential, and radial directions, respectively. Hereafter, the top dead center side of the piston 106 will also be referred to as the upper side, and the bottom dead center side of the piston 106 will also be referred to as the lower side.

[0021] Figure 2 shows a schematic configuration of the ignition system 200 according to this embodiment. However, the example in Figure 2 is merely one example of the ignition system 200. As will be described later, the shape and arrangement of each component of the ignition system 200 are not limited to the example in Figure 2.

[0022] As shown in Figure 2, the ignition system 200 comprises a first sub-chamber 202, a second sub-chamber 204, and an ignition device 206.

[0023] The first sub-chamber 202 is a space that communicates with the combustion chamber 108. The first sub-chamber 202 is partitioned by the first sub-chamber housing 202a. The first sub-chamber housing 202a includes an upper housing 202a1 and a lower housing 202a2.

[0024] The upper housing 202a1 has a cylindrical shape. The upper housing 202a1 is positioned coaxially with the central axis of the piston 106. The lower part of the upper housing 202a1 is connected to the upper part of the lower housing 202a2. The upper housing 202a1 is in communication with the lower housing 202a2.

[0025] The lower housing 202a2 has a cylindrical shape. The diameter of the lower housing 202a2 is smaller than the diameter of the upper housing 202a1. The lower housing 202a2 is positioned coaxially with the central axis of the piston 106. In other words, the lower housing 202a2 is positioned coaxially with the upper housing 202a1. The lower part of the lower housing 202a2 protrudes into the combustion chamber 108. The portion of the lower housing 202a2 that protrudes into the combustion chamber 108 separates the combustion chamber 108 from the first sub-chamber 202.

[0026] The first sub-chamber 202 communicates with the combustion chamber 108 via the first communication holes 202b. For example, multiple first communication holes 202b are provided in the first sub-chamber housing 202a. Multiple first communication holes 202b are provided in the lower part of the first sub-chamber housing 202a. Multiple first communication holes 202b are provided in the portion of the first sub-chamber housing 202a facing the combustion chamber 108.

[0027] Multiple first communication holes 202b are provided at intervals from each other in the circumferential direction. For example, multiple first communication holes 202b are provided at equal intervals in the circumferential direction. However, the number and arrangement of the first communication holes 202b are not limited. For example, the number of first communication holes 202b may be one. For example, multiple first communication holes 202b may be provided at unequal intervals in the circumferential direction. The cross-sectional shape of the first communication hole 202b, which is perpendicular to the direction of extension, is, for example, circular. However, the cross-sectional shape of the first communication hole 202b is not limited. For example, the cross-sectional shape of the first communication hole 202b may be elliptical or polygonal.

[0028] The second sub-room 204 is a space that communicates with the first sub-room 202. For example, the volume of the second sub-room 204 is smaller than the volume of the first sub-room 202. The second sub-room 204 is partitioned by the second sub-room housing 204a.

[0029] The second sub-chamber housing 204a has a cylindrical shape. The second sub-chamber housing 204a is positioned coaxially with the central axis of the piston 106. In other words, the second sub-chamber housing 204a is positioned coaxially with the first sub-chamber housing 202a. The lower part of the second sub-chamber housing 204a protrudes into the first sub-chamber 202. The portion of the second sub-chamber housing 204a that protrudes into the first sub-chamber 202 separates the first sub-chamber 202 from the second sub-chamber 204.

[0030] The second sub-chamber 204 communicates with the first sub-chamber 202 via a second communication hole 204b. For example, multiple second communication holes 204b are provided in the second sub-chamber housing 204a. Multiple second communication holes 204b are provided in the lower part of the second sub-chamber housing 204a. Multiple second communication holes 204b are provided in the portion of the second sub-chamber housing 204a facing the first sub-chamber 202.

[0031] Multiple second communication holes 204b are provided at intervals from each other in the circumferential direction. For example, multiple second communication holes 204b are provided at equal intervals in the circumferential direction. However, the number and arrangement of the second communication holes 204b are not limited. For example, the number of second communication holes 204b may be one. For example, multiple second communication holes 204b may be provided at unequal intervals in the circumferential direction. The cross-sectional shape of the second communication hole 204b, which is perpendicular to the direction of extension, is, for example, circular. However, the cross-sectional shape of the second communication hole 204b is not limited. For example, the cross-sectional shape of the second communication hole 204b may be elliptical or polygonal.

[0032] The ignition device 206 is provided to ignite the mixture of fuel gas and air. The ignition device 206 is located in the second sub-chamber 204. Details of the configuration of the ignition device 206 will be described later.

[0033] As shown by the dashed arrow in Figure 2, during the compression stroke, a mixture of fuel gas and air is guided from the combustion chamber 108 through the first communication hole 202b to the first sub-chamber 202. As shown by the dashed arrow in Figure 2, the mixture guided to the first sub-chamber 202 is then guided from the first sub-chamber 202 through the second communication hole 204b to the second sub-chamber 204. The mixture in the second sub-chamber 204 is then ignited by the ignition device 206, producing burnt gas.

[0034] Subsequently, as shown by the solid arrows in Figure 2, the burnt gas is ejected from the second sub-chamber 204 through the second communication hole 204b into the first sub-chamber 202. The burnt gas ejected into the first sub-chamber 202 ignites the fuel-air mixture inside the first sub-chamber 202. Then, as shown by the solid arrows in Figure 2, the burnt gas is ejected from the first sub-chamber 202 through the first communication hole 202b into the combustion chamber 108. The burnt gas ejected into the combustion chamber 108 ignites the fuel-air mixture inside the combustion chamber 108.

[0035] As described above, the ignition system 200 includes a second sub-chamber 204 having a smaller volume than the first sub-chamber 202, in addition to the first sub-chamber 202. The fuel-air mixture in the second sub-chamber 204 is then ignited by the ignition device 206. Therefore, compared to directly igniting the fuel-air mixture in the first sub-chamber 202, the combustion of the fuel-air mixture in the second sub-chamber 204 can be completed earlier, accelerating the timing of flame generation. Thus, the combustion in the first sub-chamber 202 can be accelerated, and consequently, the combustion in the combustion chamber 108 can be promoted.

[0036] As described above, in the ignition system 200, there are two types of gas flows passing through the second communication hole 204b: the flow of the fuel-air mixture flowing from the first sub-chamber 202 to the second sub-chamber 204 (i.e., the flow indicated by the dashed arrow in Figure 2), and the flow of the burnt gas flowing out from the second sub-chamber 204 to the first sub-chamber 202 (i.e., the flow indicated by the solid arrow in Figure 2). The direction of the fuel-air mixture flowing from the second communication hole 204b to the second sub-chamber 204 is preferably set so that the ignition of the fuel-air mixture by the ignition device 206 in the second sub-chamber 204 is stable. On the other hand, the direction of the burnt gas flowing out from the second communication hole 204b to the first sub-chamber 202 is preferably set so that the ignition of the fuel-air mixture by the burnt gas in the first sub-chamber 202 is smooth.

[0037] For example, if the second communication hole 204b is formed in a straight line, it becomes difficult to individually adjust the flow direction of the mixture flowing from the second communication hole 204b into the second sub-chamber 204 and the flow direction of the burned gas flowing out from the second communication hole 204b into the first sub-chamber 202. Therefore, in this embodiment, as will be described later, by forming the second communication hole 204b to be curved, it becomes possible to individually adjust each of the above flow directions, and consequently, combustion in the combustion chamber 108 can be further promoted.

[0038] Figure 3 shows a schematic configuration of the second sub-chamber 204 and the ignition device 206 in the ignition system 200 according to this embodiment. In Figure 3, the second sub-chamber 204 and the ignition device 206 of the ignition system 200 are shown as an excerpt.

[0039] The ignition device 206 includes a first electrode 206a, a second electrode 206b, and an electrode gap 206c. In the example shown in Figure 3, the ignition method by the ignition device 206 is a spark-based method. However, the ignition method by the ignition device 206 is not limited and may include pilot ignition or laser ignition, etc.

[0040] The first electrode 206a has, for example, a rod shape. The first electrode 206a extends linearly downward from the upper part of the second sub-chamber 204. The first electrode 206a is positioned coaxially with the central axis A0 of the second sub-chamber 204.

[0041] The second electrode 206b has, for example, a substantially disc shape and is positioned coaxially with the central axis A0 of the second sub-chamber 204. An insertion hole 206b1 is formed in the center of the second electrode 206b. The insertion hole 206b1 penetrates the center of the second electrode 206b. In the example of Figure 3, the second electrode 206b has a frustoconical shape that inclins upward as it extends radially outward. However, the second electrode 206b does not have to inclin as it extends radially outward; it may inclin downward as it extends radially outward.

[0042] The outer surface of the second electrode 206b is fitted into the inner surface of the second sub-chamber housing 204a. As a result, the space inside the second sub-chamber 204 is divided by the second electrode 206b into a first space 204c on the side of the first sub-chamber 202 and a second space 204d on the opposite side of the first sub-chamber 202.

[0043] A through hole 206b2 that communicates the first space 204c and the second space 204d is formed in the second electrode 206b. The through hole 206b2 penetrates the second electrode 206b in the central axis direction of the second sub-chamber 204 (that is, the direction along the central axis A0 of the second sub-chamber 204). For example, a plurality of through holes 206b2 are provided at intervals in the circumferential direction of the second sub-chamber 204. For example, the plurality of through holes 206b2 are provided at equal intervals in the circumferential direction of the second sub-chamber 204. However, the number and arrangement of the through holes 206b2 are not limited. For example, the number of the through holes 206b2 may be singular. For example, the plurality of through holes 206b2 may be provided at unequal intervals in the circumferential direction. The shape of the through hole 206b2 is, for example, circular. However, the shape of the through hole 206b2 is not limited. For example, the shape of the through hole 206b2 may be elliptical or polygonal.

[0044] The first electrode 206a is inserted into the insertion hole 206b1 of the second electrode 206b. The outer peripheral surface of the tip portion (that is, the lower end portion) of the first electrode 206a faces the inner peripheral surface of the insertion hole 206b1 of the second electrode 206b. The electrode gap 206c is an annular space formed between the tip portion of the first electrode 206a and the inner peripheral surface of the insertion hole 206b1 of the second electrode 206b. The electrode gap 206c is also called a spark gap. The potential of the second electrode 206b is, for example, held at the ground potential. The ignition device 206 can generate a spark discharge in the electrode gap 206c due to the potential difference between the first electrode 206a and the second electrode 206b by applying a voltage to the first electrode 206a.

[0045] FIG. 4 is a view of the second sub-chamber housing 204a in the ignition system 200 according to the present embodiment as viewed from below. As shown in FIG. 4, for example, four second communication holes 204b are provided at equal intervals in the circumferential direction in the second sub-chamber housing 204a. However, as described above, the number and arrangement of the second communication holes 204b are not limited to the example of FIG. 4.

[0046] As shown in FIG. 3, in the ignition system 200 according to the present embodiment, the second communication hole 204b is bent. That is, the extending direction of the second communication hole 204b changes midway. Specifically, in the example of FIG. 3, the second communication hole 204b includes a first portion 204b1 on the side of the first sub-chamber 202 and a second portion 204b2 on the side of the second sub-chamber 204. And the central axis A1 of the first portion 204b1 and the central axis A2 of the second portion 204b2 are not parallel and intersect.

[0047] The first portion 204b1 is a portion of the second communication hole 204b that includes the opening on the side of the first sub-chamber 202. The second portion 204b2 is a portion of the second communication hole 204b that includes the opening on the side of the second sub-chamber 204. The first portion 204b1 and the second portion 204b2 are continuous with each other. At the connection point between the first portion 204b1 and the second portion 204b2, the second communication hole 204b is not curved but bent at a predetermined angle.

[0048] In the example of FIG. 3, the inclination angle θ1 of the central axis A1 of the first sub-chamber 202 side (that is, the first portion 204b1) of the second communication hole 204b with respect to the central axis A0 of the second sub-chamber 204 and the inclination angle θ2 of the central axis A2 of the second sub-chamber 204 side (that is, the second portion 204b2) of the second communication hole 204b with respect to the central axis A0 of the second sub-chamber 204 are different from each other. Specifically, the inclination angle θ1 is smaller than the inclination angle θ2.

[0049] As described above, in the compression stroke, the air-fuel mixture flows from the first sub-chamber 202 into the second sub-chamber 204 through the second communication hole 204b. At this time, as indicated by the dashed arrow in FIG. 3, the flow direction of the air-fuel mixture flowing from the second communication hole 204b into the second sub-chamber 204 is along the central axis A2 on the side of the second sub-chamber 204 of the second communication hole 204b. In the example of FIG. 3, the air-fuel mixture that has flowed into the second sub-chamber 204 from the second communication hole 204b is sent to the second space 204d through the through-hole 206b2.

[0050] Subsequently, as shown by the dashed arrow in Figure 3, the mixture is sent from the second space 204d to the first space 204c through the electrode gap 206c. In other words, the mixture passes downward through the electrode gap 206c. By making the flow of the mixture through the electrode gap 206c unidirectional in this way, turbulence in the gas flow within the electrode gap 206c can be suppressed. Therefore, the growth of the flame kernel in the electrode gap 206c can be promoted without being inhibited. Thus, ignition of the mixture by the ignition device 206 within the second sub-chamber 204 is performed stably.

[0051] Subsequently, the burnt gas flows out from the second sub-chamber 204 to the first sub-chamber 202 through the second communication hole 204b. At this time, as shown by the solid arrow in Figure 3, the direction of flow of the burnt gas flowing out from the second communication hole 204b to the first sub-chamber 202 is along the central axis A1 on the side of the second communication hole 204b that is on the side of the first sub-chamber 202. Here, in order to ensure that the ignition of the mixture by the burnt gas in the first sub-chamber 202 is carried out smoothly, it is preferable that the burnt gas does not immediately collide with the wall surface of the first sub-chamber housing 202a after flowing out from the second communication hole 204b to the first sub-chamber 202. Therefore, for example, it is preferable to set the inclination angle θ1 such that the burnt gas flowing out from the second communication hole 204b travels a distance equal to the diameter of the second communication hole 204b multiplied by a predetermined factor before reaching the wall surface of the first sub-chamber housing 202a. This ensures that the ignition of the fuel-air mixture by the already burned gas in the first sub-chamber 202 proceeds smoothly.

[0052] As described above, the ignition system 200 according to this embodiment includes a first sub-chamber 202 communicating with the combustion chamber 108 via at least one first communication hole 202b, a second sub-chamber 204 in which an ignition device 206 is provided, and at least one curved second communication hole 204b connecting the first sub-chamber 202 and the second sub-chamber 204. This makes it possible to individually adjust the flow direction of the air-fuel mixture flowing into the second sub-chamber 204 from the second communication hole 204b and the flow direction of the burnt gas flowing out of the second communication hole 204b into the first sub-chamber 202. Therefore, it is possible to stabilize the ignition of the air-fuel mixture by the ignition device 206 in the second sub-chamber 204 and to facilitate the ignition of the air-fuel mixture by the burnt gas in the first sub-chamber 202, thereby further promoting combustion in the combustion chamber 108.

[0053] Furthermore, in the ignition system 200 described above, the second sub-chamber 204 is formed in a cylindrical shape, and the inclination angle θ1 of the central axis A1 on the first sub-chamber 202 side of the second communication hole 204b with respect to the central axis A0 of the second sub-chamber 204, and the inclination angle θ2 of the central axis A2 on the second sub-chamber 204 side of the second communication hole 204b with respect to the central axis A0 of the second sub-chamber 204 are different from each other. This allows for appropriate individual adjustment of the flow direction of the air-fuel mixture flowing into the second sub-chamber 204 from the second communication hole 204b and the flow direction of the burned gas flowing out of the second communication hole 204b into the first sub-chamber 202.

[0054] In the example above, the second sub-chamber 204 is cylindrical, but the second sub-chamber 204 may be a cylindrical shape other than a cylindrical shape (for example, a rectangular cylinder).

[0055] In the above, an example of the second communication hole 204b was described with reference to the ignition system 200. However, the configuration of the second communication hole 204b is not limited to the above example. Various modifications of the ignition system 200 described above will be explained below.

[0056] Figure 5 shows a schematic configuration of the second sub-chamber 204 and ignition device 206 in the ignition system 200A according to the first modified example of the present disclosure. In the ignition system 200A according to the first modified example, the inclination angle θ1 of the central axis A1 on the first sub-chamber 202 side of the second communication hole 204b with respect to the central axis A0 of the second sub-chamber 204, and the inclination angle θ2 of the central axis A2 on the second sub-chamber 204 side of the second communication hole 204b with respect to the central axis A0 of the second sub-chamber 204 are different compared to the ignition system 200 described above.

[0057] In ignition system 200A, the inclination angle θ1 is larger than that of ignition system 200 described above. In ignition system 200A, the inclination angle θ2 is approximately 90°. In other words, the central axis A2 of the second communication hole 204b on the second sub-chamber 204 side is perpendicular to the central axis A0 of the second sub-chamber 204. Therefore, in ignition system 200A, during the compression stroke, as shown by the dashed arrow in Figure 5, the flow direction of the air-fuel mixture flowing from the second communication hole 204b into the second sub-chamber 204 is perpendicular to the central axis A0 of the second sub-chamber 204. Thus, the air-fuel mixture flowing from the second communication hole 204b into the second sub-chamber 204 is sent into the first space 204c without passing through the through hole 206b2.

[0058] Subsequently, as shown by the dashed arrow in Figure 5, the air-fuel mixture is sent from the first space 204c to the second space 204d through the electrode gap 206c. In other words, the air-fuel mixture passes upward through the electrode gap 206c. Thus, in the ignition system 200A, as with the ignition system 200 described above, the flow of the air-fuel mixture through the electrode gap 206c is unidirectional, thereby suppressing turbulence in the gas flow within the electrode gap 206c. Therefore, the growth of the flame kernel in the electrode gap 206c can be promoted without being hindered. Consequently, ignition of the air-fuel mixture by the ignition device 206 in the second sub-chamber 204 is performed stably.

[0059] Subsequently, the burnt gas flows out from the second sub-chamber 204 to the first sub-chamber 202 through the second communication hole 204b. More specifically, the burnt gas is sent from the second space 204d through the through hole 206b2 to the first space 204c, and then flows out to the first sub-chamber 202 through the second communication hole 204b, as shown by the solid arrow in Figure 5.

[0060] Figure 6 shows a schematic configuration of the second sub-chamber 204 and ignition device 206 in the ignition system 200B according to a second modification of the present disclosure. In the ignition system 200B according to the second modification, the inclination angle θ1 of the central axis A1 on the first sub-chamber 202 side of the second communication hole 204b with respect to the central axis A0 of the second sub-chamber 204 is different compared to the ignition system 200 described above.

[0061] In the ignition system 200B, the inclination angle θ1 is approximately 0°. That is, the central axis A1 of the second communication hole 204b on the first sub-chamber 202 side is parallel to the central axis A0 of the second sub-chamber 204. Therefore, in the ignition system 200B, as shown by the solid arrow in Figure 6, the flow direction of the burnt gas flowing out from the second communication hole 204b into the first sub-chamber 202 is downward.

[0062] Figure 7 shows a schematic configuration of the second sub-chamber 204 and ignition device 206 in the ignition system 200C according to a third modification of the present disclosure. In the ignition system 200C according to the third modification, the shape of the connection point between the first portion 204b1 and the second portion 204b2 in the second communication hole 204b is different compared to the ignition system 200 described above.

[0063] In the ignition system 200C, the second communication hole 204b is curved at the connection point between the first part 204b1 and the second part 204b2. However, in the ignition system 200C, the inclination angle θ1 of the central axis A1 on the first sub-chamber 202 side of the second communication hole 204b with respect to the central axis A0 of the second sub-chamber 204, and the inclination angle θ2 of the central axis A2 on the second sub-chamber 204 side of the second communication hole 204b with respect to the central axis A0 of the second sub-chamber 204 are the same as in the ignition system 200 described above. Therefore, the flow of the fuel mixture and the burned gas is the same as in the ignition system 200 described above.

[0064] In the ignition systems 200A, 200B, and 200C described above, similar to the ignition system 200 described above, the inclination angle θ1 of the central axis A1 on the first sub-chamber 202 side of the second communication hole 204b with respect to the central axis A0 of the second sub-chamber 204 and the inclination angle θ2 of the central axis A2 on the second sub-chamber 204 side of the second communication hole 204b with respect to the central axis A0 of the second sub-chamber 204 are different from each other. As a result, similar to the ignition system 200 described above, it is possible to appropriately adjust individually the flow direction of the air-fuel mixture flowing from the second communication hole 204b into the second sub-chamber 204 and the flow direction of the burned gas flowing out from the second communication hole 204b into the first sub-chamber 202.

[0065] The above describes an example in which the central axis A1 of the second communication hole 204b on the first sub-chamber 202 side and the central axis A2 of the second communication hole 204b on the second sub-chamber 204 side lie on the same plane as the central axis A0 of the second sub-chamber 204 and are not eccentric with respect to the central axis A0 of the second sub-chamber 204. However, at least one of the central axes A1 and A2 may be eccentric with respect to the central axis A0 of the second sub-chamber 204. Below, an example in which at least one of the central axes A1 and A2 is eccentric with respect to the central axis A0 of the second sub-chamber 204 will be described.

[0066] Figure 8 is a cross-sectional view of the second sub-chamber housing 204a in the ignition system 200D according to the fourth modification of the present disclosure, viewed in the direction of the central axis of the second sub-chamber 204. In the ignition system 200D according to the fourth modification, both central axes A1 and A2 are eccentric with respect to the central axis A0 of the second sub-chamber 204.

[0067] In the ignition system 200D, three second communication holes 204b are provided at equal intervals in the circumferential direction. In the ignition system 200D, when viewed in the direction of the central axis of the second sub-chamber 204, in each second communication hole 204b, the central axis A1 on the first sub-chamber 202 side of the second communication hole 204b and the central axis A2 on the second sub-chamber 204 side of the second communication hole 204b lie on the same straight line. In the ignition system 200D, when viewed in the direction of the central axis of the second sub-chamber 204, in each second communication hole 204b, both the central axis A1 and the central axis A2 lie on a straight line that does not pass through the central axis A0 of the second sub-chamber 204, and are eccentric with respect to the central axis A0.

[0068] As described above, the central axis A1 of the second communication hole 204b on the first sub-chamber 202 side may be eccentric with respect to the central axis A0 of the second sub-chamber 204. In that case, the burnt gas flowing out from the second sub-chamber 204 to the first sub-chamber 202 through the second communication hole 204b flows while swirling in the circumferential direction of the first sub-chamber 202. Here, depending on the specifications of the combustion chamber 108 or the first sub-chamber 202 (for example, shape or dimensions), it may be possible to smooth the ignition of the air-fuel mixture by the burnt gas in the first sub-chamber 202 by swirling the burnt gas in the first sub-chamber 202, and further by adjusting the degree of swirling of the burnt gas. In such cases, by making the central axis A1 eccentric with respect to the central axis A0 of the second sub-chamber 204, the ignition of the air-fuel mixture by the burnt gas in the first sub-chamber 202 can be made even smoother.

[0069] Furthermore, as described above, the central axis A2 of the second communication hole 204b on the second sub-chamber 204 side may be eccentric with respect to the central axis A0 of the second sub-chamber 204. In that case, the air-fuel mixture flowing from the first sub-chamber 202 to the second sub-chamber 204 through the second communication hole 204b flows while swirling in the circumferential direction of the second sub-chamber 204. Here, depending on the specifications of the second sub-chamber 204 or the ignition device 206, etc. (for example, shape or dimensions), it may be possible to stabilize the ignition of the air-fuel mixture by the ignition device 206 in the second sub-chamber 204 by swirling the air-fuel mixture in the second sub-chamber 204, and further by adjusting the degree of swirling. In such cases, by making the central axis A2 eccentric with respect to the central axis A0 of the second sub-chamber 204, the ignition of the air-fuel mixture by the ignition device 206 in the second sub-chamber 204 can be further stabilized.

[0070] In the ignition system 200D, for example, similar to the ignition system 200 described above, the inclination angle θ1 of the second sub-chamber 204 with respect to the central axis A0 of the central axis A1 and the inclination angle θ2 of the second sub-chamber 204 with respect to the central axis A0 of the central axis A2 are different from each other. As a result, similar to the ignition system 200 described above, it is possible to appropriately adjust individually the flow direction of the air-fuel mixture flowing from the second communication hole 204b into the second sub-chamber 204 and the flow direction of the burned gas flowing out from the second communication hole 204b into the first sub-chamber 202.

[0071] Figure 9 is a cross-sectional view of the second sub-chamber housing 204a in the ignition system 200E according to the fifth modification of the present disclosure, viewed in the direction of the central axis of the second sub-chamber 204. In the ignition system 200E according to the fifth modification, of the central axes A1 and A2, only central axis A1 is eccentric with respect to the central axis A0 of the second sub-chamber 204.

[0072] In the ignition system 200E, similar to the ignition system 200D described above, three second communication holes 204b are provided at equal intervals in the circumferential direction. In the ignition system 200E, when viewed in the direction of the central axis of the second sub-chamber 204, the central axis A2 of each second communication hole 204b on the side of the second sub-chamber 204 lies on a straight line passing through the central axis A0 of the second sub-chamber 204 and is not eccentric with respect to the central axis A0. On the other hand, when viewed in the direction of the central axis of the second sub-chamber 204, the central axis A1 of each second communication hole 204b on the side of the first sub-chamber 202 lies on a straight line that does not pass through the central axis A0 of the second sub-chamber 204 and is eccentric with respect to the central axis A0. Thus, when viewed in the direction of the central axis of the second sub-chamber 204, the central axis A1 and the central axis A2 intersect each other in each second communication hole 204b.

[0073] As described above, in the ignition system 200E, similar to the ignition system 200D described above, the central axis A1 of the second communication hole 204b on the first sub-chamber 202 side is eccentric with respect to the central axis A0 of the second sub-chamber 204. This can sometimes make the ignition of the fuel-air mixture by the already burned gas in the first sub-chamber 202 smoother.

[0074] Furthermore, as described above, in the ignition system 200E, when viewed in the direction of the central axis of the second sub-chamber 204, the central axis A1 of the second communication hole 204b on the first sub-chamber 202 side and the central axis A2 of the second communication hole 204b on the second sub-chamber 204 side intersect with each other. This allows for appropriate individual adjustment of the flow direction of the fuel mixture flowing into the second sub-chamber 204 from the second communication hole 204b and the flow direction of the burned gas flowing out of the second communication hole 204b into the first sub-chamber 202.

[0075] In the ignition system 200E, the inclination angle θ1 of the second sub-chamber 204 of the central axis A1 with respect to the central axis A0 and the inclination angle θ2 of the second sub-chamber 204 of the central axis A2 with respect to the central axis A0 may be different from each other, or they may not be different from each other.

[0076] Figure 10 is a cross-sectional view of the second sub-chamber housing 204a in the ignition system 200F according to the sixth modification of the present disclosure, viewed in the direction of the central axis of the second sub-chamber 204. In the ignition system 200F according to the sixth modification, of the central axes A1 and A2, only central axis A2 is eccentric with respect to the central axis A0 of the second sub-chamber 204.

[0077] In the ignition system 200F, similar to the ignition system 200D described above, three second communication holes 204b are provided at equal intervals in the circumferential direction. In the ignition system 200F, when viewed in the direction of the central axis of the second sub-chamber 204, the central axis A1 of each second communication hole 204b on the side of the first sub-chamber 202 lies on a straight line passing through the central axis A0 of the second sub-chamber 204 and is not eccentric with respect to the central axis A0. On the other hand, when viewed in the direction of the central axis of the second sub-chamber 204, the central axis A2 of each second communication hole 204b on the side of the second sub-chamber 204 lies on a straight line that does not pass through the central axis A0 of the second sub-chamber 204 and is eccentric with respect to the central axis A0. Thus, when viewed in the direction of the central axis of the second sub-chamber 204, the central axis A1 and the central axis A2 intersect each other in each second communication hole 204b.

[0078] As described above, in the ignition system 200F, similar to the ignition system 200D described above, the central axis A2 of the second communication hole 204b on the second sub-chamber 204 side is eccentric with respect to the central axis A0 of the second sub-chamber 204. This can sometimes stabilize the ignition of the fuel-air mixture by the ignition device 206 within the second sub-chamber 204.

[0079] Furthermore, as described above, in the ignition system 200F, similar to the ignition system 200E described above, when viewed in the direction of the central axis of the second sub-chamber 204, the central axis A1 of the second communication hole 204b on the first sub-chamber 202 side and the central axis A2 of the second communication hole 204b on the second sub-chamber 204 side intersect with each other. This allows for appropriate individual adjustment of the flow direction of the air-fuel mixture flowing from the second communication hole 204b into the second sub-chamber 204 and the flow direction of the burned gas flowing out from the second communication hole 204b into the first sub-chamber 202.

[0080] In addition, in the ignition system 200F, similar to the ignition system 200E described above, the inclination angle θ1 of the second sub-chamber 204 of the central axis A1 with respect to the central axis A0 and the inclination angle θ2 of the second sub-chamber 204 of the central axis A2 with respect to the central axis A0 may be different from each other or they may not be different from each other.

[0081] Figure 11 is a cross-sectional view of the second sub-chamber housing 204a in the ignition system 200G according to the seventh modification of the present disclosure, viewed in the direction of the central axis of the second sub-chamber 204. In the ignition system 200G according to the seventh modification, both central axes A1 and A2 are eccentric with respect to the central axis A0 of the second sub-chamber 204.

[0082] In the ignition system 200G, similar to the ignition system 200D described above, three second communication holes 204b are provided at equal intervals in the circumferential direction. In the ignition system 200G, when viewed in the direction of the central axis of the second sub-chamber 204, both the central axis A1 and the central axis A2 are located on a straight line that does not pass through the central axis A0 of the second sub-chamber 204 in each second communication hole 204b, and are eccentric with respect to the central axis A0. In the ignition system 200G, when viewed in the direction of the central axis of the second sub-chamber 204, the central axis A1 and the central axis A2 intersect each other in each second communication hole 204b.

[0083] As described above, in the ignition system 200G, similar to the ignition system 200D described above, the central axis A1 of the second communication hole 204b on the first sub-chamber 202 side is eccentric with respect to the central axis A0 of the second sub-chamber 204. This can sometimes make the ignition of the fuel-air mixture by the already burned gas in the first sub-chamber 202 smoother.

[0084] Furthermore, as described above, in the ignition system 200G, similar to the ignition system 200D described above, the central axis A2 of the second communication hole 204b on the second sub-chamber 204 side is eccentric with respect to the central axis A0 of the second sub-chamber 204. This can sometimes stabilize the ignition of the fuel-air mixture by the ignition device 206 within the second sub-chamber 204.

[0085] Furthermore, as described above, in the ignition system 200G, similar to the ignition system 200E described above, when viewed in the direction of the central axis of the second sub-chamber 204, the central axis A1 of the second communication hole 204b on the first sub-chamber 202 side and the central axis A2 of the second communication hole 204b on the second sub-chamber 204 side intersect with each other. This allows for appropriate individual adjustment of the flow direction of the air-fuel mixture flowing from the second communication hole 204b into the second sub-chamber 204 and the flow direction of the burned gas flowing out from the second communication hole 204b into the first sub-chamber 202.

[0086] In addition, in the ignition system 200G, similar to the ignition system 200E described above, the inclination angle θ1 of the second sub-chamber 204 of the central axis A1 with respect to the central axis A0 and the inclination angle θ2 of the second sub-chamber 204 of the central axis A2 with respect to the central axis A0 may be different from each other or they may not be different from each other.

[0087] While embodiments of this disclosure have been described above with reference to the attached drawings, it goes without saying that this disclosure is not limited to such embodiments. It will be obvious to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of this disclosure.

[0088] The shapes of the first sub-chamber housing 202a and the second sub-chamber housing 204a are not limited to the example in Figure 2. For example, the upper housing 202a1 may be omitted from the example in Figure 2, and the first sub-chamber housing 202a may have a cylindrical shape as a whole.

[0089] The positional relationships of each component are not limited to the example in Figure 2. For example, the first sub-chamber housing 202a, the second sub-chamber housing 204a, and the ignition device 206 do not have to be arranged coaxially with the central axis of the piston 106. For example, the first sub-chamber housing 202a and the second sub-chamber housing 204a do not have to be arranged coaxially with each other.

[0090] This disclosure contributes to promoting combustion in the combustion chamber and can therefore contribute, for example, to Sustainable Development Goal (SDG) 7, "Ensure access to affordable, reliable, sustainable and modern energy," and Goal 13, "Take urgent action to combat climate change and its impacts."

[0091] 108: Combustion chamber 200: Ignition system 200A: Ignition system 200B: Ignition system 200C: Ignition system 200D: Ignition system 200E: Ignition system 200F: Ignition system 200G: Ignition system 202: First sub-chamber 202b: First connecting hole 204: Second sub-chamber 204b: Second connecting hole 204b1: First part (side of the second connecting hole facing the first sub-chamber) 204b2: Second part (side of the second connecting hole facing the second sub-chamber) 206: Ignition device A0: Central axis A1: Central axis A2: Central axis θ1: Inclination angle θ2: Inclination angle

Claims

1. An ignition system comprising: a first sub-chamber communicating with a combustion chamber via at least one first communication hole; a second sub-chamber in which an ignition device is provided; and at least one curved second communication hole connecting the first sub-chamber and the second sub-chamber.

2. The ignition system according to claim 1, wherein the second sub-chamber is formed in a cylindrical shape, and the angle of inclination of the central axis of the second communication hole on the side of the first sub-chamber with respect to the central axis of the second sub-chamber and the angle of inclination of the central axis of the second communication hole on the side of the second sub-chamber with respect to the central axis of the second sub-chamber are different from each other.

3. The ignition system according to claim 1, wherein the second sub-chamber is formed in a cylindrical shape, and when viewed in the direction of the central axis of the second sub-chamber, the central axis of the second communication hole on the first sub-chamber side and the central axis of the second communication hole on the second sub-chamber side intersect with each other.

4. The ignition system according to any one of claims 1 to 3, wherein the second sub-chamber is formed in a cylindrical shape, and the central axis of the second communication hole on the side of the first sub-chamber is eccentric with respect to the central axis of the second sub-chamber.

5. The ignition system according to any one of claims 1 to 3, wherein the second sub-chamber is formed in a cylindrical shape, and the central axis of the second communication hole on the side of the second sub-chamber is eccentric with respect to the central axis of the second sub-chamber.

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