engine

Abstract

To suppress discharge of unburnt fuel.SOLUTION: An engine 100 includes: a piston 106; a cylinder liner 102 for accommodating the piston 106; and a gas jetting hole (air jetting hole 116) installed in an inside wall of the cylinder liner 102, facing a direction intersecting a radial direction of the cylinder liner 102 when being viewed in an axial direction of the cylinder liner 102 and jetting an incombustible gas (air) at least during compression stroke.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to engines. [Background technology]

[0002] There is an engine having a combustion chamber, an intake valve, and an exhaust valve. In such an engine, as disclosed in Patent Document 1, for example, an intake port communicating with the combustion chamber is opened and closed by the intake valve. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 049878 Summary of the Invention [Problem to be solved by the invention]

[0004] During the intake stroke, the intake valve opens, creating a gas flow from the intake port toward the combustion chamber. In the combustion chamber, part of the air-fuel mixture flows along the inner wall of the cylinder liner. The mixture flowing along the inner wall of the cylinder liner enters the space between the top land of the piston and the inner wall of the cylinder liner, or the space near the connection between the cylinder liner and the cylinder head. Since fuel that enters these spaces is difficult to burn during the combustion stroke, it may be discharged as unburned fuel. From the perspective of improving thermal efficiency and reducing greenhouse gas emissions, it is desirable to reduce the discharge of unburned fuel.

[0005] An object of the present disclosure is to provide an engine that can suppress the emission of unburned fuel. [Means for solving the problem]

[0006] In order to solve the above problems, the engine of the present disclosure includes a piston, a cylinder liner that houses the piston, and a gas injection hole that is provided on an inner wall of the cylinder liner, faces in a direction that intersects with a radial direction of the cylinder liner when viewed in the axial direction of the cylinder liner, and injects a non-flammable gas at least during a compression stroke. The inner wall of the cylinder liner is provided with a first gas injection hole and a second gas injection hole disposed closer to the bottom dead center than the first gas injection hole, and the first gas injection hole faces in a direction inclined toward the top dead center with respect to the circumferential direction of the cylinder liner when viewed in the radial direction, and the second gas injection hole faces in a direction inclined toward the bottom dead center with respect to the circumferential direction when viewed in the radial direction. . In addition, in order to solve the above problems, the engine of the present disclosure comprises a piston, a cylinder liner that accommodates the piston, a gas injection hole provided on the inner wall of the cylinder liner that faces in a direction that intersects the radial direction of the cylinder liner when viewed in the axial direction of the cylinder liner and that injects non-flammable gas at least during the compression stroke, a combustion chamber formed by the piston and the cylinder liner, an intake flow path that communicates with the combustion chamber, and a connecting flow path that connects the intake flow path and the gas injection hole, and air flowing through the intake flow path is supplied to the gas injection hole via the connecting flow path.

[0007] The gas injection device may include a flow path connected to the gas injection hole and an on-off valve provided in the flow path, and the on-off valve may be opened to inject non-flammable gas from the gas injection hole.

[0008] The engine may include a control device that controls the operation of the on-off valve, and the control device may inject non-flammable gas from the gas injection hole by opening the on-off valve at least during the compression stroke. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to suppress the emission of unburned fuel. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of an intake and exhaust system according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of each cylinder of the engine according to the embodiment of the present disclosure. [Figure 3] FIG. 3 is a diagram showing a combustion chamber of an engine according to an embodiment of the present disclosure as viewed in the axial direction of a cylinder liner. [Figure 4] FIG. 4 is a diagram illustrating the inner wall of the cylinder liner of the engine according to the embodiment of the present disclosure as viewed in the radial direction of the cylinder liner. [Figure 5] FIG. 5 is a diagram showing the duration of the compression stroke of each cylinder of the engine according to the embodiment of the present disclosure. [Figure 6] FIG. 6 is a view showing the inner wall of a cylinder liner of an engine according to a modified example, viewed in the radial direction of the cylinder liner. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. Dimensions, materials, and other specific numerical values ​​shown in the embodiments are merely examples for ease of understanding and, unless otherwise specified, do not limit the present disclosure. In this specification and drawings, elements having substantially the same functions and configurations are designated by the same reference numerals to avoid redundant explanation, and elements not directly related to the present disclosure are not shown.

[0014] Fig. 1 is a schematic diagram showing the configuration of an intake and exhaust system 1 according to this embodiment. The intake and exhaust system 1 is a system related to the intake and exhaust of an engine 100. As shown in Fig. 1, the intake and exhaust system 1 includes the engine 100, an intake flow path 200, an exhaust flow path 300, a turbocharger 400, a connecting flow path 500, and a control device 600. The control device 600 is included in the engine 100.

[0015] Engine 100 has multiple cylinders. In the example of FIG. 1, engine 100 has a first cylinder #1, a second cylinder #2, a third cylinder #3, a fourth cylinder #4, a fifth cylinder #5, and a sixth cylinder #6. However, the number of cylinders in engine 100 may be other than six. FIG. 2 is a schematic diagram showing the configuration of each cylinder of engine 100 according to this embodiment. In FIG. 2, intake port 104a, exhaust port 104b, fuel injection valve 112, and ignition device 114 are illustrated on the same cross section. However, intake port 104a, exhaust port 104b, fuel injection valve 112, and ignition device 114 do not have to be located on the same cross section.

[0016] 2, the engine 100 includes a cylinder liner 102, a cylinder head 104, and a piston 106. The piston 106 is housed in the cylinder liner 102. The cylinder liner 102, the cylinder head 104, and the piston 106 form a combustion chamber 108. Hereinafter, the axial direction, radial direction, and circumferential direction of the cylinder liner 102 will also be simply referred to as the axial direction, radial direction, and circumferential direction.

[0017] The piston 106 has a piston body 106a and piston rings 106b, 106c, and 106d. The piston body 106a has a generally cylindrical shape. The piston body 106a is arranged coaxially with the cylinder liner 102. The piston rings 106b, 106c, and 106d are fitted into grooves formed on the outer peripheral surface of the piston body 106a. The piston rings 106b, 106c, and 106d are arranged side by side in the axial direction in this order from the top dead center side. The portion of the outer peripheral surface of the piston body 106a that is closer to the top dead center than the piston ring 106b is called a top land portion TL.

[0018] 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 to the combustion chamber 108. The intake valve 110a opens and closes the opening of the intake port 104a on the combustion chamber 108 side. The exhaust valve 110b opens and closes the opening of the exhaust port 104b on the combustion chamber 108 side. The opening and closing operations of the intake valve 110a and the exhaust valve 110b are performed in accordance with the rotation of a camshaft (not shown).

[0019] A pipe that forms a branch passage 202 of an intake passage 200 (described later) is connected to the intake port 104a. An air-fuel mixture flows into the combustion chamber 108 via the intake port 104a. A pipe that forms a branch passage 302 of an exhaust passage 300 (described later) is connected to the exhaust port 104b. Exhaust gas is discharged from the combustion chamber 108 via the exhaust port 104b.

[0020] The fuel injection valve 112 is connected to a fuel supply source. The fuel supply source is, for example, a fuel tank (not shown) or a pipeline for city gas or the like. The fuel injection valve 112 is provided in a branch flow path 202 of the intake flow path 200. The tip of the fuel injection valve 112 faces the intake port 104a. The fuel injection valve 112 injects fuel gas into the intake port 104a. The fuel gas is generated, for example, by gasifying LNG (liquefied natural gas). The fuel gas is not limited to LNG, and may be, for example, gasified LPG (liquefied petroleum gas), light oil, heavy oil, ammonia, hydrogen, or the like. The engine 100 is a gas engine that uses fuel gas as fuel. Hereinafter, fuel gas may also be simply referred to as fuel.

[0021] The ignition device 114 is provided in the cylinder head 104. The tip of the ignition device 114 protrudes into the combustion chamber .

[0022] The engine 100 is a four-stroke engine. During the intake stroke, fuel is injected from the fuel injector 112, the intake valve 110a opens, and the exhaust valve 110b closes. As the piston 106 moves toward bottom dead center, intake air and fuel are drawn into the combustion chamber 108 through the intake port 104a. During the compression stroke, the intake valve 110a and the exhaust valve 110b close. As the piston 106 moves toward top dead center, the air-fuel mixture in the combustion chamber 108 is compressed. The air-fuel mixture is ignited and combusted by the ignition device 114, and during the combustion stroke, the piston 106 is pressed toward the bottom dead center. During the exhaust stroke, the intake valve 110a closes and the exhaust valve 110b opens. As the piston 106 moves toward top dead center, the burned exhaust gas is discharged from the combustion chamber 108 through the exhaust port 104b.

[0023] Air injection holes 116 are provided on the inner wall of the cylinder liner 102. As will be described later, the air injection holes 116 are an example of gas injection holes. Air is injected from the air injection holes 116 into the combustion chamber 108. As will be described later, the air injected from the air injection holes 116 is an example of non-flammable gas injected from a gas injection hole. When the piston 106 is located at the bottom dead center position, the air injection holes 116 are located closer to the top dead center than the piston ring 106b. Note that when the piston 106 is located at the top dead center position, the air injection holes 116 may be located closer to the top dead center than the piston ring 106b, or may be located closer to the bottom dead center than the piston ring 106b. A pipe that forms a branch flow path 502 of a connection flow path 500, which will be described later, is connected to the air injection holes 116. Details of the air injection holes 116 will be described later. Returning to FIG. 1 , the description will continue below.

[0024] The intake flow path 200 communicates with the combustion chambers 108 of the engine 100. Intake air, which is air supplied to the combustion chambers 108, flows through the intake flow path 200. An intake port (not shown) is provided at the upstream end of the intake flow path 200, through which air is taken in from the outside. The intake flow path 200 has a plurality of branch flow paths 202 that communicate with the plurality of combustion chambers 108, respectively. The plurality of branch flow paths 202 are provided downstream of the intake flow path 200. As described above, the piping that forms the branch flow paths 202 is connected to the intake port 104a of the engine 100. The intake port 104a corresponds to the downstream end of the branch flow paths 202. The intake port 104a is included in the intake flow path 200.

[0025] The exhaust flow path 300 communicates with the combustion chambers 108 of the engine 100. Exhaust gas discharged from the combustion chambers 108 flows through the exhaust flow path 300. An exhaust port (not shown) is provided at the downstream end of the exhaust flow path 300, through which the exhaust gas is discharged to the outside. The exhaust flow path 300 has a plurality of branch flow paths 302 that communicate with the plurality of combustion chambers 108, respectively. The plurality of branch flow paths 302 are provided on the upstream side of the exhaust flow path 300. As described above, the pipe that forms the branch flow path 302 is connected to the exhaust port 104b of the engine 100. The exhaust port 104b corresponds to the upstream end of the branch flow path 302. The exhaust port 104b is included in the exhaust flow path 300.

[0026] The supercharger 400 has a compressor 402 and a turbine 404. The impeller of the compressor 402 and the impeller of the turbine 404 rotate as a unit. The impeller of the compressor 402 and the impeller of the turbine 404 are connected by a shaft.

[0027] The compressor 402 is provided in the intake air flow path 200, upstream of the branch flow path 202. The compressor 402 compresses the intake air taken in through the intake port and sends it downstream. An intercooler C1 is provided in the intake air flow path 200, upstream of the branch flow path 202 and downstream of the compressor 402. The intake air flowing through the intercooler C1 is cooled by heat exchange with air outside the intercooler C1. The intake air that has passed through the intercooler C1 is sent to each combustion chamber 108 via each branch flow path 202. Note that the intercooler C1 may also be one that uses cooling water, such as engine cooling water or industrial water, to cool the intake air.

[0028] The turbine 404 is provided in the exhaust flow path 300 downstream of the branch flow paths 302. The exhaust gas discharged from the engine 100 is sent to the turbine 404 via each branch flow path 302. The exhaust gas sent to the turbine 404 passes through the turbine 404 and is discharged from an exhaust port. The turbine 404 generates rotational power when an impeller of the turbine 404 is rotated by the exhaust gas. The rotational power generated by the turbine 404 is transmitted to the compressor 402 via a shaft.

[0029] The connection flow path 500 connects the intake flow path 200 and the air injection holes 116 of each cylinder. The connection flow path 500 is provided to supply air flowing through the intake flow path 200 to the air injection holes 116 of each cylinder. In the connection flow path 500, air flows from the intake flow path 200 toward each cylinder. In the following, the upstream side of the connection flow path 500 refers to the intake flow path 200 side, and the downstream side of the connection flow path 500 refers to the cylinder side.

[0030] In the example of FIG. 1, the upstream end of the connection passage 500 is connected to a portion of the intake passage 200 that is upstream of the branch passage 202 and downstream of the intercooler C1. A plurality of branch passages 502 are provided downstream of the connection passage 500. Each branch passage 502 is connected to the air injection holes 116 of each cylinder. In the example of FIG. 1, the branch passages 502 include branch passages 502a, 502b, 502c, 502d, 502e, and 502f. The branch passages 502a, 502b, 502c, 502d, 502e, and 502f are connected to the air injection holes 116 of the first cylinder #1, the second cylinder #2, the third cylinder #3, the fourth cylinder #4, the fifth cylinder #5, and the sixth cylinder #6, respectively.

[0031] An on-off valve 504 is provided in each branch flow path 502. The on-off valve 504 is capable of opening and closing the branch flow path 502. In the example of Fig. 1, on-off valves 504a, 504b, 504c, 504d, 504e, and 504f are provided as the on-off valves 504. The on-off valves 504a, 504b, 504c, 504d, 504e, and 504f are provided in the branch flow paths 502a, 502b, 502c, 502d, 502e, and 502f, respectively.

[0032] The control device 600 includes a central processing unit (CPU), a ROM storing programs and the like, a RAM as a work area, and the like. The control device 600 controls the operation of each device in the intake and exhaust system 1. For example, the control device 600 controls the operation of the engine 100. For example, the control device 600 controls the operation of each on-off valve 504.

[0033] During the intake stroke of each cylinder of the engine 100, the intake valve 110a opens and an air-fuel mixture is supplied from the intake port 104a to the combustion chamber 108. In the engine 100, air is injected into the combustion chamber 108 from the air injection holes 116, forming an air layer in the area AL indicated by the dashed line along the inner wall of the cylinder liner 102, as shown in FIG. 2. This prevents fuel from entering spaces where combustion is difficult, and prevents unburned fuel from being discharged. The injection of air from the air injection holes 116 will be described in detail below.

[0034] FIG. 3 is a diagram showing the combustion chamber 108 of the engine 100 as viewed in the axial direction of the cylinder liner 102. FIG. 3 shows a cross section perpendicular to the central axis CA of the cylinder liner 102 and passing through the air injection holes 116. As shown in FIG. 3, the injection direction DA of the air injected from the air injection holes 116 intersects with the direction DR from the air injection holes 116 toward the central axis CA of the cylinder liner 102. Thus, the air injection holes 116 face in a direction intersecting with the radial direction of the cylinder liner 102 when viewed in the axial direction of the cylinder liner 102. This causes the air injected from the air injection holes 116 to flow circumferentially along the inner wall of the cylinder liner 102. Therefore, an air layer is appropriately formed in the region AL shown in FIG. 2. From the viewpoint of allowing the air injected from the air injection holes 116 to flow along the inner wall of the cylinder liner 102, it is preferable that the injection direction DA of the air injection holes 116 be close to the tangential direction of the cylinder liner 102 when viewed in the axial direction.

[0035] FIG. 4 is a diagram showing the inner wall of the cylinder liner 102 of the engine 100 as viewed radially of the cylinder liner 102. The upper side in FIG. 4 is the top dead center side, and the lower side in FIG. 4 is the bottom dead center side. As shown in FIG. 4, the injection direction DA of the air injected from the air injection hole 116 intersects with the circumferential direction DC of the cylinder liner 102. Thus, the air injection hole 116 faces in a direction intersecting with the circumferential direction DC of the cylinder liner 102 when viewed radially of the cylinder liner 102. This makes it easier for the air injected from the air injection hole 116 to move axially while flowing circumferentially along the inner wall of the cylinder liner 102. For example, the air injected from the air injection hole 116 flows spirally along the inner wall of the cylinder liner 102. This more appropriately achieves the formation of an air layer in the region AL shown in FIG. 2.

[0036] 4, the air injection holes 116, when viewed in the radial direction of the cylinder liner 102, face in a direction inclined toward the top dead center with respect to the circumferential direction DC of the cylinder liner 102. However, the air injection holes 116 may face in a direction inclined toward the bottom dead center with respect to the circumferential direction DC of the cylinder liner 102 when viewed in the radial direction of the cylinder liner 102.

[0037] FIG. 5 shows the duration of the compression stroke for each cylinder of engine 100. In FIG. 5, the duration of the compression stroke for each cylinder is indicated by the crank angle, with the crank angle at the start of the compression stroke for first cylinder #1 being 0 degrees. The periods indicated by arrows in FIG. 5 are the durations of the compression strokes. In engine 100, combustion occurs in the following order: first cylinder #1, third cylinder #3, fifth cylinder #5, sixth cylinder #6, fourth cylinder #4, and second cylinder #2. Therefore, the compression strokes are performed in the following order: first cylinder #1, third cylinder #3, fifth cylinder #5, sixth cylinder #6, fourth cylinder #4, and second cylinder #2.

[0038] As shown in FIG. 5, the compression stroke of each cylinder takes place over a period of approximately 180° in crank angle. For example, the compression stroke of the first cylinder #1 is from approximately 0° to 180° in crank angle. The compression stroke of the third cylinder #3 is from approximately 120° to 300° in crank angle. The compression stroke of the fifth cylinder #5 is from approximately 240° to 420° in crank angle. The compression stroke of the sixth cylinder #6 is from approximately 360° to 540° in crank angle. The compression stroke of the fourth cylinder #4 is from approximately 480° to 660° in crank angle. The compression stroke of the second cylinder #2 is from approximately 600° to 60° in crank angle. In this way, the start timing of the compression stroke for each cylinder is shifted by 120° in crank angle.

[0039] Here, the control device 600 opens the on-off valve 504 provided in the branch passage 502 connected to the cylinder during the compression stroke, thereby allowing the control device 600 to inject air from the air injection hole 116 in each cylinder during the compression stroke.

[0040] Note that the control device 600 only needs to inject air from the air injection holes 116 in each cylinder at least during the compression stroke. The control device 600 may also inject air from the air injection holes 116 from the start to the end of the compression stroke. The control device 600 may also inject air from the air injection holes 116 during a portion of the compression stroke. For example, the control device 600 may inject air from the air injection holes 116 only during the compression stroke when the air injection holes 116 are positioned closer to the top dead center than the piston ring 106b. The control device 600 may also start injecting air from the air injection holes 116 slightly before the end of the intake stroke. In this case, air is injected from the air injection holes 116 from just before the end of the intake stroke through the compression stroke.

[0041] As shown in Fig. 5, control device 600 opens on-off valve 504a provided in branch passage 502a during the compression stroke of first cylinder #1. As a result, air is injected from air injection hole 116 of first cylinder #1 during the compression stroke of first cylinder #1. Similarly, as shown in Fig. 5, control device 600 opens on-off valves 504b, 504c, 504d, 504e, and 504f during the compression stroke of second cylinder #2, third cylinder #3, fourth cylinder #4, fifth cylinder #5, and sixth cylinder #6, respectively. As a result, air is injected from the air injection holes 116 of the second cylinder #2, third cylinder #3, fourth cylinder #4, fifth cylinder #5, and sixth cylinder #6 during the compression stroke of the second cylinder #2, third cylinder #3, fourth cylinder #4, fifth cylinder #5, and sixth cylinder #6, respectively.

[0042] As described above, in the engine 100, the air injection holes 116 are provided on the inner wall of the cylinder liner 102. When viewed in the axial direction of the cylinder liner 102, the air injection holes 116 face in a direction intersecting the radial direction of the cylinder liner 102. The air injection holes 116 inject air at least during the compression stroke. As a result, as shown in FIG. 2 , the air injected from the air injection holes 116 forms an air layer in an area AL along the inner wall of the cylinder liner 102 during the compression stroke. The area AL where the air layer is formed includes the space between the top land portion TL of the piston 106 and the inner wall of the cylinder liner 102, and the space near the connection between the cylinder liner 102 and the cylinder head 104. This prevents fuel from entering these spaces where combustion is difficult. This also reduces the emission of unburned fuel. This improves thermal efficiency and reduces greenhouse gas emissions.

[0043] In particular, in the engine 100, air is injected from the air injection holes 116 by opening an on-off valve 504 provided in the branch flow path 502. As a result, the injection timing of air from the air injection holes 116 is optimized by the on-off valve 504. Therefore, the emission of unburned fuel is more appropriately suppressed. The branch flow path 502 corresponds to an example of a flow path connected to the air injection holes 116.

[0044] In particular, in the engine 100, the control device 600 injects air from the air injection holes 116 by opening the on-off valve 504 at least during the compression stroke. This makes it possible to more appropriately control the injection timing of air from the air injection holes 116. Therefore, the emission of unburned fuel is more appropriately suppressed.

[0045] In the above, an example has been described in which the air injection holes 116 are provided as gas injection holes in the engine 100. However, the gas injection holes provided in the engine 100 are not limited to the air injection holes 116 as long as they are holes that inject non-combustible gas into the combustion chamber 108. For example, the engine 100 may be provided with gas injection holes that inject exhaust gas into the combustion chamber 108. In this case as well, the same effects as those described above are achieved.

[0046] In the above, an example has been described in which air flowing through the intake flow path 200 is supplied to the air injection holes 116. However, the air supplied to the air injection holes 116 may be air other than the air flowing through the intake flow path 200. In this case, the upstream end of the connection flow path 500 is connected to a separately provided air supply source such as a compressor (not shown).

[0047] The above description has been given of the connection flow path 500 as a mechanism for supplying air to the air injection holes 116. However, components may be added or removed from the connection flow path 500 as appropriate. For example, in order to appropriately supply air to the air injection holes 116, a device such as a pump that pressurizes air may be added to the connection flow path 500. Furthermore, for example, if the intake valve 110a closes before the piston 106 reaches bottom dead center during the intake stroke, the on-off valve 504 may be omitted from the connection flow path 500. In this case, air may be supplied to the air injection holes 116 via the connection flow path 500 at a timing when the in-cylinder pressure decreases after the intake valve 110a closes. This allows air to be injected from the air injection holes 116 at least during the compression stroke, without the need for the control device 600. In this case, the same effects as those described above can be achieved.

[0048] In the above, with reference to Figure 2, it has been described that the air injection holes 116 are provided in the inner wall of the cylinder liner 102. However, the axial position of the air injection holes 116 in the cylinder liner 102 is not limited to the example shown in Figure 2. The closer the axial position of the air injection holes 116 is to the bottom dead center, the smaller the effect of combustion pressure on the air injection holes 116. On the other hand, the closer the axial position of the air injection holes 116 is to the top dead center, the longer the period during the compression stroke during which the air injection holes 116 are located closer to top dead center than the piston ring 106b, thereby lengthening the period during which air is injected from the air injection holes 116 into the combustion chamber 108. The axial position of the air injection holes 116 can be set as appropriate, taking these points into consideration.

[0049] In the above, an example has been described in which the fuel injection valve 112 is provided in the branch passage 202 of the intake passage 200 and injects fuel gas into the intake port 104a. However, the fuel injection valve 112 may also be provided in the cylinder head 104 so as to face the combustion chamber 108 and inject fuel gas directly into the combustion chamber 108. Even in this case, an air layer is formed in the area AL by the air injected from the air injection hole 116, thereby suppressing the emission of unburned fuel.

[0050] FIG. 6 is a view showing the inner wall of the cylinder liner 102 of an engine 100A according to a modified example, viewed in the radial direction of the cylinder liner 102. The upper side in FIG. 6 is the top dead center side, and the lower side in FIG. 6 is the bottom dead center side. As shown in FIG. 6, in the engine 100A according to the modified example, a first air injection hole 116a and a second air injection hole 116b are provided as air injection holes 116 on the inner wall of the cylinder liner 102. The first air injection hole 116a corresponds to an example of a first gas injection hole. The second air injection hole 116b corresponds to an example of a second gas injection hole. The second air injection hole 116b is positioned closer to the bottom dead center than the first air injection hole 116a. In the example of FIG. 6, the circumferential positions of the first air injection hole 116a and the second air injection hole 116b are approximately the same. However, the circumferential positions of the first air injection holes 116a and the second air injection holes 116b may be different.

[0051] The injection direction DAa of the air injected from the first air injection holes 116a is inclined toward the top dead center with respect to the circumferential direction DC of the cylinder liner 102. In this way, the first air injection holes 116a face in a direction inclined toward the top dead center with respect to the circumferential direction DC of the cylinder liner 102 when viewed in the radial direction of the cylinder liner 102. Therefore, the air injected from the first air injection holes 116a moves toward the top dead center while flowing circumferentially along the inner wall of the cylinder liner 102.

[0052] On the other hand, the injection direction DAb of the air injected from the second air injection holes 116b is inclined toward the bottom dead center with respect to the circumferential direction DC of the cylinder liner 102. In this way, the second air injection holes 116b face in a direction inclined toward the bottom dead center with respect to the circumferential direction DC of the cylinder liner 102 when viewed in the radial direction of the cylinder liner 102. Therefore, the air injected from the second air injection holes 116b moves toward the bottom dead center while flowing circumferentially along the inner wall of the cylinder liner 102.

[0053] As described above, the engine 100A is provided with the first air injection holes 116a and the second air injection holes 116b as the air injection holes 116. As a result, the air injected from the first air injection hole 116a provided on the top dead center side moves toward the top dead center side, and the air injected from the second air injection hole 116b provided on the bottom dead center side moves toward the bottom dead center side. Therefore, an air layer can be appropriately formed over a wide axial range near the inner wall of the cylinder liner 102.

[0054] In the above, an example has been described in which two air injection holes 116 are provided in the inner wall of the cylinder liner 102. However, the number of air injection holes 116 provided in the inner wall of the cylinder liner 102 may be three or more. For example, in the engine 100A described above, another air injection hole 116 may be added at an axial position between the axial positions of the first air injection hole 116a and the second air injection hole 116b.

[0055] Although the embodiments of the present disclosure have been described above with reference to the accompanying drawings, it goes without saying that the present disclosure is not limited to such embodiments. It is clear that a person skilled in the art can conceive of various modifications and alterations within the scope of the claims, and it is understood that such modifications and alterations also fall within the technical scope of the present disclosure. [Explanation of symbols]

[0056] 100 Engine 100A engine 102 Cylinder liner 106 Piston 116 Air injection hole (gas injection hole) 116a First air injection hole (first gas injection hole) 116b Second air injection hole (second gas injection hole) 502 Branch channel (channel) 504 On-off valve 600 control device

Claims

1. The piston and a cylinder liner that houses the piston; a gas injection hole provided in an inner wall of the cylinder liner, facing in a direction intersecting a radial direction of the cylinder liner when viewed in the axial direction of the cylinder liner, and for injecting a non-flammable gas at least during a compression stroke; Equipped with a first gas injection hole and a second gas injection hole disposed on the bottom dead center side of the first gas injection hole are provided on the inner wall of the cylinder liner as the gas injection holes, the first gas injection hole faces in a direction inclined toward the top dead center side with respect to the circumferential direction of the cylinder liner when viewed in the radial direction, the second gas injection hole faces in a direction inclined toward the bottom dead center side with respect to the circumferential direction when viewed in the radial direction, engine.

2. a flow path connected to the gas injection hole; an on-off valve provided in the flow path; Equipped with When the on-off valve is opened, non-flammable gas is injected from the gas injection hole.

10. The engine of claim 1.

3. a control device for controlling the operation of the on-off valve; the control device injects non-flammable gas from the gas injection hole by opening the on-off valve at least during the compression stroke.

3. The engine of claim 2.

4. A piston, a cylinder liner that houses the piston; a gas injection hole provided in an inner wall of the cylinder liner, facing in a direction intersecting a radial direction of the cylinder liner when viewed in the axial direction of the cylinder liner, and for injecting a non-flammable gas at least during a compression stroke; a combustion chamber defined by the piston and the cylinder liner; an intake passage communicating with the combustion chamber; a connecting flow path that connects the intake flow path and the gas injection hole; Equipped with The air flowing through the intake passage is supplied to the gas injection hole via the connecting passage. engine.

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