Engine

Abstract

To suppress emission of unburned fuel.SOLUTION: An engine 100 comprises: a piston 106; a cylinder liner 102 accommodating the piston 106; a gas injection hole 116 that is provided in an inner wall 102a of the cylinder liner 102 for injecting gas; a cylindrical portion 106e1 that is a portion of a top land part 106e of the piston 106 on the bottom dead center side; a small diameter portion 106e2 that is a portion of the top land part 106e of the piston 106 on the top dead center side and has an outer diameter smaller than the outer diameter of the cylindrical portion 106e1; a first gap 118a formed between the cylindrical portion 106e1 and an inner wall 102a of the cylinder liner 102; and a second gap 118b that is formed between the small diameter portion 106e2 and the inner wall 102a of the cylinder liner 102 and has a volume larger than the volume of the first gap 118a.SELECTED DRAWING: Figure 3

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, for example, Patent Document 1, 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, and a gas flow from the intake port toward the combustion chamber occurs. In the combustion chamber, a part of the mixture flows along the inner wall of the cylinder liner. The mixture flowing along the inner wall of the cylinder liner may enter a gap formed between the top land portion of the piston and the inner wall of the cylinder liner. The fuel that enters this gap is difficult to burn during the combustion stroke, and may be discharged as unburned fuel. From the viewpoint of improving thermal efficiency or suppressing greenhouse gas emissions, it is desirable to suppress the emission of unburned fuel.

[0005] An object of the present disclosure is to provide an engine that is capable of suppressing 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 accommodates the piston, gas injection holes provided in the inner wall of the cylinder liner for injecting gas, a cylindrical portion that is a portion of the top land portion of the piston on the bottom dead center side, a small diameter portion that is a portion of the top land portion of the piston on the top dead center side and has an outer diameter smaller than the outer diameter of the cylindrical portion, a first gap formed between the cylindrical portion and the inner wall of the cylinder liner, and a second gap formed between the small diameter portion and the inner wall of the cylinder liner and having a volume larger than the volume of the first gap.

[0007] A control device may be provided that injects gas from the gas injection holes toward the first gap or the second gap.

[0008] In order to solve the above problems, the engine of the present disclosure includes a piston, a cylinder liner that houses the piston, a gas injection hole provided in the inner wall of the cylinder liner for injecting gas, and a control device that injects gas from the gas injection hole toward a gap formed between a top land portion of the piston and the inner wall of the cylinder liner.

[0009] The piston may have a cylindrical portion which is a portion of the top land portion of the piston on the bottom dead center side, and a small diameter portion which is a portion of the top land portion of the piston on the top dead center side and has an outer diameter smaller than the outer diameter of the cylindrical portion, and the gap may include a first gap formed between the cylindrical portion and an inner wall of the cylinder liner, and a second gap formed between the small diameter portion and the inner wall of the cylinder liner and having a volume larger than the volume of the first gap.

[0010] The volume of the first gap, the volume of the second gap, and the geometric compression ratio of the engine may satisfy the relationship represented by the following equation (1). V2 / V1≧(R-1) (1) however, V1: Volume of the first gap V2: Volume of the second gap R: Engine geometric compression ratio

[0011] The small diameter portion may have a tapered shape in which the outer diameter becomes smaller toward the top dead center.

[0012] The control device may inject gas from the gas injection holes when the piston is located at bottom dead center.

[0013] The control device may inject gas from the gas injection hole when the piston moves upward from the bottom dead center to the top dead center.

[0014] The gas injection holes may face in a direction intersecting with the radial direction of the cylinder liner when viewed in the axial direction of the cylinder liner.

[0015] The gas injection holes may face in a direction inclined toward the bottom dead center side with respect to a direction perpendicular to the axial direction of the cylinder liner. Effect of the Invention

[0016] According to the present disclosure, it is possible to suppress the emission of unburned fuel. [Brief description of the drawings]

[0017] [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. [Diagram 2] FIG. 2 is a schematic diagram showing the configuration of each cylinder of the engine according to the embodiment of the present disclosure. [Diagram 3] FIG. 3 is a partial enlarged view of each cylinder of the engine according to the embodiment of the present disclosure. [Figure 4] FIG. 4 is a partial enlarged view of each cylinder of the engine according to the embodiment of the present disclosure. [Diagram 5] FIG. 5 is a diagram showing a combustion chamber of the engine according to the embodiment of the present disclosure as viewed in the axial direction of the cylinder liner. [Figure 6] FIG. 6 is a diagram showing an inner wall of a cylinder liner of an engine according to an embodiment of the present disclosure as viewed in the radial direction of the cylinder liner. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present disclosure will be described with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values ​​shown in the embodiments are merely examples for ease of understanding, and do not limit the present disclosure unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are given the same reference numerals to avoid repeated explanations, and elements not directly related to the present disclosure are not illustrated.

[0019] 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 connection flow path 500, and a control device 600. The control device 600 is included in the engine 100.

[0020] The engine 100 has multiple cylinders. In the example of Fig. 1, the 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 of the engine 100 may be other than six.

[0021] Fig. 2 is a schematic diagram showing the configuration of each cylinder of the engine 100 according to this embodiment. In Fig. 2, the intake port 104a, the exhaust port 104b, the fuel injection nozzle 112, and the ignition device 114 are illustrated on the same cross section. However, the intake port 104a, the exhaust port 104b, the fuel injection nozzle 112, and the ignition device 114 do not have to be located on the same cross section.

[0022] 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. A combustion chamber 108 is formed by the cylinder liner 102, the cylinder head 104, and the piston 106. 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.

[0023] 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 circumferential 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 piston body 106a on the top dead center side of the piston ring 106b is called a top land portion 106e.

[0024] 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 intake valve 110a and the exhaust valve 110b open and close in accordance with the rotation of a camshaft (not shown).

[0025] A pipe that forms a branch passage 202 of an intake passage 200, which will be 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, which will be described later, is connected to the exhaust port 104b. Exhaust gas is discharged from the combustion chamber 108 via the exhaust port 104b.

[0026] The fuel injection nozzle 112 is connected to a fuel supply source via a fuel supply flow path (not shown). The fuel supply source is, for example, a fuel tank (not shown) or a pipeline for city gas or the like. Fuel gas is supplied to the fuel injection nozzle 112 from the fuel supply source via the fuel supply flow path. The fuel injection nozzle 112 is provided in a branch flow path 202 of the intake flow path 200. The tip of the fuel injection nozzle 112 faces the intake port 104a. However, the fuel injection nozzle 112 may be provided in the intake port 104a.

[0027] The fuel injection nozzle 112 injects the 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 the fuel gas as fuel. Hereinafter, the fuel gas is also simply referred to as fuel.

[0028] The ignition device 114 is provided in the cylinder head 104. A tip portion of the ignition device 114 protrudes into the combustion chamber .

[0029] The engine 100 is a four-stroke engine. During the intake stroke, fuel is injected from the fuel injection nozzle 112, the intake valve 110a opens, and the exhaust valve 110b closes. The piston 106 moves toward the bottom dead center, and intake air and fuel are drawn into the combustion chamber 108 from the intake port 104a. During the compression stroke, the intake valve 110a and the exhaust valve 110b close. The piston 106 moves toward the top dead center, and the air-fuel mixture in the combustion chamber 108 is compressed. The air-fuel mixture is ignited by the ignition device 114 and combusted, 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. The piston 106 moves toward the top dead center, and the exhaust gas after combustion is discharged from the combustion chamber 108 through the exhaust port 104b.

[0030] Gas injection holes 116 are provided on the inner wall 102a of the cylinder liner 102. Gas such as air is injected from the gas injection holes 116 into the combustion chamber 108. In the following, an example will be described in which the gas injected from the gas injection holes 116 is air. However, as will be described later, the gas injected from the gas injection holes 116 may be gas other than air. A pipe that forms a branch flow path 502 of a connection flow path 500, which will be described later, is connected to the gas injection holes 116. Details of the gas injection holes 116 will be described later. Returning to FIG. 1, the description will be continued below.

[0031] The intake passage 200 communicates with the combustion chamber 108 of the engine 100. In the intake passage 200, intake air, which is air supplied to the combustion chamber 108, flows. An intake port (not shown) through which air is taken in from the outside is provided at the upstream end of the intake passage 200. The intake passage 200 has a plurality of branch passages 202 that communicate with the plurality of combustion chambers 108, respectively. The plurality of branch passages 202 are provided on the downstream side of the intake passage 200. As described above, the pipe that forms the branch passage 202 is connected to the intake port 104a of the engine 100. The intake port 104a corresponds to the downstream end of the branch passage 202. The intake port 104a is included in the intake passage 200. The intake port 104a is a portion of the intake passage 200 inside the cylinder head 104.

[0032] The exhaust flow passage 300 communicates with the combustion chamber 108 of the engine 100. Exhaust gas discharged from the combustion chamber 108 flows through the exhaust flow passage 300. An exhaust port (not shown) is provided at the downstream end of the exhaust flow passage 300, through which the exhaust gas is discharged to the outside. The exhaust flow passage 300 has a plurality of branch flow passages 302 that communicate with the plurality of combustion chambers 108, respectively. The plurality of branch flow passages 302 are provided on the upstream side of the exhaust flow passage 300. As described above, the pipe that forms the branch flow passage 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 passage 302. The exhaust port 104b is included in the exhaust flow passage 300. The exhaust port 104b is a portion of the exhaust flow passage 300 inside the cylinder head 104.

[0033] The turbocharger 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.

[0034] 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 from 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 be one that uses cooling water such as engine cooling water or industrial water to cool the intake air.

[0035] The turbine 404 is provided in the exhaust passage 300 downstream of the branch passages 302. The exhaust gas discharged from the engine 100 is sent to the turbine 404 via each branch passage 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 by rotating a blade of the turbine 404 by the exhaust gas. The rotational power generated by the turbine 404 is transmitted to the compressor 402 via a shaft.

[0036] The connection flow passage 500 connects the intake flow passage 200 and the gas injection holes 116 of each cylinder. The connection flow passage 500 is provided to supply air flowing through the intake flow passage 200 to the gas injection holes 116 of each cylinder. In the connection flow passage 500, air flows from the intake flow passage 200 toward each cylinder. In the following, the upstream side of the connection flow passage 500 means the intake flow passage 200 side, and the downstream side of the connection flow passage 500 means the cylinder side.

[0037] In the example of FIG. 1, the upstream end of the connection passage 500 is connected to the intake passage 200 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 gas injection hole 116 of each cylinder. In the example of FIG. 1, branch passages 502a, 502b, 502c, 502d, 502e, and 502f are provided as the branch passages 502. The branch passages 502a, 502b, 502c, 502d, 502e, and 502f are connected to the gas 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.

[0038] 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.

[0039] The pressure of the air flowing through the connection point of the intake flow passage 200 with the upstream end of the connection flow passage 500 is increased by the compressor 402. Therefore, when the on-off valve 504 is opened, air is sucked from the intake flow passage 200 into the connection flow passage 500 and sent to the gas injection holes 116 via the branch flow passage 502. Then, the air is injected from the gas injection holes 116 into the combustion chamber 108. However, from the viewpoint of smoothly supplying air to the gas injection holes 116 via the connection flow passage 500, a device such as a pump that pressurizes the air may be added to the connection flow passage 500.

[0040] The control device 600 includes a central processing unit (CPU), a ROM in which programs and the like are stored, 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. Specifically, the control device 600 can inject air from the gas injection holes 116 into the combustion chamber 108 by opening the on-off valve 504. The control device 600 can also control the timing of air injection from the gas injection holes 116 by controlling the timing of opening the on-off valve 504.

[0041] In each cylinder of the engine 100, the intake valve 110a opens during the intake stroke, and the air-fuel mixture is supplied to the combustion chamber 108 from the intake port 104a. In the combustion chamber 108, a part of the air-fuel mixture flows along the inner wall 102a of the cylinder liner 102. In the engine 100 according to this embodiment, by using the gas injection hole 116, the air-fuel mixture flowing along the inner wall 102a of the cylinder liner 102 is prevented from entering the gap formed between the top land portion 106e of the piston 106 and the inner wall 102a of the cylinder liner 102, and the discharge of unburned fuel is suppressed. Hereinafter, the operation of the engine 100 using the gas injection hole 116 will be described in detail.

[0042] Figures 3 and 4 are partial enlarged views of each cylinder of the engine 100. Specifically, in Figures 3 and 4, the gas injection holes 116 and their surroundings are shown in an enlarged manner.

[0043] FIG 3 shows a state where the piston 106 is located at the bottom dead center after the piston 106 descends toward the bottom dead center during the intake stroke. For example, FIG 3 shows a state where the piston 106 transitions from the intake stroke to the compression stroke. FIG 4 shows a state where the piston 106 is located at the bottom dead center after the piston 106 descends toward the bottom dead center during the intake stroke. For example, FIG 4 shows a state where the piston 106 is located near the top dead center during the compression stroke.

[0044] As shown in FIGS. 3 and 4, the top land portion 106e of the piston 106 includes a cylindrical portion 106e1 and a small diameter portion 106e2.

[0045] The cylindrical portion 106e1 is a portion of the top land portion 106e on the bottom dead center side. The cylindrical portion 106e1 has a cylindrical shape. The outer diameter of the cylindrical portion 106e1 is approximately constant regardless of the axial position. The cylindrical portion 106e1 is disposed coaxially with the cylinder liner 102. The end of the cylindrical portion 106e1 on the bottom dead center side corresponds to the end of the top land portion 106e on the bottom dead center side.

[0046] The small diameter portion 106e2 is a portion of the top land portion 106e on the top dead center side. The small diameter portion 106e2 has an outer diameter smaller than that of the cylindrical portion 106e1. In the example of FIG. 3 and FIG. 4, the small diameter portion 106e2 has a tapered shape in which the outer diameter becomes smaller as it advances toward the top dead center side. The end portion of the small diameter portion 106e2 on the bottom dead center side is connected to the end portion of the cylindrical portion 106e1 on the top dead center side. The outer diameter of the end portion of the small diameter portion 106e2 on the bottom dead center side is the same as the outer diameter of the end portion of the cylindrical portion 106e1 on the top dead center side. The outer diameter of the small diameter portion 106e2 gradually becomes smaller as it advances toward the top dead center side. The end portion of the small diameter portion 106e2 on the top dead center side corresponds to the end portion of the top dead center side of the top land portion 106e.

[0047] A gap 118 is formed between the top land portion 106e and the inner wall 102a of the cylinder liner 102. Specifically, the gap 118 is defined by the outer circumferential surface of the top land portion 106e and the inner wall 102a of the cylinder liner 102. The gap 118 exists in the axial range from the axial position of the end of the top land portion 106e on the bottom dead center side to the axial position of the end of the top dead center side. The gap 118 includes a first gap 118a and a second gap 118b.

[0048] The first gap 118a is formed between the cylindrical portion 106e1 and the inner wall 102a of the cylinder liner 102. Specifically, the first gap 118a is defined by the outer circumferential surface of the cylindrical portion 106e1 and the inner wall 102a of the cylinder liner 102. The first gap 118a exists in the range from the axial position of the end of the cylindrical portion 106e1 on the bottom dead center side to the axial position of the end of the cylindrical portion 106e1 on the top dead center side in the axial direction. The first gap 118a has an annular shape coaxial with the cylinder liner 102. The cross-sectional area of ​​the first gap 118a in a cross section perpendicular to the axial direction of the cylinder liner 102 is approximately constant regardless of the axial position.

[0049] The second gap 118b is formed between the small diameter portion 106e2 and the inner wall 102a of the cylinder liner 102. Specifically, the second gap 118b is defined by the outer circumferential surface of the small diameter portion 106e2 and the inner wall 102a of the cylinder liner 102. The second gap 118b exists in the range from the axial position of the end of the small diameter portion 106e2 on the bottom dead center side to the axial position of the end of the small diameter portion 106e2 on the top dead center side in the axial direction. The second gap 118b has a substantially annular shape coaxial with the cylinder liner 102. The cross-sectional area of ​​the second gap 118b in a cross section perpendicular to the axial direction of the cylinder liner 102 gradually increases toward the top dead center side. The volume of the second gap 118b is larger than the volume of the first gap 118a. The axial length of the second gap 118b may be longer, may be the same as, or may be shorter than the axial length of the first gap 118a.

[0050] As shown in Fig. 3, when the piston 106 is located at the bottom dead center, the gas injection hole 116 faces the gap 118. In the example of Fig. 3, the gas injection hole 116 faces the second gap 118b. Then, the control device 600 injects air A1 from the gas injection hole 116 toward the gap 118 when the piston 106 is located at the bottom dead center after the piston 106 descends toward the bottom dead center during the intake stroke. In the example of Fig. 3, the control device 600 injects air A1 from the gas injection hole 116 toward the second gap 118b.

[0051] As a result, as shown in Fig. 3, the first gap 118a and the second gap 118b are filled with air A1. At this time, the air A1 sent from the gas injection hole 116 to the second gap 118b is sent smoothly to the first gap 118a along the tapered outer circumferential surface of the small diameter portion 106e2. However, the small diameter portion 106e2 may have a shape other than a tapered shape. For example, the small diameter portion 106e2 may be formed in a cylindrical shape having a constant outer diameter smaller than the outer diameter of the cylindrical portion 106e1.

[0052] As described above, in the example of FIG. 3, the control device 600 injects the air A1 from the gas injection hole 116 toward the second gap 118b. However, the control device 600 may also inject the air A1 from the gas injection hole 116 toward the first gap 118a. For example, when the piston 106 is located at the bottom dead center, the gas injection hole 116 may face the first gap 118a, and the air A1 may be injected from the gas injection hole 116 toward the first gap 118a. In this case, for example, the air A1 sent from the gas injection hole 116 to the first gap 118a is also sent to the second gap 118b via the first gap 118a. Therefore, the first gap 118a and the second gap 118b are filled with the air A1.

[0053] As shown in Fig. 4, after the air A1 is injected from the gas injection hole 116, the piston 106 rises from the bottom dead center to the top dead center. At this time, the air-fuel mixture in the combustion chamber 108 is compressed. Accordingly, the air A1 filling the gap 118 is also compressed.

[0054] As described above, in the engine 100, the air A1 is injected from the gas injection hole 116 toward the gap 118, and the gap 118 is filled with the air A1. Therefore, during the compression stroke, the air A1 filling the gap 118 is compressed as the piston 106 rises, but as shown in FIG. 4, when the piston 106 is located near the top dead center and combustion starts, a part of the gap 118 is filled with the air A1. Therefore, the air-fuel mixture supplied to the combustion chamber 108 from the intake port 104a is suppressed from entering the gap 118. Thus, the discharge of unburned fuel is suppressed.

[0055] In particular, the top land portion 106e includes a cylindrical portion 106e1 and a small diameter portion 106e2. The volume of the second gap 118b is larger than the volume of the first gap 118a. Therefore, a large amount of air A1 can be pre-filled in the second gap 118b. Therefore, when the air A1 filled in the gap 118 is compressed, it is easy to realize a state in which the air A1 is filled in the first gap 118a. This suppresses the intrusion of the mixture supplied from the intake port 104a to the combustion chamber 108 into the first gap 118a. Since the radial width of the first gap 118a is narrow, when the mixture intrudes into the first gap 118a, the mixture is particularly difficult to burn in the combustion stroke. Therefore, by suppressing the intrusion of the mixture into the first gap 118a, the discharge of unburned fuel is more effectively suppressed.

[0056] In particular, in engine 100, the volume V1 of first gap 118a, the volume V2 of second gap 118b, and the geometric compression ratio R of engine 100 satisfy the relationship represented by the following formula (1). The geometric compression ratio R is a value obtained by dividing the volume of combustion chamber 108 when piston 106 is located at bottom dead center by the volume of combustion chamber 108 when piston 106 is located at top dead center.

[0057] V2 / V1≧(R-1) (1)

[0058] By modifying the above equation (1), the following equation (2) is derived.

[0059] (V1+V2) / R≧V1 (2)

[0060] The left side of formula (2) corresponds to the volume when the air A1 filling the gap 118 is compressed at the geometric compression ratio R as the piston 106 moves to the top dead center in the case where the air A1 filling the gap 118 is filled with the entire gap 118 when the piston 106 is located at the bottom dead center. Therefore, according to formula (2), in the case where the air A1 filling the gap 118 is filled with the entire gap 118 when the piston 106 is located at the bottom dead center, at least the first gap 118a is filled with the air A1 when the piston 106 moves to the top dead center.

[0061] 4, when the piston 106 is located near the top dead center during the compression stroke, at least the first gap 118a is appropriately filled with air A1. This more effectively prevents the air-fuel mixture supplied from the intake port 104a to the combustion chamber 108 from entering the first gap 118a. This more effectively prevents the discharge of unburned fuel.

[0062] However, the volume V1 of the first gap 118a, the volume V2 of the second gap 118b, and the geometric compression ratio R of the engine 100 do not necessarily need to satisfy the relationship represented by the above formula (1).

[0063] Hereinafter, the gas injection holes 116 will be described in detail with reference to FIGS.

[0064] Fig. 5 is a diagram showing the combustion chamber 108 of the engine 100 as viewed in the axial direction of the cylinder liner 102. Fig. 5 shows a cross section perpendicular to the central axis CA of the cylinder liner 102 and passing through the gas injection holes 116.

[0065] As shown in FIG. 5, a plurality of gas injection holes 116 are provided at intervals in the circumferential direction of the cylinder liner 102 in each cylinder of the engine 100. In the example of FIG. 5, four gas injection holes 116 are provided at equal intervals in the circumferential direction of the cylinder liner 102. However, the number and arrangement of the gas injection holes 116 are not limited to the example of FIG. 5. For example, the number of the gas injection holes 116 may be one, two, three, or five or more. For example, the plurality of gas injection holes 116 may be provided at unequal intervals in the circumferential direction of the cylinder liner 102. From the viewpoint of filling the gap 118 with the air A1 evenly, it is preferable that the plurality of gas injection holes 116 are provided at equal intervals in the circumferential direction of the cylinder liner 102.

[0066] As shown in FIG. 5, the injection direction DA of the air A1 injected from the gas injection hole 116 intersects with the direction DR from the gas injection hole 116 toward the central axis CA of the cylinder liner 102. In this way, the gas injection hole 116 faces a direction intersecting with the radial direction of the cylinder liner 102 when viewed in the axial direction of the cylinder liner 102. As a result, the air A1 injected from the gas injection hole 116 is smoothly filled into the gap 118 extending in the circumferential direction along the inner wall 102a of the cylinder liner 102. From the viewpoint of smoothly filling the gap 118 with the air A1 injected from the gas injection hole 116, it is preferable that the injection direction DA of the gas injection hole 116 is close to the tangential direction of the cylinder liner 102 when viewed in the axial direction. However, the gas injection hole 116 may face the radial direction of the cylinder liner 102 when viewed in the axial direction of the cylinder liner 102.

[0067] FIG. 6 is a diagram showing the inner wall 102a of the cylinder liner 102 of the engine 100 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, the injection direction DA of the air A1 injected from the gas injection hole 116 is inclined toward the bottom dead center side with respect to the circumferential direction DC of the cylinder liner 102. In this way, the gas injection hole 116 faces in a direction inclined toward the bottom dead center side with respect to the direction perpendicular to the axial direction of the cylinder liner 102. As a result, the air A1 injected from the gas injection hole 116 is smoothly filled into the gap 118 that is closed on the bottom dead center side and open on the top dead center side. However, the gas injection hole 116 does not have to face in a direction inclined toward the bottom dead center side with respect to the direction perpendicular to the axial direction of the cylinder liner 102.

[0068] As described above, the engine 100 includes the piston 106, the cylinder liner 102 that houses the piston 106, and the gas injection hole 116 that is provided in the inner wall 102a of the cylinder liner 102 and injects gas. By using the gas injection hole 116, the gap 118 formed between the top land portion 106e of the piston 106 and the inner wall 102a of the cylinder liner 102 can be filled with air A1. Although the air A1 filled in the gap 118 is compressed as the piston 106 rises, when the piston 106 is located near the top dead center, a state in which the air A1 is filled in a part of the gap 118 is realized. Therefore, the mixture supplied from the intake port 104a to the combustion chamber 108 is suppressed from entering the gap 118. Thus, the discharge of unburned fuel is suppressed.

[0069] In particular, the engine 100 includes a cylindrical portion 106e1, which is a portion of the top land portion 106e of the piston 106 on the bottom dead center side, and a small diameter portion 106e2, which is a portion of the top land portion 106e of the piston 106 on the top dead center side and has an outer diameter smaller than that of the cylindrical portion 106e1. The gap 118 includes a first gap 118a formed between the cylindrical portion 106e1 and the inner wall 102a of the cylinder liner 102, and a second gap 118b formed between the small diameter portion 106e2 and the inner wall 102a of the cylinder liner 102 and having a volume larger than that of the first gap 118a. As a result, although the air A1 filled in the first gap 118a and the second gap 118b is compressed as the piston 106 rises, it is easy to realize a state in which the air A1 is filled in the first gap 118a when the piston 106 is located near the top dead center. Therefore, the air-fuel mixture supplied from the intake port 104a to the combustion chamber 108 is prevented from entering the first gap 118a, and thus the discharge of unburned fuel is more effectively prevented.

[0070] However, the top land portion 106e of the piston 106 does not necessarily have to be provided with the small diameter portion 106e2.

[0071] In particular, the engine 100 includes a control device 600 that injects gas from the gas injection holes 116 toward the gap 118. This allows the gap 118 to be appropriately filled with the air A1.

[0072] In the above, an example has been described in which the control device 600 injects the air A1 from the gas injection holes 116 when the piston 106 is located at the bottom dead center. In this case, the air A1 can be supplied from the gas injection holes 116 into the combustion chamber 108 when the volume of the combustion chamber 108 is large and the in-cylinder pressure is low. Therefore, it is easy to supply the air A1 from the gas injection holes 116 into the combustion chamber 108.

[0073] However, the control device 600 may inject the air A1 from the gas injection hole 116 when the piston 106 rises from the bottom dead center to the top dead center. For example, when the piston 106 rises from the bottom dead center to the top dead center, the gas injection hole 116 may face the gap 118, and the air A1 may be injected from the gas injection hole 116 toward the gap 118. In this case, the distance between the position of the piston 106 at the time when the gap 118 is filled with the air A1 and the top dead center becomes shorter. Therefore, the degree to which the air A1 filled in the gap 118 is compressed becomes smaller. Therefore, when the piston 106 is located near the top dead center, the amount of air A1 filled in the gap 118 becomes larger, so that the discharge of unburned fuel is more effectively suppressed.

[0074] In the above, an example has been described in which the gas injected from the gas injection hole 116 is air flowing through the intake passage 200. However, the gas injected from the gas injection hole 116 may be any gas that does not contain fuel, and is not limited to the above example. For example, the upstream end of the connection passage 500 may be connected to an air supply source other than the intake passage 200, and air other than the air flowing through the intake passage 200 may be injected from the gas injection hole 116. For example, an inert gas such as argon may be injected from the gas injection hole 116. For example, oxygen may be injected from the gas injection hole 116. In that case, the oxygen filled in the gap 118 is easily combusted in the combustion stroke.

[0075] 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 think of various modified or altered examples within the scope of the claims, and it is understood that these also naturally belong to the technical scope of the present disclosure.

[0076] The present disclosure can reduce unburned fuel emissions and, therefore, can contribute to, for example, Sustainable Development Goal (SDG) 7, "Ensure access to affordable, reliable, sustainable and modern energy." [Explanation of symbols]

[0077] 100 Engine 102 Cylinder liner 102a Internal wall 106 Piston 106e Topland Division 106e1 Cylinder section 106e2 Small diameter section 116 Gas injection hole 118 Gap 118a First Gap 118b Second gap 600 Control device R Engine geometric compression ratio V1 Volume of the first gap V2 Volume of the second gap

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 for injecting gas; A cylindrical portion which is a portion of the top land portion of the piston on the bottom dead center side; a small diameter portion that is a portion of the top land portion of the piston on the top dead center side and has an outer diameter smaller than an outer diameter of the cylindrical portion; a first gap formed between the cylindrical portion and an inner wall of the cylinder liner; a second gap formed between the small diameter portion and an inner wall of the cylinder liner and having a volume larger than a volume of the first gap; Equipped with engine.

2. a control device for injecting gas from the gas injection hole toward the first gap or the second gap; 2. The engine of claim 1.

3. The piston and a cylinder liner that houses the piston; a gas injection hole provided in an inner wall of the cylinder liner for injecting gas; a control device that injects gas from the gas injection hole toward a gap formed between a top land portion of the piston and an inner wall of the cylinder liner; Equipped with engine.

4. A cylindrical portion which is a portion of the top land portion of the piston on the bottom dead center side; a small diameter portion that is a portion of the top land portion of the piston on the top dead center side and has an outer diameter smaller than an outer diameter of the cylindrical portion; Equipped with The gap is a first gap formed between the cylindrical portion and an inner wall of the cylinder liner; a second gap formed between the small diameter portion and an inner wall of the cylinder liner and having a volume larger than a volume of the first gap; Including, 4. An engine as claimed in claim 3.

5. The volume of the first gap, the volume of the second gap, and the geometric compression ratio of the engine satisfy a relationship represented by the following formula (1): An engine according to claim 1, 2 or 4. V2 / V1≧(R-1)...(1) however, V1: Volume of the first gap V2: Volume of the second gap R: geometric compression ratio of the engine

6. The small diameter portion has a tapered shape in which the outer diameter becomes smaller toward the top dead center. An engine according to claim 1, 2 or 4.

7. The control device injects gas from the gas injection hole when the piston is located at the bottom dead center. An engine according to any one of claims 2 to 4.

8. The control device injects gas from the gas injection hole when the piston rises from the bottom dead center to the top dead center. An engine according to any one of claims 2 to 4.

9. The gas injection hole faces in a direction intersecting a radial direction of the cylinder liner when viewed in an axial direction of the cylinder liner. An engine according to any one of claims 1 to 4.

10. The gas injection hole faces in a direction inclined toward the bottom dead center side with respect to a direction perpendicular to the axial direction of the cylinder liner. An engine according to any one of claims 1 to 4.

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