Engine

Abstract

To provide an engine capable of improving reliability by reducing the thermal load on a combustion chamber wall surface.SOLUTION: An engine comprises: a cylinder; a piston that is disposed inside the cylinder to be slidable along the axial direction, and that forms a combustion chamber between the cylinder and a top surface thereof, the piston having a cavity formed in a central part of the top surface, and a plurality of valve recess portions deeper than a squish portion formed farther outward in the radial direction than the cavity of the top surface; and a fuel injection nozzle including, at different positions in the circumferential direction in the combustion chamber, a plurality of injection holes for injecting a fuel. The plurality of injection holes include a plurality of narrow-angle injection holes having a central axis inclined outward in the radial direction toward the piston side in the axial direction, and a plurality of wide-angle injection holes having a central axis inclined farther outward in the radial direction than the narrow-angle injection holes toward the piston side in the axial direction. The direction in which at least one narrow-angle injection hole of the plurality of narrow-angle injection holes is oriented is configured to pass through a region in the circumferential direction in which the valve recess portions are present.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Some engines have a fuel injection nozzle with multiple injection holes arranged in a combustion chamber formed between a cylinder and a piston (for example, Patent Document 1). Patent Document 1 discloses a fuel injection nozzle with a first injection hole that injects fuel toward the bottom wall of a cavity in the piston and a second injection hole that injects fuel toward the peripheral wall of the cavity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 62-173555 Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors discovered that when a piston has a valve recess, the spray flame from the nozzle holes may reach the inner wall surface on which the piston slides, raising the temperature of the inner wall surface, and that circumferential arrangement of the nozzle holes with consideration for the valve recess can suppress the temperature rise of the inner wall surface. If the temperature of the inner wall surface rises excessively, the viscosity of the lubricating oil used to slide the piston will decrease, potentially resulting in a deterioration in the sliding properties of the piston. However, Patent Document 1 does not disclose the circumferential arrangement of the nozzle holes with consideration for the valve recess.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide an engine capable of improving reliability by reducing the thermal load on the combustion chamber wall surface. [Means for solving the problem]

[0006] In accordance with at least one embodiment of the present disclosure, the engine comprises: Cylinder and a piston slidably disposed inside the cylinder along an axial direction, forming a combustion chamber between the cylinder and a top surface, the piston having a cavity formed in a central portion of the top surface, and a plurality of valve recesses that are deeper than squish portions formed radially outward from the cavity on the top surface; a fuel injection nozzle including a plurality of injection holes for injecting fuel at different positions in the circumferential direction of the combustion chamber, The plurality of nozzle holes include: a plurality of narrow-angle injection holes having central axes inclined outward in the radial direction toward the piston in the axial direction; a plurality of wide-angle injection holes having central axes inclined radially outwardly relative to the narrow-angle injection holes toward the piston in the axial direction, At least one of the plurality of narrow-angle injection holes is configured to point in a direction that passes through a region in the circumferential direction where the valve recess portion is present. [Effects of the Invention]

[0007] According to at least one embodiment of the present disclosure, an engine is provided that can improve reliability by reducing the thermal load on the combustion chamber wall surface. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic view of an engine according to an embodiment of the present disclosure, viewed from one side in the axial direction of a cylinder. [Figure 2] 1 is a schematic cross-sectional view taken along the central axis of a combustion chamber of an engine according to an embodiment of the present disclosure. FIG. [Figure 3] 1 is a schematic cross-sectional view taken along the central axis of a combustion chamber of an engine according to an embodiment of the present disclosure. FIG. [Figure 4] 1 is a schematic view of an engine according to an embodiment of the present disclosure, viewed from one side in the axial direction of a cylinder. [Figure 5]1 is a schematic view of an engine according to an embodiment of the present disclosure, viewed from one side in the axial direction of a cylinder. [Figure 6] 1 is a schematic view of an engine according to an embodiment of the present disclosure, viewed from one side in the axial direction of a cylinder. [Figure 7] 1 is a schematic view of an engine according to an embodiment of the present disclosure, viewed from one side in the axial direction of a cylinder. [Figure 8] 4 is a graph for explaining the circumferential distribution of heat flux on an inner wall surface of a cylinder in one embodiment of the present disclosure. [Figure 9] FIG. 4 is an explanatory diagram for explaining the velocity distribution of a swirl flow in a combustion chamber according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, several embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present disclosure.

[0010] (engine) Figures 1 and 4 are each a schematic view of an engine 1 according to an embodiment of the present disclosure, viewed from one side in the axial direction of a cylinder 2. Figures 2 and 3 are each a schematic cross-sectional view taken along a central axis CM of a combustion chamber 20 of the engine 1 according to an embodiment of the present disclosure. As shown in Figures 1 to 3, the engine 1 according to some embodiments includes a cylinder 2, a piston 3, and a fuel injection nozzle 6.

[0011] As shown in FIGS. 2 and 3 , the piston 3 is slidably disposed inside the cylinder 2 along the axial direction of the cylinder 2, and a combustion chamber 20 is formed between the cylinder 2 and a top surface 31. The fuel injection nozzle 6 is configured to inject liquid fuel into the combustion chamber 20. The engine 1 is a diesel engine configured to ignite the liquid fuel by injecting it into charge air compressed and heated by the piston 3 in the combustion chamber 20. The charge air is a combustion gas, such as air, that is used for combustion in the combustion chamber 20. The engine 1 of the present disclosure can be used for automobiles, marine applications, or industrial applications (e.g., land-based power generation).

[0012] 2 and 3, the cylinder 2 includes a cylinder block 21 in which a cylinder bore (cylindrical hole) 22 extending along a central axis CM of the combustion chamber 20 is formed, and a cylinder head 23 having a closing portion 24 that closes the open end of the cylinder bore 22. The cylinder block 21 has an inner wall surface 221 that forms the cylinder bore 22. Hereinafter, the direction in which the central axis CM of the combustion chamber 20 extends is defined as the axial direction of the cylinder 2, and the axial, radial, and circumferential directions of the cylinder 2 may be simply referred to as the axial direction, radial direction, and circumferential direction.

[0013] The piston 3 is housed inside the cylinder bore 22 and is configured to be able to reciprocate along the extension direction of the central axis CM of the combustion chamber 20. The piston 3 includes a cavity 4 formed in the center of the top surface 31, and a plurality of valve recesses 5 formed radially outward of the cavity 4 in the top surface 31. The valve recesses 5 are recesses that are deeper than the top surface 31 of the squish portion and are provided to prevent the piston 3 from coming into contact with an intake valve (not shown) and an exhaust valve (not shown).

[0014] In the illustrated embodiment, the closing portion 24 of the cylinder head 23 has a surface 241 that serves as the ceiling surface of the combustion chamber 20. The cavity 4 includes a bottom surface 41, an annular inner wall surface 42 that extends from the outer peripheral edge of the bottom surface 41 along the axial direction toward the cylinder head 23 (upper side in FIGS. 2 and 3 ), and an inclined surface 43 that slopes toward the cylinder head 23 in the axial direction as it extends radially inward from the inner peripheral edge of the bottom surface 41. The top surface 31 of the piston 3 includes an outer peripheral end surface 32 that extends radially outward from the end of the inner wall surface 42 on the cylinder head 23 side. The outer peripheral end surface 32 is the top surface 31 of the squish portion. A bottom surface 51 of the valve recess portion 5 is located farther from the ceiling surface of the combustion chamber 20 than the outer peripheral end surface 32 in the axial direction and is located closer to the ceiling surface than the bottom surface 41.

[0015] 1, the fuel injection nozzle 6 includes a plurality of injection holes 60 for injecting fuel to different circumferential positions in the combustion chamber 20. The fuel injection nozzle 6 is supported by the cylinder head 23, and the plurality of injection holes 60 are formed in a protruding portion that protrudes into the combustion chamber 20. The plurality of injection holes 60 are configured to inject fuel simultaneously. In order to suppress interference between the spray flames, it is preferable that the circumferential distance between the plurality of injection holes 60 in the circumferential direction be as large as possible.

[0016] The multiple injection holes 60 include multiple narrow-angle injection holes 61 and multiple wide-angle injection holes 62. The multiple narrow-angle injection holes 61 and the multiple wide-angle injection holes 62 each have a central axis CA1, CA2 that is inclined radially outward toward the piston 3 in the axial direction (lower side in FIGS. 2 and 3). The central axis CA2 of the wide-angle injection hole 62 is inclined radially outward from the central axis CA1 of the narrow-angle injection hole 61 toward the piston in the axial direction. In other words, the inclination angle θ2 (see FIG. 3) of the central axis CA2 of the wide-angle injection hole 62 with respect to the axial direction is larger than the inclination angle θ1 (see FIG. 2) of the central axis CA1 of the narrow-angle injection hole 61 with respect to the axial direction.

[0017] The symbol JD1 in the drawing indicates the traveling direction of the spray (spray flame) injected from the narrow-angle nozzle hole 61, and this traveling direction extends along the extension direction of the central axis CA1 of the narrow-angle nozzle hole 61. As shown in Fig. 2, the spray (spray flame) injected from the narrow-angle nozzle hole 61 flows along the inclined surface 43 toward the bottom surface 41 of the cavity 4.

[0018] The symbol JD2 in the drawing indicates the traveling direction of the spray (spray flame) injected from the wide-angle nozzle hole 62, and this traveling direction extends along the extension direction of the central axis CA2 of the wide-angle nozzle hole 62. As shown in Fig. 3, the spray (spray flame) injected from the wide-angle nozzle hole 62 flows toward the inner wall surface 42 of the cavity 4.

[0019] The wide-angle injection hole 62 is preferably formed closer to the ceiling surface 241 in the axial direction than the narrow-angle injection hole 61 in order to suppress interference of spray flames with the narrow-angle injection hole 61. The wide-angle injection hole 62 may be formed at the same position as the narrow-angle injection hole 61 in the axial direction, or closer to the piston 3 than the narrow-angle injection hole 61.

[0020] The cylinder head 23 of the cylinder 2 is formed with at least one intake port 7 for introducing intake air into the combustion chamber 20 and at least one exhaust port 8 for discharging exhaust gas from the combustion chamber 20. In the illustrated embodiment, the cylinder head 23 is formed with a first intake port 71 for introducing intake air into the combustion chamber 20 through a first intake port 711 formed in a ceiling surface 241 that defines the combustion chamber 20, and a second intake port 72 for introducing intake air into the combustion chamber 20 through a second intake port 721 formed in the ceiling surface 241. The cylinder head 23 is formed with a first exhaust port 81 for discharging exhaust gas from the combustion chamber 20 through a first exhaust port 811, and a second exhaust port 82 for discharging exhaust gas from the combustion chamber 20 through a second exhaust port 821.

[0021] Each of the multiple valve recesses 5 is provided at a position corresponding to the first air inlet 711, the second air inlet 721, the first exhaust port 811, and the second exhaust port 821. In one embodiment, the valve recesses 5 are provided at positions facing the air inlet and the exhaust port with an axial gap between them. In the illustrated embodiment, four valve recesses 5 are formed in the top surface 31 of the piston 3 at intervals in the circumferential direction.

[0022] As shown in FIG. 1 , a circumferential region of the combustion chamber 20 where the valve recesses 5 are present is defined as a first region A1, and a circumferential region of the combustion chamber 20 where the valve recesses 5 are not present is defined as a second region A2. The first region A1 exists in a circumferential range from one circumferential end P1 of each of the valve recesses 5 to the other circumferential end P2. The second region A2 exists in a circumferential range from one circumferential end P1 of a valve recess 5 to the other circumferential end P2 of the adjacent valve recess 5 on that side, and in a circumferential range from the other circumferential end P2 of a valve recess 5 to the one circumferential end P1 of the adjacent valve recess 5 on the other side. That is, the combustion chamber 20 is configured so that the first region A1 and the second region A2 alternate in the circumferential direction.

[0023] In some embodiments, the direction of orientation of at least one of the plurality of narrow-angle injection holes 61 described above is configured to pass through a first region A1 in the circumferential direction where the valve recess portion 5 is present. Here, the direction of orientation of the narrow-angle injection hole 61 means the traveling direction JD1 of the spray (spray flame) injected from the narrow-angle injection hole 61, specifically, the extension direction of the central axis CA1 of the narrow-angle injection hole 61.

[0024] If wide-angle injection holes 62 with a relatively large inclination angle θ2 relative to the axial direction were arranged circumferentially toward the first region A1 where the valve recess 5 is located in the circumferential direction, the spray (spray flame) injected from the wide-angle injection holes 62 would flow into the valve recess 5, which is recessed relative to the outer peripheral end face 32, and would therefore be prone to interfere with the inner wall surface 221 facing the combustion chamber 20 near the valve recess 5. Particularly under high-load conditions where the load on the engine 1 is relatively high, the amount of fuel injected from the injection holes 60 increases, and the spray flame from the injection holes 60 may reach the inner wall surface 221 on which the piston 3 slides, raising the temperature of the inner wall surface 221. If the temperature of the inner wall surface 221 rises excessively, the viscosity of the lubricating oil used to slide the piston 3 decreases, which may result in a deterioration in the sliding properties of the piston 3.

[0025] By circumferentially arranging the narrow-angle injection holes 61, which have a relatively small inclination angle θ1 with respect to the axial direction, toward the first region A1 in which the valve recess 5 is located in the circumferential direction, the wide-angle injection holes 62, which have a relatively large inclination angle θ2 with respect to the axial direction, can be circumferentially arranged to avoid the first region A1 in which the valve recess 5 is located as much as possible. This prevents the spray flame injected from the wide-angle injection holes 62 from flowing into the valve recess 5, thereby preventing the spray flame injected from the wide-angle injection holes 62 from interfering with the combustion chamber wall surface (the inner wall surface 221 facing the combustion chamber 20) near the valve recess 5. Reducing the thermal load on the combustion chamber wall surface and suppressing a temperature rise on the combustion chamber wall surface can prevent deterioration of the sliding properties of the piston 3 due to a decrease in the viscosity of the lubricating oil, thereby improving the reliability of the engine 1.

[0026] In some embodiments, the direction of orientation of at least one of the plurality of wide-angle injection holes 62 described above is configured to pass through a second region A2 in the circumferential direction where no valve recess portion 5 exists. Here, the direction of orientation of the wide-angle injection hole 62 means the traveling direction JD2 of the spray (spray flame) injected from the wide-angle injection hole 62, specifically, the extension direction of the central axis CA2 of the wide-angle injection hole 62.

[0027] By circumferentially arranging the wide-angle injection holes 62 toward the second region A2 where no valve recesses 5 exist in the circumferential direction, the spray flame injected from the wide-angle injection holes 62 can be more reliably prevented from flowing into the valve recesses 5, thereby effectively preventing the spray flame injected from the wide-angle injection holes 62 from interfering with the combustion chamber wall surface near the valve recesses 5. Note that, by circumferentially arranging the wide-angle injection holes 62 toward the circumferential ends of the first region A1 rather than the circumferential center thereof, the spray flame injected from the wide-angle injection holes 62 can also be prevented to some extent from flowing into the valve recesses 5. In some embodiments, the direction of at least one of the plurality of wide-angle injection holes 62 described above is configured to pass through the circumferential ends of the first region A1.

[0028] 5 and 6 are each a schematic diagram of an engine 1 according to an embodiment of the present disclosure, viewed from one side in the axial direction of a cylinder 2. In some embodiments, as shown in Fig. 1, Fig. 5, and Fig. 6, each of the plurality of narrow-angle injection holes 61 described above is configured so that the direction in which each narrow-angle injection hole 61 points passes through a first region A1 in which the valve recess portion 5 exists in the circumferential direction.

[0029] In the illustrated embodiment, the fuel injection nozzle 6 is formed with four narrow-angle injection holes 61, the same number as the number of valve recesses 5. The four narrow-angle injection holes 61 are configured to pass through the first region A1 in which each of the four valve recesses 5 is present.

[0030] By arranging each of the multiple narrow-angle injection holes 61 circumferentially toward the first region A1 in which the valve recess portion 5 is located in the circumferential direction, the wide-angle injection holes 62 can be circumferentially arranged to avoid the first region A1 in which the valve recess portion 5 is located in the circumferential direction as much as possible.

[0031] 1, 5, and 6, the multiple narrow-angle injection holes 61 are arranged at equal intervals in the circumferential direction. Here, being arranged at equal intervals in the circumferential direction means that when the circumferential angle (60°) obtained by dividing one circumference (360°) by the number of narrow-angle injection holes 61 (for example, four) is taken as the division angle, the holes are arranged at circumferential positions at a division angle of ±10° (preferably, a division angle of ±5°) from adjacent narrow-angle injection holes 61 in the circumferential direction.

[0032] By arranging the multiple narrow-angle nozzle holes 61 at equal intervals in the circumferential direction, it is possible to prevent the spray flames sprayed from these multiple narrow-angle nozzle holes 61 from interfering with the spray flames sprayed from other nozzle holes 60, and it is possible to prevent a reduction in the air utilization rate of each spray flame due to interference between the spray flames.

[0033] 1 , the plurality of wide-angle injection holes 62 are arranged one by one between two circumferentially adjacent narrow-angle injection holes 61. Each of the plurality of wide-angle injection holes 62 is arranged at equal intervals in the circumferential direction relative to the two circumferentially adjacent narrow-angle injection holes 61. Here, being arranged at equal intervals in the circumferential direction relative to the two circumferentially adjacent narrow-angle injection holes 61 means that, when the circumferential angle between the two adjacent narrow-angle injection holes 61 (e.g., 90°) is divided by the number of wide-angle injection holes 62 (e.g., 1) arranged between the two narrow-angle injection holes 61 plus one (45°), the wide-angle injection holes 62 are arranged at circumferential positions at a division angle of ±10° (preferably, a division angle of ±5°) relative to the adjacent narrow-angle injection hole 61.

[0034] 1, the fuel injection nozzle 6 is formed with four wide-angle injection holes 62, the same number as the narrow-angle injection holes 61. The four wide-angle injection holes 62 are configured to pass through different second regions A2 where no valve recess portion 5 exists.

[0035] By arranging each of the multiple wide-angle nozzle holes 62 at equal intervals in the circumferential direction relative to two circumferentially adjacent narrow-angle nozzle holes 61, it is possible to prevent the spray flames sprayed from these multiple wide-angle nozzle holes 62 from interfering with the spray flames sprayed from the circumferentially adjacent narrow-angle nozzle holes 61, and it is possible to prevent a reduction in the air utilization rate of each spray flame due to interference between the spray flames.

[0036] In some embodiments, as shown in Fig. 5, the plurality of wide-angle injection holes 62 described above are arranged two by two between two circumferentially adjacent narrow-angle injection holes 61. In the embodiment shown in Fig. 5, the fuel injection nozzle 6 is formed with eight wide-angle injection holes 62, which is twice the number of narrow-angle injection holes 61. At least one of the two wide-angle injection holes 62 arranged between two circumferentially adjacent narrow-angle injection holes 61 is configured so that the direction of the wide-angle injection hole 62 passes through a second region A2 in which no valve recess portion 5 exists in the circumferential direction. This wide-angle injection hole 62 is configured so that it passes through a second region A2 that is different from the wide-angle injection holes 62 arranged between narrow-angle injection holes 61 other than the combination of two circumferentially adjacent narrow-angle injection holes 61.

[0037] By circumferentially arranging at least one of the two wide-angle injection holes 62 arranged between two circumferentially adjacent narrow-angle injection holes 61 toward the second region A2 where no valve recess portion 5 exists in the circumferential direction, the spray flame injected from these wide-angle injection holes 62 can be more reliably prevented from flowing into the valve recess portion 5, thereby effectively preventing the spray flame injected from the wide-angle injection hole 62 from interfering with the combustion chamber wall surface near the valve recess portion 5.

[0038] In some embodiments, as shown in Fig. 6, the plurality of wide-angle injection holes 62 described above are arranged two by two between two circumferentially adjacent narrow-angle injection holes 61. In the embodiment shown in Fig. 6, the fuel injection nozzle 6 is formed with eight wide-angle injection holes 62, which is twice the number of narrow-angle injection holes 61. The plurality of wide-angle injection holes 62 are arranged at equal intervals in the circumferential direction. Here, being arranged at equal intervals in the circumferential direction (all around) means that when the circumferential angle (45°) obtained by dividing one circumference (360°) by the number of wide-angle injection holes 62 (e.g., eight) is defined as the division angle, the wide-angle injection holes 62 are arranged at circumferential positions separated by a division angle of ±10° (preferably, a division angle of ±5°) from the adjacent wide-angle injection holes 62 in the circumferential direction.

[0039] By arranging each of the multiple wide-angle nozzle holes 62 at equal intervals in the circumferential direction, it is possible to prevent the spray flames sprayed from these multiple wide-angle nozzle holes 62 from interfering with the spray flames sprayed from adjacent wide-angle nozzle holes 62 in the circumferential direction, and to prevent a reduction in the air utilization rate of each spray flame due to interference between the spray flames.

[0040] In some other embodiments, the wide-angle injection holes 62 may include a first group consisting of one wide-angle injection hole 62 arranged between each pair of circumferentially adjacent narrow-angle injection holes 61, and a second group consisting of two wide-angle injection holes 62 arranged between each pair of circumferentially adjacent narrow-angle injection holes 61. The wide-angle injection holes 62 may be arranged such that the first and second groups alternate in the circumferential direction. The wide-angle injection holes 62 including the first and second groups may be arranged at equal intervals in the circumferential direction (all around the circumference), or may be arranged at equal intervals in the circumferential direction relative to each pair of circumferentially adjacent narrow-angle injection holes 61. Furthermore, the wide-angle injection holes 62 including the first and second groups may be arranged in the circumferential direction toward a second region A2 in which no valve recess 5 exists in the circumferential direction.

[0041] 7 is a schematic diagram of an engine 1 according to an embodiment of the present disclosure, viewed from one side in the axial direction of a cylinder 2. In some embodiments, as shown in FIG. 4, the second intake port 72 branches off from the first intake port 71, and the distance from the branch point with the first intake port 71 to the second intake port 721 is longer than the distance from the branch point to the first intake port 711.

[0042] 7, the valve recess 5 corresponding to the first air intake port 711 is defined as the valve recess 5A, the valve recess 5 corresponding to the second air intake port 721 is defined as the valve recess 5B, a line passing through a circumferential midpoint P3 between the valve recesses 5A and 5B and the central axis CM of the combustion chamber 20 is defined as a first reference line BL1, and a line on the central axis CM perpendicular to the first reference line BL1 is defined as a second reference line BL2. The side of the first reference line BL1 on which the first air intake port 711 is located is defined as a first air intake side AS1, and the side of the first reference line BL1 on which the second air intake port 721 is located is defined as a second air intake side AS2. The circumferential intermediate position P3 between the valve recesses 5A and 5B is defined as 0°, and the circumferential angle α is defined as the positive direction from the intermediate position P3 toward the second air supply side AS2.

[0043] In the embodiment shown in FIG. 4, the second exhaust port 82 merges with the first exhaust port 81, and the distance from the junction with the first exhaust port 81 to the second exhaust port 821 is longer than the distance from the junction to the first exhaust port 811. The first exhaust port 811 and the second exhaust port 821 are formed on the opposite side of the second reference line BL2 to the side on which the first air supply port 711 and the second air supply port 721 are formed. In the embodiment shown in FIG. 7, the first exhaust port 811 is formed on the first air supply side AS1, and the second exhaust port 821 is formed on the second air supply side AS2. Alternatively, the first exhaust port 811 may be formed on the second air supply side AS2, and the second exhaust port 821 may be formed on the first air supply side AS1.

[0044] FIG. 8 is a graph illustrating the circumferential distribution of heat flux on the inner wall surface 221 of the cylinder 2 according to an embodiment of the present disclosure. In FIG. 8, the horizontal axis represents the circumferential angle α, and the vertical axis represents the heat flux on the inner wall surface 221. The solid line L1 in FIG. 8 indicates the circumferential distribution of heat flux on the inner wall surface 221 when the injection holes 60 (61, 62) are arranged taking into account the circumferential position of the valve recess 5 (an embodiment of the present disclosure). The dotted line L2 in FIG. 8 indicates the circumferential distribution of heat flux on the inner wall surface 221 when the injection holes 60 (62) are arranged evenly in the circumferential direction without taking into account the circumferential position of the valve recess 5. The dotted line L2 indicates the circumferential distribution of heat flux when the multiple injection holes 60 do not include any narrow-angle injection holes 61, and all of the injection holes 60 are wide-angle injection holes 62. As shown in FIG. 8, by arranging the injection holes 60 (61, 62) in consideration of the circumferential position of the valve recess portion 5, the heat flux on the inner wall surface 221 can be reduced.

[0045] FIG. 9 is an explanatory diagram illustrating the velocity distribution of the swirl flow within the combustion chamber 20 according to one embodiment of the present disclosure. In FIG. 9, the dot density decreases as the velocity of the swirl flow increases. Because the distance from the branch to the combustion chamber 20 of the first intake port 71 is shorter than that of the second intake port 72, the flow velocity of the intake air flowing from the first intake port 71 into the combustion chamber 20 is low, and the swirl flow on the first intake side AS1 is weaker than that on the second intake side AS2. In areas where the swirl flow is weak, the spray flame is less affected by the swirl flow and is more likely to interfere with the combustion chamber wall surface. As shown in FIG. 8, the heat flux on the inner wall surface 221 of the first intake side AS1 is higher than that of the second intake side AS2.

[0046] In some embodiments, the narrow-angle injection holes 61 located on the first intake side AS1 are configured so that their orientation passes through a first region A1 in which the valve recess 5 is located in the circumferential direction. By circumferentially arranging the narrow-angle injection holes 61 on the first intake side AS1 toward the first region A1, the wide-angle injection holes 62 on the first intake side AS1 can be circumferentially arranged to avoid the region in the circumferential direction in which the valve recess 5 is located as much as possible. This makes it possible to suppress interference of the spray flame injected from the wide-angle injection holes 62 with the combustion chamber wall surface on the first intake side AS1, where the spray flame is likely to interfere with the combustion chamber wall surface. The first intake side AS1 has a greater effect of reducing the heat flux on the inner wall surface 221 than the second intake side AS2.

[0047] In some embodiments, the wide-angle injection hole 62 located on the first air intake side AS1 is configured so that the direction of the wide-angle injection hole 62 does not pass through the first region A1 in the circumferential direction where the valve recess 5 is located. In other words, the wide-angle injection hole 62 located on the first air intake side AS1 is configured so that the direction of the wide-angle injection hole 62 passes through the second region A2.

[0048] The wide-angle injection holes 62 of the first air intake side AS1 can be circumferentially arranged toward an area in the circumferential direction where there is no valve recess 5. This more reliably prevents the spray flame injected from the wide-angle injection holes 62 from interfering with the combustion chamber wall surface on the first air intake side AS1, where the spray flame is likely to interfere with the combustion chamber wall surface, and therefore effectively prevents the spray flame injected from the wide-angle injection holes 62 from interfering with the combustion chamber wall surface.

[0049] In this specification, expressions expressing relative or absolute arrangement such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" not only express such an arrangement strictly, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions such as "identical," "equal," and "homogeneous" that indicate that something is in an equal state not only indicate a state of strict equality, but also indicate a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions representing shapes such as a rectangular shape or a cylindrical shape not only represent rectangular shapes or cylindrical shapes in the strict geometric sense, but also represent shapes including uneven portions, chamfered portions, etc., to the extent that the same effect can be obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components.

[0050] The present disclosure is not limited to the above-described embodiments, but also includes modifications to the above-described embodiments and appropriate combinations of these modifications.

[0051] The contents of the above-described embodiments can be understood, for example, as follows.

[0052] 1) An engine (1) according to at least one embodiment of the present disclosure includes: Cylinder (2), a piston (3) disposed inside the cylinder (2) so as to be slidable in the axial direction and forming a combustion chamber (20) between the cylinder (2) and a top surface (31), the piston (3) having a cavity (4) formed in a central portion of the top surface (31) and a plurality of valve recesses (5) formed radially outward from the cavity (4) on the top surface and deeper than a squish portion; a fuel injection nozzle (6) including a plurality of injection holes (60) for injecting fuel at different circumferential positions in the combustion chamber; The plurality of nozzle holes (60) a plurality of narrow-angle injection holes (61) each having a central axis inclined radially outward toward the piston (3) in the axial direction; a plurality of wide-angle injection holes (62) having central axes inclined radially outwardly relative to the narrow-angle injection holes (61) toward the piston (3) in the axial direction, The direction in which at least one of the plurality of narrow-angle injection holes (61) points is configured to pass through a region in the circumferential direction in which the valve recess portion (5) is present.

[0053] According to the configuration 1), the narrow-angle injection holes (61) having a relatively small inclination angle with respect to the axial direction are circumferentially arranged toward the region where the valve recesses (5) are present, thereby enabling the wide-angle injection holes (62) having a relatively large inclination angle with respect to the axial direction to be circumferentially arranged so as to avoid the region where the valve recesses (5) are present as much as possible. This prevents the spray flame injected from the wide-angle injection holes (62) from flowing into the valve recesses, thereby preventing the spray flame injected from the wide-angle injection holes (62) from interfering with the combustion chamber wall surface near the valve recesses (5). Reducing the thermal load on the combustion chamber wall surface and suppressing a temperature rise on the combustion chamber wall surface prevents deterioration of piston sliding properties due to a decrease in the viscosity of the lubricating oil, thereby improving engine reliability.

[0054] 2) In some embodiments, the engine (1) described in 1) above, Each of the plurality of narrow-angle injection holes (61) The direction in which each of the valves is directed passes through the area in the circumferential direction where the valve recess portion (5) is present.

[0055] According to the configuration 2), each of the narrow-angle injection holes (61) is circumferentially arranged toward the area where the valve recess portion (5) is present in the circumferential direction, so that the wide-angle injection holes (62) can be circumferentially arranged to avoid the area where the valve recess portion (5) is present as much as possible in the circumferential direction.

[0056] 3) In some embodiments, the engine (1) according to 1) or 2) above, The plurality of narrow-angle injection holes (61) are arranged at equal intervals in the circumferential direction.

[0057] According to the configuration 3) above, by arranging the plurality of narrow-angle nozzle holes (61) at equal intervals in the circumferential direction, it is possible to prevent the spray flames sprayed from the plurality of narrow-angle nozzle holes (61) from interfering with the spray flames sprayed from the other nozzle holes (60), and it is possible to prevent a reduction in the air utilization rate of each spray flame due to interference between the spray flames.

[0058] 4) In some embodiments, the engine (1) according to any one of 1) to 3) above, The direction in which at least one of the wide-angle nozzle holes (62) points is configured to pass through a region in the circumferential direction where no valve recess portion (5) exists.

[0059] According to the configuration of 4) above, by circumferentially arranging the wide-angle nozzle hole (62) toward an area in the circumferential direction where the valve recess portion (5) does not exist, it is possible to more reliably prevent the spray flame injected from the wide-angle nozzle hole (62) from flowing into the valve recess portion, and therefore it is possible to effectively prevent the spray flame injected from the wide-angle nozzle hole (62) from interfering with the combustion chamber wall surface near the valve recess portion (5).

[0060] 5) In some embodiments, the engine (1) according to any one of 1) to 4) above, The plurality of wide-angle nozzle holes (62) One nozzle hole is disposed between each pair of the narrow-angle nozzle holes (61) adjacent to each other in the circumferential direction, Each of the wide-angle injection holes (62) is disposed at equal intervals in the circumferential direction with respect to the two narrow-angle injection holes (61) adjacent to each other in the circumferential direction.

[0061] According to the configuration of 5) above, by arranging each of the plurality of wide-angle nozzle holes (62) at equal intervals in the circumferential direction relative to two circumferentially adjacent narrow-angle nozzle holes (61), it is possible to prevent the spray flames sprayed from the plurality of wide-angle nozzle holes (62) from interfering with the spray flames sprayed from the circumferentially adjacent narrow-angle nozzle holes (61), and it is possible to prevent a reduction in the air utilization rate of each spray flame due to interference between the spray flames.

[0062] 6) In some embodiments, the engine (1) according to any one of 1) to 4) above, The plurality of wide-angle nozzle holes (62) Two nozzle holes are arranged between two of the narrow-angle nozzle holes (61) adjacent to each other in the circumferential direction, At least one of the two wide-angle nozzle holes (62) arranged between two circumferentially adjacent narrow-angle nozzle holes (61) is configured so that the direction of the wide-angle nozzle hole (62) passes through an area in the circumferential direction where the valve recess portion (5) does not exist.

[0063] According to the configuration of 6) above, at least one of the two wide-angle injection holes (62) arranged between two circumferentially adjacent narrow-angle injection holes (61) is circumferentially arranged toward an area in the circumferential direction where no valve recess portion (5) exists, thereby more reliably preventing the spray flame injected from these wide-angle injection holes (62) from flowing into the valve recess portion, and therefore effectively preventing the spray flame injected from the wide-angle injection hole (62) from interfering with the combustion chamber wall surface near the valve recess portion (5).

[0064] 7) In some embodiments, the engine (1) according to any one of 1) to 4) above, The plurality of wide-angle nozzle holes (62) a plurality of wide-angle injection holes (62) arranged two by two between two of the narrow-angle injection holes (61) adjacent to each other in the circumferential direction, The wide-angle injection holes (62) are arranged at equal intervals in the circumferential direction.

[0065] According to the configuration of 7) above, by arranging each of the plurality of wide-angle nozzle holes (62) at equal intervals in the circumferential direction, it is possible to prevent the spray flames sprayed from the plurality of wide-angle nozzle holes (62) from interfering with the spray flames sprayed from the wide-angle nozzle holes (62) adjacent in the circumferential direction, and it is possible to prevent a reduction in the air utilization rate of each spray flame due to interference between the spray flames.

[0066] 8) In some embodiments, the engine (1) described in 1) above, The cylinder (2) has: a first intake port (71) for introducing intake air into the combustion chamber (20) through a first intake port (711) formed in a surface (241) that defines the combustion chamber (20); a second intake port (72) branching from the first intake port (71) and for introducing intake air into the combustion chamber (20) through a second intake opening (721) formed in a surface (241) forming the combustion chamber (20), wherein the distance from a branching point with the first intake port (71) to the second intake opening (721) is longer than the distance from the branching point to the first intake opening (711), When viewed from one side in the axial direction, a side on which the first air inlet (711) is located with respect to a reference line (BL1) passing through an intermediate position between the valve recess (5A) corresponding to the first air inlet (711) and the valve recess (5B) corresponding to the second air inlet (721) in the circumferential direction and a central axis (CM) of the combustion chamber (20) is defined as a first air inlet side (AS1), The direction of the narrow-angle injection hole (61) located on the first intake side (AS1) is configured to pass through a region in the circumferential direction where the valve recess portion (5) exists.

[0067] According to the configuration of 8) above, the distance from the branch portion to the combustion chamber (20) of the first intake port (71) is shorter than that of the second intake port (72). Therefore, the flow velocity of the intake air flowing from the first intake port (71) into the combustion chamber (20) is low, and the swirl flow on the first intake side (AS1) is also weak. In an area where the swirl flow is weak, the spray flame is less affected by the swirl flow and is more likely to interfere with the wall surface of the combustion chamber. By circumferentially arranging the narrow-angle injection holes (61) on the first intake side (AS1) toward the area where the valve recesses (5) are present, the wide-angle injection holes (62) on the first intake side (AS1) can be circumferentially arranged to avoid, as much as possible, the area where the valve recesses (5) are present. This makes it possible to suppress interference of the spray flame injected from the wide-angle nozzle hole (62) with the wall surface of the combustion chamber on the first air intake side (AS1) where the spray flame is likely to interfere with the wall surface of the combustion chamber.

[0068] 9) In some embodiments, the engine (1) according to 8) above, The direction of the wide-angle injection hole (62) located on the first intake side (AS1) is configured not to pass through a region in the circumferential direction where the valve recess portion (5) exists.

[0069] According to the configuration 9), the wide-angle injection holes (62) on the first air intake side (AS1) can be circumferentially arranged toward an area in the circumferential direction where no valve recesses (5) are present. This makes it possible to more reliably prevent the spray flame injected from the wide-angle injection holes (62) from interfering with the combustion chamber wall surface on the first air intake side (AS1), where the spray flame is likely to interfere with the combustion chamber wall surface, and therefore makes it possible to effectively prevent the spray flame injected from the wide-angle injection holes (62) from interfering with the combustion chamber wall surface. [Explanation of symbols]

[0070] 1 engine 2-cylinder 3 pistons 4 cavities 5, 5A, 5B Valve recess 6 fuel injection nozzles 7 Air supply port 8 exhaust port 20 Combustion chamber 21 Cylinder block 22 cylinder bore 23 Cylinder head 24 Occlusion 31 Top surface 32 Outer peripheral end face 41,51 bottom 42,221 Inner wall surface 43 Slope 60 nozzle holes 61 Close-angle nozzle hole 62 Wide-angle nozzle 71 First air supply port 72 Second air supply port 81 First exhaust port 82 Second exhaust port 711 1st air supply port 721 2nd air supply port 811 First exhaust outlet 821 Second exhaust port A1, First Domain A2, Second Field AS1 First air supply side AS2 Second air supply side BL1 First Baseline BL2 Second Baseline CA1, CA2 central axes P1, P2 terminals P3 Middle position

Claims

1. Cylinder and a piston slidably disposed inside the cylinder along an axial direction, forming a combustion chamber between the cylinder and a top surface, the piston having a cavity formed in a central portion of the top surface, and a plurality of valve recesses that are deeper than squish portions formed radially outward from the cavity on the top surface; a fuel injection nozzle including a plurality of injection holes for injecting fuel at different positions in the circumferential direction of the combustion chamber, The plurality of nozzle holes are a plurality of narrow-angle injection holes having central axes inclined outward in the radial direction toward the piston in the axial direction; a plurality of wide-angle injection holes having central axes inclined radially outwardly relative to the narrow-angle injection holes toward the piston in the axial direction, a direction in which at least one of the plurality of narrow-angle injection holes is directed passes through a region in the circumferential direction in which the valve recess portion is present; engine.

2. Each of the plurality of narrow-angle injection holes is Each of the directions is configured to pass through an area in the circumferential direction where the valve recess portion is present.

10. The engine of claim 1.

3. the plurality of narrow-angle injection holes are arranged at equal intervals in the circumferential direction.

10. The engine of claim 1.

4. a direction in which at least one of the wide-angle injection holes is directed passes through a region in the circumferential direction in which the valve recess portion is not present; An engine according to any one of claims 1 to 3.

5. The plurality of wide-angle nozzle holes are one nozzle hole is disposed between each pair of the narrow-angle nozzle holes adjacent to each other in the circumferential direction, each of the plurality of wide-angle injection holes is disposed at equal intervals in the circumferential direction with respect to the two narrow-angle injection holes adjacent to each other in the circumferential direction; An engine according to any one of claims 1 to 3.

6. The plurality of wide-angle nozzle holes are two nozzle holes are disposed between two of the narrow-angle nozzle holes adjacent to each other in the circumferential direction, At least one of the two wide-angle injection holes disposed between the two narrow-angle injection holes adjacent in the circumferential direction is configured so that the direction of the wide-angle injection hole passes through a region in the circumferential direction where no valve recess portion is present. An engine according to any one of claims 1 to 3.

7. The plurality of wide-angle nozzle holes are two nozzle holes are disposed between two of the narrow-angle nozzle holes adjacent to each other in the circumferential direction, the plurality of wide-angle injection holes are arranged at equal intervals in the circumferential direction. An engine according to any one of claims 1 to 3.

8. The cylinder has: a first intake port for introducing intake air into the combustion chamber through a first intake port formed in a surface that defines the combustion chamber; a second intake port branching from the first intake port and configured to introduce intake air into the combustion chamber via a second intake port formed on a surface that defines the combustion chamber, wherein the distance from a branch point between the first intake port and the second intake port to the second intake port is longer than the distance from the branch point to the first intake port; When viewed from one side in the axial direction, a side on which the first air intake port is located with respect to a reference line that passes through a central axis of the combustion chamber and an intermediate position in the circumferential direction between the valve recess portion corresponding to the first air intake port and the valve recess portion corresponding to the second air intake port, is defined as a first air intake side, a direction in which the narrow-angle injection hole located on the first air intake side is directed passes through a region in the circumferential direction in which the valve recess portion is present; 10. The engine of claim 1.

9. a direction in which the wide-angle injection hole located on the first air intake side is directed does not pass through a region in the circumferential direction in which the valve recess portion is present; 9. The engine of claim 8.

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