Engine

Abstract

This engine includes: a cylinder; a piston that is disposed inside the cylinder so as to be slidable along the axial direction, and that forms a combustion chamber between the cylinder and a top surface, the piston including a cavity formed in a central part of the top surface, and a plurality of valve recess parts deeper than a squish area 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 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 so as to pass through a region in the circumferential direction in which the valve recess parts are present.

Description

engine

[0001] This application claims priority to Japanese Patent Application No. 2024-072114, filed with the Japan Patent Office on April 26, 2024, the contents of which are incorporated herein by reference.

[0002] Some engines have a fuel injection nozzle with multiple injection holes arranged in a combustion chamber formed between a cylinder and a piston (see, 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.

[0003] Japanese Utility Model Application Publication No. 62-173555

[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 any 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.

[0006] An engine according to at least one embodiment of the present disclosure comprises: a cylinder; a piston slidably disposed within the cylinder along the 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 deeper than a squish portion formed radially outward from the cavity in the top surface; and a fuel injection nozzle including a plurality of nozzle holes for injecting fuel at different circumferential positions in the combustion chamber, wherein the plurality of nozzle holes include a plurality of narrow-angle nozzle holes having central axes inclined radially outward toward the piston in the axial direction, and a plurality of wide-angle nozzle holes having central axes inclined radially outward more than the narrow-angle nozzle holes toward the piston in the axial direction, and the direction of at least one of the plurality of narrow-angle nozzle holes is configured to pass through a region in the circumferential direction in which the valve recesses are present.

[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.

[0008] FIG. 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. FIG. 2 is a schematic cross-sectional view along the central axis of a combustion chamber of an engine according to an embodiment of the present disclosure. FIG. 3 is a schematic cross-sectional view along the central axis of a combustion chamber of an engine according to an embodiment of the present disclosure. FIG. 4 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. FIG. 5 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. FIG. 6 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. FIG. 7 is a graph for explaining the circumferential distribution of heat flux on the inner wall surface of a cylinder in an embodiment of the present disclosure. FIG. 8 is an explanatory view for explaining the velocity distribution of a swirl flow in a combustion chamber in an embodiment of the present disclosure.

[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 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. 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 Figures 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 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 the 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 from the cavity 4 of 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 contact between the piston 3 and 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 axially from the outer peripheral edge of the bottom surface 41 toward the cylinder head 23 (upper side in FIGS. 2 and 3 ) in the axial direction, and an inclined surface 43 that slopes radially inward from the inner peripheral edge of the bottom surface 41 toward the cylinder head 23 in the axial direction. 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 serves as 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 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 protrusion 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 Figure 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 Figure 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] In order to suppress interference of spray flames between the wide-angle injection hole 62 and the narrow-angle injection hole 61, it is preferable that the wide-angle injection hole 62 be formed closer to the ceiling surface 241 in the axial direction than the narrow-angle injection hole 61. Note that 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 a position opposite the air inlet ports 711, 721 and the exhaust ports 811, 821 with an axial gap therebetween. 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 valve recess 5 adjacent to that end, and in a circumferential range from the other circumferential end P2 of a valve recess 5 to the one circumferential end P1 of the valve recess 5 adjacent to that end. That is, the combustion chamber 20 is configured such that the first region A1 and the second region A2 alternate in the circumferential direction.

[0023] In some embodiments, the direction in which at least one of the plurality of narrow-angle injection holes 61 is directed passes through a first region A1 in the circumferential direction in which the valve recess 5 is located. Here, the direction in which the narrow-angle injection hole 61 is directed 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 be able to flow into the valve recess 5, which is recessed compared 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 (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 increase on the combustion chamber wall surface prevents 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, it is possible to more reliably prevent the spray flame injected from the wide-angle injection holes 62 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, it is also possible to some extent to prevent the spray flame injected from the wide-angle injection holes 62 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 the engine 1 according to an embodiment of the present disclosure, viewed from one side in the axial direction of the 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 is configured so that the direction in which each narrow-angle injection hole 61 points passes through the first region A1 in the circumferential direction where the valve recess portion 5 is located.

[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 different valve recesses 5 are 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 a circumferential angle (60°) obtained by dividing one circumference (360°) by the number of narrow-angle injection holes 61 (for example, four) is defined as a division angle, the narrow-angle injection holes 61 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, "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., one) 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 circumferentially 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 in which 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 , eight wide-angle injection holes 62, twice the number of narrow-angle injection holes 61, are formed in the fuel injection nozzle 6. 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 adjacent narrow-angle injection holes 61 in the circumferential direction. In the embodiment shown in Fig. 6 , eight wide-angle injection holes 62, which is twice the number of narrow-angle injection holes 61, are formed in the fuel injection nozzle 6. 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 the circumference) means that, when a circumferential angle (45°) obtained by dividing one circumference (360°) by the number of wide-angle injection holes 62 (e.g., eight) is defined as a 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 it is possible 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 plurality of wide-angle injection holes 62 may include a first group consisting of wide-angle injection holes 62 arranged one by one between two circumferentially adjacent narrow-angle injection holes 61, and a second group consisting of wide-angle injection holes 62 arranged two by two between two circumferentially adjacent narrow-angle injection holes 61. The plurality of wide-angle injection holes 62 may be arranged such that the first group and the second group alternate in the circumferential direction. The plurality of wide-angle injection holes 62 including the first group and the second group 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 with respect to two circumferentially adjacent narrow-angle injection holes 61. Furthermore, the plurality of wide-angle injection holes 62 including the first group and the second group may be arranged in the circumferential direction toward a second region A2 in which no valve recess portion 5 exists in the circumferential direction.

[0041] 7 is a schematic diagram of the engine 1 according to one embodiment of the present disclosure, viewed from one side in the axial direction of the 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 perpendicular to the first reference line BL1 on the central axis CM 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. Furthermore, a circumferentially intermediate position P3 between the valve recesses 5A and 5B is defined as 0°, and the circumferential angle α is defined as a positive angle in the direction from the intermediate position P3 toward the second air supply side AS2. In the illustrated embodiment, the intermediate position P3 is the circumferentially intermediate position between a circumferential end P1 of the valve recess 5A adjacent to the valve recess 5B and a circumferential end P2 of the valve recess 5B adjacent to the valve recess 5A.

[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. Note that 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 swirl flow velocity 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 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 air 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 air intake side AS1 toward the first region A1, the wide-angle injection holes 62 on the first air 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 air intake side AS1, where the spray flame is likely to interfere with the combustion chamber wall surface. The first air intake side AS1 has a greater effect of reducing the heat flux on the inner wall surface 221 than the second air 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 in which the wide-angle injection hole 62 points does not pass through the first region A1 in which the valve recess 5 is located in the circumferential direction. In other words, the wide-angle injection hole 62 located on the first air intake side AS1 is configured so that the direction in which the wide-angle injection hole 62 points passes through the second region A2.

[0048] The wide-angle injection holes 62 on the first air intake side AS1 can be circumferentially arranged toward an area in the circumferential direction that does not include the valve recess portion 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 arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, 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 expressing that things are in an equal state, such as "identical," "equal," and "homogeneous," not only express a state in which there is a strict equivalence, but also express 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 expressing shapes such as a rectangular shape or a cylindrical shape not only express shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is 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: a cylinder (2); and a piston (3) slidably disposed within the cylinder (2) along an 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 recess portions (5) that are deeper than a squish portion formed radially outward from the cavity (4) on the top surface; and a fuel injection nozzle (6) including a plurality of injection holes (60) for injecting fuel to different circumferential positions in the combustion chamber, the plurality of injection holes (60) including: a plurality of narrow-angle injection holes (61) having central axes inclined radially outward toward the piston (3) in the axial direction; and a plurality of wide-angle injection holes (62) having central axes inclined radially outward from the narrow-angle injection holes (61) toward the piston (3) in the axial direction. The direction of orientation of at least one of the plurality of narrow-angle injection holes (61) is configured to pass through a region in the circumferential direction where the valve recess portion (5) is present.

[0053] According to the configuration 1), by circumferentially arranging the narrow-angle injection holes (61) having a relatively small inclination angle with respect to the axial direction toward the region where the valve recess (5) is located in the circumferential direction, the wide-angle injection holes (62) having a relatively large inclination angle with respect to the axial direction can be circumferentially arranged to avoid the region where the valve recess (5) is located as much as possible in the circumferential direction. This makes it possible to prevent the spray flame injected from the wide-angle injection hole (62) from flowing into the valve recess, thereby suppressing interference of the spray flame injected from the wide-angle injection hole (62) with the combustion chamber wall surface near the valve recess (5). By reducing the thermal load on the combustion chamber wall surface and suppressing a temperature increase on the combustion chamber wall surface, it is possible to suppress 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, in the engine (1) described in 1) above, each of the plurality of narrow-angle injection holes (61) is configured so that the direction of each injection hole passes through a region in the circumferential direction where the valve recess portion (5) is present.

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

[0056] 3) In some embodiments, in the engine (1) described in 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 of 3) above, by arranging the plurality of narrow-angle injection holes (61) at equal intervals in the circumferential direction, it is possible to suppress the spray flames injected from the plurality of narrow-angle injection holes (61) from interfering with the spray flames injected from other injection holes (60), and it is possible to suppress a reduction in the air utilization rate of each spray flame due to interference between the spray flames.

[0058] 4) In some embodiments, in the engine (1) described in any one of 1) to 3) above, the direction of at least one wide-angle nozzle hole (62) among the plurality of wide-angle nozzle holes (62) is configured to pass through an area in the circumferential direction where the valve recess portion (5) does not exist.

[0059] According to the configuration of 4) above, by circumferentially arranging the wide-angle nozzle hole (62) toward a region in the circumferential direction where no valve recess portion (5) exists, 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, in the engine (1) described in any one of 1) to 4) above, the plurality of wide-angle injection holes (62) are arranged one by one between two of the narrow-angle injection holes (61) adjacent in the circumferential direction, and each of the plurality of wide-angle injection holes (62) is arranged at equal intervals in the circumferential direction with respect to the two narrow-angle injection holes (61) adjacent in the circumferential direction.

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

[0062] 6) In some embodiments, in the engine (1) described in any one of 1) to 4) above, the plurality of wide-angle injection holes (62) are arranged two by two between two of the narrow-angle injection holes (61) adjacent to each other in the circumferential direction, and at least one of the two wide-angle injection holes (62) arranged between the two narrow-angle injection holes (61) adjacent to each other in the circumferential direction is configured so that the direction of the wide-angle injection 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 a region 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, in the engine (1) described in any one of 1) to 4) above, the plurality of wide-angle injection holes (62) include 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, and each of the plurality of wide-angle injection holes (62) is 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 injection holes (62) at equal intervals in the circumferential direction, it is possible to prevent the spray flames injected from the plurality of wide-angle injection holes (62) from interfering with the spray flames injected from the wide-angle injection 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, in the engine (1) described in 1), the cylinder (2) is provided with: 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) forming the combustion chamber (20); and 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 port (721) formed in the surface (241) forming the combustion chamber (20), wherein the distance from a branch point between the first intake port (71) and the second intake port (721) is longer than the distance from the branch point to the first intake port (711), When viewed from one side in the axial direction, the side on which the first air intake port (711) is located is defined as a first air intake side (AS1) with respect to a reference line (BL1) that passes through a central axis (CM) of the combustion chamber (20) and an intermediate position between the valve recess portion (5A) corresponding to the first air intake port (711) in the circumferential direction and the valve recess portion (5B) corresponding to the second air intake port (721), and the direction pointed by the narrow-angle injection hole (61) located on the first air intake side (AS1) is configured to pass through a region in the circumferential direction where the valve recess portion (5) is present.

[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), so the flow velocity of the intake air flowing from the first intake port (71) into the combustion chamber (20) is small, 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 combustion chamber wall surface. By circumferentially arranging the narrow-angle injection holes (61) on the first intake side (AS1) toward an area where the valve recess portion (5) is 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 recess portion (5) is present in the circumferential direction. This makes it possible to suppress interference of the spray flame injected from the wide-angle nozzle hole (62) 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.

[0068] 9) In some embodiments, the engine (1) described in 8) above is configured such that the direction of the wide-angle nozzle (62) located on the first air intake side (AS1) does not pass through an area in the circumferential direction where the valve recess portion (5) is present.

[0069] According to the configuration of 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 recess portion (5) exists. This makes it possible to more reliably suppress interference of the spray flame injected from the wide-angle injection holes (62) 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 suppress interference of the spray flame injected from the wide-angle injection holes (62) with the combustion chamber wall surface.

[0070] REFERENCE SIGNS LIST 1 Engine 2 Cylinder 3 Piston 4 Cavity 5, 5A, 5B Valve recess 6 Fuel injection nozzle 7 Intake port 8 Exhaust port 20 Combustion chamber 21 Cylinder block 22 Cylinder bore 23 Cylinder head 24 Blocking portion 31 Top surface 32 Outer peripheral end surface 41, 51 Bottom surface 42, 221 Inner wall surface 43 Inclined surface 60 Injection hole 61 Narrow angle injection hole 62 Wide angle injection hole 71 First intake port 72 Second intake port 81 First exhaust port 82 Second exhaust port 711 First intake port 721 Second intake port 811 First exhaust port 821 Second exhaust port A1 First region A2 Second region AS1 First intake side AS2 Second intake side BL1 First reference line BL2 Second reference line CA1, CA2 Center axis P1, P2 End P3 Intermediate position

Claims

1. An engine comprising: a cylinder; a piston arranged axially slidably inside the cylinder and 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 multiple valve recesses deeper than a squish portion formed radially outward from the cavity in the top surface; and a fuel injection nozzle including multiple injection holes for injecting fuel at different circumferential positions in the combustion chamber, wherein the multiple injection holes include multiple narrow-angle injection holes having central axes inclined radially outward toward the piston in the axial direction, and multiple wide-angle injection holes having central axes inclined radially outward more than the narrow-angle injection holes toward the piston in the axial direction, and wherein the direction of at least one of the multiple narrow-angle injection holes is configured to pass through a region in the circumferential direction where the valve recesses are present.

2. An engine according to claim 1, wherein each of the plurality of narrow-angle injection holes is configured so that the direction of each injection hole passes through a region in the circumferential direction where the valve recess portion is present.

3. The engine according to claim 1, wherein the plurality of narrow-angle injection holes are arranged at equal intervals in the circumferential direction.

4. An engine according to any one of claims 1 to 3, wherein the direction of orientation of at least one wide-angle nozzle hole among the plurality of wide-angle nozzle holes is configured to pass through an area in the circumferential direction where no valve recess portion exists.

5. An engine according to any one of claims 1 to 3, wherein the plurality of wide-angle injection holes are arranged one by one between two of the narrow-angle injection holes adjacent in the circumferential direction, and each of the plurality of wide-angle injection holes is arranged at equal intervals in the circumferential direction relative to the two narrow-angle injection holes adjacent in the circumferential direction.

6. An engine according to any one of claims 1 to 3, wherein the plurality of wide-angle injection holes are arranged two by two between two of the narrow-angle injection holes adjacent in the circumferential direction, and at least one of the two wide-angle injection holes arranged 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 an area in the circumferential direction where no valve recess portion exists.

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

8. An engine as claimed in claim 1, wherein the cylinder is formed with: a first intake port for introducing intake air into the combustion chamber via a first intake port formed in a surface that forms the combustion chamber; and a second intake port that branches off from the first intake port and introduces intake air into the combustion chamber via a second intake port formed in the surface that forms the combustion chamber, the distance from the branch point with the first intake port to the second intake port being longer than the distance from the branch point to the first intake port; and wherein, when viewed from one side in the axial direction, the side on which the first intake port is located is defined as a first intake side with respect to a reference line that passes through a central axis of the combustion chamber and a midpoint in the circumferential direction between the valve recess portion corresponding to the first intake port and the valve recess portion corresponding to the second intake port, the direction in which the narrow-angle injection hole located on the first intake side is directed passes through a region in the circumferential direction in which the valve recess portion is present.

9. An engine according to claim 8, wherein the direction of the wide-angle nozzle located on the first air intake side is configured not to pass through an area in the circumferential direction where the valve recess portion is present.

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