JP2019199825A - Combustion chamber structure of internal combustion engine - Google Patents

Abstract

To suppress the generation of smoke by sufficiently using air at a cylinder center side.SOLUTION: A combustion chamber structure of an internal combustion engine comprises: a reentrant-type cavity 11 which is recessively formed at a center part of a piston apex face; a concave part 20 which is recessed at an external peripheral part of the piston apex face while continuing to the cavity; and a fuel injection valve 7 for injecting fuel toward a piston. The concave part comprises a bottom face part 21 continuing to the cavity, and an end wall part 22 erecting in a position at a radial-direction outside end of the bottom face part. A center part of a fuel spray F which is injected from the fuel injection valve arrives at a passage X in the vicinity immediately below a lip part apex 12A of the cavity, and an upper-end edge part Fu of the fuel spray arrives at a position Y of a connecting part of the bottom face part and the end wall part.SELECTED DRAWING: Figure 4

Description

  The present disclosure relates to a combustion chamber structure of an internal combustion engine, and more particularly to a combustion chamber structure suitable for a diesel engine.

  For example, there is a combustion chamber structure of an internal combustion engine, which is a diesel engine, provided with a cavity recessed at the center of a piston top surface. The fuel injection valve injects fuel toward the piston, and injects the fuel radially outward from the position of the center of the cylinder.

  In Patent Document 1, a recess is provided on the outer side in the radial direction of the deep dish type or toroidal type cavity, and fuel is injected along the bulge on the bottom surface of the cavity, and the injected fuel is injected to the side of the cavity. It is disclosed to lead into the part, then into the recess and towards the central axis of the cylinder to reduce soot emissions.

JP-T-2006-505752 JP 2011-185242 A

  However, since Patent Document 1 employs a toroidal cavity and injects fuel along the raised inclined surface of the bottom surface of the cavity, the air at the center side of the cylinder cannot be fully utilized, leaving room for improvement. ing.

  Therefore, the present disclosure has been made in view of such circumstances, and an object of the present disclosure is to provide a combustion chamber structure of an internal combustion engine that can sufficiently suppress the generation of smoke by sufficiently utilizing the air on the cylinder center side.

According to one aspect of the present disclosure,
A reentrant cavity recessed in the center of the piston top surface;
A recess formed in the outer periphery of the top surface of the piston continuously from the cavity;
A fuel injection valve for injecting fuel toward the piston;
With
The hollow portion includes a bottom surface portion continuous with the cavity, and an end wall portion rising at a position of a radially outer end of the bottom surface portion,
The central portion of the fuel spray injected from the fuel injection valve reaches a position immediately below the top of the lip portion of the cavity, and the upper end edge of the fuel spray is connected to the bottom surface portion and the end wall portion. A combustion chamber structure for an internal combustion engine is provided that is configured to reach the position of the section.

  Preferably, the end wall portion has an undercut shape.

Preferably, the fuel injection valve injects fuel radially outward from the position of the center of the cylinder,
A plurality of the depressions are provided in the circumferential direction corresponding to each of the fuel sprays injected from the fuel injection valve,
A partition wall is provided between the recesses adjacent in the circumferential direction.

Preferably, the hollow portion includes a side wall portion that rises at positions on both side ends in the circumferential direction of the bottom surface portion,
The side wall portion has an undercut shape.

  Preferably, the said recessed part is formed in fan shape in planar view.

  According to the present disclosure, it is possible to suppress the generation of smoke by sufficiently utilizing the air at the cylinder center side.

It is a longitudinal cross-sectional view which shows a combustion chamber structure. It is a fragmentary top view which shows a piston. It is III-III sectional drawing of FIG. It is a longitudinal cross-sectional view corresponding to FIG. 1 which shows the flow of fuel spray. FIG. 3 is a partial plan view corresponding to FIG. 2 showing a flow of fuel spray. It is a longitudinal cross-sectional view corresponding to FIG. 3 which shows the flow of fuel spray. FIG. 3 is a cross-sectional view corresponding to III-III in FIG. 2, showing a first modification of the partition wall. It is a III-III cross section equivalent figure of Drawing 2 showing the 2nd modification of a partition. FIG. 6 is a cross-sectional view corresponding to the III-III section of FIG. 2, showing a third modification of the partition wall. It is a longitudinal cross-sectional view corresponding to FIG. 4 which shows the modification of a hollow part. FIG. 6 is a partial plan view corresponding to FIG. 5, showing a modification of the cavity. It is a longitudinal cross-sectional view corresponding to FIG. 4 which shows the modification of a cavity.

  Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the following embodiments.

  The combustion chamber structure according to the present embodiment is applied to a diesel engine that is a typical example of an internal combustion engine. The engine is for vehicles, and is used as a vehicle power source for large vehicles such as trucks. However, the types and applications of the internal combustion engine and the vehicle are not limited to these. For example, the vehicle may be a small vehicle such as a passenger car, and the engine may be a gasoline engine.

  As shown in FIGS. 1 and 2, the combustion chamber structure 1 of the present embodiment includes a piston 2, a cylinder 3 in which the piston 2 can be moved up and down and accommodated coaxially, and a cylinder head 4 that closes an upper end opening of the cylinder 3. A plurality of (three in this embodiment) piston rings 5 mounted on the outer peripheral surface 9 of the piston 2 and a combustion chamber 6 which is a closed space defined by these piston rings 5 are provided. The combustion chamber structure 1 includes a fuel injection valve 7 that is attached to the cylinder head 4 and injects fuel toward the piston 2.

  As shown in FIG. 1, the piston 2 is arranged coaxially with a cylinder axis C that is a central axis of the cylinder 3. Hereinafter, unless otherwise specified, the axial direction, radial direction, and circumferential direction based on the cylinder axis C are simply referred to as axial direction, radial direction, and circumferential direction. The central axis of the piston 2, that is, the piston axis, is coaxial with the cylinder axis C. The piston 2 has a top surface (piston top surface) 8 and an outer peripheral surface 9. The top surface 8 is a flat surface perpendicular to the cylinder axis C. A plurality of (three in the present embodiment) ring grooves 10 for fitting the piston ring 5 are formed on the outer peripheral surface 9.

  The piston 2 has a cavity 11 that is recessed in the center of the top surface 8 thereof. The cavity 11 is a reentrant type cavity, and has a shape in which the upper opening is narrowed with respect to the lower part. The cavity 11 is formed with a lip portion 12 that forms an upper opening and projects radially inward, a side wall portion 13 that extends to the lip portion 12 and expands in an undercut shape below the lip portion 12, and a bottom wall that continues to the side wall portion 13. Part 14. Here, the undercut is a shape in which the lower part is removed from the upper part.

  As shown in FIG. 1, the cross-sectional shape of the lip portion 12 is an arc shape having a curvature radius R1, and the cross-sectional shape of the side wall portion 13 is also an arc shape having a curvature radius R2. R1 <R2. The cross-sectional shape of the bottom wall portion 14 is a mountain shape. The bottom wall portion 14 includes a bottom wall portion top portion 15 formed in the vicinity of the cylinder axis C and having an arc-shaped cross section, and a slope portion 16 that descends in a straight section from the bottom wall portion top portion 15 to the side wall portion 13.

  Further, the combustion chamber structure 1 of the present embodiment has a recess 20 that is continuous with the cavity 11 and is recessed in the outer peripheral portion of the piston top surface 8. The hollow portion 20 includes a bottom surface portion 21 that is continuous with the lip portion 12 of the cavity 11 and an end wall portion 22 that rises at the position of the radially outer end of the bottom surface portion. The bottom surface portion 21 is a flat surface perpendicular to the cylinder axis C and parallel to the piston top surface 8. The end wall portion 22 is located on the radially inner side from the piston outer peripheral surface 9 and has an undercut shape in which the lower portion is removed from the upper portion. The end wall portion 22 includes a lower portion 22A that protrudes in a circular arc shape toward the outer side in the radial direction and an upper portion 22B that protrudes in a circular arc shape toward the inner side in the radial direction, and has an overall S-shaped cross section. .

  As shown in FIGS. 1, 2, and 5, the fuel injection valve 7 is disposed coaxially with the cylinder axis C and injects fuel radially outward from the position of the center of the cylinder. Yes. N (N is an integer of 2 or more) injection holes 23 are formed at the tip of the fuel injection valve 7 disposed in the combustion chamber 6 at equal intervals in the circumferential direction, that is, a predetermined angle θ = 360 / N (° ) Are arranged at intervals. Therefore, the fuel injection valve 7 injects N fuel sprays F radially at a predetermined angle θ interval. In this embodiment, N = 8 and θ = 45 °, but these values can be appropriately changed. In the figure, the nozzle hole axis, which is the center line of the nozzle hole 23, is denoted by reference symbol Cf.

  Corresponding to each nozzle hole 23 and fuel spray F, a plurality of recesses 20 are provided in the circumferential direction, that is, N. That is, one recess 20 is provided for each nozzle hole 23 and fuel spray F. A partition wall 24 is provided between the recessed portions 20 adjacent in the circumferential direction. The recessed portion 20 includes side wall portions 25 that rise at positions on both sides in the circumferential direction of the bottom surface portion 21, and the side wall portions 25 form part of the partition wall 24, that is, both circumferential side portions of the partition wall 24. The upper surface of the partition wall 24 is formed by the piston top surface 8. The partition walls 24 extend in the radial direction and are arranged at equal intervals in the circumferential direction, that is, at predetermined angle θ intervals. The depression 20 is formed in a fan shape in plan view as shown in FIG.

  As shown in FIG. 3, the side wall part 25 is also made into the undercut shape by which the lower part was gotten from the upper part. The side wall portion 25 includes a lower portion 25A that protrudes in a circular arc shape toward the inner side in the width direction of the partition wall 24 along the circumferential direction, and an upper portion 25B that protrudes in a circular arc shape toward the outer side in the width direction. The cross section is S-shaped.

  4 to 6 show a state in which fuel is injected from the fuel injection valve 7 at the fuel injection timing. As shown in FIG. 4, the fuel spray F injected from the injection hole 23 extends radially outward and downward and obliquely downward along the injection hole axis Cf, and as it moves away from the injection hole 23, the injection hole axis. It has a conical shape that gradually expands around Cf. Here, an angle α between the nozzle hole axis Cf and the cylinder axis C is referred to as an injection angle, and an angle β at which the fuel spray F expands with respect to the nozzle hole axis Cf is referred to as a spread angle.

  As shown in FIG. 4, the nozzle hole axis Cf extends from the nozzle hole 23 and reaches a position X in the vicinity immediately below the lip top 12 </ b> A of the cavity 11. Accordingly, the central portion of the fuel spray F located near the nozzle hole axis Cf also reaches the position X. This position X is referred to as a spray center arrival position for convenience. This position X is naturally a position on the surface of the piston 2. The lip portion top portion 12A refers to a portion of the lip portion 12 that is located on the innermost radial direction. The position X is located in the vicinity of the connection portion between the lip portion 12 and the side wall portion 13, and at this position X, the surface of the piston 2 is an inclined surface that goes radially inward as it goes upward. This inclined surface is an almost inclined surface that is slightly inclined with respect to the cylinder axis C.

  On the other hand, the upper end edge portion Fu of the fuel spray F does not hit the lip portion 12 and passes above the lip portion 12, and also passes above the bottom surface portion 21 of the recessed portion 20, so that the connection portion between the bottom surface portion 21 and the end wall portion 22. Position Y is reached. This position Y is referred to as the spray upper edge arrival position for convenience.

  The lower end edge portion Fd of the fuel spray F reaches the vicinity of the height intermediate portion of the side wall portion 13 of the cavity 11.

  As shown in FIG. 5, the nozzle hole axis Cf extends along the center in the circumferential direction of the recess 20. Therefore, the spray center portion reaching position X and the spray upper edge portion reaching position Y extend over an angular range of the spread angle β with the center in the circumferential direction of the recess 20 as the center.

  Next, the flow of fuel spray in each part of the combustion chamber structure 1 is shown. In addition, the term fuel spray includes, in addition to the literal fuel spray, a mixture of fuel and air, and a combustion gas or flame generated as a result of ignition of the fuel spray.

  As shown in FIG. 4, the fuel spray F injected from the injection hole 23 is divided into upper and lower portions with the position of the lip portion 12 of the cavity 11 as a boundary. The fuel spray divided downward is in an amount exceeding half of the whole and is injected into the cavity 11. On the other hand, the fuel spray divided upward is less than half of the whole and is substantially injected into the recess 20.

  Of the fuel spray injected into the cavity 11, the fuel spray that reaches below the spray center arrival position X collides with the side wall 13 of the cavity 11 and is bent downward as indicated by an arrow a. 11 along the side wall 13. And it flows along the bottom wall part 14, and goes to a radial inside. Accordingly, the fuel spray can be ignited and burned by being well mixed with the air on the cylinder center side and the lower side, and the air on the cylinder center side can be used effectively.

  Further, among the fuel sprays injected into the cavity 11, those that reach above the spray center arrival position X collide with the lip portion 12 of the cavity 11, as shown by the arrow b, It is bent upward and diagonally upward. Then, it mixes well with the air at the center and upper side of the cylinder, and ignites and burns. Therefore, it is possible to effectively utilize the air at the cylinder center side.

  On the other hand, the fuel spray injected into the recess 20 is guided by the bottom surface 21 of the recess 20 toward the outer side in the radial direction and gathers in the vicinity of the spray top edge arrival position Y as indicated by an arrow c. And it is guided by the end wall part 22 and is bent toward the diagonally upper side in the radial direction and upward. Since the end wall 22 has an undercut shape, the fuel spray can be reliably bent obliquely upward. As in this embodiment, it is advantageous to make the lower portion 22A of the end wall portion 22 arc-shaped in a cross section projecting outward in the radial direction because the fuel spray can be bent smoothly and easily.

  The fuel spray traveling obliquely upward is ignited and combusted with good mixing with the air on the cylinder outer peripheral side and the upper side. Further, the fuel spray directed obliquely upward is bent by the lower surface of the cylinder head 4 and directed radially inward as indicated by an arrow d. This fuel spray is ignited and burned with good mixing with the air at the center and upper side of the cylinder. Therefore, it is possible to effectively utilize the air at the cylinder center side.

  Here, by bending the fuel spray diagonally upward toward the radially inner side by the end wall portion 22, a flow of the fuel spray that goes over the end wall portion 22 and moves further outward in the radial direction as shown by an arrow e is generated as much as possible. There is no such thing. When such a flow e reaches the inner wall of the cylinder 3, a flame formed in the vicinity of the inner wall comes into contact with the inner wall, and the heat of combustion is lost to the inner wall, resulting in a decrease in thermal efficiency. Therefore, in this embodiment, the fuel spray is prevented from reaching the vicinity of the inner wall of the cylinder as much as possible, thereby suppressing a decrease in thermal efficiency.

  Further, since the fuel spray injected into the depression 20 reaches the spray upper end edge arrival position Y at the longest, the fuel spray is diffused for a long distance and mixed well with air to generate a rich mixture. Can be suppressed.

  On the other hand, as shown in FIG. 5, the fuel spray injected into the cavity 11 collides with the lip portion 12 or the side wall portion 13 of the cavity 11 as shown by the arrow f, and then changes to the left and right with respect to the injection hole axis Cf. It is bent outward and divided into left and right. Here, the left and right are the left and right when the traveling direction of the fuel spray from the nozzle hole 23 toward the outside in the radial direction is set to the front.

  Further, as shown by an arrow g, the fuel spray injected into the recess 20 collides with the end wall 22 of the recess 20 and then bends to the left and right outside the nozzle hole axis Cf and is divided into left and right. The The fuel sprays directed toward the left and right outer sides respectively hit the corresponding left and right side wall portions 25 or partition walls 24, and are bent rearward, that is, radially inward by them. Thereby, the air on the cylinder center side and the upper side can be effectively used, and the fuel sprays in the adjacent recesses 20 can be prevented from interfering with each other and mixing. Therefore, it is possible to suppress the generation of a rich mixture generated by mixing and the generation of particulate matter (hereinafter referred to as PM) and smoke due to incomplete combustion of the rich mixture. At the same time, generation of CO and HC due to incomplete combustion of the rich mixture can be suppressed.

  In particular, as shown in FIG. 6, since the side wall portion 25 has an undercut shape, as shown by an arrow h, the fuel spray that attempts to get over the side wall portion 25 is separated from the side wall portion 25 (to the nozzle hole axis Cf). It can be bent diagonally upward and upward. Thereby, interference of the fuel sprays in the adjacent dent portions 20 can be further suppressed. As in this embodiment, the lower portion 25A of the side wall portion 25 is formed into a circular arc shape that protrudes inward in the width direction of the partition wall 24. This is advantageous because the fuel spray can be bent smoothly and easily.

  As understood from the above, the combustion chamber structure 1 of the present embodiment individually burns one fuel spray F injected from one injection hole 23 in a circumferential region where one recess 20 is present. It has a structure to let you. Then, interference between adjacent fuel sprays F is suppressed, and the generation of the rich mixture and the generation of PM and smoke are effectively suppressed.

  As described above, in the combustion chamber structure 1 of the present embodiment, the central portion of the fuel spray F injected from the fuel injection valve 7 is a position near the lip top portion 12A of the reentrant cavity 11 (spray center portion arrival position). The fuel spray upper end edge portion Fu is configured to reach the position Y (spray upper end edge portion arrival position) Y of the connecting portion between the bottom surface portion 21 and the end wall portion 22 of the hollow portion 20. . For this reason, the fuel spray F injected from the fuel injection valve 7 can be divided vertically into one that reaches into the cavity 11 and one that reaches into the recess 20. Of those that reach the cavity 11, those that reach the spray center portion reaching position X can be bent radially inward and upward, as indicated by the arrow b. Thereby, the air on the cylinder center side can be effectively utilized. Further, the fuel spray that reaches the hollow portion 20 can also be bent obliquely upward in the radial direction and upward as indicated by the arrow c. This also makes it possible to effectively use the air on the cylinder center side. As a result, it is possible to suppress the occurrence of smoke by fully utilizing the air at the cylinder center side.

  Further, since the end wall portion 22 has an undercut shape, it is possible to reliably generate the fuel spray flow c that bends inward in the radial direction and obliquely upward.

  In Patent Document 1, since the wall surface corresponding to the end wall portion 22 is simply a wall surface parallel to the cylinder axis, the fuel spray cannot be actively bent radially inward as in the present embodiment. Moreover, in patent document 1, since there exists a flow which goes over the end wall part 22 and goes to a radial direction outer side like the arrow e, it is disadvantageous at the point of thermal efficiency.

  Moreover, in this embodiment, since the partition wall 24 was provided between the recessed parts 20 adjacent in the circumferential direction, the interference of the fuel sprays in the adjacent recessed parts 20 can be suppressed, and the generation of the rich mixture and the PM and smoke can be suppressed. Generation can be effectively suppressed.

  Further, in this embodiment, the side wall portion 25 that forms the side surface portion of the partition wall 24 has an undercut shape. Therefore, as shown by the arrow h, the fuel spray that tries to get over the side wall portion 25 is separated from the side wall portion 25. Can be bent diagonally upward. Thereby, interference of the fuel sprays in the adjacent dent portions 20 can be further suppressed.

  Further, in this embodiment, since the recess 20 is formed in a fan shape in plan view, the bottom area of the recess 20 is expanded in the circumferential direction, and the fuel spray in the recess 20 is diffused in a wide area in the circumferential direction. Fuel spray and air can be mixed in a wide area. Therefore, it is possible to suppress the generation of the rich mixture and the generation of PM and smoke.

  In addition, the site | part corresponded to the hollow part 20 of patent document 1 is a planar view semicircle shape, The bottom area is small. Therefore, in Patent Document 1, it is impossible to obtain the advantages as in the present embodiment.

  As mentioned above, although embodiment of this indication was described in detail, this indication can also have other embodiments and modifications as follows.

  (1) For example, the cross-sectional shape of the partition wall 24 can be modified as shown in FIGS. In the first modification shown in FIG. 7, the side wall 25 of the partition wall 24 has an undercut shape, but the cross section of the side wall 25 has a linear shape inclined toward the width center side of the partition wall 24 as it goes downward. The The cross-sectional shape of the partition wall 24 is an inverted trapezoidal shape. Even in this case, the fuel spray that tries to get over the side wall portion 25 can be bent obliquely upward in a direction away from the side wall portion 25.

  In the second modification shown in FIG. 8, the side wall 25 of the partition wall 24 is not undercut, and the cross section of the side wall 25 is simply a straight line extending in the vertical direction. The cross-sectional shape of the partition wall 24 is rectangular. In this case, it is difficult to bend the fuel spray that tries to get over the side wall portion 25 in a direction away from the side wall portion 25, but the interference between the fuel sprays in the adjacent recess portions 20 is still greater than when the partition wall 24 is not provided. Can be suppressed.

  In the third modified example shown in FIG. 9, the side wall 25 of the partition wall 24 is not undercut, and the cross section of the side wall portion 25 is inclined linearly toward the width center side of the partition wall 24 as it goes upward. Is done. The upper ends of the side wall portions 25 are connected to each other, and the cross-sectional shape of the partition wall 24 is triangular. Even in this case, the interference between the fuel sprays in the adjacent depressions 20 can be suppressed as compared with the case where there is no partition wall 24.

  (2) You may apply the cross-sectional shape of the side wall part 25 as shown to FIGS. Moreover, the cross-sectional shape of the side wall part 25 and the end wall part 22 is not restricted to the above-mentioned thing, It can change into arbitrary shapes.

  (3) As shown in FIG. 10, the bottom surface portion 21 of the hollow portion 20 may be an inclined surface inclined with respect to a direction perpendicular to the cylinder axis C. The bottom surface portion 21 is a flat inclined surface that goes downward as it goes outward in the radial direction. In the case of the illustrated example, the position of the radially inner end of the bottom surface portion 21 is the same as that of the basic embodiment (FIG. 1), and the position of the radially outer end of the bottom surface portion 21 is positioned below the basic embodiment.

  According to this modification, since the volume of the dent part 20 can be enlarged, mixing of the fuel spray F and air in the dent part 20 can be promoted, and the generation of PM and smoke can be suppressed.

  (4) As shown in FIGS. 11 and 12, a partition wall 30 may be provided in the cavity 11. For the sake of convenience, the partition wall 30 is referred to as a cavity partition wall in distinction from the partition wall 24 described above. A plurality of cavity partition walls 30 are provided at the same circumferential position as the partition walls 24. The cavity partition wall 30 protrudes radially inward from the lip part 12 and the side wall part 13.

  In the present embodiment, the cavity partition wall 30 has a cross-sectional shape that protrudes in a substantially V shape in plan view as shown in FIG. Moreover, as shown in FIG. 12, the cavity partition 30 has the upper end surface 31 and the edge part 32 of a radial inside. The upper end surface 31 is generally at the same height as the bottom surface portion 21 of the recess 20 and is a slightly inclined surface that goes downward as it goes radially inward. The end edge portion 32 is generally slightly inclined with respect to the direction of the cylinder axis C and slightly inclined toward the radially outer side as it goes downward.

  According to this, as shown in FIG. 11, the fuel spray f that has collided with the lip portion 12 or the side wall portion 13 of the cavity 11 and bent outwardly to the left and right is indicated by the corresponding left and right cavity partition walls as indicated by arrows j. 30. Then, the collided fuel spray j can be bent rearward, that is, radially inward by the cavity partition wall 30 and directed toward the center of the cylinder.

  Therefore, like the partition wall 24, it is possible to suppress the interference and mixing of the fuel sprays j that flow opposite to each other, and it is possible to suppress the generation of a rich mixture and the generation of PM and smoke. Further, the air at the cylinder center side in the cavity 11 can be effectively utilized.

  The shape of the cavity partition wall 30 is not limited to the above-described shape, and can be changed as appropriate. The configurations of the above-described embodiments and modifications can be combined partially or wholly unless there is a particular contradiction. The embodiment of the present disclosure is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present disclosure defined by the claims. Therefore, the present disclosure should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present disclosure.

DESCRIPTION OF SYMBOLS 1 Combustion chamber structure 2 Piston 7 Fuel injection valve 8 Top surface 11 Cavity 12A Lip part top part 20 Recess part 21 Bottom part 22 End wall part 24 Partition 25 Side wall part F Fuel spray Fu Upper end edge X Spray center part arrival position Y Spray upper end Edge reaching position

Claims (5)

A reentrant cavity recessed in the center of the piston top surface;
A recess formed in the outer periphery of the top surface of the piston continuously from the cavity;
A fuel injection valve for injecting fuel toward the piston;
With
The hollow portion includes a bottom surface portion continuous with the cavity, and an end wall portion rising at a position of a radially outer end of the bottom surface portion,
The central portion of the fuel spray injected from the fuel injection valve reaches a position immediately below the top of the lip portion of the cavity, and the upper end edge of the fuel spray is connected to the bottom surface portion and the end wall portion. A combustion chamber structure of an internal combustion engine characterized by being configured to reach the position of the part. The combustion chamber structure for an internal combustion engine according to claim 1, wherein the end wall portion has an undercut shape. The fuel injection valve injects fuel radially outward from the position of the center of the cylinder,
A plurality of the depressions are provided in the circumferential direction corresponding to each of the fuel sprays injected from the fuel injection valve,
The combustion chamber structure for an internal combustion engine according to claim 1, wherein a partition wall is provided between the recesses adjacent in the circumferential direction. The hollow portion includes a side wall portion that rises at positions on both side ends in the circumferential direction of the bottom surface portion,
The combustion chamber structure of the internal combustion engine according to any one of claims 1 to 3, wherein the side wall portion has an undercut shape. The combustion chamber structure of the internal combustion engine according to any one of claims 1 to 4, wherein the hollow portion is formed in a fan shape in a plan view.

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