Combustion Chamber Structure of a Direct Injection Diesel Engine

Abstract

To provide a combustion chamber structure of a direct injection diesel which is engine more advantageous for fuel economy.SOLUTION: A combustion chamber structure 100 of a direct injection diesel engine comprises: a first rising part 102 rising upward from a bottom surface 101 of a cavity 10; a first horizontal part 103 continuing to the upper end of the first rising part 102, and extending substantially horizontally in an outer peripheral direction of the cavity 10; a second rising part 104 continuing to the first horizontal part 103, and rising upward; a second horizontal part 105 continuing to the upper end of the second rising part 104, and extending substantially horizontally in the outer peripheral direction of the cavity 10; and a third rising part 106 continuing to the second horizontal part 105, and rising upward to reach a piston top surface 9a. A combustion chamber has a first-stage combustion chamber V1, a second-stage combustion chamber V2, and a third-stage combustion chamber V3. The volume ratio of the third-stage combustion chamber V3 to the entire combustion chamber is 2% or more and 40% or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] One aspect of the present invention relates to a combustion chamber structure of a direct injection diesel engine.

Background Art

[0002] As a combustion chamber structure of a direct injection diesel engine, a structure is known in which steps are provided from a squish area to a combustion space with respect to the re-entrant type combustion chamber shape and a lip structure is provided at the combustion chamber inlet (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A combustion chamber structure more advantageous in fuel consumption is required than the combustion chamber structure described in Patent Document 1 described above.

[0005] One aspect of the present invention has been made in view of the above circumstances, and an object thereof is to provide a combustion chamber structure of a direct injection diesel engine that is more advantageous in fuel consumption.

Means for Solving the Problems

[0006] A combustion chamber structure for a direct injection diesel engine according to one aspect of the present invention is a combustion chamber structure for a direct injection diesel engine that includes a cavity recessed downward relative to the piston crown, into which fuel is injected radially from the center of the cylinder ceiling to self-ignite, comprising: a first rising portion rising upward from the bottom surface of the cavity; a first horizontal portion continuous with the upper end of the first rising portion and extending substantially horizontally in the direction of the outer circumference of the cavity; and a second rising portion continuous with the first horizontal portion and rising upward. The combustion chamber comprises a second horizontal section that is continuous with the upper end of the second rising section and extends substantially horizontally in the direction of the outer circumference of the cavity, and a third rising section that is continuous with the second horizontal section and rises upward to the top surface of the piston. The combustion chamber has a first chamber partitioned by the bottom surface of the cavity and the first rising section, a second chamber partitioned by the first horizontal section and the second rising section, and a third chamber partitioned by the second horizontal section and the third rising section, with the volume ratio of the third chamber to the total volume of the combustion chamber being 2% or more and 40% or less.

[0007] In a combustion chamber structure of a direct-injection diesel engine according to one aspect of the present invention, so-called lip portions are formed in three locations, each consisting of a rising portion (first rising portion, second rising portion, third rising portion) and a horizontal portion (first horizontal portion, second horizontal portion, piston top surface). As a result, the combustion chamber structure forms a first chamber partitioned by the bottom surface of the cavity and the first rising portion, a second chamber partitioned by the first horizontal portion and the second rising portion (the second chamber being formed on the outer circumference and above the first chamber), and a third chamber partitioned by the second horizontal portion and the third rising portion (the third chamber being formed on the outer circumference and above the second chamber). In conventional combustion chamber structures, there are only two so-called lip portions, and a combustion chamber corresponding to the third chamber of the present invention is not formed. In contrast, in the present invention, where a third chamber is formed outside and above the second chamber, the fuel spray flowing in the outer direction can reach the third rising section (vertical wall of the uppermost combustion chamber) leading to the piston crown via the third chamber, and the third chamber, which was not present in conventional designs, can be actively utilized as a space for mixing fuel spray and air. In other words, in the present invention, since a space (third chamber) for mixing fuel spray and air is formed on the outer circumference of the cavity, the opportunities for contact and reaction (combustion) between fuel and oxygen can be increased, thereby promoting combustion. Furthermore, in the present invention, by setting the volume ratio of the third chamber to the entire combustion chamber to 2% or more and 40% or less, combustion on the outer circumference of the cavity can be promoted while preventing the third chamber from becoming too large and slowing down combustion. As described above, according to one aspect of the present invention, a combustion chamber structure for a direct injection diesel engine that is more fuel-efficient can be provided.

[0008] The length of the third rising section rising above the cavity may be 3% or more and 9.5% or less of the length of the cavity bottom surface in the direction intersecting the vertical direction. By setting the length of the third rising section that partitions the third chamber in this way, it is possible to ensure a sufficient size for the third chamber and promote combustion on the outer circumference of the cavity, while also preventing the third chamber from becoming too large and slowing down combustion.

[0009] The length of the second horizontal section in the direction intersecting the vertical direction may be 10% or more and 18% or less of the length of the bottom surface of the cavity in the direction intersecting the vertical direction. By setting the length of the second horizontal section that partitions the third chamber in this way, it is possible to ensure a sufficient size for the third chamber and promote combustion on the outer periphery of the cavity, while also preventing the third chamber from becoming too large and slowing down combustion. [Effects of the Invention]

[0010] According to one aspect of the present invention, a combustion chamber structure for a direct-injection diesel engine that is more fuel-efficient can be provided. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of a diesel engine equipped with a mechanism for recirculating exhaust gases. [Figure 2] This is a schematic diagram showing the combustion chamber structure of a diesel engine. [Figure 3] This is a diagram illustrating the structure of the combustion chamber. [Figure 4] This diagram illustrates the structural differences between a two-stage lip structure and a three-stage lip structure. [Figure 5] This diagram illustrates the difference in combustion conditions between a two-stage lip structure and a three-stage lip structure. [Figure 6] This diagram illustrates the difference in combustion conditions between a two-stage lip structure and a three-stage lip structure. [Figure 7] This graph shows the relationship between the volume ratio of the third-stage combustion chamber and the effect on fuel efficiency improvement. [Modes for carrying out the invention]

[0012] The combustion chamber structure of the diesel engine according to this embodiment will be described below with reference to the drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals, and redundant explanations will be omitted.

[0013] Figure 1 is a schematic diagram of a diesel engine 1 equipped with an exhaust gas recirculation mechanism. The diesel engine 1 is a direct injection diesel engine and may employ so-called exhaust gas recirculation (EGR), for example, which reduces NOx generation by extracting a portion of the exhaust gas from the exhaust side and returning it to the respiration side, thereby suppressing the combustion of fuel in the engine and lowering the combustion temperature with the exhaust gas returned to the respiration side.

[0014] In the diesel engine 1, the exhaust passage 3 through which exhaust gas 2 flows and the intake passage 4 are connected by an EGR pipe 5. A portion of the exhaust gas 2 is recirculated along with the intake air 7 through an EGR valve 6 installed in the middle of the EGR pipe 5 and sent into the cylinder of the diesel engine 1, thereby lowering the combustion temperature in the cylinder and reducing NOx emissions.

[0015] A porous injector 8 is provided at the cylinder ceiling 11, which is the top of each cylinder of the diesel engine 1, to inject fuel (diesel oil) into the cylinder. In addition, a downward-facing cavity 10 is formed on the top surface of the piston 9, and fuel is injected radially from the tip of the injector 8 into the inner circumferential surface of the cavity 10, causing self-ignition due to the high cylinder temperature at the end of the compression stroke.

[0016] The injection operation of the injector 8 in the diesel engine 1 is controlled by a fuel injection command 8a from the control device 12, which is part of the engine control computer. The fuel injection command 8a is output to the injector 8 near top dead center of the compression stroke, causing it to inject fuel.

[0017] Furthermore, the control device 12 receives inputs such as an accelerator opening signal 13a from an accelerator sensor 13, which detects the accelerator opening as a load on the diesel engine 1, and a rotation speed signal 14a from a rotation sensor 14, which detects the engine speed of the diesel engine 1. In this way, the operating state of the diesel engine 1 is constantly monitored in order to perform various engine control operations.

[0018] As shown in FIG. 1, the diesel engine 1 includes a crankshaft 15, an exhaust port 16, an exhaust valve 17, an expiratory port 18, and an expiratory valve 19. The expiratory valve 19 and the exhaust valve 17 are opened at an appropriate timing according to the stroke of each cylinder via a push rod and a rocker arm by a cam provided on an engine-driven camshaft (not shown).

[0019] Next, referring to FIGS. 2 to 6, the combustion chamber structure 100 of the diesel engine 1 including the cavity 10 described above will be described.

[0020] As shown in FIG. 2, the combustion chamber structure 100 includes a cavity 10 that is recessed downward with respect to the piston top surface 9a, which is the top surface of the piston 9, and is a combustion chamber structure of a direct injection diesel engine that injects fuel radially from the center of the cylinder ceiling portion 11 (see FIG. 1) into the cavity 10 to cause self-ignition.

[0021] The combustion chamber structure 100 includes a first rising portion 102, a first horizontal portion 103, a second rising portion 104, a second horizontal portion 105, and a third rising portion 106.

[0022] The first rising portion 102 is a wall-like portion that rises upward from the radially outer end of the bottom surface 101 of the cavity 10, which is circular in plan view, so as to surround the bottom surface 101 (bottom). The first horizontal portion 103 is a portion that is continuous with the upper end of the first rising portion 102 and extends substantially horizontally in the outer peripheral direction (radially outward) of the cavity 10. The second rising portion 104 is a wall-like portion that is continuous with the radially outer end of the first horizontal portion 103 and rises upward. The second horizontal portion 105 is a portion that is continuous with the upper end of the second rising portion 104 and extends substantially horizontally in the outer peripheral direction (radially outward) of the cavity 10. The third rising portion 106 is a wall-like portion that is continuous with the radially outer end of the second horizontal portion 105 and rises upward. The upper end of the third rising portion 106 reaches the piston top surface 9a. The third rising portion 106 functions as a flame prevention wall for avoiding flame collision with the liner.

[0023] The first lip portion 201 is formed by the first rising portion 102 and the first horizontal portion 103. The second lip portion 202 is formed by the second rising portion 104 and the second horizontal portion 105. The third lip portion 203 is formed by the third rising portion 106 and the piston top surface 9a.

[0024] The width dimension D' (in the direction intersecting the vertical direction) of the third rising portion 106, which is a flame-preventing wall in the cavity 10, may be 95% or less of the length of the bore. Also, the length L' (length of the second horizontal portion 105 in the direction intersecting the vertical direction) of the portion of the second horizontal portion 105 that extends approximately horizontally may be 10% or more and 18% or less of the diameter d (length of the bottom surface 101 in the direction intersecting the vertical direction) of the bottom surface 101 of the cavity 10. Furthermore, the length h' of the third rising portion 106 that rises upward may be 3% or more and 9.5% or less of the diameter d of the bottom surface 101 of the cavity 10 as described above.

[0025] Figure 3 is a diagram illustrating the combustion chamber structure 100. The combustion chamber included in the combustion chamber structure 100 is composed of a first-stage combustion chamber V1 (first chamber), a second-stage combustion chamber V2 (second chamber), and a third-stage combustion chamber V3 (third chamber), as shown in Figure 3. The first-stage combustion chamber V1 is the region partitioned by the bottom surface 101 and the first rising portion 102 of the cavity 10. The second-stage combustion chamber V2 is the region partitioned by the first horizontal portion 103 and the second rising portion 104 (the region shown by the shaded area in Figure 3). The third-stage combustion chamber V3 is the region partitioned by the second horizontal portion 105 and the third rising portion 106 (the region shown by the filled area in Figure 3). The volume ratio of the third-stage combustion chamber V3 to the total volume of the combustion chamber is, for example, 2% or more and 40% or less, preferably 4% or more and 35% or less. Furthermore, the volume ratio of the combined area of ​​the second-stage combustion chamber V2 and the third-stage combustion chamber V3 to the entire combustion chamber is, for example, 50% or more and 80% or less.

[0026] As described above, the combustion chamber structure 100 according to this embodiment has three lip sections, and an additional step (third-stage combustion chamber V3) is provided in the squish area S (see Figure 1) of a conventional combustion chamber (a combustion chamber having two lip sections), and the shape of the second lip section 202, which is the lip section within the step, is offset downward by a dimension equivalent to the depth of the step. By providing the step in this way, the volume inside the cavity 10 increases, but by offsetting the position of the bottom of the cavity 10 upward by the amount of this volume increase, it is adjusted so that the volume is equivalent to that of a conventional combustion chamber. This reduces squish flow, reduces cooling loss, and improves fuel efficiency. It should be noted that if the squish flow is reduced to an extreme degree, combustion efficiency may deteriorate, but assuming that EGR is kept low, smoke can be effectively suppressed even with low squish flow. Hereinafter, a structure with only two lip sections, like a conventional combustion chamber structure, may be described as a two-stage lip structure, and a structure with three lip sections, like the combustion chamber structure 100 according to this embodiment, may be described as a three-stage lip structure.

[0027] Figure 4 illustrates the structural differences between the two-stage lip structure and the three-stage lip structure. In Figure 4, the structure around the lip portion of the cavity 10 is shown, with dashed lines representing the structure of the two-stage lip structure and solid lines representing the structure of the three-stage lip structure. As shown in Figure 4, the three-stage lip structure has three lip portions: the first lip portion 201, the second lip portion 202, and the third lip portion 203. The area that was at the same height as the piston top surface 9a in the two-stage lip structure is offset downwards to form the second horizontal portion 105. In the three-stage lip structure, the bottom of the cavity 10 is offset upwards by the volume increase due to the downward offset mentioned above, resulting in a volume equivalent to that of the two-stage lip structure.

[0028] Figure 5 illustrates the difference in combustion between a two-stage lip structure and a three-stage lip structure. In Figure 5, the left side shows the combustion of the two-stage lip structure at each crank angle (8°, 12°, 16°), and the right side shows the combustion of the three-stage lip structure at each crank angle (8°, 12°, 16°). In Figure 5, the fuel flow rate is indicated by the intensity of the color (see the legend in Figure 5). Here, the two-stage lip structure is described as being composed of a first rising section 102, a first horizontal section 103, and a second rising section 104.

[0029] As shown in the left diagram of Figure 5, in the case of a two-stage lip structure, when the crank angle is 8°, the fuel spray that collides with the inner lip is promoted to flow only upward in the upper combustion chamber, which is partitioned by the first horizontal section 103 and the second rising section 104, resulting in a squish flow, which is a vertical swirling flow. In this case, the fuel spray will only spread within the range of the swirling flow. Therefore, when the crank angle is 12°, the fuel spray has spread to only about half of the area of ​​the uppermost piston crown surface 9a. Thus, in the two-stage lip structure, there is no space on the outer circumference of the cavity 10, and combustion can be said to be the rate-limiting factor. Furthermore, when the crank angle is 16°, the fuel injected from the nozzle opening (shown densely in the figure) and the fuel that collides with the inner lip and spreads into the combustion chamber (shown lightly in the figure) interfere with each other, and the problem arises that the fuel spray hinders the use of air in the combustion chamber, worsening combustion.

[0030] On the other hand, as shown in the right-hand diagram of Figure 5, in the case of a three-stage lip structure, when the crank angle is 8°, the fuel spray that collides with the inner lip portion promotes upward flow and maintains outward flow within the upper combustion chamber partitioned by the first horizontal section 103 and the second rising section 104. This is because the three-stage lip structure ensures sufficient space on the outer circumference of the cavity 10. As a result, when the crank angle is 12°, the outward-flowing fuel spray flows radially outward within the uppermost combustion chamber and spreads until it reaches the vertical wall of the uppermost combustion chamber. The outward-flowing fuel spray is stronger in the three-stage lip structure than in the two-stage lip structure, and the vertical vortex caused by the descent of the middle combustion chamber is weaker. Therefore, the squish flow, which is a vertical swirling flow generated by the upward-flowing fuel spray, is weaker in the three-stage lip structure than in the two-stage lip structure. For this reason, the fuel spray spreads not only within the range of the squish flow but also into the area inside the combustion chamber. In this three-stage lip structure, under conditions where EGR is low and oxygen is abundant, a space is secured for the fuel spray to spread into the air and mix with it, and sufficient opportunity is secured for the fuel and oxygen to come into contact and react (combust), resulting in more active combustion and an increase in the heat generation rate (ROHR) at crank angles of 8° to 12°. Furthermore, as mentioned above, in the three-stage lip structure, the fuel spray spreads outward, so less fuel is distributed into the combustion chamber. As a result, at a crank angle of 16°, the fuel injected from the nozzle opening (shown as a dark area in the diagram) and the fuel that collides with the inner lip and spreads into the combustion chamber (shown as a light area in the diagram) are less likely to interfere with each other.

[0031] Figure 6 illustrates the difference in combustion between a two-stage lip structure and a three-stage lip structure. In Figure 6, the horizontal axis represents the crank angle, and the vertical axis represents the rate of heat generation due to combustion (ROHR). As shown in Figure 6, the three-stage lip structure is able to activate combustion more effectively compared to the two-stage lip structure when the crank angle is between 8° and 16°.

[0032] Next, the effects and advantages of the combustion chamber structure 100 of the direct injection diesel engine according to this embodiment will be described.

[0033] The combustion chamber structure 100 of the direct injection diesel engine according to this embodiment includes a cavity 10 recessed downward relative to the piston crown surface 9a, and injects fuel radially into the cavity 10 from the center of the cylinder ceiling 11 to cause self-ignition. The combustion chamber structure includes a first rising portion 102 rising upward from the bottom surface 101 of the cavity 10, a first horizontal portion 103 that is continuous with the upper end of the first rising portion 102 and extends substantially horizontally in the direction of the outer circumference of the cavity 10, a second rising portion 104 that is continuous with the first horizontal portion 103 and rises upward, and the upper part of the second rising portion 104 The combustion chamber comprises a second horizontal section 105 that is continuous with the end and extends substantially horizontally in the direction of the outer circumference of the cavity 10, and a third rising section 106 that is continuous with the second horizontal section 105 and rises upward to the piston top surface 9a. The combustion chamber has a first-stage combustion chamber V1 partitioned by the bottom surface 101 of the cavity 10 and the first rising section 102, a second-stage combustion chamber V2 partitioned by the first horizontal section 103 and the second rising section 104, and a third-stage combustion chamber V3 partitioned by the second horizontal section 105 and the third rising section 106. The volume ratio of the third-stage combustion chamber V3 to the total volume of the combustion chamber is 2% or more and 40% or less.

[0034] In the combustion chamber structure 100 of the direct-injection diesel engine according to this embodiment, so-called lip portions are formed in three locations, each consisting of a rising portion (first rising portion 102, second rising portion 104, third rising portion 106) and a horizontal portion (first horizontal portion 103, second horizontal portion 105, piston crown surface 9a). As a result, the combustion chamber structure forms a first-stage combustion chamber V1 partitioned by the bottom surface 101 of the cavity 10 and the first rising portion 102, a second-stage combustion chamber V2 partitioned by the first horizontal portion 103 and the second rising portion 104, and a third-stage combustion chamber V3 partitioned by the second horizontal portion 105 and the third rising portion 106. In conventional combustion chamber structures, there are only two so-called lip portions, and a combustion chamber corresponding to the third-stage combustion chamber V3 of this embodiment is not formed. In contrast, in the configuration according to this embodiment, where the third-stage combustion chamber V3 is formed outside and above the second-stage combustion chamber V2, the fuel spray flowing in the outer direction can reach the third rising portion 106 (vertical wall of the uppermost combustion chamber) that reaches the piston crown surface 9a via the third-stage combustion chamber V3, and the third-stage combustion chamber V3, which was not conventionally configured, can be actively utilized as a space for mixing fuel spray and air. In other words, in the configuration according to this embodiment, a space for mixing fuel spray and air (third-stage combustion chamber V3) is formed on the outer circumference side of the cavity 10, which increases the opportunities for fuel and oxygen to come into contact and react (combust), thereby promoting combustion. Furthermore, in the configuration according to this embodiment, by setting the volume ratio of the third-stage combustion chamber V3 to the total combustion chamber to 2% or more and 40% or less, it is possible to promote combustion on the outer circumference side of the cavity 10 while suppressing the third-stage combustion chamber V3 from becoming too large and slowing down combustion. As described above, the combustion chamber structure 100 according to this embodiment can provide a combustion chamber structure for a direct injection diesel engine that is more fuel-efficient.

[0035] Figure 7 is a graph showing the relationship between the volume ratio of the third-stage combustion chamber V3 and the fuel efficiency improvement effect. In Figure 7, the horizontal axis shows the volume ratio of the third-stage combustion chamber V3 to the entire combustion chamber, and the vertical axis shows fuel consumption (i.e., fuel efficiency improvement effect). A volume ratio of the third-stage combustion chamber V3 of 0 (horizontal axis of 0) means that there is no third-stage combustion chamber V3, which corresponds to a configuration with a conventional two-stage lip structure. Using this state as a baseline, a state where fuel consumption is lower than when the volume ratio of the third-stage combustion chamber V3 is 0 indicates improved fuel efficiency, and a state where fuel consumption is higher indicates worsened fuel efficiency.

[0036] As shown in Figure 7, when the volume ratio of the third-stage combustion chamber V3 is around 2-3%, a reduction in fuel consumption (improved fuel efficiency) is observed, and when the volume ratio of the third-stage combustion chamber V3 is around 4%, the reduction in fuel consumption (improved fuel efficiency) becomes clearly apparent. Furthermore, when the volume ratio of the third-stage combustion chamber V3 is increased, fuel efficiency improves as the volume ratio of the third-stage combustion chamber V3 increases up to around 8%. Further increasing the volume ratio of the third-stage combustion chamber V3 up to around 8-11% does not significantly increase or decrease fuel consumption. Further increasing the volume ratio of the third-stage combustion chamber V3, a fuel efficiency improvement effect is observed up to around 35% of the third-stage combustion chamber V3, and at around 40% of the third-stage combustion chamber V3, fuel consumption becomes similar to the standard (volume ratio of the third-stage combustion chamber V3 is 0). If the volume ratio of the third-stage combustion chamber V3 exceeds 40%, fuel consumption will increase above the standard, and fuel efficiency will worsen. Thus, regarding the volume ratio of the third-stage combustion chamber V3, increasing it to a certain extent will increase the space for mixing air and fuel, improving fuel efficiency. However, if it is increased too much, combustion will slow down, and the effect of improving fuel efficiency will be reduced.

[0037] The length of the third rising portion 106 rising above may be 3% or more and 9.5% or less of the length of the bottom surface 101 of the cavity 10 in the direction intersecting the vertical direction. By setting the length of the third rising portion 106 that partitions the third stage combustion chamber V3 in this way, it is possible to ensure a sufficient size for the third stage combustion chamber V3 and promote combustion on the outer circumference side of the cavity 10, while also preventing the third stage combustion chamber V3 from becoming too large and slowing down combustion.

[0038] The length of the second horizontal section 105 in the direction intersecting the vertical direction may be 10% or more and 18% or less of the length of the bottom surface 101 of the cavity 10 in the direction intersecting the vertical direction. By setting the length of the second horizontal section 105 that partitions the third-stage combustion chamber V3 in this way, it is possible to ensure a sufficient size for the third-stage combustion chamber V3 and promote combustion on the outer circumference side of the cavity 10, while also preventing the third-stage combustion chamber V3 from becoming too large and slowing down combustion. [Explanation of Symbols]

[0039] 1...Diesel engine, 9a...Piston crown, 10...Cavity, 11...Cylinder ceiling, 100...Combustion chamber structure, 101...Bottom, 102...First rising section, 103...First horizontal section, 104...Second rising section, 105...Second horizontal section, 106...Third rising section, V1...First stage combustion chamber (first chamber), V2...Second stage combustion chamber (second chamber), V3...Third stage combustion chamber.

Claims

1. A combustion chamber structure of a direct injection diesel engine having a cavity recessed downward from a piston top surface, in which fuel is injected radially from the center of a cylinder ceiling into the cavity to cause self-ignition, a first rising portion rising upward from the bottom surface of the cavity; a first horizontal portion that is continuous with an upper end of the first rising portion and extends substantially horizontally in a circumferential direction of the cavity; a second rising portion that is continuous with the first horizontal portion and rises upward; a second horizontal portion that is continuous with an upper end of the second rising portion and extends substantially horizontally in the outer circumferential direction of the cavity; a third rising portion that is continuous with the second horizontal portion and rises upward to reach the piston top surface, The combustion chamber is a first chamber defined by a bottom surface of the cavity and the first raised portion; a second chamber defined by the first horizontal portion and the second rising portion; a third chamber defined by the second horizontal portion and the third rising portion, A combustion chamber structure for a direct injection diesel engine, wherein the volume ratio of the third chamber to the entire combustion chamber is 2% or more and 40% or less.

2. 2. A combustion chamber structure for a direct injection diesel engine according to claim 1, wherein the upwardly rising length of the third rising portion is 3% or more and 9.5% or less of the length of the bottom surface of the cavity in a direction intersecting the vertical direction.

3. 3. A combustion chamber structure for a direct injection diesel engine according to claim 1, wherein the length of the second horizontal portion in a direction intersecting the vertical direction is 10% or more and 18% or less of the length of the bottom surface of the cavity in the direction intersecting the vertical direction.

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