Combustion chamber structure

Abstract

To provide a combustion chamber structure that can activate combustion more than before.SOLUTION: A combustion chamber structure 100 includes: a cavity 10 recessed downward relative to a piston top surface; an injector 8 for jetting fuel radially into the cavity 10 and causing the fuel to self-ignite; and a passage part 20 having a first opening 21a that is open toward a bottom surface 101 of the cavity 10 and extending so as to be capable of storing air therein.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] One aspect of the present invention relates to a combustion chamber structure. [Background technology]

[0002] A known combustion chamber structure for a direct injection diesel engine has a reentrant combustion chamber shape, in which a step is provided from the squish area to the combustion space 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] Patent No. 4906055 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for a combustion chamber structure that can further activate combustion compared to the combustion chamber structure described in the above-mentioned Patent Document 1.

[0005] One aspect of the present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a combustion chamber structure that can further activate combustion. [Means for solving the problem]

[0006] A combustion chamber structure according to one embodiment of the present invention includes a cavity recessed downward relative to a piston top surface, an injector that radially injects fuel into the cavity to cause self-ignition, and a passage portion that has a first opening that opens toward the bottom of the cavity and extends to allow air to be stored.

[0007] In the combustion chamber structure of the engine according to one aspect of the present invention, the passage portion having the first opening portion opening toward the bottom of the cavity extends to an extent that air can be stored. In this configuration, during the compression stroke of the engine, fresh air flows into the passage portion from the first opening portion opening toward the bottom of the cavity. Then, when the pressure becomes equal to or lower than the compression pressure during the expansion stroke, the air stored in the passage portion is discharged from the first opening portion to the bottom of the cavity due to the pressure difference. In general, during the expansion stroke (later half of combustion), the amount of air tends to be small, particularly at the bottom of the cavity. That is, during the expansion stroke, the combustion is not likely to be active, particularly near the bottom of the cavity, and the flame is likely to stagnate. In this regard, in the combustion chamber structure of the engine according to one aspect of the present invention, during the expansion stroke, the air previously stored in the passage portion is discharged from the first opening portion to the bottom of the cavity, so that the afterburning combustion near the bottom of the cavity can be activated. As described above, according to one aspect of the present invention, a combustion chamber structure capable of further activating combustion can be provided.

[0008] The passage portion has a first communication passage having a first opening, and a second communication passage having a second opening that is continuous with the first communication passage and opens toward the squish area located above the cavity. In this way, the passage portion is composed of the first communication passage and the second communication passage, and the first communication passage and the second communication passage have sufficient lengths such that the second opening opens toward the squish area, so that a sufficient amount of air can be stored in the passage portion. Furthermore, since the first communication passage has the first opening, and the second communication passage has the second opening, and both ends of the passage portion are configured to be penetrated, it is possible to more easily store air in the passage portion during the compression stroke.

[0009] The first and second communication passages may have the same diameter, and this configuration allows air to pass through the passage more easily, making it easier to store air in the passage.

[0010] The location where the first communication passage and the second communication passage are connected to each other may be located below the bottom of the cavity. With this configuration, air accumulated in the passage can be more reliably discharged to the bottom of the cavity.

[0011] The second opening may be provided so as to avoid an axis of a fuel injection direction of the injector when viewed from above. With this configuration, it is possible to prevent a flame from flowing into the passage from the second opening.

[0012] The first communication passage may extend in a direction along a swirl flow, which is a swirling flow around the cylinder axis, in a top view, and the first opening may be provided in a direction not facing the swirl flow in a top view. With this configuration, it is possible to prevent a flame (a flame flowing along the swirl flow) from flowing into the passage from the first opening.

[0013] The first communication passage may extend in a direction along the flow of the flame in the vertical cross section, and the first opening may be provided in a direction not facing the flow of the flame in the vertical cross section. With this configuration, it is possible to prevent the flame from flowing into the passage from the first opening.

[0014] The combustion chamber structure may include a plurality of passages each having a first communication passage and a second communication passage. With such a configuration, the passages can be used to store and discharge air more effectively, and combustion can be more activated.

[0015] The combustion chamber structure may further include a connecting passage that connects the plurality of passages together. By providing such a connecting passage, a buffer portion for storing air can be provided, and the air can be stored and discharged more effectively, thereby activating combustion. Effect of the Invention

[0016] According to one aspect of the present invention, it is possible to provide a combustion chamber structure that can further activate combustion. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram of a diesel engine equipped with an exhaust gas recirculation mechanism. [Diagram 2] FIG. 2 is a perspective view that illustrates a combustion chamber structure of a diesel engine. [Diagram 3] FIG. 3 is a plan view that illustrates a schematic diagram of the combustion chamber structure. [Figure 4] FIG. 4(a) is a plan view showing the fuel injection state, and FIG. 4(b) is a vertical sectional view showing the fuel injection state. [Diagram 5] FIG. 5(a) is a vertical cross-sectional view showing the inflow of fresh air during the compression stroke, FIG. 5(b) is a vertical cross-sectional view showing the discharge of air during the expansion stroke, and FIG. 5(c) is a vertical cross-sectional view explaining the combustion state. [Figure 6] FIG. 6(a) is a graph showing the results of a simulation showing the difference in heat generation rate depending on whether or not there is a passage portion, and FIG. 6(b) is an enlarged view of a part of FIG. 6(a). [Figure 7] FIG. 7(a) is a diagram showing the simulation results showing the air flow velocity when there is no passage portion, and FIG. 7(b) is a diagram showing the simulation results showing the air flow velocity when there is a passage portion. [Figure 8] Figures 8(a) and (b) are graphs showing the results of an actual machine, showing the difference between having and not having a passage. [Figure 9] FIG. 9(a) is a plan view showing a combustion chamber structure according to a modified example, and FIG. 9(b) is a vertical cross-sectional view showing a passage portion according to the modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, a combustion chamber structure of a diesel engine according to an embodiment will be described with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference numerals, and duplicated description will be omitted.

[0019] 1 is a schematic diagram of a diesel engine 1 equipped with a mechanism for recirculating exhaust gas. The diesel engine 1 is a direct injection diesel engine, and may be, for example, an engine that employs so-called exhaust gas recirculation (EGR), in which a portion of the exhaust gas from the exhaust side is extracted and returned to the intake side, and the exhaust gas returned to the intake side is used to suppress the combustion of fuel in the engine, lowering the combustion temperature and reducing the generation of NOx.

[0020] In the diesel engine 1, an exhaust passage 3 through which exhaust gas 2 flows is connected to an intake passage 4 by an EGR pipe 5. A part of the exhaust gas 2 is recirculated together with intake air 7 via an EGR valve 6 provided in the middle of the EGR pipe 5 and sent into the cylinders of the diesel engine 1, thereby lowering the combustion temperature in the cylinders and reducing NOx.

[0021] A multi-hole injector 8 that injects fuel (diesel) into each cylinder is provided on a cylinder ceiling 11, which is the ceiling of each cylinder of the diesel engine 1. A cavity 10 that is recessed downward is formed on the top surface of the piston 9, and fuel is injected radially from the tip of the injector 8 onto the inner peripheral surface of the cavity 10, and self-ignites due to the high in-cylinder temperature at the end of the compression stroke. In this way, the injector 8 is configured to radially inject fuel into the cavity 10 to cause self-ignition. Note that the shape of the cavity 10 is depicted in a simplified form in FIG. 1.

[0022] The injection operation of the injector 8 in the diesel engine 1 is controlled by a fuel injection command 8a from a control device 12, which constitutes an engine control computer, and the fuel injection command 8a is output to the injector 8 near the top dead center of the compression stroke to cause the injector 8 to inject fuel.

[0023] Further, the control device 12 receives an accelerator opening signal 13a from an accelerator sensor 13 that detects the accelerator opening as a load on the diesel engine 1, a revolution speed signal 14a from a revolution sensor 14 that detects the engine revolution speed of the diesel engine 1, and the like. In this manner, the operating state of the diesel engine 1 is constantly monitored to execute various engine controls.

[0024] 1, the diesel engine 1 includes a crankshaft 15, an exhaust port 16, an exhaust valve 17, an exhalation port 18, and an exhalation valve 19. The exhalation valve 19 and the exhaust valve 17 are opened and closed at appropriate timing according to the stroke of each cylinder via a push rod or a rocker arm by a cam provided on a camshaft driven by the engine (not shown).

[0025] Fig. 2 is a perspective view that shows a combustion chamber structure 100 of a diesel engine 1 including the above-mentioned cavity 10. Fig. 3 is a plan view that shows the combustion chamber structure 100. As shown in Figs. 2 and 3, the combustion chamber structure 100 is formed in a bottomless cylindrical shape. The combustion chamber structure 100 is a combustion chamber structure of a direct injection diesel engine that includes a cavity 10 that is recessed downward with respect to a piston top surface 9a (see Fig. 1), which is the top surface of a piston 9 (see Fig. 1), and an injector 8 that radially injects fuel from the center of a cylinder ceiling portion 11 (see Fig. 1) into the cavity 10 to cause self-ignition.

[0026] 2 and 3, the combustion chamber structure 100 includes a plurality of (eight here) passage sections 20, 20, 20, 20, 20, 20, 20, 20. The passage sections 20, 20, 20, 20, 20, 20, 20, 20 are arranged at regular intervals in the circumferential direction of the combustion chamber structure 100. Here, the passage sections 20, 20, 20, 20, 20, 20, 20, 20 are described as having a common configuration, but may have different configurations.

[0027] The passage section 20 has a first opening 21a that opens toward the bottom surface 101 (bottom) of the cavity 10, and is a cylindrical air flow path that extends so as to be able to store air. The passage section 20 has a first communication passage 21 that has the first opening 21a, and a second communication passage 22 that is continuous with the first communication passage 21 and has a second opening 22a that opens toward the squish area S located above the cavity 10.

[0028] The first communication passage 21 and the second communication passage 22 are both cylindrical air passages and have the same diameter. The portion where the first communication passage 21 and the second communication passage 22 are connected to each other (connected portion 25) is located below the bottom surface 101 of the cavity 10, as shown in FIG. 4(b). The first communication passage 21 extends along the circumferential direction of the combustion chamber structure 100, and extends upward from the connected portion 25 toward the first opening 21a. More specifically, the first communication passage 21 extends in a direction (circumferential direction) along a swirl flow, which is a swirling flow around the cylinder axis, in the top view shown in FIG. 3 (details will be described later). The first opening 21a opens toward the bottom surface 101 at a position connected to the bottom surface 101 of the cavity 10, as shown in FIG. 4(b). The second communication passage 22 extends radially outward and upward from the continuous portion 25 toward the second opening 22a of the combustion chamber structure 100. The second opening 22a opens toward the squish area S at a position continuous with the squish area S.

[0029] Fig. 4(a) is a plan view showing the fuel injection state, and Fig. 4(b) is a vertical cross-sectional view showing the fuel injection state. Fig. 4(a) and Fig. 4(b) show only a part of the combustion chamber structure 100, and for example, Fig. 4(b) shows only about half of the structure of the cavity 10. As shown in Fig. 4(b), the cavity 10 is configured to include a bottom surface 101, a first rising portion 102, a first horizontal portion 103, a second rising portion 104, and a second horizontal portion 105.

[0030] The first rising portion 102 is a wall-like portion rising upward from the radial outer end of the bottom surface 101 so as to surround the bottom surface 101 of the cavity 10, which is circular in plan view. The first horizontal portion 103 is a portion that is continuous with the upper end of the first rising portion 102 and extends approximately horizontally in the outer circumferential direction (radial outer side) of the cavity 10. The second rising portion 104 is a wall-like portion that is continuous with the radial 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 approximately horizontally in the outer circumferential direction (radial outer side) of the cavity 10. The first rising portion 102 and the first horizontal portion 103 form a first lip portion 201. The second rising portion 104 and the second horizontal portion 105 form a second lip portion 202. The above-mentioned second communication passage 22 extends along the first rising portion 102 and the second rising portion 104 on the radially outer side of the first rising portion 102 and the second rising portion 104, as shown in FIG. 4(b).

[0031] As shown in Fig. 4(a), the second opening 22a of the second communication passage 22 is provided so as to avoid being on the injection direction axis SH of the fuel by the injector 8 in top view. The flow of the flame F is formed along the injection direction axis SH. Also, as shown in Fig. 4(a), the first communication passage 21 extends in a direction along the swirl flow SW, which is a swirling flow around the cylinder axis, that is, in a direction along the circumferential direction of the combustion chamber structure 100 in top view. And the first opening 21a is provided in a direction not facing the swirl flow SW in top view.

[0032] 4(b), the flame F collides with the first rising portion 102 and the like, and flows toward the injector 8 in a turning-back manner as indicated by the arrow in the figure. The first communication passage 21 extends in a direction along the flow of such flame F (the flow that collides with the first rising portion 102 and turns back) in the vertical cross section shown in FIG. 4(b). The first opening 21a is provided in a direction that does not face such a flow of flame F.

[0033] FIG. 5(a) is a vertical cross-sectional view showing the inflow of fresh air during the compression stroke, FIG. 5(b) is a vertical cross-sectional view showing the discharge of air during the expansion stroke, and FIG. 5(c) is a vertical cross-sectional view explaining the combustion state. As shown in FIG. 5(a), during the compression stroke of the engine, air AR (fresh air) flows into the first communication passage 21 of the passage section 20 from the first opening 21a opening toward the bottom surface 101 of the cavity 10. As a result, the air AR is stored in the first communication passage 21 and the second communication passage 22. Then, during the expansion stroke of the engine, when the pressure in the first communication passage 21 and the second communication passage 22 becomes equal to or lower than the compression pressure, the air AR is discharged from the first opening 21a to the bottom surface 101 of the cavity 10 due to the pressure difference, as shown in FIG. 5(b). The bottom surface 101 of the cavity 10 is prone to retaining flame F as shown in FIG. 5(c), and there may be little air and an inactive area 500. By discharging the air AR stored in advance into such an inactive area 500, the combustion in the inactive area 500 can be activated.

[0034] Fig. 6(a) is a graph of the simulation results showing the difference in heat generation rate depending on whether or not the passage portion 20 is present, and Fig. 6(b) is a partially enlarged view of Fig. 6(a). In Fig. 6, the horizontal axis indicates the crank angle, the left vertical axis indicates the pressure, and the right vertical axis indicates the heat generation rate, with the solid line indicating the result when the passage portion 20 is present and the dashed line indicating the result when the passage portion 20 is not present. In Fig. 6(a), the upper curve indicates the pressure in the passage portion 20, and the lower curve indicates the heat generation rate. As shown in Fig. 6(b), the simulation results show that the presence of the passage portion 20 improves the heat generation rate.

[0035] Fig. 7(a) is a diagram showing a simulation result showing the air flow velocity in the case where there is no passage portion 20, and Fig. 7(b) is a diagram showing a simulation result showing the air flow velocity in the case where there is a passage portion 20. As shown in the enlarged view of Fig. 7(b), in the case where there is a passage portion 20, it can be seen that the air velocity distribution can be seen due to the passage portion 20.

[0036] 8(a) and (b) are graphs of the results of an actual machine (single-cylinder engine) showing the difference depending on whether or not there is a passage portion 20. In FIG. 8(a), the horizontal axis indicates the crank angle, the left vertical axis indicates the pressure, and the right vertical axis indicates the heat generation rate, with the solid line indicating the result when there is a passage portion 20 and the dashed line indicating the result when there is no passage portion 20. In addition, in FIG. 8(a), the upper curve indicates the pressure in the passage portion 20, and the lower curve indicates the heat generation rate. As shown in FIG. 8(a), the presence of the passage portion 20 in the actual machine also allowed the heat generation rate to be improved. In FIG. 8(b), the horizontal axis indicates the amount of NOx, and the vertical axis indicates the amount of smoke. As shown in FIG. 8(b), the presence of the passage portion 20 allowed the smoke to be reduced.

[0037] The effects of the engine combustion chamber structure 100 according to this embodiment will be described.

[0038] The combustion chamber structure 100 of this embodiment comprises a cavity 10 recessed downward relative to the piston top surface, an injector 8 that radially injects fuel into the cavity 10 to cause self-ignition, and a passage portion 20 that has a first opening 21a that opens toward the bottom surface 101 of the cavity 10 and extends so as to be capable of storing air.

[0039] In the combustion chamber structure 100 of the engine according to the present embodiment, the passage section 20 having the first opening 21a opening toward the bottom surface 101 of the cavity 10 extends to an extent that allows air to be stored. In such a configuration, during the compression stroke of the engine, fresh air flows into the passage section 20 from the first opening 21a opening toward the bottom surface 101 of the cavity 10. Then, when the pressure becomes equal to or lower than the compression pressure during the expansion stroke, the air stored in the passage section 20 is discharged from the first opening 21a to the bottom surface 101 of the cavity 10 due to the pressure difference. In general, air tends to be scarce during the expansion stroke (later combustion), and air tends to be scarce at the bottom surface 101 of the cavity 10 in particular. That is, during the expansion stroke, combustion is less likely to be active, particularly near the bottom surface 101 of the cavity 10, and flames tend to stagnate. In this regard, in the combustion chamber structure 100 of the engine according to this embodiment, air that has been stored in advance in the passage portion 20 is discharged from the first opening 21a to the bottom surface 101 of the cavity 10 during the expansion stroke, so that it is possible to activate afterburning combustion near the bottom surface 101 of the cavity 10. As described above, according to this embodiment, it is possible to provide a combustion chamber structure 100 that can further activate combustion.

[0040] The passage section 20 may have a first communication passage 21 having a first opening 21a, and a second communication passage 22 having a second opening 22a that is continuous with the first communication passage 21 and opens toward the squish area S located above the cavity 10. In this way, the passage section 20 is composed of the first communication passage 21 and the second communication passage 22, and the first communication passage 21 and the second communication passage 22 have a sufficient length such that the second opening 22a opens toward the squish area S, so that a sufficient amount of air can be stored in the passage section 20. In addition, the first communication passage 21 has the first opening 21a, and the second communication passage 22 has the second opening 22a, and both ends of the passage section 20 are configured to be penetrated, so that air can be more easily stored in the passage section 20 during the compression stroke.

[0041] The diameters of the first communication passage 21 and the second communication passage 22 may be the same. With such a configuration, air can easily pass through the passage portion 20, and air can be more easily stored in the passage portion 20.

[0042] The location where the first communication passage 21 and the second communication passage 22 are continuous with each other may be located below the bottom surface 101 of the cavity 10. With this configuration, the air accumulated in the passage portion 20 can be discharged to the bottom surface 101 of the cavity 10 more reliably.

[0043] The second opening 22a may be provided, in a top view, so as to avoid being positioned on the axis SH of the fuel injection direction of the injector 8. With this configuration, it is possible to prevent a flame from flowing into the passage portion 20 from the second opening 22a.

[0044] The first communication passage 21 extends in a direction along the swirl flow SW, which is a swirling flow around the cylinder axis, in a top view, and the first opening 21a may be provided in a direction not facing the swirl flow SW in a top view. With this configuration, it is possible to suppress the inflow of flame (flame flowing along the swirl flow SW) from the first opening 21a into the passage portion 20.

[0045] The first communication passage 21 extends in a direction along the flow of the flame in the vertical cross section, and the first opening 21a may be provided in a direction not facing the flow of the flame in the vertical cross section. With this configuration, it is possible to prevent the flame from flowing into the passage portion 20 from the first opening 21a.

[0046] The combustion chamber structure 100 may include a plurality of passage sections 20 each having a first communication passage 21 and a second communication passage 22. According to such a configuration, the air can be stored and discharged more effectively using the passage sections 20, and combustion can be more activated.

[0047] Although the configuration according to this embodiment has been described above, the present invention is not limited to the above embodiment. FIG. 9(a) is a plan view showing a combustion chamber structure according to a modified example, and FIG. 9(b) is a vertical cross-sectional view showing a passage section according to the modified example. As shown in FIG. 9(a) and (b), in the configuration according to the modified example, a connecting section 700 for connecting each passage section 20 is further provided. The connecting section 700 is provided in a ring shape so as to connect the holes of all the passage sections 20. By providing such a connecting section 700, a buffer section for storing air can be provided, and the air can be stored and discharged more effectively, thereby activating combustion more. [Explanation of symbols]

[0048] 1... diesel engine, 8... injector, 10... cavity, 20... passage portion, 21... first communication passage, 21a... first opening, 22... second communication passage, 22a... second opening, 100... combustion chamber structure, 101... bottom surface (bottom portion), 700... connecting portion, S... squish area, SH... injection direction axis, SW... swirl flow.

Claims

1. A cavity recessed downward relative to the piston top surface; an injector for radially injecting fuel into the cavity to cause self-ignition; a passage portion having a first opening portion that opens toward a bottom portion of the cavity and extending so as to be capable of storing air.

2. 2. The combustion chamber structure according to claim 1, wherein the passage portion includes a first communication passage having the first opening, and a second communication passage having a second opening that is continuous with the first communication passage and opens toward a squish area located above the cavity.

3. The combustion chamber structure according to claim 2 , wherein the first communication passage and the second communication passage have the same diameter.

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