JP2023006979A - Combustion Chamber Structure of Direct Injection Diesel Engine - Google Patents

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

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

As a combustion chamber structure of a direct-injection diesel engine, there is known a structure in which a step is provided from a squish area to a combustion space and a lip structure is provided at the entrance of the combustion chamber, in contrast to a reentrant combustion chamber shape (see, for example, Patent Document 1).

Patent No. 4906055

There is a demand for a combustion chamber structure that is more advantageous in terms of fuel consumption than the combustion chamber structure described in Patent Document 1 mentioned above.

SUMMARY OF THE INVENTION It is an object of one aspect of the present invention to provide a combustion chamber structure for a direct-injection diesel engine that is more advantageous in terms of fuel efficiency.

A combustion chamber structure for a direct-injection diesel engine according to one aspect of the present invention includes a cavity recessed downward with respect to the top surface of a piston, and fuel is radially injected into the cavity from the center of the cylinder ceiling to A combustion chamber structure for a direct-injection diesel engine for ignition, comprising: a first rising portion rising upward from the bottom surface of the cavity; a second rising portion continuous with the first horizontal portion and rising upward; a second horizontal portion continuous with the upper end of the second rising portion and extending substantially horizontally in the outer peripheral direction of the cavity; and a third rising portion that rises upward and reaches the top surface of the piston, and the combustion chamber includes a first chamber defined by the bottom surface of the cavity and the first rising portion, and a first horizontal portion and a second rising portion. and a third chamber defined by the second horizontal portion and the third rising portion, and the volume ratio of the third chamber to the entire combustion chamber is 2% or more and 40 % or less.

In the combustion chamber structure of a direct injection diesel engine according to one aspect of the present invention, the rising portion (first rising portion, second rising portion, third rising portion) and horizontal portions (first horizontal portion, second horizontal portion, piston The so-called lip portions are formed at three locations. Therefore, as the structure of the combustion chamber, the first chamber defined by the bottom surface of the cavity and the first rising portion, the second chamber defined by the first horizontal portion and the second rising portion (the outer peripheral side and above the first chamber) and a third chamber (a third chamber formed on the outer peripheral side and above the second chamber) partitioned by the second horizontal portion and the third rising portion. becomes. In the conventional combustion chamber structure, there are only two so-called lip portions, and a combustion chamber corresponding to the third chamber of the present invention is not formed. On the other hand, in the configuration in which the third chamber is formed outside and above the second chamber as in the present invention, the fuel spray flowing in the outer peripheral direction reaches the top surface of the piston via the third chamber. The third rising portion (the vertical wall of the uppermost combustion chamber) can be reached, and the third chamber, which has not been constructed in the past, can be actively used as a space where fuel spray and air are mixed. . That is, in the present invention, since the space (third chamber) where fuel spray and air are mixed is formed on the outer peripheral side of the cavity, the chances of contact and reaction (combustion) between fuel and oxygen are increased, and combustion is enhanced. can be promoted. In the present invention, the volume ratio of the third chamber to the entire combustion chamber is 2% or more and 40% or less. Slow combustion can also be suppressed. As described above, according to one aspect of the present invention, it is possible to provide a combustion chamber structure for a direct-injection diesel engine that is more advantageous in terms of fuel efficiency.

The upwardly rising length of the third rising portion may be 3% or more and 9.5% or less of the length of the bottom surface of the cavity in the direction crossing the vertical direction. In this way, by setting the length of the third rising portion that defines the third chamber, the third chamber is sufficiently large in size to promote combustion on the outer peripheral side of the cavity. It is also possible to suppress slow combustion due to excessive increase in .

The length of the second horizontal portion 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 portion that defines the third chamber in this manner, the third chamber is sufficiently large in size to promote combustion on the outer peripheral side of the cavity while the third chamber is It is also possible to suppress slow combustion due to excessive increase in .

According to one aspect of the present invention, it is possible to provide a combustion chamber structure for a direct-injection diesel engine that is more advantageous in terms of fuel efficiency.

1 is a schematic diagram of a diesel engine with an exhaust gas recirculation mechanism; FIG. It is a figure which shows typically the combustion-chamber structure of a diesel engine. It is a figure explaining a combustion chamber structure. It is a figure explaining the structural difference between a two-stage lip structure and a three-stage lip structure. FIG. 4 is a diagram for explaining the difference in combustion state between the two-stage lip structure and the three-stage lip structure; FIG. 4 is a diagram for explaining the difference in combustion state between the two-stage lip structure and the three-stage lip structure; It is a graph which shows the relationship between the volume ratio of a 3rd-stage combustion chamber, and a fuel consumption improvement effect.

A combustion chamber structure of a diesel engine according to an embodiment will be described below with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference numerals, and overlapping descriptions are omitted.

FIG. 1 is a schematic diagram of a diesel engine 1 with an exhaust gas recirculation mechanism. The diesel engine 1 is a direct-injection diesel engine. For example, part of the exhaust gas from the exhaust side is extracted and returned to the expiration side, and the exhaust gas returned to the expiration side suppresses combustion of fuel in the engine. A so-called exhaust gas recirculation (EGR) system may be used, which reduces the generation of NOx by lowering the combustion temperature.

In the diesel engine 1, an exhaust passage 3 through which the exhaust gas 2 flows and an exhalation passage 4 are connected by an EGR pipe 5, and the exhaust gas 2 is released through an EGR valve 6 provided in the middle of the EGR pipe 5. A part of it is recirculated together with the intake air 7 and sent into the cylinder of the diesel engine 1 to lower the combustion temperature in the cylinder and reduce NOx.

A cylinder ceiling portion 11, which is the ceiling portion of each cylinder of the diesel engine 1, is provided with a perforated injector 8 for injecting fuel (light oil) into the cylinder. In addition, a cavity 10 is formed on the top surface of the piston 9 and is recessed downward, and fuel is radially injected from the tip of the injector 8 against the inner peripheral surface of the cavity 10, thereby increasing the cylinder pressure at the end of the compression stroke. It self-ignites depending on the internal temperature.

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 that constitutes an engine control computer. It is designed to output and inject fuel.

The controller 12 also receives an accelerator opening signal 13a from an accelerator sensor 13 that detects the accelerator opening as a load on the diesel engine 1, and a rotation speed signal from a rotation sensor 14 that detects the engine speed of the diesel engine 1. 14a etc. are input. In this manner, the operating state of the diesel engine 1 is constantly monitored in order to execute various engine controls.

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, as shown in FIG. The exhalation valve 19 and the exhaust valve 17 are opened at an appropriate timing corresponding to the stroke of each cylinder via a push rod or a rocker arm by a cam provided on an engine-driven camshaft (not shown). there is

Next, a combustion chamber structure 100 of the diesel engine 1 including the cavity 10 described above will be described with reference to FIGS. 2 to 6. FIG.

As shown in FIG. 2, the combustion chamber structure 100 includes a cavity 10 recessed downward with respect to the piston top surface 9a, which is the top surface of the piston 9. ) is the combustion chamber structure of a direct-injection diesel engine in which fuel is injected radially from the center to cause self-ignition.

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

The first rising portion 102 is a wall-shaped portion that rises upward from the radial outer end of the bottom surface 101 so as to surround the bottom surface 101 (bottom portion) of the cavity 10 that is circular in plan view. The first horizontal portion 103 is a portion that continues to the upper end of the first rising portion 102 and extends substantially horizontally in the outer peripheral direction (outside in the radial direction) of the cavity 10 . The second rising portion 104 is a wall-shaped portion that continues to the radially outer end of the first horizontal portion 103 and rises upward. The second horizontal portion 105 is a portion that continues to the upper end of the second rising portion 104 and extends substantially horizontally in the outer peripheral direction (outside in the radial direction) of the cavity 10 . The third rising portion 106 is a wall-shaped portion that continues to 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 riser 106 functions as a flame barrier to avoid flame impingement on the liner.

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

The width dimension D' (in the direction crossing the vertical direction) of the third raised portion 106, which is the flame barrier in the cavity 10, may be 95% or less of the length of the bore. In addition, the length L′ of the substantially horizontally extending portion of the second horizontal portion 105 (the length of the second horizontal portion 105 in the direction intersecting the vertical direction) is equal to the diameter d of the bottom surface 101 of the cavity 10 (the length intersecting the vertical direction). 10% or more and 18% or less of the length of the bottom surface 101 in the direction in which the Moreover, the length h′ of the third rising portion 106 rising upward may be 3% or more and 9.5% or less of the diameter d of the bottom surface 101 of the cavity 10 described above.

FIG. 3 is a diagram illustrating the combustion chamber structure 100. FIG. The combustion chambers included in the combustion chamber structure 100 are, as shown in FIG. 3, 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). The first-stage combustion chamber V<b>1 is a region defined by the bottom surface 101 of the cavity 10 and the first rising portion 102 . The second-stage combustion chamber V2 is a region defined by the first horizontal portion 103 and the second rising portion 104 (the hatched region in FIG. 3). The third-stage combustion chamber V3 is an area defined by the second horizontal portion 105 and the third rising portion 106 (the area indicated by the solid color in FIG. 3). The volume ratio of the third-stage combustion chamber V3 to the entire combustion chamber is, for example, 2% or more and 40% or less, preferably 4% or more and 35% or less. Further, the volume ratio of the combined region 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.

As described above, in the combustion chamber structure 100 according to the present embodiment, three lip portions are formed, and a step ( A third-stage combustion chamber V3) is provided, and the shape of the second lip portion 202, which is a lip portion within the stage, is offset downward by a dimension equivalent to the depth of the step. By providing the steps in this way, the volume inside the cavity 10 increases. is adjusted to be As a result, the squish flow is reduced, the cooling loss is reduced, and the fuel consumption is improved. It should be noted that if the squish flow is extremely reduced, the combustion efficiency may deteriorate. can. Below, a structure in which only two lip portions are formed like the conventional combustion chamber structure is referred to as a two-stage lip structure, and a structure in which three lip portions are formed like the combustion chamber structure 100 according to the present embodiment is referred to as a three-stage lip structure. It may be described as a stepped lip structure.

FIG. 4 is a diagram for explaining the structural difference between the two-stage lip structure and the three-stage lip structure. In FIG. 4, the structure around the lip portion of the cavity 10 is illustrated, the dashed line indicates the structure in the case of the two-step lip structure, and the solid line indicates the structure in the case of the three-step lip structure. As shown in FIG. 4, in the three-step lip structure, three lip portions, a first lip portion 201, a second lip portion 202, and a third lip portion 203, are formed. A second horizontal portion 105 is formed by offsetting a region that has the same height as the surface 9a downward. In the three-step lip structure, the volume is equal to that of the two-step lip structure by offsetting the bottom of the cavity 10 upward by the volume increase due to the above-described downward offset.

FIG. 5 is a diagram for explaining the difference in combustion state between the two-stage lip structure and the three-stage lip structure. In FIG. 5, the left side shows the combustion state of the two-stage lip structure at each crank angle (8°, 12°, 16°), and the right side shows each crank angle (8°, 12°, 16°). , the combustion situation of the three-stage lip structure is shown. In FIG. 5, the fuel flow rate is indicated by color intensity (see legend to FIG. 5). In addition, here, the two-step lip structure is described as being configured by the first raised portion 102 , the first horizontal portion 103 , and the second raised portion 104 .

As shown in the left diagram of FIG. 5 , in the case of the two-stage lip structure, when the crank angle is 8°, the fuel spray that collides with the inner lip portion reaches the first horizontal portion 103 and the second rising portion 104. Only an upward flow is promoted in the partitioned upper stage combustion chamber, and a squish flow, which is a vertical swirling flow, is generated. In this case, the fuel spray spreads only within the range of the swirling flow. Therefore, when the crank angle is 12°, the fuel spray spreads only over about half the area of the uppermost piston top surface 9a. Thus, in the two-stage lip structure, there is no space on the outer peripheral side of the cavity 10, and it can be said that combustion is rate-determining. Furthermore, when the crank angle is 16°, the fuel injected from the nozzle hole (shown dark in the figure) and the fuel that collided with the inner lip and spread inside the combustion chamber (shown in the figure The part that is displayed lightly) interferes with each other, and the problem is that the fuel spray hinders the use of air in the combustion chamber and deteriorates combustion.

On the other hand, as shown in the right diagram of FIG. 5, in the case of the three-stage lip structure, when the crank angle is 8°, the fuel spray that collides with the inner lip portion rises to the first horizontal portion 103 and the second rising portion. In the upper combustion chamber defined by the portion 104, the upward flow is promoted and the outward flow is maintained. This is because a sufficient space is secured on the outer peripheral side of the cavity 10 in the three-stage lip structure. As a result, when the crank angle is 12°, the outward-flowing fuel spray flows radially outward in the uppermost combustion chamber and spreads until it reaches the vertical wall of the uppermost combustion chamber. Regarding the outward flow of fuel spray, the 3-stage lip structure is stronger than the 2-stage lip structure, but the vertical vortex due to the downward movement of the middle stage combustion chamber is weaker, so the vertical swirling flow generated by the upward fuel spray For some squish flows, they are weaker in a three-stage lip design than in a two-stage lip design. Therefore, the fuel spray spreads not only to the range of the squish flow but also to the inner region of the combustion chamber. In such a three-stage lip structure, under conditions where EGR is low and oxygen is sufficiently present, a space is secured where the fuel spray spreads into the air and mixes with the air, and the fuel and oxygen come into contact with each other. Since the opportunity for reaction (combustion) is sufficiently secured, combustion becomes active and the rate of heat release (ROHR) increases at a crank angle of 8° to 12°. As described above, in the three-stage lip structure, the fuel spray spreads outward, so less fuel is distributed to the inside of the combustion chamber. As a result, when the crank angle is 16°, the fuel injected from the nozzle hole (shown dark in the figure) collides with the inner lip and spreads inside the combustion chamber (shown in the figure). The part that is displayed lightly in ) is less likely to interfere.

FIG. 6 is a diagram for explaining the difference in combustion state between the two-stage lip structure and the three-stage lip structure. In FIG. 6, the horizontal axis indicates the crank angle, and the vertical axis indicates the heat release rate (ROHR) due to combustion. As shown in FIG. 6, the three-stage lip structure enables more active combustion than the two-stage lip structure when the crank angle is 8° to 16°.

Next, the effects of the combustion chamber structure 100 for a direct injection diesel engine according to this embodiment will be described.

A combustion chamber structure 100 for a direct-injection diesel engine according to this embodiment includes a cavity 10 recessed downward with respect to a piston top surface 9a, and fuel is injected radially into the cavity 10 from the center of a cylinder ceiling portion 11. A combustion chamber structure of a direct-injection diesel engine that self-ignites by igniting, and is continuous with a first rising portion 102 rising upward from the bottom surface 101 of the cavity 10, and the upper end of the first rising portion 102, and in the outer peripheral direction of the cavity 10. a first horizontal portion 103 extending substantially horizontally, a second rising portion 104 continuing to the first horizontal portion 103 and rising upward; A second horizontal portion 105 extending horizontally and a third rising portion 106 continuing from the second horizontal portion 105 and rising upward to reach the top surface 9a of the piston. A first-stage combustion chamber V1 defined by a rising portion 102, a second-stage combustion chamber V2 defined by a first horizontal portion 103 and a second rising portion 104, and a second horizontal portion 105 and a third rising portion 106. and a partitioned third-stage combustion chamber V3, and the volume ratio of the third-stage combustion chamber V3 to the entire combustion chamber is 2% or more and 40% or less.

In the combustion chamber structure 100 of the direct injection diesel engine according to the present embodiment, the rising portions (first rising portion 102, second rising portion 104, third rising portion 106) and horizontal portions (first horizontal portion 103, second horizontal So-called lip portions are formed at three locations, each of which is composed of the portion 105 and the piston top surface 9a). Therefore, as the structure of the combustion chamber, a first-stage combustion chamber V1 defined by the bottom surface 101 of the cavity 10 and the first rising portion 102, and a second-stage combustion chamber defined by the first horizontal portion 103 and the second rising portion 104 A third stage combustion chamber V3 defined by V2, the second horizontal portion 105 and the third rising portion 106 is formed. In the conventional combustion chamber structure, 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. On the other hand, in the configuration in which the third-stage combustion chamber V3 is formed outside and above the second-stage combustion chamber V2, as in the configuration according to the present embodiment, the fuel spray flowing in the outer peripheral direction is The third rising portion 106 (vertical wall of the uppermost combustion chamber) reaching the top surface 9a of the piston through the combustion chamber V3, which is not conventionally formed, is formed. It can be actively used as a space where fuel spray and air are mixed. That is, in the configuration according to the present embodiment, since a space (third-stage combustion chamber V3) where fuel spray and air are mixed is formed on the outer peripheral side of the cavity 10, fuel and oxygen contact and react (combustion ) and promote combustion. In the configuration according to the present embodiment, the volume ratio of the third-stage combustion chamber V3 to the entire combustion chamber is 2% or more and 40% or less, thereby promoting combustion on the outer peripheral side of the cavity 10. It is also possible to suppress slow combustion due to excessive enlargement of the third-stage combustion chamber V3. As described above, according to the combustion chamber structure 100 according to the present embodiment, it is possible to provide a combustion chamber structure for a direct-injection diesel engine that is more advantageous in terms of fuel efficiency.

FIG. 7 is a graph showing the relationship between the volume ratio of the third-stage combustion chamber V3 and the effect of improving fuel efficiency. In FIG. 7, the horizontal axis indicates the volume ratio of the third-stage combustion chamber V3 to the entire combustion chamber, and the vertical axis indicates the fuel consumption (that is, fuel efficiency improvement effect). A volume ratio of the third-stage combustion chamber V3 of 0 (the horizontal axis is 0) means that there is no third-stage combustion chamber V3 and corresponds to a conventional two-stage lip structure. Based on this state, a state in which fuel consumption is less than that in the case where the volume ratio of the third-stage combustion chamber V3 is 0 is a state in which fuel consumption is improved, and a state in which fuel consumption is high is a state in which fuel consumption is deteriorated.

As shown in FIG. 7, when the volume ratio of the third-stage combustion chamber V3 is about 2 to 3%, the effect of reducing fuel consumption (improving fuel consumption) is confirmed, and the volume ratio of the third-stage combustion chamber V3 is 4%. When it reaches a certain degree, the effect of reducing fuel consumption (improving fuel consumption) is clearly recognized. Further, when the volume ratio of the third stage combustion chamber V3 is increased, the fuel efficiency is improved as the volume ratio of the third stage combustion chamber V3 increases up to about 8%. Furthermore, when the volume ratio of the third stage combustion chamber V3 is increased, even if the volume ratio of the third stage combustion chamber V3 is increased, fuel consumption is large until the volume ratio of the third stage combustion chamber V3 is about 8 to 11%. does not increase or decrease. Further, when the volume ratio of the third stage combustion chamber V3 is increased, the fuel consumption improvement effect is recognized up to a volume ratio of about 35% of the third stage combustion chamber V3, and the volume ratio of the third stage combustion chamber V3 is about 40%. , the fuel consumption becomes approximately the same as the reference (the volume ratio of the third-stage combustion chamber V3 is 0). When the volume ratio of the third-stage combustion chamber V3 exceeds 40%, the fuel consumption increases from the standard, resulting in deterioration of fuel efficiency. As described above, increasing the volume ratio of the third-stage combustion chamber V3 to a certain extent increases the space where air and fuel mix and improves fuel consumption, but if the volume ratio is increased too much, combustion will be impaired. becomes slow and the effect of improving fuel consumption becomes small.

The upwardly rising length of the third rising portion 106 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 crossing the vertical direction. By setting the length of the third rising portion 106 that defines the third-stage combustion chamber V3 in this way, the size of the third-stage combustion chamber V3 is sufficiently ensured, and combustion on the outer peripheral side of the cavity 10 is achieved. is promoted, it is also possible to suppress slow combustion due to excessive enlargement of the third-stage combustion chamber V3.

The length of the second horizontal portion 105 in the direction crossing 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 crossing the vertical direction. By setting the length of the second horizontal portion 105 that defines the third-stage combustion chamber V3 in this way, the size of the third-stage combustion chamber V3 is sufficiently secured, and combustion on the outer peripheral side of the cavity 10 is achieved. is promoted, it is also possible to suppress slow combustion due to excessive enlargement of the third-stage combustion chamber V3.

Reference Signs List 1 Diesel engine 9a Piston top surface 10 Cavity 11 Cylinder ceiling 100 Combustion chamber structure 101 Bottom surface 102 First rising portion 103 First horizontal portion 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 (3)

A combustion chamber structure for a direct-injection diesel engine that includes a cavity that is recessed downward with respect to the top surface of the piston, and in which fuel is radially injected from the center of the 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 continuous with the upper end of the first rising portion and extending substantially horizontally in the outer peripheral direction of the cavity;
a second rising portion continuous with the first horizontal portion and rising upward;
a second horizontal portion continuous with the upper end of the second rising portion and extending substantially horizontally in the outer peripheral direction of the cavity;
a third rising portion continuous with the second horizontal portion and rising upward to reach the top surface of the piston;
The combustion chamber is
a first chamber defined by the bottom surface of the cavity and the first rising 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. The direct injection diesel engine according to claim 1, wherein the length of said third rising portion rising above is 3% or more and 9.5% or less of the length of the bottom surface of said cavity in a direction crossing the vertical direction. combustion chamber structure. 3. The length of the second horizontal portion in the direction crossing the vertical direction is 10% or more and 18% or less of the length of the bottom surface of the cavity in the direction crossing the vertical direction. Combustion chamber structure of direct injection diesel engine.

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