JPH09236016A - Combustion chamber of direct injection diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately introduce air into fuel spray, and besides, prevent the deterioration of the performance of a combustion chamber. SOLUTION: A recessed part 22 which is curvedly bored outward in a diametral direction from a position lower than the upper end 25 of the side wall of a cavity side wall 21 by a predetermined height A until a lower end, is arranged in the cavity side wall 21 on which fuel spray 12 is sprayed. A trapezoidal bottom 24 having a slant surface 28 smoothly connected from the recessed part 22 is arranged on a cavity bottom wall 23. A recessed groove 13 along the spray axial line Q of the fuel spray 12 is formed in the downward position of the fuel spray 12 out of the slant surface 28 of the bottom 24. Hereby, the air introduction to the fuel spray 12 can be improved without imparting an air fluidity in a cavity, and excellent combustion in which a smoke and so on is reduced can be obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a combustion chamber of a direct injection diesel engine.

[0002]

2. Description of the Related Art The applicant of the present invention has previously proposed a combustion chamber of a direct injection type diesel engine capable of reducing smoke (Japanese Utility Model Laid-Open No. 4-116631). This combustion chamber is provided with a curved recess on the side wall of the cavity at the top of the piston and a trapezoidal bottom that connects smoothly from the recess, and the shape of the recess and the bottom can be selected appropriately. Thus, a portion where the turbulence of the intake air is strong is generated at an appropriate position near the side wall. That is, by injecting fuel toward the center of this turbulence, mixing of fuel and air is promoted, and good combustion can be obtained.

[0003]

By the way, in this type of combustion chamber, in order to further promote mixing, the collision angle between the fuel spray and the cavity wall surface should be as vertical as possible to the wall surface. Is preferred. That is, as shown in FIG. 6, when the angle θ ₁ between the axis 2 of the fuel spray 1 and the perpendicular 4 of the wall surface 3 is large, the reflection thickness T ₁ after collision becomes small (a), but the position of the injection port 5 is changed. If the angle θ ₂ is decreased by lowering the angle θ ₂ , the reflection thickness T ₂ increases and the volume of the fuel spray 1 increases. The fact that the same fuel has a large atomization volume means that the fuel becomes lean, which leads to good air mixing in the cavity.

However, when the position of the injection port 5 is lowered as shown in FIG. 4 (b), the fuel spray 1 comes too close to the bottom inclined surface and it becomes difficult to introduce air in the process until it reaches the wall surface 3. That is, there is a problem that a good fuel spray 1 cannot be obtained and the promotion of mixing is hindered. As a countermeasure against this, it is conceivable to scrape the bottom inclined surface to secure a distance from the fuel spray 1, but since the compression ratio is reduced by the reduction amount, the volume must be made up in other parts of the cavity. For example, if it is installed on the side wall, the air flow performance of the combustion chamber is deteriorated, or the H
There is a possibility of causing deterioration of C and the like.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a cavity side wall on which fuel spray is sprayed,
A pedestal provided with a curved recessed portion radially outward from a position lower by a predetermined height than the upper end of the side wall to a lower end, and an inclined surface smoothly connecting from the recessed portion to the bottom wall of the cavity. A bottom portion having a shape is provided, and a concave groove along the spray axis is formed at a position below the fuel spray on the inclined surface of the bottom portion. With this configuration, the air introduction of the fuel spray can be improved without impairing the air flow function in the cavity, and good combustion with reduced smoke and HC can be obtained. The concave groove is preferably formed so as to widen toward the side wall of the cavity. Further, it is preferable that the inclined surface located between the concave grooves has a curved portion on the center side of the cavity in which the concave grooves on both sides of the concave groove smoothly continue.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIGS. 1 and 2 show a first embodiment of a combustion chamber of a direct injection type diesel engine according to the present invention. This combustion chamber has a recess 2 formed in a curved shape radially outward in each of a side wall 21 and a bottom wall 23 of a basic cavity having a short columnar shape formed at the top of a piston.
2 and a trapezoidal (conical trapezoidal) bottom portion 24 are provided. The recessed groove 13 along the spray axis Q is formed only on the position below the fuel spray 12 on the inclined surface 28 of the bottom portion 24.

The recessed portion 22 is formed from a position below the upper end 25 of the side wall by a predetermined height A to a position where it becomes the lower end 26 of the combustion chamber, and its longitudinal section is formed by a curved surface of a substantially semicircular shape. Then, in the cavity side wall 21, the recess 22
The side wall vertical portion 27 corresponding to the portion left above is formed so that its depth (height A) is 1/6 of the combustion chamber depth H. That is, if the combustion chamber depth H is 24 mm,
It is formed so that A = 4 mm. Also the bottom 24
Is composed of an inclined surface 28 that is smoothly connected to the recess 22 and a flat surface 14 centered on the position of the shaft center 3. Slope 2
The angle α from the horizontal direction (cavity bottom wall 23) of 8 is, for example, about 25 degrees. The flat surface 14 is formed so that the depth h from the piston upper surface 11 is about 1/2 of the combustion chamber depth H. That is, if the combustion chamber depth H is 24 mm, h = approx.
It is formed to be 12 mm. The shapes of the recessed portion 22 and the bottom portion 24 are set in consideration of the results of the turbulence of intake air and the smoke generation test (simulation). That is, the center of the strong turbulence of air is near the inside of the side wall vertical portion 27 and the recessed portion 22 and at the side wall upper end 2
Located below 5 and the spray axis Q of the fuel spray 12
Have been selected to penetrate. The other cavity dimensions are appropriately set depending on the compression ratio and the like. The combustion chamber diameter Dc is, for example, 0.65 in ratio with the piston outer diameter, and the radial protrusion length B of the side wall vertical portion 27 is the combustion chamber diameter Dc. It can be about 0.05.

On the other hand, an injection port 1 of a fuel injection nozzle (not shown)
The position 5 is formed so as to protrude below the piston upper surface 11 at the injection timing. This fuel injection is performed at a high pressure so that the fuel particle size becomes small, and the spray angle is formed to be about 20 degrees. The spread of the fuel spray 12 when reaching the side wall vertical portion 27 and the depression 22 is the total height (depth) of the combustion chamber when the position of the side wall upper end 25 is 0 and the position of the combustion chamber lower end 26 is 1. H
However, it is formed to have a position range of about 1/8 to 3/4 thereof. Further, as shown in FIG. 2, the circumferential position of the nozzles 15 (splitting angle of the nozzles) is such that the fuel sprays 12 are at 60 degrees from each other.
Six pieces are arranged at equal intervals so as to be radially at an angle of degrees. In addition, in FIG.
And its spray axis Q and the corresponding groove 13 are shown. The number of injection holes is not limited to six, but an optimum number should be selected according to conditions such as injection pressure, swirl (swirl speed), supercharging, etc. For example, eight injection holes may be provided. It is desirable that these nozzles are arranged at equal angles to each other.

The groove 13 has a flat surface 1 when viewed in a plane.
4 is formed as a triangular notch groove with the peripheral edge of No. 4 as the base and the position of the lower end 26 of the combustion chamber as the apex. Each groove 13
Are in contact with each other at the peripheral edge of the flat surface,
The plan view shape is a regular hexagon inscribed in the upper surface circle 16 of the basic shape (frustum). It should be noted that the shape in plan view is preferably a polygon equal to the number of nozzles, and for example, if the number of nozzles is eight, it is a regular octagon. Further, as shown in FIG. 3, the depth of the recessed groove 13 is maximum at the position of the flat surface 14 and becomes 0 at the position reaching the recess 22.
It decreases monotonically as it goes radially outward. That is, the bottom surface 17 of the groove and the lower limit 18 of the fuel spray 12 are formed to be substantially parallel to each other.

With this structure, as shown in FIG. 3, the fuel injected from the injection port 15 takes in the air a existing in the concave groove 13 and becomes a good fuel spray 12, and the side wall vertical portion 27 and the recessed portion 22. Head to. Then, it collides with the wall surface at an angle close to vertical, resulting in a thin state in which the reflection thickness (T) is large. That is, the air is properly introduced, and the mixing of the fuel and the air immediately after the collision is promoted. Further, the concave groove 13 is formed at the minimum necessary position along the spray axis Q on the inclined surface 28 of the bottom portion 24, and does not impair the air flow function at the bottom portion 24. The cutout volume of the concave groove 13 is smaller than that when the entire bottom portion 24 is dug down, and it is not necessary to largely fill the side wall vertical portion 27 and the recessed portion 22 in order to match the compression ratio. Therefore, if the amount corresponding to the cutout volume is applied over the entire circumference of the side wall, the shrinkage of the cavity diameter is extremely small, the air flow function is not impaired, and the diameter reduction does not adversely affect the HC.

Further, in the present embodiment, the recessed portion 22
Since the bottom portion 24 and the bottom portion 24 are selectively formed to have a predetermined ratio with respect to the combustion chamber depth H, the fuel spray 12 can be prevented from flowing out of the cavity, and the intake air can be effectively used. The center of the turbulence of the intake air can be generated at an appropriate position near the side wall, and the center (Q) of the fuel spray 12 can be applied to this center, which promotes the mixing of fuel and air and reduces smoke. Is achieved.

As a prior art to be compared with the present invention,
A groove formed on the top surface of a raised portion in a cavity (Japanese Patent Laid-Open No. 50-13706, Japanese Patent Laid-Open No. 63-198720).
Publication). However, these are for suppressing halfway air introduction in the low swirl region near the fuel injection nozzle. On the other hand, the concave groove 13 of the present invention
Is for positively introducing air in the vicinity of the fuel injection nozzle. This difference is due to the assumption that the injection pressure of the diesel engine to which the present invention is applied is higher than the injection pressure to which the conventional technique is applied. That is, in low-pressure injection, because the fuel particle size of the spray is relatively large, incomplete combustion will occur unless air is introduced in the active swirl region (outside the cavity), so a groove for air introduction suppression is required. However, since the fuel particle diameter of the spray is small in high-pressure injection, it is possible to introduce air to some extent even in the low swirl region (cavity center side). In consideration of this, in the present invention, air is positively introduced from a position near the fuel injection nozzle to achieve ideal spraying and air mixing.

Next, a second embodiment of the present invention will be described with reference to FIGS. This combustion chamber extends along the spray axis Q on the inclined surface 32 of the substantially frustoconical bottom 31 as shown in the first embodiment, and as it goes to the cavity side wall 21 (recess 22). A concave groove 33 whose width w is enlarged is formed. As the degree of expansion of the concave groove 33, for example, the angle of expansion as viewed from the center of the cavity (axial center 3) in plan view corresponds to the shape of the spray.
Try to be 20 degrees. The spread angle may be 20 degrees or more. Further, the depth of the recessed groove 33 is formed so as to be the deepest at the position of the outer periphery of the flat surface 34 and to be 0 at the position reaching the recessed portion 22, as in the first embodiment.

The inclined surface 32 located between the concave grooves 33
Has a substantially triangular shape in plan view, and its apex is formed by the curved portion 35. That is, on the side of the center O of the cavity, the concave grooves 33 on both sides of the inclined surface 32 are smoothly connected, and the flat surface 34 at the bottom is a circle (short cylindrical shape) appropriately separated from the inclined surface 32. There is. The curved portion 35 has, for example, an arc shape having a central angle β of about 90 degrees in a plan view and is formed so as to rise vertically in a side view. The shape of the curved portion 35 in plan view is not limited to a circular arc, and may be any shape as long as it is rounded. Moreover, as a side view shape, it may be inclined.

With this structure, it is possible to avoid the collision between the fuel spray 12 and the bottom portion 31 outside the combustion chamber. That is, the fuel spray 12 spreads in the lower part of the groove 33 (outside the combustion chamber), but especially under a light load (condition where the combustion temperature is low), the bottom part 31 and the fuel spray 12 may collide with each other to generate HC. . According to this embodiment, since the concave groove 33 is shaped so as to follow the spread of the fuel spray 12, the injected fuel does not collide with the inclined surface 32 even at the position outside the combustion chamber, and the recessed portion is formed. It is led to 22. Further, by providing the curved portion 35 on the inclined surface 32, soot is accumulated in a narrow portion between the flat surface 34 and the upper portion of the concave groove 33, or stress is concentrated on the narrowed tip portion of the inclined surface 32. It is possible to prevent cracks from occurring.

In the above embodiment, the concave grooves 13 and 3 are formed.
Although the planar shape of 3 is substantially triangular, it may be partitioned by, for example, a rectangle or a curved line. In addition, the groove 13,3
The depth of 3 does not have to change in the radial direction and may be constant. However, at the position near the fuel injection nozzle,
It is preferable to make it deeper. The shape of the cavity is not limited to the illustrated example, and the present invention is widely applied to a combustion chamber having a similar bottom portion and the like.

[0018]

In summary, according to the present invention, it is possible to properly introduce air into the fuel spray, achieve good air mixing, and exhibit the excellent effect of not impairing the combustion chamber performance. To do. Further, by providing the concave groove that widens toward the side wall of the cavity, it is possible to prevent HC from being generated under a light load or the like. Further, by providing an inclined surface having a curved portion, it is possible to prevent the accumulation of soot and the generation of cracks.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a first embodiment of the present invention.

FIG. 2 is a plan view of a main part of FIG.

FIG. 3 is an enlarged view of a main part of FIG. 1;

FIG. 4 is a plan view showing a second embodiment of the present invention.

FIG. 5 is a sectional view taken along line VV of FIG. 4;

FIG. 6 is a side sectional view for explaining a problem of the conventional technique.

[Explanation of symbols]

 3 axial center (cavity center) 12 fuel spray 13, 33 concave groove 15 injection port 21 cavity side wall 22 dent 23 cavity bottom wall 24, 31 bottom 25 side wall upper end 26 combustion chamber lower end 27 side wall vertical portion 28, 32 inclined surface 35 curved section A Specified height Q Spray axis w Width of groove

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Asayuki Itoh Central Research Institute, Inc. 8 Tsutana, Fujisawa City, Kanagawa Prefecture

Claims (3)

[Claims] 1. A cavity bottom wall is provided with a cavity formed on a side wall of a cavity on which fuel spray is sprayed, which is curved outward in a radial direction from a position lower than a top end of the side wall by a predetermined height to a lower end. Is provided with a trapezoidal bottom having an inclined surface that is smoothly connected to the recess, and a groove along the spray axis is formed at a position below the fuel spray on the inclined surface of the bottom. The combustion chamber of a direct injection diesel engine. 2. The combustion chamber of a direct injection diesel engine according to claim 1, wherein the groove is formed so as to widen toward the side wall of the cavity. 3. The combustion chamber of a direct injection diesel engine according to claim 1, wherein the inclined surface located between the recessed grooves has a curved portion on the center side of the cavity in which the recessed grooves on both sides thereof are smoothly continuous.