JP2001055923A - Combustion chamber structure of direct injection type diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To diffuse fuel at the initial stage of combustion and to excellently mix together fuel and air at the terminal stage of combustion by a method wherein the opening diameter of a combustion chamber is decreased to a value lower than the internal diameter of the combustion, an annular wall surface protrusion part is formed on a combustion chamber wall in an injection range of fuel, and a central protrusion part to vary an advancing direction of fuel is formed on the bottom of the combustion chamber. SOLUTION: The height h3 of a central protrusion 7 protruding from the central part of the bottom 5 of a combustion chamber 100 is higher than the height h2 of a wall protrusion part 4 and set to height enough to prevent collision with injecting fuel 2. The fuel 2 is separated into two courses by the wall protrusion part 4, one runs upward along a dent 6 and the other runs toward the central direction of the combustion chamber 100 along a wall 9 and a bottom 5. A part of fuel flowing toward above advances to a squish area through an opening part 3 and a rest is diffused in the combustion chamber. Further, fuel flowing toward a central part varies its course to above at a curve 8 and is raised along a central protrusion part 7. Since fuel is caused to effect convection in a high air flow region by the central protrusion part 7, excellent mixture of air and fuel is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion chamber structure of a direct injection diesel engine having a shallow combustion chamber and a small cylinder diameter.

[0002]

2. Description of the Related Art In the combustion chamber of a conventional direct injection diesel engine having a shallow combustion chamber and a small cylinder diameter, the kinetic energy of fuel injected from a fuel injection nozzle colliding with the combustion chamber wall surface is large. The fuel reflected on the combustion chamber wall stagnates at the bottom of the combustion chamber, making it difficult to mix the fuel and air in the latter stage of the combustion, resulting in poor exhaust smoke density and undesirable engine performance.

[0003]

Accordingly, in the present invention, in the initial stage of combustion in which fuel collides with the combustion chamber wall surface, the kinetic energy of the fuel promotes splitting and evaporation on the combustion chamber wall surface so that the fuel near the combustion chamber wall surface is accelerated. It is an object of the present invention to provide a combustion chamber structure in which fuel can be diffused into a space portion and, in a later stage of combustion, mixing of fuel and air can be favorably performed by swirling (air flow) in the combustion chamber.

[0004]

According to the present invention, the opening diameter of the combustion chamber is set smaller than the inner diameter of the combustion chamber, and the annular wall surface is formed on the wall surface of the combustion chamber within a range where fuel is injected from the fuel injection nozzle. Protrusions are provided so that the fuel does not collide with the fuel injected from the fuel injection nozzle and collides with the combustion chamber wall surface, so that the fuel proceeds from the combustion chamber wall surface to the combustion chamber center along the combustion chamber bottom toward the upper side. A central projection having a height capable of changing the traveling direction of the fuel is provided at the bottom of the combustion chamber. According to a second aspect of the present invention, in the first aspect, the injection center axis of the fuel injected from the fuel injection nozzle is set to be above the wall surface projection. According to a third aspect of the present invention, in the first or second aspect of the present invention, an annular concave portion having a smooth surface is provided above the wall surface projection, and the wall surface projection is smoothly connected to the depression. Then, the path of the fuel colliding with the combustion chamber wall surface is divided into two directions, that is, the cylinder head side and the combustion chamber bottom side. According to a fourth aspect of the present invention, in the third aspect of the present invention, the angle formed by the tangent to the depression in the wall projection and the vertical line is set in the range of 45 degrees to 90 degrees. According to a fifth aspect of the present invention, in the first aspect of the present invention, a value obtained by dividing the height from the bottom of the combustion chamber to the projection of the wall by the depth of the combustion chamber is set in the range of 0.3 to 0.5. In the invention of claim 6, in the invention of claim 4 or claim 5, the shape of the combustion chamber is set to be larger in the order of the opening diameter of the opening of the combustion chamber, the inner diameter of the combustion chamber, and the maximum diameter of the recess. In the invention of claim 7, in the invention of claim 1, the combustion area of the fuel in the center of the combustion chamber is reduced by connecting the bottom of the combustion chamber and the central projection with a smooth curved surface. The larger the radius of curvature of the curved surface is, the larger the volume of the central projection is, and the easier the fuel is to mix with air in the region of the combustion chamber where the airflow is large. In the invention of claim 8, the height of the central projection from the bottom of the combustion chamber is higher than the height of the wall projection from the bottom of the combustion chamber. According to the ninth aspect of the present invention, the depth of the combustion chamber and the magnitude of the piston diameter are set so that the value obtained by dividing the combustion chamber depth by the piston diameter is smaller than 0.2.

[0005]

FIG. 1 is a schematic sectional view of a combustion chamber 100 of a direct injection diesel engine according to the first to ninth aspects of the present invention. The combustion chamber 100 shown in FIG. 1 shows only the characteristic portions of the first to ninth aspects of the present invention.

The annular side wall 9 of the combustion chamber 100 is provided with an annular wall projection 4. An annular depression 6 is provided above the wall projection 4, and the wall projection 4 and the depression 6 are smoothly continuous. Opening 3 at the upper end of the side wall 9
Is provided. The diameter d _{1 of the} opening 3 is set smaller than the inner diameter d _{3 of the} side wall 9.

The bottom 5 of the combustion chamber 100 is provided with a central projection 7. The central protrusion 7 protrudes in the center of the combustion chamber 100, and its height h ₃ is higher than the height h ₂ of the wall surface protrusion 4 and the fuel 2 injected from the fuel injection nozzle 1.
It does not collide with the height. Also, the central projection 7 and the bottom 5
And are connected by a smooth curved surface 8.

In the combustion chamber 100 formed as described above, the fuel 2 injected from the fuel injection nozzle 1 collides with the wall surface 9 while spreading in the form of a mist, and as shown by a dashed line in FIG. The injection direction of the fuel injection nozzle 1 is set so that the injection center axis 2a is located above the wall surface projection 4.

Fuel 2 injected from fuel injection nozzle 1
(FIG. 2A) collides with the wall surface 9 provided with the wall surface projection 4 and the depression 6. The fuel 2 colliding with the wall 9 is shown in FIG.
As shown in (b), the path is divided into two by the wall surface projection 4, one of which is upward along the recess 6 (on the cylinder head side).
And another toward the center of the combustion chamber 100 along the wall surface 9 and the bottom portion 5.

[0010] Some of the upwardly directed fuel passes through the opening 3 into the squish area 10 and the rest diffuses in the combustion chamber. Also, the fuel heading toward the center
As shown in FIG. 2C, the course is smoothly changed upward by the curved surface 8 and rises along the wall surface of the central projection 7.

A swirl (air flow) is present in the combustion chamber 100, and the swirl is more active in the peripheral portion (closer to the wall surface 9) than in the central portion of the combustion chamber 100. Therefore,
Mixing of fuel and air is better in the peripheral part than in the central part. By providing the central projection 7, the fuel can be convected in a region where the air flow is large, so that the mixing of the air and the fuel is performed well, and as a result, the combustion is performed well. In addition, the larger the radius of the curved surface 8 is, the narrower the central area of the combustion chamber 100 is, and the more the fuel is distributed in the peripheral area where the air flow is large, so that it becomes easier to mix the air and the fuel satisfactorily. .

In a conventional reentrant combustion chamber, thick fuel accumulates near the bottom of the combustion chamber. On the other hand, in the combustion chamber 100 of the present invention, the wall projection 4 and the depression 6 are formed.
As a result, the fuel 2 is dispersed up and down, and the fuel is distributed to a portion where the air flow due to the swirl is large, so that the fuel and the air are mixed well.

The recess 6 in the wall projection 4 shown in FIG.
The angle θ ₁ formed by the tangent to the vertical line and the tangent of
When the temperature is set within the range of 0 degrees, the fuel and the air are satisfactorily mixed, and good combustion can be performed, and the exhaust color also becomes good.

Instead of the wall surface projections 4 of FIG. 1, wall surface projections 14 and 15 shown in FIG. 3 may be used. At this time, if the angle θ ₂ formed by the straight line connecting the wall surface projections 14 and 15 and the vertical line is set within a range of 45 degrees to 90 degrees,
The fuel and the air are mixed well, and good combustion can be performed, and the exhaust color also becomes good.

As shown in FIG. 1, when the height from the bottom 5 to the wall surface projection 4 is h ₂ and the depth of the combustion chamber is H, the relationship 0.3 <h ₂ /H<0.5. When the condition is satisfied, the fuel and the air are satisfactorily mixed, and good combustion can be performed, and the exhaust color also becomes good.

When the height h ₃ of the central projection 7 is higher than the height h ₂ of the wall projection 4, the fuel that proceeds toward the center along the bottom 5 further proceeds to the center than the central projection 7. Not be able to change the direction of travel upwards,
It is possible to prevent the fuel from traveling to the central region of the combustion chamber where the air flow is relatively small.

The opening diameter of the opening 3 is d ₁ , the maximum diameter of the depression 6 is d ₂ , and the inner diameter of the combustion chamber 100 (the inner diameter of the wall 9) is d _3.
If the diameters are set so as to satisfy the relationship of d ₁ <d ₃ <d ₂ , the fuel and the air can be mixed well, good combustion can be performed, and the exhaust color can be improved.

If the depth of the combustion chamber 100 is H and the piston diameter is D, the depth H of the combustion chamber 100 and the piston diameter D are set so as to satisfy the relationship of H / D <0.2. The fuel and the air are mixed well, and good combustion can be performed, and the exhaust color also becomes good.

[0019]

According to the first aspect of the present invention, by providing the wall surface projections 4, good combustion can be obtained during the entire combustion period. By providing the wall surface projections 4, the kinetic energy of the fuel 2 itself causes the fuel 2 to be separated and spread to the bottom 5 side and the upper side (opening 3 side), thereby promoting the mixing of fuel and air at the beginning of combustion. it can. By providing the central projection 7, the mixing of fuel and air can be promoted by swirl even in the later stage of combustion.

According to the invention of claim 2, the center line 2a of the fuel 2 is provided.
Is set above the wall projection 4 so that the fuel 2
Is sprayed on the wall surface 9, so that the ratio of the fuel divided into upper and lower parts becomes good, and the fuel and air can be more properly mixed in the combustion chamber 100.

According to the third aspect of the present invention, by providing the recessed portion 6, a part of the fuel 2 colliding with the wall surface 9 can be guided to the opening 3 side (cylinder head side).
The fuel can be diffused evenly in the peripheral region except the region above the central projection 7.

According to the fourth aspect of the present invention, the angle θ ₁ formed by the tangent to the depression 6 in the wall projection 4 shown in FIG. 1 and the vertical line is set in the range of 45 degrees to 90 degrees, The fuel and the air can be mixed well and good combustion can be performed, and the exhaust color can be made good.

According to the fifth aspect of the present invention, the height from the bottom 5 to the wall projection 4 is h _2, and the depth of the combustion chamber is H.
By satisfying the relationship of 3 <h ₂ /H<0.5, good combustion can be performed, and the exhaust color also becomes good.

According to the invention of claim 6, the opening diameter of the opening 3 of the combustion chamber 100 is d ₁ , the maximum diameter of the depression 6 is d ₂ , and the combustion chamber 1
If the internal diameter of 00 (the inner diameter of the wall surface 9) is d ₃ , d ₁ <d
_Since each diameter is set so as to satisfy the relationship of ₃ <d ₂ , the fuel and the air are satisfactorily mixed, good combustion can be performed, and the exhaust color becomes good.

According to the seventh aspect of the present invention, since the bottom portion 5 and the central projection 7 are connected by the smooth curved surface 8, it is possible to reduce the combustion area of the fuel in the central portion of the combustion chamber where the swirl air flow is relatively small. As a result, the swirl promotes the combustion of the fuel and air in the vicinity of the combustion chamber where the air flow generated by the swirl is relatively large, so that good combustion can be performed and the exhaust color can be improved.

If the height h ₃ of the central projection 7 is low, the fuel passes over the central projection 7 to the central portion of the combustion chamber, but in the invention of claim 8, by setting h ₂ <h ₃ , The fuel traveling along the side wall of the central protrusion 7 can be directed upward in the combustion chamber, and can be burned in a region where fuel and air are easily mixed, so that good combustion can be obtained.

According to the ninth aspect of the present invention, the air in the entire combustion chamber can be used for combustion because the depth H of the combustion chamber is small.
By setting such that H / D <0.2, the fuel and the air are satisfactorily mixed, the combustion is improved, and the exhaust color is also improved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a combustion chamber structure of a direct injection diesel engine to which the inventions of claims 1 to 9 are applied.

FIG. 2A is a schematic cross-sectional view showing a combustion chamber structure of a direct injection diesel engine until fuel injected from a fuel injection nozzle collides with a wall surface. (B) is a schematic cross-sectional view of the combustion chamber showing a state in which fuel is separated at the protrusion.
(C) is a schematic cross-sectional view of the combustion chamber in which the paths of the separated fuels are indicated by arrows.

FIG. 3 is a schematic sectional view of a combustion chamber showing another shape of a wall projection.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel injection nozzle 2 Fuel 3 Opening 4 Wall projection 5 Bottom 6 Depression 7 Central projection 8 Curved surface 9 Side wall 10 Squish area 14, 15 Wall projection

Claims (9)

[Claims] An opening diameter of the combustion chamber is set smaller than an inner diameter of the combustion chamber, an annular wall projection is provided on a wall surface of the combustion chamber within a range where fuel is injected from the fuel injection nozzle, and the fuel is injected from the fuel injection nozzle. Of a height that does not collide with the fuel and that can change the direction of travel of the fuel so that the fuel that collides with the combustion chamber wall surface and proceeds from the combustion chamber wall surface to the center of the combustion chamber along the bottom of the combustion chamber is directed upward. A combustion chamber structure for a direct injection diesel engine, wherein a central projection is provided at the bottom of the combustion chamber. 2. The combustion chamber structure of a direct injection diesel engine according to claim 1, wherein the injection center axis of the fuel injected from the fuel injection nozzle is set above the wall projection. 3. A concave portion having an annular shape and a smooth surface is provided above the wall surface projection, and the wall surface projection and the depression are smoothly connected to each other so that the path of the fuel colliding with the combustion chamber wall surface is reduced. The combustion chamber structure of a direct injection type diesel engine according to claim 1 or 2, wherein the combustion chamber is divided into two directions, a cylinder head side and a combustion chamber bottom side. 4. The combustion chamber structure of a direct injection diesel engine according to claim 3, wherein the angle formed by the tangent to the depression in the wall projection and the vertical line is set in the range of 45 degrees to 90 degrees. 5. The direct injection diesel engine according to claim 1, wherein a value obtained by dividing the height from the bottom of the combustion chamber to the projection of the wall by the depth of the combustion chamber is set in a range of 0.3 to 0.5. Engine combustion chamber structure. 6. The diameter of the opening of the combustion chamber, the diameter of the inside of the combustion chamber,
The combustion chamber structure of a direct injection type diesel engine according to claim 4 or 5, wherein the diameter of the hollow portion increases in the order of the maximum diameter. 7. A direct injection diesel engine according to claim 1, wherein a combustion area of fuel in a central portion of the combustion chamber is reduced by connecting a bottom portion of the combustion chamber and a central projection portion with a smooth curved surface in the combustion chamber. Engine combustion chamber structure. 8. The height of the central projection from the bottom of the combustion chamber is higher than the height of the wall projection from the bottom of the combustion chamber.
The combustion chamber structure of a direct injection diesel engine according to the above. 9. The combustion of a direct injection diesel engine according to claim 1, wherein the combustion chamber depth and the piston diameter are set such that a value obtained by dividing the combustion chamber depth by the piston diameter is smaller than 0.2. Room structure.