JP3013570B2 - Combustion chamber of a swirl chamber type diesel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a combustion chamber of a vortex chamber type diesel engine, and more particularly, to an improvement in a piston side cavity structure.

[0002]

2. Description of the Related Art In a swirl chamber type diesel engine, a groove-shaped trench extending from the lower part of the injection port toward the center of the piston is provided on the top surface of the piston, and a pair of large cavities is continuously formed at the tip of the trench. A configuration in which a so-called cloverleaf-type cavity is formed in a recessed manner (for example, Japanese Utility Model Laid-Open No. Sho 63-79435) is generally used. However, in this type of cavity structure, it is attempted to go straight from the injection port along the trench portion. Jet flow is too strong,
The ratio of the flame that goes over the large cavity portion and collides with the cylinder bore to extinguish the flame is relatively large, and the flame is hardly diffused in a wide area of the main combustion chamber.

Accordingly, the present applicant has previously disclosed in Japanese Patent Laid-Open No. 1-2
No. 00012, etc., a pair of substantially circular large cavities are continuously formed in the shape of an approximately figure 8 on the piston top surface with the center line of the jet from the jet port interposed therebetween, and on the jet center line and There has been proposed a combustion chamber structure in which a dispersion table is raised in an island shape near an injection port, and a lower portion of the injection port and the large cavity section communicate with each other through concave portions on both sides of the dispersion table.

In this apparatus, since the jet flow spouted from the swirl chamber collides with the dispersion table and the linear velocity component is weakened, the number of flames which extinguish by colliding with the cylinder bore is reduced, and the jet flow is divided into right and left smoothly. A relatively strong swirling flow is generated in the substantially circular large cavity portion, and as a result, a good air utilization rate in the main combustion chamber can be obtained.

[0005]

In the conventional combustion chamber as described above, it is possible to further increase the swirling flow in the large cavity by forming the dispersion table relatively thin. Even if the swirling flow is strengthened, sufficient turbulence cannot be given in the later stage of combustion on the main combustion chamber side, so that mixing of the combustion gas and air is not always sufficient. Therefore, there is room for further improvement in terms of suppressing unburned fuel and smoke emissions.

[0006]

According to the present invention, there is provided an injection port which is opened at a peripheral portion of a main combustion chamber and which is inclined so that a jet from a vortex chamber is directed toward the center of the main combustion chamber, and has a recess provided on a piston top surface. And, while expanding in a substantially circular shape to the left and right respectively across the center line of the jet, a pair of large cavities continuous with each other at the center, and raised near the injection port of the large cavity and on the center line A dispersion table, and a guide portion that is recessed from the vicinity of the lower part of the nozzle toward the center of the piston, and that is continuous with the large cavity portion through both sides of the dispersion table;
In the combustion chamber of a vortex chamber type diesel engine comprising: a spare chamber part which is recessed in the outer periphery of the jet flow center line of the outer shell on the side opposite the injection port of the large cavity part toward the outer periphery of the piston, and which is continuous with the large cavity part And that the curvature of the outer shell on the injection port side is larger than the curvature of the outer shell on the anti-injection side so that the tip of the outer shell near the guide section of the large cavity portion points toward the preliminary chamber. Features.

[0007]

The combustion gas ejected from the swirl chamber near the compression top dead center through the injection port tries to go straight toward the center of the piston, and collides with the dispersion table and is divided into right and left. This flow flows into the large cavities through the guides and swirls in the large cavities. The air near the large cavity is effectively used by this swirling flow. And
The combustion gas that has swirled from the outer shell on the injection port side of the large cavity portion along the outer shell near the guide portion travels from the outer shell near the guide portion to the preliminary chamber portion on the anti-injection side, and the preliminary chamber Hits the outer shell of the part. In this preliminary chamber, the flows guided from the two large cavities collide with each other as described above,
In addition, a part of the jet flowing straight over the dispersion table collides with its outer shell and can be turned. Therefore, a lot of turbulence occurs, and the mixing with air is promoted.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings.

FIGS. 1 and 2 show one embodiment of the present invention, in which 1 denotes a cylinder block, 2 denotes a cylinder head, and 3 denotes a piston. The lower surface of the cylinder head 2 that covers the upper surface of the cylinder bore 4 is formed as a flat surface, and the main combustion chamber 5 is formed between the lower surface and the top surface of the piston 3.

The vortex chamber 6 is located along the side of the cylinder head 2, and an injection port 7 extending from the vortex chamber 6 opens to the periphery of the main combustion chamber 5. The injection port 7 has a flat passage section with a slightly wide width direction, and is inclined so that the jet from the vortex chamber 6 is directed toward the center of the main combustion chamber 5. In FIG. 1, the center line of the above-mentioned jet on the plane of the piston 3 is indicated by a symbol L.

On the top surface of the piston 3 defining the main combustion chamber 5, a pair of large cavities 8 having a substantially circular shape are recessed at a constant depth near the center of the piston 3. The large cavity portion 8 extends right and left with the center line L interposed therebetween, and has a figure-eight shape as a whole, and central portions along the center line L are continuously integrated with each other. The outer shell 8a on the side opposite to the injection port 7 on the center line L serving as a connection portion between the two, that is, the outer shell 8a is substantially semicircularly recessed toward the outer peripheral side of the piston 3, thereby being the same as the large cavity section 8. A preliminary chamber portion 9 that is continuous in depth is formed. still,
The large cavity section 8 also serves as a valve recess of the intake / exhaust valve.

At a position near the injection port 7 of the large cavity portion 8, there is provided a dispersion table 10 which protrudes like an island to the same height as the top surface of the piston 3. The dispersion table 10 is provided with a nozzle 7
And has an oval planar shape that is located on the center line L so as to face the air flow and is narrow on the upstream side of the jet flow. That is, the width of the dispersion table 10 is narrower than the opening width of the injection port 7 and the both side surfaces 10 a and 10 b are inclined so as to be directed to the inside of the large cavity portion 8 outside the preliminary chamber portion 9.

At a position near the injection port 7 on the top surface of the piston 3, a groove-shaped guide portion 11 extending from the vicinity below the injection port 7 toward the center of the piston 3 is recessed. This guide 11
Is a plane having the same depth as the large cavity portion 8, the end on the side of the nozzle 7 is formed in an arc shape along the opening shape of the nozzle 7, and is fan-shaped toward the side of the large cavity 8. It has a shape and is continuous with the large cavity portion 8 through both sides of the dispersion table 10. Note that the wall surface of the outer shell forming the large cavity portion 8, the dispersion table 10, and the guide portion 11 is perpendicular to the top surface of the piston 3.

Here, the curvature of the outer shell of the large cavity portion 8 is not uniform in each portion, and the outer shell 8c on the injection port 7 side has a larger curvature than the outer shell 8b on the opposite injection port 7 side. Then, the outer shell 8d near the guide portion 11 which is the downstream end of the swirling flow
Is directed toward the center of the piston 3, more specifically, in the spare chamber 9.

Next, the operation of the above embodiment will be described.

The fuel injected into the swirl chamber 6 before the compression top dead center ignites and burns in the swirl chamber 6, and becomes a flame containing unburned fuel near the compression top dead center, from the injection port 7 to the main combustion chamber 5. Spout to the side. This combustion gas jet flows along the injection port 7 along the piston 3
Although it tries to go straight to the center side, it collides with the dispersion table 10 and diverges right and left as shown by an arrow a in FIG. That is, it flows along the guides 11 on the left and right sides of the dispersion table 10 and flows into each large cavity 8. This jet flows while circling along the outer shell 8b of the large cavity portion 8 as shown by the arrow b,
As a result, a strong swirling flow is generated in each large cavity portion 8. Therefore, the air around the large cavity 8 is widely taken in, and the combustion is rapidly diffused. The center line L
, The component traveling straight toward the preliminary chamber 9 is suppressed by the dispersion table 10, so that the collision of the flame with the cylinder bore 4 and the extinction of the flame are suppressed, and a correspondingly strong swirling flow is generated.

The jet swirled in the large cavity portion 8 flows along the outer shell 8c on the side of the injection port 7 in the latter half of the swirling, and finally flows from the outer shell 8d closer to the guide portion 11 to the preliminary chamber portion 9. Flows toward the outer shell 8a as shown by the arrow c.
The flow indicated by the arrow c similarly occurs in the left and right large cavities 8, which collide with each other in the preliminary chamber 9.
Further, a part of the combustion gas going over the dispersion table 10 and going straight ahead also flows into the preliminary chamber 9 as shown by an arrow d.
It collides with the outer shell 8a. The flow colliding with the outer shell 8a in this way is changed in the direction of the flow and diffuses toward the large cavity portion 8. Therefore, a very active turbulence occurs around the pre-chamber 9 and the mixing of the combustion gas and the air is promoted. That is, an active gas flow is obtained in the later stage of combustion in which the piston 3 is descending, and the air utilization rate in the main combustion chamber 5 can be further increased. As a result, emission of unburned fuel at low load can be suppressed, and smoke at high load can be reduced.

The swirling flow in the large cavity portion 8 is relatively directed toward the inner peripheral side by the outer shell 8c on the side of the injection port 7, so that the swirling flows generated in the pair of large cavity portions 8 collide with each other. Interference is also suppressed, and there is also an effect that the swirling flow in the large cavity portion 8 can be kept so strong.

[0019]

As is apparent from the above description, according to the combustion chamber of the vortex chamber type diesel engine according to the present invention, the combustion in the main combustion chamber in the spare chamber provided on the side opposite to the injection port of the large cavity portion. Active turbulence can be caused in the later stage, and the gas flow can be activated to promote the mixing of the combustion gas and air. Therefore, in combination with the strong swirling flow generated in the large cavity portion, the air utilization rate can be further increased, and the emission of unburned fuel at low load can be suppressed, and the smoke at high load can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view of a piston top surface showing an embodiment of a combustion chamber according to the present invention.

FIG. 2 is a cross-sectional view of a main part of the combustion chamber along the line AA in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 3 ... Piston 5 ... Main combustion chamber 6 ... Swirl chamber 7 ... Injection port 8 ... Large cavity part 9 ... Preparatory chamber part 10 ... Dispersion table 11 ... Guiding part

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F02B 19/08-19/18 F02F 3/26-3/28

Claims (1)

(57) [Claims] 1. An injection opening which is open to a peripheral portion of a main combustion chamber and is inclined so that a jet from the vortex flow chamber is directed toward a center of the main combustion chamber, and a recess provided on a piston top surface and a center line of the jet. A pair of large cavities, which are approximately circular to the left and right, and are continuous with each other at the center, and a dispersion table raised near the nozzle of the large cavity and above the center line, and from near the lower part of the nozzle A guide portion that is recessed toward the center of the piston, and that is continuous with the large cavity portion through both sides of the dispersion table. The portion of the outer shell above the jet flow center line is recessed toward the outer periphery of the piston to form a spare chamber portion that is continuous with the large cavity portion, and the tip of the outer shell near the guide portion of the large cavity portion is the spare chamber portion. Oriented A combustion chamber for a vortex chamber type diesel engine, wherein the curvature of the outer shell on the nozzle side is made larger than the curvature of the outer shell on the anti-injection side.