JPH0561426U - Combustion chamber of swirl chamber type diesel engine - Google Patents

Abstract

(57) [Abstract] [Purpose] To widely diffuse a jet flow ejected from a swirl chamber without using a dispersion stand and to generate turbulence to improve the air utilization rate. A pair of large cavities 8 are provided on the top surface of the piston 3 so as to sandwich the jet centerline L, and a lateral cavity 10 is provided on the front side so as to spread laterally. At the connecting portion of the pair of large cavities 8, a facing wall portion 9 extending in a tongue shape is formed. Between the swirl chamber and the main combustion chamber, in addition to the main injection port 7, a thin sub injection port 12 is provided. The sub injection port 12 is open on the jet flow center line L and closer to the center of the main combustion chamber than the main injection port 7, and the opening end is inclined toward the main injection port 7.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an improvement in a combustion chamber of a swirl chamber type diesel engine, and more particularly to an improvement in a piston side cavity structure.

[0002]

[Prior Art]

 In a swirl chamber type diesel engine, a so-called clover bar is provided in which a groove-shaped trench extending from the lower side 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 are continuous at the tip of the trench. A configuration in which a leaf-type cavity is recessed (for example, Japanese Utility Model Laid-Open No. 63-79435) is generally used. However, in this type of cavity structure, the flow of the jet flow that attempts to go straight along the trench portion from the injection port. Is too strong, the proportion of flames that cross over large cavities and collide with the cylinder bores to extinguish is relatively large, and the flames are hard to spread over a wide area of the main combustion chamber.

Therefore, the applicant of the present invention has previously disclosed that, in Japanese Patent Laid-Open No. 1-200012, etc., a pair of large cavities are provided on the top surface of the piston so as to sandwich the center line of the jet from the nozzle, and Proposal of a combustion chamber structure in which a dispersion base is raised like an island on the center line and near the injection port, and side cavities communicating with the large cavity are formed on both sides of the front side of the dispersion base. is doing.

[0004] In this structure, the jet jet initially ejected from the swirl chamber collides with the dispersion table and diffuses into the lateral cavity portion, and at the same time, a part of the gas whose straight velocity component is weakened by the collision is dispersed into the dispersion table. Overcoming the flow into the large cavity, where a swirl flow is generated. In addition, as the piston descends, most of the jet flow passes over the dispersion table and flows into the large cavity.However, at this stage, the straight velocity component is weak, so again the swirling flow along the inner circumference of the large cavity. Cause. Therefore, it is possible to obtain a good air utilization rate in the main combustion chamber.

[0005]

[Problems to be solved by the device]

 However, in the structure where the disperser is provided on the top surface of the piston as described above, the disperser has a locally protruding shape in the main combustion chamber and is strongly affected by the jet flow from the swirl chamber, which causes a partial heat load. Is likely to be high, which is not preferable in terms of durability.

Therefore, the present invention seeks to provide a combustion chamber structure that can similarly increase the air utilization rate without using a dispersion base.

[0007]

[Means for Solving the Problems]

 The combustion chamber of the swirl chamber type diesel engine according to the present invention has a main injection port which is opened in the peripheral portion of the main combustion chamber and is inclined so that the jet flow from the swirl chamber is directed toward the center of the main combustion chamber, and the center of the jet flow. It opens on the line and closer to the center of the main combustion chamber than the main injection port, and its opening end is recessed in the piston top surface and the auxiliary injection port that is perpendicular to the piston top surface or inclined toward the main injection port. In addition, a pair of large cavities that spread out to the left and right in a roughly circular shape across the jet centerline, and a recess at the piston top surface near the main injection port are provided along the periphery of the piston from below the main injection port. The lateral cavity that communicates with the large cavity and a part of the outer shell that defines the lateral cavity, and the jet from the lateral cavity swirls in the large cavity. Tangential line of flow A guide wall portion for guiding the direction, the connection portions of the pair of the large cavity, and with its formed as part of the shell, and wherein a call with an opposite wall portion extending toward the main nozzle hole.

[0008]

[Action]

 Combustion gas containing unburned fuel generated in the swirl chamber ejects in the form of flame mainly from the main injection port into the main combustion chamber near the top dead center of the piston. The jet exiting this main jet collides with the bottom surface of the lateral cavity portion and tries to go straight along the jet center line. On the other hand, a part of the combustion gas in the swirl chamber is jetted vertically or toward the main jet through the sub jet. Therefore, the jet from the main jet is dispersed right and left, and diffuses into the lateral cavity.

Further, a part of the jet flow exiting the main jet goes straight as it is, but the straight velocity component is weakened by the collision with the jet from the sub jet. Therefore, this straight jet is smoothly diverted by the opposing wall to generate a swirling flow in the large cavity, and the air near the large cavity is effectively used. At this time, active turbulence occurs due to collision with the jet flow from the sub-injection port, and mixing of air and fuel is promoted. Then, the jet flow heading to the lateral cavity portion merges into the large cavity portion along the guide wall portion from a substantially tangential direction of the swirling flow.

[0010]

【Example】

 An embodiment of the present invention will be described below in detail with reference to the drawings.

1 and 2 show an embodiment of the present invention, in which 1 is a cylinder block, 2 is a cylinder head, and 3 is 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 a main combustion chamber 5 is formed between the top surface of the piston 3 and the top surface.

The substantially spherical swirl chamber 6 is located along the side of the cylinder head 2, and a main injection port 7 extending substantially tangentially from the swirl chamber 6 opens in the peripheral portion of the main combustion chamber 5. is doing. The main injection port 7 has a flat passage cross-section that is slightly wider in the width direction, and is inclined so that the jet flow from the swirl chamber 6 is directed toward the center of the main combustion chamber 5. In FIG. 1, the center line of the jet on the plane of the piston 3 is indicated by the symbol L.

On the top surface of the piston 3 that defines the main combustion chamber 5, a pair of substantially circular large cavities 8 are formed at a constant depth near the center of the piston 3. The large-cavity portion 8 extends laterally across the center line L, has a shape of a figure 8 as a whole, and central portions along the center line L are continuous and integral with each other. The outer shell on the center line L, which is the connecting portion between the two, extends in a tongue shape toward the main injection port 7 and forms an opposing wall portion 9 that partitions both large cavity portions 8. The large cavity portion 8 also serves as a valve recess for an intake / exhaust valve (not shown).

At a position near the main injection port 7 on the top surface of the piston 3, a lateral cavity portion 10 is provided recessed from the lower vicinity of the main injection port 7 to the left and right along the periphery of the piston 3. The lateral cavity portion 10 has a constant depth in each part, specifically, the same depth as the large cavity portion 8, and the lateral cavity portion 10 and the large cavity portion 8 are located in front of the main injection port 7. The parts of are in communication with each other. The outer shell 11a of the side cavity portion 10 on the rear side of the main injection port 7 has an arc shape along the peripheral edge of the piston 3. In addition, the outer shells on both the left and right sides are smoothly curved toward the center of the piston 3, and guide the jet flow from the lateral cavity portion 10 in a substantially tangential direction of the swirl flow generated in the large cavity portion 8. The wall part 11b is formed. The wall surface of the outer shell forming the large cavity portion 8 and the lateral cavity portion 10 is a surface perpendicular to the top surface of the piston 3.

A sub-injection port 12 is provided between the swirl chamber 6 and the main combustion chamber 5 in addition to the main injection port 7 described above. The auxiliary injection port 12 has a passage cross-sectional area smaller than that of the main injection port 7. The auxiliary injection port 12 extends from the lower part of the swirl chamber 6 toward the center of the main combustion chamber 5, and is bent downward by approximately 90 ° to the main direction. The opening end 12a on the combustion chamber 5 side is slightly inclined toward the main injection port 7. That is, the auxiliary injection port 12 is open on the main combustion chamber 5 side, on the jet center line L, and closer to the main combustion chamber 5 center side than the main injection port 7. The end portion 12b on the side of the swirl chamber 6 is open along the forward direction of the swirl flow formed in the swirl chamber 6 by the main injection port 7. The hot plug 13 forming the lower half portion of the swirl chamber 6 has an oval shape close to a fan shape so as to include the sub injection port 12.

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

The fuel injected into the swirl chamber 6 before the compression top dead center is ignited and burned in the swirl chamber 6, and becomes a flame containing unburned fuel near the compression top dead center and is mainly ejected from the main injection port 7. To do. The jet of the combustion gas collides with the bottom surface of the lateral cavity portion 10 facing the main jet port 7 and tries to go straight along the jet center line L. On the other hand, a part of the combustion gas in the swirl chamber 6 is ejected toward the main combustion chamber 5 side also through the sub injection port 12. The jet flow exiting the sub jet port 12 becomes a thin rod-like flow, and heads toward the main jet port 7 side so as to face the jet flow from the main jet port 7. Therefore, the jet flow from the main jet port 7 collides with the thin jet flow from the sub jet port 12 and is dispersed to the left and right. That is, the jet flow spreads to the left and right of the lateral cavity portion 10 as shown by the arrow a in FIG. 1, and takes in the air around it.

Further, a part of the jet flow exiting the main jet port 7 goes straight along the jet center line L, and is split left and right by the facing wall portion 9 as shown by an arrow b in FIG. A swirl flow is generated within 8. As a result, the combustion is diffused while taking in the air near the large cavity portion 8. At this time, since the straight-flow velocity component of the jet flow is weakened by the collision with the jet flow from the sub-injection port 12, the number of flames extinguished by colliding with the cylinder bore 4 by overcoming the opposing wall part 9 is reduced, and at the same time, the opposing wall part is reduced. 9 allows smooth guiding to each large cavity portion 8, and a stronger swirling flow can be obtained. Then, as described above, the jet flow spreading to the left and right of the lateral cavity portion 10 is guided to the large cavity portion 8 side along the inner wall portion 11b, and as shown by an arrow c in FIG. It smoothly joins the swirl flow from the tangential direction. Therefore, the swirl flow in the large cavity portion 8 is further strengthened.

Further, as a result of the jet flow attempting to go straight from the main jet port 7 intersecting with the thin jet flow coming out of the sub jet port 12, active jet turbulence is generated in the jet flow toward the large cavity portion 8 and air near the large cavity portion 8 is generated. Mixing with unburned fuel is further promoted.

In this way, good combustion with a high air utilization rate can be secured in a wide range of the main combustion chamber 5, and smoke and HC can be reduced. Further, in the above configuration, since there are no local protrusions exposed to high temperature in the main combustion chamber 5, it is advantageous in terms of heat load as compared with the one having the dispersion base.

By the way, in the compression stroke, a strong swirl flow is generated in the swirl chamber 6 by pushing the air in the main combustion chamber 5 into the swirl chamber 6 through the main injection port 7. At that time, Since the air flowing into the swirl chamber 6 through the sub-injection port 12 is also guided along the forward direction of the swirl flow, the swirl flow in the swirl chamber 6 is not weakened.

Although the opening end 12a of the auxiliary injection port 12 on the side of the main combustion chamber 5 is inclined toward the main injection port 7 in the above-described example, even if it is oriented in a direction close to vertical, It is possible to sufficiently obtain the action of dispersing the jet flow emitted from the main jet port 7.

[0023]

[Effect of the device]

 As is clear from the above description, in the combustion chamber of the swirl chamber type diesel engine according to the present invention, the jet ejected from the auxiliary jet collides with the main jet ejected from the main jet, so that the jet is generated in the same manner as the dispersion stand. The jet flow can be diffused to the left and right of the one cavity, and the straight velocity component can be weakened to some extent to efficiently generate a swirl flow in the large cavity. Moreover, the jet flow is accompanied by active turbulence due to the collision of the two. Therefore, the air utilization ratio can be increased over the entire area of the main combustion chamber, and smoke and HC are reduced. Moreover, since no local protrusions are used unlike the dispersion stand, it is advantageous in terms of heat load and durability.

[Brief description of 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 the main part of the combustion chamber taken along the line AA of FIG.

[Explanation of symbols]

 3 ... Piston 5 ... Main combustion chamber 6 ... Vortex chamber 7 ... Main injection port 8 ... Large cavity part 9 ... Opposing wall part 10 ... Side cavity part 11b ... Guide wall part 12 ... Sub injection port

Claims (1)

[Scope of utility model registration request] 1. A main injection port which is open in the peripheral portion of the main combustion chamber and is inclined so that a jet flow from the swirl chamber is directed toward the center of the main combustion chamber, and a main jet on the center line of the jet flow and more than the main jet port. A sub-injection opening to the center of the combustion chamber, the opening end of which is perpendicular to the piston top surface or inclined toward the main injection port, and recessed in the piston top surface, and left and right across the jet center line. A pair of large cavities that spread in a substantially circular shape, and a recess at a position near the main injection port on the top surface of the piston, and spread laterally along the periphery of the piston from below the main injection port and communicate with the large cavity. A pair of a side cavity portion and a guide wall portion that forms a part of an outer shell that defines the side cavity portion and guides a jet flow from the side cavity portion in a substantially tangential direction of the swirling flow in the large cavity portion, Large cavity part A combustion chamber of a swirl chamber type diesel engine, characterized in that the connection part of the swirl chamber type diesel engine is provided with a facing wall part formed as a part of the outer shell thereof and extending toward the main injection port.