JP2658407B2 - Combustion chamber of a swirl chamber type diesel engine - Google Patents

Description

The present invention relates to an improvement in the shape of a combustion chamber of a vortex chamber type diesel engine.

(Prior Art) To improve the combustion of a vortex chamber type diesel engine,
There is a proposal formed in a combustion chamber as shown in FIG. 6 and FIG. 6 (Japanese Utility Model Laid-Open No. 63-79435).

A swirl chamber 5 provided in the cylinder head 4 communicates with a main combustion chamber 9 above the piston 3 via an injection port 6, and guides a jet from the injection port 6 of the swirl chamber 5 to the top surface of the piston 3. For this purpose, a groove-shaped trench portion 11 extending radially from the lower surface of the nozzle toward the center, and a pair of substantially circular shallow cavities 10 extending on both sides from the tip of the trench portion 11 are recessed. A leaf-shaped piston cavity is formed.

Along with the ignition of the fuel injected into the swirl chamber 5 near the compression top dead center, a combustion flame is ejected from the injection port 6 into the main combustion chamber 9. This jet flows into the main combustion chamber 9 by the trench 11 of the piston 3.
And further diffused as a swirling flow along the inner circumference of both cavity portions 10 as shown by arrow a,
While mixing with the air in the main combustion chamber 9, the combustion mainly occurs in a region shown by a broken line in FIG.

(Problems to be Solved by the Invention) However, in such a piston cavity, since the momentum of the linear jet flowing from the injection port 6 toward the center along the trench portion 11 as it is is too strong, the two cavity portions 10
The power of the swirling flow dispersed toward the
It is difficult for the combustion flame to spread over a wide area, resulting in a decrease in air utilization rate and, depending on operating conditions, smoke, HC, CO
However, there is a problem that the number increases.

On the other hand, the present applicant raised the dispersion table at the portion of the bottom surface of the cavity where the combustion gas jet from the injection port collides, and formed side cavities slightly smaller than the main cavity in the left and right direction to disperse the dispersion. It has been proposed that the jet diverted to the left and right due to the impact on the table can be diffused in the side cavity to promote the use of air in this part. When the momentum is strong, there is a problem that the force of the jet in the side cavities relatively decreases and a sufficient air utilization rate cannot always be obtained.

An object of the present invention is to solve such a problem.

(Means for Solving the Problems) In view of the above, the present invention provides a vortex chamber type diesel engine in which an injection port from a vortex chamber is opened at a periphery of the main combustion chamber so that the jet flows toward the center of the main combustion chamber. Along with raising the dispersion table on the surface on the center line of the jet flowing from the jet port toward the center of the piston and near the jet port,
A large cavity portion communicating with each other and extending in a substantially circular shape is recessed on both sides in front of the dispersion table, and a side cavity portion communicating with each other is recessed on both sides in front of the dispersion table. Each side cavity part is communicated on both sides of the dispersion table, and a part of the outer shell that defines each side cavity part, a jet flowing from the injection port toward the center of the piston has a large left and right cavity downstream of the dispersion table. A guide portion for guiding a jet flow passing through the side cavity portion so as to merge from the tangential direction toward the center of the piston downstream of the dispersion table with respect to the swirling flow generated by splitting the portion, while forming the side cavity portion The large cavity portion is formed such that the bottom surface of the large cavity portion is a continuous slope, and the cavity depth increases from the side cavity portion toward the large cavity portion.

(Operation) A part of the jet of the combustion gas containing the fuel from the vortex flow chamber passes over the dispersion table and is diverted to the left and right large cavities to form swirling flows, respectively. Due to the collision, the flow is split into the left and right lateral cavities, guided by the guide portion toward the center of the piston, and merges with the swirling flow of the large cavity portion from the tangential direction.

The jet merged in the large cavity portion enhances the swirling flow in the large cavity portion, and diffuses combustion over a wide range while entraining the air in the main combustion chamber.

The side cavities are shallower than the large cavities, so that the diffusion speed of the combustion gas jet is high, and the initial combustion ratio in the main combustion chamber can be increased. Also, since the bottom surface becomes deeper from the side cavity to the large cavity,
The velocity component of the jet flowing straight from the nozzle is attenuated, so that the number of jets colliding with the cylinder bore over the shell defining the large cavity can be reduced, and the flame extinguished by the collision is reduced.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

In the first embodiment shown in FIGS. 1 and 2, an injection port 6 for jetting a jet containing fuel from a swirl chamber 5 of a cylinder head 4 opens in a peripheral portion of a main combustion chamber 9 above the piston 3. A dispersion table 13 is formed on the top surface 8 of the piston 3 at a position close to the injection port 6 on the plane of the jet flow line 1 toward the center of the main combustion chamber 9.

A pair of substantially circular large cavities 12 are defined by an arc-shaped outer shell 17 symmetrically arranged with respect to the jet center line l in front of the dispersion table 13 which is formed to have a substantially rhomboid shape. Is done. A part of the outer shell 17 is formed with a facing wall portion 17A which is located on the jet flow center line 1 and protrudes in a substantially V-shape.

In addition, a side cavity portion 14 that communicates with the left and right sides is also formed in front of the dispersion table 13, and the side cavity portion 14 also communicates with the large cavity portion 12 on both side surfaces of the dispersion table 13.

An outer shell 18 defining the side cavity portion 14 is formed such that the back side of the injection port 6 is formed in an arc shape along the outer periphery of the piston 3 and gradually decreases its curvature on the connection side with the large cavity portion 12. A guide 18A curved in such a manner that the jetting gas flowing from the side cavity 14 into the large cavity 12 is joined to the dispersion table 13 so as to join from the tangential direction of the swirling flow generated in the large cavity 12 To the destination.

And, as is clear from FIG.
The bottom surface 3B of the side cavity portion 12 and the side cavity portion 14 is formed as an inclined surface such that the cavity depth continuously increases from the side cavity portion 14 toward the large cavity portion 12.

The same components as those in FIGS. 5 and 6 are denoted by the same reference numerals, and the operation will be described below.

As the phase shifts from the compression top dead center to the expansion stroke, the vortex chamber 5
The flame jet containing the unburned fuel ejected from the nozzle to the main combustion chamber 9 through the injection port 6 is partially dispersed in the dispersion table 13 immediately before the jet.
As shown by the arrow b in FIG. 1, the flow diverges into the left and right side cavities 14, and a part of the flow passes over the dispersion table 13. A swirling flow is generated in the left and right large cavities 12 with the boundary of 17A as shown by an arrow c.

In this case, the large cavity 12
As the cavity depth increases toward the, the velocity component of the jet that goes straight is attenuated, and the component that collides with the cylinder bore through the opposing wall 17A and the outer shell 17 decreases, and most of the jet flows into the inner circumference of the outer shell 17. The swirling flow is formed while being guided.

Also, the jet diverted into the side cavity portion 14 as shown by the arrow b from the front of the dispersion table 13 is guided inward by the outer guide portion 18A toward the jet center line l ahead of the dispersion table 13, Although the swirling flow merges with the swirling flow of the large cavity portion 12 from the tangential direction, the inflow speed is high, and the swirling flow can be further enhanced without causing stagnation at the merging portion.

At this time, since the outer wall 18 is smoothly curved and the cavity depth is shallow, the diffusion speed of the jet flow in the side cavity portion 14 is high, and the mixing of fuel and air is sufficiently promoted.

In this way, the jet containing the unburned fuel component diffuses outward while taking in air while generating a strong swirling flow in the large cavity portion 12, and the main combustion shown by the dotted line in FIG. The flame propagates and spreads over a wide area of the chamber 9.

As a result, good combustion with a high air utilization rate is secured over the entire area of the main combustion chamber 9, and the unburned fuel component (H
C, SOF, etc.) and the amount of smoke emission under high load can be significantly reduced.

Next, the embodiment shown in FIG. 3 and FIG. 4 will be described. This forms a gentle dish-shaped recess 12A near the center of the left and right large cavities 12 and turns generated in the large cavities 12. It is intended to further strengthen the flow.

By thus enhancing the swirling flow in the large cavity portion 12, the mixing of the unburned fuel and the air is further promoted, and efficient combustion can be performed in a short time.

(Effects of the Invention) As described above, according to the present invention, a part of the jet from the injection port is diverted from the front of the dispersion table to the shallow side cavity portion and diffused to increase the initial combustion ratio, and further cross the dispersion table. By mixing the jet from the side cavity with the swirl due to the jet that has entered the large cavity, the swirling flow in the large cavity can be strengthened and the mixing of fuel and air can be promoted. The cavity is relatively shallow, and the bottom of the cavity is formed so that the depth of the cavity gradually increases with the slope that continues toward the large cavity, so that the diffusion of the jet in the side cavity can be surely promoted. Therefore, it is possible to prevent the jet flowing toward the large cavity portion from colliding with the cylinder bore and causing quench, and as a result, a high air utilization rate can be obtained throughout the entire main combustion chamber. Good combustion can be ensured, and the effect of reliably reducing unburned fuel components (HC, SOF, etc.) at low load and smoke emission at high load can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view of a first embodiment of the present invention, and FIG.
FIG. 3 is a sectional view taken along line AA of FIG. 3, FIG. 3 is a plan view of the second embodiment,
FIG. 4 is a sectional view taken along the line BB of FIG. 3, FIG. 5 is a plan view of a conventional example, and FIG. 6 is a sectional view of the same. 3 ... piston, 3B ... bottom, 4 ... cylinder head,
5 vortex chamber, 6 nozzle, 9 main combustion chamber, 12 large cavity section, 13 dispersion table, 14 side cavity section, 18A guide section.

Claims (1)

(57) [Claims] In a vortex chamber type diesel engine having an injection port from a vortex chamber opened to a peripheral portion of a main combustion chamber so that a jet flows toward a center of the main combustion chamber, a top surface of the piston is formed on the top surface of the piston from the injection port toward the center of the piston. The dispersing table is raised so as to be located on the center line of the heading jet and close to the nozzle, and a large cavity that extends in a substantially circular shape and communicates with each other on both sides in front of the dispersing table is recessed. The side cavities communicating with each other are recessed on both sides, each side cavity is communicated on both sides of the dispersion table with each large cavity, and a part of the outer shell that defines each side cavity is formed. The swirl flow generated by the jet flowing from the injection port toward the center of the piston splitting into the left and right large cavities downstream of the dispersion table is combined from the tangential direction toward the piston center downstream of the dispersion table. The guide portion for guiding the jet flowing through the side cavity portion is formed so that the bottom surface of the side cavity portion and the bottom surface of the large cavity portion are continuous slopes, and the cavity depth increases from the side cavity portion to the large cavity portion. A combustion chamber for a swirl chamber type diesel engine, characterized in that the combustion chamber is formed so as to increase in height.