JPH0343618A - Combustion chamber of vortex chamber diesel engine - Google Patents

Abstract

PURPOSE:To improve combustion efficiency by letting one part of jet from a vortex chamber pass over a dispersion board and flow into right and left large cavities, and by letting the other part thereof collide with the dispersion board and flow into right and left side cavities. CONSTITUTION:A nozzle hole 6 by which a fuel jet is blown out of a vortex chamber 5 of a cylinder head 4, is opened to a periphery of a main combustion chamber 9 on the upper part of a piston 3. In the vicinity of a nozzle hole 6 on a jet center line 1 directed to the center of the main combustion chamber 9, a dispersion board 13 is arranged. In front of the dispersion board 13, a pair of large cavities 12 is formed out of arc outer shells 17 arranged symmetrically around the jet center line 1. Before the dispersion board 13, a pair of right and left side cavities 14 communicating with each other is formed. An outer shell 18 that forms the side cavities 14, forms a guiding part 18A curved so as for a curvature to be gradually smaller, on the connecting side with the large cavities 12.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in the shape of the combustion chamber of a swirl chamber type diesel engine.

(Prior art) In order to improve the combustion of swirl chamber type diesel engines, the methods shown in Fig. 5,
There is a proposal for forming a combustion chamber as shown in No. 612 (Japanese Utility Model Application No. 63-79435).

A swirl chamber 5 provided in the cylinder head 4 communicates with the main combustion chamber above the piston 3 via a nozzle 6, and a top surface of the piston 3 is provided to guide the jet from the nozzle 6 of the swirl chamber 5. A groove-shaped trench portion 11 extending radially from the lower surface toward the center, and a pair of approximately circular shallow cavity portions IO extending from the tip of the trench portion 11 to both sides are recessed in the groove, thereby forming a so-called crowbar. - Forms a leaf-shaped piston cavity.

As the fuel injected into the swirl chamber 5 is ignited near compression top dead center, combustion flame is ejected from the nozzle port 6 into the main combustion chamber 9. This jet flow is transmitted to the main combustion chamber 9 by the trench portion 11 of the piston 3.
It is guided to the center of the combustion chamber 9, and further diffuses as a swirling flow along the inner periphery of both cavity parts 0 as shown by arrow a, and as it mixes with the air in the main combustion chamber 9, mainly the It burns in the area indicated by the dashed line.

(Problems to be Solved by the Invention) However, in such a piston cavity, the force of the linear jet flow directly from the nozzle 6 toward the center along the trench portion 11 is too strong.
The force of the swirling flow that disperses toward zero becomes weaker, and the combustion flame spreads over a wide area of the main combustion chamber 9. As a result, the air utilization rate decreases, and depending on the operating conditions, smoke and HC
, C0 increases.

The present invention aims to solve such problems.

<Means for Solving the Problems> Accordingly, the present invention provides a swirl chamber type diesel engine in which a jet nozzle from a swirl chamber is opened at the periphery of the main combustion chamber so that the jet flows toward the center of the main combustion chamber. A dispersion table is raised on the surface so as to be located on the center line of the jet stream and near the nozzle, and a large approximately circular cavity portion that communicates with each other is recessed on both sides of the dispersion table, and a large cavity portion in the front side of the dispersion table is recessed. A part of the outer shell that is recessed with side cavities that communicate with each other on both sides, and that communicates with each large cavity when both sides of the dispersing table are opened, and that defines each side cavity. A guide part is formed to guide the jet flow from the side cavity part in the tangential direction of the swirling flow generated in the large cavity part. The cavity was formed so that the depth increased from the top toward the large cavity.

(Function) Part of the jet of combustion gas containing fuel from the swirl chamber passes over the dispersion table and flows into the left and right large cavities, creating a swirling flow along the inner circumference of the cavity. The flow is split into the left and right side cavities due to the collision with the flow, and flows into the large cavity ahead of the dispersion table from the tangential direction of the swirling flow while being guided by the guide section.

The jets that merge in the large cavity strengthen the swirling flow in the large cavity, and spread combustion over a wide area while drawing in air from the main combustion chamber.

The side cavity portions are shallower than the large cavity portion, and therefore the diffusion rate of the jet of combustion gas is faster, increasing the initial combustion rate in the main combustion chamber. In addition, because 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, causing the jet to cross over the outer shell that defines the large cavity and collide with the cylinder bore. This reduces the number of flames extinguished by collision.

(Example) Embodiments of the present invention will be described below based on the drawings.

In the first embodiment shown in FIGS. 1 and 2, a jet port 6 for jetting a jet containing fuel from a swirl chamber 5 of a cylinder rad 4 is opened in the periphery of a main combustion chamber 9 above a piston 3. However, on the plane, a dispersion table 13 is formed on the top surface 8 of the piston 3 at a position close to the nozzle 6, located on the jet center line 2 toward the center of the main combustion chamber 9.

A pair of substantially circular large cavity portions 12 are defined by arc-shaped outer shells 17 arranged symmetrically across the jet flow center line l at the forward end of the dispersing table 13 formed by protruding into a substantially diamond shape. be done. A part of this outer shell 17 has the jet center line l.
A facing wall portion 17A is formed which is located above and protrudes in a substantially V-shape.

Further, in front of the dispersing table 13, there is formed a side cavity part (4) which also communicates with each other on the left and right sides, and this side cavity part 14 also communicates with the large cavity part 12 on both sides of the dispersing table 13.

The outer shell 18 defining the side cavity part 14 has an arcuate shape on the back side of the nozzle 6 along the outer periphery of the piston 3, and its curvature gradually decreases on the side connected to the large cavity part 12. Guide portion 18A curved as shown in FIG.
The dispersing table 1 is shaped such that the jet gas flowing from the side cavity part 14 into the large cavity part 12 is merged from the tangential direction of the swirling flow generated in the large cavity part 12.
I will guide you towards the destination of 3.

As is clear from Fig. 2, the large cavity part 1
2 and the bottom surface 3B of the side cavity part 14 are formed as inclined slopes such that the cavity depth increases continuously from the side cavity part 14 toward the large cavity part 12.

The structure is as described above, and the same parts as in FIGS. 5 and 6 are given the same reference numerals, and the operation will be explained next.

As it moves from the compression top dead center to the expansion stroke, a part of the flame jet containing unburned fuel ejected from the vortex chamber 5 into the main combustion chamber 9 via the jet nozzle 6 is transferred to the dispersion table 13 located immediately in front of the jet.
The jet collides with the jet, and the flow is divided into the left and right side cavity parts 14 as shown by the arrows in FIG. A swirling flow as shown by arrow C is generated in the left and right large cavity portions 12 with 17A as the boundary.

In this case, from the side cavity part 14 to the large cavity part 1
As the cavity depth increases toward 2, the velocity component of the straight-advancing jet is attenuated, and the component that crosses over the opposing wall 17A and the outer shell 17 and collides with the cylinder bore is reduced, and most of the jet flows toward the inner periphery of the outer shell 17. A swirling flow is formed while being guided by the flow.

Further, the jet flow branched from the front side of the dispersion table 13 to the side cavity part 14 as indicated by the arrow is guided inward by the outer guide part 18A toward the jet center line l ahead of the dispersion table 13, It joins the swirling flow in the large cavity part 12 from the tangential direction, but the inflow speed is fast and the swirling flow can be further strengthened without causing stagnation at the merging portion.

At this time, since the outer shell 18 is smoothly curved and the cavity depth is shallow, the jet flow from the side cavity portion 14 has a high diffusion rate and sufficiently promotes mixing of fuel and air.

In this way, the jet stream containing unburned fuel components generates a strong swirling flow in the large cavity part 12 and diffuses combustion outward while taking in air. The flame propagates and spreads over a wide area of room 9.

As a result, good combustion with a high air utilization rate is maintained throughout the main combustion chamber 9, and unburned fuel (H
C, SOF, etc.) and smoke emissions during high loads can be significantly reduced.

Next, the embodiment shown in FIGS. 3 and 4 will be described. In this embodiment, a gentle dish-shaped recess 12A is formed near the center of the left and right large cavity parts 12, and the turning generated in the large cavity part 12 is This is to further strengthen the flow.

By strengthening the swirling flow in the large cavity portion 12 in this manner, mixing of unburned fuel and 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 nozzle is diverted from in front of the dispersion table to the shallow side cavity part and diffused, accelerating the initial combustion rate, and further overflowing the dispersion table. This creates a swirling flow in the jet flow that has flowed into the large cavity part, and by merging the jet flow from the side cavity part in the tangential direction, the swirling flow is strengthened and the mixing of fuel and air is further promoted. By deepening the bottom of the cavity as the center of the jet moves toward it, the jet that impinges on the cylinder bore is suppressed and quenching of the combustion flame is reduced.As a result, the air utilization rate is high throughout the main combustion chamber. This ensures efficient combustion and reduces unburned fuel (HC) during low loads.
, SOF, etc.) and the amount of smoke emitted during high loads can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a plan view of the first embodiment of the present invention, and FIG. 2 is a plan view of the first embodiment of the present invention.
3 is a plan view of the second embodiment,
4 is a sectional view taken along the line B--B in FIG. 3, FIG. 5 is a plan view of the 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 part, 13 - Dispersion table , 14・
...Side cavity part, 18A...Guide part.

Claims (1)

[Claims] In a swirl chamber type diesel engine in which the jet from the swirl chamber is opened at the periphery of the main combustion chamber so that the jet flows toward the center of the main combustion chamber, the jet is located on the top surface of the piston on the center line of the jet and close to the jet. As well as raising the dispersion table,
A substantially circular large cavity portion that communicates with each other is recessed on both sides of the front side of the dispersion table, and a side cavity portion that communicates with each other is recessed on both sides of the front side of the dispersion table. A guide for communicating the side cavity parts on both sides of the side cavity part and guiding the jet flow from the side cavity part in the tangential direction of the swirling flow generated in the large cavity part to a part of the outer shell defining each side cavity part. A vortex chamber characterized in that the bottom surfaces of the side cavity part and the large cavity part are continuous slopes, and the cavity depth increases from the side cavity part to the large cavity part. Combustion chamber of a diesel engine.