JPH05306619A - Direct injection type diesel engine - Google Patents

Abstract

PURPOSE:To prevent the generation of black smoke by preventing flame from coming out by properly combusting owing to the generation of strong longitudinal vortexes. CONSTITUTION:A projection section 13 is provided at the center of the cavity 12 formed on the top of a piston 11 to form a ring-like combustion chamber 14 having a nearly circular longitudinal section. A turning area 17 is partitioned between an extension section 16 and the projection section 13 with the peripheral edge of the top 15 of the projection section 13 extended in an arc state to the center side of the longitudinal section of the combustion chamber 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection diesel engine.

[0002]

2. Description of the Related Art Generally, a direct injection type diesel engine has good output and fuel efficiency, but has a problem that it emits more NO _X and black smoke than a sub-chamber type diesel engine. As measures against this, there are those that make the shape of the combustion chamber square in plan view and generate small vortexes at the corners, or those that narrow the inlet of the combustion chamber to generate strong squish (reentrant type). Good combustion is achieved by mixing the flow and the fuel spray.

In order to meet the recent strict demand for black smoke reduction, a combustion chamber having an annular shape ("air compression type valve control internal combustion engine", JP-A-63-162925) is also proposed. ing. As shown in FIG. 7, in this proposal, an annular combustion chamber 2 is defined at the top of a piston 1, an opening 3 is provided that is slightly narrower than its outer diameter, and a central portion 4 having an upper surface of a truncated cone shape. Therefore, the fuel is injected from the fuel injection nozzle 5 so as not to overwhelm the air, and a strong vortex flow in the vertical direction is generated to obtain a high air-fuel mixture forming energy to perform good combustion. With this configuration, it is said that black smoke can be reduced especially in the low / medium speed engine rotation range including the time of starting.

[0004]

However, in the above proposal, there remains a problem that the black smoke reducing effect in the engine high speed region is small. The reason is that the longitudinal vortex flow along the side wall of the combustion chamber 2 becomes too strong in the high speed region, and flame (combustion gas) exits the combustion chamber 1 earlier when the piston descends, and the bottom surface of the cylinder head 6 and the piston It is considered that soot (black smoke) is generated due to the interference with the upper surface of 1 and cooling.

In view of the above circumstances, the present invention was devised to provide a direct-injection diesel engine which obtains a strong longitudinal vortex flow and prevents flame from coming out of the combustion chamber to obtain good combustion.

As another conventional technique, there is a "diesel combustion chamber" (Japanese Patent Laid-Open No. 62-75022). In this structure, although a strong vertical airflow can be obtained by restricting the opening, It is difficult to generate the desired strong vortex. Further, Japanese Patent Application Laid-Open No. 53-65511 (“Combustion chamber structure of internal combustion engine”) discloses a configuration capable of generating a vertical vortex flow, but it is not enough to prevent flame from coming out of the combustion chamber. Considered sufficient.

[0007]

According to the present invention, a protrusion is provided in the center of a cavity formed at the top of a piston to form an annular combustion chamber having a substantially circular vertical cross section, and a peripheral edge of an upper surface of the protrusion is formed. The combustion chamber is extended in an arc shape toward the center of the vertical cross section, and a swirl region is defined between the extended portion and the protrusion.

[0008]

With the above structure, the protrusion guides the air flowing into the combustion chamber to form a strong vertical vortex. The annular combustion chamber satisfactorily forms an air-fuel mixture with the fuel spray by a vertical vortex flow for combustion, re-combusts unburned components in the swirl region, and traps the flame to complete combustion.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an embodiment of a direct injection type diesel engine according to the present invention. In this direct injection diesel engine, a protrusion 13 is provided in the center of a cavity 12 formed at the top of the piston 11, an annular combustion chamber 14 is formed, and a peripheral edge of an upper surface 15 of the protrusion 13 burns. The chamber 14 is appropriately extended, and a swirl region 17 is defined between the extended portion 16 and the protrusion 13.

In the present embodiment, the longitudinal cross section of the annular combustion chamber 14 has a horizontally flat elliptical shape, and the lateral diameter (piston radial direction) length L ₁ is the longitudinal diameter (piston axial direction). Is formed so as to be longer than the length L ₂ (L ₁ > L ₂ ). The opening 18 is narrowed so as to have a diameter slightly smaller than the outer diameter of the combustion chamber 14, and is connected to the outer peripheral side wall 19 of the combustion chamber 14 with a smooth curved surface.
An intermediate region 20 that connects 8 and the combustion chamber 14 is defined.

The upper surface 15 of the protrusion 13 is formed in a gentle conical shape and is located below the fuel spray 22 injected from the fuel injection nozzle 21. The extending portion 16 is formed of a thin arc-shaped plate that hangs downward in an eaves-like shape, and its tip 23 extends so as to reach the center of the elliptical cross section of the combustion chamber 14. That is, the distance between the tip 23 and the outer end of the combustion chamber is half the major axis (= 1/2 L ₁ ), and the distance from the lower end of the combustion chamber is half the minor axis (= 1/2 L ₂ ). Has been done. The curved surface relating to the inflow path of the air, that is, the vertical section curve from the outer peripheral side wall 19 to the bottom wall 24, the peripheral wall 25 of the protrusion and the inner side surface of the extending portion 16 to the tip 23 is a smooth spiral curve. Is formed.

Next, the operation of this embodiment will be described.

As shown in FIG. 2, at the end of the compression stroke, the air in the gap between the upper surface 26 of the piston 11 and the lower surface 28 of the cylinder head 27 is pushed into the combustion chamber 14 through the opening 18 and is projected. It flows between the portion 13 and the extending portion 16 and the outer peripheral side wall 19 and flows along the outer peripheral side wall 19 and the bottom wall 24. During this inflow process, a strong vertical vortex is formed as shown by the arrow a in the figure. Then, this air flow continues to enter the swirl region 17 and flows along the peripheral wall 25 of the protrusion 13 and the inside of the extending portion 16, whereby a similar vertical vortex flow is generated.

Then, as shown in FIG. 3, when the fuel is injected near the top dead center of the piston, the spray 22 collides with the longitudinal vortex flow to form an appropriate air-fuel mixture, and is rapidly self-ignited by high compression. .. The flame F spreads from the ignition point A to the periphery thereof in accordance with the spray shape, and most of it spreads on the longitudinal vortex flow and spreads to the mixture in the swirling region 17, and good combustion is performed. At this time, the soot or unburned fuel produced by the combustion of the fuel stuck to the outer peripheral side wall 19 is caught in the flame F and recombusted. And the flame F in the turning area 17
Is blocked by the extension portion 16 and is prevented from flowing into the gap with the lower surface 28 of the cylinder head, and combustion is continued for a sufficient time.

Next, as shown in FIG. 4, in the latter stage of combustion when the piston 11 descends, the flame F, which has been trapped, spouts upward, but extremely strong turbulence is generated near the tip 23 of the extending portion 16. , Soot partially remaining in flame F (unburned)
Is also burned again.

As described above, the protrusion 13 forming the annular combustion chamber 14 having an elliptical cross section, and the extension 16 appropriately extended in an arc shape so as to define the swirl region 17 between the protrusion 13 and the protrusion 13. Since it is provided, a strong vertical vortex is formed in the combustion chamber 14 and good combustion is obtained, and the flame F is generated in the swirl region 17.
Can be confined for a predetermined time, and in particular, in a high speed region, the flame F can be prevented from coming out of the combustion chamber 14, and the generation of black smoke can be significantly reduced.

Since the upper half of the protrusion 13 and the extension 16 are heated to a high temperature, as shown in FIG. 5, this portion 31 is molded with a heat resistant material such as ceramics or heat resistant metal material to improve durability. You may make it improve. This molding can be manufactured by bolting or integral casting.

Further, as shown in FIG. 6, the central upper surface 42 of the protrusion 41 may be recessed to reduce the weight.
It should be noted that the fuel spray does not enter this recess 43, and even if there is, it is a very small amount, so there is no possibility that it will evaporate and burn immediately and remain as unburned fuel.

In the above embodiment, the cross section of the annular combustion chamber 14 is a horizontally long ellipse, but the present invention is not limited to this, and may be any substantially circular shape so that a vertical vortex flow is appropriately formed. Further, although the tip of the extending portion is located at the center of the cross-sectional shape, it may be formed in any manner as long as it is capable of confining the flame by partitioning the swirling chamber suitable for the longitudinal vortex flow.

[0021]

In summary, according to the present invention, the following excellent effects are exhibited.

A protrusion is provided in the center of the cavity to form an annular combustion chamber having a substantially circular vertical section, and the upper edge of the protrusion extends toward the center of the vertical section to define the swirl region. Good combustion can be obtained by the longitudinal vortex flow, and the flame can be prevented from exiting from the combustion chamber by confining the flame in the swirling region, so that the generation of black smoke can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an embodiment of a direct injection diesel engine according to the present invention.

FIG. 2 is a side sectional view showing the state at the end of the compression stroke for explaining the operation of FIG.

FIG. 3 is a side sectional view showing a combustion stroke which is the next stage of FIG.

FIG. 4 is a side sectional view showing a latter stage of the combustion stroke, which is the next stage of FIG.

FIG. 5 is a side sectional view showing another embodiment of FIG.

6 is a side sectional view showing a modified example of FIG.

FIG. 7 is a side sectional view showing a conventional direct injection diesel engine.

[Explanation of symbols]

 Reference Signs List 11 piston 12 cavity 13 protrusion 14 annular combustion chamber 15 protrusion upper surface 16 extension 17 swirl region

Claims (1)

[Claims] 1. A protrusion is provided in the center of a cavity formed at the top of a piston to form an annular combustion chamber having a substantially circular vertical cross section, and the upper peripheral edge of the protrusion is the vertical cross section of the combustion chamber. A direct-injection diesel engine, which is characterized in that it extends in an arc shape toward the center side, and a swirl region is defined between the extending portion and the protrusion.