JPH04347330A - Piston combustion chamber of direct injection diesel engine - Google Patents

Abstract

PURPOSE:To improve combustion by optimizing a gas flow on and after mid combustion, in a piston combustion chamber of a direct-injection diesel engine. CONSTITUTION:A combustion space 14 is formed by a piston 2 so as to be opened to a top face of this piston 12, and it is provided with a protuberance 16 at the bottom center. A cavity 18 is formed in this protuberance 16, and plural pieces of connecting passages 20 are opened to a peripheral part of the protuberance 16, while they interconnect the cavity 18 and the combustion space 14 with each other.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston combustion chamber for a direct injection diesel engine, and more particularly to a piston combustion chamber for a direct injection diesel engine that can improve combustion after mid-term combustion.

0002

2. Description of the Related Art Conventional techniques for improving fuel combustion in the piston combustion chamber of a direct injection diesel engine include the following. (a) Improving the shape and structure of the intake port provided in the cylinder head to create appropriate swirl and turbulence in the piston combustion chamber during the introduction of intake air into the cylinder. (b) By improving the shape of the piston combustion chamber, appropriate vortices, vertical flows, etc. are generated within the piston combustion chamber before fuel injection, and fuel is injected at high pressure into the turbulent gas flow within the piston combustion chamber. Optimize the mixing of fuel and air.

0003

[Problems to be Solved by the Invention] All of these conventional improvement techniques relate to optimizing gas flow during initial combustion, but do not contribute to improving fuel combustion after mid-stage combustion.

An object of the present invention is to provide a piston combustion chamber for a direct injection diesel engine that can improve combustion by optimizing gas flow after mid-term combustion.

[0005]

[Means for Solving the Problems] The piston combustion chamber of this direct injection diesel engine has the following components (a) to (d). (a) A combustion space formed in the piston so as to open at the top surface of the piston (b) A raised portion raised at the bottom of this combustion space (c
) A cavity formed within the raised portion; and (d) a plurality of communicating passages that open at the periphery of the raised portion and communicate the combustion space and the cavity with each other.

[0006]

[Operation] During the compression stroke, high-pressure gas is introduced from the combustion space into the cavity through the communication path and is stored in the cavity. When the expansion stroke reaches mid-stage combustion or later, the gas pressure inside the cavity increases compared to the gas pressure in the combustion space, and the high-pressure gas stored in the cavity flows back through the communication path and flows into the combustion space from the periphery of the bulge. is derived. As a result, a longitudinal flow is generated in the combustion space.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 2 and 3 are a longitudinal sectional view and a plan view of the piston 12 of a direct injection diesel engine. A piston combustion chamber 10 is provided at the top of the piston 12. A indicates the flow direction of the vortex in the combustion space 14, and I indicates the fuel spray injected from the nozzle hole of the injection nozzle (not shown).

FIG. 1 is a detailed view of the piston combustion chamber 10. The combustion space 14 is formed in the piston 12 so as to open at the top surface of the piston 12, and has a substantially heart-shaped longitudinal section. The raised portion 16 defines the bottom surface of the combustion space 14 and is raised to a height that does not reach the top surface of the piston 12. A cavity 18 is formed within the ridge 16. As shown in FIG. 3, the plurality of communication passages 20 are arranged at equal angular intervals in the circumferential direction, extend in the radial direction when viewed from above the piston 12, and open to the combustion space 14 at the periphery of the raised portion 16. The combustion space 14 and the cavity 18 are communicated with each other. The communication passage 20 rises obliquely toward the opening on the combustion space 14 side at an angle of θ (0°<θ<45°) with respect to a plane parallel to the top surface of the piston 12. . The communication path 20 has a rectangular cross section rather than a circular cross section. A demolition core is used to form the cavity 18 and the communication path 20 within the raised portion 16. In FIG. 1, B1, C1
B2 and C2 respectively indicate the longitudinal flow and the gas flow in the communication passage 20 during the compression stroke, and B2 and C2 respectively indicate the longitudinal flow and the gas flow in the communication passage 20 after the middle combustion of the expansion stroke.

FIG. 4 shows the relationship between crank angle and cylinder pressure. Fuel injection from the injection nozzle is
Combustion is carried out a little before TDC, combustion starts immediately after TDC, and the peak of the in-cylinder pressure is a little after TDC. Initial combustion is from the start of combustion to the peak of the cylinder pressure, middle combustion is from the peak until the cylinder pressure falls to a predetermined value, and late combustion is after the middle combustion.

[0010] The operation of the embodiment will be described. In the compression stroke, high-pressure gas is generated into a vertical flow as shown in B1 in FIG. stored. When the expansion stroke reaches mid-term combustion or later, the gas pressure in the cavity 18 increases compared to the gas pressure in the combustion space 14, and the high-pressure gas stored in the cavity 18 is released as shown in FIG.
As shown in C2, the fuel flows backward through the communication path 20 and is led out from the periphery of the protuberance into the combustion space 14, producing a vertical flow as shown in B2 in the combustion space 14. This vertical flow contributes to improving the combustion of the fuel after mid-term combustion.

On the other hand, soot adheres to the communication passage 20, but since the communication passage 20 has a rectangular cross section rather than a circular cross section as in the case of drilling, it is difficult for soot to adhere to it. When the high-pressure gas is blown out from the cavity 18 to the combustion space 14, the soot is blown off and the communication passage 20 is prevented from being clogged with soot.

0012

According to the present invention, the cavity is formed within the protuberance at the bottom of the combustion space, and communicates with the combustion space through a plurality of communicating passages that open at the periphery of the protuberance. Therefore, the high-pressure gas introduced into the cavity through the communication passage during the compression stroke can be blown out into the combustion space through the communication passage after mid-term combustion during the expansion stroke, thereby generating a vertical flow within the combustion space. In this way, combustion after the middle stage combustion can be improved due to good longitudinal flow.

[Brief explanation of drawings]

FIG. 1 is a detailed view of the piston combustion chamber.

FIG. 2 is a longitudinal cross-sectional view of a piston of a direct injection diesel engine.

FIG. 3 is a longitudinal cross-sectional view of a piston of a direct injection diesel engine.

FIG. 4 is a graph showing the relationship between crank angle and cylinder pressure.

[Explanation of symbols]

10 Piston combustion chamber 12 Piston 14 Combustion space 16 Raised part 18 Hollow 20 Communication path

Claims (1)

[Claims] 1. A combustion space formed in the piston so as to open at the top surface of the piston, a raised part raised at the bottom of the combustion space, a cavity formed in the raised part, and a cavity formed in the raised part. A piston combustion chamber for a direct injection diesel engine, characterized in that it has a plurality of communicating passages that are open to the periphery and communicate the combustion space and the cavity with each other.