JP2019070337A - Self-ignition type internal combustion engine and piston - Google Patents

Abstract

To provide a self-ignition type internal combustion engine capable of enhancing utilization efficiency of air in a squish area.SOLUTION: A self-ignition type internal combustion engine of this invention includes a combustion chamber N which is defined and formed between a cylinder head 20 and a cavity 11 provided on a top surface of a piston 10, and an injector I for injecting fuel in the combustion chamber N. The cavity 11 presents an inclined shape in which an inner peripheral side surface 11a of the cavity 11 is formed linearly from a bottom surface to the opening end in such a manner that an opening diameter of the cavity 11 is enlarged as going to the opening end from the bottom surface side, and the injector I injects the fuel toward a boundary area between the inner peripheral side surface 11a of the cavity 11 and the bottom surface.SELECTED DRAWING: Figure 3

Description

  The present disclosure relates to a self-ignition internal combustion engine and a piston.

  Conventionally, as a self-ignition internal combustion engine (hereinafter also referred to as "diesel engine"), one having a reentrant combustion chamber structure has been known (see, for example, Patent Document 1).

  FIG. 1 is a cross-sectional view of a reentrant combustion chamber Np according to the prior art.

  In the reentrant type combustion chamber structure, the opening of the cavity portion (concave region) N1 on the top surface of the piston N0 constituting the combustion chamber Np is narrowed by the lip portion N2 formed at the opening edge, and the bottom surface of the cavity portion N1 There is a structure in which a conical protuberance is disposed. A squish portion N3 is formed on the outer periphery of the cavity portion N1 to form a gap (hereinafter also referred to as a "squish region") with the cylinder head portion N4.

  In such a reentrant type combustion chamber structure, the fuel spray F from the injector I is injected toward the lip N2 near the top compression center of the piston and mixed with air in the cavity N1 after collision with the lip N2. And burn in the cavity N1. In a diesel engine, diffusion and combustion of fuel occur substantially simultaneously, and combustion is performed during injection of fuel.

  In the re-entrant type combustion chamber structure, at this time, the lip portion N2 promotes the generation of the swirl flow and the squish flow (the flow from the squish portion N3 to the cavity portion N1) in the cavity portion N1. It promotes the diffusion of air and fuel in the cavity N1. As a result, good combustion can be achieved and, at the same time, soot, NOx, etc. can be suppressed.

Japanese Patent Application Publication No. 2013-527360

  By the way, in the reentrant type combustion chamber structure, a part of the fuel spray F from the injector I is distributed to the squish region at the time of a collision with the lip N2 of the piston N0 to utilize the air on the squish region side. Are configured to burn.

  However, as a result of intensive studies by the inventors of the present application, even in the reentrant type combustion chamber structure according to the related art, the non-combustion state of the fuel spray F occurs due to insufficient progress of mixing of air and fuel on the squish region side. The problem of becoming a problem has become clear. In other words, in the reentrant type combustion chamber structure according to the prior art, the air on the squish region side is not sufficiently used for combustion, leading to the deterioration of the combustion efficiency of the entire diesel engine.

  The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a self-ignition type internal combustion engine and a piston that can increase the utilization efficiency of air in the squish region.

The main present disclosure to solve the above-mentioned problems is
A self-ignition internal combustion engine comprising: a combustion chamber defined between a cylinder head portion and a cavity portion provided on a top surface of the piston; and an injector for injecting fuel in the combustion chamber,
The cavity portion is inclined such that the inner peripheral side surface of the cavity portion is formed in a straight line from the bottom surface to the opening edge so that the opening diameter of the cavity portion increases from the bottom surface to the opening edge. Take shape
The injector injects fuel toward a boundary region with a bottom surface of an inner circumferential side surface of the cavity portion.
Self-igniting internal combustion engine.

And in other aspects,
A piston of a self-ignition type internal combustion engine,
A cavity portion provided on a top surface of the piston and defining a combustion chamber between the piston and the cylinder head portion;
The cavity portion is inclined such that the inner peripheral side surface of the cavity portion is formed in a straight line from the bottom surface to the opening edge so that the opening diameter of the cavity portion increases from the bottom surface to the opening edge. Take shape
An injector that injects fuel toward a boundary region with a bottom surface on an inner circumferential side surface of the cavity portion is disposed above the cavity portion.
It is a piston.

  According to the self-ignition type internal combustion engine according to the present disclosure, it is possible to increase the utilization efficiency of air in the squish region.

The figure which shows an example of the re-entrant type combustion chamber structure which concerns on a prior art The schematic diagram which shows an example of a structure of the diesel engine which concerns on one Embodiment Sectional drawing which shows the detailed structure of the combustion chamber of the diesel engine which concerns on one Embodiment The perspective view which looked at the cavity part of the combustion chamber of the diesel engine concerning one embodiment from the upper part The diesel engine which concerns on one Embodiment WHEREIN: The schematic diagram which shows the tumble flow in, when a piston is compression top dead center vicinity

  Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functions will be assigned the same reference numerals and redundant description will be omitted.

  FIG. 2 is a schematic view showing an example of the configuration of the diesel engine E according to the present embodiment.

  The diesel engine E according to the present embodiment includes a piston 10 slidably fitted in a cylinder block B, a cylinder head portion 20 held above the cylinder block B, and an injector held by the cylinder head portion 20. I etc.

  The combustion chamber N of the diesel engine E according to the present embodiment is partitioned by the cavity portion 11 formed on the top surface of the piston 10 and the flat surface on the lower surface side of the cylinder head portion 20.

  In the combustion chamber N, the injection hole of the injector I is disposed so as to allow fuel injection, and an intake port for introducing intake air and an exhaust port for exhausting the burned gas are disposed. As the intake port and the exhaust port according to the present embodiment, for example, a four-valve system provided with a variable swirl mechanism is applied.

  FIG. 3 is a cross-sectional view showing the detailed structure of the combustion chamber N of the diesel engine E according to the present embodiment. FIG. 4 is a perspective view of the cavity portion 11 of the combustion chamber N of the diesel engine E according to the present embodiment as viewed from above.

  FIG. 3 shows a state in which the piston 10 has reached near the compression top dead center in the diesel engine E according to the present embodiment. CL shown in FIG. 3 represents a central axis of the piston 10 (hereinafter, “piston central axis CL”), and the piston central axis CL corresponds to the central position of the cavity portion 11. Further, F shown in FIG. 3 represents a fuel spray in which the fuel injected from the injector I is in the form of a mist.

  The combustion chamber N of the diesel engine E according to the present embodiment is configured to include the cavity portion 11 and the squish portion 12.

  The cavity portion 11 is a recess formed in the central region of the top surface of the piston 10. The cavity portion 11 has, for example, a substantially perfect circular shape in a plan view.

  A substantially conical raised portion 11 a is formed in the central region of the bottom surface of the cavity portion 11. In other words, the bottom surface shape of the cavity portion 11 has a convex shape in which the central region is raised relative to the outer peripheral region by the raised portion 11a.

  The inner peripheral side surface 11b of the cavity portion 11 is continuous from the bottom side to the opening edge such that the diameter of the opening of the cavity portion 11 increases as the opening diameter reaches the opening edge (the top surface of the piston 10). It has a substantially linear inclined shape.

The inclination angle of the inner peripheral side surface 11b of the cavity portion 11 is the angle between the inner peripheral side surface 11b and the fuel injection direction of the injector I (representing the central axis FL (dotted line in FIG. 3 of the fuel spray F). The same applies hereinafter). More preferably, the angle θ _F is greater than 90 degrees, and more preferably, approximately 125 degrees or more and 160 degrees or less. However, the said inclination angle may be changed on the way from the bottom face side of the cavity part 11 to an opening edge part. The angle θ _F between the inner peripheral side surface 11b and the fuel injection direction of the injector I depends on the fuel injection position and the fuel injection direction of the injector I in addition to the inclination angle of the inner peripheral side surface 11b.

  The squish portion 12 is a flat portion of the top surface of the piston 10 formed so as to surround the outer periphery of the cavity portion 11. The squish portion 12 forms a gap (a squish region) between the piston compression top dead center and the bottom surface 20 u of the cylinder head portion 20. The combustion chamber N of the diesel engine E according to the present embodiment does not have the lip portion N2 of the combustion chamber Np according to the prior art, and the inner circumferential side surface 11b of the cavity portion 11 and the squish portion 12 It does not have, and is formed continuously.

  The injector I is disposed on a piston center axis CL of the combustion chamber N. Then, the injector I injects fuel radially from the injection hole in the combustion chamber N near the compression top dead center of the piston 10.

  The injector I according to the present embodiment injects fuel toward a boundary region 11F between the bottom surface of the cavity portion 11 and the inner circumferential side surface 11b. As a result, the fuel spray F strikes the bottom side of the inner peripheral side surface 11 b of the cavity portion 11 and flows from the bottom side of the cavity portion 11 to rise along the inner peripheral side surface 11 b.

The fuel injection direction θ _L of the injector I according to this embodiment is set to be larger than 90 degrees with respect to the inclination angle of the inner peripheral side surface 11 b of the cavity portion 11 as described above, for example The angle is set to about 70 degrees or more and 85 degrees or less with respect to the piston center axis CL.

  Next, the behavior at the time of combustion of the diesel engine E according to the present embodiment will be described.

  FIG. 5 is a schematic view showing the tumble flow T when the piston 10 is near the compression top dead center in the diesel engine E according to the present embodiment.

  The injector I injects fuel toward the boundary region 11F between the bottom surface of the cavity portion 11 and the inner peripheral side surface 11b when the piston 10 reaches near the compression top dead center (compression stroke). The injected fuel turns into atomized fuel spray F, and diffusion and combustion of the fuel proceed almost simultaneously.

  At this time, the fuel spray F rises while diffusing from the bottom surface side of the cavity portion 11 along the inner peripheral side surface 11b. The flow of the fuel mixture including the fuel spray F is restricted by the inner peripheral side surface 11 b of the cavity portion 11, the bottom surface 20 u of the cylinder head 20, and the raised portion 11 a of the bottom surface of the cavity portion 11. That is, the tumble flow (longitudinal vortex flow) T of the fuel mixture including the fuel spray F rises from the bottom side of the cavity 11 along the inner circumferential side 11 b, and the cavity 11 along the bottom 20 u of the cylinder head 20. It is restricted to one-way circulation of moving from the outer peripheral area to the central area and moving from the central area to the outer peripheral area of the cavity 11 along the ridges 11 a on the bottom of the cavity 11.

  As described above, the diesel engine E according to the present embodiment makes the inner peripheral side surface 11b of the cavity portion 11 sloped, and causes the injector I to fuel the bottom surface side of the inner peripheral side surface 11b. Regulate the direction. By this, it is suppressed that the tumble flows T mutually cancel each other, and a large power is generated to the piston 10.

  Further, in the diesel engine E according to the present embodiment, the structure of the combustion chamber N differs between the cavity portion 11 and the squish portion 12 unlike the reentrant type combustion chamber structure (see FIG. 1) according to the prior art. Diffusion of air or fuel spray F is easy. Accordingly, the air in the squish portion 12 is a tumble flow T, a squish flow (represents a flow from the squish portion 12 toward the cavity portion 11 in the compression stroke; not shown), and a reverse squish flow (from the cavity portion 11 to the squish in the expansion stroke) The flow toward the part 12 is represented, which is efficiently mixed with the fuel spray F, etc. As a result, in the diesel engine E according to the present embodiment, air in the squish region is sufficiently used.

  As described above, according to the diesel engine E according to the present embodiment, the cavity portion 11 has the raised portion 11a at the center position of the bottom surface, and the diameter of the opening is increased as it extends from the bottom surface to the opening edge. In addition, the inner peripheral side surface 11b exhibits a continuous linear inclined shape. In addition, the injector I has a configuration for injecting fuel toward the boundary region 11F between the bottom surface of the cavity portion 11 and the inner circumferential side surface 11b.

  Thus, the circulation direction of the tumble flow T generated in the combustion chamber N can be regulated in one direction, and the power of the tumble flow T acting on the piston 10 can be further increased.

  This also makes it possible to effectively use the air in the squish region for combustion, and also improves the combustion efficiency.

  Further, as a result, even when the fuel injection timing deviates or at the time of multi injection, the fuel spray F strikes the edge portion of the cavity portion 11 (lip portion N2 according to the prior art), and the flow of the fuel spray F changes rapidly. There is nothing to do. Therefore, it is also possible to continue stable combustion.

  Although the specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The art set forth in the claims includes various variations and modifications of the specific examples illustrated above.

  According to the self-ignition type internal combustion engine according to the present disclosure, it is possible to increase the utilization efficiency of air in the squish region.

B cylinder block E diesel engine F fuel spray I injector N combustion chamber 10 piston 11 cavity 11a ridge 11b inner circumferential side 12 squish 20 cylinder head

Claims (5)

A self-ignition internal combustion engine comprising: a combustion chamber defined between a cylinder head portion and a cavity portion provided on a top surface of the piston; and an injector for injecting fuel in the combustion chamber,
The cavity portion is inclined such that the inner peripheral side surface of the cavity portion is formed in a straight line from the bottom surface to the opening edge so that the opening diameter of the cavity portion increases from the bottom surface to the opening edge. Take shape
The injector injects fuel toward a boundary region with a bottom surface of an inner circumferential side surface of the cavity portion.
Self-igniting internal combustion engine. The inner circumferential side surface of the cavity portion is inclined such that the angle between the inner circumferential side surface and the fuel injection direction of the injector is greater than 90 degrees.
A self-ignition internal combustion engine according to claim 1. The inner peripheral side surface of the cavity portion is inclined such that the angle between the inner peripheral side surface and the fuel injection direction of the injector is 125 degrees or more and 160 degrees or less.
The self-ignition type internal combustion engine according to claim 2. The cavity has an upwardly raised ridge in a central region of the bottom surface,
The self-ignition type internal combustion engine according to any one of claims 1 to 3. A piston of a self-ignition type internal combustion engine,
A cavity portion provided on a top surface of the piston and defining a combustion chamber between the piston and the cylinder head portion;
The cavity portion is inclined such that the inner peripheral side surface of the cavity portion is formed in a straight line from the bottom surface to the opening edge so that the opening diameter of the cavity portion increases from the bottom surface to the opening edge. Take shape
An injector that injects fuel toward a boundary region with a bottom surface on an inner circumferential side surface of the cavity portion is disposed above the cavity portion.
piston.

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