JPH1162591A - Combustion chamber of direct injection type diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To promote mixing of fuel and air to improve combustibility by providing a projecting part dispersing fuel on the center of a cavity dish-likely recessedly provided on the top face of a piston, forming the upper end face into a plurality of scaly divided faces arranged around the center part, and forming the respective divided faces into slopes. SOLUTION: The piston of this direct injection type diesel engine is provided with a cavity (combustion chamber) dish-likely recessedly formed on the top part, and a projecting part (collision part) 10 is projectingly provided in the territory of the nearly center part of the cavity. The upper end face 11 of the projecting part 10 is formed with a plurality of scaly divided faces 11i (11a-11d) adjacently arranged in the circumferential direction so as to be radial around the center part 0, and the respective divided faces 11i are formed into slanted faces against the perpendicular plane to the center direction C of fuel injection. A fuel injection nozzle is arranged on the position opposed to the projecting part 10, and fuel injection F is directed to the center part 0 of the upper end face 11 of the projecting part 10. Hereby uniformalization of air and fuel is promoted.

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, in which injected fuel collides with an upper end surface provided in a cavity (combustion chamber) to diffuse the fuel, thereby atomizing the sprayed fuel. The present invention relates to a combustion chamber of a direct injection diesel engine.

[0002]

2. Description of the Related Art Diesel engine combustion chamber systems are roughly classified into a direct injection type and an indirect injection type (subchamber type). As shown, a dish-shaped concave cavity 3 is provided at the top 2 of the piston 1, and fuel F is injected directly from the fuel injection nozzle 20 into the concave space of the cavity 3.

[0003] In a direct injection diesel engine, the mixing of fuel and air is mainly performed by the diffusion capability of the fuel spray itself, and the problem of non-uniformity of the mixing of fuel and air or the difference between the spray and the combustion chamber wall surface. Due to the problem of fuel attached due to collision, combustion after ignition is not completely performed, causing HC and soot to be generated, which hinders application. Therefore, it is necessary to make the fuel injected into the cavity as uniform as possible. One of the methods is to provide a fuel collision table (projection) 10 in the cavity 3 as shown in FIG. Then, by causing the injected fuel F to collide with the upper end surface 11 of the fuel collision table 10, the fuel is diffused to atomize the sprayed fuel.
The so-called OSKA (direct injection collision diffusion stratified intake) combustion chamber is well known.

When the upper end surface 11 of the fuel collision table 10 is formed as a single flat surface as shown in FIG. 6, the colliding fuel F spreads thinly as shown by an arrow f, and FIG. As shown by the hatched portion Fr, the disk-shaped spray group Fr is formed, so that the air is entrapped into the disk-shaped spray group Fr only from the upper side and the lower side as shown by the arrow s, and mixing is not possible. Will be enough.

In consideration of this, an apparatus for further promoting the diffusion of the spray fuel by devising the shape of the upper end surface is disclosed in Japanese Patent Laid-Open No.
No. 139921 and Japanese Utility Model Laid-Open Publication No. 1-111135.

[0006]

Problems to be Solved by the Invention JP-A-62-1399
The apparatus described in Japanese Patent Publication No. 21-A-2001 provides a spherical concave portion in a fuel collision portion and forms a polygonal surface in the spherical concave portion, aiming at combustion that does not depend on a swirl flow (swirl turbulent flow) described later.
By injecting fuel into the spherical concave portion and reflecting it on a polygonal surface, the fuel particles are three-dimensionally diffused throughout the cavity (combustion chamber). Since it is necessary to provide many upper end surfaces of polygonal surfaces having different pods and inclinations, there is a problem that it takes time to process the upper end surface. Further, the fuel radiated from the concave surface goes to the fuel injection nozzle side, and adheres to the cylinder head, and it is difficult to spread over the entire cavity, so that the mixing of air and fuel becomes uneven. There's a problem.

Further, in the device described in Japanese Utility Model Laid-Open Publication No. 1-111135, in order to generate an air-fuel mixture which is easy to ignite near the ignition assist device, the collision portions are concave, convex, inclined plane, bent, respectively. Or two or more notches, and furthermore, a plurality of notches inclined in the outer diameter direction serving as a guide for the sprayed fuel are formed radially linearly at the fuel collision portion, but in this device, Since the fuel reflected at the collision portion is radiated toward the cylinder head or the bottom of the cavity, the fuel easily adheres to the cylinder head or the bottom of the cavity, generating hydrocarbons (HC) and smoke. There is a problem that mixing with air is insufficient in the entire cavity.

On the other hand, in order to improve the combustion of the direct injection type diesel engine, the air flow entering the cavity is swirled to generate a swirl flow (swirl turbulent flow).
There is a method of promoting mixing of air and fuel by the swirling turbulent flow. This swirl flow can be generated by twisting the suction port, by providing a wall for guiding swirling in the cylinder, or by providing a swirl control valve in the suction port, and generating a swirl flow by operating the valve. and so on.

However, in any of the above-described devices, the effect of promoting the mixing of air and fuel without considering the swirl flow, that is, by effectively causing the spray fuel to collide with the swirl flow, is not aimed at. In addition, since the fuel spray is merely caused to collide with the combustion collision portion and diffused, there is a problem that mixing with air is insufficient. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and an object of the present invention is to inject a relatively simple shape of an upper end surface of a projection provided in a cavity in a combustion chamber of a diesel engine based on the OSKA system. By colliding the fuel and diffusing and radiating the injected fuel into a wide range of airflow, the mixing of fuel and air can be promoted to improve combustion, and the improved combustion reduces smoke in exhaust gas. It is an object of the present invention to provide a combustion chamber of a direct injection diesel engine that can reduce fuel consumption and improve fuel economy.

[0010]

In order to achieve the above object, a combustion chamber of a direct injection diesel engine is provided with:
A direct injection diesel engine is provided with a projection that disperses fuel by raising the center of a cavity formed by denting the top surface of a piston into a dish, and injects fuel into the center of a fuel collision surface on the upper end surface of the projection. Along with providing the fuel injection nozzle to be oriented, the upper end surface is formed by a plurality of scale-like divided surfaces arranged around the center portion, and further includes a line perpendicular to the fuel injection center direction, and , Formed in a plane inclined with respect to a plane perpendicular to the fuel injection center direction, and having a thickness in the fuel injection center direction inclined with respect to the vertical plane, that is, in the depth direction of the cavity. It can be reflected as a fuel spray group. Further, the fuel spray group that is superimposed and inclined can be diffused and radiated in a direction substantially perpendicular to the direction of the center of fuel injection to collide with the air flow.

Therefore, the spray group can collide with the air and diffuse, so that the surface area of the reflected fuel group increases and the contact area between the air and the fuel becomes wide, and the turbulence of the air flow is promoted by the collision of the spray group. To ensure sufficient mixing. In addition, since the fuel collision surface does not face directly to the cylinder head direction or the outer diameter direction of the combustion chamber, the fuel after the collision does not go directly to the cylinder head or the bottom wall of the cavity, but to the whole area in the cavity. Can radiate.

In other words, by periodically providing a step in the collision portion, a group of sprays in which the reflected fuel is inclined and overlapped to increase the surface area in contact with air to introduce the surrounding air into the reflected spray flow. To increase and promote mixing and equalization,
Improve combustion and reduce black smoke emissions. Further, in a direct injection type diesel engine in which the intake air is swirled and supplied into the cylinder, a projection for dispersing fuel by raising the center of a cavity formed by recessing the top surface of the piston into a dish shape is provided. A fuel injection nozzle is provided at the center of the upper end surface of the fuel injection nozzle to direct fuel injection, and the upper end surface is formed by a plurality of scale-like divided surfaces arranged around the center portion. By including a line perpendicular to the center direction and forming a surface inclined with respect to a surface perpendicular to the center direction of fuel injection, the action surface of swirl flow is expanded to the reflected fuel spray group due to collision, Mixing with air can be remarkably promoted, and turbulence of the swirling air flow can be promoted.

[0013] Further, by forming a boundary surface between the adjacent divided surfaces into a spiral shape centered on the central portion, the boundary surface can be shaped along the flow of the reflected fuel bent by the swirl flow, The flow of the reflected fuel can be smooth and can be diffused into the cavity without reducing the momentum of the reflected fuel. In addition, by arranging the divided surfaces adjacent to each other with a step in the direction of the center of fuel injection, the fuel after collision can be further diffused in the direction of the center of fuel injection, that is, in the depth direction of the cavity. Mixing of air and fuel can be promoted.

The scaly division surface is provided to be inclined with respect to a plane perpendicular to the fuel injection center direction, and the inclined surface is formed by an inclined flat surface including a line perpendicular to the fuel injection center direction. Alternatively, as the line perpendicular to the center of fuel injection goes around, the front end of this line is formed by a curved surface such as a spiral surface obtained by descending to the bottom side of the combustion chamber. In addition, the number of divided surfaces may be two or more, and is not particularly limited.

Preferably, the number of injection holes of the fuel injection nozzle and the number of division surfaces are the same, and the direction of each injection hole is directed to each division surface, so that the injected fuel collides with each division surface more accurately. Then, it is configured to spread more efficiently.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a combustion chamber of a direct injection diesel engine according to the present invention will be described with reference to the drawings. In the direct injection diesel engine according to the embodiment of the present invention, as shown in FIG. 5, a cavity (combustion chamber) 3 formed in a dish shape is provided at the top 2 of the piston 1, and the cavity 3 The projection (collision part) 10 is provided by raising substantially the center of the area to the area.

Further, the fuel injection nozzle 20 is arranged at a position facing the projection 10, and the fuel injection F is directed to the center O of the upper end surface 11 of the projection 10. And the upper end surface of this projection 10
A plurality of scale-like divided surfaces 11a, 11b, 11 that are arranged radially adjacent to each other around the center O around the center O thereof.
c, 11d (hereinafter referred to as 11i).
i is formed as a plane inclined with respect to a plane H perpendicular to the fuel injection center direction C. The inclined surface is formed as a spiral surface obtained by lowering the tip side of the line toward the bottom of the combustion chamber as the line perpendicular to the fuel injection center direction rotates. That is,
The upper end surface 11 is formed by arranging a fan-shaped inclined divided surface 11i having a central portion O adjacent thereto and making a round.

Then, as shown in FIG. 1, boundary surfaces 12a, 12b, 12c, 12d formed between adjacent divided surfaces 11i.
(Hereinafter referred to as 12i) is formed radially around the fuel injection center axis C. Alternatively, as shown in FIG. 2 as the second embodiment, this boundary surface 12i is radiated in a spiral around the central portion O, that is, in a spiral around the fuel injection central direction axis C. Form into shape.

Alternatively, as the third embodiment shown in FIG. 3, the upper end face 11 is formed by arranging the divided faces 11i so as to be separated from each other with a step D in the direction along the fuel injection center axis C to form the upper end face 11. . In each of the above embodiments, the dividing surface 11
Although i has been described as having four surfaces, the number of the divided surfaces 11i may be two, three, or five, and is not particularly limited. It is more preferable to direct the fuel to each divided surface because the injected fuel collides with each divided surface more accurately and diffuses more efficiently.

Also, not shown, a method of twisting the suction port, a method of providing a wall for guiding rotation in the cylinder, a method of providing a swirl control valve in the suction port, and generating a swirl flow by operating the valve, etc. In a direct injection type diesel engine in which a swirl flow (swirl turbulent flow) S is generated by swirling an air flow entering the cavity 3, the same cavity 3 as described above is used.
To form

As shown in FIG. 4, the fuel sprays Fa, Fb, Fc diffused and radiated from the projection 10 as a whole are efficiently added to the swirl flow S in consideration of the piston stroke and the timing of fuel injection. , Fd (hereinafter referred to as Fi) collides with each other to form an upper end surface 11 which is a collision surface by adjusting the amount of protrusion of the projection 10. According to the above configuration, when the fuel F is injected from the fuel injection nozzle 20 into the concave space of the cavity 3, as shown in FIG. 1, the spray fuel F collides with the dividing surface 11 i of the projection 10, Most of the radiation is radiated from the fuel injection center direction axis C to the outer peripheral direction along the division surface 11i. At this time, since the division surface 11i is formed by an inclined surface, each point Pa, Pb, Pc, Pd, and Pd shown in FIG.
In Pe, as shown in FIG. 4B, the angles θa, θb,
With θc, θd, and θe, diffusion also occurs in the direction along the fuel injection center axis C, that is, in the depth direction of the cavity 3.

A part of the fuel F is supplied to the adjacent divided surface 11i.
The boundary surface 12i formed between them also diffuses and radiates with a thickness in the depth direction of the cavity 3. A fuel spray group F formed by uniting the fuel f diffusely reflected by the projection 10
Since a, Fb, Fc, and Fd (hereinafter, referred to as Fi) are such that the fuel f is radiated in the range of the angle 0 (= θa) to θe, the radiant main flow direction is substantially perpendicular to the injection center direction axis C. In other words, since the fuel is diffused into the cavity 3 without going directly to the cylinder head side or the bottom wall of the cavity 3, the mixing with the air in the cavity 3 can be efficiently promoted.

The maximum angle θe of the inclined surface depends on the shape of the cavity 3 of the engine, but is 3 to 20 degrees, preferably 5 to 10 degrees. Moreover, the fuel spray Fi is shown in FIG.
As shown in FIG. 4, the fuel distribution does not have a continuous disk-shaped fuel distribution Fr, but as shown in FIG.
Since the fuel spray groups Fi are superimposed in an inclined manner, the contact surface with the air is significantly enlarged, and the mixing with the air can be remarkably promoted.

In the case of an engine that generates a swirl flow S in the cavity 3, the swirl flow S
Since the fuel spray groups Fi can collide with each other, the air of the swirl flow S sequentially flows through the fuel spray groups Fa, Fb, and F.
Since the fuel collides with c and Fd, the turbulence further progresses, and the entire circumference of the fuel spray group Fi comes into contact with and mixes with air, so that the uniformization of fuel and air can be remarkably promoted.

Further, since the collision surface 11 of the projection 10 is constituted by the divided surface 11i which is an inclined surface, the collision surface 11 has irregularities, so that the swirl flow S rotating on this surface is made turbulent. And the mixing of fuel and air can be improved. Further, according to the second embodiment shown in FIG. 2, since the boundary surface 12i is formed in a spiral shape, the swirl flow S inhibits the flow even if the fuel has a speed in the swirling direction. Without dispersing, it is possible to disperse and radiate more smoothly.

Further, according to the third embodiment shown in FIG. 3, since the step D is formed on the projection 10 to form the divided surface 11i and the divided surface 11i is disposed adjacent to the projection 10, the fuel f after the collision is transferred to the cavity 3 at the depth. Can be more widely diffused in the vertical direction, and can further promote mixing with air. Therefore, in the diesel engine of the OSKA system, the contact between the fuel and the air can be expanded by reflecting the injected fuel by the relatively simple upper end surface 11 of the projection 10 protruding from the center of the cavity 3. And the mixing of fuel and air can be made more uniform. As a result, combustion can be improved, and an engine with low smoke combustion and good fuel efficiency can be obtained.

When the swirl flow S is present in the cavity 3, the swirl flow S and the spray group Fi can be efficiently collided with each other. A large amount of air is sprayed into this spray group Fi
By colliding with and entangled with the surface, the effect that mixing can be remarkably promoted can be achieved. In addition, since the upper end surface 11 is formed as an inclined surface with the fuel injection center direction as an axis, the upper end surface 11 can be processed relatively easily.

[0028]

As described above, according to the present invention, in the combustion chamber of a diesel engine of the OSKA system, the scale having the upper end surface of the projection projecting from the center of the cavity disposed around the collision center. By forming a plurality of divided surfaces in a shape including a line perpendicular to the fuel injection center direction, and forming a surface inclined with respect to a surface perpendicular to the fuel injection center direction, the spray fuel is formed. Since it is possible to radiate in the depth direction of the cavity and radiate it, and furthermore, to make the fuel spray group that overlaps with the number of divided surfaces inclined, the contact portion between air and fuel can be widened and collided with the air flow, The turbulence of the air flow can be promoted, and the mixing with the fuel can be significantly promoted.

Therefore, by forming the upper end surface which is relatively simple and easy to process, combustion can be improved, low smoke combustion can be realized, and as a result, fuel efficiency can be improved. Further, a boundary surface between the adjacent divided surfaces is defined as:
By forming a spiral shape around the collision center, the flow of the reflected fuel bent by the swirl flow can be made smooth, and the reflected fuel can be radiated into the cavity without reducing the momentum of the flow. Can be performed favorably.

Further, by forming the upper end surface with a divided surface provided with a step, the fuel after collision can be displaced in the fuel injection center direction.
That is, since the gas can be further diffused in the depth direction of the cavity, the mixing of the air and the fuel can be further promoted.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a protrusion of a combustion chamber of a direct injection diesel engine according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a protrusion of a combustion chamber of a direct injection diesel engine according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a protrusion of a combustion chamber of a direct injection diesel engine according to a third embodiment of the present invention, and (a).
Is a perspective view, and (b) is a side view as seen from the X direction.

FIG. 4 is a diagram schematically showing a fuel reflection state of a protrusion of a combustion chamber of the direct injection diesel engine according to the present invention;
(A) is a perspective view showing a reflection position, (b) is a diagram showing a fuel reflection direction at each reflection position, and (c) is a perspective view showing a spray group.

FIG. 5 is a side sectional view showing an outline of a combustion chamber of a direct injection diesel engine.

FIG. 6 is a perspective view showing a protrusion of a combustion chamber of a conventional direct injection diesel engine.

FIG. 7 is a perspective view schematically showing a fuel reflection state of a protrusion shown in FIG. 6;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Piston 2 Top part of piston 3 Cavity (combustion chamber) 10 Projection part 11 Upper end surface 11i, 11a, 11b, 11c, 11d Dividing surface 12i, 12a, 12b, 12c, 12d, 13b Boundary surface 20 Fuel injection nozzle 21 Injection hole C Fuel injection center direction axis D Step F Injected fuel H Plane perpendicular to fuel injection center direction O Central part of collision surface S Swirl flow f, fa, fb, fc, fd, fe Reflected fuel Fi, Fa, Fb, Fc, Fd Fuel spray group

Claims (4)

[Claims] 1. A projection for dispersing fuel by raising the center of a cavity formed by denting the top surface of a piston of a direct injection diesel engine into a dish-like shape, and distributing fuel at the center of the upper end surface of the projection. Along with providing a fuel injection nozzle for directing injection, the upper end surface is formed by a plurality of scale-like divided surfaces arranged around the central portion, and further includes a line perpendicular to the fuel injection center direction. And a combustion chamber of a direct injection diesel engine formed of a plane inclined with respect to a plane perpendicular to the center direction of the fuel injection. 2. A direct-injection diesel engine in which intake air is swirled and supplied into a cylinder, wherein a projection is provided for dispersing fuel by raising a center of a cavity formed by recessing a top surface of a piston into a dish shape, A fuel injection nozzle is provided to direct fuel injection at the center of the upper end surface of the projection, and the upper end surface is formed by a plurality of scale-like divided surfaces arranged around the center. A combustion chamber of a direct injection diesel engine, comprising a line perpendicular to the fuel injection center direction and formed with a surface inclined with respect to a surface perpendicular to the fuel injection center direction. 3. The combustion chamber of a direct injection diesel engine according to claim 1, wherein a boundary surface between the adjacent divided surfaces is formed in a spiral shape around the central portion. 4. The combustion chamber of a direct injection diesel engine according to claim 1, wherein said divided surfaces are arranged adjacent to each other with a step provided in a fuel injection center direction.