JPH11117748A - Combustion chamber for direct injection type diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To promote mixing of fuel and improve combustion to reduce smoking and improve fuel consumption by diffuse-ejecting injected fuel into an air flow of wide range with a circumference-directional velocity by the upper face for fuel collision formed in a central part of a cavity. SOLUTION: A protruded part 10 for dispersing fuel is provided by swelling a central part of a cavity of a top face of a piston, a fuel injection nozzle 20 is provided to orient fuel injection toward the central part of its upper end face, the upper end face of the protruded part 10 is formed by plural scaly divided faces arranged around its central part, the divided face is formed by a face containing a line perpendicular to a fuel injection center direction and inclined relating to a face perpendicular to the fuel injection center direction, and a boundary wall between the neighboring divided faces is formed spirally radially around the central part and recessedly.

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 The combustion chamber system of a diesel engine is 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. 5, the fuel F which has collided 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 spreading the injected fuel in a wide range of air flow with a speed in the circumferential direction, it is possible to promote the mixing of fuel and air and improve combustion. It is another object of the present invention to provide a combustion chamber of a direct injection diesel engine capable of reducing smoke in exhaust gas and improving fuel efficiency by improving the combustion.

[0010]

In order to achieve the above object, a combustion chamber of a direct injection diesel engine is provided with:
A direct injection type 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 directs fuel injection toward the center of the upper end surface of the projection. In addition to providing a fuel injection nozzle,
The upper end surface is formed of 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 a surface perpendicular to the fuel injection center direction. And a boundary wall between the adjacent divided surfaces is formed in a spiral radial shape centering on the central portion and in a concave shape.

[0011] Therefore, a part of the colliding fuel flows out in the outer peripheral direction along the dent, so that even if there is no swirl, the fuel is diffused with velocities in the radial direction and the circumferential direction (tangential direction). Fuel spray having a circumferential velocity collides with the swirl in the opposite direction and diffuses into the combustion chamber. Further, the spray fuel can be reflected in the direction of the fuel injection center inclined with respect to the vertical plane, that is, as a fuel spray group having a thickness in the depth direction of the cavity. The diffused radiation can be made to radiate in a direction substantially perpendicular to the injection center direction and collide with the air flow. Then, as the spray group collides with the air and diffuses, the surface area of the reflected fuel spray group increases and the contact area between the air and the fuel increases, and the turbulence of the air flow is promoted by the collision of the spray group to mix the two. Be sufficient.

Therefore, mixing with air can be remarkably promoted,
Due to high diffusion and high disturbance, the concentration of fuel becomes more uniform,
Good combustion is obtained. 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 addition, by periodically providing a step in the collision portion, a group of sprays in which reflected fuel is inclined and overlapped to increase the surface area in contact with air to introduce peripheral air into the reflected spray flow. The amount can be increased to promote and equalize mixing to improve combustion and reduce black smoke emissions. This scaly divided surface is provided to be inclined with respect to a surface perpendicular to the fuel injection center direction.This inclined surface may be formed as an inclined flat surface including a line perpendicular to the fuel injection center direction, As the line perpendicular to the direction of the injection center rotates, the front end of the line is formed into a curved surface such as a spiral surface obtained by descending toward the bottom of the combustion chamber. Also, the number of divided surfaces may be two or more,
There is no particular limitation.

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.

[0015]

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. 4, a cavity (combustion chamber) 3 formed in a dish shape is provided at the top 2 of the piston 1. A projection (collision portion) 10 is provided by raising a substantially central portion to an area.

Further, the fuel injection nozzle 20 is disposed at a position facing the projection 10, and the fuel injection F is directed toward the center O of the upper end surface 11 of the projection 10 as shown in FIGS. Then, a plurality of scale-like divided surfaces 11a, 11b, 11c, 11d (hereinafter, referred to as 11i) arranged radially adjacent to the upper end surface 11 of the projection 10 around its center O in a radial direction. And each of the divided surfaces 11i is formed as a surface inclined with respect to a surface H perpendicular to the fuel injection center direction C. This slope is
As the line perpendicular to the direction of the center of fuel injection goes around, the tip side of this line is formed by a spiral surface obtained by descending to the bottom side of the combustion chamber. In other words, the fan-shaped inclined divided surface 11i having the central portion O is arranged adjacently and makes a circuit so that the upper end surface is formed.
Form 11.

Then, as shown in FIG. 1, boundary walls 12a, 12b, 12c, 12d formed between adjacent divided surfaces 11i.
(Hereinafter referred to as 12i) in a spiral radial shape centered on the central portion O and a concave shape so that a part of the fuel injection F has a velocity in the circumferential direction (tangential direction) R as shown in FIG. It is formed by recessing. Although the number of the dividing surfaces 11i is described as four in the drawing, the number of the dividing surfaces 11i is three even if two.
The number of injection holes 21 may be one or five, and is not particularly limited. However, if the number of injection holes 21 of the fuel injection nozzle 20 is the same and the direction of each injection hole 21 is directed to each division surface 11i, the injection fuel F becomes more uniform. This is more preferable because it collides with each divided surface 11i and diffuses more efficiently.

In FIGS. 1 and 2, the central portion O is formed in a flat disk shape. However, as shown in FIG. 3, this disk is not always necessary, and may have a spiral shape up to the center. Also, it may be convex or concave. 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.
A part fv of the fuel F diffuses and radiates with a thickness in the depth direction of the cavity 3 also from the boundary wall 12i formed between the adjacent divided surfaces 11i.

The sprayed fuel F collides with the division surface 11i of the projection 10, and most of the fuel is diverted from the fuel injection center direction axis C to the division surface 11i.
It is radiated in the outer circumferential direction along i. At this time, split surface 11
Since i is formed by an inclined surface, at points Pa, Pb, Pc, Pd, and Pe shown in FIG. 3A, angles θa, θb, θc, and θd are obtained as shown in FIG. 3B. , Θe, and also in the direction along the fuel injection center direction axis C, that is, in the depth direction of the cavity 3.

The fuel spray groups Fa, Fb, Fc and Fd formed by combining the fuel f diffusely reflected by the projections 10
(Hereinafter referred to as Fi) indicates that the fuel f has an angle of 0 (= θa) to θ.
e, the main flow direction of the radiation is substantially perpendicular to the injection center axis C, and the fuel does not directly go to the cylinder head side or the bottom wall of the cavity 3, Therefore, mixing with air in the cavity 3 can be efficiently promoted.

Although the maximum angle θe of the inclined surface depends on the shape of the cavity 3 of the engine, it is set to 3 to 20 degrees, preferably 5 to 10 degrees. Moreover, the fuel spray Fi is shown in FIG.
As shown in FIG. 3 (c), the number of divided surfaces 11i does not become a continuous disk-shaped fuel distribution Fr, and the number of divided surfaces 11i overlaps at an angle. Since the fuel spray group Fi has v, the contact surface with air is significantly enlarged, and the mixing with air can be significantly promoted.

In the case of an engine in which a swirl flow S is generated in the cavity 3, the fuel-fuel spray group Fi having a circumferential velocity v (FIG. 2) is transmitted to the swirl flow S.
To the swirl flow S
Of the fuel spray groups Fa, Fb, Fc, F
As a result, the turbulence is further promoted, and the entire circumference of the fuel spray group Fi comes into contact with and mixes with the air.

Therefore, in the diesel engine according to the OSKA system, the protrusion projecting from the center of the cavity 3 is provided.
By reflecting the injected fuel F on the upper end surface 11 having a relatively simple shape of 10, a part of the colliding spray fuel F is caused to flow out in the outer circumferential direction P along this depression, and is discharged in the outer circumferential direction (in the radial direction). ) While diffusing with P and a velocity v in the circumferential direction (tangential direction) R, the spray fuel F can also be dispersed and radiated in the depth direction of the cavity 3 and further overlap with the number of divided surfaces 11i inclined. In the fuel spray group Fi, the contact between the fuel and the air can be expanded, the mixing of both can be further promoted, and the mixing of the fuel and the air can be made uniform.

As a result, the combustion can be improved,
An engine with low smoke combustion and good fuel efficiency can be obtained.

[0025]

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. It is composed of a plurality of divided surfaces, and the divided surfaces include a line perpendicular to the fuel injection center direction,
And, it is formed by a plane inclined with respect to a plane perpendicular to the fuel injection center direction, and further, the boundary wall between the adjacent divided planes is spirally radially centered on the center, and is concavely depressed. Since it is formed, the following effects can be obtained.

That is, a part of the colliding fuel is advanced along the spiral-shaped concave boundary wall, and a circumferential velocity is positively generated. Direction), and the fuel can be scattered and scattered in the depth direction of the cavity, and furthermore, the fuel spray group that overlaps with the number of divided surfaces inclined, Can be widened and can be made to collide with the air flow such as swirl, so that the turbulence of the air flow is promoted, and the synergy with the air flow such as swirl can significantly promote the mixing with the fuel.

In particular, since the fuel spray having the circumferential velocity collides with the swirl in the opposite direction and diffuses into the combustion chamber, the mixing with the air can be remarkably promoted. Is more uniform, good combustion is obtained, and the amount of smoke generated can be reduced. Therefore, by forming a relatively simple and easy-to-process upper end surface, combustion can be improved, low smoke combustion can be realized, and as a result, fuel efficiency can be improved.

[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 the present invention.

FIG. 2 is a plan view showing an effect of a protrusion of a combustion chamber according to the present invention.

FIG. 3 is a view 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 side view showing a spray group.

FIG. 4 is a side sectional view showing an outline of a combustion chamber of a direct injection diesel engine.

FIG. 5 is a perspective view showing a projection of a combustion chamber of a conventional direct injection diesel engine.

FIG. 6 is a side view schematically showing a fuel reflection state of a protrusion shown in FIG. 5;

[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 wall 20 Fuel injection nozzle 21 Injection hole C Fuel injection center direction axis F Injected fuel H Surface perpendicular to fuel injection center direction O Central part of collision surface S Swirl flow f, fa, fb, fc, fd, fe, fv Reflected fuel Fi, Fa, Fb, Fc, Fd Fuel spray group

Claims (1)

[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 formed in a plane inclined with respect to a plane perpendicular to the fuel injection center direction, and a boundary wall between the adjacent divided planes is spirally radially centered on the central portion and concavely depressed. Combustion chamber of a direct injection diesel engine.