JPH1193673A - Direct injection-type diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide compatibility between promotion of mixing of fuel and air in high loading and prevention of sticking of fuel to the peripheral wall surface of a combustion chamber in high-speed low loading, in a direct injection-type diesel engine. SOLUTION: A plurality of recessed parts 3 are circumferentially formed on the peripheral wall surface of a circular combustion chamber formed on a piston 1 at equal distances. Each recessed part 3 is formed into such a shape that the bottom surface may be gradually deeper from the upstream side to the downstream side and also may be shallower from the deepest part 302 with the steep gradient. A plurality of nozzle holes 41 whose injecting directions face respective recessed parts 3 are formed on a fuel injection nozzle 4 facing the combustion chamber. Even if the swirl flow is strengthened in order to promote mixing of a fuel and air in high loading, fuel sticking is restrained since the scattering direction of fuel grains and the bottom surfaces of the recessed parts 3 are made to be approximately parallel to each other in the upstream side half parts 31 of the recessed parts 3 in high-speed low loading, and centrifugal force to act on the fuel grains is weakened by the turbulence of the swirl flow in downstream side half parts 32 as small parts, and fuel sticking is restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a direct injection diesel engine.

[0002]

2. Description of the Related Art A direct-injection diesel engine has a structure in which a piston has a combustion chamber having an upper surface opening, and fuel is injected toward a peripheral wall of the combustion chamber from a fuel injection nozzle facing the combustion chamber. Compared to the sub-chamber type that mixes fuel and air before the fuel is injected into the combustion chamber, it has higher thermal efficiency and less carbon dioxide (CO2) emission per output. Widely adopted.

On the other hand, direct injection diesel engines are
Since the fuel and air are not mixed in advance, nitrogen oxides (NOx) and particulates (PM) in the exhaust gas are likely to be generated, and reduction of these is particularly demanded. The amount of these emissions in a direct-injection diesel engine is strongly affected by the combustion process in the combustion chamber. In particular, the amount of smoke and PM emission increases extremely when the mixing state of the fuel and air injected into the combustion chamber is poor. I do. Therefore, in direct injection diesel engines, the combustion chamber is made circular in order to promote the mixing of fuel and air, and the air is introduced into the intake system in the helical port that generates a vortex flow in the intake air and in the tangential direction of the cylinder. The mixing state of the fuel and the air is improved by employing a special port so that the air introduced into the combustion chamber forms a swirl flow.

When the load is large and the injection period is long and the injection period is long, the fuel injection continues for a long time even after the top dead center. Therefore, the shape of the combustion chamber is narrowed by the opening on the top surface of the piston to preserve the swirl flow. Enhanced (reentrant combustion chamber),
In the reentrant combustion chamber, a projection is formed at the center of the bottom surface to rectify the swirl flow and has a central projection with improved preservability.

[0005] Japanese Patent Application Laid-Open No. 8-326543 discloses a spiral-shaped swirl flow formed by forming spiral ribs on the peripheral wall of a reentrant combustion chamber to improve the mixing state. .

Japanese Patent Application Laid-Open No. 8-105368 discloses that
There is a fuel injection nozzle in which the mixing state is improved by cutting the downstream side of the swirl flow of the injection hole of the fuel injection nozzle to improve the diffusibility of the injected fuel to the downstream side of the swirl flow. Japanese Patent Application Laid-Open No. 8-105369 discloses a fuel injection nozzle in which the injection hole of a fuel injection nozzle is cut on the side of a piston where a combustion chamber is formed to improve the diffusion of fuel toward the bottom of the combustion chamber.

[0007]

However, in a direct-injection diesel engine having a circular combustion chamber such as a reentrant combustion chamber, the swirl flow is too strong at a low load with a large proportion of air, especially at a high speed, and the swirl flow is reduced. The injected injected fuel receives the centrifugal force and collides with and adheres to the peripheral wall surface of the combustion chamber, and is discharged as white smoke in an unburned state when exhausted. If the swirl flow is weakened, mixing of fuel and air may be insufficient at high load with a large fuel injection amount.

The above-mentioned Japanese Patent Application Laid-Open No. 8-105368 describes
Even in the method described in Japanese Patent Application Laid-Open No. 8-105369, an appropriate swirl flow according to the load cannot be obtained, and the swirl flow is insufficient at a high load and mixing is not sufficiently performed. Is too strong, and the injected fuel may collide with and adhere to the peripheral wall surface.

Accordingly, an object of the present invention is to provide a direct injection diesel engine in which mixing of fuel and air is promoted at a high load and fuel does not adhere to the wall of the combustion chamber at a high speed and a low load.

[0010]

According to the first aspect of the present invention, air forming a swirl flow is introduced into a circular combustion chamber having a top opening formed in a piston, and fuel is injected from a fuel injection nozzle facing the combustion chamber. Direct injection diesel engine that injects oil toward the peripheral wall of the combustion chamber, the bottom surface of the peripheral wall of the combustion chamber is gently spaced from the upstream side to the downstream side of the swirl flow at equal intervals in the circumferential direction. A plurality of concave portions are formed which gradually become deeper in a curved surface and become shallower in a curved surface having a steep gradient from the deepest portion. Further, the fuel injection nozzle has a plurality of injection holes each having an injection direction provided in each of the concave portions.

The injected fuel is caused to flow in a swirl flow and receives a centrifugal force to increase the radial velocity of the combustion chamber. The speed increases particularly at a low load with a small fuel injection amount. However, in the upstream part up to the deepest part of the concave portion, the vertical component of the velocity of the fuel particle with respect to the peripheral wall surface becomes small, and the flight direction of the fuel particle and the peripheral wall surface become more parallel, preventing fuel adhesion. . On the downstream side of the deepest portion of the concave portion, the air is not sufficiently rectified in the circumferential direction of the combustion chamber, the swirl flow is disturbed, and the effect of the centrifugal force is small. Thus, even at the time of high speed and low load with strong swirl flow, adhesion of fuel to the peripheral wall surface of the combustion chamber is prevented.

Further, the action of causing the turbulence in the swirl flow in the concave portion promotes the mixing of the air and the injected fuel, and also prevents the overswirl at a high load.

According to the second aspect of the present invention, air for forming a swirl flow is introduced into a circular combustion chamber having an upper surface opening formed in a piston, and fuel is injected from a fuel injection nozzle facing the combustion chamber to a peripheral wall surface of the combustion chamber. In the direct injection diesel engine configured to inject fuel toward the swirl flow, the injection hole of the fuel injection nozzle is formed toward the downstream side of the swirl flow in the radial direction of the fuel injection nozzle.

[0014] With this configuration, the fuel is injected in the downstream direction of the swirl flow, so that the fuel spray flows smoothly on the swirl flow. That is, the swirl flow is enhanced according to the fuel injection amount. When the injection amount is small and the load is low, the degree of the swirl flow is low and the adhesion of the fuel to the combustion chamber wall is prevented. Further, at the time of a high load with a large injection amount, the swirl flow is sufficiently strengthened, and the mixing of the air and the injected fuel is promoted.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIGS. 1 and 2 show a main part of a direct injection diesel engine of the present invention. FIG. 1 is a top view of a cylinder portion of an engine, in which a cylinder head and the like are omitted, and only a piston 1 and a fuel injection nozzle 4 that reciprocate in a cylinder are illustrated. FIG. 2 is a longitudinal section taken along line AA of FIG.

A circular (radius: R) combustion chamber 2 is formed in the head portion 11 of the piston 1 coaxially with the head portion 11 and opens on the upper surface. The fuel injection nozzle 4 is fixed to a cylinder head (not shown) coaxially with the combustion chamber 2, and the tip thereof faces the combustion chamber 2.

The combustion chamber 2 is a so-called reentrant combustion chamber in which the opening 21 is narrowed, and the air sucked from a helical port or the like in the cylinder generates a swirl flow. When compressed, the swirl flow is pushed into the combustion chamber 2 to increase the speed. A frustoconical projection 22 is formed at the center of the bottom surface of the combustion chamber 2 to rectify the swirl flow of the air flowing into the combustion chamber 2 and further improve its preservability.

FIG. 3 is substantially the same as FIG. 1. In FIG. 3, B, C, D, and E are BB lines, CC lines, which are cross sections of the piston 1 in FIG. It is an imaginary line showing the combustion chamber peripheral wall surface 23 in a cross section along the line DD and the line EE. On the peripheral wall surface 23 of the combustion chamber 2, recesses 3 having the same shape are formed at five locations at equal intervals, and serve as pocket portions 3. The line indicating the pocket portion 3 in FIG. 1 coincides with D in FIG.
The pocket portion 3 has an oval, monotonous curved surface that is long in the circumferential direction of the combustion chamber 2. Adjacent pocket portions 3 are continuous in a cross section along the line DD.

The shape of each pocket portion 3 is such that, for example, in a cross section along the line DD, the depth of the bottom surface monotonically increases from the swirl flow upstream point (start point) 301 to the intermediate point 302 and downstream from the intermediate point 302. It has a shape that monotonously decreases to a point (end point) 303.

The shape of the half portion 31 of the pocket portion 3 on the upstream side of the intermediate point 302 is on an arc, and the axial center X1 of the piston 1 is
Is defined by a circle Y having a radius of curvature of 3R / 5 to 5R / 6 passing through a start point 301 with a center at a position X2 eccentric by a distance 2R / 5 to 2R / 3 in the direction of an intermediate point 302 from the center point 302.
It gradually becomes deeper and forms a gentle curved surface.

The downstream half portion 32 of the pocket portion 3 from the intermediate point 302 to the end point 303 is a curved surface having a continuous shape from the upstream half portion 31 and has a curvature of the upstream half portion 31.
In the vicinity of the end point 303, the bottom surface is steep and shallow until the bottom surface is substantially parallel to the radial direction of the piston 1.

As can be seen from the drawing, the pocket portion 3 becomes deepest at an intermediate point 302 which is a boundary between the upstream half portion 31 and the downstream half portion 32. The deepest portion 302 is unevenly distributed downstream of the pocket portion 3 since the curvature of the pocket portion 3 is larger in the downstream half portion 32 than in the upstream half portion 31. That is, in the illustrated example, the circumferential length of each pocket portion 3 is expressed as θ1 = 72 (= 360/5) ° when represented by an angle centered on the axis X1 of the piston 1, and the deepest portion 30
2 is represented by an azimuth angle from the starting point 301 as θ2 =
62-67 °.

The fuel injection nozzle 4 facing the combustion chamber 2
The injection hole 41 is formed in five places, and the injection hole center line 5 is formed radially at an interval of 72 °. The injection hole center line 5 is directed slightly downward in the direction in which the azimuth angle θ3 is 5 to 15 °, and fuel is injected from the injection hole 41 toward the most upstream portion of the pocket portion 3.

The operation of the direct injection diesel engine will be described.

The swirl flow generated by the air sucked into the cylinder is intensified in the early stage of the fuel injection by the compression due to the rise of the piston 1. Fuel is injected from the fuel injection nozzle 4 in the direction of the azimuth angle θ3 to form a mixture with air and burn.

The injected fuel is caused to flow in a swirl flow and receives a centrifugal force to increase the speed in the radial direction of the combustion chamber 2. The speed increases particularly at a low load with a small fuel injection amount. In the present invention, since the bottom surface of the upstream half portion 31 of the pocket portion 3 becomes deeper toward the downstream side, the vertical component of the fuel particle velocity with respect to the peripheral wall surface 23 is reduced by a simple circular combustion such as a conventional reentrant combustion chamber. Small compared to room. That is, in the upstream half portion 31, the flight direction of the particles and the peripheral wall surface 23 become closer to parallel, and the fuel hardly adheres to the peripheral wall surface 23.

In the downstream half portion 32 of the pocket portion 3, the vertical component of the fuel particle velocity with respect to the peripheral wall surface 23 increases, but in the downstream half portion 32, the air becomes unrectified because it becomes shallow on the downstream side. The swirl flow is turbulent and the centrifugal force acting on the fuel particles is small. Therefore, the fuel hardly adheres to the peripheral wall surface 23 also in the downstream half portion 32.

Therefore, even at the time of high speed and low load with strong swirl flow, adhesion of fuel particles to the peripheral wall surface 23 is prevented.

Further, the action of causing the air to be unrectified in the downstream half portion 32 promotes the mixing of the air and the injected fuel, so that the combustion can be favorably performed even under a high load with a large fuel injection amount. The combustion efficiency can be further increased by setting the shape of the pocket portion 3 so that the combustion is performed around the area covered by the downstream half portion 32.

Further, since the effect of promoting the mixing of fuel and air is exhibited, a strong swirl flow is not required, and over-swirl can be prevented.

The shape of the pocket portion 3 is not limited to the shape described in the present embodiment. The bottom surface gradually forms a gentle curved surface from the upstream side to the downstream side of the swirl flow, and gradually becomes deeper. What is necessary is just to form a shallow surface with a steep slope.

The number of pockets 3 and injection holes 41 is
It is not limited to 5, but may be 4 or 6.

(Second Embodiment) FIG. 4 shows another embodiment of the direct injection diesel engine of the present invention.
It is a longitudinal section of a fuel injection nozzle which faces a combustion chamber (not shown).
As the combustion chamber, a circular combustion chamber such as a well-known reentrant combustion chamber is used, and the fuel injection nozzle 6 is mounted on a cylinder head (not shown) coaxially with the combustion chamber.

In FIG. 4, a fuel injection nozzle 6 has a tapered seat portion 62 formed at the tip end of a fuel passage 61 through which fuel is fed under pressure. Are arranged to be vertically movable. A plurality of injection holes 64 are formed obliquely downward in the sack portion 63 having a closed end below the seat portion 62.

FIG. 5 is a cross-sectional view taken along the line FF of FIG. 4. In FIG. 5, the injection holes 64 penetrate the wall of the nozzle 6 and are formed at symmetrical positions in the circumferential direction (six positions in the example of FIG. 4).

The injection hole 64 is not formed such that the center line of the injection hole is along the radiation X4 passing through the axis X3 of the fuel injection nozzle 6, unlike the injection hole of the conventional fuel injection nozzle. The line 8 is formed so as to pass through a position eccentric from the axis X3 and be deviated with respect to the radiation X4. This declination θ4 is set at 5 to 15 ° downstream of the swirl flow, the injection hole 64 is directed to the downstream side of the swirl flow in the radial direction of the fuel injection nozzle 6, and the fuel is slightly downstream of the swirl flow. It is to be sprayed toward.

The outer peripheral surface 65 of the fuel injection nozzle 6 has an injection hole 64.
The opening edge 641 has a shape in which the swirl flow downstream side portion 66 is shaved and the surface recedes, and the opening edge 641 is curved from the upstream side to the downstream side where the surface is receded. Is shortened downstream of the swirl flow. Thereby, the diffusion of the injected fuel to the swirl flow downstream side is improved.

Since the fuel injection is not performed in the radial direction (radiation X4 direction) of the fuel injection nozzle 6 but is performed downstream of the swirl flow, the fuel spray flows smoothly on the swirl flow. . That is, the swirl flow is strengthened in accordance with the fuel injection amount, and the swirl flow is not so much strengthened at a low load with a small injection amount, thereby preventing the fuel from adhering to the peripheral wall surface 23 of the combustion chamber 2. Further, at the time of a high load with a large injection amount, the swirl flow is sufficiently strengthened, and the mixing of the air and the injected fuel is promoted. Even when the swirl flow is weak and at low speed, the swirl flow is strengthened in accordance with the fuel injection amount, so that extremely favorable fuel injection is achieved.

Further, by directing the fuel injection direction to the swirl flow downstream side, the distance between the injection hole 64 and the peripheral wall of the combustion chamber is increased, and the amount of fuel reaching the peripheral wall and the speed at the time of arrival are suppressed. Further, fuel adhesion is reduced.

Although the effective length of the injection hole 64 is shortened on the downstream side of the swirl flow, the injection hole 64 can be simply formed by drilling the fuel injection nozzle 6 depending on the required fuel diffusion action. It may be.

The numerical values and the like shown in each of the above embodiments are not necessarily limited to those described, but are arbitrary as long as they do not contradict the spirit of the present invention.

[Brief description of the drawings]

FIG. 1 is a main part top view of a direct injection diesel engine of the present invention.

FIG. 2 is a sectional view taken along the line AA in FIG.

FIG. 3 is a top view of another main part of the direct injection diesel engine of the present invention.

FIG. 4 is a vertical sectional view of a fuel injection nozzle of another direct injection diesel engine according to the present invention.

FIG. 5 is a sectional view taken along line FF in FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piston 11 Piston head 2 Combustion chamber 23 Peripheral wall surface 3 Pocket part (recess) 4,6 Fuel injection nozzle 41,64 Injection hole X3

Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02M 61/18 320 F02M 61/18 320C 360 360J

Claims (2)

[Claims] 1. A direct-injection diesel engine having a piston and a circular combustion chamber with a top opening formed therein, wherein air forming a swirl flow is introduced into the combustion chamber, and fuel is injected from a fuel injection nozzle facing the combustion chamber. In a direct-injection diesel engine that is designed to inject toward the peripheral wall of the combustion chamber, the peripheral wall of the combustion chamber is equally spaced in the circumferential direction,
The bottom surface gradually forms a gentle curved surface from the upstream side to the downstream side of the swirl flow, gradually deepens, forms a plurality of concave portions that become shallow with a steeply curved surface from the deepest portion, and in the fuel injection nozzle, A direct injection diesel engine, wherein a plurality of injection holes having injection directions provided in the recesses are formed. 2. A direct-injection diesel engine having a piston and a circular combustion chamber with an open top, wherein air is introduced into the combustion chamber to form a swirl flow, and fuel is injected from a fuel injection nozzle facing the combustion chamber. A direct injection diesel engine adapted to inject into a combustion chamber, wherein the injection hole of the fuel injection nozzle is formed toward the downstream side of the swirl flow in the radial direction of the fuel injection nozzle. Injection diesel engine.