JPH06185364A - Combustion chamber of direct-injection type diesel engine - Google Patents

Abstract

PURPOSE:To provide a combustion chamber of a direct-injection type diesel engine in which mutual impingement of flames of fuel injection can be prevented, and which has a cavity of a wide slow-evaporating area. CONSTITUTION:In both an inner circumferential wall 7 and sloped surfaces 10, preliminary mixture and fuel films M1, M2 are independently produced, so that the slow evaporating combustion area in one cavity 3 can be extremely increased for significantly enhancing the utilization rate of air. The distance between fuel injections F1 and F2 is sufficiently secured both in the circumferential direction and in the vertical direction, so that the mutual superposition of fuel injections F1, that of fuel injections F2, that of fuel injections F1, F2, and that of the fuel films M1, M2, and also the mutual superposition of these flames can be prevented. Thus, as compared with the combustion chamber of a direct-injection type diesel engine, slow combustion in which the combustion temperature is low and also the rising rate of pressure is low can be achieved, so that NOx and smoke (particulates) can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion chamber of a direct injection type diesel engine, and more particularly to a novel combustion chamber of a direct injection type diesel engine in which the shape of the cavity and the injection direction of fuel spray are examined.

[0002]

2. Description of the Prior Art FIG. 5 shows a schematic structure of a combustion chamber of a conventional direct injection diesel engine.
In the combustion chamber of this direct injection type diesel engine, in order to improve the mixing (mixing) of the fuel and air, the swirl S is generated in the cavity a, and the combustion space of the cavity a is surrounded by the circumference. A large number of fuel sprays f ... Are supplied at intervals in the direction.

[0003]

However, even in the combustion chamber having such a structure, there is a limit to the improvement of NOx and smoke, and it is impossible to further reduce NOx and smoke (particulates). could not. Therefore,
In the combustion chamber of this kind, the present inventors have observed the injection direction of the fuel spray and the combustion flame, and when the flames of the fuel spray interfere with each other, the combustion temperature of this part is different from that of the other part. It has become considerably higher than the combustion temperature, where N
It has been found that a large amount of Ox (particulate) is generated, and oxygen is insufficient in a region where flames interfere with each other, and soot is also generated.

An object of the present invention is to provide a combustion chamber of a direct injection type diesel engine which prevents buffering of flames of fuel spray to be supplied and which has a cavity having a wide slow evaporation area.

[0005]

In order to achieve the above object, the present invention provides a cavity at the top of a piston, and a fuel injection nozzle is arranged with the injection hole facing the cavity. In a combustion chamber of a direct-injection diesel engine in which the inner peripheral wall of the is expanded spherically along its circumferential direction to form a lip-like shelf around the upper opening of the cavity, the height of the inner peripheral wall is increased by the cavity. In order to form a fuel film on the inclined surface in the injection hole portion, inclined surfaces are formed that obliquely connect the middle portion in the direction and the radially inner portion of the bottom surface of the cavity at predetermined intervals in the circumferential direction. A first injection hole for supplying the fuel spray and a second injection hole for supplying the fuel spray to form a fuel film on the inner peripheral wall excluding the slope are formed, and the axis line of the injection hole of the first injection hole and the above The angle of intersection with the axis of the fuel injection nozzle is set to the second injection Is obtained by less than the injection hole axis core and the intersection angle between the axial line of the fuel injection nozzle.

[0006]

In the intake stroke, the intake swirl of the combustion air supplied from the swirl port into the cylinder flows into the cavity from the outside in the radial direction of the piston to generate the swirl in the cavity.

At the end of the compression stroke, the fuel spray ejected from the first injection hole collides with each slope. Due to this collision, a part of the fuel spray injected from the first injection hole is atomized and scattered, and the remaining part is deposited in a thin film form on the slope and the bottom of the cavity continuous with this to form a fuel film. . The atomized fuel that has scattered is instantly vaporized by the atmosphere in the cavity and mixes with air to form a premixed gas. It gradually evaporates due to heat. When the premixed air ignites and burns, the flame and thermal energy cause the fuel film to propagate through the flame and burn slowly. Therefore, there is no ignition delay, combustion with a low heat generation rate and a slow pressure rise rate is achieved.

On the other hand, the fuel sprays ejected from the second injection holes do not interfere with each other in the circumferential direction and do not interfere with the fuel sprays ejected from the first injection hole in the vertical direction. Collide with the upper part of the surrounding wall.
Due to this collision, a part of the fuel spray is atomized and scattered, and the remaining part is deposited in a thin film form on the inner peripheral wall to form a fuel film. The portion of the fuel film upstream in the swirl direction diffuses in the depth direction, and as it is further away, it is strongly influenced by the swirl S and does not diffuse up to the slope. The atomized fuel that has scattered is instantly vaporized by the atmosphere in the cavity, mixes with air to form a premixed gas, and the fuel film gradually evaporates due to the atmosphere in the cavity and the heat of the inner peripheral wall. When the premixed air ignites and burns, the fuel film undergoes flame propagation due to this flame and thermal energy, and burns slowly. Therefore, even in the region of the inner peripheral wall, there is no ignition delay, and combustion with a low heat generation rate and a slow pressure increase rate is achieved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a top view of a piston of a direct injection diesel engine according to the present invention, FIG. 2 is a sectional view taken along line II-II of FIG. 1, and FIG. 3 is a sectional view taken along line III-III of FIG. But,
FIG. 4 shows a cross section of the fuel injection nozzle.

As shown in FIGS. 1 to 3, the piston 1 has a cavity 3 formed by recessing the piston top portion 2 along the axial direction, and the cylinder head 4 has a cavity 3 having a substantially axial center. The fuel injection nozzle 5 is attached so as to face the position. The inner peripheral wall 7 of the cavity 3 is expanded radially outward from a portion appropriately lower than the piston top 2, and the volume thereof is expanded in the radial direction. Therefore, in the portion defining the upper opening 6, the intake swirl of the combustion air supplied from the swirl port (not shown) of the cylinder head 4 and the fuel sprays F1 and F2 supplied from the fuel injection nozzle 5 are stored in the cavity 3 It will be a shelf to keep it inside. In addition, in the center of the bottom surface 8 of the cavity 3, a protrusion 9 for swirling the intake swirl of combustion air and the fuel sprays F1, F2 around the central axis of the cavity 3 is formed in a conical shape. ing. A plurality of slopes 10 are formed in the cavity 3 so as to obliquely connect the central portion of the inner peripheral wall 7 and the radially inner portion of the bottom surface portion 8 in the height direction. In the embodiment, these slopes 10 are formed by projecting the inner peripheral wall 7 inward in the radial direction. Also, these slopes 10
3 are provided for the cavities 3 at intervals of 120 ° in the circumferential direction. Both ends in the circumferential direction and both ends in the vertical direction of each slope 10 are smoothly and continuously connected to the inner peripheral wall 7 and the bottom surface portion 8 in the circumferential direction and the vertical direction.

The fuel injection nozzle 5 is, as shown in FIG.
The fuel sent from a fuel injection pump (not shown) is guided to the hydraulic chamber 12 of the nozzle body 11, and the fuel is directly applied to the conical pressure receiving surface 13a of the needle valve 13 to open the needle valve 13. The fuel spray F is formed from the first injection hole 14 and the second injection hole 15 that are closed by the opening of the needle valve 13.
It is formed so that 1 and F2 are respectively injected.
The first injection hole 14 and the second injection hole 15 are formed by piercing a nozzle tip (injection hole portion) 16. More specifically, the first injection holes 14 are provided at the tip end side portion of the nozzle tip at a total of three circumferentially at intervals of about 120 °.
Three injection holes 15 are provided at a position appropriately distant from the portion where the second injection hole 15 is formed to the rear side of the nozzle tip, at intervals of about 120 ° in the circumferential direction. The first
Regarding the positional relationship between the injection hole 14 and the second injection hole 15 in the circumferential direction, the second injection hole 15 is provided at a position deviated from the first injection hole 14 by 60 ° in the circumferential direction. The direction of each first injection hole 14 is set so that the fuel spray F1 can reach the central portion of the slope 10, and the direction of each second injection hole 15 is the direction of the fuel spray F2 injected from this. Is the fuel spray F1 injected from the first injection hole 14.
The fuel spray F2 is set so as not to cause interference in the vertical direction and the circumferential direction, and to reach the upper portion of the inner peripheral wall 7 between adjacent slopes 10 (including the vicinity of the lower edge of the shelf portion). ing. That is, the intersection angle α between the axis of the second injection hole 15 and the axis of the fuel injection nozzle 5, and the angle of intersection of the axis of the first injection hole 14 and the axis of the fuel injection nozzle 5. The relationship with β is set so that β> α. Also, the fuel spray F1 and the slope 10
More specifically, the relationship between and is set so that the axis of the fuel spray F1 and the slope 10 are at right angles, and the fuel spray F1 is evenly diffused on the slope 10.

The first injection hole 14 and the second injection hole 15 are also provided.
The caliber is set so that the fuel films M1 and M2 diffused in the forward direction of the swirl S can be formed on the slope 10 and the inner peripheral wall 7, respectively.

Next, the operation of the embodiment will be described.

In the intake stroke, the intake swirl of combustion air supplied from the swirl port into the cylinder flows into the cavity 3 from the outside of the piston 1 in the radial direction, as shown in FIGS. Swirl S is generated inside.

At the end of the compression stroke, the needle valve 13 of the fuel injection nozzle 5 is opened, the first injection hole 14 and the second injection hole 15 are opened, and the first injection hole 14 and the second injection hole 15 are respectively opened. The fuel sprays F1 and F2 are ejected (see FIG. 4).

As shown in FIGS. 1 and 2, each fuel spray F1 ejected from the first injection hole 14 collides with the slope 10. Due to this collision, a part of the fuel spray F1 injected from the first injection hole 14 is atomized and scattered, and the rest is deposited in a thin film on the slope 10 and the bottom surface 8 of the cavity 3 continuous with the slope 10. To form the fuel film M1. The dispersed atomized fuel is instantly vaporized by the atmosphere in the cavity 3 and mixed with air to form a premixture (a mixture having good ignitability and flame propagation), and the fuel film M1 is The swirl S of the cavity 3 stretches and spreads in the swirl direction, and gradually evaporates due to the atmosphere in the cavity and the wall heat of the cavity 3. When the premixed air ignites and burns, the flame and thermal energy cause the fuel film M1 to undergo flame propagation and burn slowly. Therefore, there is no ignition delay,
Slow combustion with low heat release and low pressure rise is achieved.

On the other hand, the fuel sprays F2 ejected from the second injection holes 15 do not interfere with each other in the circumferential direction,
In addition, in the vertical direction, the inner peripheral wall 7 does not interfere with the fuel spray F1 ejected from the first injection hole 14 either.
Hit the top of the. Due to this collision, the fuel spray F2 is
Part of it is atomized and scattered, and the remaining part adheres to the inner peripheral wall 7 in a thin film form to form the fuel film M2. In this case, in the fuel film M2, the portion on the upstream side in the swirl direction diffuses in the depth direction, and on the side away from it, the influence of the swirl S strongly influences the diffusion in the swirl direction. That is, the fuel film M2
Does not diffuse to the slope 10 downstream of the swirl S. The dispersed atomized fuel is instantly vaporized by the atmosphere in the cavity and mixed with air to form a premixed gas, and the fuel film M2 is gradually evaporated by the atmosphere in the cavity and the wall heat of the inner peripheral wall 7. When the premixed air ignites and burns, the fuel film M2 undergoes flame propagation by the flame and thermal energy, and burns slowly.
Therefore, there is no ignition delay even in areas other than the slope 10, that is, in the region of the inner peripheral wall 7, and slow combustion with a low heat generation rate and a low pressure increase rate is achieved.

As described above, in the combustion chamber of the direct injection diesel engine according to the present invention, the premixed gas and the fuel films M1 and M2 are independently generated on both the inner peripheral wall 7 and the slope 10. The slow evaporative combustion area in one cavity 3 is dramatically expanded to greatly increase the air utilization rate, and a sufficient space between fuel sprays is secured in the circumferential and vertical directions. The fuel sprays F1, the fuel sprays F2, the fuel sprays F1, F2, and the fuel film M.
It is possible to prevent the overlap of 1 and M2 and the overlap of these flames. Therefore, as compared with the combustion chamber of the conventional direct injection diesel engine, it is possible to achieve slow combustion with a low combustion temperature and a low pressure rise rate, thus reducing NOx and smoke (particulates) as compared with the conventional case. It is possible to suppress ignition delay and abnormal increase of combustion noise.

In the description of this embodiment, it is explained that the hole-type fuel injection nozzle is used as the fuel injection nozzle 5. However, the auxiliary injection hole which opens at any load and a predetermined load (for example, low load). ) Is used, a sub-hole is used as the second nozzle hole 14, and the main nozzle hole is used as the first nozzle hole 15. Of course, it is also possible to configure so that the air-fuel ratio can be adjusted according to the load.

[0021]

As is clear from the above description, the present invention exhibits the following excellent effects.

(1) Preventing buffering between fuel spray flames,
And it can provide a cavity with a slow evaporation area,
The emission values of x and smoke (particulate) can be further reduced as compared with the combustion chamber of the conventional direct injection diesel engine.

[Brief description of drawings]

FIG. 1 is a top view of a piston of a direct injection diesel engine according to the present invention.

FIG. 2 is a sectional view taken along the line II-II of FIG.

FIG. 3 is a sectional view taken along the line III-III of FIG.

FIG. 4 is a sectional view of a fuel injection nozzle.

FIG. 5 is a top view showing a piston of a conventional direct injection diesel engine.

[Explanation of symbols]

 2 Piston top part 3 Cavity 5 Fuel injection nozzle 6 Upper opening 7 Inner peripheral wall 10 Slope 14 First injection hole 15 Second injection hole

Claims (1)

[Claims] 1. A cavity is provided at the top of the piston, a fuel injection nozzle is disposed with the cavity facing the injection hole, and the inner peripheral wall of the cavity is expanded spherically along its circumferential direction. In a combustion chamber of a direct injection diesel engine in which a shelf is formed in a lip shape around the upper opening of the cavity, the cavity has a middle portion in the height direction of the inner peripheral wall and a radially inner portion of the cavity bottom portion in the cavity. Slanting surfaces that connect the slanting surfaces at a predetermined interval in the circumferential direction, and the inner peripheral wall excluding the slanting surface and the first injecting hole for supplying fuel spray to the slanting surface to form a fuel film on the slanting surface. A second injection hole for supplying fuel spray to form a fuel film is formed on the inner surface of the second injection hole, and the angle of intersection between the axis line of the first injection hole and the axis line of the fuel injection nozzle is defined by the injection angle of the second injection hole. Less than the angle of intersection between the hole axis and the fuel injection nozzle axis Combustion chamber of a direct injection diesel engine, which is characterized by its strength.