JP2001115844A - Combustion chamber for direct injection diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combustion chamber for a direct injection Diesel engine injecting fuel from a fuel injection nozzle, mixing the fuel sufficiently with air and generating an almost uniform mixture, and capable of performing almost uniform combustion in a combustion chamber total unit. SOLUTION: A plurality of annular hollow parts are provided in a combustion chamber wall surface injected with fuel from a fuel injection nozzle, a combustion chamber opening bore is set smaller than a maximum diameter of diameters of a plurality of the annular hollow parts and larger than a combustion chamber inner part diameter, and a central protrusion part of a height and diameter preventing collision of fuel injected from the fuel injection nozzle is provided in a combustion chamber bottom part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a combustion chamber of a direct injection diesel engine.

[0002]

2. Description of the Related Art In a combustion chamber of a conventional reentrant type direct injection type diesel engine shown by a broken line in FIG. 5, injected fuel and air are hardly mixed, and a highly concentrated air-fuel mixture stagnates near the bottom of the combustion chamber. However, it is difficult to perform unbiased and uniform combustion by fully utilizing the entire volume of the combustion chamber. As a result, black smoke, nitrogen oxides, and the like are easily generated.

[0003]

Accordingly, in the present invention, the fuel injected from the fuel injection nozzle is sufficiently mixed with the air to generate a substantially uniform mixture, and the combustion is substantially uniform throughout the combustion chamber. It is an object of the present invention to provide a combustion chamber of a direct injection diesel engine capable of performing the following.

[0004]

According to a first aspect of the present invention, in a combustion chamber of a direct injection diesel engine, a plurality of annular recesses are provided on a wall of a combustion chamber where fuel is injected from a fuel injection nozzle. Part, the opening diameter of the combustion chamber is set to be smaller than the maximum diameter of the diameters of the plurality of annular recesses and larger than the diameter of the inside of the combustion chamber, and the height and the diameter of the fuel injected from the fuel injection nozzle that do not collide are set. A central projection was provided at the bottom of the combustion chamber. In the invention of claim 2, in the invention of claim 1, the combustion chamber volume of the combustion chamber bottom side of the center axis of the fuel spray injected from the fuel injection nozzle and V _L, the total compression volume and V _C, V _L / V _C ≦
0.0088 x injection angle (θ)-0.8341 (θ:
[Deg]). In the invention of claim 3, in the invention of claim 1, assuming that the distance from the bottom of the combustion chamber to the annular recess closest to the bottom of the combustion chamber is h ₂ , and the depth of the combustion chamber is H,
0.1 <h ₂ /H<0.5. According to a fourth aspect of the present invention, assuming that the opening diameter of the combustion chamber is d ₁ , the maximum diameter of the plurality of annular recesses is d ₂ , and the diameter of the combustion chamber is d ₃ , d ₃ <d. ₁ <was d _2. According to a fifth aspect of the present invention, in the first aspect of the present invention, the chamfered annular projection is provided at the opening of the combustion chamber. In the invention of claim 6, in the invention of claim 1, the bottom of the combustion chamber and the central projection are connected by a smooth curved surface. The invention of claim 7 is the invention of claim 1, the height of the central protrusion When h _3, and the h ₂ <h _3.

[0005]

FIG. 1 is a schematic sectional view of a combustion chamber 100 of a direct injection diesel engine according to the first to seventh aspects of the present invention. As shown in FIG. 1, the combustion chamber 100 is formed on a top surface (upper end surface) 90 a of the piston 90. The wall 9 of the combustion chamber 100 is provided with an annular recess 6 having a maximum diameter d ₂ and a recess 10 having a diameter d ₅ . An annular projection 12 is formed between the annular recess 6 and the recess 10. A curved surface 11 is formed between the wall surface 9 and the concave portion 10.

The opening 3 of the combustion chamber 100 is chamfered. The height h at which the fuel 2 described below does not collide with the bottom 5
_3, and the central protrusion 7 of the diameter d ₄ is provided. The central projection 7 and the bottom 5 are connected by a smooth curved surface 8. The chamfer provided in the opening 3 may be a slope, but is more preferably a rounded shape.

[0007] Fuel 2 is injected from the fuel injection nozzle 1, and the injection angle θ is set so that the fuel 2 collides with the annular recess 6. The distance d ₃ <between the opening diameter d ₁ of the opening 3, the diameter d _{3 of the} wall surface 9, and the maximum diameter d ₂ of the annular recessed portion 6.
There is a relationship d ₁ <d ₂ .

As shown in FIG. 2A, the fuel 2 is injected from the fuel injection nozzle 1 toward the annular recess 6.
As shown in FIG. 2B, the fuel 2 that has collided with the annular concave portion 6 is miniaturized into the fuel 2b by the collision. afterwards,
As shown in FIG. 2C, the finely divided fuel 2b spreads in the combustion chamber 100 and mixes with air by swirling (air flow) to generate an air-fuel mixture 2c.

Thereafter, although not shown, the piston 90
There mixture descends flows out into the squish area 95 from the combustion chamber 100, the air-fuel mixture 2c burns pervasive in all compression volume V _C to be described later shown in Fig.

[0010] As shown in FIG. 3, the total volume which the piston 90 is formed by the piston 90 and the cylinder 91 when it reaches the top dead center to a total compression volume V _C, the piston 90, as shown in FIG. 4 The volume of the area below (on the bottom 5 side) the central axis 2a indicated by the one-dot chain line of the fuel 2 injected from the fuel injection nozzle 1 when reaching the top dead center is defined as the volume _VL.
Is set to θ, V _C , _VL and θ are set so as to satisfy the following expression (1). V _L / V _C ≦ 0.0088 × θ−0.8341 (1) (θ [deg])

In order to satisfy equation (1), V _C , V _L and θ
Is set in the combustion chamber 10 at the beginning of combustion.
Within 0, the fuel and air are well mixed, and in the later stage of combustion, uniform combustion can be performed in the entire compression volume V _C.

FIG. 5 is a schematic cross-sectional view in which a cross section of a conventional combustion chamber shown by a broken line and a cross section of a combustion chamber 100 of the present invention (the invention of claims 1 to 7) shown by a solid line are overlapped and compared. .

[0013] Combustion chamber 100 in FIG. 5, as compared with conventional combustion chamber with open space opening 3 as indicated by arrow A ₁ radially outwards, the radial wall surface 9 as indicated by an arrow A ₂ narrowing the space to inward, and spread the space further radially outwardly in part of the annular recess 6 as shown by arrow a _3.

[0014] Figure 6 is a graph showing the relationship between the injection angle θ and the volume ratio V _L / V _C of the fuel in the combustion chamber 100 of the conventional combustion chamber and the invention. As shown in FIG.
The graph of 00 is located lower than the graph of the conventional combustion chamber, and the graph of the combustion chamber 100 is represented by equation (1). Therefore, the above equation (1) shows a hatched portion in FIG. 6, and good combustion can be performed by setting V _C , _VL and θ within the range of the hatched portion.

As shown in FIG. 1, the depth of the combustion chamber 100 is defined as H, and the distance from the combustion chamber bottom 5 to the curved surface 11 (curved surface 1
When one of the height) and h _2, by setting the H and h ₂ so as to satisfy the following equation (2), and the fuel and air are mixed well in the combustion chamber 100, a good combustion It can be carried out. 0.1 <h ₂ /H<0.5 (2)

FIG. 7 is a graph showing the relationship between h ₂ / H and the relative value (degree) of exhaust smoke density. As shown in FIG. 7, in general, when the value of h ₂ / H is in the range of 0.1 to 0.5 (within a range satisfying the expression (2)), the exhaust smoke concentration is equal to or less than the allowable value of 0.8. Becomes

This is because if the height h ₂ of the curved surface 11 is too low, the fuel stays in the small bottom 5 of the swirl,
Also, the height h ₂ is too high, not spread well-balanced fuel into the combustion chamber 100, as a result the fuel and air have shown that hardly mixed well.

In the combustion chamber 100 described above, good combustion can be obtained regardless of the injection pressure of the fuel 2 injected from the fuel injection nozzle 1 and the injection amount per unit time. However, when the fuel pressure is high or the fuel injection amount is large, it is easy to generate a uniform air-fuel mixture in the combustion chamber 100 without bias.

FIG. 8 is a schematic sectional view of another combustion chamber 101 according to the first to seventh aspects of the present invention. The configuration of the combustion chamber 101 in FIG. 8 is such that a second recess 15 is provided in place of the concave portion 10 and the curved surface 11 in the combustion chamber 100 shown in FIG. 1 and an annular recess 6 is provided between the annular recess 6 and the second recess 15. Only the point that the projection 20 is formed is different from the configuration of the combustion chamber 100 of FIG.

The fuel flowing downward (from the bottom 5 side) from the annular recess 6 changes its traveling direction from the direction of the bottom 5 to the direction of the central projection 7 at the second recess 15. Therefore, the fuel does not reach the bottom 5 where the swirl (air flow) is small,
Generate air-fuel mixture mixed well and air with a large area of the swirl (air-fuel mixture 2c corresponds to a region occupied region of FIG. 2 (c)), the air-fuel mixture equivalent to V _C of the total compression volume (Fig. 3 Area) and burn.

FIG. 1 shows an annular concave portion 6 and a concave portion 10, and FIG.
In the above, the combustion chamber provided with two annular concave portions, that is, the annular concave portion 6 and the second concave portion 15, is shown. However, three or more annular concave portions may be provided.

[0022]

According to the first aspect of the present invention, a plurality of annular concave portions (in FIG. 1, the annular concave portion 6 and the concave portion 10 and the curved surface 11,
In FIG. 8, by providing the annular recess 6 and the second recess 15), the traveling direction of the fuel that collides with the wall surface (annular recess 6) and flows toward the bottom 5 can be directed toward the center of the combustion chamber. As a result, the fuel does not stay in the vicinity of the small bottom portion 5 of the swirl, and by providing the central protruding portion 7, the flow of the fuel to the center of the combustion chamber where the swirl becomes small can be prevented. Thus, the fuel can be satisfactorily mixed with the air to generate a uniform air-fuel mixture, so that good combustion can be performed. Therefore, the amount of generated nitrogen oxides and black smoke can be reduced.

By providing a plurality of annular recesses, a remarkable effect can be obtained particularly when the fuel injection pressure from the fuel injection nozzle 1 is high or when the injection amount per unit time is large.

According to the second aspect of the present invention, the fuel injection angle θ is calculated by the following equation (1) (V _L / V _C ≦ 0.0088 × θ−0.834).
By defining 1) or within the range of hatching in FIG. 6, the fuel and the air can be easily mixed, and good combustion can be performed.

According to the third aspect of the present invention, the height h ₂ of the annular recessed portion (second recessed portion 15) closest to the bottom portion 5 with respect to the depth H of the combustion chamber 100 is calculated by the formula (2) (0.1 <h ₂ ). / H <0.
By defining by 5), the exhaust smoke density can be relatively reduced as shown in FIG.

According to the fourth aspect of the invention, by setting d ₃ <d ₁ <d ₂ , a uniform air-fuel mixture is generated in the combustion chamber 100 in the early stage of the fuel, and the total compression volume V _C is obtained in the latter stage of the combustion.
And good combustion can be performed, so that the exhaust smoke density becomes good.

According to the fifth aspect of the present invention, the air-fuel mixture flows out of the combustion chamber 100 to the squish area 95 in the latter stage of the combustion by forming the opening 3 by an annular projection having a chamfer inward in the radial direction. Mixed fuel 20
Burns, and good combustion can be performed.

According to the sixth aspect of the present invention, by connecting the bottom portion 5 and the central projection portion 7 with a smooth curved surface 8, it is possible to make it difficult for the swirl to be attenuated. By creating a uniform mixture,
Good combustion can be performed.

According to the seventh aspect of the present invention, the height h of the central projection is
₃ is the annular recessed portion closest to the bottom 5 (second recessed portion 1)
By making the height h ₂ higher than the height h _{2 of} 5), the flow of fuel inward in the radial direction can be directed upward (in the direction opposite to the bottom portion 5), and the swirl of the combustion chamber 100 has a large area (FIG. 2). (The area where the mixture 2c shown in (c) is spread)
Since a uniform air-fuel mixture can be arranged in the fuel cell, good combustion can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a combustion chamber of a direct injection diesel engine according to the first to seventh aspects of the present invention.

FIG. 2 (a) is a schematic cross-sectional view of a combustion chamber immediately before fuel collides with an annular recess. (B) is a schematic cross-sectional view showing a state in which the fuel colliding with the annular hollow portion is in the middle of spreading into the combustion chamber. (C) is a schematic sectional view showing a state in which the finely divided fuel has spread into the fuel chamber.

FIG. 3 is a schematic sectional view of a combustion chamber showing a total compression volume when a piston reaches a top dead center.

FIG. 4 is a schematic sectional view showing a region below a central axis of fuel to be injected in FIG. 3;

FIG. 5 is a schematic sectional view comparing the shape of a conventional combustion chamber with the shape of the combustion chamber according to the first to seventh aspects of the present invention.

6 is a graph showing the relationship between the ratio of the volume shown in FIG. 4 to the volume shown in FIG. 3 and the fuel injection angle in the conventional combustion chamber and the combustion chamber according to the first to eighth aspects of the present invention.

FIG. 7 is a graph showing the relationship between the distance from the bottom of the annular depression to the depth of the combustion chamber and the exhaust smoke concentration.

FIG. 8 is a schematic sectional view of another combustion chamber according to the first to seventh aspects of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Fuel injection nozzle 2 Injected fuel 2a Injected fuel central axis 3 Opening 5 Bottom 6 Annular recess 7 Central projection 8 Curved surface 9 Wall 10 Depression 11 Curved surface 15 Second recess 90 Piston 90a Piston top 91 Cylinder 95 Squish area d ₁ opening opening diameter d ₂ annular recess maximum diameter d ₃ wall diameter d ₄ central protrusion diameter H the combustion chamber depth h ₂ second recess height h ₃ central projections height θ fuel injection angle V _C total compression Volume _VL Lower volume of combustion chamber

Claims (7)

[Claims] A plurality of annular recesses are provided on a wall surface of a combustion chamber from which fuel is injected from a fuel injection nozzle, and an opening diameter of the combustion chamber is smaller than a maximum diameter of the plurality of annular recesses and the inside of the combustion chamber. A combustion chamber for a direct-injection diesel engine, wherein the combustion chamber is set to be larger than the diameter, and a central projection having a height and a diameter at which fuel injected from a fuel injection nozzle does not collide is provided at the bottom of the combustion chamber. 2. The combustion chamber volume on the bottom side of the combustion chamber with respect to the center axis of the fuel spray injected from the fuel injection nozzle is _VL ,
Assuming that the total compression volume is V _C , V _L / V _C ≦ 0.0088 ×
The combustion chamber of a direct injection diesel engine according to claim 1, wherein the injection angle is (θ)-0.8341 (θ: [deg]). 3. When the distance from the bottom of the combustion chamber to the annular recess closest to the bottom of the combustion chamber is h ₂ , and the depth of the combustion chamber is H,
_2. The combustion chamber of a direct injection diesel engine according to claim 1, wherein 0.1 <h2 / H <0.5. 4. When the opening diameter of the combustion chamber is d ₁ , the maximum diameter of the plurality of annular recesses is d ₂ , and the diameter of the combustion chamber is d ₃ , d ₃ <d ₁ <d _2. A combustion chamber for a direct injection diesel engine according to item 1. 5. The combustion chamber of a direct injection diesel engine according to claim 1, wherein an annular projection with a chamfer is provided at an opening of the combustion chamber. 6. The combustion chamber of a direct injection diesel engine according to claim 1, wherein the bottom of the combustion chamber and the central projection are connected by a smooth curved surface. 7. Assuming that the height of the central projection is h ₃ , h ₂ <
combustion chamber of direct-injection diesel engine according to claim 1 which is h _3.