JPH0828276A - Combustion chamber for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide the combustion chamber of an internal combustion engine wherein the size of the central protrusion of the bottom of the combustion chamber is set to a value within a range in which combustion is excellent. CONSTITUTION:In a combustion chamber having an annular groove formed in the top surface of the piston 3 of an internal combustion engine, and having a circular arc with a radius (r) formed in a position where a bottom makes contact with a side wall surface, and indicated by a segment of a line through which the circular arc of the side wall surface and the other circular arc on the central side of a combustion chamber 4 are intercoupled, provided the maximum diameter of the combustion chamber is dc and the diameter of the central protrusion 6 of the combustion chamber is dB, 0.4<=dB/dc<=0.8 is established.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a combustion chamber of an internal combustion engine.

[0002]

2. Description of the Related Art An example of a conventional combustion chamber will be described with reference to FIG. In the figure, 1a is a cylinder head, 2a is a cylinder liner, 3a is a piston, 4a is a combustion chamber, 5a is a bottom groove of the combustion chamber, 6a is a central projection of the combustion chamber, 7a is a fuel injection valve, and Swa is a swirl of the combustion chamber. There is. The air taken into the cylinder during the intake stroke is the piston 3 during the compression stroke.
Although it is pushed into the combustion chamber 4a recessed in a, the intake swirl Swa formed at the time of intake maintains its momentum and is pushed into the combustion chamber 4a, so that the swirl velocity is accelerated near the compression top dead center. The strong swirl Swa of the fuel spray injected from the fuel injection valve 7a promotes mixing with the air.

Further, the air swirl Swa in the combustion chamber 4a
Is pushed into the ring-shaped groove 5a formed on the bottom surface of the combustion chamber 4a by the central projection 6a on the bottom surface in the latter part of the compression stroke, and the swirl strength in this region is further enhanced, while the fuel spray is after the collision with the side wall surface of the combustion chamber. Since the groove portion 5a develops in the latter stage of combustion, it is possible to promote the mixing promotion by the strong swirl Swa especially in the latter stage of combustion which requires the promotion of the mixing of the fuel and the air, so that a high swirl flow is not formed in the intake port. However, due to the shape of the combustion chamber 4a, the swirl strength of the required region in the combustion chamber 4a can be increased, and good combustion performance with less afterburning can be obtained.

[0004]

However, the above-mentioned conventional example has the following drawbacks. That is, by forming the ring-shaped groove 5a on the side wall surface side of the bottom surface of the combustion chamber 4a,
The aim is to increase the swirling velocity of the air in the groove 5a and to control the dispersion of the spray into the groove 5a to promote the mixing of the fuel and air. However, the inner diameter of the ring-shaped groove 5a, that is, the size of the central protrusion 6a. There is no clear design standard for this, and it is empirically set for each type of engine based on conventional test data, and it is not always possible to sufficiently obtain the mixing promotion effect by improving the flow velocity. In some cases, the air amount distribution becomes unsuitable, and the swirl flow velocity becomes excessive, which may cause deterioration of combustion.

That is, in FIG. 2, the ratio of the swirl strength of the groove portion 5a to the ratio d _B / d _C of the diameter d _B of the central projection to the maximum diameter d _{C of the} combustion chamber (based on the swirl strength without the central projection 6a)
And the ratio of the air outside the central projection 6a to the total amount of air in the combustion chamber 4a. As d _B / d _C is increased, that is, as the central projection diameter d _B is increased, the swirl flow velocity in the groove portion 5a increases, but the air in the area outside the central projection 5a decreases and the height of the central projection 6a increases. Depending on the situation, the height of the central protrusion 6a is h _B , and the depth of the combustion chamber is h.
When _{C, the} high normal projections of h _B / h _C = 0.4~0.
In the range of 6, d _B / d _C = 0.8, and the air amount ratio outside the protrusion is about 50 to 60%.

In the case of a diesel engine, considering that the overall excess air ratio is about 1.5 to 2.0, a further increase in the central projection diameter d _B enhances the swirl flow velocity, but fuel spray In some cases, the amount of air is insufficient mainly in the area outside the dispersed central projections 6a, which causes conversely deterioration of smoke concentration and reduction of combustion efficiency. Further, as to the improvement of the combustion efficiency by the improvement of the swirl ratio, as shown in FIG.
Under the condition of 1.1 times or more of the base swirl strength, a remarkable improvement in combustion efficiency can be obtained, while under the condition of 2 times or more, the heat loss increases and the combustion efficiency tends to apparently decrease. Further, in the conventional combustion chamber 4a, the diameter of the central projection 6a is set empirically, so that it is set outside the above-mentioned appropriate range, and the effect of promoting mixing cannot be obtained sufficiently, or conversely, combustion deterioration is caused. There was an occasion.

The object of the present invention is to provide a central projection 6a on the bottom of the combustion chamber.
To provide a combustion chamber of an internal combustion engine, the size of which is set so that the combustion is in a good range.

[0008]

A combustion chamber of an internal combustion engine according to the present invention is recessed in a piston top surface of the internal combustion engine, and has a circular arc having a radius r at a position where a bottom surface and a side wall surface intersect with each other. In a combustion chamber having a ring-shaped groove represented by a line segment that connects an arc on the side of the side wall and another arc on the side of the center of the combustion chamber opposite to this, the maximum diameter of the combustion chamber is d _C , and the center of the combustion chamber is when the projection diameter is d _B, it is characterized in that as a _{0.4 ≦ d B / d C ≦} 0.8.

[0009]

In the present invention, the relationship between the diameter of the smallest portion of the ring-shaped groove (the diameter of the central protrusion) d _B with respect to the maximum diameter d _C of the combustion chamber is 0.4 ≦.
By setting d _B / d _C ≤0.8, as shown in FIGS. 2 and 3, a sufficient amount of air necessary for combustion is secured in the region outside the central projection in the combustion chamber, and mixing is promoted. It is possible to obtain an improvement in the flow velocity at the bottom surface in an appropriate range necessary for improving the combustion efficiency.

[0010]

FIG. 1 shows the first embodiment of the present invention. In the figure, 1-7 and Sw are the same as 1a~7a and Swa in FIG. 4 (prior art), d _C is the maximum diameter of the combustion chamber 4, the d _B shows the diameter of the combustion chamber bottom central projection 6. r ₁ is the radius of an arc connecting the bottom surface of the combustion chamber and the side wall surface of the combustion chamber. In this combustion chamber, the ratio of the maximum diameter d _C of the combustion chamber to the diameter d _B of the central protrusion of the combustion chamber is d
It is set in the range of _B / d _C = _0.4~0.8.

Next, the operation of the first embodiment will be described. The relationship between the diameter of the smallest portion of the ring-shaped groove (the diameter of the central protrusion) d _B with respect to the maximum diameter d _{C of the} combustion chamber is 0.4 ≦ d _B / d _C ≦
Since it is set to 0.8, as shown in FIG. 2, the amount of air required for combustion is secured in the area outside the central projection of the combustion chamber,
It is possible to obtain an improvement in the flow velocity at the bottom portion within a proper range necessary for improving combustion efficiency by promoting mixing.

[0012]

A combustion chamber of an internal combustion engine of the present invention exhibits by setting d _B / d _C as the in the range of 0.4 to 0.8, the fuel spray as shown in FIGS. 2-3 Sufficient air for combustion in the area outside the central projection, which develops mainly,
The effect of improving the combustion efficiency by promoting the mixing of fuel and air is sufficiently obtained, and good combustion with low afterburning after the middle stage of combustion, high combustion efficiency, and low smoke concentration is obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a combustion chamber according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a change in the ratio of the specific by the bottom groove swirl flow velocity and air volume of the central protrusion radial d _B to the maximum diameter d _C combustion chamber.

FIG. 3 is an explanatory diagram showing changes in combustion efficiency depending on swirl intensity.

FIG. 4 is a configuration diagram showing an example of a conventional combustion chamber.

[Explanation of symbols]

1 ... Cylinder head, 2 ... Cylinder liner, 3 ... Piston, 4 ... Combustion chamber, 5 ... Combustion chamber bottom groove part, 6 ... Combustion chamber central projection, 7 ... Fuel injection valve, Sw ... Combustion chamber swirl, d _C
... combustion chamber maximum diameter, d _B ... combustion chamber center protrusion diameter.

Claims (1)

[Claims] 1. A piston cavity of an internal combustion engine, wherein a piston cavity is provided in the top surface of the piston and has a central projection in the center thereof, and one arc having a radius r is provided at a position where the bottom surface and the side wall surface intersect. When the maximum diameter of the ring-shaped groove represented by the line segment that connects the circular arc on the side of the side wall and the other circular arc on the center side of the combustion chamber facing it is d _C , and the diameter of the central projection of the combustion chamber is d _B , A combustion chamber of an internal combustion engine, characterized in that 0.4 ≦ d _B / d _C ≦ 0.8.