JPS6019957Y2 - Direct injection combustion chamber of diesel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a direct injection combustion chamber mainly applied to small diesel engines.

By the way, this type of direct injection combustion chamber has advantages such as a simpler structure and better startability compared to the pre-chamber type combustion chamber, but on the other hand, it has the advantage of emitting a large amount of soot and nitrogen oxides. , there are disadvantages such as poor exhaust conditions and high noise levels due to the high maximum pressure inside the cylinder, especially in small engines, the diameter of the cavity formed at the top of the piston is small, so it is injected from the nozzle. The combustion spray directly collides with the inner surface of the cavity and does not mix well with the air.In contrast, if the nozzle hole is narrowed to shorten the spray distance, the hole is likely to become clogged. This results in negative effects such as:

To address these drawbacks of direct injection combustion chambers, it is effective to create a vortex in the intake air by creating a special shape for the intake port, thereby quickly forming a uniform air-fuel mixture. However, in the case of a small engine, if the nozzle must be eccentric to the cavity due to the layout of the intake and exhaust valves, the distance from each nozzle hole to the inner surface of the cavity is not constant, so Even if a suction vortex is formed, a uniform air-fuel mixture will not be formed.
Therefore, the above-mentioned drawbacks of the direct injection combustion chamber cannot be completely eliminated.

The present invention was developed in view of these circumstances, and is a small-sized device in which the nozzle is eccentric to the cavity formed at the top of the piston with a circular planar shape, and the nozzle is installed with the nozzle orifice directed inside the cavity. In the direct injection combustion chamber of a diesel engine, a constriction part is formed in the upper part of the cavity formation range at the top of the piston, and the planar shape of the constriction part is such that the side closer to the nozzle is circular and the side farther from the nozzle is circular. By forming the side part of the nozzle into a semi-circular, semi-square shape with corners near the directional position when viewed from the plane of the nozzle nozzle, the vortex is weakened in the square part far from the nozzle nozzle and the reach distance of the fuel spray is reduced. In addition to forming a uniform air-fuel mixture, an inclined groove is formed on the inner circumferential surface of the constriction part to create a vortex in the squish and reverse squish, thereby promoting the formation or combustion of the air-fuel mixture, thereby achieving complete combustion. In this way, the exhaust condition is improved and the maximum pressure can be lowered, thereby reducing the noise level.

This will be explained below with reference to an embodiment shown in the drawings. In FIG. 1, 1 is a cylinder block, 2 is a piston, and 3 is a cylinder head, and a combustion chamber 4 is formed by these.

5 is a cavity with a circular planar shape formed by recessing the top of the piston, 6 is a fuel injection nozzle attached to the head, and the center of the cavity is an intake and exhaust valve (not shown). Due to the layout of the combustion chamber, the nozzle is eccentric from the center of the combustion chamber, and the nozzle is also eccentric from the center of the cavity. The holes are directed into the cavity 5.

However, a constriction part 7 is formed in the upper part of the cavity formation range on the upper surface of the piston, and the planar shape of the constriction part is such that the side part 7a closer to the nozzle 6 is circular as shown in FIG. The far side 7b has a rectangular shape with corners 7c, 7c near the directional position when viewed from the plane of the nozzle nozzle hole, and the entire nozzle has a semicircular and semiangular shape.

Here, the corner 7c is preferably formed to be slightly shifted from the directional position of the nozzle injection hole in the direction of the vortex.

Reference numeral 8 denotes a plurality of inclined grooves formed on the inner circumferential surface of the constricted portion so as to be inclined in a predetermined direction.

According to the above configuration, the intake vortex formed in the combustion chamber 4 due to the shape of the intake port during the intake stroke of the piston 2 is preserved without being attenuated inside the cavity 5, and the In the contraction part 7,
Since the shape of this part is a semicircle and a half rectangle, the speed decreases particularly at the rectangular side part 7b that is far from the nozzle, and the overall velocity becomes a vortex flow that is slower than the inside of the cavity.

However, when the piston 2 moves to the compression stroke in this state,
The so-called squish in which air is forced into the cavity 5 from the combustion chamber 4 is swirled by the inclined groove 8 formed on the inner peripheral surface of the constriction part 7, so that the vortex flow in the cavity is further promoted. When fuel is injected from the nozzle 6 at the end of the stroke, the fuel spray that passes through the constriction part 7 is dispersed far away because the vortex is weak in the rectangular side part 7b far from the nozzle, as shown by the chain line in FIG. Since the vortex flow is relatively strong in the circular side 7a near the nozzle, the vortex flow causes the cavity 5 to change from the state shown by the chain line in FIG.
By flowing further in the circumferential direction, the actual reach distance of the spray column becomes longer, and as a result, the state of the fuel spray on both sides becomes approximately equal, and a uniform air-fuel mixture is formed. In addition, since a strong vortex is formed inside the cavity as described above, the constriction portion 7
The air-fuel mixture formed in
The so-called reverse squish that blows out is swirled by the inclined groove 8 and the combustion gas is stirred, so that combustion is completed in a short time, and the fuel is completely burned, reducing the amount of soot and nitrogen oxide emissions. This results in a significant reduction in power output and improved output.

Note that FIG. 3 shows an embodiment in which the bottom surface of the cavity 15 formed at the top of the piston 12 is flat and has no protrusion in the center, unlike the cavity 5 in the embodiments of FIGS. 1 and 2. Also in the embodiment, the constriction portion 17 and the inclined groove 1
8 etc., the same effect as in the embodiment shown in FIGS. 1 and 2 is achieved.

As described above, the present invention provides a direct injection combustion chamber for a small engine in which the nozzle is eccentric with respect to the cavity formed at the top of the piston, and the injection hole is directed into the cavity. A constriction part is formed in the upper part of the range, and the planar shape of the constriction part is such that the side closer to the nozzle is circular, and the side farther from the nozzle has a corner near the orientation position when viewed from the plane of the nozzle nozzle. The nozzle has a semi-circular, semi-square shape with a rectangular shape, and an inclined groove in a predetermined direction is formed on the inner circumferential surface of the constriction part, thereby achieving uniform mixing even though the nozzle is eccentric with respect to the cavity. At the same time, the above-mentioned inclined grooves cause the squish and reverse squish to swirl, resulting in rapid formation or combustion of the air-fuel mixture, which improves the combustion condition and removes soot from nitrogen oxides. Emissions are reduced and exhaust conditions are improved, and the required output performance can be obtained even if the maximum pressure is lowered, so it has the effect of reducing noise, which is a disadvantage of direct injection combustion chambers. It is played.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of the vicinity of the combustion chamber in an embodiment of the present invention, FIG. 2 is a plan view of the piston in the embodiment, and FIG.
The figure is a longitudinal sectional view of a piston showing another embodiment of the cavity. 2 is a piston, 5 is a cavity, 6 is a nozzle, 7 is a constriction part, 7a is a side close to the nozzle, 7b is a side far from the nozzle, 8 is an inclined groove.

Claims (1)

[Scope of utility model registration request] In a configuration in which the nozzle is installed eccentrically with respect to the center of a cavity with a circular planar shape at the top of the piston, and the nozzle hole is directed into the upper cavity, the nozzle is constricted to the upper part within the area where the cavity is formed. At the same time, the planar shape of the constricted part is such that the side part near the nozzle is circular;
The far side has a semicircular and semiangular shape with a corner near the directional position seen from the plane of the nozzle nozzle hole, and a plurality of inclined grooves inclined in a predetermined direction are formed on the inner circumferential surface of the constriction part. A direct injection combustion chamber for a diesel engine featuring: