JPH0115860Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an improvement in the combustion chamber of a swirl chamber type diesel engine, and more particularly to an improvement in a main chamber cavity formed at the top of a piston.

(Prior Art) The swirl chamber type is known as a combustion chamber suitable for high-speed diesel engines, but the ones shown in Figures 3 and 4 have been proposed to further improve its combustion properties. (Refer to Utility Model Publication No. 57-78724).

To explain this, fuel ignited in the swirl chamber 20 near the compression top dead center of the engine becomes a flame (combustion gas) and ejects into the main chamber cavity 6 from the injection port 21.

Inside the main chamber cavity 6, the flame (flow is indicated by B) flows along the trench portion 10, collides with the connecting portion 9 of the pair of diffusion portions 7 and 8, and splits into two. The separated flames spread along the arcs of the diffusion parts 7 and 8, and combustion progresses while taking in fresh air. Incidentally, the trench portion 10 has a groove shape and a pair of diffusion portions 7,
8 is formed into a circular recess. Further, 1 is a cylinder block, 2 is a cylinder head, 23 is a fuel injection valve, and 24 is a glow plug.

By the way, in general, in order to reduce the amount of HC and smoke emitted in a swirl chamber type diesel engine, it is effective to increase the volume of the swirl chamber as much as possible to increase the air utilization rate in the swirl chamber for the injected fuel.

However, increasing the swirl chamber volume lowers the compression ratio of the engine, which lowers the compressed air temperature and increases HC emissions. Therefore, when increasing the swirl chamber volume, it is necessary to keep the main chamber cavity volume small and take into account the combustion chamber volume as a whole.

On the other hand, in order to properly burn the unburned components in the flame ejected from the swirl chamber into the main chamber, it is sufficient to improve the mixing of the flame and the air in the main chamber. It is necessary to secure the volume of the diffusion section of the chamber cavity.

The volume of the main chamber cavity is determined based on these three requirements, and the cloverleaf-shaped main chamber cavity 6 shown in FIG. 3 is formed in the right half of the top portion 4 of the piston 3 in the figure.

However, the volume of the diffusion section is small and the air utilization rate in the main room is still not sufficient.

Therefore, in order to improve the air utilization rate in the main chamber and to increase the compression ratio, it has been proposed to form a main chamber cavity at the top of the piston, in which the diffusion section is also used as a valve recess. There is. (See Utility Application No. 189037, 1983).

In this main chamber cavity, a pair of large diffusion portions consisting of circular recesses are formed at the top of the piston, and the volume of the diffusion portion is expanded.

(Problems to be solved by the invention) Good combustion in the diffusion section depends on the momentum of the flame that takes in air within the diffusion section, and if the momentum is weakened, the initial combustion will be worsened. However, due to the use of reverse skidding, most of the flame flow flows from the downstream end of the trench section as the main flow (swirling flow) guided by the circular arc around the diffusion section, but part of it flows from the upstream starting end of the trench section. It immediately becomes a side stream that flows as it is guided around the outer periphery of the diffusion section. This side flow becomes a counter flow that collides from the opposite direction with the main flame directed toward the outer periphery of the same diffusion section, and thus tends to offset its momentum. For this reason, it is thought that the mixing of the flame and air becomes sluggish and combustion deteriorates, leading to an increase in the amount of smoke emissions that tend to occur in the early stages of combustion.

An object of the present invention is to provide a swirl chamber type diesel engine that avoids interference with the mainstream flame and secures the momentum of the mainstream flame by colliding the side flow with the cylinder wall and attenuating it.

(Means for Solving the Problems) The present invention consists of a pair of diffusion parts that are located below the intake and exhaust valves and have a diameter larger than the diameter of both the valves, and a pair of diffusion parts that are connected to both the diffusion parts. The present invention is based on a swirl chamber type diesel engine in which a main chamber cavity is formed at the top of the piston and includes a groove-shaped trench portion extending on the lower surface of the nozzle port, one end of which is connected to the swirl chamber.

In the present invention, a portion located in a range between two tangent lines perpendicular to the central axis of the trench portion and touching the outer periphery of the diffusion portion and close to the outer periphery of the piston is formed to have the same depth as the bottom surface of the diffusion portion.

(Function) With this configuration, the side flow is guided in the tangential direction touching the outer periphery of the diffusion part, collides with the cylinder wall, and disappears, so it does not interfere with the mainstream flame. Although the swirling property is weakened by changing the , the flow becomes a wider swirling flow, but the expansion of the volume of the diffusion section and the active promotion of mixing with the air inside the diffusion section ensure good flame combustion. become.

(Embodiment) FIG. 1A is a plan view of the top of a piston according to an embodiment of the present invention, and FIG. 1B is a sectional view taken along line A--A in FIG. 1A.

In the figure, on the piston top 4, there is a pair of diffusion parts 7 located below the intake and exhaust valves (not shown) and consisting of a circular concave part having a diameter larger than the diameter of both valves.
A, 8A, a groove-shaped trench portion 10A is formed which extends to the lower surface of a nozzle (not shown) that is connected to the diffusion portions 7A, 8A and has one end connected to the swirl chamber. Note that the groove bottom surface 31 of this trench portion 10A
is formed by an inclined surface that is deepest on the side extending to the lower surface of the nozzle (bottom in the figure) and becomes shallower from the deepest part toward the connecting part 9A, and reaches the same depth as the connecting part step at the connecting part 9A. .

In this way, the main chamber cavity 6A is formed by the pair of diffusion parts 7A, 8A and the trench part 10A, but in the present invention, two tangents E, A portion located in the range between E and close to the piston outer periphery 40 (indicated by diagonal lines in the figure) is formed to have the same depth as the bottom surfaces 34 and 35 of the diffusion portion. That is,
The shaded portions are formed as enlarged diffusion portions 36 and 37. Note that the minimum depth of the diffusion portions 7A and 8A, which are also used as valve recesses, is the valve lift,
It is set based on the compression ratio, etc.

To explain the effect of the above configuration, the flame ejected from the nozzle to the trench portion 10A at the beginning of the expansion stroke mainly flows from the downstream end (upper part in the figure) of the trench portion 10A to the outer periphery of the pair of diffusion portions 32, 33 due to the reverse squishing action. There is a flame main stream C that is guided by the flame main stream C and swirls, but there is also a side stream D that is guided to the outer periphery of the diffusion part 32, 33 and flows immediately from the upstream starting end of the trench part (lower part in the figure). This side flow D is directly guided in the tangential direction from the outer circumferences 32 and 33 of the diffusion portions, collides with the facing cylinder wall, and attenuates and disappears. Therefore, the momentum of the mainstream flame is not slowed down by interference from side streams. For comparison, the conventional example is shown superimposed on the same figure using a two-dot chain line. The side flow and the main flame are guided from opposite directions by the same diffusion section outer periphery and collide at an approximately midpoint near the piston outer periphery 40. offsets the momentum of the mainstream flame. However, in the present invention, the side flow does not flow in the flow direction of the main flame stream. In addition,
Although flame flow is shown for only one diffusion section, the same is true for the other.

On the other hand, the swirling property of the main stream of the flame is loosened due to the change in the shape of the outer periphery of the diffusion section, but
Since the volume of the diffusion section is expanded by adding 7, the amount of air used in the mainstream of the flame increases, and the flame and air are actively mixed to promote combustion. For this reason, the smoke density at a predetermined rotation speed (1200 rpm) is shown in Figure 2, and the amount of smoke generated is reduced over a wide load range.

(Effect of the invention) According to the invention, in the range between two tangents that are perpendicular to the central axis of the trench part and in contact with the outer periphery of the diffusion part,
In addition, since the portion close to the outer circumference of the piston is formed at the same depth as the bottom surface of the diffusion section, the momentum of the mainstream flame is not offset by the side flow, and the mainstream flame promotes mixing with the air inside the diffusion section and is heated at the beginning of combustion. It is possible to reduce the amount of smoke emissions that are likely to occur.

[Brief explanation of the drawing]

FIG. 1A is a plan view of the top of a piston according to an embodiment of the present invention, FIG. 1B is a sectional view taken along line A--A in FIG. 1A, and FIG. 2 is a characteristic diagram of smoke density. Third
The figure is a longitudinal sectional view of a conventional combustion chamber, and FIG. 4 is a plan view of the top of the piston. 3...Piston, 4...Piston top, 6A
...Main room cavity, 7A, 8A...Diffusion section, 7
B, 8B... Diffusion part step, 10A... Trench part, 31... Groove bottom surface, 32, 33... Diffusion part outer periphery, 34, 35... Diffusion part bottom surface, 36, 37...
Enlarged diffusion section, 40...Piston outer periphery.

Claims (1)

[Scope of utility model registration request] A pair of diffusion parts located below the intake and exhaust valves and consisting of circular recesses having a diameter larger than the diameter of both valves, and a groove extending on the lower surface of the nozzle that is connected to both diffusion parts and has one end connected to the swirl chamber. In a swirl chamber type diesel engine in which a main chamber cavity consisting of a shaped trench portion is formed at the top of the piston, the main chamber cavity is located in the range between two tangents perpendicular to the central axis of the trench portion and in contact with the outer periphery of the diffusion portion, and is located on the outer periphery of the piston. A swirl chamber type diesel engine characterized in that the adjacent portion is formed at the same depth as the bottom surface of the diffusion section.