JP2522799Y2 - Combustion chamber of direct injection diesel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a combustion chamber of a direct injection diesel engine.

[Conventional technology]

A cavity is formed on the top surface of the piston, fuel is injected toward the substantially cylindrical inner peripheral wall of the cavity, a glow plug is arranged above the cylindrical inner peripheral surface of the cavity, and the cylindrical inner peripheral surface of the cavity is formed. A diesel engine is known in which a portion of fuel that has collided with a glow plug rises along a cylindrical inner peripheral surface of a cavity and is guided around a glow plug (see Japanese Utility Model Application Laid-Open No. 58-75921).

[Problems to be solved by the invention]

However, in this diesel engine, the fuel rising along the cylindrical inner peripheral surface of the cavity always collides with a specific area of the glow plug, so that the temperature in this specific area is extremely lowered, and it is difficult to ignite the mixture. Problem.

According to the present invention, a cavity is formed on the top surface of a piston and extends from the inner wall surface of the cylinder head to the inside of the cavity when the piston is at the top dead center. In a diesel engine equipped with a glow plug, a fuel reflection surface having a curved cross-sectional shape is formed on the inner peripheral wall surface of the cavity so that the fuel injected from the fuel injection valve collides with the fuel reflection surface, and the fuel reflection surface is formed. The cross-sectional shape is set so that the reflected fuel reflected on the fuel reflecting surface collides with the glow plug, and the collision position of the reflected fuel with the glow plug with the rise of the piston is scanned in the axial direction of the glow plug.

〔Example〕

FIG. 1 shows a side sectional view of a direct injection diesel engine.
Referring to FIG. 1, 1 is a cylinder block, 2 is a piston that can reciprocate in the cylinder block 1, 3 is a cylinder head fixed to the cylinder block 1, and 4 is a flat inner wall surface of the cylinder block 1 and a piston. Combustion chambers 5 formed between the two indicate fuel injectors arranged at the center of the top of the combustion chamber 4. Although not shown in the drawings, cylinder head 1
An intake port and an exhaust port are formed therein, and an intake valve and an exhaust valve are respectively disposed at openings of the intake port and the exhaust port into the combustion chamber 4. A helical intake port is used as an intake port to give a swirling flow to intake air flowing into the combustion chamber 4, or an intake valve with a shroud is used as an intake valve. Needless to say, a swirl flow can be given to the intake air flowing into the combustion chamber 4 by other means such as connecting the intake port into the combustion chamber 4 toward the periphery of the combustion chamber 4. In the embodiment shown in FIG. 1, the fuel injection valve 5 is arranged obliquely to avoid interference with these intake / exhaust valves and intake / exhaust ports.

As shown in FIGS. 1 and 2, the piston 2 has a flat top surface 2a, and a cavity 6 is formed on the flat piston top surface 2a. An annular lip 7 is formed at an upper end portion of the peripheral wall surface 6a of the cavity 6 so as to receive and project inward.
A pair of circular peaks 8 and 9 are formed on the inner peripheral surface of the annular lip 7 at intervals in the vertical direction. The peak 8 has a relatively sharp corner, whereas the peak 9 is formed of a smooth curved surface. Piston top surface 2a
The upper end 7a of the inner peripheral surface of the annular lip 7 extending from the lip 8 to the ridge 8 is formed in a funnel-shaped cross-sectional shape whose cross-sectional area gradually decreases downward. An intermediate portion 7b of the inner peripheral surface of the annular lip 7 extending from the peak portion 8 to the peak portion 9 is formed of a concave curved surface extending over the entire length of the cavity peripheral wall surface 6b. The intermediate portion 7b has an arc-shaped cross section as shown in FIGS. The lower end 7c of the inner peripheral surface of the annular lip 7 extending downward from the ridge 9 gradually expands downward from the ridge 9, and the lower end 7c of the inner peripheral surface is part of the lower peripheral wall surface 6b of the cavity 6. To form This cavity lower side peripheral wall surface 6b is formed from a concave curved surface,
Further, the entire cavity lower peripheral wall surface 6b bulges outward with respect to the peak portion 9. The bottom 6c of the cavity 6 is formed in a substantially conical shape with a raised central portion. On the other hand, a glow plug 10 protrudes from the cylinder head 3 into the combustion chamber 4. This glow plug 10 enters the cavity 6 and is located between the lip 7 and the fuel injection valve 5 when the piston 2 is at the top dead center position as shown in FIG.

The fuel injection valve 5 has one or a plurality of nozzle holes, and in the embodiment shown in FIG.
Fuel is injected from one or more nozzle holes toward the inner peripheral surface middle portion 7b of the annular lip 7. As shown in FIG. 3, fuel is injected from the fuel injection valve 5 toward the vicinity of the upstream side of the glow plug 10 in the flow direction of the swirl W so that the injected fuel does not directly collide with the glow plug 10. A part of the injected fuel is reflected at the inner peripheral surface intermediate portion 7b, and hence the inner peripheral surface intermediate portion 7b is hereinafter referred to as a concave fuel reflection surface. In the present invention, the function of the concave fuel reflecting surface 7b is important. Therefore, first, the function of the concave fuel reflecting surface 7b will be described with reference to FIG.

FIG. 4 (a) shows a case where the piston 2 is slightly before the top dead center and fuel injection is started, and FIG. 4 (b) shows a case where the piston 2 has reached the top dead center. ing. As shown in FIG. 4 (a), at the start of fuel injection, the injected fuel F collides with the upper end of the concave fuel reflecting surface 7b,
As shown in FIG. 2B, when the piston 2 reaches the top dead center, the injected fuel F collides with the lower end of the concave fuel reflection surface 7b. That is, in other words, the position of the concave fuel reflecting surface 7b and the direction of fuel injection from the fuel injection valve 5 cause the injected fuel F to collide with the upper end of the concave fuel reflecting surface 7b at the start of fuel injection, and the piston 2 to reach the top dead center. When it has reached, it is determined that the injected fuel F collides with the lower end of the concave fuel reflection surface 7b.

On the other hand, as described above, the concave fuel reflection surface 7b has an arc-shaped cross section. Therefore, as shown in FIGS. 4A and 4B, the angle between the concave fuel reflecting surface 7b and the injected fuel F at the fuel collision point changes as the piston 2 rises, and the traveling direction of the reflected fuel G Changes sequentially from downward to upward. On the other hand, the flow direction of the reflected fuel G is deflected by the swirl W as shown in FIG. 3, and then swirled along the inner peripheral wall surface of the annular lip 7, so that each reflected fuel G comes into contact with the glow plug 10 sequentially. Will do. However, as described above, as the piston 2 rises, the traveling direction of the reflected fuel G sequentially changes from downward to upward, so that each reflected fuel G is caused to collide with the glow plug 10 sequentially while being scanned in the axial direction of the glow plug 10, It is ignited and burned sequentially. As described above, according to the present invention, since the contact position between the reflective fuel G and the glow plug 10 changes sequentially with the rise of the piston 2, only a part of the glow plug 10 is locally cooled by the reflective fuel G. Therefore, the glow plug 10 is maintained at a high temperature throughout, so that good ignition combustion can be ensured.

Reflected on the concave fuel reflection surface 7b as described above are relatively small fuel particles of the injected fuel,
Fuel particles having a large particle diameter adhere to the concave fuel reflection surface 7b.
As shown in FIG. 4 (a), when the piston 2 approaches the top dead center, the periphery of the piston top surface 2a and the cylinder head 3
The squish flow flows out from the squish area 11 formed therebetween toward the center of the combustion chamber 4. This squish flow is at the upper end of the inner peripheral surface of the annular lip 7 as shown by the arrow S.
It flows downward along 7a. Mine 8 as described above
(FIG. 2) has a relatively sharp corner, so that the squish flow S flowing along the upper end 7a of the inner peripheral surface of the lip separates at the peak 8 and becomes a small vortex around the concave fuel reflecting surface 7b.
That is, microturbulence is generated. The vaporization of the liquid fuel attached to the concave fuel reflection surface 7b is promoted by the microturbulence. Further, a part of the liquid fuel attached to the concave fuel reflection surface 7b passes over a ridge 9 (FIG. 2) which forms a smooth curved surface due to the action of the squish flow S and the swirling flow, and is on the lower end 6b of the inner wall surface of the cavity 6. Sent to. As the liquid fuel evaporates, an air-fuel mixture is formed around the cavity 6, and this air-fuel mixture is
It is ignited and burned by the ignition fire.

5 to 8 show another embodiment. In this embodiment, as shown in FIGS. 5 and 6, the inner peripheral wall surface 7d of the annular lip 7 is formed in a funnel-like sectional shape in which the sectional area gradually decreases downward. The wall surface 7d is formed from a convex curved surface. The inner peripheral wall surface 7d of the annular lip 7 is connected to the annular lip 7 via a ridge 12 having a smooth curve.
Is connected to the lower end portion 7c of the inner peripheral surface of the.

In this embodiment, fuel is injected from the fuel injection valve 5 toward the inner peripheral wall surface 7d of the annular lip 7. Further, as shown in FIG. 7, fuel is injected from the fuel injection valve 5 toward the vicinity of the upstream side of the glow plug 10 in the flow direction of the swirl W so that the injected fuel does not directly collide with the glow plug 10. A part of the injected fuel is reflected on the inner peripheral wall surface 7d of the lip, and hence the inner peripheral wall surface 7d of the lip is hereinafter referred to as a convex fuel reflecting surface.

At the start of fuel injection as shown in FIG. 8 (a), the injected fuel F collides with the upper end of the convex fuel reflection surface 7d, and as shown in FIG. 8 (b), the piston 2 reaches the top dead center. When it reaches, the injected fuel F collides with the lower end of the convex fuel reflection surface 7d. That is, in other words, the position of the convex fuel reflecting surface 7d and the direction of fuel injection from the fuel injection valve 5 cause the injected fuel F to collide with the upper end of the convex fuel reflecting surface 7d at the start of the fuel injection, and the piston 2 is dead. When the point is reached, it is determined that the injected fuel F collides with the lower end of the convex fuel reflection surface 7d.

On the other hand, as described above, the convex fuel reflection surface 7d is formed from a convex curved surface. Accordingly, as shown in FIGS. 8 (a) and 8 (b), as the piston 2 rises, the angle between the convex fuel reflecting surface 7d and the injected fuel F at the fuel collision point changes, and the reflected fuel G advances. The direction changes sequentially from upward to downward. On the other hand, the flow direction of the reflected fuel G is deflected by the swirl W as shown in FIG. 7, and then swirled along the inner peripheral wall surface 7d of the annular lip 7. Will come in contact. However, as described above, as the piston 2 rises, the traveling direction of the reflected fuel G sequentially changes from upward to downward.
Are sequentially collided with the glow plug 10 while being scanned in the axial direction, and are sequentially ignited and burned. As described above, also in this embodiment, since the contact position between the reflective fuel G and the glow plug 10 sequentially changes as the piston 2 rises, only a part of the glow plug 10 is locally cooled by the reflective fuel G. Therefore, the glow plug 10 is maintained at a high temperature throughout, so that good ignition combustion can be ensured.

Also in this embodiment, the reflected fuel particles at the convex fuel reflecting surface 7d are the fuel particles having a relatively small particle diameter in the injected fuel, and the fuel particles having the large particle diameter adhere to the convex fuel reflecting surface 7d. By the way, as shown in FIG.
Approaching the top dead center, a squish flow flows out of the squish area 11 formed between the periphery of the piston top surface 2a and the cylinder head 3 toward the center of the combustion chamber 4. This squish flow flows downward along the convex fuel reflecting surface 7d as shown by the arrow S. At this time, the convex fuel reflection surface 7d
A part of the liquid fuel adhering to the ridge 12 forms a smooth curved surface by the action of the squish flow S and the swirling flow (FIG. 6).
And is fed onto the lower end 6b of the inner wall surface of the cavity 6. As the liquid fuel evaporates, an air-fuel mixture is formed around the cavity 6, and this air-fuel mixture is
It is ignited and burned by the ignition flame.

As described above, in any of the embodiments, the reflection fuel G
Since the contact position between the glow plug 10 and the glow plug 10 sequentially changes, the glow plug 10 is not cooled, and therefore, good ignition combustion can be ensured. Further, since the injected fuel F does not contact the glow plug 10, there is no danger that the glow plug 10 is cooled by the injected fuel F. Also, the reflected fuel G
Can be changed, so that the air utilization rate can be increased. Further, in the embodiment shown in FIGS. 5 to 8, the protrusion amount of the glow plug 10 can be reduced.

[Effect of the invention]

The fuel can be reliably ignited and burned using the glow plug while increasing the air utilization rate.

[Brief description of the drawings]

1 is a side sectional view of a diesel engine according to the present invention, FIG. 2 is an enlarged side sectional view of FIG. 1, FIG. 3 is a plan view of a piston top surface, and FIG. 4 is a diagram for explaining a combustion method. , Fifth
The figure is a side sectional view of a diesel engine showing another embodiment, FIG. 6 is an enlarged side sectional view of FIG. 5, FIG. 7 is a plan view of the piston top surface of FIG. 5, and FIG. It is a figure for explaining. 2 ... piston, 3 ... cylinder head, 5 ... fuel injection valve, 6 ... cavity, 7 ... annular lip, 7b ... concave fuel reflection surface, 7d ... convex fuel reflection surface, 10 ... glow plug.

Claims (1)

(57) [Scope of request for utility model registration] 1. A diesel engine having a glow plug having a cavity formed on a top surface of a piston and extending from an inner wall surface of a cylinder head to the inside of the cavity when the piston is at a top dead center position, wherein the glow plug is curved on an inner peripheral wall surface of the cavity. A fuel reflecting surface having a cross-sectional shape is formed to cause the fuel injected from the fuel injector to collide with the fuel reflecting surface, and the reflected fuel reflected at the fuel reflecting surface at the position and cross-sectional shape of the fuel reflecting surface is glowed. A combustion chamber of a direct-injection diesel engine in which a position where a reflected fuel collides with the plug and rises with the rise of the piston is scanned in the axial direction of the glow plug.