JP2501886Y2 - 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 concave fuel reflection surface having an arcuate cross section is formed obliquely downward on the inner peripheral wall surface of the cavity formed on the top surface of the piston to inject fuel from the fuel injection valve toward the fuel reflection surface. A direct injection diesel engine in which the injected fuel whose cross-sectional shape is reflected on the fuel reflection surface moves sequentially from the cavity periphery to the cavity center as the fuel reflection position on the fuel reflection surface goes below the fuel reflection surface. Combustion chamber is known (JP-A-63-30622).
No. 0). In this diesel engine, the advancing direction of the injected fuel sequentially moves from the peripheral portion of the cavity to the central portion, so that the air utilization rate can be increased.

[Problems to be solved by the device]

However, in the combustion chamber of this diesel engine, when the fuel reflection position is located above the fuel reflection surface, the angle formed by the fuel reflection surface and the injected fuel is small, and the reflection fuel is in the peripheral portion of the cavity, that is, the inner circumference of the cavity. Since it goes toward the wall surface, there is a problem that it is more likely to adhere to the inner wall surface of the cavity and is not sufficiently mixed as compared with the fuel reflected below the fuel reflection surface. For this reason, HC and smoke cannot be reduced.

[Means for solving the problem]

According to the present invention, a fuel reflection surface extending annularly along the cavity inner peripheral wall surface formed on the piston top surface is formed, and the fuel reflection surface is formed from a downward curved curved surface having a concave cross section. The fuel is injected from the fuel injection valve that is formed to inject the fuel toward the fuel reflection surface, and the formation position and cross-sectional shape of the fuel reflection surface are reflected on the fuel reflection surface, and the injected fuel is reflected on the fuel reflection surface. The position is determined so as to go from the peripheral portion of the cavity toward the central portion of the cavity as the position goes from the upper side to the lower side, and a recess is formed on the fuel reflection surface so that the depth becomes deeper toward the upper side of the cavity, and the fuel injection from the fuel injection valve is performed. Providing the combustion chamber of a direct-injection diesel engine whose direction is set toward the fuel reflection surface on the downstream side of the recess when viewed from the swirl flow direction in the cavity It is.

[Action]

Since the concave portion having a depth that increases as it goes upward is formed on the fuel reflecting surface, the turbulence of the flow flowing into the cavity caused by the concave portion becomes larger as it goes upward of the fuel reflecting surface. Therefore, the fuel that is reflected above the fuel reflection surface and moves toward the peripheral portion of the cavity is sufficiently mixed and diffused with air due to strong turbulence. Further, the fuel reflected below the fuel reflection surface toward the center of the cavity is less disturbed than the fuel reflected above the fuel reflection surface, and therefore the energy toward the center of the cavity is not reduced.

〔Example〕

FIG. 2 shows a side sectional view of a direct injection diesel engine.
Referring to FIG. 2, 1 is a cylinder block, 2 is a piston capable of reciprocating 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 are fuel injection valves arranged at the top of the combustion chambers 4, respectively. Although not shown in the drawing, an intake port and an exhaust port are formed in the cylinder head 1, and an intake valve and an exhaust valve are arranged at openings of the intake port and the exhaust port into the combustion chamber 4, respectively. 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. 2, the fuel injection valve 5 is obliquely arranged in order to avoid interference with these intake and exhaust valves and intake and exhaust ports.

As shown in FIGS. 2 and 3, the piston 2 has a flat top surface 2a, and a cavity 6 is formed in the flat piston top surface 2a. An annular lip 7 protruding inward is formed at the upper end of the peripheral wall surface 6a of the cavity 6,
On the inner peripheral surface of the annular lip 7, a pair of annular peaks 8 and 9 are formed at intervals in the vertical direction. As can be seen from FIGS. 2 and 3, the inner diameter of the ridge portion 8 is smaller than the inner diameter of the ridge portion 9, so that the ridge portion 8 forms the smallest diameter narrowed portion on the inner peripheral surface of the annular lip 7. . The ridges 9 have relatively sharp corners, while the ridges 8
Is formed from a smooth curved surface. The upper end 7a of the inner peripheral surface of the annular lip 7 extending from the piston top surface 2a to the ridge portion 8 is formed in a funnel-shaped cross-sectional shape in which the cross-sectional area gradually decreases downward. The inner peripheral surface middle portion 7b of the annular lip 7 extending from the ridge portion 8 to the ridge portion 9 is formed of a concave curved surface whose cross-sectional area gradually increases downward, and the annular lip 7 of the concave curved surface is formed. As shown in FIGS. 2 and 3, the inner peripheral surface middle portion 7b has an obliquely downward arcuate cross section. The inner peripheral surface middle portion 7b is directed substantially toward the center of the bottom of the cavity 6. 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 The cavity lower peripheral wall surface 6b is formed of a concave curved surface, and the cavity lower peripheral wall surface 6b is entirely bulged 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.

The fuel injection valve 5 has, for example, six nozzle holes, and the second
Fuel is injected from the six nozzle holes toward the intermediate portion 7b of the inner peripheral surface of the annular lip 7 as indicated by arrow F in the figure. A part of this 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 fuel reflecting surface.

FIG. 1 is a top view of the piston 2, and FIGS.
The figure shows enlarged sectional views taken along the lines IV-IV and VV of FIG. 1, respectively. Referring to FIG. 1, the center O _{C of the} cavity 6 is eccentric with respect to the center O _{P of the} piston 2, and the center O _I of the tip of the fuel injection valve 5 is eccentric with respect to O _C and O _P. ing. The fuel injection valve 5 is provided with the six nozzle holes as described above, and the nozzle holes are formed and arranged so that the injection directions of the injected fuel F form 60 degrees with each other.

Referring to FIG. 1, FIG. 4 and FIG. 5, three recesses 20 are formed apart from each other on the upper end 7a of the inner peripheral surface of the annular lip 7 and the fuel reflecting surface 7b. In this embodiment, the number of recesses 20 is half the number of nozzle holes of the fuel injection valve 5. The outer peripheral surface 20a of the recess 20 is formed by a vertical curved surface parallel to the central axis of the piston 2. Therefore, as shown in FIG. 4, on the fuel reflecting surface 7b, the depth D of the concave portion 20 (the distance between the fuel reflecting surface 7b and the concave portion outer peripheral surface 20a) becomes deeper toward the upper side of the fuel reflecting surface 7b. Become. Further, as shown in FIG. 5, on the fuel reflection surface 7b, the peripheral length L of the recess outer peripheral surface 20a becomes longer toward the upper side of the fuel reflection surface 7b.

FIG. 6 shows a sectional view taken along the line VI-VI in FIG. Assuming that the swirling direction of the swirling flow SW generated in the combustion chamber 4 is clockwise as indicated by the arrow SW in FIG. 1, as shown in FIG. 6, the concave outer peripheral surface 20a and the fuel reflecting surface 7b are Of the angle θ formed by the concave portion so that the angle θ _U at the upstream end 20b of the concave outer peripheral surface 20a with respect to the swirl flow SW is larger than the angle θ _D at the downstream end 20c of the concave outer peripheral surface 20a with respect to the swirl flow SW. An outer peripheral surface 20a is formed. Therefore, the swirl flow easily flows into the recess 20 from the recess upstream end 20b, while the swirl flow SW
When flowing out from the recess 20 at the downstream end 20c, it separates from the fuel reflection surface 7b, and a strong local turbulence R is generated on the downstream side. Since the diameter of the fuel reflecting surface 7b decreases toward the top, both angles θ _U and θ _D decrease toward the top. When the swirling flow SW flows into the cavity 6, a local turbulence R is generated downstream of the downstream end 20c by the recess 20. As described above, the depth D of the recess 20 (Fig. 4) is the fuel reflection surface. This turbulence R becomes stronger as it goes up above the fuel reflection surface 7b because it becomes deeper as it goes up above 7b.
Furthermore, θ _D becomes smaller as it goes upward,
The turbulence R further promotes the tendency of becoming stronger as it goes upward of the fuel reflection surface 7b.

The depth D of the recess 20 is set such that the swirl flow SW is not weakened too much, and the volume of the recess 20 is set so that the compression ratio does not change significantly due to the formation of the recess 20. For example, the volume of each recess 20 is a cavity. It is desirable to set it to 0.3% or less of the total volume of No. 6.

As shown in FIGS. 4 and 5, the recess 20 has a ridge 9.
It is not formed on the inner wall surface 6a of the lower cavity.
As a result, it is possible to prevent the gas flow in the cavity 6 from being discharged to the outside of the cavity 6 early through the recess 20 in the combustion process, and thus to suppress the quenching of unburned gas in the squish area. .

As shown in FIG. 1, at the position where the recess 20 is formed in the circumferential direction, every other fuel injection F in the circumferential direction is slightly deviated from the downstream end 20c of the outer peripheral surface of the recess in the swirling flow SW direction. Face 7
b Determined to collide on.

FIGS. 7 (a) to 7 (e) show the time lapse from the start of fuel injection to the end of fuel injection. FIG. 7 (a) shows the case where the piston 2 is slightly before the top dead center and fuel injection is started. FIG. 7 (b) shows the piston 2 slightly elevated toward the top dead center, and FIG. 7 (c).
Indicates the time when the piston 2 has reached the top dead center. Seventh
FIG. 7 (d) shows the piston 2 slightly descending beyond the top dead center, and FIG. 7 (e) shows the completion of injection when the piston 2 further descends. As shown in FIG. 7 (a), at the start of fuel injection, the injected fuel F is the fuel reflection surface 7b.
When the piston 2 reaches the top dead center as shown in FIG. 7 (c), the injected fuel F collides with the lower end of the fuel reflection surface 7b. That is, in other words, regarding the position of the fuel reflection surface 7b and the direction of fuel injection from the fuel injection valve 5, the injected fuel F collides with the upper end of the fuel reflection surface 7b at the start of fuel injection, and the piston 2 reaches the top dead center. Sometimes injected fuel F
Are set so as to collide with the lower end of the fuel reflection surface 7b.

On the other hand, the fuel reflecting surface 7b is directed obliquely downward toward the center of the bottom of the cavity 4, and the fuel reflecting surface 7b
Has an arcuate cross section. Therefore, as shown in (a) to (c) of FIG. 7, as the piston 2 rises, the angle formed by the fuel reflection surface 7b and the injected fuel F at the fuel collision point gradually increases. Reflected fuel G reflected on the axis of the injected fuel F and the fuel reflecting surface 7b
The angle formed by the axis line of and becomes smaller as the piston 2 rises. As shown in FIG. 7 (a), the reflected fuel G heads to the peripheral portion of the cavity 6 at the time of starting the fuel injection, and as shown in FIG. 7 (b), when the piston 2 is slightly raised, the reflected fuel G travels in the traveling direction. Moves from the periphery of the cavity 6 toward the center, and when the piston 2 reaches the top dead center as shown in FIG. 7 (c), the reflected fuel G moves toward the center of the cavity 6. That is, the traveling direction of the reflected fuel G continuously moves from the peripheral portion of the cavity 6 to the central portion thereof after the fuel injection is started and before the piston 2 reaches the top dead center. In other words, the shape of the fuel reflecting surface 7b is such that the traveling direction of the reflected fuel G continuously moves from the peripheral portion of the cavity 6 toward the central portion thereof after the fuel injection is started and before the piston 2 reaches the top dead center. Stipulated in. As shown in (c) to (e) of FIG. 7, the reflected fuel G continues from the central portion of the cavity 4 toward the peripheral portion thereof after the piston 2 reaches the top dead center until the fuel injection is completed. Move to.

When the fuel injection is started as shown in FIG. 7 (a), the injected fuel F collides with the upper end portion of the fuel reflection surface 7a. When the injected fuel F collides with the upper end of the fuel reflection surface 7b, the angle formed by the fuel reflection surface 7b and the injected fuel F is small as described above, and the reflected fuel G is the peripheral portion of the cavity 6.
That is, it goes to the vicinity of the inner peripheral wall surface of the cavity 6. Therefore, compared with the fuel reflected below the fuel reflection surface 7b, the fuel is more likely to adhere to the inner wall surface 6a of the cavity, which causes a problem that air cannot be mixed sufficiently. As a result, there is a problem that the emission amount of particulates, HC and smoke cannot be reduced sufficiently.

In this embodiment, since the recess 20 is formed on the fuel reflecting surface 7b, when the swirl flow SW flows into the cavity 6, a local turbulence R is generated downstream of the downstream end 20c, and this turbulence R is the fuel. It becomes stronger as it goes upward on the reflecting surface 7b. Therefore, when the injected fuel F is reflected above the fuel reflection surface 7b, the reflected fuel G is mixed with air by the locally strong turbulence R generated by the recess 20 and diffused. Therefore, even when the injected fuel F is reflected by the upper portion of the fuel reflection surface 7b and heads for the peripheral portion of the cavity 6, the fuel hardly adheres to the inner wall surface 6a of the cavity.

As shown in FIG. 7 (a), when the piston 2 approaches the top dead center, the squish flow flows from the squish area 10 formed between the peripheral portion of the piston top surface 2a and the cylinder head 3 toward the center of the combustion chamber 4. Is leaked. The squish flow flows downward along the upper end portion 7a of the inner peripheral surface of the annular lip 7 as shown by the arrow S. As mentioned above, Minebe 8 (3rd
In the figure), the squish flow S flowing along the upper end 7a of the inner peripheral surface of the lip separates at the peak 8 and is a minute vortex, that is, a micro turbulence, around the fuel reflection surface 7b. To occur. This microturbulence also prevents the fuel from adhering to the fuel reflecting surface 7b. Immediately after the fuel injection is started in this way, the injected fuel is collected in the peripheral portion of the cavity 6, so that the air-fuel mixture region P is formed in the peripheral portion of the cavity 6.

Next, as shown in FIG. 7 (b), when the piston 2 rises, the traveling direction of the reflected fuel G moves toward the center of the cavity 6. The intensity of the turbulence R becomes weaker as the fuel reflection position moves downward on the fuel reflection surface 7b, and therefore the energy of the reflection fuel G toward the center of the cavity 6 is hardly taken away. It can go to the center of the cavity 6. On the other hand, when the temperature of the fuel particles is sufficiently increased, the air-fuel mixture P (FIG. 7A) around the cavity 6 is ignited and burned. By the way, when a gas with a large mass and a gas with a small mass exist in the swirling flow, the gas with a large mass moves to the peripheral portion by the centrifugal force, and the gas with a small mass gathers in the central portion. Incidentally, the mass of the combustion gas is smaller than the mass of the air. Therefore, when the combustion gas and the air are swirling, the combustion gas moves toward the center and the air moves toward the periphery. Therefore, when the air-fuel mixture P (FIG. 7 (a)) around the cavity 6 is ignited and burned, the combustion gas moves toward the center of the cavity 6 as indicated by Q in FIG. 7 (b). To start. At the same time, the combustion flame propagates toward the center of the cavity 6. Therefore, as shown in FIG. 7 (b), the flame propagates so as to follow the reflected fuel Q. In other words, when the air-fuel mixture is formed by the reflected fuel Q, the flame immediately propagates to the air-fuel mixture in a timely manner, and the air-fuel mixture is burned. Therefore, the seventh
As shown in FIG. 6C, when the reflected fuel G moves toward the center of the cavity 6, the reflected fuel G causes the cavity 6 to move.
The air-fuel mixture formed in the central part of the is immediately ignited and burned by the flame toward the central part.

On the other hand, during this time, the air moves from the center of the cavity 6 toward the periphery. Therefore, as shown in FIGS. 7D to 7E, when the piston 2 starts descending and the traveling direction of the reflected fuel G moves from the central portion to the peripheral portion of the cavity 6, the reflected fuel G has sufficient air. Will be sent into the area. At this time, the flame goes from the center of the cavity 6 to the periphery. On the other hand, an air-fuel mixture is formed around the cavity 6 due to the evaporation of the liquid fuel attached to the peripheral wall surface of the cavity 6, and this air-fuel mixture is burned by a flame directed from the center of the cavity 6 to the periphery. Can be

As described above, according to the present embodiment, the swirl flow SW is converted into the local turbulence R which becomes stronger toward the upper side of the fuel reflection surface 7b by the concave portion 20, so that the fuel reflected above the fuel reflection surface 7b is converted. Also hardly adheres to the inner wall surface 6a of the cavity and is well mixed with air and diffused, while the fuel reflection surface
The fuel reflected below 7b can reach the center of the cavity with little influence of turbulence R.
In this way, good combustion can be obtained, and the output can be improved and the emissions of particulates, HC and smoke can be reduced.

In addition, in order to convert a part of the swirl flow SW into turbulence R, the swirl flow SW
Can be prevented from becoming too strong, so that even when a fuel injection valve having a plurality of nozzle holes is used, the fuel spray formed by the injected fuel from the nozzle holes adjacent to each other at high engine speed It is possible to prevent overlapping with each other, and as a result, it is possible to prevent an increase in the amount of smoke generated.

FIG. 8 shows the relationship between the engine speed and the torque when the fuel reflection position in the circumferential direction is changed. In the present embodiment, the fuel reflection position is located immediately downstream of the downstream end 20c of the recess 20, but when the fuel reflection position is shifted 5 degrees upstream from the position of the present embodiment, as shown in the figure, the low speed range is reached. At, the torque is significantly reduced. This is because the fuel spray leaks to the outside of the cavity at low engine speeds where the swirl flow is weak, and the smoke and HC emissions also increase. On the other hand, when the fuel injection position is shifted 5 degrees downstream from the position of this embodiment, the torque deteriorates in the low and medium speed range. From these results, it is understood that the highest effect can be obtained by locating the fuel reflection position immediately downstream of the downstream end 20c of the recess 20 as in the present embodiment.

FIG. 9 shows the relationship between the engine speed and the full load torque. According to this embodiment, the full load torque is improved in all regions.

FIG. 10 shows the relationship between the NO _x emission amount, the particulate emission amount, and the HC emission amount during idle operation. According to the present embodiment, both the particulate emission amount and the HC emission amount can be reduced, and even if the NO _x emission amount is reduced, as in the conventional example, the particulate emission amount and the HC emission amount can be reduced.
HC emissions do not increase.

FIG. 11 shows the relationship between the strength of the swirling flow and the torque. In the conventional example, when the swirl flow becomes stronger in the high speed region (3400 rpm), the torque is significantly reduced, but according to the present example, the torque can be greatly improved. This is because the concave portion 20 can weaken the swirling flow in the cavity.

FIG. 12 shows an embodiment in which the same number of recesses 20 as the nozzle holes of the fuel injection valve 5 are formed. In this embodiment, all of the injected fuel F is reflected at a position immediately downstream of the downstream end 20c of the recess 20, and a higher effect can be obtained as compared with the embodiment shown in FIG.

[Effect of device]

The fuel reflected above the fuel reflection surface and directed to the peripheral portion of the cavity can also be sufficiently mixed with air and diffused. This can reduce the generation of HC and smoke.

[Brief description of drawings]

1 is a top view of a piston of a diesel engine to which an embodiment of the present invention is applied, FIG. 2 is a side sectional view of a diesel engine according to the present invention, FIG. 3 is an enlarged side sectional view of FIG. FIG. 4 is an enlarged sectional view of an essential part taken along the line IV-IV in FIG.
FIG. 5 is an enlarged cross-sectional view taken along the line VV of FIG. 1, FIG. 6 is an enlarged cross-sectional view taken along the line VI-VI of FIG. 4, and FIG. FIG. 8 is a diagram showing the relationship between engine speed and torque when the fuel reflection position is changed, and FIG. 9 is a diagram showing relationship between engine speed and full load torque. Fig. 10 shows NO during idle operation
_x is a diagram showing the relationship between the discharge amount, the particulate discharge amount, and the HC discharge amount, FIG. 11 is a diagram showing the relationship between the strength of swirling flow and torque, and FIG. 12 is the top of the piston of another embodiment. It is a side view. 2 ... Piston, 5 ... Fuel injection valve, 6 ... Cavity, 6a ... Cavity peripheral wall surface, 7b ... Fuel reflection surface, 20 ...
… Recessed.

Claims (1)

(57) [Scope of utility model registration request] 1. A fuel reflection surface extending annularly along the cavity inner peripheral wall surface formed on the piston top surface, and the fuel reflection surface is formed from a downward curved surface having a concave cross section. Then, the fuel is injected from the fuel injection valve toward the fuel reflection surface, and the injected fuel having the formation position and the cross-sectional shape of the fuel reflection surface reflected on the fuel reflection surface is the fuel reflection position on the fuel reflection surface. Is formed so as to go from the periphery of the cavity toward the center of the cavity as it goes downward from above, and a recess whose depth becomes deeper as it goes above the cavity is formed on the fuel reflection surface, and the fuel injection direction from the fuel injection valve is also formed. Is a combustion chamber of a direct-injection diesel engine, which is set toward the fuel reflection surface at a portion downstream of the recess when viewed from the swirl flow direction in the cavity.