JPH02248615A - Engine piston - Google Patents

Abstract

PURPOSE:To prevent atomized fuel from adhering and residing before and behind a top dead center by forming a cavity side wall at an approximately right-angled inclination angle to a fuel atomizing line, and then a lip at the open end of a cavity. CONSTITUTION:The side wall 5 of a recessed cavity 2 in a piston top 20 is formed at an approximately right-angled inclination angle theta to a fuel atomizing line F from the axial side of the cavity 2. A protruding end 7 is edged into an arc shape at the open end of the cavity 2, and a lip 6 where the crossing angle of a lower surface 9 to a side wall 5 is equal to an inclination angle thetais provided. Moreover, a piston 1 is constructed by making the lip 6 and the side wall 5 continuous at a curved surface. Therefore, the connected portion of the side wall 5 and the lip 6 can be positioned outwards in a radial direction according to the size of the inclination angle theta of the side wall 5. As a result, the protruding length of the lip 6 is shortened, and all injecting fuel is supplied in the cavity 2 even under a low speed and a light duty. It is thus possible to prevent atomized fuel from adhering to the upper surface of the lip 6 in its liquid state.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to an engine piston having a cavity formed at the top of the piston to directly supply fuel spray.

[Prior Art] Normally, when pursuing high output from a turbocharged diesel engine, the supercharger pressure is set to the maximum at the maximum output point of the engine, that is, the point at which the fuel flow rate is maximum, and the maximum output point is Generally, the compression ratio is lowered so that the combustion pressure generated in the engine is less than the mechanical strength of the engine, and the lower the compression ratio, the lower the fuel consumption can be expected.

In an engine that is an-matched at the maximum output point in this way, the compression pressure, temperature, and combustion chamber (cavity) temperature tend to decrease in the low speed and light load range, that is, in the range where the supercharger pressure is low. Normally, the fuel injected from the nozzle collides with the side wall of the piston, rebounds, and burns completely in the flame, and the fuel that adheres to the side wall is also completely evaporated or carbonized by the flame.However, as mentioned above, in the case of a turbo In a low compression ratio engine matched for a supercharged engine, the fuel that collides with the side wall and is reflected may not be ignited, or the fuel adhering to the side wall may be delayed in evaporation.
It reaches the bottom of the combustion chamber, where the temperature is lower, where it liquefies, is exposed to flame, and floats in the cavity as unburned fuel, which is then exhausted during the exhaust stroke, producing blue-white smoke (HC) and a pungent exhaust odor.

For this reason, lower compression in diesel engines has not been adopted, even though it is possible to increase output by reducing friction and increasing the supercharging rate.

Therefore, in order to obtain a low compression ratio supercharged engine, it is necessary to control the state (evaporation, dispersion, distribution) of the fuel supplied to the cavity to be in a good state, and to cause accurate ignition and flame propagation.

Proposals based on this type of problem include the applicant's proposal “
Combustion chamber of direct injection diesel engine
02720).

The proposal involves recessing a cavity in the top surface of the piston, forming a lip protruding radially inward on the periphery of the opening that forms the entrance to the cavity, and making the side wall of the cavity perpendicular to the fuel spray line of the fuel injection nozzle. A conical protrusion that generates a toroidal stirring flow is formed at the center of the bottom of the cavity. By colliding the fuel at right angles with the side wall, a portion of the injected fuel is The remaining part of the fuel against the side wall adheres to the side wall in the form of a thin film and is dispersed while the particles of It is designed to trap the fuel inside the cavity.

In other words, the proposal promotes atomization of the fuel spray to generate the mixture necessary for ignition and flame propagation, while relying on the strength of the stirring flow to reduce the thin film of fuel and vapor present near the sidewalls. The flame is peeled off from the side wall and carried to the center of the cavity to propagate the flame and improve combustion.

[Problems to be Solved by the Invention] However, in order to apply the above-mentioned proposal to the above-mentioned low compression ratio high supercharged engine, it is necessary to solve the following problem.

■ It is necessary to improve the mechanical strength of the lip against the combustion pressure of a low compression ratio, high supercharged engine.

■ At the maximum output point of the engine, the engine speed is high, the amount of fuel injected is large, and the angular speed of the injection pump is large, so the dynamic injection timing is considerably retarded.

Therefore, if the optimum timing is set at the maximum output point, the dynamic injection timing will advance at low speeds, and fuel will be injected from quite early before top dead center to late after top dead center, and the top surface of the piston ( (upper surface of the lip), an excessive amount of H
C (blue-white smoke) is generated.

Therefore, an auto-timer or the like that automatically adjusts the injection timing is required as an additional device.

[Means for Solving the Problems] The present invention aims to solve the above problems, and the side wall of the cavity recessed in the top surface of the piston is inclined approximately at right angles to the fuel spray line from the cavity axis side. formed with corners,
The protruding end is framed in an arc shape on the opening edge of the cavity, and the intersecting angle between the lower surface and the side wall forms a lip having a range equivalent to the above-mentioned inclination angle, and the lip and the side wall are continuous with a curved surface to form an engine piston. This is what I did.

[Function] The side wall of the cavity is formed with an inclination angle approximately perpendicular to the fuel injection line from the cavity axis side, and the intersection angle between the lower surface and the side wall is within the same range as the inclination angle at the opening edge of the cavity. ,
In addition, by forming a lip that frames the protruding end in an arc shape, the connecting portion between the side wall and the lip can be positioned radially outward depending on the magnitude of the inclination angle of the side wall. As a result, the protruding length of the lip is shortened, and all of the injected fuel can be supplied into the cavity even at low speeds and light loads.

Therefore, at low speeds and light loads, the fuel spray does not adhere to the upper surface of the lip in a liquid state, and the amount of exhaust from the IC is greatly reduced. In addition, by shortening the protruding length of the lip and connecting the lip and the side wall with a curved surface, the bending moment due to pressure is reduced, and the degree of stress concentration is reduced, so the mechanical strength of the lip is significantly increased. .

In such a combustion chamber, the fuel jet supplied from the shaft center side collides with the side wall, part of the spray is reflected and diffused, and part of it adheres to the side wall as a fuel film and spreads. The degree of reflection and diffusion is uniquely determined by the angle of inclination of the corner and H wall with respect to the fuel injection line, but if this angle is set at a nearly right angle, reflection and diffusion will occur from the center of the fuel spray, and the degree of becomes almost uniform.

On the other hand, since the lower surface of the lip and the side wall are connected at an inclination angle in the same range as the inclination angle of the side wall, and these connecting parts are connected by a continuous curved surface, the lip is introduced into the cavity at the end of the compression stroke and is The rising squish flow is separated at the end of the curved surface and reversed again toward the bottom of the cavity. As a result, the fuel film adhering to the side wall is gradually peeled off from the side wall and vaporized, and together with the fuel that has been atomized and vaporized by the collision, it is caught in the squish flow and swirls in the vertical direction.

Therefore, the fuel spray and the mixed vaporized fuel are prevented from flowing out of the combustion chamber, and a mixture (premixture) with excellent ignitability and flame propagation performance is distributed under the lip. In other words, even at low speeds and light loads, it is possible to distribute a partially rich mixture, and even when the compression ratio is lowered, rapid ignition and relatively rapid flame propagation combustion are possible.
HC emissions can be greatly reduced.

[Embodiment] A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

As shown in FIGS. 1 and 2, a general piston 1 employed in a small direct injection diesel engine has a cavity 2 recessed in the axial direction on the top surface 20 of the piston. In this embodiment, the cavity 2 has a rectangular horizontal cross section, and the fuel injection nozzle 3 is disposed approximately on the axis of the cavity 2. The nozzle portion 4 of the fuel injection nozzle 3 has the same number of nozzles as the number of corners of the cavity 2 at equal intervals in the circumferential direction. It is configured to inject fuel spray diagonally downward.

Now, each side wall 5 of the cavity 2 is formed to form an inclination angle θ within a certain angle range with respect to the fuel spray line F from the nozzle. That is, each side wall 5 forms an inclined surface facing obliquely upward, and the inclination angle θ of this side wall surface is approximately perpendicular to the fuel spray line F from the fuel injection nozzle 3, specifically, from 90° to
The angle of inclination is in the range of 110°, and the interval in the depth direction of the inclined surface is equal to the vertical diffusion interval j of the fuel spray F.
It shall be equal to or greater than 2. The bottom surface 11 of the cavity 2 is formed by a conical protrusion 13 raised on the central axis 02 of the cavity 2 with respect to the horizontal plane.

However, the apex of the protrusion 13 is located near the middle position in the height direction of the cavity, so that a swirling flow in the toroidal direction is generated within the cavity 2.

On the other hand, a lip 6 is formed along the opening periphery forming the entrance 10 of the cavity 2 . The lip 6 is formed to protrude radially inward, and its protruding end 7 is
It is rounded with an arc centered radially outward of the lip 6, and the lower surface of the lip 6 and the side wall are connected such that their intersection angle is within the same range as the inclination angle. Further, the position of this connecting portion is set so that when the piston is at the top dead center position, the arrival point of the fuel spray is located midway in the vertical direction of the side wall. Furthermore, the side wall 5 and the lower lip surface 9
means that the squish flow V generated by the lip 6 at the end of the compression stroke is separated from the lip lower surface 9 side and is smoothly connected with an arc of curvature that can be reversed to the bottom surface side of the cavity 2, and the bottom surface and the protrusion 13 The connection part with the bottom of the is also connected smoothly with an arc. However, a straight line portion is formed between the curved surface connecting the lip lower surface 9 and the side wall 5 and the circular arc that roundly frames the lip tip 7.

By the way, the relationship between the radial distance D2 determined by the connecting portion between the side surface 5 and the bottom of the protrusion and the distance D1 between the radially opposing protruding ends of the lips is D,>D2, and , the relationship between the distance between the connecting portions between the lower surface of the lip 6 and the side wall that face each other in the radial direction, and the maximum depth H of the cavity is D3/H44. The corners 14, 15, 16.17 of the cavity 2 are formed by smoothly connecting the adjacent side walls 5 with curved surfaces 19, 20, and 21 degrees 22 in the circumferential direction, respectively. It is also formed with an inclined surface in the range of 90° to 110° with respect to the fuel spray line.

With the above configuration, the lower lip surface 9 is located below the lip lower surface 9 by the lower part of the side wall 5 and the protrusion 13.
swirling flow S of combustion air supplied into the cavity 2;
is the stirring flow S2 in the toroidal direction, and a space 24 (in the vertical direction) into which the squish flow V at the end of the compression stroke is introduced
(hereinafter referred to as a swirl part).

Next, the effect will be explained.

The side wall 5 of the cavity 2 recessed in the top surface of the piston is set at an angle of 90° to 11° with respect to the fuel spray line F from the cavity axis side.
00 range, and the intersection angle β between the lower surface 9 of the lip 6 and the side wall 5 is the angle θ of the opening of the cavity 2.
If a γ pro is formed in the same range as , and the protruding end 7 of the lip 6 is framed in an arc shape, the connection part between the side wall 5 and the lower lip surface 9 will be equal to the connection part between the side wall 5 and the protrusion 13. and the radial distance D2 determined by the bottom surface and the connection portion between the bottom of the protrusion 13.
If the distance D + stopper relationship between the protruding ends 7 of the lips 6 facing each other in the radial direction is D I > D t, then the piston 1
The fuel spray F, which starts to be injected in the vicinity of the dome point and ends in the vicinity after the top dead center, is supplied into the cavity 2 without being hindered during its flight. As a result, the fuel spray F does not adhere to the upper surface of the lip 6 even at low speeds and light loads.

On the other hand, if the lower lip surface 9 and the side wall 5 are connected by a continuous curved surface, the squish flow V that is introduced into the cavity 2 and rises along the side 9.5 at the end of the compression stroke is separated at the end of the curved surface and is again It will now be turned over to the bottom side of cavity 2. As a result, the fuel film adhering to the side wall 5 is gradually peeled off from the side wall 5 and vaporized, and together with the fuel that has been atomized and vaporized by the collision, is caught in the squish flow V and swirls in the vertical direction. Therefore, HC does not remain as a liquid on the bottom side, and the amount of HC discharged is reduced.

In this way, the fuel spray F and the mixed vaporized fuel are prevented from flowing out of the cavity 2, and a mixture (premixture) with excellent ignitability and flame propagation performance is distributed under the lip. Become. In other words, even at low speeds and light loads, it is possible to distribute a partially rich air-fuel mixture, allowing quick ignition and relatively rapid flame propagation combustion, as shown in Figure 3. 200 HC at a fuel flow rate (Q) of
It becomes possible to reduce the amount by more than ppm.

By the way, if the cavity 2 is formed to have a pentagonal horizontal cross section and configured to supply fuel spray to each corner, HC can be further reduced.

In other words, the strength of the swirling flow introduced as the swirling flow SL is attenuated at the top surface of the piston as the number of corners increases, thereby relatively increasing the penetration force of the fuel spray F, and increasing the rate of fuel reaching each corner. On the other hand, the spray flying distance J+ of the fuel spray F is set so that the distance between the lip tips 7 is the same, and the side wall 5 which is the side of the cavity 2 is set at a substantially right angle to the circumferential direction as in the conventional example. Compared to the case of square cavity 2 configured to supply ``1=0.323
The mixing time for air is increased by increasing D to j = 0.353 D, and a diffused mixture necessary for flame propagation is generated around the protrusion 13. Also, this is inversely proportional to the increase in the amount of diffused mixture produced, and the side l11
It also functions to reduce the amount of fuel reaching 5. ,
As a result, the injection timing is substantially retarded at low speeds and light loads, and the same result as when the actual compression ratio of the piston 1 is increased can be obtained.
Excessive cooling of the side wall 5 is prevented by reducing the thickness of the fuel film.

In other words, the evaporation capacity of the wall surface is maintained above a certain level even at low speeds and light loads.

Therefore, inside each corner, the inside of the swirl turning section 24 can be used as a zone that partially generates a rich mixture. A diffused mixture of suitable concentration will now exist. In other words, the combustion conditions (air-fuel mixture concentration, cavity internal atmosphere temperature, etc.) within the cavity 2 during low-speed, light-load operation are improved, and the amount of HC discharged is reduced.

Once ignition begins, the flame propagates circumferentially and burns relatively quickly. That is, the combustion temperature increases, a constant engine output is ensured, and the amount of HC emissions decreases.

Next, the square cavity 2 and the pentagonal cavity were tested as shown in FIGS. 4 to 7 regarding the amount of HC discharged when the piston 1 equipped with the cavity 2 described above is adopted for use in a low compression ratio supercharged engine. Compare based on data.

Figure 4 shows that the performance of the pentagonal cavity is superior to the rectangular cavity 2 even when the rotational speed changes, and that the performance of the pentagonal cavity is superior to the rectangular cavity 2 regardless of the rotational speed. It shows that the performance is excellent,
FIG. 5 shows that when the rotational speed and compression ratio are fixed and the injection timing is varied, the amount of HC discharged decreases when the injection timing is set to about 18 degrees before top dead center.

On the other hand, in FIGS. 6 and 7, the rotation speed is 11,000 RP.

The relationship between the amount of HC discharged and the compression ratio ε at 2200 RPM was investigated. As a result, it was confirmed that the amount of HC discharged was reduced by lowering the compression ratio ε for each rotation speed.

As is clear from the above results, the pentagonal cavity configured as described above is suitable for low compression ratio engines.
The compression ratio ε is approximately 15.4, and the fuel injection timing is approximately 18° (B
TDC), steady ignition and flame propagation combustion are guaranteed.

Therefore, there is no need to adjust the injection timing using an automatic timer in a low compression ratio engine, and even during low speed and low load operation, blue white smoke (HC) and irritating odor can be reduced, and fuel efficiency can be improved.

As is clear from the above test data, when forming the square cavity 2, expanding the square diagonally and supplying fuel spray to each corner 14 to 17 improves combustion performance ( HC, etc.) can be improved.

[Effects of the Invention] As is clear from the above explanation, the strength of the lip is greatly improved, and the fuel spray is prevented from adhering to the top surface of the piston before and after top dead center and from remaining as liquid at the bottom of the cavity. By preventing this, the amount of HC discharged can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a preferred embodiment of the present invention, FIG. 2 is a view taken along the If-n line in FIG. 1, FIG. 3 is a performance diagram showing HC performance, and FIGS. The figure is a performance diagram showing the HC performance of quadrilateral and pentagonal shapes. In the figure, 1 is a piston, 2 is a cavity, 5 is a side wall, 6 is a lip, and 14 to 18 are corners. Patent applicant Isuzu Motors Co., Ltd.

Claims (1)

[Claims] 1. The side wall of the cavity recessed in the top surface of the piston is formed at an angle of inclination approximately perpendicular to the fuel spray line from the cavity axis side, and the protruding end is framed in an arc shape at the opening edge of the cavity to form a lower surface. An engine piston formed by forming a lip whose intersecting angle with the side wall is within the same range as the inclination angle, and the lip and the side wall are continuous on a curved surface.