JP2020153239A - Combustion chamber - Google Patents

Abstract

To provide a combustion chamber capable of suppressing generation of smoke.SOLUTION: In a combustion chamber 10 recessedly formed on a center portion of a top surface 12 of a piston 11 which reciprocates inside a cylinder, a plurality of wall surfaces 20 facing a C2 direction opposite from a C1 direction which is a flow direction of a swirl flow are arranged in an annular portion 19 at an outer edge of a bottom 16 at intervals in the C1 direction, and a heat insulation film 25 is provided to cover the wall surface 20.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a combustion chamber, and more particularly to a combustion chamber that suppresses the generation of smoke.

In the combustion chamber of an engine, a plurality of grooves extending in the vertical direction are formed on the surface of a protrusion arranged in the center and projecting upward, and the passage paths of fuel flowing along the wall surface of the combustion chamber are adjacent to each other. Those located between the grooves have been proposed (see, for example, Patent Document 1). In this device, the sprayed fuel flows between the grooves after colliding with the wall surface, so that it does not flow into the grooves and does not stay there. Therefore, the exhaust emission is improved by promoting the agitation and mixing of the air-fuel mixture.

Japanese Unexamined Patent Publication No. 11-013472

By the way, in the operating region where a large amount of fuel is sprayed, it is necessary to spray a required amount of fuel according to the load within a certain period in order to avoid deterioration of fuel efficiency. Therefore, when a fuel spraying device having a small injection hole area is used, it is necessary to secure a total injection hole area capable of spraying the required amount of fuel within a certain period when the load is high. Therefore, it has been essential to increase the number of injection holes in the fuel spraying device.

However, when the number of injection holes in the fuel spraying device is increased, the distance between adjacent injection holes becomes narrower in the device described in Patent Document 1 described above. Therefore, even if a groove is provided, after the fuel sprayed from each injection hole of the fuel spray device collides with the wall surface of the combustion chamber, the fuel is flowed in the flow direction of the swirl flow by the swirl flow and the adjacent sprays interfere with each other. There was a problem of doing. The formation of a fuel-rich region in the combustion chamber due to the interference between the sprays is a factor in increasing the amount of smoke produced.

An object of the present disclosure is to provide a combustion chamber that suppresses the formation of smoke.

The combustion chamber of one aspect of the present invention that achieves the above object is a combustion chamber formed by recessing the central portion of the top surface of a piston that reciprocates inside the cylinder, in a direction opposite to the flow direction of the swirl flow. A plurality of facing wall surfaces are arranged at an annular portion on the outer edge of the bottom of the recess at intervals in the flow direction, and a heat shield film covering the wall surface is provided.

According to one aspect of the present invention, it is possible to suppress the interference between adjacent sprays by preventing the fuel sprayed by the influence of the swirl flow from flowing in the flow direction of the swirl flow by the wall surface. Further, by covering the wall surface with a heat shield film, it is possible to prevent deterioration of heat loss due to an increase in the surface area due to the provision of the wall surface. Due to the above two effects, it is possible to suppress the generation of smoke while suppressing the decrease in thermal efficiency.

It is a perspective view which illustrates the 1st Embodiment of a combustion chamber. It is an enlarged plan view of a part of FIG. It is sectional drawing which illustrates the cross section shown by the arrow III of FIG. It is sectional drawing which illustrates the cross section shown by the arrow IV of FIG. It is a top view which illustrates the 2nd Embodiment of a combustion chamber. It is sectional drawing which illustrates the cross section shown by the arrow VI of FIG. It is a top view which illustrates the 3rd Embodiment of a combustion chamber. It is sectional drawing which illustrates the cross section shown by the arrow VIII of FIG.

Hereinafter, embodiments of the combustion chamber in the present disclosure will be described. In the present disclosure, it is assumed that the cylinder (not shown) in which the piston 11 reciprocates has its central axis oriented in the vertical direction in FIG. Therefore, in the figure, the C direction is the circumferential direction around the central axis of the cylinder, the C1 direction is the swirl flow direction (counterclockwise direction) of the C direction, and the C2 direction is the direction opposite to the C1 direction. (Rightward direction), and the D direction is the radial direction of the cylinder. Further, the X direction is one of the D directions, the Z direction is the axial direction of the central axis of the cylinder, the Y direction is a direction orthogonal to each of the X direction and the Z direction, and the Z direction is not limited to the vertical direction. Shall be. Further, in the present disclosure, "corner" shall indicate a shape formed by two intersecting planes or two straight lines, and shall not be used in the sense of indicating a place. Further, in the figure, the shape having "corners" is shown by a solid line, and the shape without "corners" is shown by a dotted line.

As illustrated in FIG. 1, the combustion chamber 10 is configured such that the central portion of the top surface 12 of the piston 11 that reciprocates in the Z direction inside a cylinder (not shown) is recessed downward. The combustion chamber 10 indicates a space surrounded by this recess formed on the top surface 12, an inner wall surface of a cylinder (not shown), a fuel spray device 13, and a cylinder head in which an intake / exhaust valve is installed. The combustion chamber 10 shall indicate this depression.

The combustion chamber 10 is composed of a distribution type combustion chamber in which a tubular portion 14, a lip portion 15, and a bottom portion 16 are arranged in order from above to below. In the present disclosure, the distribution type combustion chamber means a combustion chamber having a function of colliding the fuel sprayed from the fuel spraying device 13 with the lip portion 15 and distributing the fuel in two directions up and down. The combustion chamber 10 is not limited to such a distribution type combustion chamber, and the fuel sprayed from the fuel spraying device 13 may collide with the lip portion 15 and be guided at least downward. As the combustion chamber 10, a combustion chamber 10 having no tubular portion 14 above the lip portion 15 is also exemplified.
Examples of the shape of the depression of the combustion chamber 10 include a bowl shape, a hemispherical shape, and a multispherical shape, and examples thereof include a circular shape and a multicircular shape as the cross-sectional shape (cross-sectional shape of the XY plane).

The cylinder portion 14 is composed of an inner cylinder surface of a cylinder having both ends open in the Z direction. The cylinder portion 14 may be formed of an inner cylinder surface, and the diameter of the inner cylinder surface may be increased from the upper side to the lower side or may be reduced from the upper side to the lower side. Further, the tubular portion 14 may be a stepped tubular surface whose inner tubular surface gradually changes from the upper side to the lower side.

The lip portion 15 is an annular portion located between the tubular portion 14 and the bottom portion 16 and projecting toward the center of the inner surface of the tubular portion 14 when viewed in the Z direction. The lip portion 15 may have rounded corners protruding toward the center when viewed in the Z direction. The lip portion 15 has a collision portion 17 in which the fuel sprayed from the fuel spraying device 13 collides, and a part of the fuel colliding with the collision portion 17 is upward in the Z direction, and the other fuel is Z. It functions to divide each downward in the direction. A plurality of lip portions 15 may be provided in one combustion chamber 10, and a plurality of lip portions 15 may be provided in a multi-stage shape in the Z direction.

The collision portion 17 is a portion where the fuel sprayed from the fuel spraying device 13 collides, and a plurality of collision portions 17 are arranged at intervals in the C direction of the lip portion 15. The arrangement position and the exclusive area of the collision portion 17 in the lip portion 15 are appropriately set for each fuel spraying device 13. The collision site 17 is a region where the fuel collides, and is a region surrounded by a dotted line in the figure.

The bottom portion 16 is located at the bottom of the combustion chamber 10 which is a depression, and has a bottomed tubular shape in which the upper end in the Z direction opens while the lower end closes, and the opening diameter gradually narrows from the upper side to the lower side. Form a shape. The bottom portion 16 has a bulge 18 that bulges upward toward the center, and an annular portion 19 that forms an annular shape when viewed in the Z direction on the veranda side of the bulge 18.

The bulge 18 is formed by bulging like a bowl upward from the bottom of the bottom portion 16. It is desirable that the highest position of the bulge 18 is lower than the position of the upper end of the lip portion 15. The annular portion 19 is a portion located at the outer edge portion of the bottom portion 16, and more specifically, a portion between the skirt of the bulge 18 and the lip portion 15. The surface of the annular portion 19 is recessed in an annular shape. As the annular body referred to here, a torus body (annular body) is exemplified. The annular portion 19 may be an annular portion located at the outer edge portion of the bottom portion 16, and the surface thereof is not limited to a concave portion in an annular shape.

The type of the combustion chamber 10 may be a distribution type combustion chamber in which the fuel sprayed from the fuel spraying device 13 is vertically distributed, and is not limited to the above configuration. For example, as the type of the combustion chamber 10, a pent roof type or a wedge type is exemplified according to the shape of the cylinder head. Further, as the type of the combustion chamber 10, a deep dish type (toroidal type, reentrant type, bathtub type) and a shallow dish type are exemplified according to the shape of the recess.

The combustion chamber 10 includes a plurality of wall surfaces 20. Further, the combustion chamber 10 is composed of convex portions between the recesses 21 having the wall surfaces 20 adjacent to each other in the C direction. In addition, the combustion chamber 10 includes a heat shield film 25 that covers the entire annular portion 19.

As illustrated in FIGS. 2 and 3, the wall surface 20 faces the C2 direction and forms a crescent shape when viewed in the C1 direction. In the present disclosure, facing in the C2 direction means facing so as to resist the flow of fuel in the C1 direction, and the wall surface 20 may be a surface facing in the C2 direction. As such a plane, for example, in addition to the XZ plane orthogonal to the C2 direction, a slope intersecting the C2 direction is also exemplified. Further, the shape of the wall surface 20 seen in the C1 direction is not particularly limited as long as it becomes a resistance to the flow of fuel in the C1 direction, and for example, a rectangular shape is also exemplified.

The plurality of wall surfaces 20 are arranged on the annular portion 19 of the bottom portion 16 at intervals in the C1 direction. The plurality of wall surfaces 20 are arranged in a number corresponding to the number of collision portions 17 arranged in the lip portion 15. The arrangement interval of the plurality of wall surfaces 20 corresponds to the arrangement interval of the collision portion 17 in the lip portion 15. For example, the arrangement intervals of the plurality of wall surfaces 20 are arranged at equal intervals in the C1 direction when the arrangement intervals of the collision portions 17 are equal. Further, the arrangement interval of the plurality of wall surfaces 20 is arranged so that the arrangement interval of the collision portion 17 gradually increases in the C1 direction when the arrangement interval of the collision portion 17 gradually increases in the C1 direction.

The wall surface 20 is provided along the line segment L1 from the downstream end 22 toward the center of the bottom 16 in the C1 direction at the collision site 17. As the line segment L1 referred to here, a line segment tangent to the end portion 22 of the line segments extending in the radial direction D from the center of the bottom portion 16 is exemplified. Further, the fact that the wall surface 20 is provided along the line segment L1 means that the wall surface 20 is erected above the bottom portion 16 on the line segment L1 or the bottom portion 16 of the line segment L1 displaced laterally in the C1 direction. It shall be shown that it extends in the D direction along the line segment L1. The wall surface 20 is erected on the line segment L1 or on the side of the line segment L1 in the C1 direction except for the side of the line segment L1 in the C2 direction, so that the fuel collides with the collision portion 17 and is distributed downward. It is advantageous to avoid obstructing the flow of.

The wall surface 20 may be formed by projecting the bottom portion 16 upward, but it is desirable that the wall surface 20 is formed by recessing the bottom portion 16 downward, and is composed of convex portions between the recesses 21 adjacent to each other in the C direction. Is more desirable.

The recesses 21 are arranged at intervals in the C direction of the annular portion 19 of the bottom portion 16 and are formed to be recessed downward from the bottom portion 16. Further, one recess 21 is provided for one wall surface 20, and is a portion existing in the C2 direction with respect to the wall surface 20.

The shape of the recess 21 is not particularly limited as long as it can form the wall surface 20. In this embodiment, the opening shape of the recess 21 seen in the Z direction is rectangular. Further, the depth of the recess 21 is configured so that the depth becomes shallower from the central portion of the recess 21 toward the outer edge in the D direction, and is configured to be a constant depth in the C direction.

By denting the bottom portion 16 by the dent 21 to form the wall surface 20, the total volume of the combustion chamber 10 can be increased by the dented amount. As described above, providing more space in the combustion chamber 10 is advantageous for improving the mixing with air, and the combustion period can be shortened.

However, if the depth of the recess 21 in the Z direction is increased or the opening area is increased, the total surface area of the combustion chamber 10 increases, and the heat loss due to the increase in the total surface area increases. Therefore, it is preferable that the depth and opening area of the recess 21 are set so that the heat loss reduced by shortening the combustion period obtained by increasing the total volume is larger than the heat loss increased by providing the recess 21. ..

The recess 21 has a wall surface 20 as an inner surface existing in the C1 direction, and a facing surface 23 facing the wall surface 20 in the C direction as an inner surface existing in the C2 direction. The shape of the facing surface 23 is not particularly limited, and may be formed in a shape symmetrical with respect to the wall surface 20 or may be formed in a shape different from that of the wall surface 20. When the facing surface 23 is provided facing the wall surface 20, the end portion on the downstream side with respect to the C2 direction at the collision portion 17 (with respect to the C1 direction) so as not to interfere with the progress of the spray of the fuel divided by colliding with the collision portion 17. It is preferably provided along the line segment L2 from the upstream end) 24 toward the center of the bottom 16.

The heat shield film 25 is composed of a member having a lower thermal conductivity than the member constituting the piston 11. Examples of the heat shield film 25 include oxide films and ceramics of the members constituting the piston 11, and more specifically, alumite, zirconia, and the like.

The heat shield film 25 is configured to cover at least the wall surface 20 of the annular portion 19. By covering the wall surface 20 with the heat shield film 25 in this way, it is advantageous to prevent deterioration of heat loss due to an increase in the surface area of the combustion chamber 10 due to the provision of the wall surface 20.

Further, the heat shield film 25 is configured to cover at least the surface of the wall surface 20 of the annular portion 19 and the recess 21 which is a portion existing in the C2 direction with respect to the wall surface 20 of the annular portion 19. By covering the surface of the recess 21 in addition to the wall surface 20 in this way, the heat caused by the retention of fuel generated in the recess 21 which is a portion existing in the C2 direction with respect to the wall surface 20 due to the provision of the wall surface 20. It is advantageous to prevent the loss from getting worse.

Further, the heat shield film 25 is configured to cover the entire surface of the annular portion 19 including all the wall surfaces 20 and the recess 21 when a plurality of wall surfaces 20 are arranged over the entire circumference of the annular portion 19. Is desirable. In this way, by covering the entire surface of the annular portion 19 with the heat shield film 25, it is advantageous to prevent deterioration of heat loss in the entire annular portion 19.

The heat shield film 25 may cover at least the wall surface 20, and may cover any or all of the tubular portion 14, the lip portion 15, and the bottom portion 16 of the combustion chamber 10. However, since the manufacturing cost increases by covering the entire combustion chamber 10 with the heat shield film 25, it is desirable to limit the portion covered with the heat shield film 25. Further, the heat shield film 25 that covers the wall surface 20, the recess 21, or the annular portion 19 including them, and the heat shield film that covers the rest may be made of different members.

As illustrated in FIG. 4, the annular portion 19 is cut by a line segment extending over the entire circumference of the annular portion 19 in the C direction and crossing all the wall surfaces 20 and the recess 21 arranged in the annular portion 19. It is preferable that the surface shape of the annular portion 19 appearing on the cut surface is wavy.

In the present disclosure, examples of the wave shape include a square wave, a sine wave, a triangular wave, and a sawtooth wave. The surface shape of the annular portion 19 appearing on the cut surface in this embodiment forms a square wave. The period of the square wave is based on the arrangement interval of the collision sites 17 in the lip portion 15, and the amplitude is based on the depth of the recess 21 in the Y direction.

When the fuel is sprayed from the fuel spraying device 13, the sprayed fuel collides with the collision portion 17 of the lip portion 15 and is divided in the vertical direction. The fuel divided downward tries to flow in the C1 direction due to the influence of the swirl flow, but the wall surface 20 becomes a resistance to the flow. As a result, the flow velocity of the swirl flow of the fuel divided downward is reduced, and the flow is suppressed.

As described above, according to the combustion chamber 10 of the present disclosure, by providing the wall surface 20 on the bottom 16 of the combustion chamber 10, the wall surface 20 acts as a resistance and the downward flow of fuel in the C1 direction can be suppressed. .. This is advantageous for suppressing interference between fuels adjacent to each other in the C direction, and it is possible to suppress the amount of smoke generated due to the fuel enrichment region.

Further, according to the combustion chamber 10 of the present disclosure, the fuel divided downward can improve (promote) mixing with air due to the space expanded by the recess 21 as compared with the fuel without the recess 21. it can. This is advantageous for improving the combustion state and shortening the combustion period, and by shortening the combustion period, heat loss can be reduced and the amount of smoke produced can be suppressed.

In addition, according to the combustion chamber 10 of the present disclosure, the heat shield film 25 covers the entire area of the annular portion 19 to prevent deterioration of heat loss due to an increase in the surface area due to the provision of the wall surface 20. At the same time, it is possible to prevent deterioration of heat loss due to the fuel staying in the recess 21 due to the wall surface 20.

As described above, by combining the effect of providing the wall surface 20 and the effect of providing the heat shield film 25, it is possible to suppress the generation of smoke while suppressing the decrease in thermal efficiency.

As illustrated in FIGS. 5 and 6, the combustion chamber 10 of the second embodiment is different from the first embodiment in that the recess 21 has a shape without corners. In the present disclosure, the shape without corners is a shape in which all the elements constituting the recess 21 do not have corners. Specifically, as the cross-sectional shape of the dent 21 including the opening shape of the dent 21 seen in the Z direction, a circular shape, an elliptical shape, and an oval shape are exemplified.

The depth of the recess 21 is configured to gradually become shallower from the central portion of the recess 21 toward the outer edge. Specifically, as an arbitrary vertical cross-sectional shape of the recess 21, a shape drawn by one spline curve or one Bezier curve is exemplified.

When viewed in the Z direction, the recess 21 has an elliptical shape or an oval-shaped outer edge whose longitudinal direction faces the C direction and has a curved shape along the C direction. The surface shape of the annular portion 19 that appears on the cut surface when cut along the cutting line preferably forms a sine soid. The period of the sine soid of this embodiment is based on the placement interval of the collision sites 17 on the lip portion 15, and its amplitude is based on the depth of the recess 21 in the Y direction. The change in the amplitude of the sine wave when the cutting position is changed in the X direction is based on the depth of the recess 21 in the X direction.

In this way, the shape of the recess 21 can be adjusted by changing the period and amplitude of the waveform using the sine wave. As a result, even a complicated shape having a plurality of recesses 21 can be easily manufactured.

As described above, since the recess 21 has a shape without corners, the surface area of the recess 21 can be reduced as compared with the shape with corners. This is advantageous in suppressing an increase in heat loss due to an increase in the surface area that is increased by providing the recess 21.

Further, if the recess 21 has a corner shape, the thermal stress may be concentrated on the corner during combustion, but if the recess 21 has no corner shape, the thermal stress can be prevented from being concentrated on a specific portion during combustion. This is advantageous for improving durability by avoiding damage due to concentration of thermal stress as compared with the angular shape.

As illustrated in FIGS. 7 and 8, in the combustion chamber 10 of the third embodiment, the surface of the heat shield film 25 is a portion other than that of the first embodiment (for example, the tubular portion 14 and the lip portion). The point that is rougher than the surface of 15) is different.

In the present disclosure, the surface roughness is coarser when the surface area is larger and smoother when the surface area is smaller than the surface area per unit area. Further, as the surface roughness, the surface roughness and the surface waviness obtained by the line roughness parameter defined by the Japanese Industrial Standards JIS B 0601 are also exemplified.

In the combustion chamber 10, the surface of the heat shield film 25 may be rougher than the surface of a portion other than the bottom 16. In the combustion chamber 10, when the heat shield film 25 covers the entire peripheral surface of the annular portion 19, it is more desirable that the entire surface of the heat shield film 25 is rougher than the surface of the portion other than the floor portion 16.

In the combustion chamber 10, as a method of making the surface roughness of the heat shield film 25 different, after forming the heat shield film 25 at a predetermined position, the surface finish is roughened by surface finishing such as blasting, while the surface finish is roughened. An example is a method of smoothing the surface finish of the tubular portion 14 and the lip portion 15. Further, a method of applying blasting to roughen the surface of the heat shield film 25 by blasting is also exemplified. Further, a method of forming fine dimples on the heat shield film 25 by shot peening is also exemplified. Further, if the surface of the formed heat shield film 25 is rough without using blasting or shot peening, those methods may not be used.

As described above, by making the surface of the heat shield film 25 rougher than the surface of the portion other than the bottom 16, it is advantageous to reduce the flow velocity of the swirl flow of the fuel, and interference between the fuels adjacent to each other in the C direction. The effect of suppressing is increased.

10 Combustion chamber 11 Piston 12 Top surface 16 Bottom surface 19 Circular part 20 Wall surface 25 Heat shield film C1 Swirl flow direction C2 Swirl flow direction opposite to the flow direction

Claims (4)

In a combustion chamber formed by a depression in the center of the top surface of a piston that reciprocates inside the cylinder, the wall surface facing in the direction opposite to the flow direction of the swirl flow is the bottom of the depression at intervals in the flow direction. A combustion chamber characterized by being arranged in a plurality of annular portions on the outer edge of the combustion chamber and provided with a heat shield film covering the wall surface. The combustion chamber according to claim 1, wherein the heat-shielding film covers the surfaces of both the wall surface and the portion of the annular portion that exists in the direction opposite to the wall surface. The combustion chamber according to claim 1, wherein the heat shield film covers the entire surface of the annular portion. The combustion chamber according to any one of claims 1 to 3, wherein the surface of the heat shield film is coarser than the surface of the portion not covered by the heat shield film.

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