JP2008151089A - Combustion chamber of diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce an amount of smoke while improving combustion efficiency of fuel by controlling a flow volume and flowing direction of the fuel inside a cylinder with a simple structure, with respect to a combustion chamber of a diesel engine. <P>SOLUTION: The combustion chamber includes a protrusion 3a formed in a protruding manner from an inner wall surface 3 of a cavity 2 to an inside of the cavity 2 so that a dispersing direction of fuel subjected to injection from a fuel injection nozzle 5 is branched to an upper and lower directions of the cavity 2, a first surface 3b which couples the protrusion 3a and a top surface 1a of a piston 1 together to introduce fuel flowing toward the upper direction to an outer circumferential direction of the piston 1, and a second surface 3c which couples the protrusion 3a and a bottom surface 2a of the cavity 2 to introduce fuel flowing toward the lower direction to an inner direction of the cavity 2. The first surface 3b is formed in such a shape that in a cross-sectional surface passing through a central axis of the piston 1, the nearer to a side of the protrusion 3a, the shorter the distance to the central axis and the nearer to a side of the top surface 1a, the longer the distance to the central axis. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a combustion chamber of a direct injection type diesel engine.

  Conventionally, in a combustion chamber of a direct injection type diesel engine, a cavity is formed on the top surface of a piston, and fuel is directly injected into the cavity from a fuel injection nozzle arranged in a cylinder head. That is, when the piston reaches the vicinity of the top dead center in the compression stroke, the fuel is injected from the fuel injection nozzle, the fuel collides with the inner wall surface of the cavity, is diffused throughout the cavity, and the fuel is burned. In a diesel engine equipped with such a combustion chamber, a technique has been developed in which fuel and air are uniformly mixed by controlling the flow of air inside the cavity to improve fuel consumption and reduce smoke.

For example, Patent Document 1 discloses a configuration in which a hollow is provided on a cavity wall surface in a diesel engine having a reentrant type cavity. That is, convection is generated inside the cavity by flowing the fuel along the surface shape of the recess, and mixing of the fuel and air is promoted by promoting the flow of air at the bottom of the cavity. Thereby, it is said that rapid combustion in a fuel rich state can be suppressed and black smoke (smoke) can be reduced.
JP 2001-82150 A

  By the way, in the combustion chamber of a general diesel engine, the combustibility is improved by improving the diffusibility of the fuel in the cavity. In other words, fuel diffusion to the outer peripheral side of the cylinder called a squish area is suppressed, and fuel is burned mainly on the inner peripheral side of the cylinder. For example, in the technique described in Patent Document 1, an outflow of fuel to the outside of the cavity is prevented by providing an annular protrusion at the opening of the cavity.

On the other hand, from the viewpoint of the combustion efficiency of the fuel, it is considered that if oxygen contained in the air in the squish area is used, the oxidation reaction can be further promoted and sufficient combustion can be expected. That is, it is presumed that by burning the fuel not only in the cavity but also in the squish area, the combustion efficiency in the entire cylinder area is enhanced and the generation of smoke can be suppressed.
However, if the amount of fuel flowing out of the cavity into the squish area is too large, combustion in the squish area becomes excessive and the temperature of the cylinder liner may be excessively increased. In addition, even in a configuration in which an appropriate amount of fuel is directly injected into the squish area for the purpose of accurately controlling the amount of fuel related to combustion in the squish area, the fuel easily adheres to the surface of the cylinder liner, and the engine oil of the fuel Ingredients may cause problems such as reduced wear resistance and seizure.

As described above, in the combustion chamber of the conventional diesel engine, it is difficult to control the amount of fuel diffused toward the squish area among the fuel injected toward the inside of the cavity.
The present invention has been made in view of such problems, and can control the flow rate and flow direction of fuel in a cylinder with a simple configuration to improve the combustion efficiency of the fuel and reduce smoke. An object of the present invention is to provide a combustion chamber for a diesel engine.

  In order to achieve the above object, the combustion chamber of the diesel engine of the present invention according to claim 1 has a cavity formed in the top surface of the piston so as to be recessed into the inside of the piston from the top surface. A combustion chamber of a direct injection type diesel engine having a fuel injection nozzle for injecting fuel toward an inner wall surface of the cavity in an opposing cylinder head, and to the inner wall surface of the fuel injected from the fuel injection nozzle A projecting portion projecting from the inner wall surface of the cavity toward the inside of the cavity so as to branch the fuel dispersion direction into an upper direction and a lower direction of the cavity at a collision position of Is connected to the top surface to form an upper side surface of the inner wall surface, and the fuel flowing from the protrusion to the upper direction is guided along the top surface toward the outer periphery of the piston. A surface portion, the projection portion and the bottom surface of the cavity are connected to form a lower side surface of the inner wall surface, and fuel flowing from the projection portion toward the lower direction is directed toward the inside of the cavity along the bottom surface of the cavity. And a second surface portion that guides, and in the longitudinal section passing through the central axis of the piston, the first surface portion has a shorter distance from the central axis toward the projection side and a distance from the central axis toward the top surface side. Is formed in a long shape.

Further, the combustion chamber of the diesel engine according to the second aspect of the present invention is characterized in that the projection is formed in an annular shape over the entire circumference of the inner wall surface.
The combustion chamber of the diesel engine of the present invention according to claim 3 is characterized in that the projection is formed in a triangular shape in a longitudinal section passing through the central axis of the piston.

  According to the combustion chamber of the diesel engine of the present invention (Claim 1), the fuel can be dispersed in the two directions of the upper direction and the lower direction with respect to the protrusion, and the fuel can be diffused throughout the combustion chamber. That is, air and fuel can be mixed evenly not only in the cavity but also in the squish area, combustion efficiency can be improved, and the generation of smoke can be suppressed.

Further, according to the combustion chamber of the diesel engine of the present invention (Claim 2), the processing of the protrusion is facilitated. Further, the shape of the inner wall surface of the cavity can be made the same regardless of the fuel injection direction.
Further, according to the combustion chamber of the diesel engine of the present invention (Claim 3), it is possible to accurately set the ratio of the fuel branched in the upper direction and the lower direction with the tip of the triangular projection as a boundary. It becomes. That is, it is possible to set a ratio between the amount of fuel related to combustion inside the cavity and the amount of fuel related to combustion in the squish area.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 3 illustrate a combustion chamber of a diesel engine according to an embodiment of the present invention. FIG. 1 is a longitudinal sectional view showing the entire configuration of the combustion chamber. FIG. 2 is a diagram of fuel in the combustion chamber. Partial sectional views (part A of FIG. 1) for explaining the dispersion direction and the flow direction, and FIGS. 3A to 3E are contour diagrams showing fluctuations in oxygen concentration during the combustion process in the combustion chamber. FIGS. 4A to 4E are contour diagrams showing fluctuations in oxygen concentration during the combustion process in the combustion chamber of a diesel engine as a comparative example for the present invention.

[Basic configuration]
As shown in FIG. 1, the diesel engine is a direct injection type diesel engine, and a combustion chamber 10 of the engine is formed as an in-cylinder space surrounded by a piston 1, a cylinder head 4 and a cylinder liner 7. The cylinder liner 7 is formed as a substantially cylindrical hole, and its upper end and lower end are closed by the cylinder head 4 and the piston 1, respectively.

  The piston 1 has a substantially cylindrical outer shape, and is fitted along the inner peripheral surface of the cylinder liner 7 so as to be slidable in the vertical direction in FIG. The lower portion of the piston 1 is connected to a crankshaft (not shown). Thereby, the reciprocating linear motion of the piston 1 is converted into the rotational motion of the crankshaft, so that power is transmitted. Further, a cavity 2 having a shape recessed into the piston 1 is formed on the top surface 1 a of the piston 1. Note that the cavity 2 is substantially circular when the piston 1 is viewed from above.

A fuel injection nozzle 5 for directly injecting fuel into the cylinder is provided above the cavity 2. As shown in FIG. 1, the fuel injection nozzle 5 is fixed in a state where its tip protrudes from the central portion of the cylinder head 4 facing the top surface 1 a of the piston 1. The fuel is injected from the fuel injection nozzle 5 toward the inner wall surface 3 of the cavity 2.
Note that a gap space between the top surface 1a of the piston 1 other than the cavity 2 and the cylinder head 4 in a state where the piston 1 is located near the top dead center is referred to as a squish area 6. In a state where the piston 1 is approaching the top dead center (ascending in FIG. 1), the air in the vicinity of the squish area 6 is pushed up to generate an air flow that tends to escape from the squish area 6 side to the cavity 2 side. Generally, such airflow is called squish flow. On the other hand, in a state where the piston 1 is away from the top dead center (downward in FIG. 1), air flows from the cavity 2 side to the squish area 6 side due to the suction effect accompanying the volume expansion of the squish area 6. This is called reverse squish flow.

[Internal shape of cavity]
As shown in FIGS. 1 and 2, the cross-sectional shape of the cavity 2 is a so-called open shape in which the diameter of the inlet portion is formed larger than the internal maximum diameter. That is, the inner wall surface 3 is inclined toward the outside of the cavity 2 in the vicinity of the opening of the cavity 2. Further, the bottom surface 2a of the cavity 2 is formed such that the central portion thereof is raised upward.

The inner wall surface 3 includes a protrusion 3a, a first surface 3b, and a second surface 3c. The shape of the inner wall surface 3 described in detail below is a shape in a longitudinal section passing through the central axis of the piston 1 unless otherwise specified.
The protruding portion 3 a is a portion formed so as to protrude toward the inside of the cavity 2 at a position where the fuel injected from the fuel injection nozzle 5 collides with the inner wall surface 3. The protrusion 3 a is formed in a substantially triangular shape, and one apex protrudes from the inner wall surface 3 toward the fuel injection nozzle 5. The protrusion 3 a is formed in an annular shape over the entire circumference of the inner wall surface 3.

The 1st surface part 3b is a surface which makes the upper side surface in the inner wall face 3 of the cavity 2, and has connected the upper part side and the top surface 1a of the projection part 3a with the smooth curve. The first surface portion 3b is formed in a shape such that the distance to the central axis is shorter toward the protrusion 3a and the distance from the central axis is longer toward the top surface 1a. That is, the shape of the first surface portion 3b forms the aforementioned open shape.
On the other hand, the 2nd surface part 3c is a surface which makes the lower side surface in the inner wall surface 3, and has connected the lower part side and the bottom face 2a of the projection part 3a with the smooth curve. As shown in FIG. 2, the 2nd surface part 3c is expanded to the radial direction outer side of piston 1 in the lower part side from the projection part 3a, and forms the hollow.

  In other words, the inner wall surface 3 of the cavity 2 has such a shape that a protrusion 3a is added to the open end of a so-called toroidal cavity by rounding. Note that the position of the apex of the protrusion 3a and the injection hole position of the fuel injection nozzle 5 at the time of fuel injection are connected and indicated by a broken line B in FIG. The protruding portion 3 a has a substantially line-symmetric shape with respect to the broken line B. The injection direction of the fuel injected from the fuel injection nozzle 5 is set slightly downward with respect to the broken line B.

[Action]
The combustion chamber 10 of the diesel engine according to one embodiment of the present invention is configured as described above and operates as follows.
First, when the piston 1 reaches near the top dead center in the compression stroke, the fuel is injected from the fuel injection nozzle 5 toward the inner wall surface 3 of the cavity 2. When this spray (atomized fuel) is indicated by an arrow F in FIG. 2, the spray F goes straight downward slightly from the broken line B and collides with the protruding portion 3 a of the inner wall surface 3. At this time, the projecting portion 3a is because it is formed projecting in a substantially triangular shape, spray F is divided into a first spray F _A flowing to the upper side and the second spray F _B that flows to the lower side of the projecting portion 3a.

The ratio of the first spray F _A and the second spray F _B to be divided is determined by the relative positional relationship between the injection direction of the fuel injected from the fuel injection nozzle 5 and the protruding portion 3a, and is set in advance. Value. In the present embodiment, since the injection direction of fuel injected from the fuel injection nozzle 5 is somewhat directed downward relative to the broken line B, than the amount of the first spray F _A is the amount of the second spray F _B Become more.

In the upper side of the protruding portion 3a, the first surface portion 3b is smoothly connected to the protruding portion 3a and the top surface 1a, a first spray F _A is guided to the top surface 1a side. In addition, since the shape of the first surface portion 3b is no open shape in the vicinity of the opening of the cavity 2, the first spray F _A reverse squish that tries to flow in the same direction induced by the first surface portion 3b The flow will also work. Thus, the first spray F _A is sucked from the cavity 2 side to the squish area 6 side, it diffuses in the squish area 6.

On the other hand, the lower side of the protruding portion 3a, the second surface portion 3c is smoothly connected to the protruding portion 3a and the bottom surface 2a, a second spray F _B is guided to the bottom surface 2a side, reference numeral F in FIG. 2 Diffusion inside the cavity 2 while causing convection as shown by _C. That is, air and fuel are mixed evenly not only in the cavity 2 but also in the squish area 6.

[Results of CFD analysis]
FIG. 3 shows the results obtained by CFD (Computational Fluid Dynamics) analysis. Here, a fluctuation simulation of the oxygen concentration in the combustion process of the fuel in the combustion chamber 10 is shown, and a dark colored portion indicates a low oxygen concentration portion, that is, a portion where the fuel is burning. Also, (a) shows a crank angle of 2 ° ATDC, (b) shows a crank angle of 4 ° ATDC, (c) shows a crank angle of 6 ° ATDC, and (d) shows a crank angle of 8 °. The state of ATDC, (e) corresponds to the state where the crank angle is 10 ° ATDC. FIG. 4 is a comparative example showing an analysis result in the case where the inner wall surface 3 of the cavity 2 does not have the protrusion 3a.

  First, focusing on the oxygen concentration in the vicinity of the squish area 6, in FIGS. 3A to 3C related to the combustion chamber 10, the fuel guided to the upper side of the protrusion 3 a is the top of the cylinder head 4 and the piston 1. It slightly enters the gap with the surface 1a. On the other hand, in the case of FIGS. 4A to 4C, which are comparative examples, a large amount of fuel has entered the squish area 6 and also leaks into the gap between the piston 1 and the cylinder liner 7.

Moreover, in FIG.3 (d) and (e) which concern on this combustion chamber 10, oxygen generate | occur | produces moderately and the combustion has generate | occur | produced. On the other hand, in the case of FIGS. 4D and 4E, which are comparative examples, excessive combustion has occurred so that seizure between the piston 1 and the cylinder liner 7 may occur.
Thus, in the main combustion chamber 10 having the protrusion 3a, it can be seen that the amount of spray guided to the squish area 6 side is appropriately controlled as compared with the case without the protrusion 3a.

When attention is paid to the oxygen concentration inside the cavity 2, as shown in FIG. 3 (e), the fuel guided from the protrusion 3a to the inside of the cavity 2 along the bottom surface 2a is greatly convected in the combustion chamber 10. And it burns in a wide range. On the other hand, in FIG. 4 (e), which is a comparative example, convection similar to that in the combustion chamber 10 is observed, but the black area is narrow and the combustion range is somewhat narrow.
Thus, it can be seen that in the main combustion chamber 10 having the protrusion 3a, the amount of spray guided to the cavity 2 side is appropriately controlled as compared with the case where the protrusion 3a is not provided.

As described above, the ratio between the amount of the first spray F _A guided upward from the protrusion 3 a and the amount of the second spray F _B guided downward is injected from the fuel injection nozzle 5. It is determined by the relative positional relationship between the fuel injection direction and the protrusion 3a. In this analysis, these positional relationships are set so that this ratio is about 2: 8.

[effect]
As described above, the combustion chamber 10 of the diesel engine, by providing the protruding portions 3a, it is possible to a first spray F _A along the first face 3b induces the upper direction, and the second spray F _B can be guided downward along the second surface portion 3c. Moreover, the ratio of dispersion of the spray F to the cavity 2 side and the squish area 6 side can be defined.

  That is, the fuel F can be dispersed in two directions and can be diffused throughout the combustion chamber 10. Thereby, the combustion efficiency can be enhanced not only in the cavity 2 but also in the squish area 6. In particular, since the air (oxygen) existing in the squish area 6 can be used, the generation of smoke can be suppressed as compared with the conventional diesel engine.

Moreover, since the ratio of the division into the first spray F _A and the second spray F _B can be set accurately, the amount of fuel diffused to the squish area 6 side can also be accurately controlled. That is, the fuel does not burn excessively in the squish area 6, and the temperature of the cylinder liner 7 does not rise excessively. Further, since the fuel does not adhere to the surface of the cylinder liner 7, there is no possibility that the fuel is mixed into the engine oil.

  Thus, according to the present combustion chamber 10, the fuel is not combusted simply in the squish area 6, but the amount of fuel related to the combustion in the squish area 6 is accurately controlled, so that the fuel is moderated in the squish area 6. Can be burned. In general, the combustion conditions (atmosphere temperature, swirl speed, etc.) are different between the inside of the cavity 2 and the squish area 6, but by providing the protrusion 3a according to the present invention, an amount of fuel optimum for each combustion condition is provided. Can be set.

  Further, since the protrusion 3a is formed over the entire circumference of the inner wall surface 3, it is easy to process, and the shape of the inner wall surface 3 of the cavity 2 regardless of the arrangement of the injection holes in the fuel injection nozzle 5 and the fuel injection direction. Can be the same. Even in the case where a swirl flow is generated inside the cavity 2, the projecting portion 3 a is formed on the entire circumference of the inner wall surface 3, so that the fuel guiding direction can be reliably divided vertically. There is also an advantage of being able to do it.

[Others]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.
For example, the shape of the protrusion 3a in the above-described embodiment is formed in a substantially triangular shape in a longitudinal section passing through the central axis of the piston 1, but may be an equilateral triangle shape, an isosceles triangle shape, or an isosceles trapezoid shape. Good.

Moreover, in the above-mentioned embodiment, although the 1st surface part 3b becomes a curve in the longitudinal cross section which passes along the central axis of piston 1, if it is the shape which connects the upper part side of the projection part 3a and the top surface 1a, it will be a straight line ( A line including a straight line).
Moreover, in the above-mentioned embodiment, although the projection part 3a is formed over the perimeter of the inner wall surface 3, if the length which branches at least the fuel injected from the fuel injection nozzle 5 to an upper direction and a lower direction is sufficient Good.

It is a longitudinal section showing the whole combustion chamber composition of a diesel engine concerning one embodiment of the present invention. It is a fragmentary sectional view (A section of Drawing 1) for explaining the distribution direction and distribution direction of the fuel in the combustion chamber of the diesel engine concerning one embodiment of the present invention. It is a contour figure which shows the fluctuation | variation of the oxygen concentration of the combustion process in the combustion chamber of the diesel engine which concerns on one Embodiment of this invention, (a) is a state whose crank angle is 2 degrees ATDC, (b) is a crank angle is 4 degrees. The state of ATDC, (c) is the state where the crank angle is 6 ° ATDC, (d) is the state where the crank angle is 8 ° ATDC, and (e) is the state where the crank angle is 10 ° ATDC. It is a contour figure which shows the fluctuation | variation of the oxygen concentration of the combustion process in the combustion chamber of the diesel engine as a comparative example with respect to this invention, (a) is a state whose crank angle is 2 degree ATDC, (b) is a crank angle is 4 degree ATDC. (C) is a state where the crank angle is 6 ° ATDC, (d) is a state where the crank angle is 8 ° ATDC, and (e) is a state where the crank angle is 10 ° ATDC.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piston 1a Top surface 2 Cavity 2a Bottom surface 3 Inner wall surface 3a Protrusion part 3b 1st surface part 3c 2nd surface part 4 Cylinder head 5 Fuel injection nozzle 6 Squish area 7 Cylinder liner 10 Diesel engine

Claims (3)

A cavity is formed in the top surface of the piston so as to be recessed into the inside of the piston from the top surface, and a fuel injection nozzle that injects fuel toward the inner wall surface of the cavity is provided in the cylinder head facing the top surface. A combustion chamber of a direct injection diesel engine,
From the inner wall surface of the cavity to the upper and lower directions of the cavity, the fuel is dispersed from the inner wall surface of the cavity at a position where the fuel injected from the fuel injection nozzle collides with the inner wall surface. A protrusion formed to protrude inward,
A first side that connects the protrusion and the top surface to form an upper side surface of the inner wall surface, and guides fuel flowing from the protrusion to the upper direction along the top surface toward the outer periphery of the piston. The face part,
The projection and the bottom surface of the cavity are connected to form a lower side surface of the inner wall surface, and fuel flowing from the projection to the lower direction is guided along the bottom surface of the cavity toward the inside of the cavity. A second surface portion,
In the longitudinal section passing through the central axis of the piston, the first surface portion is formed in a shape such that the distance from the central axis is shorter toward the protrusion and the distance from the central axis is longer toward the top surface. Characterized by a combustion chamber of a diesel engine. The combustion chamber of a diesel engine according to claim 1, wherein the projection is formed in an annular shape over the entire circumference of the inner wall surface. The combustion chamber of a diesel engine according to claim 1 or 2, wherein the protrusion is formed in a triangular shape in a longitudinal section passing through the central axis of the piston.

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