JP2010101244A - Piston for diesel internal combustion engines - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piston for a diesel internal combustion engine including a combustion chamber having a shape for widely agitating air in the combustion chamber and fuel spray injected from a fuel injection nozzle. <P>SOLUTION: This piston 1 for the diesel internal combustion engine including the combustion chamber 10 formed in a top 1a includes a center projecting portion 11, a peripheral projecting portion 12, and an edge portion 13. The center projecting portion 11 forms the bottom wall 10a of the combustion chamber 10, projecting in a conical shape toward the fuel injection nozzle N, and having a skirt portion 111 continuously connected to a portion on the side of the bottom wall of the peripheral wall 10b of the combustion chamber 10 by a toroidal curved surface. The peripheral projecting portion 12 is formed into a shape projecting toward the fuel injection nozzle N over the whole periphery of the peripheral wall 10b from the bottom wall 10a to the top 1a. The edge portion 13 is provided with a reentrant angle R on the peripheral wall 10b within a range to the top portion 1a from a portion on a side closer to the top portion than the peripheral projecting portion 12 and having larger diameter than the peripheral projecting portion 12. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a piston for a diesel internal combustion engine having a combustion chamber at the top where fuel is directly injected from a fuel injection nozzle.

  In a diesel engine that directly sprays fuel into the combustion chamber, the combustion efficiency varies depending on the degree of mixing of the fuel spray and air in the combustion chamber. In order to improve the combustion efficiency, Patent Document 1 discloses a piston in which a protrusion extending over the entire circumference is formed on the circumferential surface of the combustion chamber. Since this piston is provided with a protrusion on its peripheral surface, a strong air eddy current is formed in a region above the protrusion in the combustion chamber during the compression stroke. Further, since the protrusion is also provided at the bottom of the combustion chamber, a vortex is formed in a region between the protrusion at the bottom and the protrusion on the peripheral surface in the expansion stroke. In Patent Document 1, the fuel spray is diffused into the combustion chamber by the vortex of the air.

  Patent Document 2 discloses a direct injection diesel engine that injects fuel from a fuel injection nozzle into a combustion chamber provided at the top of a piston. The combustion chamber has a protrusion that distributes the injected fuel in an upper direction and a lower direction. The fuel distributed in the lower direction is guided toward the inside of the combustion chamber, and the fuel distributed in the upper direction is guided to the squish area which is the outer peripheral direction of the piston.

These pistons increase the combustion efficiency by uniformly mixing the air in the combustion chamber and the fuel spray, and reduce the generation amount of soot and the like.
Japanese Patent Laid-Open No. 7-238837 JP 2008-151089 A

  However, in the case of the piston described in Patent Document 1, the region above the protrusion is agitated by the protrusion provided on the peripheral surface during the compression stroke, and the region below the protrusion is during the expansion stroke. Is stirred by the protrusion on the bottom side. That is, the region to be stirred and its timing are different in the combustion chamber.

  Further, in the case of the piston described in Patent Document 2, by providing protrusions on the peripheral surface, fuel spray is distributed also to the squish area, and combustion efficiency is improved by using air in the squish area. However, since the flow of fuel spray inside the combustion chamber is unidirectional and the fuel density of the fuel spray is increased, combustion in the core is suppressed.

  Therefore, the present invention provides a piston for a diesel internal combustion engine having a combustion chamber having a shape capable of widely stirring the air in the combustion chamber and the fuel spray injected from the fuel injection nozzle.

  The piston of the present invention is a piston for a diesel internal combustion engine having a combustion chamber at a top portion where fuel is directly injected from a fuel injection nozzle, and includes a central protrusion, a peripheral protrusion, and an edge. The central projection forms the bottom wall of the combustion chamber, protrudes in a conical shape toward the fuel injection nozzle, and the skirt is continuously connected to the bottom wall side of the peripheral wall of the combustion chamber by a toroidal curved surface Has been. The peripheral protrusion is formed in a convex shape toward the fuel injection nozzle over the entire periphery of the peripheral wall from the bottom wall to the top. The edge portion is provided with a reentrant angle on a peripheral wall in a range from a portion having a diameter larger than that of the peripheral protrusion to the top portion on the top side of the peripheral protrusion.

  In this case, the center protrusion protrudes in a direction along the center line of the piston to a height from the position of the apex of the peripheral protrusion to the top surface of the piston. In addition, when the combustion chamber is divided by a conical surface connecting the nozzle hole of the fuel injection nozzle and the apex of the peripheral protrusion, and the top side is the first region and the bottom wall side is the second region, the first region and the second region The injection hole angle of the fuel injection nozzle is set so that the fuel spray sprayed from the fuel injection nozzle and atomized is diffused to the first region and the second region at a weight ratio equivalent to the volume ratio. Furthermore, the volume of the second region is preferably equal to or larger than the volume of the first region.

  The piston according to the present invention has the peripheral protrusion in the combustion chamber, and diffuses the air in the combustion chamber and the fuel spray injected from the fuel injection nozzle into the first region and the second region. Combustion efficiency is improved. Furthermore, by setting the nozzle hole angle of the fuel injection nozzle so that the fuel spray spreads to the first region and the second region at a weight ratio equivalent to the volume ratio between the first region and the second region, the combustion chamber Since the concentration of the fuel spray becomes uniform, the combustion efficiency is further improved. And since it has the center protrusion by which the bottom part is continuously connected by the toroidal curved surface with respect to the part by the side of the bottom wall of a surrounding wall, it is spread | diffused by the 2nd area | region, while the kinetic energy of fuel spray is large. The fuel spray flight vector can be directed upward in the center of the combustion chamber. As a result, the spread of combustion is easily promoted.

  According to the piston of the present invention in which the central protrusion protrudes in the direction along the center line of the piston to the height between the position of the top of the peripheral protrusion and the top surface of the piston, the region in which fuel is not directly injected is Can be reduced. Combustion efficiency is improved because fuel spray and unused air that is not diffused are reduced.

  When the combustion chamber is defined as the first region and the second region with the peripheral projection as a boundary, the fuel injection nozzle is arranged so that the fuel spray diffuses to each region at a weight ratio equivalent to the volume ratio of each region. According to the piston of the present invention in which the nozzle hole angle is set, the fuel spray is distributed to the respective regions, so that the surface area of the fuel spray is increased, so that the fuel spray is easily stirred. In addition, by supplying fuel spray in an amount corresponding to the amount of air in the first region and the second region, the fuel concentration is homogenized and the air usage rate in the combustion chamber is improved. As a result, the combustion efficiency is improved and the amount of soot is reduced.

  According to the piston of the present invention in which the second region is the same as or larger than the first region, the radius of curvature in the small circumferential direction of the toroidal curved surface that continuously connects the bottom wall and the peripheral wall of the combustion chamber is increased. Can be set. As a result, the fuel spray distributed to the second region is suppressed from being attenuated in kinetic energy, and is easily guided from the peripheral wall to the center of the combustion chamber along the bottom wall. In the expansion stroke, as the space expands above the combustion chamber, the fuel spray that continues to burn is expanded accordingly. The fuel spray diffused to the second region can form a wide combustion region together with the fuel spray diffused to the first region, so that the combustion efficiency is improved.

  A piston 1 according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 5. A top portion 1a of the piston 1 shown in FIG. 1 is a top portion of a piston for a diesel internal combustion engine, and has a combustion chamber 10 into which fuel is directly injected from a fuel injection nozzle N. The combustion chamber 10 is formed concentrically with the fuel injection nozzle N disposed on the center line C of the piston 1. At the end of the fuel injection nozzle N, there are a plurality of nozzle holes H through which fuel is ejected, in this embodiment, six radially open.

  The number of nozzle holes H is changed according to the diameters of the cylinder and the piston. Therefore, the number of nozzle holes is not limited to six, but is six or more, for example, seven or eight when the diameter is large, or six or less, for example, five or four when the diameter is small. Also, the number of nozzle holes can be changed as appropriate depending on the spread angle of the fuel to be ejected.

  The combustion chamber 10 includes a central protrusion 11, a peripheral protrusion 12, and an edge 13. As shown in FIG. 1, the central protrusion 11 forms a bottom wall 10 a of the combustion chamber 10, and protrudes in a conical shape toward the fuel injection nozzle N. Further, the bottom portion 111 of the central protrusion 11 is continuously connected to the bottom wall side portion of the peripheral wall 10 b of the combustion chamber 10 by a toroidal curved surface. The peripheral protrusion 12 is formed in a convex shape toward the fuel injection nozzle N over the entire periphery of the peripheral wall 10b from the bottom wall 10a to the top 1a.

  The apex of the central protrusion 11 protrudes in the direction along the center line C of the piston 1 to a height between the position of the apex 121 of the peripheral protrusion 12 and the top surface T of the piston 1. Is formed higher than the position of the apex 121 of the peripheral protrusion 12.

  As shown in FIG. 2, the combustion chamber 10 is divided into two by a conical surface P passing through the nozzle hole H of the fuel injection nozzle N and the apex 121 of the peripheral projection 12, and the top side is the first region A1 and the bottom wall side is. The second area A2. At this time, the injection hole angle S of the injection hole H of the fuel injection nozzle N is not set so that the fuel spray M is directed toward the peripheral projection 12, but is a volume ratio between the first region A 1 and the second region A 2. The fuel spray M is set so as to diffuse into the first region A1 and the second region A2 at an equal weight ratio. Therefore, the direction G in which the injection hole H of the fuel injection nozzle N opens does not necessarily coincide with the conical surface P.

  The edge 13 is provided with a reentrant angle R on the peripheral wall 10b in a range from a portion having a diameter larger than that of the peripheral protrusion 12 on the apex side of the peripheral protrusion 12 to the apex 1a. The reentrant angle R is set such that the fuel spray M1 distributed to the first region A1 side by the peripheral protrusion 12 returns to the center of the combustion chamber 10. At this time, if the reentrant angle R is less than 10 °, the fuel spray M1 is unlikely to return to the central portion. When the reentrant angle R exceeds 60 °, the fuel spray M1 collides with and adheres to the peripheral wall 10b. Therefore, the reentrant angle R is preferably set in the range of 10 ° to 60 °.

  In addition, in the volume ratio of 1st area | region A1 and 2nd area | region A2, when 2nd area | region A2 becomes large too much, it becomes impossible to ensure the length of the edge part 13, and the reentrant angle R enough. Further, considering that the fuel spray M is uniformly diffused into the combustion chamber 10, it is desirable that the volume of the first region A1 and the volume of the second region A2 are substantially the same. Therefore, the volume ratio between the first region A1 and the second region A2 is preferably about 50%: 50% to about 30%: 70%.

  The fuel jetted into the combustion chamber 10 of the piston 1 configured as described above flies to the vicinity of the peripheral wall 10b with the liquid column L as shown in FIG. In the present embodiment, the peripheral protrusion 12 is arranged so that the volume of the first region A1 is 40% of the entire combustion chamber and the volume of the second region A2 is 60% of the entire combustion chamber. Therefore, as shown in FIG. 3, the nozzle hole H of the fuel injection nozzle N is also more than the peripheral projection 12 so that 40% of the fuel is diffused in the first region A1 and 60% of the fuel is diffused in the second region A2. The fuel is ejected in the two regions A2.

  As shown in FIG. 4, the fuel liquid column L is atomized into the fuel spray M before reaching the peripheral wall 10 b. The fuel spray M is distributed by the peripheral protrusion 12 into the fuel spray M1 on the first region A1 side and the fuel spray M2 on the second region A2 side. The fuel spray M1 is diffused in the first region A1 so as to be returned to the central portion of the combustion chamber 10 along the edge 13, and the fuel spray M2 is formed on a toroidal curved surface provided from the peripheral wall 10b to the bottom wall 10a. Is diffused into the second region A2 so as to be returned to the central portion of the combustion chamber 10 along the second region A2.

  The fuel is atomized just before flying in the state of the liquid column L to the vicinity of the peripheral wall 10b and colliding with the peripheral wall 10b. Therefore, since the kinetic energy of the fuel spray M is distributed to the first region A1 and the second region A2 in a large state, the fuel sprays M1 and M2 are diffused over a wide range. As a result, as shown in FIG. 5, a combustion region B in which the mixing ratio is uniformly stable in a wide region can be obtained, so that the combustion efficiency is improved.

  In the present embodiment, the volume of the second area A2 is larger than the volume of the first area A1. Therefore, the radius of curvature in the small circumferential direction of the toroidal curved surface that continuously connects the bottom wall 10a and the peripheral wall 10b of the combustion chamber 10 can be set large. As a result, the fuel spray M2 distributed to the second region A2 is suppressed from being attenuated in kinetic energy and is easily guided from the peripheral wall 10b to the center of the combustion chamber 10 along the bottom wall 10a. In the expansion stroke, when the space expands above the combustion chamber 10, the fuel spray M that continues to burn is expanded accordingly. The fuel spray M2 diffused to the second region A2 can form a combustion region B over a wide range together with the fuel spray M1 diffused to the first region A1, so that the combustion efficiency is improved.

  A piston 1 according to a second embodiment of the present invention will be described with reference to FIGS. 6 to 9 all show an enlarged view of one side of the combustion chamber 10. The structure which has the same function as piston 1 of 1st Embodiment attaches | subjects the same code | symbol in drawing, and abbreviate | omits the description.

  In the combustion chamber 10 of the piston 1 shown in FIG. 6, the maximum diameter of the first region A1 is larger than the maximum diameter of the second region A2. Further, since the volume of the first region A1 and the volume of the second region A2 are substantially the same, the direction G in which the nozzle hole H opens coincides with the conical surface P.

  The fuel ejected from the nozzle hole H flies to the vicinity of the peripheral wall 10b with the liquid column L as shown in FIG. 7, and is atomized immediately before reaching the peripheral wall 10b as shown in FIG. It becomes. The fuel spray M is distributed by the peripheral protrusion 12 into the fuel spray M1 on the first region A1 side and the fuel spray M2 on the second region A2 side. The fuel spray M1 is diffused in the first region A1, and the fuel spray M2 is diffused in the second region A1. And as in the first embodiment, as shown in FIG. 9, a combustion region B in which the mixing ratio is homogeneously stable in a wide region can be obtained, so that the combustion efficiency is improved.

  The fuel is ejected to the peripheral protrusion 12 so that the fuel spray M is diffused by adjusting the weight ratio of the fuel to the volume ratio of the two regions in the combustion chamber 10. That is, when one of the first region A1 and the second region A2 is large, the nozzle hole angle S of the nozzle hole H of the fuel injection nozzle N is set so that the fuel is injected while being biased toward the larger region. With a simple structure, the fuel spray M having a uniform concentration can be provided over a wide range in the combustion chamber 10.

Sectional drawing of the top part which passes along the central axis of the piston of 1st Embodiment concerning this invention. Sectional drawing which expands and shows the one side of the combustion chamber of the piston shown in FIG. Sectional drawing which shows typically a mode that the fuel was injected from the fuel-injection nozzle to the combustion chamber of the piston shown in FIG. The figure which shows typically a mode that the fuel injected into the combustion chamber of the piston shown in FIG. 3 becomes a spray, and is spread | diffused in a combustion chamber. Sectional drawing which shows typically the area | region where the fuel diffused in the combustion chamber of the piston shown in FIG. 4 burns. Sectional drawing which expands and shows the one side of the top part which passes along the centerline of the piston of 2nd Embodiment which concerns on this invention. Sectional drawing which shows typically a mode that the fuel was injected from the fuel-injection nozzle to the combustion chamber of the piston shown in FIG. The figure which shows a mode that the fuel injected into the combustion chamber of the piston shown in FIG. 7 becomes a spray, and is spread | diffused in a combustion chamber. Sectional drawing which shows typically the area | region where the fuel diffused in the combustion chamber of the piston shown in FIG. 8 burns.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Piston, 1a ... Top part, 10 ... Combustion chamber, 11 ... Center protrusion, 12 ... Perimeter protrusion, 13 ... Edge part, 111 ... Bottom part, 121 ... Vertex, A1 ... 1st area | region, A2 ... 2nd area | region , H ... nozzle hole, M, M1, M2 ... fuel spray, N ... fuel injection nozzle, P ... conical surface, R ... reentrant angle, S ... nozzle hole angle.

Claims (4)

A piston for a diesel internal combustion engine having a combustion chamber at a top portion where fuel is directly injected from a fuel injection nozzle,
A central protrusion that forms a bottom wall of the combustion chamber and protrudes in a conical shape toward the fuel injection nozzle and has a skirt continuously connected to the bottom wall side portion of the peripheral wall of the combustion chamber by a toroidal curved surface. And
A circumferential protrusion formed in a convex shape toward the fuel injection nozzle over the entire circumference of the peripheral wall between the bottom wall and the top;
A piston comprising: an edge portion provided with a reentrant angle on a peripheral wall in a range from a portion having a diameter larger than that of the peripheral protrusion to the top portion on the top side of the peripheral protrusion. The piston according to claim 1,
The center protrusion protrudes in a direction along the center line of the piston to a height between the position of the apex of the peripheral protrusion and the top surface of the piston. The piston according to claim 1 or claim 2,
The combustion chamber is divided by a conical surface connecting the injection hole of the fuel injection nozzle and the apex of the peripheral projection, and the first region is defined as the first region and the bottom wall side is defined as the second region. Of the fuel injection nozzle so that the fuel spray sprayed from the fuel injection nozzle and atomized at a weight ratio equivalent to the volume ratio between the first region and the second region is diffused to the first region and the second region. The nozzle hole angle is set. The piston according to claim 3,
The volume of the second region is equal to or larger than the volume of the first region.

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