JP2015105570A - Diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an amount of smoke emission by effectively using air in a cylinder for combustion.SOLUTION: Fuel spray or flame collided with a protrusion 32 flows in a split manner to a swirl upstream side and a downstream side along guide surfaces 32-1 and 32-2, and flows in a split manner to a cylinder axial direction upper side and a lower side along guide surfaces 32-3 and 32-4. The fuel spray or the flame guided to a squish area 22 by the guide surfaces 32-1 and 32-2 and a step part 34 deviates from the fuel spray or the flame guided to the squish area 22 by the guide surface 32-4 in a cylinder circumferential direction position, and therefore, air in the squish area 22 can be effectively used for combustion.

Description

  The present invention relates to a diesel engine, and more particularly to a diesel engine in which a cavity is formed on a piston top surface facing a cylinder.

  In the diesel engine disclosed in Patent Document 1 below, fuel is injected toward the lip portion of the cavity, fuel spray is caused to reach the lip portion during the ignition delay period, and fuel vapor is formed in the vicinity of the lip portion. Due to the expansion flow, the fuel vapor in front of the ignition position is applied to the peripheral wall surface of the cavity and guided toward the bottom of the cavity. This promotes the vertical vortex and prevents the heat spot from becoming large at a specific site, while the heat spot disappears quickly and suppresses the generation of NO, while the vertical vortex promotes the reburning of soot in the fuel gas. doing.

JP 2002-364367 A U.S. Pat. No. 8,459,229 JP 2010-48260 A

  In Patent Document 1, fuel and air are mixed depending on airflow such as squish flow, reverse squish flow, and swirl flow generated inside and outside the cavity. When the inventor of the present application conducted an actual machine experiment to visualize the combustion in the cylinder, the cavity 12b was entirely covered with flames and air was used sufficiently, but as shown in FIG. In the squish area 22 formed between the portion on the outer peripheral side of the cavity 12b and the lower surface of the cylinder head, there are many areas where no flame reaches even in the latter half of the combustion, that is, areas where no air is used. I understood. For this reason, it is difficult to effectively use the air in the cylinder for combustion only by mixing the fuel and air by relying on the airflow, and it is difficult to reduce the smoke discharge amount.

  An object of the diesel engine according to the present invention is to reduce smoke emission by effectively using air in a cylinder for combustion.

  The diesel engine according to the present invention employs the following means in order to achieve the above-described object.

  A diesel engine according to the present invention is a diesel engine in which a cavity is formed on a piston top surface facing a cylinder, and a plurality of protrusions protruding inward in the cylinder radial direction are formed in the cylinder circumferential direction on the cavity inner peripheral wall. The fuel is injected from the nozzle hole of the fuel injection valve so that either the fuel or the flame after fuel ignition is collided with each projection, and each projection is formed of the fuel and the flame after fuel ignition. The gist is to distribute any of the above to both sides in the cylinder circumferential direction and both sides in the cylinder axial direction.

  In one aspect of the present invention, a step portion for guiding either the fuel distributed to both sides of the cylinder circumferential direction by the protrusion portion or the flame after fuel ignition to the squish area is provided between the protrusion portions adjacent to each other in the cylinder circumferential direction. It is suitable that it is formed.

  In one aspect of the present invention, it is preferable that the ratio of the height difference in the cylinder axial direction between the protrusion and the step to the cylinder bore diameter is greater than 0.0177 and less than 0.0531.

  In one aspect of the present invention, the projection portion forms a first predetermined angle in the cylinder circumferential direction, and the first and second guide surfaces for distributing either the fuel or the flame after fuel ignition to both sides in the cylinder circumferential direction. It is preferable that a second predetermined angle is formed in the cylinder axial direction, and third and fourth guide surfaces are formed for distributing either the fuel or the flame after fuel ignition to both sides in the cylinder axial direction. .

  In one embodiment of the present invention, it is preferable that the ratio of the length of the protrusion in the cylinder radial direction to the cylinder bore diameter is smaller than 0.118.

  In one aspect of the present invention, when a swirl flow is formed in a cylinder, the central axis of the injection hole is inclined to the swirl upstream side with respect to a plane passing through the cylinder central axis and the tip of the protrusion. Is preferred.

  In one aspect of the present invention, it is preferable that an inclination angle of the central axis of the nozzle hole with respect to the plane toward the swirl upstream side is smaller than 9 °.

  In one aspect of the present invention, it is preferable that the protrusion is recessed downward in the cylinder axial direction with respect to a portion on the outer peripheral side of the protrusion on the piston top surface.

  In one aspect of the present invention, it is preferable that the ratio of the height difference in the cylinder axial direction between the protrusion on the outer surface of the piston top surface and the protrusion to the cylinder bore diameter is smaller than 0.0295.

  According to the present invention, the fuel and flame in the squish area spread more uniformly in the circumferential direction of the cylinder, and the area where air in the squish area is not used for combustion can be greatly reduced. As a result, the air in the cylinder can be effectively used for combustion, and the amount of smoke discharged can be reduced.

It is a figure showing the schematic structure of the diesel engine concerning the embodiment of the present invention. It is a figure showing the schematic structure of the diesel engine concerning the embodiment of the present invention. It is a figure showing the schematic structure of the diesel engine concerning the embodiment of the present invention. It is a figure showing the schematic structure of the diesel engine concerning the embodiment of the present invention. It is a figure showing the schematic structure of the diesel engine concerning the embodiment of the present invention. It is a figure explaining the flow of the fuel spray in the diesel engine which concerns on embodiment of this invention, or the flame. It is a figure which shows an example of the flame range in the diesel engine which concerns on embodiment of this invention. It is a figure which shows the actual-machine experiment result which measured smoke discharge | emission amount when changing ratio DC / DB of a cavity inlet diameter and a cylinder bore diameter. It is a figure which shows the actual machine experimental result which measured smoke discharge | emission amount when changing ratio (D2-D1) / (2 * D0) of the cylinder radial direction length of the protrusion part 32, and a cavity reference diameter. It is a figure which shows the actual-machine experiment result which measured the smoke discharge | emission amount, when the inclination angle (theta) to the swirl upstream of the center axis | shaft of the nozzle hole 13a with respect to the plane 11b which passes along the cylinder center axis | shaft 11a and the front-end | tip of the protrusion part 32 was changed. . It is a figure which shows the actual machine experimental result which measured the smoke discharge | emission amount, when the ratio H1 / D0 with respect to the cavity reference diameter of the cylinder axial direction height difference of the projection part 32 and the step part 34 was changed. It is a figure which shows the other schematic structure of the diesel engine which concerns on embodiment of this invention. It is a figure which shows the other schematic structure of the diesel engine which concerns on embodiment of this invention. The actual machine experimental results of measuring the smoke discharge amount when the ratio H / D0 of the height difference in the cylinder axial direction between the protrusion 32 on the outer peripheral side of the protrusion 32 on the piston top surface 12a and the cavity reference diameter are changed. FIG. It is a figure which shows an example of the flame range at the time of conducting the actual machine experiment which visualizes the combustion in a cylinder.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

  FIGS. 1-5 is a figure which shows the structural example of the diesel engine (compression ignition internal combustion engine) 10 which concerns on embodiment of this invention. 1 shows the outline of the overall configuration, FIGS. 2 and 3 show the schematic configuration of the piston 12, FIG. 4 shows the AA cross section of FIG. 3, and FIG. 5 shows the BB cross section of FIG. . Although FIG. 1 shows a configuration for one cylinder, the configuration is the same in the case of multiple cylinders. The diesel engine 10 can be configured using, for example, a piston-crank mechanism. In the diesel engine 10, intake air (air) is sucked into the cylinder 11 from the intake port 14 in the intake stroke, and the intake air sucked into the cylinder 11 in the compression stroke is compressed by the piston 12. At that time, a swirl flow is formed in the cylinder 11. For example, when the piston 12 is positioned near the compression top dead center, fuel (for example, liquid fuel such as light oil) is directly injected into the cylinder 11 from the injector (fuel injection valve) 13, so that the fuel in the cylinder 11 is It self-ignites and burns (diesel combustion). The exhaust gas after combustion is exhausted to the exhaust port 15 in the exhaust stroke. In the diesel engine 10, a recirculation passage 16 that connects the exhaust port 15 and the intake port 14 is provided, and a part of the exhaust gas after combustion passes through the recirculation passage 16 to the intake port 14 (intake side). Exhaust gas recirculation (EGR) supplied as is performed. The recirculation passage 16 is provided with an EGR control valve 17. By controlling the opening degree of the EGR control valve 17, the recirculation amount of the exhaust gas (EGR gas) from the exhaust port 15 to the intake port 14 is controlled. The amount of EGR gas (EGR rate) supplied to the intake side and sucked into the cylinder is controlled. However, it is not always necessary to perform EGR, and the reflux passage 16 and the EGR control valve 17 can be omitted. Further, the intake air into the cylinder 11 can be pressurized by a supercharger such as a turbocharger (not shown). In addition, about the structure for forming a swirl flow in the cylinder 11, since it is realizable with a well-known structure, detailed description is abbreviate | omitted. On the other hand, it is possible not to form a swirl flow in the cylinder 11.

  As shown in FIGS. 2 to 5, a cavity 12 b is formed on the top surface 12 a of the piston 12 facing the cylinder 11. The injector 13 is disposed on the cylinder head 9 with its tip end facing the center of the cavity 12b. A plurality of nozzle holes 13a are formed uniformly at the tip of the injector 13 along the circumferential direction of the injector. For example, at the fuel injection timing when the piston 12 is positioned near the compression top dead center, the extension line 13b of the central axis of each injection hole 13a is arranged so as to hit the inner peripheral wall of the cavity 12b, and either the fuel or the flame after fuel ignition The fuel is injected radially from the injection holes 13a of the injector 13 so that they collide with the inner peripheral wall of the cavity 12b.

  In the present embodiment, a plurality of (eight in the example of FIGS. 2 and 3) projecting portions 32 projecting inward in the cylinder radial direction are formed on the inner circumferential wall of the cavity 12b evenly along the circumferential direction of the cylinder. Yes. Each protrusion 32 has a cylinder circumferential width between the guide surfaces 32-1 and 32-2 and a cylinder axial thickness between the guide surfaces 32-3 and 32-4 as it goes from the outside in the cylinder radial direction to the inside. The guide surfaces 32-1 and 32-2 form a predetermined angle θ1 in the cylinder circumferential direction, and the guide surfaces 32-3 and 32-4 form a predetermined angle θ2 in the cylinder axial direction. In the example of FIGS. 2 and 3, the guide surface 32-1 is inclined toward one side of the cylinder circumferential direction (swirl upstream side) as it goes from the inner side to the outer side in the cylinder radial direction with respect to the plane passing through the cylinder central axis 11a. The surface 32-2 is inclined toward the other side in the cylinder circumferential direction (swirl downstream side) as it goes from the inside to the outside in the cylinder radial direction, and the inclination angle of the guide surfaces 32-1 and 32-2 with respect to the cylinder radial direction is θ1 / 2. is there. The guide surface 32-3 is inclined downward in the cylinder axial direction from the inner side to the outer side in the cylinder radial direction with respect to the plane orthogonal to the cylinder central axis 11a, and the guide surface 32-4 is orthogonal to the cylinder central axis. A part of the piston top surface 12a is formed parallel to the plane.

  The injection holes 13a of the injector 13 are formed in the same number as the protrusions 32 (eight in the example of FIGS. 2 and 3), and each of the fuel and the flame after fuel ignition is caused to collide with each protrusion 32. Fuel is injected from the injection hole 13a. As shown by arrows A and B in FIG. 6, the protrusions 32 are arranged on either side of the cylinder in the circumferential direction according to the guide surfaces 32-1 and 32-2 (on the swirl upstream side and the swirl side). To the downstream side), and as shown by arrows C and D in FIG. When a swirl flow is formed in the cylinder 11, in order to cause the fuel spray before ignition and the flame after ignition to collide with the tip (innermost inner diameter position) of the projection 32, the central axis of the injection hole 13a at the fuel injection timing The center of the injection hole 13a with respect to the plane 11b passing through the cylinder center axis 11a and the tip of the projection 32 so that the extension line 13b of the projection hits the swirl upstream side (guide surface 32-1) slightly from the tip of the projection 32. It is preferable to slightly tilt the shaft toward the upstream side of the swirl. On the other hand, when the swirl flow is not formed in the cylinder 11, in order to cause the fuel spray before ignition and the flame after ignition to collide with the tip of the protrusion 32, an extension line of the central axis of the injection hole 13a at the fuel injection timing It is preferable to arrange the central axis of the injection hole 13a in the plane 11b passing through the cylinder central axis 11a and the tip of the protrusion 32 so that 13b hits the tip of the protrusion 32.

  Furthermore, in this embodiment, the step part 34 is formed between the protrusion parts 32 adjacent to the cylinder circumferential direction, and the protrusion part 32 and the step part 34 are alternately arrange | positioned in the cylinder circumferential direction. In the example of FIGS. 2 and 3, the stepped portion 34 is disposed at an intermediate position between the adjacent protruding portions 32. Each step 34 is recessed below the projection 32 in the cylinder axial direction, and the upper surface 34-1 of each step 34 is lower than the guide surface 32-4 (piston top surface 12a) of the projection 32 in the cylinder axial direction. The inner peripheral surface 34-2 of each step 34 is located on the outer side in the cylinder radial direction from the tip (innermost inner diameter position) of the protrusion 32. The fuel distributed to both sides in the circumferential direction of the cylinder (the swirl upstream side and the downstream side) according to the guide surfaces 32-1 and 32-2 at the protrusion 32 and the flame after fuel ignition are indicated by arrows E and F in FIG. As shown, it is guided upward in the cylinder axial direction by the step portion 34 and pushed out to the squish area 22 formed between the portion on the outer peripheral side of the cavity 12b on the piston top surface 12a and the lower surface of the cylinder head 9.

  The fuel spray injected from each injection hole 13a of the injector 13 collides with the projection 32 before ignition, or becomes a flame after ignition and collides with the projection 32. As the fuel spray before ignition and the flame after ignition collide with the protrusion 32, the flow of fuel spray and flame is swirled according to the guide surfaces 32-1 and 32-2 as shown by arrows A and B in FIG. While being distributed to the upstream side and the downstream side, as shown by arrows C and D in FIG. 6, they are distributed to the upper and lower sides in the cylinder axial direction according to the guide surfaces 32-3 and 32-4. The fuel spray or flame distributed to the lower side in the cylinder axial direction by the guide surface 32-3 of the protrusion 32 flows in the cavity 12b, and combustion is performed using the air in the cavity 12b efficiently. On the other hand, the fuel spray or flame distributed to the upper side in the cylinder axial direction by the guide surface 32-4 of the protrusion 32 is guided to the squish area 22. Further, the fuel spray and flame distributed to the swirl upstream side and the downstream side by the guide surfaces 32-1 and 32-2 of the protrusion 32 are also squished by the step 34 as shown in the arrows E and F of FIG. Led to.

  According to the present embodiment, as shown by arrows A, B, E, and F in FIG. 6, the fuel spray and flame guided to the squish area 22 by the guide surfaces 32-1 and 32-2 and the stepped portion 34 are illustrated in FIG. As shown by the arrow D in FIG. 6, the cylinder circumferential direction position is shifted with respect to the fuel spray or flame guided to the squish area 22 by the guide surface 32-4, and the fuel spray or flame in the squish area 22 is difficult to reach. Fuel spray and flame can be guided to the region (region where it is difficult to use air for combustion). Therefore, the fuel spray or flame in the squish area 22 spreads more uniformly in the circumferential direction of the cylinder. For example, as shown in FIG. 7, the area where the air in the squish area 22 is not used for combustion can be greatly reduced. The air in the area 22 can be efficiently used for combustion. As a result, it is possible to reduce the amount of smoke discharged and achieve a low emission under the conditions equivalent to the excess air ratio, that is, without increasing the work of the supercharger. Further, by providing a step 34 between the protrusions 32 adjacent to each other in the cylinder circumferential direction, the fuel spray or flame distributed to the swirl upstream side and the downstream side by the guide surfaces 32-1 and 32-2 As a result, it is possible to efficiently lead to a region where the fuel spray or flame in the squish area 22 is difficult to reach (a region where it is difficult to use air for combustion), and the air in the squish area 22 can be used more efficiently for combustion.

  In Patent Document 2, an edge portion is provided at a portion of the cavity wall where the fuel collides, and the flow of the fuel colliding with the edge portion is switched. However, in Patent Document 2, in which direction the flow of the fuel that collided with the edge portion is switched, more specifically, the flow of fuel is changed to both sides in the cylinder circumferential direction (upward and downstream of the swirl) and both sides in the cylinder axial direction. There is no indication of allocating. Further, Patent Document 2 does not show provision of a step portion between edge portions adjacent to each other in the cylinder circumferential direction.

  Moreover, when there is no step part 34, a reverse squish flow becomes strong in an expansion stroke. When the reverse squish flow becomes strong, only the flame in the portion where the air current is strong is carried from the cavity 12b toward the squish area 22 and carried far away in the cylinder radial direction. As a result, the flame grows unevenly in the circumferential direction of the cylinder, a region where the flame does not reach and no air is used remains, and the air utilization rate for combustion decreases. On the other hand, in this embodiment, by providing the step 34 between the protrusions 32 adjacent in the cylinder circumferential direction, the reverse squish flow in the expansion stroke can be weakened, and the flame distributed by the protrusion 32 is jetted. It is possible to grow more uniformly in the cylinder radial direction depending on the speed. As a result, the area where no flame exists between sprays is reduced, and the air utilization rate for combustion can be increased.

  If the length of the protrusion 32 in the cylinder radial direction (1/2 of the difference between the outermost diameter D2 and the innermost diameter D1) is changed under a constant compression ratio, the length of the protrusion 32 in the cylinder radial direction (D2) is changed. The angle θ1 formed by the guide surfaces 32-1 and 32-2 becomes smaller as -D1) / 2 increases. If the length (D2-D1) / 2 of the projection 32 in the cylinder radial direction is too long and the angle θ1 formed by the guide surfaces 32-1 and 32-2 is too small, the fuel spray or flame collides with the projection 32. Depending on whether the swirl is upstream or downstream, the distribution of fuel spray and flame to the swirl upstream and downstream sides varies greatly. On the other hand, if the length (D2-D1) / 2 of the protruding portion 32 in the cylinder radial direction is too short and the angle θ1 formed by the guide surfaces 32-1 and 32-2 is too large, the fuel spray and flame swirl upstream and downstream The distribution effect to the side is reduced. As a result, the cylinder radial direction length (D2-D1) / 2 of the protrusion 32 affects the smoke discharge amount.

  The ratio DC / DB between the cavity inlet diameter DC and the cylinder bore diameter DB also affects the smoke discharge amount. FIG. 8 shows a result of an actual machine experiment in which the smoke discharge amount was measured when the ratio DC / DB of the cavity inlet diameter DC and the cylinder bore diameter DB was changed under a constant compression ratio. From the result of the actual machine experiment shown in FIG. 8, the ratio DC / DB between the cavity inlet diameter DC and the cylinder bore diameter DB that minimizes the smoke discharge amount was 59% regardless of the engine. Hereinafter, the cavity inlet diameter (59% of the cylinder bore diameter DB) D0 that minimizes the smoke discharge amount is defined as the cavity reference diameter.

  The amount of smoke discharged when the ratio (D2-D1) / (2 × D0) of the length (D2-D1) / 2 of the protrusion 32 and the reference diameter D0 of the cavity is changed under the condition that the compression ratio is constant. FIG. 9 shows the result of an actual machine experiment in which measurement is performed. From the actual machine experiment results shown in FIG. 9, in order to reduce the smoke discharge amount compared to the configuration in which the protrusion 32 is not provided (the length of the protrusion 32 in the cylinder radial direction is 0), the length of the protrusion 32 in the cylinder radial direction is reduced. The ratio (D2-D1) / (2 × D0) between (D2-D1) / 2 and the cavity reference diameter D0 is preferably smaller than 0.2. That is, it is preferable that the ratio (D2−D1) / (2 × DB) of the length (D2−D1) / 2 of the protruding portion 32 to the cylinder bore diameter DB is smaller than 0.118. Further, in order to minimize the smoke discharge amount, the ratio (D2−D1) / (2 × D0) of the length (D2−D1) / 2 of the protrusion 32 to the cylinder reference diameter D0 is set to 0. 175 (or approximately 0.175) is preferable, and the ratio (D2-D1) / 2 of the length (D2-D1) / 2 of the protrusion 32 to the cylinder bore diameter DB is set to 0. 103 (or almost 0.103) is preferable.

  Moreover, when the specifications of the cavity 12b and the injector 13 of a diesel engine are considered, it is preferable that the number of the protrusion parts 32 and the injection holes 13a is in the range of 8-10. And it is preferable that angle (theta) 1 which the guide surfaces 32-1 and 32-2 comprise exists in the range of 100 degrees-140 degrees. In consideration of providing the step 34 between the adjacent protrusions 32, the ratio D2 / D0 of the outermost diameter D2 and the cavity reference diameter D0 of the protrusion 32 is larger than 1.1 and smaller than 1.5. It is preferable to be within. In consideration of the point at which the tip (inner diameter) of the protrusion 32 protrudes inward in the cylinder radial direction from the cavity reference diameter D0, the ratio D1 / D0 between the inner diameter D1 of the protrusion 32 and the cavity reference diameter D0 is 0. It is preferably in the range of more than 9 and less than 1.0.

  Further, the arrangement of the central axis of the nozzle hole 13a also affects the position where the fuel spray or flame collides with the projection 32, and as a result, the smoke discharge amount. Furthermore, when a swirl flow is formed in the cylinder 11, the fuel spray injected from the injection hole 13a is swept to the swirl downstream side by the swirl flow. Results of an actual machine experiment in which the smoke discharge amount was measured when the inclination angle θ (see FIG. 3) of the central axis of the injection hole 13a with respect to the plane 11b passing through the cylinder central axis 11a and the tip of the protrusion 32 toward the swirl upstream side was changed. Is shown in FIG. From the actual machine experiment results shown in FIG. 10, in order to reduce the smoke discharge amount as compared with the configuration in which the protrusion 32 is not provided, the inclination angle θ of the central axis of the injection hole 13 a with respect to the plane 11 b to the swirl upstream side is 9 °. It is preferable to make it small. Further, in order to minimize the smoke discharge amount, it is preferable to set the inclination angle θ of the central axis of the injection hole 13a with respect to the plane 11b to the swirl upstream side to 5 ° (or approximately 5 °).

  In addition, regarding the inclination angle θ of the central axis of the injection hole 13a with respect to the plane 11b toward the swirl upstream side, during the time t until the fuel spray injected from the injection hole 13a reaches the tip of the protrusion 32, the swirl It can be estimated as the angle that is caused to flow downstream by the swirl. The swirl ratio at the bottom dead center is SR, the spin-up coefficient for correcting the swirl increase rate near the top dead center is C, the engine speed is Ne [rpm], and the fuel from the nozzle hole 13a to the tip of the projection 32 When the spray arrival time is t [ms], the relationship between θ and t is expressed by the following equation (1).

  θ = t / 1000 × 360/60 × SR × C × Ne (1)

  Here, the spin-up coefficient C is set to C = 1.6 based on the calculated values in the actual machine specifications. Further, the fuel spray arrival time t can be calculated using a Guang'an equation according to the following equation (2). From the Guang'an equation, it can be seen that the fuel spray arrival time t is affected by the cavity reference diameter D0, the nozzle hole diameter, the fuel injection pressure, the filling efficiency, and the like, but considering the actual machine specifications, 0.07 ms <t <0. It is possible to estimate by calculation that it falls within the range of 18 ms. From the result, it is preferable to make θ smaller than 9 °.

  Further, the step 34 between the adjacent protrusions 32 serves to push out the fuel spray and flame distributed to the swirl upstream side and the downstream side by the guide surfaces 32-1 and 32-2 of the protrusion 32 to the squish area 22. Fulfill. If the cylinder shaft height difference H1 (see FIG. 5) between the protrusion 32 (guide surface 32-4) and the step portion 34 (upper surface 34-1) is too large, the fuel distributed to the swirl upstream side and downstream side The action of pushing out the spray or flame to the squish area 22 becomes weak, fuel spray or flame tends to accumulate in the cavity 12b, and combustion tends to deteriorate. On the other hand, if the height difference H1 in the cylinder axial direction between the protrusion 32 and the stepped portion 34 is too small, the action of distributing fuel spray and flame to the swirl upstream side and downstream side by the guide surfaces 32-1 and 32-2 becomes weak. Thus, it easily flows out to the squish area 22 as it is. As a result, the cylinder axial height difference H1 between the protrusion 32 and the stepped portion 34 also affects the smoke discharge amount.

  The ratio H1 / D0 of the cylinder axial height difference H1 between the protrusion 32 (guide surface 32-4) and the stepped portion 34 (upper surface 34-1) to the cavity reference diameter D0 was changed under the condition that the compression ratio was constant. FIG. 11 shows the results of an actual machine experiment in which smoke emission was measured. From the result of the actual machine experiment shown in FIG. 11, in order to reduce the smoke discharge amount as compared with the configuration without the protrusion 32, the cylinder axial height difference H1 between the protrusion 32 and the step portion 34 with respect to the cavity reference diameter D0. It is preferable that the ratio H1 / D0 is larger than 0.03 (3%) and smaller than 0.09 (9%). That is, the ratio H1 / DB of the cylinder shaft height difference H1 between the protrusion 32 and the stepped portion 34 to the cylinder bore diameter DB is greater than 0.0177 (1.77%) and 0.0531 (5.31%). It is preferable to make it small. Furthermore, in order to minimize the smoke discharge amount, the ratio H1 / D0 of the cylinder shaft height difference H1 between the protrusion 32 and the stepped portion 34 to the cavity reference diameter D0 is set to 0.06 to 0.075 (6% -7.5%), and the ratio H1 / DB of the cylinder shaft height difference H1 between the projection 32 and the stepped portion 34 to the cylinder bore diameter DB is 0.0354 to 0.0443 (3 .54% to 4.43%) is preferable.

  Moreover, in this embodiment, as shown, for example in FIG. 12, 13, each protrusion part 32 (guide surface 32-4) is a part on the outer peripheral side from the protrusion part 32 (guide surface 32-4) in the piston top surface 12a. On the other hand, it may be recessed downward in the cylinder axial direction. By providing a step between the protrusion 32 (guide surface 32-4) on the outer peripheral side of the piston top surface 12a and each protrusion 32 (guide surface 32-4), the squish flow and the reverse squish flow are weakened. The fuel spray and flame can be optimally distributed inside and outside the cavity 12b (upper and lower sides in the cylinder axial direction). Combining optimization of the circumferential distribution of the cylinder by the protrusion 32 and optimization of the distribution of the cylinder axial direction by this step can optimize the mixing of fuel and air in the combustion chamber without relying on the airflow. Thus, further reduction of emissions can be realized.

  The volume of the cavity 12b is an important specification for determining the compression ratio. The compression ratio is a value determined in consideration of the upper limit of the cylinder pressure and the ignitability of the fuel at the time of low temperature start. In the normal combustion chamber design, the volume of the cavity 12b is set in accordance with the target compression ratio. Is generally adjusted. In the current engine, the cavity reference diameter D0 is about 59% of the cylinder bore diameter, and the diameter of the cavity 12b tends to become shallower. 12 and 13, the cylinder axial height difference H between the protrusion 32 (guide surface 32-4) on the outer peripheral side of the piston top surface 12a and the protrusion 32 (guide surface 32-4). If it is too large, the depth of the cavity 12b will become further shallow and it will be difficult to form vertical vortices in the cavity 12b, and the air utilization rate in the cavity 12b will decrease and the smoke discharge will increase. As a result, the height difference H in the cylinder axial direction between the protrusion 32 on the outer peripheral side of the protrusion 32 on the piston top surface 12a also affects the smoke discharge amount.

  Cavity reference of the cylinder shaft height difference H between the protrusion 32 (guide surface 32-4) and the protrusion 32 (guide surface 32-4) on the outer peripheral side of the piston top surface 12a under a constant compression ratio. FIG. 14 shows a result of an actual machine experiment in which the smoke discharge amount was measured when the ratio H / D0 with respect to the diameter D0 was changed. From the actual machine experiment results shown in FIG. 14, in order to reduce the smoke discharge amount as compared with the configuration without the protrusion 32, the ratio H / D0 of the cylinder axial height difference H to the cavity reference diameter D0 is set to 0.05 ( 5%) is preferable. That is, it is preferable to make the ratio H / DB of the cylinder axial height difference H to the cylinder bore diameter smaller than 0.0295 (2.95%). Further, in order to minimize the smoke discharge amount, the ratio H / D0 of the cylinder axial height difference H to the cavity reference diameter D0 is preferably set to 0.03 (or substantially 0.03). The ratio H / DB of the height difference H to the cylinder bore diameter is preferably 0.0177 (or almost 0.0177).

  In the above embodiment, the inclination angles of the guide surfaces 32-1 and 32-2 with respect to the cylinder radial direction are equal to each other. However, the inclination angles of the guide surfaces 32-1 and 32-2 with respect to the cylinder radial direction are the same. It is also possible to make the sizes different from each other. For example, when a swirl flow is formed in the cylinder 11, fuel spray or flame is swept downstream of the swirl by the swirl flow, so that the inclination angle of the guide surface 32-1 with respect to the cylinder radial direction is set to the guide surface 32- It is also possible to make the angle greater than 2.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to such embodiment at all, and it can implement with a various form in the range which does not deviate from the summary of this invention. Of course.

  DESCRIPTION OF SYMBOLS 10 Diesel engine, 11 Cylinder, 12 Piston, 12a Top surface, 12b Cavity, 13 Injector, 13a Injection hole, 14 Intake port, 15 Exhaust port, 16 Recirculation passage, 17 EGR control valve, 22 Squish area, 32 Protrusion part, 32 -1, 32-2, 32-3, 32-4 Guide surface, 34 steps.

Claims (9)

A diesel engine having a cavity formed in a piston top surface facing in a cylinder,
A plurality of protrusions protruding inward in the cylinder radial direction are formed in the cavity inner peripheral wall side by side in the cylinder circumferential direction,
Injecting fuel from the nozzle hole of the fuel injection valve so that either the fuel or the flame after fuel ignition collides with each projection,
Each protrusion is a diesel engine that distributes either the fuel that collided or the flame after fuel ignition to both sides in the cylinder circumferential direction and both sides in the cylinder axial direction. The diesel engine according to claim 1,
A diesel engine in which a step portion for guiding either the fuel distributed to both sides of the cylinder circumferential direction by the protrusion or the flame after fuel ignition to the squish area is formed between the protrusions adjacent to each other in the cylinder circumferential direction. . The diesel engine according to claim 2,
A diesel engine in which a ratio of a height difference between a projection and a step in a cylinder axial direction to a cylinder bore diameter is larger than 0.0177 and smaller than 0.0531. The diesel engine according to any one of claims 1 to 3,
The protrusion has a first predetermined angle in the cylinder circumferential direction, and first and second guide surfaces for distributing either the fuel or the flame after fuel ignition to both sides of the cylinder circumferential direction, and the first in the cylinder axial direction. 2 A diesel engine having a predetermined angle and formed with third and fourth guide surfaces for distributing either the fuel or the flame after fuel ignition to both sides in the cylinder axial direction. The diesel engine according to any one of claims 1 to 4,
A diesel engine in which the ratio of the cylinder radial length of the protrusion to the cylinder bore diameter is smaller than 0.118. The diesel engine according to any one of claims 1 to 5,
A diesel engine in which, when a swirl flow is formed in a cylinder, the central axis of the nozzle hole is inclined upstream of the swirl with respect to a plane passing through the cylinder central axis and the tip of the protrusion. The diesel engine according to claim 6, wherein
A diesel engine having an inclination angle of the central axis of the nozzle hole with respect to the plane toward the swirl upstream side is smaller than 9 °. The diesel engine according to any one of claims 1 to 7,
A diesel engine in which the protrusion is recessed downward in the cylinder axial direction with respect to the outer peripheral portion of the protrusion on the piston top surface. The diesel engine according to claim 8, wherein
A diesel engine in which the ratio of the height difference in the cylinder axial direction between the protrusion on the outer peripheral side of the protrusion on the top surface of the piston and the cylinder bore diameter is smaller than 0.0295.

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