JP2011174388A - Structure of combustion chamber of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structure of a combustion chamber of an internal combustion engine in which the formation of an excessively rich area of fuel is suppressed by preventing the mist of fuel which is injected from an injector toward a cavity from expanding circumferentially along the wall surface of the cavity so as to prevent the adjacent mists from being interfered with each other, and a heat loss from the mists of fuel to the wall surface of the cavity is reduced. <P>SOLUTION: In this structure of a combustion chamber of an internal combustion engine, a cavity 3 with which a plurality of mists F of fuel injected at intervals from an injector 2 disposed above in the circumferential direction are collided is recessed in the top part of a piston 1. A plurality of guide projections 4 in the radial direction of the cavity 3 are provided to the wall surface 3x of the cavity 3 at positions where the mists F are collided so as to suppress the interference of the adjacent mists F due to the expansion of the mists F along the wall surface 3x in the circumferential direction of the cavity 3. The guide projections 4 are formed of a heat insulation material to suppress a heat loss from the mist F to the wall surface 3x. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a combustion chamber structure of an internal combustion engine in which fuel is injected from an injector disposed above a piston into a cavity recessed at the top of the piston.

  Hazardous substances such as particulate matter (PM) and nitrogen oxides (NOx) are present in the exhaust gas of diesel engines mounted on vehicles such as trucks and buses. PM and NOx have a trade-off relationship in general diesel combustion (diffusion combustion). When PM is reduced, NOx increases, and when NOx is reduced, PM increases.

  In recent years, premixed compression ignition combustion (PCI combustion) has been attracting attention as a combustion technique for simultaneously reducing both PM and NOx. In PCI combustion, fuel is injected from an injector disposed above a piston toward a cavity recessed at the top of the piston before the piston reaches top dead center earlier than conventional general diesel combustion. In this combustion method, a uniform premixed gas is formed, and the premixed gas is ignited after the fuel injection is completed, and PM and NOx can be simultaneously reduced.

  However, the PCI combustion is limited to a light load in the operating range. On the other hand, by reducing the area of the nozzle hole of the injector, the fuel to be injected is atomized to promote evaporation, and a lean and uniform premixed gas is quickly generated. Attempts have been made to enlarge to the side (see Patent Document 1).

JP 2007-2111768

  By the way, in a full load in which a large amount of fuel is injected or in an operation region close thereto, in order not to deteriorate fuel consumption, a required amount of fuel corresponding to the load is injected within a certain period (for example, within 30 degrees in crankshaft angle). There is a need. Therefore, when an injector having a small nozzle hole area is used, it is necessary to secure a total nozzle hole area capable of injecting a required amount of fuel at a full load within a certain period, and it is essential to increase the number of nozzle holes.

  However, when the number of injection holes is increased, the interval between adjacent injection holes is narrowed. Therefore, as shown in FIGS. 4 (a) to 4 (c), the fuel spray F injected from each injection hole of the injector is generated. After colliding with the wall surface 3x of the cavity 3, when spreading in the circumferential direction of the cavity 3 along the wall surface 3x (left and right direction in FIG. 4), the sprays F of adjacent nozzle holes interfere with each other. As a result, a fuel rich region is formed in the portion FL where the sprays F overlap, and the amount of smoke (soot) generated increases.

  In order to solve this problem, the present inventor is located at a portion where each spray F collides with the wall surface 3x of the cavity 3, and guides along the inner and outer directions of the cavity 3 (the front and back directions in FIG. 4) (see FIG. 4). A combustion chamber structure in which a plurality of (not shown) are formed has been devised. According to this combustion chamber structure, since the fuel spray F injected from each injection hole of the injector collides with the wall surface 3x of the cavity 3, it is guided along the guide groove in the inside and outside of the cavity 3. Interference between adjacent sprays F due to F spreading in the circumferential direction of the cavity 3 along the wall surface 3x is suppressed. As a result, the formation of a fuel rich region is suppressed, and the amount of smoke generated is reduced.

  However, when a plurality of guide grooves along the inner and outer directions of the cavity 3 are formed on the wall surface 3x of the cavity 3 where the spray F collides, the collision surface area between the spray F and the wall surface 3x of the cavity 3 is caused by the unevenness of each guide groove. It becomes larger than the normal one without the guide groove. For this reason, the amount of heat loss from the spray F to the wall surface 3x of the cavity 3, that is, the surface of the combustion chamber, increases, resulting in deterioration of fuel consumption.

  The purpose of the present invention, which was created in view of the above circumstances, is that the fuel spray injected from the injector toward the cavity spreads in the circumferential direction along the wall surface of the cavity and the adjacent sprays interfere with each other. It is an object of the present invention to provide a combustion chamber structure for an internal combustion engine that suppresses the formation of an excessively rich region and reduces heat loss from the spray to the cavity wall surface.

  In order to achieve the above object, a combustion chamber structure of an internal combustion engine according to the present invention comprises a concave portion formed at the top of a piston and a plurality of fuels injected at intervals in the circumferential direction from an injector disposed above the piston. A cavity in which the spray collides, and a plurality of guide protrusions that are provided on the wall surface of the cavity at a portion where the spray collides and are formed along the inner and outer directions of the cavity, the guide protrusions, It is made of a heat insulating material.

  The guide protrusion may be formed in parallel to the injection direction of fuel injected from the injector toward the cavity.

  The guide protrusion may be made of ceramic.

  The guide protrusion may be fixed to the wall surface of the cavity by welding.

According to the combustion chamber structure of the internal combustion engine according to the present invention, the following effects can be exhibited.
(1) Since a plurality of guide protrusions are provided along the inside and outside directions of the cavity located at the portion where the spray collides with the wall surface of the cavity, the fuel spray injected from the injector toward the cavity follows the guide protrusion. While spreading is promoted, spreading in a direction intersecting the guide protrusion is suppressed. As a result, it is possible to suppress the spray from spreading in the circumferential direction along the wall surface of the cavity, to suppress the formation of a fuel rich region due to the interference between adjacent sprays, and to reduce the generation of smoke.
(2) In addition, since the guide protrusion is formed of a heat insulating material, heat loss from the spray to the cavity wall surface can be reduced, and fuel consumption deterioration can be suppressed.
(3) That is, a guide projection that performs the same function as the “guide groove” in the “combustion chamber structure of an internal combustion engine” previously created by the present inventor is formed of a heat insulating material, and also serves as a heat insulating material for fuel spraying. Since it is provided on the wall surface of the cavity, it is possible to reduce the generation of smoke while suppressing deterioration of fuel consumption.

It is explanatory drawing which shows the combustion chamber structure of the internal combustion engine which concerns on one Embodiment of this invention, (a) is a top view of a piston, (b) is a sectional side view of the piston. It is the II-II sectional view taken on the line of FIG.1 (b), and shows the cross section of a guide protrusion. It is explanatory drawing which shows a mode that the spray collided with the guide protrusion, (a) is sectional drawing of a guide protrusion and spray, (b) is the top view which looked at the guide protrusion and spray from the injection direction. It is explanatory drawing of the prior art example which shows typically a mode that the spray of the fuel injected from the injection hole of the injector collides with a cavity wall surface, and adjacent sprays interfere, (a) is just before a collision, (b) is Immediately after the collision, (c) is an explanatory view after a predetermined time has elapsed after the collision.

  An embodiment of the present invention will be described with reference to the accompanying drawings.

  As shown in FIGS. 1 (a) and 1 (b), a combustion chamber structure A of an internal combustion engine according to the present embodiment includes a cavity 3 recessed in the top of a piston 1 of a diesel engine, and a wall surface of the cavity 3 A plurality of guide protrusions 4 provided along the inner and outer directions of the cavity 3 are provided in 3x.

  The shape of the cavity 3 may be various shapes such as a toroidal type, a reentrant type, and a shallow dish type. The fuel spray F (see FIG. 3A) injected from the injector 2 collides with the cavity 3. In addition, the arrow Fx shown with a virtual line in Fig.1 (a) and FIG.1 (b) represents the injection direction of fuel, ie, the spray F. FIG.

  The injector 2 is mounted on a cylinder head 5 above the piston 1, and a plurality of injection holes are formed in the lower end portion of the injector 2 at intervals in the circumferential direction of the cavity 3. The injection timing of the fuel injected from each nozzle hole of the injector 2 toward the cavity 3 is earlier than that of general diesel combustion (diffusion combustion) in order to perform PCI combustion, and before the piston 1 reaches the top dead center. Is set to

  The diameter of each nozzle hole in the injector 2 is to atomize the injected fuel to promote evaporation and to quickly generate a lean and uniform premixed gas, so that the PCI combustion operating range can be changed from a light load range to a medium to high load range. In order to expand to the region side, the diameter is reduced. Specifically, the diameter of each nozzle hole is set to, for example, about 0.1 to 0.05 mm in consideration of fuel atomization and workability. However, it is not limited to this value. Further, in an operation region (for example, a high load region) where PCI combustion cannot be applied even if the diameter of each nozzle hole is reduced, the injection timing of the fuel injected from each nozzle hole is changed to a general diffusion combustion (fuel This is set to the injection timing when the air-fuel mixture is ignited during the injection, i.e., when the piston 1 reaches top dead center or in the vicinity thereof.

  In the injector 2 in which the diameter of the nozzle hole is reduced in this way, as described above, in order not to deteriorate the fuel consumption at the full load, the required fuel amount is set for a certain period (for example, within 30 degrees in crankshaft angle). However, the present invention is not limited to this, and it is necessary to ensure the total area of the injection holes that can be injected into the inside, and the formation of multiple injection holes is essential. For this reason, the injector 2 is provided with a plurality of (for example, twenty, but not limited to) nozzle holes at intervals in the circumferential direction. As a result, the interval between the adjacent nozzle holes becomes narrow, and after the fuel spray F injected from the adjacent nozzle holes collides with the wall surface 3x of the cavity 3, it spreads in the circumferential direction and easily interferes, and the amount of smoke generated Tend to increase.

  Therefore, as shown in FIGS. 1A and 1B, a plurality of guide protrusions 4 along the inner and outer directions of the cavity 3 are located at the portion where each spray F collides with the wall surface 3 x of the cavity 3. The spray F (see FIGS. 3A and 3B) is prevented from spreading in the circumferential direction of the cavity 3. In FIG. 1A, only the guide projection 4 corresponding to the fuel spray F injected from the four injection holes of the injector 2 in the injection direction indicated by the arrow Fx is shown. Since a plurality of (for example, 20) fuels are injected from 2 at intervals in the circumferential direction, the guide projections 4 are provided at each of the portions where the plurality of sprays F collide with the wall surface 3x of the cavity 3.

  The guide protrusion 4 is formed in parallel with the injection direction Fx of the fuel injected from each nozzle hole of the injector 2 toward the cavity 3 in a plan view from above the top of the piston 1. A guide projection group 4x composed of a plurality of guide projections 4 is formed. Each guide projection group 4x functions as a dike (resistance) for fuel that guides the fuel injected from each injection hole of the injector 2 in the inside and outside of the cavity 3 and spreads in the circumferential direction of the cavity 3.

  As shown in FIG. 1B, the guide protrusions 4 constituting the guide protrusion group 4x may be arranged from the central portion 3a of the cavity 3 to the bottom surface 3b and the side surface 3c. As shown in FIG. 4, the same arrangement may be adopted except for the vicinity of the central portion 3a of the cavity 3. In short, the guide protrusion 4 may be disposed at least in the cavity 3 where the spray F collides.

  Between adjacent guide projection groups 4x, a region 6 where no projection exists is formed as shown in FIG. However, the guide protrusion 4 may be provided also in this region 6. The guide protrusion 4 provided in the region 6 is not limited to be parallel to the guide protrusion group 4x as long as the spread of the spray F in the cavity circumferential direction can be suppressed.

  In the guide projection group 4x, the height H from the valley bottom to the peak of each guide projection 4 is zero at the central portion 3a of the cavity 3, and gradually extends from the central portion 3a to the bottom surface 3b as shown in FIG. It may be set to a substantially constant height from the bottom surface 3b to the side surface 3c, but it may be set to a substantially constant height over the entire region. You may make it low gradually etc. over other parts along it. Further, the height H may be varied depending on the position of one guide projection group 4x in the cavity circumferential direction. In short, it is sufficient that the spread of the spray F in the circumferential direction of the cavity can be suppressed.

  The specific height H of the guide protrusion 4 and the distance W between adjacent peaks are not particularly limited. For example, the height H is about 1 to 5 mm, and the distance W is 2 to 10 mm. It is conceivable to make the degree.

  By the way, when the above-described guide protrusion 4 (guide protrusion group 4x) is provided on the wall surface 3x of the cavity 3 on which the spray F collides, the collision surface area between the spray F and the wall surface 3x of the cavity 3 is caused by the unevenness of each guide protrusion 4. It becomes larger than a normal thing without the guide protrusion 4. For this reason, the amount of heat loss from the spray F to the wall surface 3x of the cavity 3, that is, the surface of the combustion chamber is increased, and fuel consumption is deteriorated.

  Therefore, the guide protrusion 4 is formed of a heat insulating material (a material having a lower heat transfer coefficient than the piston 1 in which the cavity 3 is recessed) to suppress heat loss from the spray F to the wall surface 3x of the cavity 3.

  As shown in FIGS. 2, 3 (a), and 3 (b), the guide projection group 4 x made up of a plurality of guide projections 4 covers the portion where the spray F collides with the wall surface 3 x of the cavity 3. Is provided. Therefore, by forming the guide projection group 4x with the heat insulating material, the portion of the wall surface 3x of the cavity 3 where the spray F collides is covered with the heat insulating material, and when the spray F collides with the guide projection group 4x, Heat loss from F to the wall surface 3x of the cavity 3 is reduced. 2 and 3 (a), the number of guide protrusions 4 constituting the guide protrusion group 4x is different. However, this is only for convenience of drawing for easy viewing, and is actually the same number.

Ceramic is used for the heat insulating material. For example, ceramics such as alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), etc., and hollow ceramic beads are confined in these ceramics. A composite material or the like is used.

  The guide protrusion 4 made of ceramic is fixed to the wall surface 3x of the cavity 3 by welding or the like. For example, as shown by a broken line 7 in FIG. 2, the above-mentioned ceramic single body or the composite material in which the hollow ceramic beads are confined in the ceramic is placed on the wall surface 3x of the metal cavity 3 (the inside and outside directions of the cavity 3). ) To form the first layer by welding like overlay welding, and similarly, the same material is welded narrower than the first layer to form the second layer, and the welding is repeated in the same procedure thereafter. The mountain-shaped guide protrusion 4 is formed. The first layers of the adjacent guide protrusions 4 are connected to each other, and a guide protrusion group 4x composed of a plurality of guide protrusions 4 covers a portion where the spray F on the wall surface 3x of the cavity 3 collides.

  The operation of this embodiment will be described.

  As shown in FIGS. 3A and 3B, the fuel spray F injected from each injection hole of the injector 2 collides with the guide projection group 4 x provided on the wall surface 3 x of the cavity 3.

  The fuel that has collided with the guide projection group 4x is guided along the guide projection 4 of the guide projection group 4x by a groove 8 (see FIG. 2) formed between adjacent guide projections 4 to the inside and outside of the cavity 3. The crest portion of each guide projection 4 functions as a bank (resistance) when the fuel about to spread in the circumferential direction of the cavity 3 gets over, so that the spread of the cavity 3 in the circumferential direction is suppressed. In FIGS. 3A and 3B, the symbol Fa indicates the neck region of the spray F, and the symbol Fb indicates the spreading region of the spray F.

  When the fuel spray F injected from each injection hole of the injector 2 collides with the guide projection group 4x provided on the wall surface 3x of the cavity 3, a plurality of guide projections 4 as shown by arrows X in FIG. Since the resistance is small with respect to the extending direction of each of them, it spreads along that direction, and on the other hand, as shown by the arrow Y, each of them in the direction crossing the guide protrusion 4 (adjacent direction of the plurality of guide protrusions 4). Since it is necessary to get over the mountain portion of the guide protrusion 4, the resistance is relatively large and the spread is suppressed.

  In the present embodiment, as shown in FIG. 1A, the guide protrusion 4 is formed in parallel with the fuel injection direction Fx in plan view from the top of the piston 1. Therefore, the guide protrusion 4 is arranged orthogonal to the fuel that is going to spread in the circumferential direction of the cavity 3 as indicated by the arrow Y, and gives resistance to the fuel that is going to spread in the circumferential direction of the cavity 3 accurately. be able to.

  Therefore, the fuel spray F injected from each nozzle hole of the injector 2 is prevented from spreading in the circumferential direction along the wall surface 3x of the cavity 3 after colliding with the wall surface 3x of the cavity 3, and the adjacent sprays F It is possible to suppress the formation of a fuel rich region due to the interference, and to reduce the generation of smoke.

  In addition, since the guide protrusion 4 with which the spray F collides is formed of a heat insulating material, the portion of the wall surface 3x of the cavity 3 where the spray F collides is covered with the heat insulating material, and the spray F collides with the guide protrusion group 4x. When it does, the heat loss from the spray F to the wall surface 3x (combustion chamber wall surface) of the cavity 3 is reduced. Therefore, it is possible to reduce deterioration in fuel consumption due to such heat loss.

  As described above, in the present invention, the “guide groove” (refer to the description of the “problem to be solved by the invention”) in the “combustion chamber structure of an internal combustion engine” previously created by the present inventor and Since the guide protrusion 4 that performs the same function is formed of a heat insulating material and is mounted on the wall surface 3x of the cavity 3 as a heat insulating material for the fuel spray F, it is possible to reduce the generation of smoke while suppressing deterioration of fuel consumption. it can.

DESCRIPTION OF SYMBOLS 1 Piston 2 Injector 3 Cavity 3x Wall surface 4 Guide protrusion 4x Guide protrusion group F Spray Fx Injection direction A Combustion chamber structure

Claims (4)

A cavity that is recessed at the top of the piston and that collides with a plurality of fuel sprays that are circumferentially spaced from an injector disposed above the piston;
A plurality of guide projections provided along the inner and outer directions of the cavity, provided on the wall surface of the cavity at positions where the spray collides,
A combustion chamber structure of an internal combustion engine, wherein the guide protrusion is formed of a heat insulating material. The combustion chamber structure of the internal combustion engine according to claim 1, wherein the guide protrusion is formed in parallel to an injection direction of fuel injected from the injector toward the cavity. The combustion chamber structure of the internal combustion engine according to claim 1, wherein the guide protrusion is made of ceramic. The combustion chamber structure of the internal combustion engine according to any one of claims 1 to 3, wherein the guide protrusion is fixed to a wall surface of the cavity by welding.

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