JP4456528B2 - Premixed compression self-ignition internal combustion engine - Google Patents

Description

  The present invention relates to a premixed compression self-ignition internal combustion engine.

  In recent years, in the field of internal combustion engines such as diesel engines, stricter exhaust regulations have been enforced year by year due to the growing environmental problems, reducing emissions of soot, smoke, CO, NOx and other air pollutants, and fuel consumption There is a strong demand for improvement.

  However, since diesel engines spray fuel on compressed air in a cylinder and burn it by self-ignition, light and dark mixing tends to occur in the mixture of air and fuel, and soot and smoke can be produced where the fuel concentration is high. It is easy to generate NOx near the theoretical ratio.

  In view of such circumstances, in recent years, a premixed compression self-ignition system has attracted attention. This premixed compression auto-ignition method injects fuel from the beginning to the middle of the compression stroke before the piston reaches top dead center, so that the fuel and air are uniformly mixed in advance in the combustion chamber. This is a technology that raises the temperature and raises the pressure by compression by the self-ignition at the ignition point of the fuel. According to this method, the generation of smoke can be suppressed by a high excess air ratio, and the generation of NOx can be suppressed because the flame temperature can be made uniform. Also known is a technique in which a normal spray combustion system is combined with a premixed compression self-ignition system to perform a plurality of stages of injection.

  However, in the premixed compression self-ignition system, fuel is injected when the piston is at a low position before reaching the top dead center, so that the fuel may directly collide with the cylinder liner. In the process of raising the piston, the temperature and pressure in the cylinder do not rise so much, so the fuel that has collided with the cylinder liner is likely to adhere as it is without evaporating. The adhering fuel may be scraped off by the piston to dilute the oil, or may be discharged as white smoke without contributing to the combustion as it is, and naturally also causes a deterioration in fuel consumption.

  On the other hand, in Patent Document 1 below, a fuel injection port is formed in which a concave dome (head cavity) is formed on the explosion surface of the cylinder head facing the top surface of the piston, and the bottom of the dome opens toward the peripheral wall surface of the dome. A diesel engine with an injection nozzle having the following is disclosed.

  When premixed compression auto-ignition is performed using this technique, the fuel collides with the peripheral wall of the dome before reaching the cylinder liner, and the direction is changed and atomized. It becomes possible to prevent adhesion.

JP 10-141622 A

  In Patent Document 1, the dome of the cylinder head is formed in a hemispherical shape, and most of the fuel that collides with the peripheral wall surface of this dome diffuses downward, but part of it diffuses upward. However, since there is little space above the fuel collision portion, there is a drawback that a fuel rich mixture is generated and smoke is likely to be generated.

  In the premixed compression self-ignition internal combustion engine, the present invention prevents the injected fuel spray from directly colliding with the cylinder liner and promotes the diffusion of the fuel and the mixing with the air, thereby producing a uniform lean mixture. The purpose of this is to suppress the generation of NOx and smoke.

In the first aspect of the present invention, a concave head cavity is formed on the explosion surface of the cylinder head facing the top surface of the piston, and a plurality of fuels are injected at the bottom of the head cavity toward the peripheral wall surface of the head cavity. An injection nozzle having a fuel injection port is provided, the bottom surface of the head cavity is formed in a flat surface substantially parallel to the explosion surface of the cylinder head, and the peripheral wall surface of the head cavity is directed toward the piston side. are inclined in expanded form, the peripheral wall surface of the head cavity, the portion where the fuel collides, bulging portion that bulges to the injection nozzle side is provided with the top portion of the bulging portion, the injection It is linearly formed in the radial direction centering on the nozzle, and the peripheral wall surface has an uneven shape along the circumferential direction centering on the injection nozzle .

According to the second aspect of the present invention, a concave head cavity is formed on the explosion surface of the cylinder head facing the top surface of the piston, and a plurality of fuels are injected at the bottom of the head cavity toward the peripheral wall surface of the head cavity. An injection nozzle having a fuel injection port is provided, the bottom surface of the head cavity is formed in a flat surface substantially parallel to the explosion surface of the cylinder head, and the peripheral wall surface of the head cavity is directed toward the piston side. are inclined in expanded form, the peripheral wall surface of the head cavity, the portion where the fuel collides, the bulge portion is provided with a bulge to the injection nozzle side, the apex of the bulging portion, away from the injection nozzle according to you it is inclined to the downstream side of the swirl flow.

According to a third aspect of the present invention, a concave head cavity is formed on the explosion surface of the cylinder head facing the top surface of the piston, and a plurality of fuels are injected at the bottom of the head cavity toward the peripheral wall surface of the head cavity. An injection nozzle having a fuel injection port is provided, the bottom surface of the head cavity is formed in a flat surface substantially parallel to the explosion surface of the cylinder head, and the peripheral wall surface of the head cavity is directed toward the piston side. It is inclined in expanded form, the inclination angle of the peripheral wall surface of the head cavity, that are different in part between the impinging fuel injected from the fuel injection port adjacent to each other.

In a fourth aspect of the present invention, a concave head cavity is formed on the explosion surface of the cylinder head facing the top surface of the piston, and a plurality of fuels are injected at the bottom of the head cavity toward the peripheral wall surface of the head cavity. An injection nozzle having a fuel injection port is provided, the bottom surface of the head cavity is formed in a flat surface substantially parallel to the explosion surface of the cylinder head, and the peripheral wall surface of the head cavity is directed toward the piston side. are inclined in expanded form, the inclination angle of the peripheral wall surface of the head cavity, are different in the portion between the colliding fuel injected from the fuel injection port adjacent to each other, wherein the circumferential wall surface of the head cavity depth that is formed in a plurality of stages of stepwise directionally.

According to the present invention, since the fuel injected from the fuel injection port collides with the peripheral wall surface of the head cavity, it is prevented from directly adhering to the cylinder liner, and the fuel is atomized by the collision. Mixing with air is promoted. In addition, since the bottom surface of the head cavity is formed on a flat surface substantially parallel to the explosion surface of the cylinder head, it is possible to form a wider space on the bottom surface side of the head cavity than the collision portion of the fuel. And mixing of fuel and air in the head cavity can be promoted.

According to the first aspect of the present invention, the fuel can be actively diffused in the circumferential direction of the injection nozzle by causing the fuel to collide with the bulging portion formed on the peripheral wall surface of the head cavity, so that it is uniform with the air. Mixing can be promoted.

According to the second aspect of the present invention, the fuel can be actively diffused by causing the fuel to collide with the bulging portion formed on the peripheral wall surface of the head cavity, and further, the diffused fuel can be placed on the swirl flow. To promote uniform mixing with air.

According to the invention of claim 3 , after the fuel injected from the adjacent fuel injection port collides with the peripheral wall surface of the head cavity, it is less likely to overlap each other, and the occurrence of fuel concentration is suppressed, Uniform mixing can be promoted. In addition, since unevenness is formed on the peripheral wall surface of the head cavity and the surface area is enlarged, evaporation of the attached fuel can be promoted.

According to the invention of claim 4 , the fuel injected from the adjacent fuel injection ports does not overlap each other after colliding with the peripheral wall surface of the head cavity, and not only improves the space utilization rate of the air-fuel mixture. Further, it is possible to suppress the occurrence of fuel density and promote uniform mixing with air. In addition, since unevenness is formed on the peripheral wall surface of the head cavity and the surface area is enlarged, evaporation of the attached fuel can be promoted.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The internal combustion engine of the present embodiment is a premixed compression auto-ignition type diesel engine, and a basic operation process will be briefly described before the details of the structure are described. FIG. 1 is an explanatory diagram showing an outline of the operation process of the diesel engine of the present embodiment. In this diesel engine, a piston 11 is slidably fitted to a cylinder 10, and a fuel injection nozzle 13, an intake hole 14, and an exhaust hole 15 are provided in a cylinder head 12, and the intake hole 14 and the exhaust hole 15 are provided. These can be opened and closed by intake and exhaust valves 17 respectively. A combustion chamber 18 is formed between the top surface of the piston 11, the side surface of the cylinder 10, and the bottom surface of the cylinder head 12.

  In FIG. 1, (a) is an intake stroke, (b) is a compression stroke, (c) is an expansion stroke, and (d) is an exhaust stroke. In the intake stroke (a), the piston 11 moves from the top dead center to the bottom dead center, and air is taken into the combustion chamber 18 from the intake hole 14 during that time. In the compression stroke of (b), the intake air is compressed and fuel S is injected (pre-injected) from the fuel injection nozzle 13 from the initial stage to the middle stage of compression to form a mixture of air and fuel ( Premix). When the piston 11 is in the vicinity of the top dead center, the premixed gas is heated and pressurized by compression and self-ignited. Further, near the top dead center, the fuel S is injected again (main injection; shown in (c)), the fuel S immediately diffuses while evaporating, and self-ignites in a high-temperature and high-pressure atmosphere. The combustion by the main injection improves the output and burns HC and CO generated by the combustion of the premixed gas. In the expansion stroke (c), the piston 11 is lowered, and in the exhaust stroke (d), the exhaust valve 17 is opened, and the exhaust in the combustion chamber 18 is discharged from the exhaust hole 15 by the lift of the piston 11.

  Therefore, in the present embodiment, multiple stages of injection are performed, that is, pre-injection for premixing and main injection for normal compression self-ignition combustion (diesel combustion). And in order to perform such multi-stage injection, optimization of the shape of the said cylinder 10, the piston 11, and the fuel-injection nozzle 13 is achieved. Hereinafter, this point will be described in detail.

[Configuration of Piston 11]
2 and 3 are cross-sectional views of a cylinder top portion of a diesel engine to which the present invention is applied. In particular, FIG. 2 is a state where the piston 11 is below the top dead center (a state where pre-injection is performed), FIG. 3 shows a state where the piston 11 is near top dead center (a state where main injection is performed). As shown in FIG. 2, a concave piston cavity 20 is formed on the top surface of the piston 11. A central protrusion 21 that protrudes toward the cylinder head 12 is formed at the center of the bottom of the piston cavity 20, and the central protrusion 21 has a large outer diameter at the base (bottom) and a smaller outer diameter at the top. The outer peripheral surface 22 is an inclined surface that is inclined so as to expand toward the anti-cylinder head 12 side. C is attached to the expansion angle of the outer peripheral surface 22.

  The bottom surface 24 of the piston cavity 20 is formed in an arc surface that is gently connected to the inclined surface 22 of the central projecting portion 21. The outer peripheral surface 25 of the piston cavity 20 is formed as a circular arc surface continuous from the bottom surface 24 and extends to the top surface of the piston 11. The opening 26 of the piston cavity 20 is slightly inward in the radial direction from the outer peripheral surface 25, thereby forming a lip portion 27 that protrudes inward in the radial direction. In FIG. 2, φY is given to the opening diameter of the piston cavity 20, and φZ is given to the maximum outer diameter of the outer peripheral surface 25 of the piston cavity 20.

[Configuration of Cylinder Head 12]
FIG. 5 is an enlarged cross-sectional view of the cylinder head. As shown in FIGS. 2, 3, and 5, the explosive surface 28 of the cylinder head 12 facing the top surface of the piston 11 is provided with a concave head cavity 29. It is formed in a conical shape. That is, the bottom surface 30 of the head cavity 29 is formed as a flat surface substantially parallel to the explosion surface 28, and the peripheral wall surface 31 of the head cavity 29 is expanded toward the piston 11 side (lower side in FIG. 2). It is inclined to. In FIG. 2, φX is attached to the opening diameter of the head cavity 29, and A is attached to the opening angle of the peripheral wall surface 31.

  6 is a cross-sectional view taken along the line VI-VI in FIG. The cylinder head 12 is provided with two valve seats 33 for intake and exhaust, and each valve seat 33 is provided with a valve 17 for intake and exhaust. The head cavity 29 is surrounded by the four valves 17 and has a size that circumscribes each valve seat 33. However, even if it does not necessarily circumscribe each valve seat 33, it can be formed as large as possible within the range of the circumscribed circle.

  As shown in FIG. 5, in the present embodiment, a fuel collision portion 34 formed of a material different from the cylinder head 12 is provided on the peripheral wall surface 31 of the head cavity 29. The fuel collision portion 34 has a width over the entire depth of the head cavity 29 and is formed to have a uniform thickness over the width. As a raw material, what has heat resistance and heat insulation is used, for example, SUH heat-resistant steel etc. are used. However, the fuel collision part 34 may be omitted, and the peripheral wall surface 31 may be made of the material of the cylinder head 12 itself.

[Configuration of Fuel Injection Nozzle 13]
As shown in FIGS. 2 and 3, the fuel injection nozzle 13 is provided at the center of the bottom surface 30 of the head cavity 29. The injection nozzle 13 has a small-diameter portion 36 that accommodates a needle valve in the lower portion, and a large-diameter portion 37 that is larger in diameter than the small-diameter portion 36 in the upper portion. A stepped portion 38 is formed in the upper portion. The injection nozzle 13 is attached to a holding hole 39 formed in the cylinder head 12 via a holder 40. The holder 40 is formed in a cylindrical shape, and the inside of the cylinder is formed in a shape that matches the outer shape of the injection nozzle 13. Between the inner surface of the holder 40 and the small-diameter portion 36, a cylindrical first sealing material 41 is provided to keep the airtight therebetween, and an annular second seal is provided between the holder 40 and the step portion 38. A material 42 is interposed. The tip of the holder 40 is exposed on the bottom surface of the head cavity 29 through the holding hole 39. In addition, a bent portion 43 protrudes from the front end portion of the holder 40 in the radially inward direction, and the first seal material 41 is received from the lower side by the bent portion 43.

  As shown in FIG. 5, a plurality of fuel injection ports 44 are formed at the tip of the injection nozzle 13. Four to ten fuel injection ports 44 are formed radially about the nozzle axis O1. Each injection port 44 opens toward the peripheral wall surface 31 (fuel collision part 34) of the head cavity 29, respectively.

[Relationship Between Head Cavity 29 and Fuel Injection Nozzle 13]
As shown in FIG. 2, the fuel injected from the fuel injection port 44 of the injection nozzle 13 diffuses in a radial direction conically or horizontally as a whole. When the diffusion angle (spray angle) of the spray axis X1 at this time is B, 120 ° ≦ B ≦ 180 ° is set. By setting in this way, the fuel directly collides with the peripheral wall surface 31. By this collision, the direction of the fuel is changed and the fuel is atomized.

  Therefore, when pre-injection is performed (FIGS. 1B and 2), it is possible to prevent the fuel from directly colliding with the cylinder liner 46 and adhering thereto. Further, since the fuel is atomized by the collision with the peripheral wall surface 31, the mixing with the air can be further promoted. In FIG. 2, as a comparison, the spray axis X <b> 2 when it does not collide with the peripheral wall surface 31 of the head cavity 29 is illustrated by a two-point difference line. In this case, the fuel collides with the cylinder liner 46.

  If the spray angle B is set to 120 ° or more, it is necessary to form the head cavity 29 deep in order to cause the fuel to collide with the peripheral wall surface 31 of the head cavity 29. This is because it involves a change in structure. The reason why the spray angle B is set to 180 ° or less is that if it is more than that, the flow coefficient in the injection nozzle 13 decreases. In addition, when performing the main injection, a large amount of fuel diffuses in the upper side (the bottom surface 30 side) in the head cavity 29, and the fuel concentration in the portion becomes high, which causes the generation of smoke.

  On the other hand, the expansion angle A of the peripheral wall surface 31 of the head cavity 29 is set to 60 ° ≦ A ≦ 120 °. The smaller the spread angle A, the lower the possibility that the fuel after the collision will adhere to the cylinder liner 46. However, reducing the expansion angle A hinders fuel diffusion when performing main injection (FIGS. 1C and 3). That is, it becomes difficult to promote the mixing of the fuel after the main injection and collides with the peripheral wall 31 and a large amount of air existing outside in the cylinder 10 in the radial direction, which hinders the formation of a uniform air-fuel mixture. Further, a large amount of fuel colliding with the peripheral wall surface 31 of the head cavity 29 is diffused to the upper side in the head cavity 29, and smoke is likely to be generated due to excessive fuel concentration in the head cavity 29. Therefore, in the present embodiment, by setting the expansion angle A as described above, appropriate mixture formation is realized in both the pre-injection and the main injection.

  Further, assuming that the intersection angle between the peripheral wall surface 31 of the head cavity 29 and the fuel spray axis X1 on the piston 11 side is D, 120 ° ≦ D <180 ° is set. When D is 120 ° or less, in the case of performing main injection, the diffusion of fuel to the upper side in the head cavity 29 increases, and smoke is likely to be generated. This is because the fuel hardly collides with the peripheral wall surface 31.

  The head cavity 29 has a bottom surface 30 formed on a flat surface substantially parallel to the explosion surface 28 of the cylinder head 12, and a corner 47 is formed at the boundary between the bottom surface 30 and the peripheral wall surface 31 as shown in FIG. 5. Has been. Due to the presence of the corner portion 47, a space R wider than the conventional technique (dome-shaped or conical head cavity) is secured on the upper side in the head cavity 29. Therefore, even if the fuel that collided with the peripheral wall surface 31 of the head cavity 29 diffuses to the upper side (the bottom surface 30 side) of the head cavity 29, mixing with air is promoted as compared with the prior art.

  The fuel injected from the fuel injection port 44 does not have to collide with the peripheral wall surface 31 as long as it is set so that at least the spray axis X1 collides with the peripheral wall surface 31. In other words, when the distance in the cylinder axial direction between the portion where the spray axis X1 collides with the peripheral wall surface 31 and the explosion surface 28 is E, it is only necessary to satisfy the condition of E> 0. The speed of the fuel droplets is highest on the spray axis X1, and the speed decreases due to the shearing action with the surrounding air as it goes radially outward, so the fuel below the spray axis X1 becomes mist-like. The penetrating force is reduced, so that the cylinder liner 46 is less likely to reach the cylinder liner 46 without colliding with the peripheral wall surface 31, and the cylinder liner 46 is diffused by the fuel colliding with the peripheral wall surface 31 being diffused as a downward component. This is because the penetrating ability to go to is further weakened.

  The fuel is in the form of a liquid column immediately after exiting from the fuel injection port 44 and then reaches the peripheral wall surface 31 while diffusing in a mist form. In the present embodiment, the distance (length) L of the spray axis X1 from the fuel injection port 44 to the peripheral wall surface 31 and the diameter φd of the fuel injection port 44 are set in a relationship of L / φd ≧ 50. By setting in this way, the liquid column portion S1 (length is indicated by L1) of the fuel S directly collides with the peripheral wall surface 31 and does not adhere thereto.

  If the liquid columnar fuel adheres to the peripheral wall surface 31 of the head cavity 29 during low load operation such as when starting the engine, white smoke is discharged without being involved in combustion. Such a problem can be solved by setting the diameter φd. The above relationship between the distance L and the diameter φd is particularly effective when the fuel injection pressure is about 50 MPa or more.

  As described above, the fuel collision portion 34 having heat insulation and heat resistance is provided on the peripheral wall 31 of the head cavity 29. Although the cylinder head 12 is cooled by the cooling water, the temperature of the fuel collision part 34 is difficult to be lowered due to the heat insulating property. Therefore, the fuel that has collided with the fuel collision part 34 is easily evaporated by the heat of the fuel collision part 34, and the attached fuel is prevented from being discharged as white smoke.

  As shown in FIG. 6, the head cavity is provided so as to circumscribe the four valve seats 33 for intake and exhaust. That is, the valve seat 33 is formed to the maximum extent that does not erode. As a result, the distance from the fuel injection nozzle 13 to the peripheral wall surface 31 of the head cavity 29 can be made as long as possible, and the liquid column portion S1 of the fuel is prevented from adhering to the peripheral wall surface 31.

[Relationship between head cavity and piston cavity]
The opening diameter φX of the head cavity 29 is formed smaller than the diameter φY of the opening 26 of the piston cavity 20. Specifically, there is a relationship of φY ≧ 1.2 × φX. Therefore, in the case of performing main injection (FIGS. 1C and 3), most of the fuel injected from the injection nozzle 13 and colliding with the peripheral wall surface 31 of the head cavity 29 is introduced into the piston cavity 20. The squish flow into the piston cavity 20 during the compression stroke and the reverse squish flow outside the piston cavity 20 during the expansion stroke cause a strong turbulence in the flow of the fuel, and the air flows outside the piston 11 in the radial direction. Mixing is promoted more.

  The diameter φY of the opening 26 of the piston cavity 20 is formed smaller than the outer diameter (maximum outer shape) φZ of the outer peripheral surface 25 of the piston cavity 20, and the opening 26 has a lip portion protruding radially inward. Since 27 is formed, a stronger squish flow and a reverse squish flow can be obtained.

[Relationship between injected fuel and piston cavity 20]
The protrusion 21 formed in the piston cavity 20 is formed in a mountain shape as described above, and the expansion angle C of the outer peripheral surface 22 is set to C ≦ 140 °. In the case of performing the main injection (FIGS. 1C and 3), the fuel injected from the injection nozzle 13 and colliding with the head cavity 29 spreads further in a conical shape, and the outer peripheral surface 22 of the protrusion 21 in the piston cavity 20. Collide with the slope. Therefore, even after colliding with the projecting portion slope 22, the fuel is further guided radially outward to promote mixing with air.

  As shown in FIG. 3, the diameter φV of the portion where the fuel collides with the piston cavity 20 and the maximum outer diameter φZ of the piston cavity 20 are in a relationship of φV ≧ 0.5 × φZ. Therefore, when the main injection is performed, the fuel spreads radially outward in the piston cavity, and mixing with air is promoted. Therefore, the fuel is injected near the center of the piston cavity 20 to prevent the occurrence of “thermal pinch” in which the flame contracts without using radially outward air.

  The main injection may be delayed not only when the piston 11 is substantially at the top dead center but also after passing the top dead center mainly for NOx reduction. In such a case, if the injected fuel is injected out of the piston cavity 20, the generation of a uniform air-fuel mixture is hindered and smoke is increased. Therefore, in the present embodiment, when the piston 11 is within the range of the crank angle ± 40 ° from the top dead center, the fuel injection angle B and the peripheral wall surface are ensured so that the injected fuel surely enters the piston cavity 20. An expansion angle A of 31, an opening diameter φY of the piston cavity 20 and the like are set. As an example, FIG. 4 shows the arrangement of the pistons 11 when the crank angle is top dead center ± 30 °.

  In the present embodiment, when the fuel spray axis X1 that collides with the peripheral wall surface 31 spreads out to the maximum in the radial direction, that is, after the fuel spray axis X1 collides with the peripheral wall surface 31, The spray axis X 1 is set so as to enter the piston cavity 20, assuming the case of diffusion along the inclination of the wall surface 31.

[Second Embodiment]
7 and 8 are cross-sectional views showing a second embodiment related to the combustion collision portion 34. In this embodiment, a recessed portion 55 is formed on the contact surface of the fuel collision portion 34 with respect to the cylinder head 12, and the heat insulating layer 56 is formed by allowing air to exist in the recessed portion 55.

  The recess 55 shown in FIG. 7 has a rectangular cross section, and the recess 55 shown in FIG. 8 has a semicircular cross section, and a plurality (three) of them are formed in the depth direction of the head cavity 29.

  As in the present embodiment, a heat insulating layer made of an air layer is formed between the cylinder head 12 and the fuel collision part 34 to improve heat insulation, maintain the surface temperature of the fuel collision part 34, and Evaporation can be promoted.

[Third Embodiment]
9A and 9B show a third embodiment of the head cavity 29, where FIG. 9A is a plan view of the head cavity viewed from the piston 11 side, and FIG. 9B is a cross-sectional view taken along the line bb in FIG. It is. In the present embodiment, a plurality of bulging portions 58 that bulge radially inward are formed on the circumferential wall surface 31 of the head cavity 29 in the circumferential direction, and the circumferential wall surface 31 substantially has an uneven shape.

  The bulging portion 58 has a substantially triangular mountain shape, and the top portion 58 </ b> A is linearly formed in the radial direction with the injection nozzle 13 as the center. A fitting portion 59 is formed between the adjacent bulging portions 58, and a bottom portion 59 </ b> A of the fitting portion 59 is also formed linearly in a radial direction centering on the injection nozzle 13.

  The fuel injection nozzle 13 has eight fuel injection ports 44 at equal intervals, and eight bulging portions 58 are formed corresponding to the number of fuel injection ports 44. The fuel injected from each fuel injection port 44 collides with the top 58 </ b> A of the corresponding bulging portion 58. In FIG. 9, the spray axis X1 of the fuel injected from each fuel injection port 44 is indicated by a one-dot chain line.

  In the present embodiment, the fuel injected from the fuel injection port 44 can be diffused in the circumferential direction toward the fitting portion 59 by colliding with the bulging portion 58. Therefore, it is further useful for forming a uniform air-fuel mixture.

  The top portion 58A of the bulging portion 58 and the bottom portion 59A of the fitting portion 59 may be formed in a gently curved waveform.

[Fourth Embodiment]
10A and 10B show a fourth embodiment of the head cavity 29, where FIG. 10A is a plan view of the head cavity viewed from the piston 11 side, and FIG. 10B is a sectional view taken along the line bb in FIG. It is. This embodiment is the same as the third embodiment in that the bulging portion 58 is formed on the peripheral wall surface 31 of the head cavity 29, but the top portion 58A of the bulging portion 58 is inclined in the circumferential direction. Is different. Specifically, the top portion 58 </ b> A of the bulging portion 58 is inclined toward the downstream side of the swirl flow (indicated by the arrow T) as the distance from the injection nozzle 13 increases.

  In the present embodiment, the fuel injected from the fuel injection port 44 collides with the swirl flow downstream surface of the swollen portion 58. Therefore, a large amount of the fuel after the collision is diffused downstream of the swirl flow and appropriately flows along the swirl flow. Thereby, mixing with air can be promoted and a uniform air-fuel mixture can be formed.

  In addition, even when the top portion 58A of the bulging portion 58 is formed radially around the injection nozzle 13 as in the third embodiment, the fuel collides with the surface of the bulging portion 58 on the downstream side of the swirl flow. As a result, substantially the same effect can be obtained.

[Fifth Embodiment]
11A and 11B show a fifth embodiment of the head cavity 29, where FIG. 11A is a plan view of the head cavity viewed from the piston 1 side, and FIG. 11B is a cross-sectional view taken along the line bb in FIG. It is. In the present embodiment, the inclination of the peripheral wall surface 31 of the head cavity 29 is different between portions where fuels injected from the fuel injection ports 44 adjacent to each other collide. That is, a portion 31A of the peripheral wall surface 31 where the fuel injected from a certain fuel injection port 44 collides and a portion 31B of the peripheral wall surface 31 where the fuel injected from the adjacent fuel injection port 44 collide have different inclinations. It has become.

  In the case of the present embodiment, the distances from the adjacent fuel injection ports 44 to the peripheral wall surface 31 of the head cavity 29 are different from each other, and the reflection angle after the collision is also different. Therefore, the fuels are less likely to overlap after colliding with the peripheral wall surface 31, and the density of the fuel is less likely to occur. Therefore, uniform mixing with air can be further promoted.

  Furthermore, when the inclination angle of the peripheral wall surface 31 is changed, irregularities are formed on the peripheral wall surface 31, and the surface area is increased. Therefore, evaporation of the fuel that has collided with the peripheral wall surface 31 can be promoted.

[Sixth Embodiment]
FIG. 12 shows a sixth embodiment relating to the head cavity 29, where (a) is a plan view of the head cavity viewed from the piston 11 side, and (b) is a cross-sectional view taken along the line bb in (a). FIG. This embodiment is a further modification of the fifth embodiment, in which the peripheral wall surface 31 is formed in a plurality of steps in the depth direction of the head cavity 29.

  In the present embodiment, the same operational effects as in the above-described embodiment can be obtained. However, since the surface area of the peripheral wall surface 31 is further increased, evaporation of the collided fuel can be further promoted. Moreover, since the fuel colliding with the peripheral wall surface 31 is reflected and diffused in various directions, uniform mixing with air can be further promoted.

[Seventh Embodiment]
13 and 14 show a seventh embodiment relating to the fuel injection nozzle 13, FIG. 13 is a cross-sectional view of the upper portion of the piston, and FIG. 14 is a cross-sectional view of the tip of the injection nozzle. In the present embodiment, the fuel injection ports 44 of the fuel injection nozzle 13 are provided in two upper and lower stages. In each of the upper and lower stages, a plurality of fuel injection ports are formed radially.

  The upper fuel injection port 44 (44A) is configured to collide with the peripheral wall surface 31 of the head cavity 29 as described in the above embodiment. The lower fuel injection port 44 (44B) is configured to inject fuel toward the piston as it is without colliding with the peripheral wall surface 31 of the head cavity 29.

  By dividing the fuel into two upper and lower stages in this way, the injected fuels can be prevented from overlapping each other, and it is possible to prevent the fuel in the combustion chamber 18 from being shaded and injected from the upper fuel injection port. As described in the above embodiments, the fuel does not adhere to the cylinder liner 46, and the fuel injected from the lower fuel injection port 44 </ b> B adheres to the cylinder liner 46 because it is injected toward the piston. There is no.

  By forming the upper and lower multi-stage fuel injection ports 44A and 44B, the total number of the fuel injection ports 44 can be substantially increased, and the diameters φd and φd ′ of the fuel injection ports 44 can be maintained while maintaining the fuel flow rate. Can be reduced. When the diameters of the fuel injection ports 44A and 44B are reduced, the atomization of the fuel is promoted, so that uniform mixing with air can be further promoted.

  The present invention is not limited to the above-described embodiment, and the design can be changed as appropriate.

  The present invention can be suitably employed in a premixed compression auto-ignition diesel engine.

It is explanatory drawing which shows the outline | summary of the operation process of the diesel engine of this embodiment. It is sectional drawing of the cylinder top part of the diesel engine concerning 1st Embodiment of this invention. It is sectional drawing of the cylinder top part. It is sectional drawing of the cylinder top part. It is sectional drawing which expands and shows a head cavity and a fuel injection nozzle. FIG. 6 is a cross-sectional view taken along the line VI-VI in FIG. 2. It is sectional drawing which expands and shows a head cavity and a fuel-injection nozzle concerning 2nd Embodiment of this invention. It is sectional drawing which expands and shows a head cavity and a fuel-injection nozzle concerning 2nd Embodiment of this invention. The 3rd Embodiment of this invention is shown, (a) is a top view of the head cavity seen from the piston 11 side, (b) is bb arrow sectional drawing of (a). The 4th Embodiment of this invention is shown, (a) is a top view of the head cavity seen from the piston 11 side, (b) is bb arrow sectional drawing of (a). FIG. 10 shows a fifth embodiment of the present invention, where (a) is a plan view of a head cavity viewed from the piston 11 side, and (b) is a cross-sectional view taken along the line bb in (a). The 6th Embodiment of this invention is shown, (a) is a top view of the head cavity seen from the piston 11 side, (b) is bb arrow sectional drawing of (a). It is sectional drawing of the cylinder top part to which this invention concerning 7th Embodiment of this invention is applied. It is sectional drawing of the tip of the same injection nozzle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Cylinder 11 Piston 12 Cylinder head 13 Fuel injection nozzle 20 Piston cavity 21 Projection part 21A Top surface 22 Outer surface 25 Outer surface 26 Opening 28 Explosion surface 29 Head cavity 30 Bottom surface 31 Peripheral wall surface 34 Fuel collision part 44 Fuel injection port 46 Cylinder liner

Claims (4)

A concave head cavity is formed on the explosion surface of the cylinder head facing the top surface of the piston, and an injection nozzle having a plurality of fuel injection ports for injecting fuel toward the peripheral wall surface of the head cavity is provided at the bottom of the head cavity. And
The bottom surface of the head cavity is formed as a flat surface substantially parallel to the explosion surface of the cylinder head, and the peripheral wall surface of the head cavity is inclined so as to expand toward the piston side ,
A bulging portion that bulges toward the injection nozzle is provided at a portion of the peripheral wall surface of the head cavity where the fuel collides, and the top of the bulging portion is linear in a radial direction centering on the injection nozzle. A premixed compression self-ignition internal combustion engine which is formed in a shape and has a concavo-convex shape along the circumferential direction centering on the injection nozzle . A concave head cavity is formed on the explosion surface of the cylinder head facing the top surface of the piston, and an injection nozzle having a plurality of fuel injection ports for injecting fuel toward the peripheral wall surface of the head cavity is provided at the bottom of the head cavity. And
The bottom surface of the head cavity is formed as a flat surface substantially parallel to the explosion surface of the cylinder head, and the peripheral wall surface of the head cavity is inclined so as to expand toward the piston side ,
A bulging portion that bulges toward the injection nozzle is provided at a portion of the peripheral wall surface of the head cavity where the fuel collides, and the top of the bulging portion is inclined toward the downstream side of the swirl flow as the distance from the injection nozzle increases. and that, the premixed-charge compression auto-ignition internal combustion engine. A concave head cavity is formed on the explosion surface of the cylinder head facing the top surface of the piston, and an injection nozzle having a plurality of fuel injection ports for injecting fuel toward the peripheral wall surface of the head cavity is provided at the bottom of the head cavity. And
The bottom surface of the head cavity is formed as a flat surface substantially parallel to the explosion surface of the cylinder head, and the peripheral wall surface of the head cavity is inclined so as to expand toward the piston side ,
The angle of inclination of the peripheral wall surface of the head cavity is different in the portion between the colliding fuel injected from the fuel injection port adjacent premixed compression self-igniting internal combustion engine. A concave head cavity is formed on the explosion surface of the cylinder head facing the top surface of the piston, and an injection nozzle having a plurality of fuel injection ports for injecting fuel toward the peripheral wall surface of the head cavity is provided at the bottom of the head cavity. And
The bottom surface of the head cavity is formed as a flat surface substantially parallel to the explosion surface of the cylinder head, and the peripheral wall surface of the head cavity is inclined so as to expand toward the piston side ,
The inclination angle of the peripheral wall surface of the head cavity is different between portions where the fuel injected from the fuel injection ports adjacent to each other collides, and the peripheral wall surface has a plurality of steps in the depth direction of the head cavity. that is formed, the premixed-charge compression auto-ignition internal combustion engine.

Images