JP2014224495A - Direct injection diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the interference between fuel sprays caused by an influence of a swirl and the generation of soot, in a direct injection diesel engine having two injection hole groups different in penetration forces.SOLUTION: A fuel injection nozzle arranged in the center of a reentrant-type cavity combustion chamber 5 has a first injection hole group and a second injection hole group which are different in magnitudes of inclined angles with respect to a cylinder center axial line, and an injection hole diameter of the second injection hole group is larger than an injection hole diameter of the first injection hole group. A first injection hole and a second injection hole are alternately arranged in the circumferential direction, however, a spray center axial line of F1 of the first injection hole is shifted to a swirl upstream side from a center position of spray center axial lines F2 of the second injection holes at both sides. The linearity of sprays 52, 53 (62, 63) of the second injection hole is high, and on the other hand, a spray 51 (61) of the first injection hole receives an influence of a swirl S and flows to the downstream side, but is suppressed in interference with the spray 53 (63) located at the downstream side.

Description

  The present invention relates to an improvement in a direct-injection diesel engine in which a cavity combustion chamber is formed at the center of a piston top surface, and a fuel injection nozzle having multiple injection holes is disposed at a substantially central position of the cavity combustion chamber.

  In direct-injection diesel engines, in recent years, attempts have been made to improve fuel efficiency by reducing the cooling loss by relatively reducing the gas flow in the cylinder. Soot) tends to increase.

  In order to cope with such a problem, Patent Document 1 discloses a direct injection diesel engine using a fuel injection nozzle having two injection hole groups having different inclination angles with respect to the cylinder center axis. Here, the penetration force of the other nozzle hole group directed to the lower side is set larger than the penetration force of one nozzle hole group directed to the upper side, and these two types of nozzle holes are arranged in the circumferential direction. Alternatingly arranged. As a result, the fuel is widely dispersed in the combustion chamber to reduce soot.

JP 2005-120732 A

  In the above conventional configuration, the nozzle holes having a large spray penetration force and the nozzle holes having a small spray penetration force are alternately arranged at equal intervals. However, in the presence of a swirl, the spray formed by each nozzle hole Flows downstream of the swirl. At this time, the spray having a small penetrating force is more strongly affected by the swirl than the spray having a large penetrating force, and flows more greatly on the downstream side of the swirl. Therefore, when both are arranged at regular intervals as in the conventional case, as a result of the spray having a small penetration force flowing largely downstream of the swirl when viewed in the circumferential direction, the penetration force adjacent to the swirl downstream side is large. It interferes with spraying (this is less likely to move downstream in the swirl due to its strong straightness in the radial direction), and a region with a high fuel concentration is generated locally. As a result, there was a problem that soot was generated due to lack of oxygen.

This invention has a cavity combustion chamber in the central portion of the piston top surface, a fuel injection nozzle having a multi-injection hole is disposed at a substantially central position of the cavity combustion chamber, and a direct injection type in which a swirl is generated in a cylinder. In diesel engines,
The fuel injection nozzle has a first nozzle hole group and a second nozzle hole group having different inclination angles with respect to the cylinder central axis,
The nozzle hole diameter of the second nozzle hole belonging to the second nozzle hole group is larger than the nozzle hole diameter of the first nozzle hole belonging to the first nozzle hole group. The plurality of second nozzle holes are arranged so that the axial lines are radially spaced in the circumferential direction, and the first spray nozzles are arranged so that each spray center axis is radially spaced in the circumferential direction. The holes and the second nozzle holes are alternately arranged in the circumferential direction,
Further, in the circumferential direction, the spray center axis of the first nozzle hole is offset toward the swirl upstream side from the center position of the spray center axes of the two second nozzle holes located on both sides of the first nozzle hole. It is characterized by that.

  Since the nozzle hole diameter of the second nozzle hole is larger than the nozzle hole diameter of the first nozzle hole, the second nozzle hole is at least under a condition where the total fuel injection amount (in other words, engine load) is larger than a certain level. The penetrating force of the spray due to is larger than the penetrating force of the spray due to the first nozzle hole, and the amount of fuel injected becomes large. Therefore, in the presence of the swirl, the straightness of the spray by the second nozzle hole is relatively high, and conversely, the spray by the first nozzle hole is low in the straightness and easily affected by the swirl.

  In the present invention, in consideration of such a difference in straightness with respect to the swirl, the spray center axis of the first nozzle hole is arranged to be offset toward the swirl upstream side. Accordingly, interference in the circumferential direction between the spray of the first nozzle hole and the spray of the second nozzle hole due to the influence of the swirl is suppressed, and the occurrence of a region having a high fuel concentration is avoided.

In a preferred aspect of the present invention, the direct injection diesel engine includes a swirl control valve that generates a swirl according to the configuration of the intake port itself and strengthens the swirl in a specific operation region.
The deviation of the spray center axis of the first nozzle hole is the difference between the spray of the first nozzle hole flowing in the swirl and the first spray when the swirl control valve is inactive and the engine operating condition is medium and medium load. It is set so that the sprays of the two nozzle holes are equally spaced.

  According to the present invention, the fuel can be widely dispersed by including the two nozzle hole groups having different inclination angles and nozzle hole diameters with respect to the cylinder center axis. In consideration of the difference in straightness of each spray with respect to the swirl, since the spray center axis of the second nozzle hole is offset toward the upstream side of the swirl, the spray of the first nozzle hole by the swirl and Interference can be avoided and the generation of wrinkles can be suppressed.

Sectional drawing which shows one Example of the direct injection type diesel engine which concerns on this invention. Sectional drawing of the principal part which shows the combustion chamber part of this Example. Explanatory drawing which shows the direction of the spray center axis line of a 1st nozzle hole group and a 2nd nozzle hole group. Explanatory drawing which shows the state of the spray in a combustion chamber. Sectional drawing of the principal part which shows 2nd Example of this invention. Explanatory drawing which shows the driving | running condition used as the object of adjustment of a spraying direction.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view of a main part of a direct injection diesel engine according to the present invention, in which a piston 1 is slidably fitted in a cylinder 4 formed in a cylinder block 3, and this cylinder The cylinder head 2 is placed and fixed on the upper surface of the block 3. The lower surface of the cylinder head 2 is formed flat and covers the upper end opening of the cylinder 4.

  A reentrant cavity combustion chamber 5 is recessed in the top surface of the piston 1. The cavity combustion chamber 5 has a rotating body shape centered on the piston center axis, that is, has a perfect circle shape in the plan view of the piston 1 and is formed at the center of the piston 1. On the cylinder head 2 side, a fuel injection nozzle 6 with multiple injection holes is disposed at the center position of the cylinder 4 corresponding to the center of the cavity combustion chamber 5. In this embodiment, the fuel injection nozzle 6 is disposed along the central axis of the cylinder 4, that is, vertically.

  The cylinder head 2 is provided with a pair of intake valves 7 and a pair of exhaust valves 8, which open and close the front end openings of the intake port 9 and the exhaust port 10, respectively. The intake valve 7 and the exhaust valve 8 are arranged in a vertical posture in which each valve stem is parallel to the central axis of the cylinder 4. Here, the pair of intake ports 9 that are opened and closed by the pair of intake valves 7 are configured such that one is a helical port and the other is a straight port, and the swirl control valve 11 disposed on the straight port side is closed. The strength of the swirl generated in the direction of the arrow S (see FIGS. 3 and 4) in the cylinder 4 can be variably controlled. Even if the swirl control valve 11 is inactive (opened), a relatively weak swirl in the direction of arrow S is generated depending on the shape of the intake port 9 itself, which is a helical port.

  FIG. 2 shows a more specific cross-sectional shape of the cavity combustion chamber 5. This cavity combustion chamber 5 is a reentrant type, and has a mountain-shaped central protrusion 5a at the center of the bottom surface, and the diameter of the lip portion 5b at the inlet portion is relatively smaller than the maximum diameter at the height position near the middle. It has become a thing. The piston top surface 13 remaining annularly around the cavity combustion chamber 5 is along a plane orthogonal to the piston center axis, and is substantially the same plane as the top surface of the cylinder block 3 at the piston top dead center position. It becomes. Accordingly, at the piston top dead center position, a gap substantially equivalent to the thickness of the cylinder head gasket 12 (see FIG. 1) is squished between the piston top surface 13 and the lower surface of the cylinder head 2 (ceiling surface of the combustion chamber). Remains as an area. Although not shown, relatively shallow valve recesses are recessed at positions corresponding to the valve heads of the intake valve 7 and the exhaust valve 8.

  In contrast to the cavity combustion chamber 5 configured as described above, the fuel injection nozzle 6 includes two injection hole groups having different inclination angles with respect to the cylinder center axis. The straight line indicated by reference numeral F1 indicates the spray center axis of the first nozzle hole group. This first nozzle hole group includes a plurality of nozzle holes, for example, five nozzle holes arranged at equal intervals in the circumferential direction, and these nozzle holes (hereinafter referred to as the first nozzle hole as necessary). Have the same inclination angle θ1 with respect to the cylinder center axis. Accordingly, the plurality of sprays are formed along a cone having an inclination angle θ1 centered on the cylinder center axis. Here, the spray center axis F1 of each nozzle hole belonging to the first nozzle hole group is directed near the cylindrical surface of the lip portion 5b at the piston top dead center position.

  Moreover, the straight line shown with the code | symbol F2 has shown the spray center axis line of the 2nd nozzle hole group. Like the first nozzle hole group, the second nozzle hole group includes a plurality of nozzle holes arranged at equal intervals in the circumferential direction, for example, five nozzle holes. (Also referred to as a second nozzle hole if necessary) have the same inclination angle θ2 with respect to the cylinder center axis. Accordingly, the plurality of sprays are formed along a cone having an inclination angle θ2 centered on the cylinder center axis. Here, the inclination angle θ2 of the second nozzle hole group is smaller than the inclination angle θ1 of the first nozzle hole group, and the spray center axis F2 of each nozzle hole belonging to the second nozzle hole group is the piston top dead center. In the position, it is directed to a position below the lower end of the lip portion 5b, that is, the inside of the cavity combustion chamber 5 whose diameter is larger than that of the lip portion 5b.

  Furthermore, the nozzle hole diameter of the second nozzle hole belonging to the second nozzle hole group is larger than the nozzle hole diameter of the first nozzle hole belonging to the first nozzle hole group. Thus, at least under the condition that the total fuel injection amount (in other words, the engine load) is larger than a certain level, the penetration force of each spray by the second nozzle hole group becomes the penetration force of each spray by the first nozzle hole group. Will be bigger. In addition, the amount of fuel ejected from each nozzle hole is larger in the second nozzle hole than in the first nozzle hole. Therefore, the straightness of the spray from the second nozzle hole is relatively higher than the straightness of the spray from the first nozzle hole.

  FIG. 3 is an explanatory diagram showing the spray center axis F1 of the first nozzle hole group and the spray center axis F2 of the second nozzle hole group in a plan view when the cylinder 4 is viewed from above. Here, each spray center axis is indicated by a radial arrow, and the length of this arrow corresponds to the spray penetration force.

  As shown in the figure, in plan view, the first nozzle holes are arranged at equal intervals in the circumferential direction so that the spray center axes F1 of the first nozzle hole group are radially spaced. In one embodiment, since it includes five first nozzle holes, these first nozzle holes are arranged every 72 ° in the circumferential direction, and the spray center axis F1 is generated every 72 °. Similarly, each of the second nozzle holes belonging to the second nozzle hole group is arranged at equal intervals in the circumferential direction so that the spray center axis F2 is radially spaced, and in one embodiment, Five second nozzle holes are arranged every 72 °. In the circumferential direction, the first nozzle holes and the second nozzle holes are alternately arranged.

  Here, the spray center axis F1 of the first nozzle hole is located closer to the swirl upstream side than the spray center axis F2 of the second nozzle hole. That is, as shown in FIG. 3, when focusing on a certain spray center axis F1, angles α, from the spray center axis F1 to two spray center axes F2 by the second nozzle holes adjacent to both sides thereof, β is different from each other, and the angle α on the upstream side of the swirl is smaller than the angle β on the downstream side of the swirl. In other words, when the center position of the two spray center axes F2 is used as a reference, the spray center axis F1 is positioned so as to be offset from the reference angular position toward the swirl upstream side.

  In the configuration as described above, the fuel spray injected at a predetermined injection timing before the compression top dead center reaches the piston 1 when the piston 1 is near the top dead center. Here, the fuel spray injected along the spray center axis lines F1 and F2 from each nozzle hole is influenced by the swirl S existing in the cylinder, and flows somewhat to the downstream side of the swirl S. FIG. 4 schematically illustrates such spray diffusion, and reference numeral 51 indicates an initial spray shape formed by the first nozzle hole along the spray center axis F1. The spray 51 expands as shown by reference numeral 61 and flows downstream by the swirl S when it collides with the piston 1 with time. Reference numerals 52 and 53 show the shapes of the initial sprays formed along the spray center axis F2 by the adjacent second nozzle holes, respectively. These sprays 52 and 53 spread as shown by reference numerals 62 and 63 and slightly flow toward the downstream side of the swirl S when they collide with the piston 1 with time. As described above, all the sprays 51, 52, 53 are affected by the swirl S. However, as described above, the spray of the second nozzle hole having a large nozzle hole diameter is highly straight and hardly affected by the swirl S. On the other hand, the spray of the first nozzle hole having a small nozzle hole diameter is easily affected by the swirl S.

  In contrast to these differences, in the above embodiment, the spray center axis F1 of the first nozzle hole is preliminarily arranged on the upstream side of the swirl, so that swirl 61, 62, 63 as shown in FIG. When the fuel flows to the downstream side due to S, the sprays are substantially equidistant, and interference between the sprays and, as a result, generation of a region having a high fuel concentration is avoided. Although not shown, if the three initial sprays 51, 52, 53 shown in FIG. 4 are equally spaced, the spray 61 of the first nozzle hole spreads downstream by the swirl S. As a result, the swirl downstream Interfering with the spray 63 of the second nozzle hole adjacent to the side, a locally dark region is generated.

  Therefore, according to the above embodiment, the fuel is widely dispersed in the cavity combustion chamber 5 by the first nozzle hole group and the second nozzle hole group having different inclination angles with respect to the cylinder center axis. The air can be used more effectively. In addition, since the diameter of the second nozzle hole group toward the inside of the cavity combustion chamber 5 is set to be larger, the fuel in an appropriate ratio corresponding to the shape of the cavity combustion chamber 5 is supplied from each nozzle hole group. can do. In the circumferential direction, the spray center axis F1 of the first nozzle hole group is arranged to be offset from the center position of the spray center axis F2 of the second nozzle hole group to the upstream side of the swirl. Interference between sprays caused by the above can be avoided, and the generation of a locally dark region and thus the generation of wrinkles can be prevented.

  The degree to which the spray center axis F1 of the first nozzle hole group is offset from the center position of the spray center axis F2 depends on the assumed strength of the swirl S, but in one embodiment, FIG. 6, when the engine operating condition is medium and medium load, the spray 61 of the first nozzle holes and the sprays 62 and 63 of the second nozzle holes flowing in the swirl S are equally spaced. The degree of deviation is set so that In this embodiment, the swirl control valve 11 is turned on (that is, closed) only in a predetermined low speed and low load region. Therefore, in the region A, the swirl control valve 11 is open, and swirl strengthening by the swirl control valve 11 is performed. Is not done. The region A is also a region where a relatively large amount of exhaust gas recirculation is performed by an exhaust gas recirculation device (external exhaust gas recirculation device or internal exhaust gas recirculation mechanism) (not shown). In the region on the higher load side and the region on the high speed side than the region A, the combustion speed is high, and therefore, the generation of soot is relatively small even if there is a slight overlap between the sprays. On the contrary, on the low-speed and low-load side from the region A, since sufficient oxygen exists in the combustion chamber, the generation of soot is also small. In the region where the swirl control valve 11 is turned on, the swirl strength is very high, so local overlap of spray does not cause a problem. On the other hand, in the medium speed / medium load region A, the combustion speed is relatively slow in combination with a large amount of exhaust gas recirculation, and the amount of fuel is relatively large compared to the amount of air. In some cases, oxygen is locally deficient, and soot is easily generated.

  Next, FIG. 5 shows a second embodiment of the present invention. In this embodiment, the spray center axis F1 of the first nozzle hole group having a small nozzle hole diameter is directed slightly lower than the lip portion 5b of the cavity combustion chamber 5, and the second nozzle nozzle having a large nozzle hole diameter. The spray center axis F2 of the nozzle hole group is directed to the inside of the cavity combustion chamber 5 on the lower side. The arrangement of the spray center axes F1 and F2 in a plan view is the same as in FIGS. 3 and 4 described above, and the spray center axis F1 of the first nozzle hole is the same as that of the second nozzle hole with high straightness. It is arranged offset from the center position of the spray center axis F2 toward the swirl upstream side.

  In each of the above-described embodiments, the second nozzle hole group having a large nozzle hole diameter is directed downward from the first nozzle hole group. The present invention can be applied in the same manner even when the two nozzle hole groups are oriented upward from the first nozzle hole group.

DESCRIPTION OF SYMBOLS 1 ... Piston 5 ... Cavity combustion chamber 5b ... Lip part 6 ... Fuel injection nozzle F1, F2 ... Spray center axis

Claims (4)

In a direct injection diesel engine having a cavity combustion chamber at the center of the piston top surface, a fuel injection nozzle with multiple injection holes arranged at a substantially central position of the cavity combustion chamber, and generating a swirl in the cylinder,
The fuel injection nozzle has a first nozzle hole group and a second nozzle hole group having different inclination angles with respect to the cylinder central axis,
The nozzle hole diameter of the second nozzle hole belonging to the second nozzle hole group is larger than the nozzle hole diameter of the first nozzle hole belonging to the first nozzle hole group. The plurality of second nozzle holes are arranged so that the axial lines are radially spaced in the circumferential direction, and the first spray nozzles are arranged so that each spray center axis is radially spaced in the circumferential direction. The holes and the second nozzle holes are alternately arranged in the circumferential direction,
Further, in the circumferential direction, the spray center axis of the first nozzle hole is offset toward the swirl upstream side from the center position of the spray center axes of the two second nozzle holes located on both sides of the first nozzle hole. This is a direct injection diesel engine.   2. The direct injection type according to claim 1, wherein the first nozzle hole group is directed toward a relatively upper position, and the second nozzle hole group is directed toward a relatively lower position. diesel engine.   The cavity combustion chamber is a reentrant type cavity combustion chamber, the first nozzle hole group is directed to the inlet portion of the cavity combustion chamber, and the second nozzle hole group is directed to the inside of the cavity combustion chamber; The direct-injection diesel engine according to claim 2. A swirl is generated by the configuration of the intake port itself, and a swirl control valve that strengthens the swirl in a specific operation region is provided,
The deviation of the spray center axis of the first nozzle hole is the difference between the spray of the first nozzle hole flowing in the swirl and the first spray when the swirl control valve is inactive and the engine operating condition is medium and medium load. The direct injection type diesel engine according to any one of claims 1 to 3, wherein the sprays of the two nozzle holes are set at equal intervals.

Images