JPH0736089Y2 - Direct injection diesel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to fuel injection of a direct injection diesel engine, particularly a swirl generation direct injection diesel engine.

(Prior Art) In a direct-injection diesel engine, a so-called direct-injection diesel engine, a combustion chamber cavity is generally provided at the top of a piston, and fuel is generally injected from a plurality of injection ports toward the peripheral wall of the cavity in a sprayed state. The injected fuel collides with the wall surface of the cavity and mixes with air by diffusion and evaporation, but a strong swirl is usually formed in the combustion chamber to enhance the mixing action of this fuel and air.

In such a direct injection diesel engine, good combustion cannot be performed unless the fuel injected from the plurality of injection ports is mixed with air in a well-balanced manner. For that purpose, it is desirable to arrange the fuel injection nozzle as close to the center of the cavity as possible so that the conditions for spraying from the respective injection ports become equal. However, in the case of a relatively small direct injection diesel engine, in particular, a so-called two-valve engine having one intake valve and one exhaust valve, the diameters of the intake valve and the exhaust valve are increased in order to secure a necessary passage area. Therefore, it is structurally difficult to bring the fuel injection nozzle to the center of the cylinder. Therefore, in the two-valve engine, the fuel injection nozzle is usually provided offset from the center of the cylinder. In this case, the cavity at the top of the piston must also be offset by the same amount as the injection nozzle in order to make the conditions for spraying from each injection port of the fuel injection nozzle uniform, but the cavity deviates too much from the center of the cylinder. Therefore, it is often impossible to offset the cavity by the same amount as that of the fuel injection nozzle, because a problem such as nonuniformity of the squish area becomes large. Therefore, it is normal to arrange the cavity slightly offset from the center of the cylinder and further arrange the fuel injection nozzle offset from the cavity. In that case, the direction of each spray port should be adjusted so that the area between sprays is equalized by making the spread of spray from each spray port in the cavity as uniform as possible to improve the air utilization rate especially in the high load area. There are many proposals in which the nozzle diameters are set, or when the areas between the sprays cannot be made equal, the respective nozzle diameters are set in proportion to the area ratio. Further, as described in Japanese Utility Model Laid-Open No. 52-160706, the cavity circle is divided into eight equal parts with a point where an extension line of a line connecting the center of the cavity and the center of the nozzle intersects with the cavity circle, It is also known that the nozzles are provided so as to be directed to four equal points adjacent to the base point so that the difference in the length of the spray from each nozzle is reduced. In addition, Japanese Patent Publication No. 55-8655 discloses that the difference in the fuel dispersion capacity due to the difference in the relationship between the swirl direction and the collision angle of the spray on the cavity wall surface is different for each injection port. In addition, it is described that the angle between the nozzles is set so that the air is distributed according to the nozzle diameter, that is, the injection amount in that case.

However, the fuel spray ejected from each injection port of the fuel injection nozzle flows on the swirl after colliding with the peripheral wall of the cavity.Therefore, if there is a difference in the distance between the sprays on the cavity circle, the spray overlaps in some parts. Therefore, there arises a problem that the air utilization ratio is deteriorated and smoke is likely to be generated particularly in a region where the excess air ratio is low such as at low speed and high load. The prior art cannot adequately deal with such a spray overlapping problem. Some of them, as described in Japanese Utility Model Application Laid-Open No. 52-160706, result in equal distances between sprays on the cavity circle. However, there is no suggestion of a technical problem and a solution to prevent overlapping of fuel sprays on the cavity wall surface due to swirl, and at the same time, to prevent deterioration of fuel distribution due to variation of spray-to-spray area to improve air utilization rate. Absent.

(Purpose of the Invention) The present invention, in a direct-injection diesel engine, prevents the overlap of the spray on the peripheral wall of the cavity due to swirl, and prevents the deterioration of the fuel distribution due to the variation in the area between the sprays. The purpose of this is to improve the air utilization rate in the room and prevent the generation of smoke.

(Structure of the Invention) The present invention recognizes that the overlap of the fuel spray on the peripheral wall of the cavity due to the swirl causes the deterioration of the air utilization rate particularly at low speed and high load, and has found a solution to the problem. The structure is as follows. That is, the direct injection diesel engine according to the present invention is a swirl in which fuel is radially injected toward the peripheral wall of the cavity from a plurality of nozzles of a fuel injection nozzle that is arranged offset with respect to the cavity formed at the top of the piston. In the direct injection diesel engine of the generation type, with the intersections of the cavity circle defining the shape of the cavity and the center lines of the plurality of injection orifices set with the orientation of each injection orifice at substantially equal intervals on the cavity circle, The diameter of each nozzle is set according to the ratio of the cavity area between the center line of each nozzle and the center line of the nozzle adjacent to the swirl downstream side.

(Action) The swirl becomes the strongest on the cavity circle. And, since the intersections of this cavity circle and the center lines of the plurality of nozzles are at substantially equal intervals on the cavity circle, the distance traveled by each nozzle or the movement distance of the spray flowing on the swirl after colliding with the cavity peripheral wall The rate of movement relative to the distance between sprays is almost equal. Further, by setting the diameter of each nozzle according to the ratio of the cavity area between the center line of each nozzle and the center line of the nozzle adjacent to the downstream side, the fuel corresponding to the ratio of the inter-spray area is set. Is ejected from each nozzle. Therefore, the swirls do not cause the sprays to overlap with each other on the peripheral wall of the cavity, and the fuel distribution is prevented from being deteriorated due to the variation in the inter-spray area, thereby improving the air utilization rate.

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

FIG. 1 is a sectional view showing the main part of a direct injection diesel engine according to an embodiment of the present invention.

The engine 1 is a two-valve direct injection diesel engine in which one intake valve 3 and one exhaust valve (not shown) are arranged in a cylinder head 2, and a cylinder 4 is provided with a dry type cylinder liner 5. A circular combustion chamber cavity 7 is provided substantially at the center of the top of the piston 6 mounted and reciprocating therein. The fuel injection nozzle 8 is arranged in the cylinder head 2 offset from the cavity 7 as shown in FIG.

In the case of this embodiment, the injection nozzle 8 is of a 4-injection type,
The nozzle center O _N is offset from the center O _C of the cavity circle C _C , and the four nozzles are oriented in the directions shown by the radial center lines with arrows in the figure. The circumferential lengths l ₁ , l ₂ , l ₃ , l ₄ between the intersections of the center line of each nozzle and the cavity circle C _C are made equal. In this case, the cavity areas A, B, C, D of the four parts between the injection holes have a relationship of B>C>A> D. The diameter of each nozzle is set according to the ratio of the area of the portion on the downstream side of each swirl. Therefore, in the figure
The nozzle diameters indicated by a, b, c, and d have a relationship of b>c>a> d.

FIG. 3 shows a modification of the above embodiment. In this case, as shown in the figure, the area A, B, C, D between the nozzles is C> B.
>D> A. The perimeters l ₁ , l ₂ , l ₃ , l ₄ are of course equal. The diameter of the injection port is c>b>d> a.

FIG. 4 shows another modification of the above embodiment. In this case, a 5-nozzle type injection nozzle is used.
The perimeters l ₁ , l ₂ , l ₃ , l ₄ between the nozzle center lines are equal, and the area between the nozzles is the same.
A, B, C and D have a relationship of D>C>E>B> A. And
The nozzle diameter is d>c>e>b> a.

Next, an example of a direct injection diesel engine having a cavity other than a circular shape will be described.

First, FIG. 5 shows the case of what has a so-called rectangular cavity. In the case of a rectangular cavity, especially in relation to the swirl, what defines the shape of the cavity is the circle whose radius is the distance from the center of the cavity to the shortest wall surface, that is, the inscribed circle C _{I of} the rectangular cavity. . Therefore, in this case, the intersections of the cavity circle, that is, the inscribed circle C _{I of the} cavity and the center line of each injection port are arranged at substantially equal intervals on the inscribed circle, that is, the circumference is l _{1 in} FIG.
The orientation of each nozzle is set so that = l ₂ = l ₃ = l ₄ . Further, the areas A, B, C, D between the nozzles are C>D>B> A, and therefore the nozzle diameters are c>d>b> a.

Further, FIG. 6 shows the case of an engine having a petal-shaped cavity, and in this case also, the inscribed circle C _{I of the} cavity
In the above, the perimeter between the nozzle center lines is set to be l ₁ = l ₂ = l ₃ = l ₄ . The area between the nozzles is D>C>B>
Therefore, the nozzle diameter is set to d>c>b> a.

The present invention is not limited to the above embodiments, but can be implemented in various other modes.

(Effect of the Invention) Since the present invention is configured as described above, in a direct injection diesel engine, it is possible to prevent overlapping of the spray on the cavity peripheral wall due to swirl, and to deteriorate the fuel distribution due to the variation of the inter-spray area. It is possible to improve the air utilization rate and reduce the smoke emission amount especially in the low speed and high load range.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a direct injection diesel engine according to an embodiment of the present invention, FIG. 2 is an explanatory view showing a nozzle opening direction and a nozzle diameter of a fuel injection nozzle in the embodiment, FIGS. 3 and 4 FIG. 7 is an explanatory view showing a modified example of the above embodiment, and FIGS. 5 and 6 are explanatory views showing another embodiment of the present invention. 1: Engine, 6: Piston, 7: Cavity, 8: Fuel injection nozzle, C _C : Cavity circle, C _I : Inscribed circle.

Claims (1)

[Scope of utility model registration request] 1. A swirl generation type direct injection diesel engine in which fuel is radially injected from a plurality of injection holes of a fuel injection nozzle arranged offset with respect to a cavity formed at the top of a piston toward a peripheral wall of the cavity. In, while the orientation of each nozzle is set so that the intersections of the cavity circle defining the shape of the cavity and the center lines of the plurality of nozzles are substantially evenly spaced on the cavity circle,
A direct injection diesel engine, characterized in that the diameter of each injection port is set according to the ratio of the cavity area between the center line of each injection port and the center line of each injection port adjacent on the downstream side of each swirl.