KR790000952B1 - A combustion chamber of direct-injeetion diesel engine - Google Patents

Abstract

A device for controlling the swirling strength and the scattering distribution of the injection fuel was composed of the cavity of a rectangular combustion chamber, in which the swirling (S) is formed inside of the combustion chamber in the upper part of the piston (P) and the fuel is ejected radiatedly inside of the cavity (W) by the fuel injection nozzle (N) having 4-8 injection holes filted in the center of the cavity (C).

Description

Combustion chamber of direct injection diesel engine

A and b in FIG. 1 indicate a combustion chamber of a conventionally known circular cavity,

a is a top view.

b is a longitudinal cross-sectional view.

FIG. 2 is an enlarged explanatory view of part of FIG.

3, a and b show a combustion chamber consisting of a quadrilateral cavity according to the present invention,

a is a top view.

b is a longitudinal cross-sectional view.

4 is an enlarged explanatory view of part of FIG.

5 is a graph of the engine performance: NOX / Pme change for the ratio of the inscribed radius to the arc radius.

6 is the engine performance for fuel throw angle: θ. NOX.Pme change graph.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a combustion chamber of a direct injection diesel engine, in particular to making the cavity of the combustion chamber a quadrangular shape, controlling the strength of swirl and controlling the distribution of the injection fuel.

In general, in a direct injection diesel tube, the fuel is first joined to the intake air in the combustion chamber, so the mixing of the air directly influences the engine's performance. Therefore, in order to promote such mixing, a swirling vortex movement, that is, a swirl is applied to the air in the combustion chamber to achieve a good distribution of the injected fuel.

As a means for generating such a swirl, there are known means such as a helical port, a die recreational port, a shroud valve, and the like.

Such means have been developed such that any swirl can occur for any of the above mixtures, but recently it has been found that when the swirl tends to be too strong, the NOx component in the exhaust gas increases.

In other words, in order to reduce NOX, the swirl should not be lowered. In other words, it was found that weakening the swirl is one big requirement.

However, weakening the swirl means that the distribution of the injected fuel is deteriorated, and that the mixing of the fuel and air described above is not sufficiently performed, resulting in a deterioration of the combustion state, resulting in a decrease in output, torque, and increase in smoke. Bad phenomena occur due to the back.

As described above, the present invention solves the contradiction of weakening the swirl for NOx reduction and strengthening the swirl for combustion, and does not strengthen the swirl and improves the distribution of the injected fuel to improve mixing. It is to provide a common thing to do.

The combustion chamber of a conventionally known direct injection diesel engine is formed by the cavity C installed in the head of the piston P as shown in Figs. 1A and 1B, and the planar shape of the cavity C is circular, and is divided into multiples near its central axis. The nozzle N of the cavity was disposed, and the fuel was ejected radially from the nozzle N toward the cavity inner wall W.

In the cavity C, swirl S is generated as a means of electric announcement.

In such a circular cavity C, the fuel ejected from the nozzle N on its central axis diffuses as shown in FIG. That is, the fuel injection flow P ejected from the nozzle N collides perpendicularly to the inner wall W of the cavity C, and forms the downstream side reflection flow f 'and the upstream side reflection flow f "of the swirl S.

In such a state, the upstream side reflection flow f "tends to flow by the swirl S and overlap with the main injection flow F. On the other hand, the downstream reflection flow f 'flows further downstream than this, So, where the sprays overlap, a thick mixer is formed, where it is not, a very thin mixer is formed, the distribution of the fuel is weakened, and a strong swirl S is used to compensate for this deterioration. It is necessary, and also because the extremely easy to ignite the mixture is also generated, Swirl S is to fall, so that the rapid combustion of this part occurs to generate a high temperature to generate a large amount of NOx.

In addition, if the swirl S is too strong, the reverse skid shoe S seen after passing through the top dead center of the piston P is not used well, and the fuel is confined in the cavity C, which further causes a bad result.

Of course, if the swirl S is weak, the fuel injection flow F, the upstream and downstream reflection flows f ', f "cannot spread in the cavity C, and thus the fuel is not a good distribution dispersion, and thus the mixed state becomes poor.

And even worse, the Swirl S and strength are stronger with increasing engine rotational speeds, so sometimes Swirl S is a suitable strength at some rotational speeds, but it is strong or too weak at other rotational speeds. This is a fatal flaw in the circular cavity C, where the flow flow of the jet flow F is perpendicular to the inner wall W of the cavity C, and the defects described above are not solved while using the circular cavity C.

Here, the inventors attempt to improve the distribution dispersion as described above by making the fuel main injection flow at an angle and collide with the cavity inner wall on the rough plane and effectively using the reflection. Here, it is proposed to make the shape of the cavity into a quadrangular shape.

When explaining as an Example of this invention shown to FIG. 3 a, b, the cavity C formed in the head of piston P in the figure is a substantially square shape, and the four sides X of a straight line or a substantially straight line, and these It consists of the four corners Y on the arc connecting the sides X of.

In addition, the nozzle N has four (8) injection holes equal to the side portion X and the same number (or drainage), and is disposed near the center side of the cavity C.

In Fig. 4, although the shape is experimentally configured, the ratio between the radius R of the circle D (tangential to the drawing) inscribed in the quadrangular cavity C and the radius R of the arc forming the corner Y is between 0.40 and 0.75. It is formed.

The fuel injected from the four injection holes H of the nozzle N is disposed so that the main injection flow F can collide in the inclined direction with respect to the cavity inner wall W, respectively.

In the combustion chamber having the hollow C cavity C according to the present invention configured as described above, the swirl S, which tends to become strong in proportion to the rotational speed of the engine, can be controlled very well as follows.

In other words, when considering a circular cavity C 'having a volume equal to that of the four-hole cavity C (two dashed lines in the drawing), the side portion X of the four-hole cavity C is hollow as much as t compared to the circular cavity C'. It can be said that it sticks out in the axial direction.

In other words, this protruding part, the side part X, is an obstacle to the swirling movement of Swirl S.

Therefore, in an engine that has set the strength of the swirl during the low speed rotation of the engine, when the engine rotational speed increases and the swirl S tends to become strong, the swirl S is gradually interposed between the obstacle, that is, the side portion X. Strong friction begins to develop, and forces to support the swirling motion of the Swirl S begin to work.

Since the damping effect of the swirl S increases in proportion to the square of the swirl speed, the stronger the swirl S, the stronger the side portion X acts as an obstacle, and the swirl S is appropriately attenuated. . That is, since the force is appropriately attenuated by the swirl S which increases with the increase of the engine speed, the distribution of fuel is always good without being affected by the increase of the engine speed, and the deterioration of the distribution of fuel as described above is deteriorated. It is possible to greatly reduce the generation of NOX.

5 is a graph showing the effect of the ratio of the radius R of the circle D inscribed to the cavity C and the radius r of the circular arc forming the corner Y on the performance of the engine. The number of discharged NOX (PPM) divided by the output (average effective pressure Pme) is indicated.

As indicated in this graph, when the radius (r / R) is 0.8 or more, the result is almost the same as that of the shape of the circular cavity C '. As described above, the side X acts as an obstacle very little, and the swirl damping action is very small. Therefore, due to the strong swirl S that does not solve the defects of the circular cavity and does not distribute, mix and attenuate bad fuel, the engine performance (NOX / Pme) is higher than that of the circular cavity indicated by the dotted line. No improvement

However, when the radius ratio reaches 0.75 or 0.70, the engine performance begins to improve extremely.

This is because the attenuation effect of Swallow S begins to be remarkable in the vicinity of the radius ratio, the distribution and mixing of the fuel are improved, and the Swallow S is also attenuated appropriately, so that the output increases and the NOx decreases simultaneously. You can see that it shows good results.

If the radius ratio is less than 0.40, the engine performance tends to be lowered again. If the radius ratio is less than 0.35, the circular cavity C 'is worse than itself.

This is because the corner Y becomes too small arc (less R) and becomes a square quadrangle cavity C, so the damping effect of the swirl S becomes too large, resulting in jet fuel lagging at the corner Y and swelling, resulting in poor mixing. Decreases. NOX, on the other hand, means that the distribution distribution of the fuel deteriorates and, on the contrary, tends to increase again. Therefore, in order to obtain high output and low-NOX engines, the radius ratio r / R must be between 0.40 and 0.75. Furthermore, the graph is due to the combustion chamber having a constant engine speed and a constant angle of impact against the cavity inner wall W of the fuel injection stream F. In addition, the vertical axis of the graph is displayed in logarithm.

Moreover, as shown in FIG. 4, the dashed-dotted line which connected the junction Z of the side part X and the central axis of cavity C (in FIG. 4, the Example which arrange | positioned nozzle X on the central axis of cavity C is shown, Is connected to the central axis of the nozzle N), and the angle at which the fuel main injection flow F ejected from the nozzle N impinges on the cavity inner wall W and the line connecting the cavity central axis and the reference line is an angle θ. When measured in the direction opposite to the rotational direction of S, it was found that the change in the angle θ was in the influence on the engine performance and the control as shown in FIG. That is, in the case where the fuel injection flow F is ejected such that the angle θ is from 0 ° to 55 °, the fuel injection flow F collides close to the right angle to the cavity inner wall W, so that the reflection flow f 'as in the circular cavity described in FIG. . f "produces little effect on NOX reduction and output.

Therefore, the effect that the injection hole H of the nozzle N was arrange | positioned within the angle except the said angle (theta), and made into a square cavity is lost.

Moreover, the reason that the above-mentioned angle θ does not become symmetrical (33 to 55 degrees) with respect to the cavity inner wall W is because of the presence of swirl S.

In addition, if the angle other than the angle, the overall engine performance is greatly improved, but the angle θ is particularly excellent in the range of 5 ° to 25 °.

This is because the downstream opposite flow f 'of the fuel injection flow F impinging on the cavity inner wall W is very large (there is almost no upstream reflection flow f ") and at the same time the reflection flow f' is diffused very well by swirl S. to be.

Furthermore, the air or mixer at the corner Y stays intact and is not constrained to the swirl S (because it is attenuated), so that the fuel in the cavity is inverted by the inverse skew S, which acts after passing through the top dead center of the piston P. Because it spreads all over.

And according to the experiment, by the change of the angle (theta) which falls in the range from 5 degrees to 25 degrees, the influence which shows on engine performance is comparatively insensitive.

In other words, it was found that even if the fuel injection flow F collided anywhere within this range, there was no difference in the period performance. This is extremely advantageous when considering the manufacturing and assembly errors of the engine.

That is, there is an absolute effect that mass production of engines with uniform performance can be achieved without imposing strict design conditions.

Furthermore, although the description has been made with the gist of the nozzle N being on the central axis of cavity C in the present specification, the nozzle N is sometimes experienced to be repositioned in the central axis under various conditions such as the relationship between the hop and the exhaust valve. In order to implement, the position of the nozzle N can be changed from the center axis as long as it is in the range of about 15% of the above-mentioned inscribed circle radius R. In addition, although only four injection nozzles N are shown in the figure shown in the Example, there exists an effect by this invention even if it is an 8 injection hole.

Claims (1)

In the combustion chamber having a cavity formed in the head of the piston P, swirl S can be generated by known means, and fuel injection has four or eight injection holes H disposed near the central axis of the cavity C. In the combustion chamber of a direct injection diesel engine in which fuel is ejected radially toward the cavity inner wall W by the nozzle N, the cavity C is regulated by four straight lines or a curved side portion X approximating a straight line, and the edge portion X is 4 Connected by a circular arc (corner Y) to form a planar shape of cavity C in a quadrangular shape, and furthermore, the ratio r / R of the radius r of the corner Y to the radius R of the circle D inscribed to the cavity C is 0.40 to 0.75. The fuel injection flow F collides against the cavity inner wall W in a direction opposite to the swirling direction of the swirl S at the reference line connecting the intersection Z of the side X of the central axis of the cavity C to the range of. When measuring fingers angle θ, the angle θ is a direct injection type combustion chamber of a diesel engine, it characterized in that the enable others be in the range of from 40 ° 55 °, regulate the direction of the screw hole H of the minute nozzle N.

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