JPS6056893B2 - combustion chamber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion chamber, specifically a combustion chamber for a direct injection diesel engine.

In addition to processing Co, HC, NOx, etc., diesel engines have to deal with smoke concentration regulations, which are issues that gasoline engines do not have, and they also have to deal with regulations regarding smoke concentration, which is an issue that gasoline engines do not have.
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Therefore, compliance with exhaust regulations for diesel engines is more difficult than for gasoline engines. For example, as a means to reduce NOx, the fuel injection timing is delayed. (timing retard) is known to be effective, but if this timing retard is used in a general toroidal combustion chamber, the smoke characteristics will be extremely deteriorated, so both conditions for NOx smoke cannot be met. . Also, it has been confirmed that with a combustion chamber known as a Saurer type or a skittle lip type, smoke does not deteriorate much even if the timing retard is applied.
This type of combustion chamber suffers from a significant drop in output due to its strongly constricted inlet, and also has problems with low-temperature startability and odor, as well as problems such as an excessive heat load on the inlet. As with the example, it does not satisfy all the various conditions.

The present invention has been made in view of these points, and is based on C
It not only reduces harmful exhaust gases such as o and HC, but also NOx and smoke, and there is almost no decrease in output.
Furthermore, it is an object of the present invention to provide a combustion chamber for a direct injection diesel engine that has good low-temperature startability and little odor.

The present invention will be described in detail below with reference to illustrated embodiments. In FIGS. 1 and 2, 1 is a piston with a combustion chamber 2 formed at its top; A multi-nozzle fuel injection nozzle 3 is positioned approximately in the center so that fuel can be injected radially toward the side wall 21 of the combustion chamber 2 near top dead center.

The combustion chamber 2 has a compression ratio E in the range of 14 to 20, and has a volume that allows setting the optimum value for the specifications of the engine.

If the compression ratio E is set to a small value outside of this range, the startability will be significantly deteriorated due to insufficient compression temperature during the compression stroke, white smoke and odor will be generated significantly, and the output will also decrease. On the other hand, if the compression ratio E is set to a large value that exceeds this range, the compression temperature will rise too much, the ignition delay of the fuel will decrease, and the balance between premix combustion and diffusion combustion will be disrupted, resulting in the generation of black smoke and increased noise. Therefore, the first requirement is to set the compression ratio E within the above range.
In order to obtain such a compression ratio E and ensure a balance between the premix combustion and diffusion combustion, the ratio of the diameter D2 of the side wall 21 to the diameter D1 of the piston 1 is set to 0.5 to 0.6. Moreover, the ratio of the depth H of the combustion chamber 2 to the diameter D2 is set to 0.3 to 0.4, so that the combustion chamber 2 is not flat and not too deep.

Of course, if it is too deep, premixed combustion will increase, leading to an increase in NOx and noise, and conversely, if it is too deep and diffusive combustion increases, HC
This may lead to an increase in fuel consumption, poor startability, and an increase in odor. To explain this with reference to Fig. 5, Fig. 5 shows the ratio D2lDl of the diameter D2 of the combustion chamber side wall to the piston outer diameter D1.
and the combustion chamber side wall diameter D2 of the height (depth) H of the combustion chamber.
This is a graph showing the influence of the ratio HID2 on the exhaust mode values of NO and HC.
The mode values are NO going down from left to right, and HC going down from left to right. Both curves rise to a point slightly exceeding 0.6 of D2lDl or slightly less than 0.3 of H'D2! or intersect at small points. or,
At a point smaller than 0.5 of D2lDl, also 0.3 of HlD2
At larger points, the HC curve has a constant mode value. In the present invention, from the above results, a combustion chamber with good influence on the exhaust mode values of NO and HC was obtained. Further, as is clear from FIG. 2, the inlet 22 of the combustion chamber 2 has a protruding portion 23 inwardly by a thickness t with respect to the side wall 21.
Aperture is given to .

The degree of constriction is determined by the diameter D3 of the inlet 22 (i.e., D2-2t) with respect to the diameter D2, which is 0.85
It is set as 0.97. That is, compared to the aforementioned Saurer type or squish lip type combustion chamber, the degree of restriction is extremely weak. There is a small radius portion C at the bottom of the protrusion 23, which is smoothly connected to the side wall 21 with an appropriate curvature R1. This curvature R1
is approximately equal to or less than the thickness t, and at the same time is set so as to cooperate with the radius portion C to appropriately alleviate the thermal load on the protruding i portion 23. Further, the side wall 21 connected to the curved tooth ridge has a straight portion (cylindrical portion or flat portion) 24 that is substantially straight over a length l, and the straight portion 24 is located at the top of the piston 1. Almost perpendicular to plane 11 (01)
It has been done. If this angle 01 deviates significantly from a right angle, the degree of constriction of the inlet 22 determined by the diameters D2 and D3 will change. Further, the side wall 21 is smoothly continuous with the bottom portion 25 with a relatively large curvature R2, and this curvature R2 is determined by experience to be within the range of the depth H(7) 0.5 to 0.3.
If it is set to 5, the air utilization rate will be improved.

Although an example is shown in which a convex portion 26 is present in the center of the low portion 25, this is also a configuration for improving the air utilization rate, but this may be omitted depending on the case.

The fuel F injected from the nozzle 3 is then
The nozzle 3 is positioned so that the nozzle 3 collides with the top, and the angle θ2 formed between the fuel F and the side wall 21 is set to 70° to 85°, so that the fuel F is appropriately distributed in the vertical direction of the combustion chamber 2. , as in the aforementioned Saurer-type combustion chamber, prevents much of the fuel F from being smeared onto the side wall 21, thereby maintaining a balance between premix combustion and diffusive combustion.

That is, when this angle θ2 becomes smaller, the amount of fuel adhered increases, resulting in a decrease in output, poor starting performance, and deterioration of odor characteristics.On the other hand, when θ2 becomes large, the fuel is poorly distributed to the bottom 25 of the combustion chamber 2. This reduces air utilization and increases smoke. To further explain this with reference to FIG. 6, FIG. 6 shows that the angle θ2 formed by the fuel F and the side wall 21 is
2 is a graph showing the effect on Pme and smoke. If the smoke value is less than θ2=700, further reduction can be expected, and if the value exceeds 02=850, the smoke value increases rapidly beyond the allowable amount. Also, the average effective pressure P which is proportional to the output
me decreases rapidly below 02=700, and θ2=85
2a Satljate when it grows
. From the above results, the present invention has the effect of suppressing smoke while keeping the output approximately constant S when θ2=70 to 85a. To summarize the above, the combustion chamber 2 of the present invention is a combination of the following conditions.

According to the combustion chamber of the present invention having such a configuration, a relatively strong squish can be obtained due to the presence of the protrusion 23, and this cooperates with the swirl generated in the combustion chamber 2 to combine the fuel and Encourage proper air mixing.

After the piston 1 passes the top dead center, reverse squishing occurs and the air-fuel mixture attempts to diffuse out of the combustion chamber 2, but the protrusion 23 moderately suppresses this, and the protrusion 23 Even when timing retard is performed to reduce NOx by generating micro-eddy currents in the lower part of the engine to promote mixture formation, the smoke characteristics do not deteriorate. Figure 4 is a graph showing the influence of the ratio D3lD2 of the diameter D3 of the combustion chamber inlet to the diameter D2 of the side wall of the combustion chamber on the shaft average effective pressure Pme corresponding to the engine output and smoke (pot number). (solid line)
The change in average effective pressure and smoke due to D3lD2 at medium speed (dotted and dashed line) is shown, but when D3lD2 is 0.
Below 85 and above 0.97, smoke increases rapidly and the average effective pressure decreases. In the present invention, from the following results, good results were obtained in which D3lD2 was set to 0.85 to 0.97 and smoke was kept at a reduced level while maintaining the output at the highest level. In addition, this. Since the protrusion 23 does not provide much resistance to the inflow of air into the combustion chamber 2 and the outflow of combustion gas generated therein, there is almost no reduction in output as seen in Saurer-type combustion chambers. Somehow (see Figure 4),
Further, the thermal load and durability of the protrusion 23 do not become a problem. These things mainly depend on the compression ratio and the above (2)
), (3), (6), etc. In addition, because the fuel applied to the side wall 21 is regulated according to the conditions (5) and (6) above, diffusion combustion is limited, which solves the engine's low-temperature startability and odor problems, and also suppresses HC emissions. be able to.

Of course, as mentioned above, the compression ratio conditions also have a large effect on startability. Regarding the balance with the above-mentioned diffusion combustion or premix combustion, see (1) above.
, (2), (6), etc. maintain this, and the air utilization rate is 1 because (1), (2), (4), etc. are related and improve this. .

For the convenience of explanation, each of the above conditions and their effects have been described individually, two or three at a time, but each condition should not be considered separately from the others, but should be considered in a way that promotes the advantages of each condition. However, in order to skillfully offset the drawbacks, it is essential to appropriately combine all these conditions, and only then can we obtain the above-mentioned comprehensive effects and create a combustion chamber that can achieve the objectives. Obtainable.

FIG. 3 shows another embodiment of the present invention, in which the present invention is applied to a polygonal combustion chamber as shown in Japanese Patent No. 819266.

In the case of such a polygonal combustion chamber, the side wall 21 of the combustion chamber 2 is made up of a side portion X and a corner portion Y that smoothly connects the side portions X, and the fuel F is allowed to collide diagonally against the side wall 21. As a result, the distribution and dispersion of fuel is improved, so the air utilization rate is even higher, and the swirl is properly controlled by the side portions X, so the NOx reduction effect is even greater. In this example of a polygonal combustion chamber, the diameter D2 of the side wall 21 is determined by each side portion X indicated by a dashed line in FIG.
Similarly, the diameter D3 of the inlet 22 is taken as the diameter of the circle inscribed in
is the diameter of a circle inscribed in each protrusion 23.

As described above, according to the present invention, it is possible to obtain an appropriately strong squish during the upward stroke of the piston 1, and also to appropriately suppress the air-fuel mixture that tends to scatter from the combustion chamber 2 after passing through the top dead center. In addition, by generating a micro vortex flow under the protruding portion 23 due to the reverse squishing, and further colliding an appropriate fuel injection axis F against the side wall 21, its distribution dispersion is improved and the air utilization efficiency is improved. By maintaining a balance between premix combustion and diffusion combustion, it is possible to obtain a durable, quiet, high-output engine with good startability, low emissions of CO, HC, NOx, and smoke, and low odor.

[Brief explanation of drawings]

FIG. 1 is a plan view of a piston showing one embodiment of the present invention, FIG. 2 is a sectional view taken along line A-A in FIG. 1, and FIG. 3 is a plan view of a piston showing another embodiment of the present invention. A plan view, FIG. 4 is a diagram showing the relationship between the D31D2, Pme and smoke according to the present invention, and FIG.
A diagram showing the relationship with the mode value of HC, Figure 6 is the same as the above-mentioned θ2
It is a figure showing the relationship between Pme and smoke. 1: Piston, 2: Combustion chamber, 3: Fuel injection nozzle, 21
: side wall, 22: inlet, 23: protrusion, 25: bottom.

Claims (1)

[Claims] 1. A protrusion protruding inward from the side wall of the combustion type is provided at the inlet of the combustion chamber for a direct injection diesel engine formed at the top of the piston, and the side wall, the protrusion, and the bottom of the combustion chamber each have a relatively small curvature. and a curvature larger than the curvature, and a straight portion is formed between the connecting positions of the two curvatures on the side wall, and the injected fuel collides with the straight portion approximately above the center of the combustion chamber. The fuel injection nozzle is arranged at a position such that the diameter of the piston is D_1, the diameter between the side walls of the combustion chamber is D_2, the diameter of the inlet is D_3, the depth is H, the thickness of the protrusion is t, and the diameter of the combustion chamber is D_3. The angle that the straight part of the side wall makes with the top surface of the piston is θ_1, the angle between the fuel injection axis and the straight part of the side wall is θ_2, and the small curvature is R_
1, 0.5<D_2/D_1<
0.6, 0.3<H/D_2<0.4, 0.85<D_
1/D_2<0.97, θ_1=90°, R_1≦t,
A combustion chamber characterized by having a relationship of 70°<θ_2<85.