JPH02223630A - Combustion chamber structure for diesel engine - Google Patents

Abstract

PURPOSE:To restrain the coefficient of heat generation at the beginning for reducing NOx by injecting and supplying fuel into both a communication path which is led from a nozzle room to the outer periphery portion of a cylinder and a cavity which is recessedly provided in the approximate center portion of a piston top face. CONSTITUTION:A nozzle room 8 which is open on the side of a piston 3 is formed in the approximate center portion of a cylinder 1 of a cylinder head 4. Then, a fuel injecting nozzle 9 is provided in the nozzle room 8 and a main cavity 5 is recessedly provided in the approximate center portion of the top face of the piston 3. Also, a communication path 10 which is led from the nozzle room 8 to the outer periphery portion of the cylinder 1 is so formed as to penetrate the cylinder head 4. In this way, fuel is injected and supplied into both the communication path 10 and the main cavity 5. Fuel injection causes combustion inside both the communication path 10 and the main cavity 5. Therefore, heat generation divided into several positions is performed, thus restraining the occurrence of NOx.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to the combustion structure of diesel engines, particularly direct injection diesel engines.

BACKGROUND OF THE INVENTION Direct injection diesel engines generally have a combustion chamber mainly formed by a cavity recessed in the top surface of the piston, and fuel is injected into the cavity.

For example, in Japanese Utility Model Application Publication No. 63-73529, as shown in FIG. Each cavity 32.33
A configuration is disclosed in which fuel is injected and supplied toward the respective locations.

This is mainly intended to suppress the NOx in the exhaust gas, and is intended to suppress NOx by causing slow combustion.

Problems to be Solved by the Invention However, with the above conventional configuration, initial combustion is slow and NOx can be suppressed, but on the other hand, the squib area, that is, the space sandwiched between the lower surface of the cylinder hept 34 and the top surface of the piston 31 In the late stage of combustion when using 36 air, the mixture of fuel and air tends to be insufficient, and the overall combustion period becomes excessively long, resulting in poor fuel efficiency and smoke in the exhaust. Also cavity 32
．． As a result of the depth of the piston 33, the overall height of the piston 31 increases, which also causes the problem of an increase in weight.

Means for Solving the Problems In the combustion chamber structure of a diesel engine according to the present invention, a nozzle chamber with an opening on the piston side is formed approximately at the center of the cylinder head, and a fuel injection nozzle is provided there, and the piston top A cavity is recessed approximately in the center of the surface so as to face the opening of the nozzle chamber, and a communication passage from the nozzle chamber to the outer circumference of the cylinder is formed through the cylinder head, and both the communication passage and the cavity are formed. It is characterized by the fact that fuel is injected and supplied towards.

Effect: In the above configuration, combustion occurs both inside the cavity and inside the communication passage due to the fuel injection 7. That is, heat generation is performed in multiple locations, and as a result, NOx generation is suppressed.

Further, the high-temperature combustion gas reaches the periphery of the cylinder through the communication passage, combustion starts early in the periphery of the cylinder, and mixing with air is promoted by the flame ejected from the communication passage. This shortens the overall combustion period.

EXAMPLE Hereinafter, an example of the present invention will be described based on FIG.

In the figure, 1 is a cylinder formed in a cylinder block 2, 3 is a piston fitted into this cylinder 1, and 4 is a cylinder head.

On the top surface of the piston 3, a main cavity 5 having a substantially deep dish shape with a slightly constricted opening is recessed in the substantially center thereof, and a sub cavity having a substantially hemispherical shape is provided at the outer periphery. A plurality of cavities 5.6 are arranged at equal intervals, and a combustion chamber 7 is formed between the lower surface of the cylinder head 4 and the main body of these cavities 5.6.

Further, a substantially cylindrical nozzle chamber 8 with an opening on the piston 3 side is formed at a substantially central position of the cylinder inside the cylinder head 4, and a fuel injection nozzle 9 is provided in the nozzle chamber 8. The opening 8a of the nozzle chamber 8 is located above the center of the main cavity 5 of the piston 3. A plurality of communicating passages 10 are formed radially from the side wall surface of the nozzle chamber 8. The communication passage 10 is formed obliquely penetrating toward the outer periphery of the cylinder l on the lower surface of the cylinder head 4, and its tip openings 10a are located above the sub-cavities 6, respectively. Therefore, at the top dead center position of the piston 3, the main cavity 5 faces the opening 8a of the nozzle chamber 8, and each sub-cavity 6 faces the tip opening 10a of each communication path 1O, as shown in the figure.

Further, the fuel injection nozzle 9 is of a multi-nozzle hole type, and particularly has a first nozzle hole group oriented toward the opening 8a side of the nozzle chamber 8 and a second nozzle hole group oriented toward the communication path 10 side. ing. That is, as shown by symbols F+ and F* in the figure, a relatively large portion of the fuel is injected and supplied to the main cavity 5 side, and a portion of the fuel is injected toward the communication passage IO. There is. Note that the number of second nozzle holes is the same as the number of communication passages 10.

Now, in the above configuration, combustion starts by injecting fuel from the fuel injection nozzle 9 just before the compression top dead center of the piston 3, but at that time, the fuel is injected into the main cavity 5 and each communication path ]0 The fuel is injected towards both sides, and combustion occurs in each direction. In other words, heat generation is performed in multiple locations, and NOx generation at the initial stage of combustion is suppressed. In particular, if the volume and injection amount of each part are determined so that one of the two combustion regions will achieve rich combustion,
It is possible to further suppress NOx. In this embodiment, for example, the injection amount from the first nozzle hole group is set to be larger than the volume of the main cavity 5, and rich combustion occurs on the main cavity 5 side.

Further, the combustion generated in the communication passage 10 becomes a flame and is ejected toward the auxiliary cavity 6 side. Therefore, the sub-cavity 6
Combustion starts early in the squish region around the combustion chamber, and the ejected gas promotes mixing with the surrounding air, significantly improving the heat release rate in the latter half of combustion and shortening the combustion period.

Therefore, it is possible to improve fuel efficiency and exhaust smoke while sufficiently reducing NOx.

Furthermore, if the fuel consumption rate and the like are to be maintained at the conventional level, it is possible to delay the injection timing by the amount that the combustion time is shortened, so that a further significant reduction in NOx can be achieved.

Note that the communication path IO is connected to the nozzle chamber 8 during the compression stroke.
It functions as an air introduction passage. That is, as the piston 3 rises, a strong air flow can be generated toward the fuel injection nozzle 9, and atomization of the fuel spray can be promoted.

Next, FIG. 2 shows an embodiment in which, in place of the sub-cavity 6 on the piston 3 side, substantially hemispherical recesses 11 are formed at the end openings of the communicating passages 10 on the cylinder head 4 side. Furthermore, these recesses l! The sub-cavity 6 is not necessarily essential and can be omitted.

Further, as the fuel injection nozzle 9, a type in which fuel is injected from each nozzle hole at the same time can of course be used, but for example, as shown in Japanese Patent Application Laid-Open No. 62-159765, By using a fuel injection nozzle that allows the injection timing of the nozzle hole group to be different from the injection timing of the second nozzle hole group, a more optimal heat release rate pattern can be obtained.

Fig. 3 shows an example of the configuration of the nozzle body 2.
1, a one-dollar valve 22 and a second needle valve 23 are slidably disposed in a mutually fitted state. The tip of the two-needle valve 23 seals the second injection hole 25. And this first one. The first nozzle spring 26 and the second nozzle spring 27 bias the second needle valves 22 and 23 in the closing direction, and their opening pressures are set to different values. Therefore, when fuel is pressure-fed from the fuel injection pump, the first dollar valve 22 and the second needle valve 23 are lifted at different timings, and the fuel is injected into the main cavity 5 and each communication path 10 at different timings. can be supplied. For example, by appropriately shifting the injection timing of both, the initial heat release rate can be further suppressed, and the N
It is possible to further reduce Ox.

Effects of the Invention As is clear from the above explanation, the combustion chamber structure of a diesel engine according to the present invention can suppress the initial heat generation rate and reduce NOx, while at the same time promoting and improving combustion in the latter half. As a result, the overall combustion period can be shortened, and fuel efficiency and smoke can be improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of a combustion chamber structure according to the present invention, FIG. 2 is a sectional view showing a different embodiment, and FIG. 3 is an example of a fuel injection nozzle used in the combustion chamber structure of the present invention. FIG. 4 is a sectional view showing an example of a conventional combustion chamber structure. 3...Piston, 4...Cylinder head, 5...
Main cavity, 8... Nozzle chamber, 9... Fuel injection nozzle, 10... Communication passage. Fig. 1 3-m-piston 4-1 cylinder to 1 sof 5-1 life 21 mavity 8-m-nozzle! 9---Tue l, f41]Wlffnos°゛]shi1o---
-itiu& Figure 2

Claims (1)

[Claims] (1) A nozzle chamber with an opening on the piston side is formed approximately at the center of the cylinder head, and a fuel injection nozzle is provided there, and a fuel injection nozzle is provided at approximately the center of the top surface of the piston so as to face the opening of the nozzle chamber. The cavity is recessed,
A combustion chamber structure for a diesel engine, characterized in that a communication passage from the nozzle chamber to the outer circumference of the cylinder is formed through the cylinder head, and fuel is injected and supplied toward both the communication passage and the cavity. .