JPS633373Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a direct injection diesel engine that injects fuel directly into a combustion cavity formed at the top of a piston.

(Prior art) In a direct injection diesel engine, a combustion cavity is formed at the top of the piston to create an air vortex or squish during the compression process, and fuel is injected into the squish to mix air and fuel. There is an evaporative combustion method in which fuel is injected onto the wall of a combustion cavity and brought into contact with a wide area of the piston wall to evaporate the fuel, thereby promoting mixing of air and fuel. Each of these combustion methods has its advantages and disadvantages, and the mixed combustion method has the drawbacks of rapid combustion and difficulty in achieving good mixing.
Although the evaporative combustion method does not have the above-mentioned problems, it has the drawbacks of poor startability and the tendency to cause incomplete combustion at low loads.

Solve these problems and give a good mixture,
Direct-injection diesel engines are known that have a so-called squirt-lip type combustion cavity that extends from the top of the piston to the inside in order to improve fuel efficiency and obtain high output. is mixed with air due to the squish generated during the compression process, and a portion of it evaporates when it hits the cavity wall and mixes with air. Japanese Patent Publication No. 52-33242 discloses that in an engine equipped with a combustion cavity as described above, the collision angle between the fuel and the cavity wall is limited to prevent the fuel from being injected onto the top surface of the piston. The structure is such that the fuel that hits the wall surface evaporates in a favorable manner. In this disclosure, it is possible to obtain a good mixing condition in an engine with fixed fuel injection timing, but it is known that the fuel injection timing is changed in order to obtain high output. In such an engine, changing the timing changes the position of the fuel that hits the combustion cavity wall, and when the injection timing is advanced, initially the fuel crosses the combustion cavity and hits the top of the piston, causing the temperature in this area to become localized. A phenomenon occurs in which the amount increases and some parts are lost. This phenomenon tends to occur on the exhaust port side, where heat is difficult to dissipate, especially on the exhaust port side where the heat load is high.

In order to prevent such defects, if the fuel injection direction is uniformly corrected downward so that the fuel does not exceed the combustion cavity, a problem arises in that high output cannot be maintained.

(Objective of the Present Invention) Therefore, an object of the present invention is to provide a direct injection diesel engine that can effectively prevent the piston from being damaged while ensuring high output.

(Configuration of the present invention) The above object of the present invention can be achieved by the following configuration. That is, the present invention provides a direct injection type diesel engine in which a ski-lip type combustion cavity is formed at the top of the piston and injects fuel toward the wall of the combustion cavity. It is characterized in that the direction is downward compared to the direction of fuel injection to other wall surfaces.

(Effects of the Present Invention) According to the present invention, the direction of fuel injection toward the exhaust port side is directed downward relative to the other side. As a result, even if the fuel injection timing is advanced, fuel will not be injected beyond the combustion cavity on the exhaust port side, and damage to the lip portion of the top surface of the piston can be prevented. Also,
In the present invention, since fuel injection in directions other than the exhaust port side is set in the normal direction, high output can be maintained.

(Description of Examples) Examples of the present invention will be described with reference to the drawings.

FIG. 1 shows a top section of an engine 10, in which a piston 16 is adapted to slide within a cylinder 14 formed in a cylinder block 12. A ski-lipped combustion cavity 18 is formed at the top of the piston 16 and extends toward the interior of the piston. The cylinder head 20 is provided with a fuel injection nozzle 22 for injecting fuel toward the wall of the combustion cavity 18. Further, an exhaust port 24 that opens toward the top of the cylinder and an exhaust passage 26 that is continuous with the exhaust port 24 are provided. The exhaust port 24 is combined with an exhaust valve 28 that opens and closes the exhaust port at predetermined timing. Referring to FIG. 2, the positional relationship of the upper part of the engine is shown in a plan view, and the intake port 30 and intake passage 32 are arranged symmetrically with the arrangement of the exhaust port 24 and the exhaust passage 26. Furthermore, the center O of the cylinder 14, the center P of the fuel cavity 18, and the center N of the injection nozzle 22 are located at the intake port 3.
0 and exhaust port 24 approximately on the axis of symmetry. Fuel injection from the nozzle in this example is performed in the directions of arrows A, B, C, and D in the figure.

As shown in Figure 3, fuel injection from the nozzle is as follows:
It starts before the piston reaches top dead center and stops slightly past top dead center.

In this case, when the injection timing is changed depending on the operating condition and the injection start is advanced, as shown in FIG. 4, if the normal injection direction is maintained, the initial stage of injection, that is, the piston 16 is relatively low. When in position, as shown by line A, fuel is injected onto the top surface of the lip portion 18a of the combustion cavity 18 of the piston 16. When fuel is injected into the lip portion 18a, the lip portion is difficult for heat to dissipate, so the temperature of this portion locally rises, and especially in the exhaust side portion where the heat load is high, as shown in FIG. The problem arises that . In this example,
In the injection direction where such defects are likely to occur, the injection timing is advanced and even if injection starts when the piston is downward, the fuel is corrected downward as shown in Figure 4 A'. does not exceed the cavity 18, and therefore the occurrence of the above-mentioned defects can be prevented. In this example, the fuel injection direction is corrected only in the injection directions A and B on the exhaust side, where heat load is high and defects are likely to occur, and the other directions C and D are kept as normal. Output reduction is not a problem.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the top of the engine, Fig. 2 is a schematic plan view of the top of the engine, Fig. 3 is a graph representing the injection time of the nozzle, and Fig. 4 shows the line X in Fig. 2.
FIG. 5, a partial cross-sectional view taken along the line -X, is a cross-sectional view showing the state of the lip portion being damaged. Explanation of symbols, 10...Engine, 12...Cylinder block, 14...Cylinder, 16...Piston, 18...Combustion cavity, 20...Cylinder head, 22...Fuel injection nozzle, 24...Exhaust port, 26...Exhaust passage.

Claims (1)

[Scope of Claim for Utility Model Registration] In a direct injection diesel engine in which a squirt-lip type combustion cavity is formed at the top of the piston and fuel is injected toward the wall of the combustion cavity, A direct injection diesel engine characterized by the direction of combustion injection being directed downwards compared to the direction of fuel injection to other walls.