JPH02267313A - Combustion chamber for diesel engine - Google Patents

Abstract

PURPOSE:To perform the ignition and combustion of fuel rapidly and positively by connecting a combined passage to an auxiliary combustion chamber from the tangential direction, disposing a fuel injection valve coaxially in proximity to the combined passage and connecting a communicating hole communicated with a main combustion chamber to the intermediate part of the combined passage. CONSTITUTION:A cylindrical auxiliary combustion chamber 10 with a circular inner peripheral surface is formed between a cylinder head 1 and a mouthpiece 5 fitted thereto. The auxiliary combustion chamber 10 is also provided with a rectilinear combined passage 12, communicated in parallel from the tangential direction of the auxiliary combustion chamber 10 toward the vicinity of its base part formed at one part of the mouthpiece 5. A communicating hole 11 communicated with a main combustion chamber 4 is connected to the intermediate part of the combined passage 12 diagonally from below. A cylinder head 1 positioned at the end part of the combined passage 12 is provided with a fuel injection valve 13 disposed laterally so as to perform fuel injection in the axial direction of the combined passage 12. The fuel is thereby injected in the axial direction from the fuel injection valve 13 to the combined passage 12 so as to accelerate activation partially on the way to the auxiliary combustion chamber 10.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates in particular to improvements in the combustion chamber of a diesel engine having a main combustion chamber and a sub-combustion chamber.

(Prior Art) A diesel engine having a main combustion chamber and a sub-combustion chamber is constructed as follows, as disclosed in, for example, Japanese Utility Model Application Publication No. 57-30327.

This is also shown in FIG. 5, but in contrast to the main combustion chamber 4 defined above the piston 3 of the cylinder block 2, the auxiliary combustion chamber (vortex chamber) 6 formed in the cylinder head 1 is located in the mouthpiece 5. It communicates with the formed injection lower, and as the piston 3 rises, high-temperature air from the main combustion chamber 4 is forced into the auxiliary combustion chamber 6 via the injection lower.

At this time, since the injection lower is connected to the sub-combustion chamber 6 from the tangential direction, a strong swirling flow is generated within the sub-combustion chamber.

When fuel is injected from the fuel injection valve 9 near compression top dead center, the injected fuel is
Dispersion, evaporation, and further mixing with air of the fuel spray are promoted, eventually leading to ignition and combustion. In addition, for fuel with poor P granulation at the end of injection, combustion is promoted by promoting evaporation and mixing with air introduced from the main combustion chamber 4 through the auxiliary communication hole 8 near the fuel injection valve 9. We are working to improve this.

The combustion gas in the auxiliary combustion chamber 6 flows violently from the injection lower into the main combustion chamber 4 during the downward expansion stroke of the piston 3, and continues to be combusted while taking in new air.

(Problems to be Solved by the Invention) This diesel engine aims to improve combustion by forming a strong swirling flow in the auxiliary combustion chamber and by promoting fuel atomization at the end of fuel injection. It was not very effective in reducing combustion noise, which is one of the biggest concerns for diesel engines.

Combustion noise becomes louder when the injected fuel is combusted after a certain ignition delay, but when the fuel is injected directly into the auxiliary combustion chamber, which has a relatively large volume, as in this conventional example, There is a strong tendency for fuel to ignite early<<, but to ignite rapidly after a certain time delay after injection.

As a result, the knocking noise characteristic of diesel engines is unavoidable, especially during idle operation, low rotation speeds, and low load conditions.

The present invention aims to solve such problems.

(Means for Solving the Problems) Therefore, the present invention provides a combustion chamber for a diesel engine having a main combustion chamber formed above the piston and a sub-combustion chamber formed in the cylinder head in communication with the main combustion chamber. The sub-combustion chamber is formed so that at least a portion thereof has a circular cross section,
A mixing passage tangentially connected to this sub-combustion chamber is provided,
The fuel injection valve is arranged to face the mixing passage so that the fuel spray direction substantially coincides with the axis of the mixing passage, and a communication hole communicating with the main combustion chamber is connected in the middle of the mixing passage.

(Operation) During the compression stroke of the engine, air from the main combustion chamber flows tangentially from the communication hole through the mixing passage into the sub-combustion chamber, creating a strong swirling flow within the sub-combustion chamber.

When fuel is injected from the fuel injection valve into the mixing passage before compression top dead center, this fuel flows into the sub-combustion chamber while mixing vigorously with the airflow, but by the time the fuel spray is diffused in the sub-combustion chamber, Partial thermal decomposition occurs due to accelerated atomization and evaporation. Therefore, when the swirling flow is encountered in the auxiliary combustion chamber, ignition occurs immediately, and during the expansion stroke when the piston begins to descend, the air-fuel mixture containing the combustion flame is violently jetted from the mixing passage into the main combustion chamber via the communication hole. The combustion proceeds further while mixing with a large amount of air in the main combustion chamber.

In this way, ignition and combustion start within a very short time after the fuel is injected, so there is little ignition delay immediately after injection, and combustion noise is much reduced compared to the conventional method.

(Example) Embodiments of the present invention will be described below based on the drawings.

In the embodiment shown in FIGS. 1 and 2, an auxiliary combustion chamber 10 is formed between the cylinder head 1 and the mouthpiece 5 fitted into the cylinder head 1. This sub-combustion chamber 10 has a cylindrical shape and has a circular inner peripheral surface. A linear mixing passage 12 is formed in a part of the mouthpiece 5 so as to communicate with the auxiliary combustion chamber 10 from a tangential direction near the bottom of the sub-combustion chamber 10 in a substantially parallel manner.

A communication hole 11 is provided in the middle of this mixing passage 12 and is connected from diagonally downward, and communicates with the main combustion chamber 4 through this communication hole 11.

A fuel injection valve 13 is provided in the cylinder head 1 at the end of the mixing passage 12, and in this embodiment, the fuel injection valve 1
Reference numeral 3 is a bottle-shaped fuel injection valve, which is installed horizontally so as to inject fuel in the axial direction of the mixing passage 12.

Other parts that are the same as the conventional example are given the same reference numerals.
Next, the effect will be explained.

As the piston 3 rises during the compression stroke, high-temperature, high-pressure air from the main combustion chamber 4 is forced into the sub-combustion chamber 10 via the communication hole 11 and the mixing passage 12. Since it is tangentially connected to the chamber 10, a horizontal swirling flow is generated within the sub-combustion chamber along the inner circumferential surface.

When the compression top dead center approaches, fuel is injected from the fuel injection valve 13 toward the axis of the mixing passage 12 at a predetermined timing.

At this point, the forced jet from the communication hole 11 still exists in the mixing passage 12, so the injected fuel heads toward the sub-combustion chamber 10 while vigorously mixing with this high-temperature air flow, and the fuel spray is diffused in the sub-combustion chamber 10. Before this, the atomization and evaporation of the fuel are promoted and the fuel partially progresses to the stage of thermal decomposition.

When the fuel spray, which has been activated in this way and is in a state where it is very easy to ignite, encounters the swirling airflow in the sub-combustion chamber 10, ignition and combustion begin immediately, and the pressure in the sub-combustion chamber 10 further increases. . At this time, the piston 3 moves to the expansion stroke where it begins to descend, and the pressure difference between the main combustion chamber 4 and the sub-combustion chamber 10, which are expanding thereafter, is about to increase.

As a result, from the sub-combustion chamber 10, the mixing passage 12,
Combustion flame and activated mixed gas are violently ejected into the main combustion chamber 4 through the communication hole 11. Combustion proceeds rapidly while mixing with a large amount of high-temperature air in the main combustion chamber 4, and combustion is completely completed within a short period of time.

In addition, in this embodiment, since the mixing passage 12 is tangentially connected to the vicinity of the bottom of the sub-combustion chamber 10, the flame and activated gas are biased toward the bottom, and therefore, during the expansion stroke, these flames and the like quickly escape from the communication hole 11. The fuel can be ejected into the main combustion chamber 4, which is more effective in shortening the combustion time.

In this way, in the present invention, the fuel is not suddenly injected into the large volume space of the sub-combustion chamber 10, but is injected from the axial direction into the mixing passage 12 where a high-temperature, high-speed air flow exists,
Since the fuel is partially thermally decomposed before it diffuses into the sub-combustion chamber 10, the fuel is in a state where it is very easy to ignite when it reaches the sub-combustion chamber 10, where it violently comes into contact with a lot of high-temperature air. By doing so, ignition and combustion can be started immediately, and compared to the conventional method of directly injecting fuel into the auxiliary combustion chamber, there is a delay in fuel ignition and explosive combustion immediately after ignition. As a result, combustion noise caused by ignition delay can be significantly reduced even during idle operation, low speed, and low load.

In addition, since the entire amount of air forced into the sub-combustion chamber 10 from the communication hole 11 passes through the mixing passage 12, the flow velocity is very high and the turbulence of the flow is large. Partial thermal decomposition and activation of the injected fuel can be greatly promoted.

Next, the embodiment shown in FIG. 3 will be explained. In this embodiment, the fuel injection valve is a pole-type fuel injection valve 14, which is mounted on the cylinder head 1 from an oblique direction, but the fuel injection direction is the same as that described above. It is aligned with the axial direction of the passage 12.

In this case, the fuel can be injected in a direction different from the axial direction of the fuel injection valve 14, so as long as the fuel injection direction is aligned with the axis of the mixing passage 12, the fuel injection valve 14 can be injected into the cylinder head 1. On the other hand, it can be installed not from the horizontal direction, but from diagonally above, which gives a greater degree of freedom in assembling it to the cylinder head.

In the embodiment shown in FIG. 4, the shape of the sub-combustion chamber 10 is not cylindrical but spherical, and the mixing passage 12 communicates with the sub-combustion chamber 10 from its tangential direction. A strong swirling flow can be generated within the sub-combustion chamber.

(Effects of the Invention) As described above, according to the present invention, fuel is injected from the axial direction into the mixing passage through which high-temperature, high-velocity air flows, and the fuel is partially thermally decomposed and activated before reaching the sub-combustion chamber. It is possible to immediately start ignition and combustion through contact with the strong swirling airflow in the sub-combustion chamber, thus realizing stable and good combustion characteristics with little ignition delay, and reducing combustion noise such as so-called diesel knock. It is highly effective in reducing

[Brief explanation of drawings]

FIG. 1 is a vertical sectional view showing the first embodiment of the present invention, and FIG.
1J is a sectional view taken along the line A-A in FIG. 1, FIG. 3 is a longitudinal sectional view of the second embodiment, FIG. 4 is a longitudinal sectional view of the third embodiment, and FIG. 5 is a longitudinal sectional view of the conventional example. It is a diagram. 1... Cylinder head, 3... Piston, 4...
Main combustion chamber, 5... Mouthpiece, 12... Mixing passage, 10... Sub-combustion chamber, 1... Communication hole, 3.14... Fuel injection valve.

Claims (1)

[Claims] In a combustion chamber of a diesel engine having a main combustion chamber formed above the piston and a sub-combustion chamber formed in the cylinder head in communication with the main combustion chamber, the sub-combustion chamber has at least a circular cross section. A mixing passage tangentially connected to the auxiliary combustion chamber is provided, and a fuel injection valve is faced to the mixing passage so that the fuel spray direction substantially coincides with the axis of the mixing passage, and a fuel injection valve is provided in the middle of the mixing passage. A combustion chamber for a diesel engine, characterized in that a communication hole communicating with the main combustion chamber is connected.