JP2552908B2 - Diesel engine combustion chamber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a direct injection diesel engine, and in particular,
The present invention relates to a technique for improving a combustion chamber structure for promoting mixing of fuel and air to improve engine performance.

<Prior Art> A conventional diesel engine combustion chamber is, for example, the second
There is one as shown in the figure (see JP-A-56-106021).

The structure of this will be described in combination with the operation. In the compression stroke, the piston 1 rises and the air in the cylinder 2 is compressed. The compressed high-temperature and high-pressure air flows into the combustion chamber 3. When the piston 1 reaches the top dead center, the fuel is injected and supplied from the combustion injection valve 4 to the combustion chamber 3, and goes through the evaporation process and the mixing process with air to reach the combustion. By the way, when the piston 1 approaches the top dead center, the annular projection 5 provided on the top surface of the piston 1 enters the annular groove 7 provided in the cylinder head 6. As a result, the space 8 above the top surface on the outer peripheral side of the piston 1 around the annular projection 5 is pressurized to a pressure higher than the compression pressure of the normal compression stroke. This space, that is, the compression chamber 8 and the combustion chamber 3 are connected by a communication hole 9, and the air in the compression chamber 8 is ejected into the combustion chamber 3.

Since this air jet forms a turbulent flow in the combustion chamber 3, the mixing of fuel and air in the combustion chamber 3 is activated, and good fuel characteristics are obtained.

<Problems to be Solved by the Invention> However, in such a conventional combustion chamber 3 of a diesel engine, an air jet from the compression chamber 8 is injected into the combustion chamber 3 through the communication hole 9. Therefore, although the mixing property of the fuel and the air in the combustion chamber 3 can be improved, there is almost no effect of improving the ignition performance of the engine, and the ignition delay is delayed as compared with other diesel engines without the compression chamber 8 and the communication hole 9. There is little effect of shortening the period.

For this reason, the tendency that the prepared air-fuel mixture during the ignition delay period burns explosively immediately after ignition remains, and as a result, problems such as high combustion noise and easy generation of nitrogen oxides remain unsolved. There was a problem that it remained as it was.

Therefore, in view of the above conventional problems, the present invention,
By forcibly supplying the air pressurized in the cylinder toward the spray from the fuel injection valve and improving the mixture of the spray and air to a combustion chamber structure that can be enhanced from the initial stage of injection, the above conventional problems It is an object of the present invention to solve the above-mentioned problems and particularly to inject high-pressure air with respect to spray.

<Means for Solving the Problems> Therefore, the present invention provides a diesel engine in which fuel is directly injected from a combustion injection valve provided in a cylinder to a combustion chamber bored at the top of the piston. A protrusion projecting upward is provided substantially in the center of the bottom surface of the combustion chamber, a protrusion projecting downward is provided in the substantially center of the lower surface of the cylinder head, and a protrusion on the piston side is provided on the lower surface of the protrusion on the cylinder head side. A recess into which the portion enters, between the upper surface of the protrusion on the piston side and the inner surface of the recess,
A compression chamber is provided that is pressurized above the compression pressure of the normal compression stroke when the piston approaches top dead center, and the fuel spray immediately after the pressurized air is communicated with the compression chamber from the combustion injection valve is provided. A passage portion to be supplied to the cylinder head side is provided on the protrusion portion on the cylinder head side.

<Operation> In such a configuration, when the piston approaches the compression top dead center of the engine, the protrusion on the piston enters inside the recess on the cylinder head side, and the air retained in the compression chamber is compressed higher than that in the combustion chamber. Will be received.

 At approximately this time, fuel is injected from the combustion injection valve.

This fuel spray is supplied to the combustion chamber, but the compressed chamber air is supplied to this fuel spray through the passage portion provided on the protrusion on the cylinder head side, and the fuel and air are initially injected. To improve the mixing. That is, the atomization of fuel, evaporation, and the mixing property with air are improved, and ignition is quickly achieved.

For this reason, the explosive combustion immediately after ignition which has conventionally occurred is eliminated, and as a result, two effects of reducing combustion noise and suppressing generation of nitrogen oxides can be obtained.

Further, since the compression chamber is defined by the upper surface of the projection on the piston side and the inner surface of the recess, and does not communicate with other parts, for example, the mating portion of the pin ring, there is no fear of leakage of compressed air. Further, it is possible to inject higher pressure air toward the fuel spray, and the atomization effect of the fuel is high.

<Example> Hereinafter, an example of the present invention is described based on a drawing.

In the following drawings, the same elements as those in FIG. 2 are designated by the same reference numerals to simplify the description.

FIG. 1 shows an embodiment in which the present invention is applied to a two-cycle diesel engine.

In the figure, the cylinder head 6 is provided with the fuel injection valve 4 along the central axis of the cylinder 2, and the toroidal combustion chamber 3 is bored in the central portion of the top surface of the piston 1 in the same manner as in the prior art.

A compression chamber is provided between the cylinder head 6 and the top of the piston 1 so that the piston 1 is pressurized to a pressure higher than the normal compression pressure when the piston 1 approaches the top dead center. or,
The cylinder 2 is provided with a passage portion that communicates with the compression chamber and supplies pressurized air toward the fuel spray immediately after being injected from the fuel injection valve 4.

That is, in the figure, a cylindrical protrusion 18 protruding upward is integrally formed at the central portion of the bottom surface of the combustion chamber 3 of the piston 1. A projecting portion 19 projecting downward is integrally formed in the central portion of the lower surface of the cylinder head 6, and a circular recess 20 is formed in the lower surface of the projecting portion 19.

The protrusion 18 on the piston 1 side is the protrusion on the cylinder 2 side.
It is designed to fit inside the recess 20 of the groove 19.

In this case, the outer diameter of the protrusion 18 and the inner diameter of the recess 20 are substantially equal,
The gap formed between the outer peripheral surface of the protrusion 18 and the inner peripheral surface of the recess 20 is kept minute.

A compression chamber 21 is formed between the upper surface of the protrusion 18 and the inner surface of the recess 20.

A hole 22 having a bottom is formed in the protrusion 19 so as to be integrally connected to a mounting hole of the fuel injection valve 4 formed in the cylinder head 6.

In addition, one end of the protrusion 19 is opened to the inner surface of the hole 22 and the other end is opened to the peripheral surface of the protrusion 19, and a mixing hole 23 that communicates the inner space of the hole 22 with the inside of the combustion chamber 3 is formed. A vent hole 24 serving as the passage portion that communicates between the compression chamber 21 and the inside of the mixing hole 23 is formed by opening one end on the upper surface in the recess 20 and the other end on the inner surface of the hole 22. .

The mixing hole 23 and the vent hole 24 are formed at four locations that are separated by 90 degrees in the circumferential direction about the central axis of the protrusion 19.

Next, in this embodiment, when the piston 1 approaches the compression top dead center of the engine, the protrusion 18 enters the inside of the recess 20 and the air retained in the compression chamber 21 is compressed higher than that in the combustion chamber 3. Vent hole 24 and mixing hole for fuel spray
Air in the compression chamber 21 is supplied via 23, and the mixing of the fuel and air is improved from the beginning of injection. That is, the atomization of fuel, evaporation, and the mixing property with air are improved, and ignition is quickly achieved.

For this reason, the explosive combustion immediately after ignition which has conventionally occurred is eliminated, and as a result, two effects of reducing combustion noise and suppressing generation of nitrogen oxides are obtained.

Particularly, according to such a configuration, the compression chamber 21 has the piston 1
Since it is defined by the upper surface of the protrusion 18 on the side and the inner surface of the recess 20 and does not penetrate other portions, for example, the mating portion of the piston ring, there is no concern about compressed air leakage, and higher pressure air Can be injected toward the fuel spray, and there is an advantage that the effect of atomizing the fuel is high.

Although the above-described embodiment applies the present invention to the combustion chamber of a two-cycle engine, it can be applied to a combustion chamber of a four-cycle engine as a matter of course.

<Effects of the Invention> As described above, according to the combustion chamber of the diesel engine of the present invention, the air pressurized in the cylinder is forcibly supplied toward the spray from the combustion injection valve to generate the spray. Since the mixing with air was increased from the beginning of injection, atomization of fuel, evaporation and mixing with air were improved, and ignition could be reached quickly, so explosive fuel immediately after ignition disappeared. 2) Reduction of combustion noise and suppression of nitrogen oxide production
One effect is obtained.

In particular, according to the present invention, the compression chamber is provided between the upper surface of the protrusion on the piston side and the inner surface of the recess, and the compressed air is communicated with the compression chamber to direct the fuel spray immediately after being injected from the combustion injection valve. Since the passage portion for supplying the compressed air is provided on the protrusion on the cylinder head side, the compression chamber is configured so as not to communicate with other portions, for example, the mating port of the piston ring, and there is no risk of compressed air leakage. Further, there is an advantage that higher pressure air can be injected toward the fuel spray, and the atomization effect of the fuel is high.

[Brief description of drawings]

FIG. 1 is a front sectional view showing an embodiment of a combustion chamber of a diesel engine according to the present invention, and FIG. 2 is a front sectional view showing an example of a combustion chamber of a conventional diesel engine. 1 ... Piston, 2 ... Cylinder, 3 ... Combustion chamber, 4 ...
... fuel injection valve, 6 ... cylinder head, 21 ... compression chamber,
24 …… Vent

Claims (1)

(57) [Claims] 1. In a diesel engine for directly injecting fuel from a combustion injection valve provided in a cylinder to a combustion chamber bored at the top of a piston, the fuel injection valve projects upward to approximately the center of the bottom of the combustion chamber of the piston. A protrusion that protrudes downward at approximately the center of the lower surface of the cylinder head, and a recess that allows the protrusion on the piston side to enter on the lower surface of the protrusion on the cylinder head. A compression chamber is provided between the upper surface of the protrusion and the inner surface of the recess, the pressure being higher than the compression pressure of the normal compression stroke when the piston approaches the top dead center, and the compressed air is communicated with the compression chamber. A combustion chamber of a diesel engine, wherein a passage portion for supplying the fuel to the fuel spray immediately after being injected from the combustion injection valve is provided in the protrusion on the cylinder head side.