JPS5910733A - Structure of combustion chamber for diesel engine - Google Patents

Abstract

PURPOSE:To promote combustion and reduce the fuel consumption by shaping spherically or cylindrical extruded part on the circumferential wall face of a combustion chamber to which the fuel from a fuel injection nozzle is dashed for increasing the flow speed of gas on the surface of the extruded parts along the circumferential wall of the combustion chamber. CONSTITUTION:At the top of a piston 2, a combustion chamber 8 is provided to be cylindrically concaved, and along its circumferential wall 9, spherical extruded parts 10 are provided to be extruded from the circumferential wall 9 at proper intervals. At the center of a bottom wall face 12 of a combustion chamber 8, a convex projected part 13 is provided to promote the swirling stream of gas in the combustion chamber 8. Extruded parts 10 on the circumferential wall 9 increase the flow speed of the air swirl along the circumferential wall 9 on the surface of the extruded parts 10, while the increase of the flow speed also reduces the thickness of the boundary layer on the surface of extruded parts 10 for promoting the atomization and mixing with fuel F. This construction permits to stabilize and improve the combustion in the combustion chamber 8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion chamber structure of a diesel engine, and more particularly to a peripheral wall surface of a combustion chamber formed at the head of a piston, which is hit by fuel from a fuel injection nozzle injected into the combustion chamber. By providing a spherical or cylindrical protrusion on the surface of the combustion chamber to increase the flow velocity of the gas in the combustion chamber at the protrusion surface (1) of the peripheral wall of the combustion chamber, combustion of the fuel adhering to the protrusion is promoted. The present invention relates to a combustion chamber structure for a diesel engine that can achieve good combustion in the chamber and reduce the amount of fuel injection.

[Technical background of the invention and its problems]

In general, direct injection diesel engines inject fuel directly from a fuel injection nozzle into the compressed, high-temperature, high-pressure air in the combustion chamber. Those formed with a concave shape are widely used. The fuel injected from the fuel injection nozzle is atomized and mixed with the air swirl generated within the combustion chamber, and combustion progresses.

However, although fuel sometimes lands on the wall surface of the combustion chamber where fuel is sprayed from the fuel injection nozzle, it is often discharged as unburned 1C hydrocarbons (IC). However, in the past, no special measures were taken to promote the evaporation and combustion of the sprayed fuel on the combustion chamber wall, which resulted in increased fuel consumption and However, the processing of IC in the exhaust gas was delayed.

[Purpose of the invention]

The present invention has been devised to effectively solve the above-mentioned conventional problems, and an object of the present invention is to provide a spherical or cylindrical protrusion on the peripheral wall surface of the combustion chamber where fuel from the fuel injection nozzle hits. By forming a part to increase the flow velocity of gas in the combustion chamber on the surface of the protrusion along the peripheral wall of the combustion chamber,
The combustion of the fuel injected towards the protrusion surface is promoted7'1
An object of the present invention is to provide a combustion chamber structure for diesel enodine that can achieve good combustion in the combustion chamber and reduce fuel consumption.

[Embodiments of the invention]

A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 1, 1 is a cylinder, and a piston 2 is fitted into the cylinder 1 so as to be able to reciprocate. In the cylinder head 3 at the top of the cylinder 1,
An intake passage 4 for supplying air into the cylinder 1 and an exhaust passage 5 for discharging exhaust gas from the cylinder 1 are formed. The intake passage 4 has an intake valve 6 that opens and closes it.
However, each exhaust passage 5 is still provided with an exhaust valve 7.

On the other hand, a combustion chamber 8 is formed in the head of the piston 2 by recessing it into a cylindrical shape. On the circumferential wall surface of the combustion chamber 80, spherical protrusions 10 are provided at appropriate intervals along the circumferential wall surface to protrude from the circumferential wall surface 9, as shown enlarged in FIGS. 2 and 3. In the example, there are 4 locations). In addition, a piston 2 is installed in the cylinder head 3 to compress the air inside the cylinder 1.
A fuel injection nozzle 11 is provided to inject the fuel F into the combustion chamber 8 when /ζ rises. It is formed so as to face each protrusion 1o of the peripheral wall surface 9. At the center of the bottom wall surface 12 of the combustion chamber 8, an extending portion 13 is formed in a raised mountain shape in order to promote swirling of the gas within the combustion chamber.

Next, the operation of this embodiment will be described.

The air sucked into the cylinder 1 from the intake passage 4 during the intake stroke is deposited on the inner wall surface of the cylinder 1? L'1 draws a swirling flow, that is, an air swirl, and is compressed by the rise of the piston 2, resulting in high temperature and high pressure, and this high temperature and high pressure combustion chamber 8
Fuel F is injected from each injection port 11a of the fuel injection nozzle 11 into the air swirl. The injected fuel F is atomized and mixed with the air swirl, spontaneously ignites, and burns while stirring the gas in the combustion chamber. However, in the conventional combustion chamber, since the combustion chamber is simply cylindrical or prismatic, the swirl velocity of the peripheral wall surface of the combustion chamber is almost uniform over its entire surface. Therefore, the fuel that adheres to the peripheral wall surface that is hit by the fuel sprayed from the fuel injection nozzle is not quickly evaporated and burned, but is discharged together with the exhaust gas.

However, in the present invention, since the protrusion 10 is provided on the circumferential wall surface of the combustion chamber 80 that is hit by the fuel F injected from the fuel injection nozzle 11, the protrusion 10 is disposed in the following manner.
The fuel F injected toward the target is quickly evaporated and burned.

That is, since the protrusion 10 is formed on the peripheral wall surface 9, the air swirl velocity along the circumferential wall surface 9 increases on the surface of the protrusion 10, and as the flow velocity increases, the thickness of the boundary layer on the surface of the protrusion 10 also increases. As a result, the atomization and mixing with the injected fuel F is promoted, and the fuel F adhering to the protrusion 10 is reduced.
The evaporation of the gas will be accelerated and it will be burned quickly. Furthermore, in this way, the fuel F injected toward the protrusion 10
is quickly combusted and the combustion in the combustion chamber 8 becomes stable and good, so the temperature of the protrusion 10 also rises and the evaporation of the fuel F in the protrusion 10 is further promoted.

By providing the protrusion 10, the swirl flow at the protrusion 10 is I/2ρυ2 (ρ is density, V is flow velocity)
Although it loses its energy due to the head loss of the protrusion 1
The thickness cl protruding inward from the combustion chamber 8 is set to 30% or less of the radius R of the combustion chamber 8, and the head loss due to the protrusion 10 is affected by the square of the flow velocity, so normal combustion There is no risk of interfering with the relatively low-speed air swirl flow at the time of combustion, and on the contrary, it suppresses the strength of high-speed overswirl when explosive and rapid combustion occurs. Furthermore, since the protruding part 10 is formed in a spherical shape facing the injection port 11a of the combustion injection nozzle 11, the fuel F that hits the protruding part 10 is scattered in all directions, thereby improving the diffusion of the fuel F.

Figure 4 shows the measurement results of HC, CO, and smoke contained in the exhaust gases discharged from the combustion chamber of the present invention in which a protrusion is provided on the peripheral wall surface of the combustion chamber, and a conventional combustion chamber in which no protrusion is provided. show. In the figure, the solid line 9 is the value for the present invention, and the broken line is the value for the conventional case. ○, Δ, and 1 are the measured values of IC, CO, and smoke according to the present invention and the conventional method. This graph shows that in the present invention, the amount of CO contained in the exhaust gas is lower than that in the conventional example.

It can be seen that the amount of smoke and HC is reduced.

In the embodiment described in -, the combustion chamber 8 has a cylindrical shape, but it may have a prismatic shape or any other shape. In the case of a prismatic shape, the thickness of the protrusion may be set to 30% or less of the radius of the inscribed circle inscribed in the rectangle of the prismatic cross section. Historically, the protrusion 10 is not only spherical, but also cylindrical, etc., as long as it increases the flow velocity on the surface of the protrusion 10 without interfering with the swirl flow. Unfortunately, there is still no peace of mind that the shapes of the protrusions will all be the same.

However, the number of nozzles 11a of the fuel injection nozzle 11 is not limited to four, but may be freely provided, such as providing five or more.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the following excellent effects can be achieved.

(1) It is possible to increase the flow velocity of the gas in the combustion chamber on the protrusion table 1ni, and to reduce the thickness of the boundary layer on the protrusion surface as the flow velocity increases, so that the air swirl of the fuel injected toward the protrusion In addition, the evaporation of the fuel adhering to the protrusion is promoted, and rapid combustion can be achieved.

(2) Therefore, it is possible to reduce the amount of HC, CO, smoke, etc. contained in the exhaust gas that is combusted and exhausted.

(3) Conventionally, ICs that adhere to the wall of the combustion chamber and are ejected unburned can be quickly combusted in the combustion chamber.
The amount of fuel injection or consumption can be reduced.

(4) It is possible to suppress the high-speed superswirl flow during rapid combustion, and to alleviate the shock wave that is applied to the porpoise, etc.

(5) It has a simple structure, can be easily implemented, and is highly useful.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of an embodiment of a diesel engine according to the present invention, FIG. 2 is an enlarged plan view of the piston shown in FIG. 1, and FIG. 3 is a partial side sectional view of FIG.・1
The figure is a graph showing various measured values of exhaust gas (including HC, etc.) discharged from the combustion chamber of the present invention and the combustion chamber of ILY. is a piston, 3 is a linter\
8 is a combustion chamber, 9 is a peripheral wall surface, 10 is a protrusion, 11 is a fuel injection nozzle, and Fid combustion chamber 1. Patent applicant Izuso Automobile Co., Ltd.

Claims (3)

[Claims] (1) A combustion chamber is formed by recessing the head of a piston provided reciprocally within the /su/da, and in the combustion chamber,
In a diesel engine that injects fuel from a fuel injection nozzle provided on the cylinder head side of the cylinder, the peripheral wall surface of the combustion chamber that is hit by the fuel injected from the fuel injection nozzle has a spherical or cylindrical shape, etc. 1. A combustion chamber structure for a diesel engine, characterized in that a protrusion is formed to increase the flow velocity of gas within the combustion chamber on the surface of the protrusion. (2) In the case where the combustion chamber is cylindrical, the thickness of the protruding portion protruding in the direction of the combustion chamber is set to 30% or less of the radius of the cylindrical combustion chamber. Combustion chamber structure of the diesel engine according to item 1. (3) In the case where the combustion chamber is prismatic, the thickness of the protruding portion protruding in the direction of the combustion chamber is set to 30% or more of the radius of the inscribed circle inscribed in the prismatic shape. A combustion chamber structure for a diesel engine according to claim 1, characterized in that: