JPH05214938A - Direct injection type spark ignition engine - Google Patents

Abstract

PURPOSE:To stratify the air-fuel mixture near an ignition plug and stably attain lean combustion by accelerating the gasification of fuel at the valve face sections of exhaust valves, and retaining the fuel in impregnation layers on the surface of the valve face sections. CONSTITUTION:The combustion chamber ceiling wall 11 of a cylinder head is inclined into a penthouse roof shape, an ignition plug 8 is provided at the center section, and multiple intake valves 9 and exhaust valves 10 are arranged respectively face to face across the ignition plug 8. A fuel injection valve 3 is arranged on the combustion chamber ceiling wall 11 to face the exhaust valves 10 across the ignition plug 8. The fuel injection valve 3 is set to diffuse the fuel sprays from multiple nozzle holes 4 toward valve face sections 10a of the exhaust valves 10 clear of the ignition plug 8. Fuel impregnation layers including fine irregularities and pores are formed on the surface of the valve face sections 10a of the exhaust valves 10 facing a combustion chamber. The gasification of fuel is accelerated near the ignition plug 8, and the air-fuel mixture is stratified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a direct injection spark ignition engine.

[0002]

2. Description of the Related Art A premixed spark ignition engine equipped with a carburetor and a fuel injection valve in an intake pipe has a problem that output characteristics and exhaust composition are deteriorated due to fuel transportation delay, especially during transient operation. In order to solve this, a direct injection spark ignition engine has been considered in which a fuel injection valve faces the combustion chamber and the fuel is directly injected and injected into the combustion chamber.

As this direct injection type spark ignition engine, the one disclosed in Japanese Patent Laid-Open No. 57-62915 has been disclosed.
Fuel is injected into the combustion chamber during the intake stroke, and an intake swirl is generated in the combustion chamber to promote mixing of fuel and air.

[0004]

However, evenly mixing the fuel and air in the combustion chamber contributes to the stabilization of combustion, but on the other hand, the air-fuel ratio of the air-fuel mixture is very thin and the fuel consumption performance is excellent. In the case of realizing lean combustion, such homogeneous mixing method tends to make the ignition by the spark plug very unstable.

As one method for stabilizing the ignition performance in lean combustion, stratification of the air-fuel mixture that makes the air-fuel ratio near the spark plug richer than the other is effective. In this way, fuel and air are separated from the intake stroke. When mixing, it is difficult to form and maintain a rich air-fuel mixture layer around the spark plug immediately before ignition, stable ignition performance cannot be secured in operation with a lean air-fuel mixture, and improvement of fuel consumption and exhaust composition is also difficult. Becomes

It is an object of the present invention to provide a direct injection type spark ignition engine which enables stable lean combustion by stratification of an air-fuel mixture.

[0007]

SUMMARY OF THE INVENTION The present invention is a direct injection type spark ignition engine in which a combustion chamber faces an ignition plug and a fuel injection valve. A plurality of exhaust valves, and a fuel injection valve is provided at a position facing the exhaust valve with the spark plug interposed therebetween, and fuel spray injected from the fuel injection valve during a compression stroke avoids the spark plug. The direction of the injection port is set so as to face the exhaust valve, and an impregnated layer having fine irregularities is formed on the surface of the valve face portion facing the combustion chamber of the exhaust valve.

[0008]

In the compression stroke in which the piston rises, the fuel spray injected from the fuel injection valve into the combustion chamber is directed toward the exhaust valve while avoiding the spark plug and hits the valve face portion of the exhaust valve.

The valve face, which is exposed to combustion gas and has a very high temperature, is formed of an impregnating member, has a large surface area for collision with fuel, and has a high fuel holding function due to fine pores. It is possible to instantly evaporate and vaporize and retain a large amount of fuel near the valve face portion.

Since the valve face portion is arranged in the vicinity of the spark plug, most of the fuel atomized and vaporized by the valve face portion stays in the vicinity of the spark plug, and a rich air-fuel mixture exists in the vicinity of the spark plug. Form the layers.

Since the fuel injection timing is in the compression stroke, the stratified state of the air-fuel mixture is maintained even during ignition, stable ignition performance is secured even when the air-fuel mixture is diluted, and fuel consumption is reduced.
Emissions can be reduced and higher output can be achieved. Also, in the region far from the spark plug of the combustion chamber, the air-fuel ratio becomes super lean,
Since the self-ignition reaction leading to knocking is suppressed, as a result, the compression ratio is increased and the thermal efficiency and output are improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment in which the present invention is applied to a 4-stroke engine will be described below with reference to the accompanying drawings.

As shown in FIGS. 1 and 2, the combustion chamber ceiling wall 11 of the cylinder head 1 is inclined in a pent roof type, and an ignition plug 8 faces the center thereof, and the ignition plug 8 is sandwiched therebetween.
One intake valve 9 and two exhaust valves 10 are provided facing each other. In the figure, 6 is an intake port and 7 is an exhaust port.

The fuel injection valve 3 is arranged on the combustion chamber ceiling wall 11 so as to face each exhaust valve 10 with the spark plug 8 interposed therebetween. In this embodiment, the fuel injection valve 3 is on the side of the intake valve 9,
It is also located in the middle of both intake valves 9.

The fuel injection timing is set so that the fuel injection pressure does not rise above the pressure in the combustion chamber 5 during the compression stroke.

The fuel injection valve 3 is mounted substantially horizontally (in the direction orthogonal to the cylinder axis), and the injected fuel is the exhaust valve 1
It is set so as to face the valve face portion 10a of 0. In this embodiment, the fuel injection valve 3 has two injection ports 4, and each injection port 4 is formed toward each exhaust valve 10. In FIG. 1, O ₄ is the center line of each injection port 4, and each center line O ₄ intersects with the center line O ₁₀ of each exhaust valve 10 on the valve face portion 10a. The two center lines O ₄ have a predetermined sandwiching angle θ on the plan view of FIG. 1, and diffuse the fuel spray from each injection port 4 toward the valve face portion 10 a of each exhaust valve 10 while avoiding the spark plug 8. ..

On the other hand, an impregnated layer containing fine irregularities and pores is formed on the surface of the valve face portion 10a of the exhaust valve 10 which faces the combustion chamber 5. This impregnated layer is formed by placing an impregnating substance such as a ceramic compound on the surface of the valve face portion 10a, melting it with a burner and firing it in a furnace, or by so-called ceramic spraying, or by using one of the valve face portion 10a. A porous material with minute pores is used for the valve part, or the valve face part 10a
This can be achieved by forming fine irregularities on the surface of the metal by metal spraying.

The exhaust valve 1 is provided on the ceiling wall 11 of the combustion chamber.
A squish area 12 located on the side of 0 is formed in parallel with the stepped portion of the top surface of the piston (not shown), and causes a squish toward the center of the combustion chamber 5 near the top dead center of the piston. ..

Next, the operation will be described.

The fuel injection timing is set so that the pressure in the combustion chamber 5 does not exceed the injection pressure during the compression stroke, and the fuel spray injected from the two injection ports 4 of the fuel injection valve 3 avoids the spark plug 8. The valve faces the exhaust valves 10 and hits the valve face portions 10a of the exhaust valves 10, respectively.

Since the fuel spray does not directly hit the spark plug 8, so-called fuel fog is prevented and a good ignition action of the spark plug 8 can be maintained.

Since the valve face portion 10a of each exhaust valve 10 is exposed to the combustion gas and has a temperature higher than that of the other combustion chamber ceiling wall 11, the fuel colliding with the valve face portion 10a is instantly evaporated and vaporized. Also, the valve face part 1
0a has an impregnated layer formed on the surface thereof, has a large surface area for collision with fuel, and has a high fuel retention function due to fine irregularities and pores, so that the collision fuel is instantly evaporated and vaporized, and at the same time, the valve face 10a A large amount of fuel can be retained in the vicinity.

Since the fuel is injected in the compression stroke and is pushed into the upper part of the combustion chamber as the piston rises, the fuel around the valve face portion 10a does not spread over a wide range. On the other hand, when fuel injection is performed in the intake stroke, the strong air flow flowing from the intake port 6 into the combustion chamber 5 causes the fuel spray to spread over a wide area, forming a rich mixture layer near the spark plug 8. I can't make it.

On the other hand, as the piston rises, air compressed between the squish area 12 and the piston causes a squish toward the center of the combustion chamber 5, causing a large amount of fuel distributed in the vicinity of each valve face portion 10a. Push back in the direction of the spark plug 8 in the center of the combustion chamber. The rich air-fuel mixture layer around the valve face portion 10a near the spark plug 8 stabilizes the ignition by the spark plug 8 even if there is no squish action, but the squish causes more rich air-fuel mixture in the vicinity of the spark plug 8. Collected.

In this way, most of the fuel is collected in the vicinity of the spark plug 8, and a rich air-fuel mixture layer is formed in the vicinity of the spark plug 8 immediately before ignition, that is, the air-fuel mixture is stratified and the ignitability by the spark plug 8 is improved. It can be raised. Therefore, even when lean combustion is performed at a mixture ratio considerably lower than the stoichiometric air-fuel ratio, by making the vicinity of the spark plug 8 denser than the average air-fuel ratio of the combustion chamber 5, the spark plug 8 is surely ignited and a stable initial flame is obtained. Can generate nuclei. As a result, stable lean combustion is realized, fuel consumption is reduced, emissions are reduced, and high output is achieved.

Further, due to the stratification of the air-fuel mixture, the air-fuel ratio is increased in a region far from the spark plug 8 of the combustion chamber 5, that is, the air-fuel ratio is super-diluted. It is possible to make the ignition reaction less likely to occur, and for this reason, the compression ratio can be substantially increased to improve the thermal efficiency and the output.

[0027]

As described above, according to the present invention, in the direct injection type spark ignition engine, an ignition plug is provided in the central portion of the ceiling wall of the combustion chamber, and a plurality of exhaust valves are arranged around the ignition plug to perform the ignition. A fuel injection valve is provided at a position facing the exhaust valve across the plug, and the direction of the injection port is set so that the fuel spray injected from the fuel injection valve during the compression stroke is directed to the exhaust valve while avoiding the spark plug. In addition, since the impregnated layer having fine irregularities is formed on the surface of the valve face portion facing the combustion chamber of the exhaust valve, the high temperature valve face portion promotes evaporation and vaporization of the fuel in the vicinity of the spark plug, and at the same time the impregnated layer is formed. More fuel is retained and retained, and stratification of the air-fuel mixture that collects a large amount of vaporized fuel near the spark plug near the valve face is achieved, maintaining stable ignition performance even with a lean air-fuel mixture. , Fuel consumption and exhaust It is possible to achieve a significant improvement of the cushion.

[Brief description of drawings]

FIG. 1 is a plan view of a combustion chamber ceiling wall showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the same.

[Explanation of symbols]

 3 Fuel injection valve 4 Injection port 5 Combustion chamber 8 Spark plug 9 Intake valve 10 Exhaust valve 10a Valve face part 11 Combustion chamber ceiling wall

Claims (1)

[Claims] 1. A direct injection spark ignition engine in which a spark plug and a fuel injection valve are exposed to a combustion chamber, the spark plug is provided at a central portion of a combustion chamber ceiling wall, and a plurality of exhaust valves are arranged around the spark plug. A fuel injection valve is provided at a position facing the exhaust valve with the spark plug interposed therebetween, and the fuel spray injected from the fuel injection valve during the compression stroke is directed to the exhaust valve while avoiding the spark plug. A direct-injection spark ignition engine, characterized in that an impregnated layer having fine irregularities is formed on the surface of a valve face portion facing the combustion chamber of this exhaust valve.