JPH09217627A - Direct injection lean burn high compression ratio gasoline engine - Google Patents

Abstract

(57) An object of the present invention is to form a central combustion chamber in a piston or a cylinder head, set a low compression ratio with a rich mixture in the central combustion chamber, and compress a main combustion chamber with a high lean mixture. A direct-injection lean burn high compression ratio gasoline engine that improves the thermal efficiency by making a lean mixture in the combustion chamber as a whole is provided. According to the present invention, a central combustion chamber 2 is formed in a cylinder head 12, and a cavity 20 is formed near the top dead center of a piston.
The piston 3 is formed with a protrusion 6 which can be closed by closing the opening 30. It is set so that the fuel from the fuel injection nozzle 4 can be injected into the central combustion chamber 2, and the rich air-fuel mixture in the central combustion chamber 2 is ignited by the spark plug 5. At the piston compression top dead center, the compression ratio of the central combustion chamber 2 is set lower than the compression ratio of the main combustion chamber 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection lean burn high compression ratio gasoline engine having a central combustion chamber formed in a cylinder head or a piston.

[0002]

2. Description of the Related Art Conventionally, an engine in which a cylinder head is provided with a projecting portion for projecting into a combustion chamber is, for example, an actual open sho 53.
No. 153102. The engine has a cylinder head formed with a protrusion capable of entering a combustion chamber formed in a piston, and the cylinder head is provided with an injection nozzle. The air velocity of the squish flow flowing into the combustion chamber is increased in the minimum clearance formed between the piston and the protrusion before the piston top dead center.

The combustion chamber of the internal combustion engine disclosed in Japanese Patent Laid-Open No. 6-264747 has a piston provided with a protrusion,
By forming a combustion chamber forming space in the cylinder head and sufficiently ensuring combustion improvement by squish, deterioration of startability and misfire during operation are prevented.

Further, in the direct injection layered combustion engine disclosed in Japanese Unexamined Patent Publication No. 6-317161, a fuel injection nozzle and a spark plug are provided in a cylinder head, and fuel from the fuel injection nozzle is supplied to a combustion chamber formed in a piston. The fuel is injected and ignited and burned by ignition of the spark plug near the top dead center of the piston.

Further, the combustion chamber of the compact combustion chamber internal combustion engine disclosed in Japanese Patent Laid-Open No. 7-259566 discloses a combustion chamber formed by forming a cavity in a cylinder head or a piston, and the combustion chamber near the top dead center. The protrusion is formed to rush into. In the combustion chamber, the residual gas flow rate in the combustion chamber and the injection timing are calculated, and the air fuel consumption is calculated and controlled. To do this, the cavities and the protrusions are effective, and the agitation from many nozzles Air fuel consumption control can be performed locally.

[0006]

Generally, in a gasoline engine, a mixture produced by mixing fuel and air is ignited by a spark plug to ignite and burn the mixture, but the mixture must be a theoretical mixture. Good ignition and combustion is not possible. Therefore, in order to ignite and burn the fuel, the gasoline engine generates a theoretical mixture, and ignites the generated theoretical mixture with a spark plug to ignite and burn the fuel. However, when the fuel is burned with a theoretical mixture, the theoretical thermal efficiency is better when the mixture is thinner,
You can't improve fuel economy. On the other hand, the theoretical thermal efficiency of the engine is greatly affected by the compression ratio (expansion ratio), and the theoretical thermal efficiency improves as the compression ratio increases. However, if the compression ratio is increased, the friction loss increases, so that there is an optimum value for the compression ratio, and generally, the compression ratio of 15 to 16 is good. However, in a gasoline engine, the compression ratio cannot be increased due to the problem of knocking, which is a major factor that deteriorates fuel efficiency.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and a rich air-fuel mixture which is a theoretical air-fuel mixture only in a part of a combustion chamber (hereinafter, to distinguish from a lean air-fuel mixture). , Rich mixture), and lean mixture in other parts, ignite the spark plug against the rich mixture, ignite and burn fuel, and achieve thermal efficiency equal to or higher than that of diesel engine. It is to provide a direct injection lean burn high compression ratio gasoline engine that secures.

According to the present invention, a central combustion chamber constituted by a cavity formed in a cylinder head, a lip portion forming an opening peripheral edge portion of the cavity, a reciprocating motion in the cylinder and a peripheral edge of the cavity near the top dead center of the piston. A piston having a protrusion protruding into the opening to close the opening, a main combustion chamber formed on the cylinder side around the protrusion of the piston, and the cylinder for injecting fuel into the central combustion chamber The present invention relates to a direct injection lean burn high compression ratio gasoline engine including a fuel injection nozzle arranged in a head and a spark plug arranged in the cylinder head so as to ignite an air-fuel mixture in the central combustion chamber.

Alternatively, according to the present invention, a central combustion chamber constituted by a cavity formed in a piston that reciprocates in a cylinder, a lip portion forming an opening peripheral edge portion of the cavity, and a peripheral edge of the cavity near the top dead center of the piston. A protrusion projecting from the lower surface of the cylinder head that rushes into the opening and can close most of the opening, a main combustion chamber formed on the cylinder side around the protrusion, and the cylinder so that fuel can be injected into the central combustion chamber. The present invention relates to a direct injection lean burn high compression ratio gasoline engine including a fuel injection nozzle arranged in a head and a spark plug arranged in the cylinder head so as to ignite an air-fuel mixture in the central combustion chamber.

Further, in this direct injection type lean burn high compression ratio gasoline engine, the compression ratio in the central combustion chamber is set lower than the compression ratio in the main combustion chamber at the piston compression top dead center. Further, the fuel injection from the fuel injection nozzle is injected and diffused along the wall surface of the central combustion chamber.

In this direct injection type lean burn high compression ratio gasoline engine, a rich air-fuel mixture is formed in the central combustion chamber and a lean air-fuel mixture is formed in the main combustion chamber. Further, the rich mixture is ignited and burned by ignition of the spark plug near the top dead center of the piston closed in the central combustion chamber by the protrusion, and then burned and propagated to the lean mixture in the main combustion chamber. .

Since this direct injection type lean burn high compression ratio gasoline engine is constructed as described above, when the total compression ratio ε is set to about 16 and air is compressed, the cylinder of the lip portion of the central combustion chamber is compressed. The compression ratios ε ₁ and ε ₂ of the combustion chambers from the time when the side end surface (that is, the lower surface of the cylinder head) and the top surface of the protrusion cross to the piston compression top dead center are the central combustion chamber and the main combustion chamber. Since there is almost no air movement between the two combustion chambers, the compression ratios ε ₁ and ε ₂ between the two combustion chambers can be greatly changed. For example,
When the top surface of the protrusion of the piston is flush with the lower surface of the cylinder head, the distance between the top surface of the protrusion and the bottom surface of the central combustion chamber is L ₁ , and the piston top surface and the cylinder are The compression ratio between the central combustion chamber and the main combustion chamber is as follows, where L ₂ is the distance from the lower surface of the head and L is the distance by which the piston further rises to the top dead center. The compression ratio ε ₁ of the central combustion chamber is L ₁ / (L ₁ -L), and the compression ratio ε ₂ of the main combustion chamber is L ₂ / (L ₂ -L) /
It is. Therefore, in order to set ε ₂ > ε ₁ , it suffices to set L ₁ > L ₂ .

Therefore, the compression ratio ε ₁ of the central combustion chamber and the compression ratio ε ₂ of the main combustion chamber can be properly controlled by selecting L ₁ , L ₂ and L. When a difference in compression pressure occurs in both combustion chambers, air movement occurs through the gap between the lip and the protrusion,
This passage area is 0.
Since it can be set to about 1 to 0.5%, it is sufficient to calculate and consider the amount of air to be moved in advance.

Further, in this direct injection type lean burn high compression ratio gasoline engine, the air-fuel mixture in the central combustion chamber is a rich air-fuel mixture (in particular, it is not necessary that the air-fuel mixture is a rich air-fuel mixture; A rich mixture compared to the main combustion chamber) requires a concentration close to the theoretical mixture to ignite and propagate the flame (air excess ratio 1 to 1.2), and knocking This is because it is necessary to control to such an extent that does not occur. In order to make the concentration of the central combustion chamber close to the theoretical mixture, it is necessary to inject the fuel so that the fuel injected from the fuel injection nozzle easily accumulates in the central combustion chamber. When it is provided in the head, it can be achieved by injecting spirally along the inner peripheral wall surface of the central combustion chamber and injecting it so that a part of the fuel flows out to the main combustion chamber. Alternatively, when the central combustion chamber is provided in the piston, the fuel injected from the fuel injection nozzle is injected toward the central combustion chamber, and a part of the fuel is injected so as to flow out to the main combustion chamber. To be achieved. Furthermore, since the main combustion chamber is a lean air-fuel mixture and knocking does not occur, it is possible to set a high compression ratio.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a direct injection type lean burn high compression ratio gasoline engine according to the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view showing an embodiment of a direct injection lean burn high compression ratio gasoline engine according to the present invention, FIGS. 2 to 4 are explanatory views showing the operation of the gasoline engine of FIG. 1, and FIG. FIG. 6 is a diagram showing a change in in-cylinder pressure.

In this direct injection type lean burn high compression ratio gasoline engine, for example, a cylinder liner 14 constituting a cylinder 11 arranged in a hole 18 formed in a cylinder block 13 and a gasket 16 in the cylinder block 13 are provided.
And a fuel injection nozzle 4 attached to the cylinder head 12 and a piston 3 that reciprocates in the cylinder 11. The fuel injection nozzle 4 is formed with a single hole or multiple injection holes. In this gasoline engine, a main combustion chamber 1 is formed on a cylinder 11 side in a region surrounded by a cylinder head lower surface 17 and a piston top surface 10, and a central combustion chamber 2 is formed in a cavity 20 formed in a cylinder head 12. There is. Further, the cylinder head 12 has a fuel injection nozzle 4
And a spark plug 5 are arranged, the fuel injection nozzle 4 injects fuel into the central combustion chamber 2, and the spark plug 5 is set to be ignited in the central combustion chamber 2.

The cylinder block 13 has holes 18 corresponding to the number of cylinders of the engine. Cylinder 1
1 may be formed by the cylinder liner 14 fitted into the hole 18 as described above, or may be directly constituted by the hole 18 of the cylinder block 13. An intake port 23 and an exhaust port 21 are formed in the cylinder head 12, an intake valve 22 is arranged in the intake port 23, and an exhaust valve 19 is arranged in the exhaust port 21. The port may be provided in the lower portion of the cylinder to have a two-stroke structure.

This direct-injection lean burn high compression ratio gasoline engine has, in particular, a central combustion chamber 2 constituted by a cavity 20 formed in a cylinder head 12, a lip portion 7 forming an opening peripheral portion of the cavity 20, a cylinder 1.
1. A piston 11 having a protrusion 6 that reciprocates in 1 and protrudes into the peripheral opening 30 of the cavity 20 near the top dead center of the piston, and a cylinder 11 around the protrusion 6 of the piston 3.
Side main combustion chamber 1, a fuel injection nozzle 4 arranged in a cylinder head 12 for injecting fuel into the central combustion chamber 2, and a cylinder head 12 for igniting an air-fuel mixture in the central combustion chamber 2. It is composed of the spark plug 5 arranged at. By the protrusion 6 of the piston 3 protruding into the central combustion chamber 2 of the cylinder head 12, the gap 9 between the protrusion 6 and the lip 7 is extremely small, and the opening 30 is almost closed.

In this direct injection type lean burn high compression ratio gasoline engine, the fuel injection from the fuel injection nozzle 4 is
As shown in FIG. 2, the injection direction of the fuel from the fuel injection nozzle 4 is set so that the fuel is injected and diffused along the wall surface of the central combustion chamber 2, whereby the injected fuel into the central combustion chamber 2 is The amount becomes large and the amount of fuel injected into the main combustion chamber 1 becomes small. Further, since the lip 7 is provided, the injected fuel in the central combustion chamber 2 becomes larger. The injection timing from the fuel injection nozzle 4 toward the central combustion chamber 2 is the injection timing indicated by reference symbol A in FIG. 2 or FIG. 5, but in some cases,
It is also possible to set the injection timing indicated by symbol B. Therefore, a rich air-fuel mixture is formed in the central combustion chamber 2, and a lean air-fuel mixture is formed in the main combustion chamber 1.

In this direct injection lean burn high compression ratio gasoline engine, the compression ratio in the central combustion chamber 2 is set lower than that in the main combustion chamber 1 at the piston compression top dead center. In order to set the compression ratio in the central combustion chamber 2 lower than that in the main combustion chamber 1, for example, as shown in FIGS. At the time C when the surface is flush with 17, the distance between the top surface 8 of the protrusion 6 and the bottom surface 15 of the central combustion chamber 2 is L _1, and the distance between the piston top surface 10 and the cylinder head lower surface 17 is Is L ₂ , the piston 3 further rises to the piston compression top dead center TDC from this point, but when the distance by which the piston 3 further rises to the top dead center is L, the compression ratio ε ₁ of the central combustion chamber 2 is [= L ₁ / (L ₁ −
L)] is the compression ratio ε ₂ [= L ₂ / (L ₂ −) of the main combustion chamber 1.
L)], it may be set to L ₁ > L ₂ .

In addition, in this direct injection type lean burn high compression ratio gasoline engine, from the time C when the top surface 8 of the protrusion 6 is flush with the cylinder head lower surface 17, the interior of the central combustion chamber 2 follows the compression stroke. The pressure changes along the curve CP of FIG. 5, and the in-cylinder pressure of the main combustion chamber 1 changes along the curve MP of FIG.
Higher compression is achieved. Therefore, the concentration in the central combustion chamber 2 is close to the theoretical mixture, but the pressure becomes low, self-ignition does not occur until ignition of the spark plug 5, knocking does not occur, and a stable state can be maintained. Moreover, the in-cylinder pressure in the main combustion chamber 1 can be increased because it is a lean air-fuel mixture, the compression ratio can be increased in the entire combustion chamber, and the thermal efficiency can be improved.

Further, as shown in FIGS. 4 and 5, the piston top dead center TDC in which the inside of the central combustion chamber 2 is closed by the projection 6
In the vicinity, the rich air-fuel mixture is ignited and burned by the ignitions S ₁ and S ₂ of the spark plug 5 and shifts to the explosion stroke, the cylinder pressure further rises, the piston 3 descends in the cylinder 11, and the crank after top dead center cranks. The protrusion 6 of the piston 3 again at an angle of 20 °
At a time point O when the top surface 8 of the cylinder is flush with the lower surface 17 of the cylinder head, the central combustion chamber 2 communicates with the main combustion chamber 1, and the in-cylinder pressure becomes equal to burn the lean mixture in the main combustion chamber 1. It will propagate.

Next, another embodiment of the direct injection type lean burn high compression ratio gasoline engine according to the present invention will be described with reference to FIGS. This embodiment has the same configuration as that of the above embodiment except that the cavity forming the central combustion chamber is formed in the piston, so that the same parts are designated by the same reference numerals and overlapping description will be omitted. Omit it.

The embodiment shown in FIGS. 6 to 9 is a cylinder 11
The central combustion chamber 2 formed by the cavity 25 formed in the piston 3 that reciprocates inside, the lip portion 27 that forms the opening peripheral edge of the cavity 25, and the peripheral opening 30 of the cavity 25 that protrudes near the top dead center of the piston. The cylinder head 12 is provided so that fuel can be injected into the main combustion chamber 1 and the central combustion chamber 2 formed on the cylinder 11 side around the protrusion 24 that protrudes from the cylinder head lower surface 17 that can close most of the opening 30. And a spark plug 5 arranged in the cylinder head 12 so that the air-fuel mixture in the central combustion chamber 2 can be ignited. The fuel injection nozzle 4 and the spark plug 5 are arranged so as to project from the protrusion 24. Further, when the protrusion 24 of the cylinder head 12 penetrates the central combustion chamber 2 of the piston 3, the gap 29 between the protrusion 24 and the lip 27 is extremely small, and the opening 30 is almost closed.

Regarding the operation timing of this embodiment,
Comparing to the above embodiment and comparing, the fuel injection nozzle 4
7 showing the fuel injection timing from the fuel injection system corresponds to the operation timing of FIG. 2 of the above embodiment. At this time, the fuel is injected from the fuel injection nozzle 4 toward the central combustion chamber 2 of the piston 3 so that the fuel collides with the central combustion chamber 2. If fuel is injected into the central combustion chamber 2,
Most of the fuel is retained in the central combustion chamber 2 by the lip portion 27. Further, FIG. 8 showing the crossing time point C between the top surface 26 of the protrusion 24 and the piston top surface 10 corresponds to the operation timing at the crossing time point C in FIG. 3 of the above embodiment. Further, FIG. 9 showing the operation timing of ignition of the spark plug 5 at the piston compression top dead center TDC corresponds to the operation timing of FIG. 4 of the above embodiment.

In this embodiment, as in the above embodiment, in order to set the compression ratio in the central combustion chamber 2 to be lower than that in the main combustion chamber 1, for example, as shown in FIGS. , When the top surface 26 of the protrusion 24 of the cylinder head 12 is flush with the top surface 10 of the piston 3, the protrusion 24
The distance between the top surface 26 of the and the bottom surface 28 of the central combustion chamber 2 is L
_1, and when the distance between the piston top surface 10 and the cylinder head lower surface 17 and L _2, but increases from this point the piston 3 is further to the piston compression top dead center TDC, further increasing piston 3 to the top dead center When the distance is L, the compression ratio ε ₁ [= L ₁ / (L ₁ −L)] of the central combustion chamber 2 becomes equal to the compression ratio ε ₂ [= L ₂ / (L ₂ −L)] of the main combustion chamber 1. ] To make it smaller, it is sufficient to set L ₁ > L ₂ .

In this embodiment, the central combustion chamber 2 is connected to the piston 3
Since it is formed as described above, the following operational effects can be obtained. Since the fuel injected from the fuel injection nozzle 4 collides with the wall surface of the central combustion chamber 2 of the piston 3, the piston 3 is cooled and the suction efficiency can be improved. Since the fuel is sprayed onto the wall surface of the central combustion chamber 2 of the piston 3 to recover the heat energy from the wall surface, the thermal efficiency can be improved. That is, in the embodiment shown in FIGS. 1 to 4, since the central combustion chamber 2 is provided in the cylinder head 12, the temperature of the cylinder head 12 is lower than the temperature of the piston. The recovery rate of heat energy from the wall surface is smaller than that in the examples shown in FIGS. Further, since the inside of the central combustion chamber 2 is intensively cooled by the fuel, an increase in the air temperature in the central combustion chamber 2 near the compression top dead center can be reduced. Further, since the fuel may be injected from the fuel injection nozzle 4 toward the inside of the central combustion chamber 2 of the piston 3, the distribution of the in-cylinder air-fuel mixture can be freely controlled by the fuel injection timing.

[0028]

Since the direct injection type lean burn high compression ratio gasoline engine according to the present invention is constructed as described above,
It is possible to obtain a high compression ratio and a high expansion ratio without causing knocking or the like, to enable lean combustion in the entire combustion chamber, and to secure thermal efficiency equivalent to or higher than that of a diesel engine. Further, since the central combustion chamber is a homogeneous mixture that constitutes premixed combustion, lean combustion occurs in the entire combustion chamber, so NO
It is possible to significantly reduce the generation of _X. In other words, the direct-injection lean burn high compression ratio gasoline engine according to the present invention is a premixed uniform lean mixture in view of the entire combustion chamber, so that the generation of NO _X is tens of pp.
It can be reduced to m or less, and since it is a homogeneous mixture, no particulates are generated. That is, in the lean mixture of the premixed combustion in the central combustion chamber, when the actual mixture ratio is 1 and the theoretical mixture ratio is 0.6, the excess air ratio is (1 / 0.6) = 1.67, the occurrence of NO _X at that time can be reduced to about 10ppm~50ppm. In a gasoline engine, when fuel is burned with a theoretical mixture, NO _X is generated at 2000 ppm.
That is all.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of a direct injection type lean burn high compression ratio gasoline engine according to the present invention.

FIG. 2 is an explanatory diagram showing an injection timing for injecting fuel from a fuel injection nozzle in the gasoline engine of FIG.

FIG. 3 is an explanatory diagram showing a cross timing of a top surface of a protrusion of a piston and a lower surface of a cylinder head in the gasoline engine of FIG.

4 is an explanatory diagram showing ignition timing of a spark plug near a piston top dead center in the gasoline engine of FIG. 1. FIG.

5 is a diagram showing a relationship between in-cylinder pressure and fuel injection timing with respect to a crank angle in the gasoline engine of FIG. 1. FIG.

FIG. 6 is an explanatory view showing another embodiment of a direct injection lean burn high compression ratio gasoline engine according to the present invention.

7 is an explanatory diagram showing an injection timing for injecting fuel from a fuel injection nozzle in the gasoline engine of FIG.

8 is an explanatory diagram showing a cross timing between a top surface of a protrusion of a piston and a lower surface of a cylinder head in the gasoline engine of FIG.

9 is an explanatory diagram showing ignition timing of a spark plug near a piston top dead center in the gasoline engine of FIG. 6. FIG.

[Explanation of symbols]

 1 Main Combustion Chamber 2 Central Combustion Chamber 3 Piston 4 Fuel Injection Nozzle 5 Spark Plug 6,24 Projection Part 7,27 Lip Part 8,26 Projection Top Surface 9,29 Gap 10 Piston Top Surface 11 Cylinder 12 Cylinder Head 15, 28 Cavity bottom surface 17 Cylinder head lower surface 20, 25 Cavity

Claims (6)

[Claims] 1. A central combustion chamber formed by a cavity formed in a cylinder head, a lip portion forming an opening peripheral edge portion of the cavity, a reciprocating motion in the cylinder, and a peripheral edge opening of the cavity near the piston top dead center. A piston having a protrusion that rushes in to close most of the opening, a main combustion chamber formed on the cylinder side around the protrusion of the piston, and the cylinder head so that fuel can be injected into the central combustion chamber. A direct-injection lean burn high compression ratio gasoline engine comprising a fuel injection nozzle arranged and a spark plug arranged in the cylinder head so as to ignite the air-fuel mixture in the central combustion chamber. 2. A central combustion chamber constituted by a cavity formed in a piston that reciprocates in a cylinder, a lip portion forming an opening peripheral edge portion of the cavity, and a protrusion which protrudes into the peripheral edge opening of the cavity near the top dead center of the piston. A protrusion protruding from the lower surface of the cylinder head that can close most of the opening, a main combustion chamber formed on the cylinder side around the protrusion, and the central combustion chamber so that fuel can be injected into the cylinder head. A direct injection lean burn high compression ratio gasoline engine comprising a fuel injection nozzle and a spark plug arranged in the cylinder head so as to ignite the air-fuel mixture in the central combustion chamber. 3. The direct injection lean burn high compression ratio gasoline engine according to claim 1, wherein the compression ratio in the central combustion chamber is set lower than the compression ratio in the main combustion chamber at the piston compression top dead center. 4. The fuel injection from the fuel injection nozzle is injected and diffused along a wall surface of the central combustion chamber.
4. The direct injection lean burn high compression ratio gasoline engine according to any one of 3 above. 5. The direct injection lean burn high compression ratio gasoline according to claim 1, wherein a rich air-fuel mixture is formed in the central combustion chamber, and a lean air-fuel mixture is formed in the main combustion chamber. engine. 6. A rich air-fuel mixture is ignited and burned by ignition of the spark plug in the vicinity of the top dead center of the piston closed in the central combustion chamber by the protrusion, and then burned and propagated to the lean air-fuel mixture in the main combustion chamber. A direct injection lean burn high compression ratio gasoline engine according to any one of claims 1 to 5.