JP3952710B2 - Compression self-ignition internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a compression self-ignition internal combustion engine that performs compression self-ignition combustion under at least predetermined operating conditions.
[0002]
[Prior art]
An example of a compression self-ignition internal combustion engine is described in JP-A-10-196424. This is equipped with a control piston as an auxiliary compression means in addition to the piston in the cylinder, and the mixture is further compressed by the control piston against the mixture compressed to a high temperature just before self-ignition. It is configured to self-ignite all at once.
[0003]
A compression self-ignition internal combustion engine having a spark plug is disclosed in Japanese Patent Laid-Open No. 11-210539. This is because it is determined whether the gas temperature in the cylinder at the end of the compression stroke is a target temperature that causes self-ignition of the entire air-fuel mixture when ignited, and by controlling the opening timing of the intake valve, the cylinder at the end of the compression stroke is controlled. The inside gas temperature is controlled to be maintained at the target temperature.
[0004]
[Problems to be solved by the invention]
Both of the above two prior arts attempt to forcibly control the ignition timing of self-ignition combustion. However, the technique of Japanese Patent Laid-Open No. 10-196424 using a control piston complicates the structure of the engine. It is too difficult to put it into practical use.
On the other hand, in the technique disclosed in Japanese Patent Application Laid-Open No. 11-210539 using spark ignition, it is difficult to perform stable ignition timing control because the width of the auxiliary pressure increase that can be given by spark ignition is small.
[0005]
As a method of increasing the pressure increase range due to spark ignition, a region with a high fuel concentration is formed in a part of the combustion chamber, and the air-fuel mixture in this region is spark-ignited so that the fuel in a limited region is subjected to flame propagation combustion. However, if the situation in the combustion chamber changes variously, the range of the flame propagation combustion region also changes variously, and the amount of NOx generated frequently due to flame propagation combustion is suppressed to a certain amount or less. It becomes difficult.
[0006]
Therefore, the present invention pays attention to the formation of the air-fuel mixture field and optimizes the air-fuel mixture distribution in the cylinder for the compression self-ignition internal combustion engine, thereby enabling stable ignition timing control and NOx generation. The purpose is to suppress the amount below a certain value.
[0007]
[Means for Solving the Problems]
Therefore, according to the first aspect of the present invention, there is provided a compression self-ignition internal combustion engine that includes an injection valve that directly injects fuel into a cylinder and an ignition plug, and that performs compression self-ignition combustion under at least predetermined operating conditions. The injection valve is an injection valve capable of directly injecting fuel and air into the cylinder, dividing the fuel injection into two times, and executing the first fuel injection from the intake stroke to the first half of the compression stroke, Thereafter, in the compression stroke, only air is injected, and subsequently, the second fuel injection is performed, so that the in- cylinder air- fuel mixture field is brought close to the spark plug by the second fuel injection. And a thin air-fuel mixture region formed away from the spark plug by the first fuel injection, and between the thick air-fuel mixture and the thin air-fuel mixture is injected by only the air. the layer that does not flame propagation, This was burned by flame propagation by spark ignition in rich mixture by fire plugs, the thin air-fuel mixture by increasing the in-cylinder pressure and temperature caused by the combustion, characterized in that so as to self-ignition.
[0008]
In the invention of claim 2, a thick mixture is disposed in the center of the cylinder, a layer that does not propagate the flame is disposed so as to surround the periphery, and the thin mixture that causes self-ignition by burning the dense mixture around it. It is characterized by care.
In the invention of claim 3, a thick air-fuel mixture is arranged at a position eccentric from the center of the cylinder, and a thin air-fuel mixture that leads to self-ignition is disposed by burning the rich air-fuel mixture at a position not intersecting with this rich air-fuel mixture, The thick air-fuel mixture and the thin air-fuel mixture are separated by a layer that does not propagate flame.
[0011]
【The invention's effect】
According to the first aspect of the present invention, the in-cylinder air-fuel mixture field is divided into two layers, a rich air-fuel mixture region and a thin air-fuel mixture region, and the thick air-fuel mixture layer and the thin air-fuel mixture layer are separated by a layer that does not propagate flame. The spark ignition timing should be controlled because the flame caused by spark ignition of the rich mixture layer does not propagate to the thin mixture layer, and the thin mixture layer self-ignites due to pressure and temperature rise due to combustion of the dense mixture layer. Thus, the self-ignition timing can be reliably controlled, while the amount of fuel contributing to flame propagation combustion can be reliably prevented from exceeding the set amount, and the generation of NOx can be suppressed.
Further, by using an injection valve capable of directly injecting fuel and air into the cylinder, fuel injection is divided into two times, and only air is injected between the first fuel injection and the second fuel injection. As a result, the fuel from the first fuel injection mixes with the air in the combustion chamber and is diluted, and the subsequent air injection forms an air-only region, and the subsequent second fuel injection causes a high back pressure. A high concentration air-fuel mixture is formed. As a result, the rich mixture for spark ignition and the thin mixture for self-ignition can be reliably separated by the air layer so as not to propagate the flame, and stable self-ignition combustion while suppressing NOx Can be realized.
[0012]
According to the invention of claim 2, a sharp mixture is suppressed by disposing a rich mixture at the center of the cylinder and a thin mixture that self-ignites from the center of the cylinder to a relatively low temperature region outside. In addition to expanding the compression self-ignition combustion area to the high load side, the rich air-fuel mixture is burned at the center of the cylinder, reducing unburned air-fuel mixture and reducing HC emissions. It becomes possible to do.
[0013]
According to the invention of claim 3, by arranging the rich air-fuel mixture at a position eccentric from the center of the cylinder, the dense air-fuel mixture generates heat at a position eccentric from the center of the cylinder, thereby causing unevenness in the in-cylinder temperature distribution. As a result, steep combustion can be suppressed, and the compression self-ignition combustion region can be expanded to the high load side.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram of a compression self-ignition internal combustion engine (particularly a gasoline engine) showing an embodiment of the present invention.
However, in this engine, it is possible to switch between spark ignition combustion and compression self-ignition combustion so that compression auto-ignition combustion is performed under predetermined operating conditions and spark ignition combustion is performed under other operating conditions.
[0017]
In FIG. 1, 1 is a cylinder, 2 is a cylinder head, 3 is a piston, 4 is a combustion chamber, 5 is an intake port, 6 is an intake valve, 7 is an exhaust port, 8 is an exhaust valve, 9 is an air-fuel mixture injection valve, 10 Is a spark plug.
The air-fuel mixture injection valve 9 has an air-fuel mixture chamber formed therein, mixes high-pressure air and fuel supplied from the outside in the air-fuel mixture chamber, and injects the obtained air-fuel mixture into the combustion chamber 4. This is an injection valve. Further, only the high-pressure air can be injected into the combustion chamber 4 by opening the mixture injection valve 9 without supplying fuel to the mixture chamber.
[0018]
Here, the air-fuel mixture injection valve 9 is vertically attached to the center portion of the cylinder head 2 so that its injection port faces the combustion chamber 4, while the spark plug 10 is obliquely attached to the cylinder head 2 and its tip portion is attached. By projecting into the combustion chamber 4, the spark gap of the spark plug 10 is arranged close to the fuel spray (spray cone) formed by the air-fuel mixture injection valve 9.
[0019]
An electronic control unit (hereinafter referred to as ECU) 20 that controls the engine includes a combustion mode determination unit 21 that determines whether to perform a spark ignition combustion or a compression self-ignition combustion according to the operating conditions. A spark ignition combustion control unit 22 that controls the combustion control parameters during the spark ignition combustion operation and a compression self ignition combustion control unit 23 that controls the combustion control parameters during the compression self ignition combustion operation are provided.
[0020]
The combustion form determination unit 21, the spark ignition combustion control unit 22, and the compression self-ignition combustion control unit 23 can be configured by a hard-wired logic circuit, but in this embodiment, are realized as a microcomputer program. .
Under such a configuration, compression self-ignition combustion is performed in the low / medium rotation and low / medium load regions as shown in FIG. 2, and spark ignition combustion is performed in the high rotation / high load region.
[0021]
Next, the characteristics of compression self-ignition combustion will be described.
FIG. 3 shows a range in which self-ignition combustion at the ignition timing for the same load is established. If the ignition timing is made earlier, the knock strength increases and exceeds the knock limit. Conversely, if the ignition timing is delayed, the stability deteriorates and exceeds the stability limit. Therefore, the allowable range of the ignition timing (the range within the knock limit and the stability limit), which is the formation range of the compression self-ignition combustion, is an extremely narrow range.
[0022]
FIG. 4 shows in-cylinder pressure and heat generation waveforms when the ignition timing is changed. A broken line waveform is a waveform when the ignition timing is advanced and immediately after the compression top dead center, and a solid line waveform is a waveform when the ignition timing is retarded from the compression top dead center. As can be seen, when the ignition timing is advanced, the change in the in-cylinder pressure becomes steep.
During compression self-ignition combustion, if the ignition timing is advanced from an optimal timing due to some influence, the change in the in-cylinder pressure becomes steep as described above, and the in-cylinder temperature also increases accordingly. This influence is brought into the next cycle in the form of an increase in the in-cylinder residual gas temperature, and the ignition timing of the next cycle tends to advance further. On the contrary, if the ignition timing is retarded from the optimal timing, the ignition timing of the next cycle tends to be further retarded.
[0023]
Thus, since the ignition timing in compression self-ignition combustion is very unstable, it is necessary to forcibly control the ignition timing.In the present invention, a high-concentration mixture and a lean mixture are The high-concentration air-fuel mixture is spark-ignited and burned by flame propagation, and the lean air-fuel mixture is self-ignited by the rise in in-cylinder pressure and temperature accompanying this combustion. According to this method, the self-ignition timing can be reliably controlled by controlling the spark ignition timing.
[0024]
However, in this method, the amount of NOx generated increases as compared with the case where all fuels are self-ignited and combusted. Therefore, the amount of fuel that contributes to spark ignition and subsequent flame propagation combustion (hereinafter referred to as spark ignition combustion). It is desirable to minimize
Therefore, in the present invention, the high-concentration air-fuel mixture and the lean air-fuel mixture are separated and formed in the combustion chamber, thereby reliably preventing the amount of fuel contributing to spark ignition combustion from exceeding a set amount. Yes.
[0025]
Next, the flow of control will be described with reference to the flow of FIG.
First, at S1, the engine speed N and the load T are detected.
Next, in S2, the combustion mode is determined. That is, it is determined whether the detected values of the engine speed N and the load T are within the spark ignition combustion region or the compression self-ignition combustion region of the map of FIG.
[0026]
As a result, when it is determined that it is in the spark ignition combustion region, the spark ignition combustion is controlled in S3, and when it is determined that it is the compression self ignition combustion region, the compression self ignition combustion is controlled in S4.
In the spark ignition combustion control performed in S3, the air-fuel mixture injection valve 9 is driven during the intake stroke to inject and supply the air-fuel mixture into the combustion chamber 4, and the spark plug 10 is driven late in the compression stroke to perform spark ignition. . In this case, the flame generated by spark ignition propagates to the air-fuel mixture throughout the combustion chamber 4.
[0027]
In the compression self-ignition combustion control performed in S4, control for increasing the temperature of the intake air in order to satisfy the self-ignition condition (for example, control for closing the exhaust valve 8 during the exhaust stroke to increase the residual gas amount) is performed. In addition, the air-fuel mixture injection valve 9 is controlled to separate and form a high-concentration air-fuel mixture and a lean air-fuel mixture in the combustion chamber.
Specifically, as shown in FIG. 6, the mixture injection valve 9 performs the first mixture injection from the intake stroke to the first half of the compression stroke, and then injection of only high-pressure air in the compression stroke. And the second mixture injection is executed.
[0028]
The air-fuel mixture by the first air-fuel mixture injection is mixed with the air in the combustion chamber 4 to be diluted, and a lean air-fuel mixture is formed throughout the combustion chamber 4 (see FIG. 6A). Subsequent air injection forms an air-only region around the mixture injection valve 9 (see FIG. 6 (b)), and the second mixture injection that is subsequently executed results in the periphery of the mixture injection valve 9. A high-concentration air-fuel mixture is formed (see FIG. 6C)).
[0029]
The second air-fuel mixture injection is executed in the latter half of the compression stroke, that is, under a high back pressure, so that the reach of the air-fuel mixture is short, and ignition is performed by the spark plug 10 before the diffusion progresses so much. The fuel concentration of the mixture becomes relatively high. As a result, a high-concentration air-fuel mixture exists around the air-fuel mixture injection valve 9, a lean air-fuel mixture exists in the periphery, and an air-fuel mixture distribution in which an air layer exists between two air-fuel mixture regions (see FIG. ) Can be realized. In FIG. 7, the high-concentration mixture region is indicated as a spark ignition region, the lean mixture region is indicated as a compression ignition region, and the air layer between them is indicated as a region where no flame is propagated.
[0030]
When the spark plug 10 adjacent to the air-fuel mixture injection valve 9 is ignited by forming such air-fuel mixture distribution, the high-concentration air-fuel mixture is burned by flame propagation, and the in-cylinder pressure and temperature are increased due to this combustion. The lean air-fuel mixture burns by self-ignition.
At this time, since the high-concentration mixture and the lean mixture are spatially separated by the air layer, spark ignition combustion and self-ignition combustion can be separated as shown in FIG. For this reason, it is possible to prevent the amount of fuel ignited by spark ignition from becoming excessively larger than the set amount and causing the NOx generation amount to become excessive.
[0031]
Note that the spark ignition combustion and the self-ignition combustion need only be separated spatially, and may overlap as shown in FIG. 9 in terms of time. 8 and 9 show heat generation patterns, and dQ / dθ is a heat generation rate.
In addition, the air layer that separates the high-concentration mixture from the lean mixture does not need to be a layer composed of only air, and the fuel layer is so thin that the propagation flame of the high-concentration mixture does not propagate to the lean mixture. Just do it.
[0032]
Further, it is not essential to form a high-concentration air-fuel mixture (spark ignition region), a lean air-fuel mixture (compression ignition region), and an air layer (region where flame does not propagate) on a concentric circle as shown in FIG. 10 and FIG. 11 may be used to separate and form a high-concentration mixture (spark ignition region) and a lean mixture (compression ignition region). In the embodiment of FIGS. 10 and 11, the air-fuel mixture injection valve 9 is obliquely attached to the periphery of the cylinder head 2, and the spark plug 10 is disposed in the vicinity thereof.
[Brief description of the drawings]
FIG. 1 is a system diagram of an internal combustion engine showing an embodiment of the present invention. FIG. 2 is a diagram showing a compression self-ignition combustion region. FIG. 3 is a diagram showing a range in which compression self-ignition combustion is established. FIG. 5 is a flow chart showing the flow of control when the pressure is changed in the cylinder. FIG. 6 is a flow chart showing the control flow. FIG. FIG. 8 is a diagram showing an example of a heat generation pattern. FIG. 9 is a diagram showing another example of a heat generation pattern. FIG. 10 is a system diagram of an internal combustion engine showing another embodiment of the present invention. 11 is a diagram showing the in-cylinder mixture distribution in the embodiment of FIG.
1 cylinder
2 Cylinder head
3 Piston
4 Combustion chamber
5 Intake port
6 Intake valve
7 Exhaust port
8 Exhaust valve
9 Mixture injection valve
10 Spark plug
20 ECU
21 Combustion form determination unit
22 Spark ignition combustion control unit
23 Compression self-ignition combustion controller

Claims (3)

In a compression self-ignition internal combustion engine that includes an injection valve that directly injects fuel into a cylinder and an ignition plug, and that performs compression self-ignition combustion under at least predetermined operating conditions,
As the injection valve, an injection valve capable of directly injecting fuel and air into the cylinder is used, the fuel injection is divided into two times, and the first fuel injection is performed between the intake stroke and the first half of the compression stroke, and thereafter In the compression stroke, the injection of only air is performed, followed by the second fuel injection,
The in-cylinder air- fuel mixture field is divided into a rich air- fuel mixture region formed close to the spark plug by the second fuel injection, and a thin air-fuel mixture region formed away from the spark plug by the first fuel injection. Divided into a layer that does not propagate the flame by jetting only the air between the rich mixture and the thin mixture ,
A compression self-ignition system characterized in that a rich air-fuel mixture is ignited by a spark plug and burned by flame propagation, and a thin air-fuel mixture is self-ignited by an increase in in-cylinder pressure and temperature accompanying this combustion. Internal combustion engine. A thick air-fuel mixture is placed in the center of the cylinder, a layer that does not propagate flame is placed around it, and a thin air-fuel mixture that leads to self-ignition is disposed around the dense air-fuel mixture. The compression self-ignition internal combustion engine according to claim 1.   A thick air-fuel mixture is arranged at a position that is eccentric from the center of the cylinder, and a thin air-fuel mixture that causes self-ignition is disposed by burning the rich air-fuel mixture at a position that does not intersect with the rich air-fuel mixture. 2. The compression self-ignition internal combustion engine according to claim 1, wherein the air-fuel mixture is separated by a layer that does not propagate flame.

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