JP2003049650A - Compression self-ignition internal combustion engine - Google Patents

Abstract

(57) [Problem] To optimize the control of ignition timing by optimizing the mixture distribution in a cylinder for compression self-ignition combustion, and to suppress the NOx generation amount to a certain value or less. I do. SOLUTION: A first air-fuel mixture injection is performed in an intake stroke or the like using an air-fuel mixture injection valve 9 to form a lean air-fuel mixture layer in a combustion chamber 4. Thereafter, only air is injected in the compression stroke to form an air layer that does not propagate the flame. Subsequently, a second fuel-air mixture injection is performed to form a high-concentration air-fuel mixture layer under a high back pressure, and the spark plug 10 spark-ignites the mixture. The rise in pressure and temperature due to the spark ignition combustion causes the lean mixture layer to self-ignite.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compression self-ignition type internal combustion engine which performs compression self-ignition combustion under at least predetermined operating conditions.

[0002]

2. Description of the Related Art As an example of a compression self-ignition internal combustion engine,
There is one 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 by further adding compression by the control piston to the air-fuel mixture compressed to a high temperature on the verge of self-ignition, the air-fuel mixture is compressed. It is configured to self-ignite all at once.

A compression self-ignition type internal combustion engine equipped with an ignition plug is disclosed in Japanese Patent Application Laid-Open No. 11-210539. This is to determine whether the gas temperature in the cylinder at the end of the compression stroke is the target temperature that causes self-ignition of the entire 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 internal gas temperature is controlled to be maintained at the target temperature.

[0004]

Both of the above-mentioned two prior arts attempt to forcibly control the ignition timing of self-ignition combustion, but the technique of Japanese Patent Laid-Open No. 10-196424 using a control piston is used. Is difficult to put into practical use because the structure of the engine becomes too complicated. on the other hand,
In the technique disclosed in Japanese Patent Laid-Open No. 11-210539 using spark ignition, the width of the auxiliary pressure increase that can be provided by spark ignition is small, and it is difficult to perform stable ignition timing control.

As a method of increasing the pressure rise width due to spark ignition, a region having a high fuel concentration is formed in a part of the combustion chamber, and the mixture gas in this region is spark ignited to propagate the fuel in a limited region by flame. Combustion may be considered, but if the conditions inside the combustion chamber change in various ways, the range of the flame propagation combustion region also changes, and the amount of NOx produced, which is often generated by flame propagation combustion, falls below a certain amount. It becomes difficult to suppress.

Therefore, the present invention focuses on 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. , NOx production amount is suppressed to a certain value or less.

[0007]

For this reason, in the invention of claim 1, a compression self-ignition is provided, which is provided with an injection valve for injecting fuel directly into the cylinder and performs compression self-ignition combustion under at least a predetermined operating condition. In the internal combustion engine, the in-cylinder air-fuel mixture field is divided into a rich air-fuel mixture region and a thin air-fuel mixture region, and a layer that does not propagate flame between the rich air-fuel mixture and the thin air-fuel mixture is characterized.

According to the second aspect of the present invention, a rich air-fuel mixture is provided in the center of the cylinder, and a thin air-fuel mixture is provided so as to surround it so that no flame is propagated, and the rich air-fuel mixture is burned around it. The feature is that a thin air-fuel mixture that causes self-ignition is provided. According to the invention of claim 3, a rich air-fuel mixture is arranged at a position eccentric from the center of the cylinder, and a thin air-fuel mixture leading to self-ignition by combusting the rich air-fuel mixture is arranged at a position not intersecting with the 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.

According to the invention of claim 4, the fuel injection is capable of directly injecting the fuel and air into the cylinder, and the fuel injection is divided into two times to perform the first fuel injection and the second fuel injection. It is characterized by injecting only air during the period. According to the invention of claim 5, a sub-chamber opened to the combustion chamber is provided, and the injection valve capable of directly injecting the fuel and the air into the sub-chamber is used to perform the fuel injection by dividing the fuel injection into two times. It is characterized in that only air is injected between the fuel injection and the second fuel injection.

In the sixth aspect of the present invention, while the injection valve is provided substantially in the center of the cylinder head, a plurality of injection ports are provided for injecting fuel in the cylinder axial direction and in the direction toward the bore wall near the top dead center. It is characterized by having.

[0011]

According to the first aspect of the present invention, the in-cylinder air-fuel mixture field is made into two layers, a thick air-fuel mixture region and a thin air-fuel mixture region, and a layer that does not propagate flame between the thick air-fuel mixture layer and the thin air-fuel mixture layer. , The flame due to spark ignition of the rich mixture layer does not propagate to the thin mixture layer, and the pressure and temperature rise due to combustion of the rich mixture layer causes the thin mixture layer to self-ignite, resulting in spark ignition. By controlling the timing, it is possible to reliably control the self-ignition timing, while it is possible to reliably prevent the amount of fuel contributing to flame propagation combustion from exceeding a set amount and suppress the generation of NOx. it can.

According to the second aspect of the present invention, by providing a rich air-fuel mixture in the center of the cylinder and a thin air-fuel mixture that self-ignites in a region of a relatively low temperature outside the center of the cylinder, a steep mixture is provided. Combustion can be suppressed, the compression self-ignition combustion region can be expanded to the high load side, and since a rich air-fuel mixture is burned in the center of the cylinder, unburned air-fuel mixture is suppressed and HC emissions are reduced. It is possible to reduce the amount.

According to the third aspect of the present invention, by disposing the rich air-fuel mixture at a position eccentric from the center of the cylinder, the rich air-fuel mixture generates heat at a position eccentric from the center of the cylinder, thereby causing the temperature distribution in the cylinder. As a result, the steep combustion can be suppressed, and the compression self-ignition combustion region can be expanded to the high load side. According to the invention of claim 4,
Using an injection valve that can inject fuel and air directly into the cylinder,
The fuel injection is divided into two, and the first fuel injection and the two
By injecting only air during the first fuel injection, 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. By the second fuel injection performed as described above, a high-concentration air-fuel mixture is formed under high back pressure. As a result, the rich air-fuel mixture for spark ignition and the thin air-fuel mixture for self-ignition can be reliably separated from each other by the air layer so that flame does not propagate, and stable self-ignition combustion while suppressing NOx. Can be realized.

According to the fifth aspect of the present invention, the sub-chamber communicating with the combustion chamber is provided, and the injection valve capable of directly injecting fuel and air into the sub-chamber is used to divide the fuel injection into two times. Done,
By injecting only air between the first fuel injection and the second fuel injection, the fuel from the first fuel injection is reliably scavenged from the sub chamber by the subsequent air injection and mixed with the air in the combustion chamber. As a result, the fuel injected by the second fuel injection forms a rich air-fuel mixture in the sub chamber because the air injected before the second fuel injection blocks the sub chamber opening.
As a result, a rich air-fuel mixture for spark ignition and a thin air-fuel mixture for self-ignition are provided by the air layer at the sub-chamber opening.
It is possible to reliably separate the inside and the outside of the sub-chamber so as not to propagate a flame, and to further ensure the separation of the air-fuel mixture, thereby suppressing NOx and realizing stable self-ignition combustion.

According to the sixth aspect of the present invention, the fuel is injected from the injection valve provided substantially in the center of the cylinder head in the cylinder axial direction and in the direction toward the bore wall near the top dead center. , A rich mixture layer for spark ignition and a thin mixture layer for self-ignition can be made into two layers, and these layers can be separated by a layer that does not propagate flame. It is possible to realize stable self-ignition combustion while suppressing the above.

[0016]

BEST MODE FOR CARRYING OUT 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 self-ignition combustion is performed under predetermined operating conditions and spark ignition combustion is performed under other operating conditions.

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, and 9 is a mixture injection. The valve 10 is a spark plug. Mixture injection valve 9
Is an injection valve in which an air-fuel mixture chamber is formed, high-pressure air and fuel supplied from the outside are mixed in the air-fuel mixture chamber, and the resulting air-fuel mixture is injected into the combustion chamber 4. . Further, the mixture injection valve 9 is supplied without supplying fuel to the mixture chamber.
It is also possible to inject only high-pressure air into the combustion chamber 4 by opening the valve.

Here, the mixture injection valve 9 is vertically attached to the center of the cylinder head 2 so that its injection port faces the inside of the combustion chamber 4, while the spark plug 10 is attached obliquely to the cylinder head 2. By projecting the tip 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 mixture injection valve 9.

An electronic control unit (hereinafter referred to as "ECU") 20 for controlling the engine determines a combustion mode for determining which combustion mode, spark ignition combustion or compression self-ignition combustion, is to be performed according to operating conditions. It includes a unit 21, a spark ignition combustion control unit 22 that controls combustion control parameters during spark ignition combustion operation, and a compression self-ignition combustion control unit 23 that controls combustion control parameters during compressed self-ignition combustion operation.

The combustion mode determination unit 21, the spark ignition combustion control unit 22, and the compression self-ignition combustion control unit 23 can be configured by hard-wired logic circuits, but in this embodiment, they are realized as a program of a microcomputer. Has been done. With such a configuration, as shown in FIG. 2, compression self-ignition combustion is performed in the low and medium rotation and low and medium load regions, and spark ignition combustion is performed in the high rotation and high load regions.

Next, the characteristics of compression self-ignition combustion will be described. FIG. 3 shows a range in which self-ignition combustion at ignition timing for the same load is established. When the ignition timing is set earlier, the knock strength increases and exceeds the knock limit. On the contrary, when 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 range in which the compression self-ignition combustion is established, is an extremely narrow range.

FIG. 4 shows waveforms of in-cylinder pressure and heat generation when the ignition timing is changed. The broken line waveform is a waveform when the ignition timing is advanced immediately after the compression top dead center, and the solid line waveform is a waveform when the ignition timing is retarded from the compression top dead center. As can be seen from this, when the ignition timing is advanced, the change in the cylinder pressure becomes steep. During compression self-ignition combustion, if the ignition timing is advanced from the optimum timing for some reason, the change in cylinder pressure becomes sharp as described above,
Along with this, the temperature inside the cylinder also rises. This effect is brought to the next cycle in the form of an increase in the residual gas temperature in the cylinder, and the ignition timing of the next cycle tends to advance further. On the contrary, when the ignition timing is retarded from the optimum timing, the ignition timing of the next cycle tends to be further retarded.

As described above, since the ignition timing in compression self-ignition combustion is extremely unstable, it is necessary to forcibly control the ignition timing. In the present invention, a high-concentration air-fuel mixture and a lean mixture are diluted. An air-fuel mixture is formed, and a high-concentration air-fuel mixture is ignited by sparks and burned by flame propagation, and the lean air-fuel mixture is self-ignited by an increase in cylinder pressure and temperature accompanying the combustion. According to this method
By controlling the spark ignition timing, it is possible to reliably control the self-ignition timing.

However, in this method, the amount of NOx produced is increased as compared with the case where all fuels are self-ignited and burned, so that it contributes to spark ignition and subsequent flame propagation combustion (hereinafter referred to as spark ignition combustion). It is desirable to minimize the amount of fuel. Therefore, in the present invention, by separating and forming a high-concentration air-fuel mixture and a lean air-fuel mixture in the combustion chamber, it is possible to reliably prevent the amount of fuel contributing to spark ignition combustion from exceeding a set amount. There is.

Next, the control flow will be described with reference to the flow chart of FIG. First, in 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 of the map of FIG. 2 or within the compression self-ignition combustion region.

As a result, if it is determined to be in the spark ignition combustion region, control of spark ignition combustion is performed in S3, and if it is determined to be in the compression self ignition combustion region, control of compression self ignition combustion is performed in S4. I do. 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 in the latter stage of the compression stroke to perform spark ignition. . In this case, the flame generated by the spark ignition propagates to the air-fuel mixture in the entire combustion chamber 4.

In the compression self-ignition combustion control performed in S4, control is performed to raise the temperature of intake air in order to satisfy the condition of self-ignition (for example, the exhaust valve 8 is closed during the exhaust stroke to increase the residual gas amount). Control) and also controls the mixture injection valve 9 for separating and forming a high-concentration mixture and a lean mixture in the combustion chamber. Specifically, FIG.
As shown in (1), the mixture injection valve 9 performs the first mixture injection from the intake stroke to the first compression stroke, and then performs the injection of high-pressure air only in the compression stroke, and further the second injection. The air-fuel mixture injection is performed.

The air-fuel mixture produced by the first injection of the air-fuel mixture mixes with the air in the combustion chamber 4 and is diluted, forming a lean air-fuel mixture throughout the combustion chamber 4 (see FIG. 6A). By the subsequent air injection, an air-only region is formed around the air-fuel mixture injection valve 9 (see FIG. 6B), which is continuously executed 2
A high-concentration air-fuel mixture is formed around the air-fuel mixture injection valve 9 by the second air-fuel mixture injection (see FIG. 6C)).

The second mixture injection is performed in the latter half of the compression stroke,
That is, since it is executed under high back pressure, the arrival distance of the injection mixture is short, and the spark plug 1
Since the ignition by 0 is performed, the fuel concentration of this 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 peripheral portion, and an air layer exists between the two air-fuel mixture regions (see FIG. 7). ) Can be realized. Incidentally, FIG.
In, a high-concentration air-fuel mixture region is described as a spark ignition region, a lean mixture region is described as a compression ignition region, and an air layer between them is described as a region where flame does not propagate.

When the ignition plug 10 adjacent to the air-fuel mixture injection valve 9 is driven by ignition 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 of the combustion are increased. As it rises, the lean mixture burns by self-ignition. At this time, the high-concentration air-fuel mixture and the lean air-fuel mixture are spatially separated by the air layer.
Spark ignition combustion and self-ignition combustion can be separated as shown in FIG. Therefore, it is possible to prevent the amount of fuel that is spark-ignited and burned from becoming excessively larger than the set amount and the amount of NOx produced becoming excessive.

The spark-ignition combustion and the self-ignition combustion may be separated spatially, and may temporally overlap with each other as shown in FIG. 8 and 9 show heat generation patterns, and dQ / dθ is the heat generation rate. Further, the air layer that separates the high-concentration air-fuel mixture and the lean air-fuel mixture does not have to be a layer consisting of only air, and the fuel layer is so lean that the propagating flame of the high-concentration air-fuel mixture does not propagate to the lean air-fuel mixture. Just do it.

Further, it is not essential to form the high-concentration air-fuel mixture (spark ignition region), the lean air-fuel mixture (compression ignition region), and the air layer (region where flame does not propagate) on concentric circles as shown in FIG. Alternatively, the high-concentration air-fuel mixture (spark ignition region) and the lean air-fuel mixture (compression ignition region) may be formed separately with the distributions shown in FIGS. 10 and 11. In the embodiment of FIGS. 10 and 11, the air-fuel mixture injection valve 9 is provided around the cylinder head 2.
Is obliquely attached, and the spark plug 10 is arranged in the vicinity thereof.

When it is necessary to more reliably separate the high-concentration air-fuel mixture and the lean air-fuel mixture, a sub-chamber communicating with the combustion chamber (main combustion chamber) is provided, and the air-fuel mixture is injected into this sub-chamber. A valve and a spark plug may be provided to control the mixture injection valve as described above. In this case, the air injection performed after the first air-fuel mixture injection temporarily scavenges the air-fuel mixture in the sub-chamber and forms an air layer near the opening of the sub-chamber, and by the second air-fuel injection performed thereafter, By forming the high-concentration air-fuel mixture in the sub chamber, the air-fuel mixture can be separated more reliably.

12 and 13 further show another embodiment of the present invention. In the system of FIG. 12, the fuel injection valve 15
Is attached vertically to the central portion of the cylinder head 2, and the spark plug 10 is arranged in the vicinity thereof. In this case, the fuel injection valve 15 is, as shown in FIG.
A first injection port 15a for injecting fuel in the cylinder axis direction,
A second injection port 15b for injecting fuel in a direction (a direction close to horizontal) directed to the bore wall near the top dead center is provided.

In this structure, by injecting the fuel from the fuel injection valve 15 in the compression stroke, the fuel injected in the cylinder axis direction is not diffused to form a rich air-fuel mixture layer and is injected in the bore wall direction. By forming a thin air-fuel mixture layer by the diffusing fuel, the air-fuel mixture distribution shown in 7 can be realized and the heat generation pattern shown in FIG. 8 or 9 can be realized.

[Brief description of 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 of establishment of compression self-ignition combustion.

FIG. 4 is a diagram showing waveforms of in-cylinder pressure and heat generation when the ignition timing is changed.

FIG. 5 is a flowchart showing the flow of control.

FIG. 6 is a diagram showing a method for forming a mixture separation during compression self-ignition combustion.

FIG. 7 is a diagram showing an air-fuel mixture distribution in a cylinder.

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.

FIG. 11 is a diagram showing a mixture distribution in a cylinder in the embodiment of FIG.

FIG. 12 is a system diagram of an internal combustion engine showing another embodiment of the present invention.

FIG. 13 is an enlarged view of a fuel injection valve injection port portion in the embodiment of FIG.

[Explanation of symbols]

1 cylinder 2 cylinder head 3 pistons 4 Combustion chamber 5 intake ports 6 intake valve 7 exhaust port 8 exhaust valve 9 Mixture injection valve 10 Spark plug 15 Fuel injection valve 15a First nozzle 15b Second nozzle 20 ECU 21 Combustion mode determination unit 22 Spark ignition combustion control unit 23 Compressed self-ignition combustion control unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02B 23/10 F02B 23/10 DK F02D 41/02 351 F02D 41/02 351 41/32 41/32 Z 41/38 41/38 B F02M 61/14 310 F02M 61/14 310D 61/18 320 61/18 320Z 360 360 360G 360J F Term (reference) 3G023 AA01 AA04 AA05 AB06 AC01 AC05 AG01 3G066 AA02 AB02 BA14 BA25 BA26 CC26 CC46 CC48 DA04 DA09 3G301 HA04 HA16 JA25 JA26 LB04 MA23

Claims (6)

[Claims] 1. A compression self-ignition internal combustion engine comprising an injection valve for injecting fuel directly into a cylinder, and performing compression self-ignition combustion under at least a predetermined operating condition. A compression self-ignition internal combustion engine, characterized in that it is divided into a region and a thin air-fuel mixture region, and a layer that does not propagate flames is provided between the rich air-fuel mixture and the thin air-fuel mixture. 2. A rich air-fuel mixture is provided in the center of the cylinder, and a thin air-fuel mixture is provided so as to surround the interior of the cylinder so that flame propagation does not occur, and the rich air-fuel mixture burns around it to cause self-ignition. The compression self-ignition internal combustion engine according to claim 1, wherein a thin air-fuel mixture is provided. 3. A rich air-fuel mixture is provided at a position eccentric from the center of the cylinder, and a thin air-fuel mixture that causes self-ignition by burning the rich air-fuel mixture at a position that does not intersect with the rich air-fuel mixture is provided. 2. The compression self-ignition internal combustion engine according to claim 1, wherein the air-fuel mixture and the thin air-fuel mixture are separated by a layer that does not propagate flames. 4. An injection valve capable of directly injecting fuel and air into a cylinder is used to divide fuel injection into two injections, and only air is provided between the first fuel injection and the second fuel injection. The compression self-ignition internal combustion engine according to claim 1, wherein the internal combustion engine is injected. 5. A fuel injection system comprising a sub-chamber opening to a combustion chamber, the fuel injection being capable of directly injecting fuel and air into the sub-chamber, the fuel injection is divided into two, and the first fuel injection is performed. The compressed self-ignition internal combustion engine according to any one of claims 1 to 3, wherein only air is injected between the second fuel injection and the second fuel injection. 6. The injection valve is provided substantially in the center of the cylinder head, and a plurality of injection ports for injecting fuel are provided in the cylinder axial direction and in the direction toward the bore wall near the top dead center. A compression self-ignition type internal combustion engine according to any one of claims 1 to 3.