JP4023434B2 - Internal combustion engine capable of premixed compression self-ignition operation using two types of fuel - Google Patents

Description

  The present invention relates to an internal combustion engine capable of premixed compression self-ignition operation using two types of fuel.

  In recent years, as a combustion method for internal combustion engines, a new combustion method has been sought that replaces the "premixed spark ignition combustion method" like a normal gasoline engine or the "diffuse combustion method" like a normal diesel engine. . As one of such new combustion methods, there is a “premixed compression self-ignition combustion method” in which an air-fuel mixture is formed in advance in a combustion chamber, and this is compressed and self-ignited. The premixed compression auto-ignition combustion method is a combustion method that compresses an ultra-lean mixture at a high compression ratio, completes combustion in a short time by self-ignition combustion at once, and in principle it is included in the exhaust gas It is thought that the amount of air pollutants and fuel consumption can be reduced at the same time.

  In order to employ this premixed compression self-ignition combustion method in a wide operating range, stable self-ignition combustion is performed during low-load operation, and intense combustion noise due to pre-ignition is generated during high-load operation. It is necessary to prevent this.

  As a technique for stably performing premixed compression self-ignition combustion in a wide operation region, a technique is known in which two types of fuels having different octane numbers are used and the octane number of fuel supplied in the combustion chamber is variably controlled. According to this technique, at the time of low load operation, the octane number of the supplied fuel in the combustion chamber can be lowered by increasing the supply ratio of the low octane fuel having excellent ignitability, and stable self-ignition combustion operation can be performed. On the other hand, at the time of high load operation, by increasing the supply ratio of the high-octane fuel excellent in knock resistance, the octane number of the supplied fuel in the combustion chamber can be increased and the occurrence of knocking can be suppressed.

JP 2000-179368 A JP 2001-254660 A JP-A-9-68061 Japanese Patent Laid-Open No. 2001-3800 JP 2001-207890 A

  However, in the technology for variably controlling the octane number of the fuel supplied in the combustion chamber as described above, since all the fuel supplied to the combustion chamber is subjected to compression auto-ignition combustion almost simultaneously, the combustion noise is reduced particularly during high-load operation. There has been a problem that the operating range in which the operation by compression auto-ignition combustion can be performed is limited.

  The present invention has been made to solve the above-described conventional problems, and suppresses combustion noise during high-load operation without impairing the advantages of the premixed compression auto-ignition combustion method. An object of the present invention is to provide a technique that enables operation of an internal combustion engine by a mixed compression auto-ignition combustion system.

In order to solve the above problems, an internal combustion engine of the present invention is an internal combustion engine capable of premixed compression self-ignition operation,
A combustion chamber composed of a cylinder and a piston;
An intake valve and an exhaust valve provided in the combustion chamber;
A first fuel injection valve for injecting low octane fuel;
A second fuel injection valve that directly injects high octane fuel into the combustion chamber;
A control unit for controlling the operation of the internal combustion engine;
With
The control unit forms a premixed gas in the combustion chamber by the first fuel injection by the first fuel injection valve, and after the compression auto-ignition of the premixed gas, the control unit performs the first fuel injection by the second fuel injection valve. A first operation mode in which two fuel injections are performed.

  In this internal combustion engine, the premixed mixture of low-octane fuel formed in the combustion chamber by the first fuel injection is subjected to compression auto-ignition combustion, thereby reducing air pollutant emissions such as NOx, fuel consumption, and smoke. The effect of can be obtained. In addition, after compression self-ignition combustion, the combustion noise can be reduced by diffusing and burning the high-octane fuel injected into the combustion chamber by the second fuel injection. Therefore, the operation by the premixed compression auto-ignition combustion method can be performed in a wide operation region.

  In the internal combustion engine, the first fuel injection in the first operation mode may be performed within a valve opening period of the intake valve.

  According to such an operation mode, since the time from the time of the first fuel injection until the injected low-octane fuel is self-ignited and combusted becomes longer, a more homogeneous premixed gas can be formed. Moreover, since there is sufficient time for the low-octane fuel and air to be mixed, the amount of smoke generated can be further reduced.

  In the internal combustion engine, the first fuel injection valve may be a port injection valve that injects fuel into an intake port that supplies fresh air into the combustion chamber.

  According to this configuration, since the first fuel injection valve is not installed in the cylinder head, the degree of freedom in designing the cylinder head can be improved.

  Further, in the internal combustion engine, the control unit further forms a premixed gas in the combustion chamber by fuel injection by the first fuel injection valve, and performs second combustion of the premixed gas by compression autoignition combustion. It may have an operation mode.

  According to the second operation mode, by compressing and igniting all the fuel supplied into the combustion chamber, it is possible to obtain more effects of reducing air pollutant emissions and reducing fuel consumption.

  Further, in the internal combustion engine, the control unit further performs the first fuel injection using both the first and second fuel injection valves during the valve opening period of the intake valve, thereby causing the combustion chamber to And a third operation mode in which the second fuel injection by the second fuel injection valve is performed after the compression ignition of the premixed gas.

  According to the third operation mode, the low-octane fuel and the high-octane fuel are supplied into the combustion chamber during the opening period of the intake valve, and a premixed gas including the low-octane fuel and the high-octane fuel is formed. By changing the ratio between the low-octane fuel injection amount and the high-octane fuel injection amount, the knock resistance of the pre-mixed gas formed in the combustion chamber can be changed, and the self-ignition timing of the pre-mixed gas is controlled. be able to. Therefore, self-ignition combustion can be performed at a more suitable time.

  In the internal combustion engine, the control unit further performs the first fuel injection by the first fuel injection valve during the valve opening period of the intake valve, and the second fuel injection in the second half of the compression stroke. A second fuel injection by the valve is performed to form a premixed gas in the combustion chamber, and a fourth fuel injection by the second fuel injection valve is performed after compression autoignition of the premixed gas. It is good also as having the operation mode of.

  According to the fourth operation mode, the high-octane fuel injected in the latter half of the compression stroke stratifies in the vicinity of the center of the combustion chamber. Therefore, it is possible to obtain the effect of reducing the fuel consumption by reducing the cooling loss.

Further, in the internal combustion engine, a recess is formed on the top surface of the piston,
The control unit further performs the first fuel injection by the first fuel injection valve during the valve opening period of the intake valve, and the second fuel injection by the second fuel injection valve in the first half of the compression stroke. And a fifth operation mode in which a third fuel injection by the second fuel injection valve is performed after compression auto-ignition of the pre-mixture is formed. Good.

  According to the fifth operation mode, the high-octane fuel injected in the first half of the compression stroke is well held in the recess formed on the piston top surface and stratified combustion is performed as it is. In addition, the injected high octane fuel is easy to vaporize at a low boiling point, and since there is a relatively long time from the high octane fuel injection to the stratified combustion in the first half of the compression stroke, the mixing of fuel and air further proceeds. Therefore, it is possible to obtain the effect of reducing the fuel consumption by reducing the cooling loss, and to obtain the effect of reducing the fluctuation between cycles and reducing the smoke.

  The said internal combustion engine WHEREIN: The said control part is good also as switching operation mode according to the load of the said internal combustion engine.

  According to this configuration, it is possible to select an optimum operation mode according to the load of the internal combustion engine, and it is possible to perform the operation by the premixed compression autoignition combustion method in a wide operation region, and to perform premixed compression autoignition combustion. More merit of the method can be obtained.

  Note that the present invention can be realized in various modes, for example, in modes such as an internal combustion engine, an operation method of the internal combustion engine, a fuel injection device of the internal combustion engine, and a fuel injection method of the internal combustion engine. Can do.

Next, embodiments of the present invention will be described in the following order based on examples.
A. First embodiment:
B. Second embodiment:
C. Third embodiment:
D. Fourth embodiment:
E. Example 5:
F. Variation:

A. First embodiment:
FIG. 1 is an explanatory diagram conceptually showing the structure of an engine 100 as a first embodiment of the present invention. FIG. 1 shows a cylinder structure when a cross section is taken at the center of the cylinder of engine 100.

  The combustion chamber of the engine 100 includes a hollow cylindrical cylinder 142 provided in the cylinder block 140, a piston 144 that slides up and down in the cylinder 142, and a cylinder head 130 provided on the cylinder block 140. Is formed by. A cylindrical body constituted by the cylinder block 140 and the cylinder head 130 is called a “cylinder” in a broad sense. Each combustion chamber is provided with an in-cylinder pressure sensor 36 (also referred to as “combustion pressure sensor”) for measuring the internal pressure (also referred to as “in-cylinder pressure”) of the combustion chamber. In the present specification, the direction in which the piston 144 approaches the cylinder head 130 along the central axis of the cylinder 142 is described as an upward direction, and the direction in which the piston 144 is separated from the cylinder head 130 is described as a downward direction.

  The cylinder head 130 includes an intake valve 132 that opens and closes an opening of an intake port 133 through which intake air flows, an exhaust valve 134 that opens and closes an opening of an exhaust port 135 through which exhaust gas flows out, a spark plug 136, a combustion A high-octane fuel injection valve 72 for injecting a fuel spray of high-octane fuel into the room is provided.

  The intake valve 132 and the exhaust valve 134 are driven by electric actuators 162 and 164, respectively. The electric actuators 162 and 164 can open and close the respective intake valves 132 and exhaust valves 134 at an arbitrary timing. Instead of the electric actuator, the intake valve 132 and the exhaust valve 134 may be driven by another type of variable valve mechanism such as a hydraulic actuator or a cam mechanism.

  The high-octane fuel injection valve 72 is supplied with high-octane fuel stored in the high-octane fuel tank 76 by a fuel pump 74.

  The intake port 133 is provided with a low-octane fuel injection valve 82 for injecting fuel spray of low-octane fuel into the intake port 133. The low-octane fuel injection valve 82 is supplied with the low-octane fuel stored in the low-octane fuel tank 86 by the fuel pump 84.

  As described above, the engine 100 is an engine that operates using two types of fuels, a high-octane fuel and a low-octane fuel. High-octane fuels usually have a relatively low boiling point, and are excellent in knock resistance and easily vaporized. On the other hand, low-octane fuels usually have a relatively high boiling point, have excellent ignitability and are difficult to vaporize.

  An intake passage 12 that guides intake air is connected to the intake port 133, and an exhaust passage 16 through which exhaust gas passes is connected to the exhaust port 135. A catalyst 26 for purifying air pollutants contained in the exhaust gas and a turbine 52 of the supercharger 50 are provided downstream of the exhaust passage 16. Exhaust gas passing through the exhaust passage 16 is released into the atmosphere after rotating the turbine 52. The intake passage 12 is provided with a compressor 54 for the supercharger 50. The compressor 54 is connected to the turbine 52 via a shaft 56, and the compressor 54 also rotates when the turbine 52 rotates by the exhaust gas. As a result, the compressor 54 pressurizes the air sucked from the air cleaner 20 and then pumps it toward the intake port 133.

  Since air temperature rises when pressurized by the compressor 54, an intercooler 62 is provided downstream of the compressor 54 in order to cool the intake air. A surge tank 60 and a throttle valve 22 are also provided in the intake passage 12. The surge tank 60 has a function of relaxing pressure waves generated when the combustion chamber sucks air, and the throttle valve 22 is set to an appropriate opening degree by the electric actuator 24 to adjust the intake air amount. It has a function to do.

  The piston 144 is connected to a crankshaft 148 via a connecting rod 146, and a crank angle sensor 32 that detects a crank angle is attached to the crankshaft 148.

  The operation of the engine 100 is controlled by an engine control unit (hereinafter, ECU) 30. The ECU 30 detects the engine rotational speed Ne, the accelerator opening degree θac, and the in-cylinder pressure Ps, and based on these, controls the opening degree of the throttle valve 22, the ignition timing control of the spark plug 136, and the fuel of the fuel injection valves 72 and 82. The injection control and the control of the fuel pumps 74 and 84 are executed. The engine rotation speed Ne is detected by a crank angle sensor 32, and the accelerator opening degree θac is detected by an accelerator opening degree sensor 34 built in the accelerator pedal. Further, the in-cylinder pressure Ps is detected by the in-cylinder pressure sensor 36 as described above.

  FIG. 2 is an explanatory diagram showing an enlarged cross section of a cylinder of the engine 100 in the first embodiment. As described above, the cylinder head 130 is provided with the high-octane fuel injection valve 72, and the intake port 133 is provided with the low-octane fuel injection valve 82.

  FIG. 3 is an explanatory diagram conceptually showing an example of the operation of the engine 100 in the first embodiment. The engine 100 opens and closes the two valves of the intake valve 132 and the exhaust valve 134 at appropriate timing while moving the piston 144 up and down in the cylinder 142, and the fuel injection valve 72 for the high octane fuel and the fuel for the low octane fuel Power is extracted by burning a mixture of fuel and air while injecting fuel from the injection valve 82 at an appropriate timing.

  When the piston 144 is lowered while the intake valve 132 is opened from the state where the piston 144 is at the top (top dead center), air flows from the intake valve 132 into the combustion chamber and the intake stroke is started. In FIG. 3A, the state in which air is flowing from the intake port 133 into the combustion chamber is indicated by arrows. At this time, low octane fuel is injected into the intake port 133 from the low octane fuel fuel injection valve 82 in accordance with the inflow of air. In FIG. 3A, the injected low-octane fuel spray is indicated by hatching. The injected low-octane fuel spray flows into the combustion chamber together with the intake air.

  The intake air and the low-octane fuel spray flowing into the combustion chamber are then stirred in the combustion chamber and dispersed with a substantially uniform density in the combustion chamber to form an air-fuel mixture. The intake valve 132 is closed as the piston 144 is fully lowered (bottom dead center), and the piston 144 is raised to start the compression stroke. FIG. 3B shows a state in which the piston 144 is rising during the compression stroke, and the mixture of low-octane fuel dispersed at a uniform density is hatched.

 In the compression stroke, the pre-mixture of low-octane fuel formed in the combustion chamber is adiabatically compressed, so that the temperature rapidly increases as the piston 144 rises. When the piston 144 rises to the top dead center, the pre-mixture of the low octane fuel reaches the self-ignition temperature, and the pre-mixture in the combustion chamber self-ignites almost simultaneously, and the combustion is completed quickly. FIG. 3C shows a state in which the pre-mixture of low-octane fuel in the combustion chamber is self-igniting and burning near the top dead center of the piston 144. The pressure in the combustion chamber is further increased by the self-ignition combustion of the premixed gas, and as a result, the piston 144 is pushed down with a strong force. In this way, the engine 100 starts the expansion stroke.

  After the pre-mixture of the low octane fuel is self-ignited and combusted, the high octane fuel is injected from the high octane fuel fuel injection valve 72 into the combustion chamber. FIG. 3D shows a state where high octane fuel is injected into the combustion chamber. In FIG. 3 (d), the injected high-octane fuel spray is shown with fine hatching, and the combustion gas after the low-octane fuel premixture is self-ignited and burned is shown with rough hatching. Represents.

  Since the high-octane fuel used in this embodiment has a low boiling point, the high-octane fuel spray injected into the combustion chamber is heated by the high-temperature combustion gas and immediately vaporizes and mixes with the air in the combustion gas while diffusing. Together, it forms a mixture of high octane fuel. The formed high-octane fuel mixture is self-ignited and combusted at the air-fuel ratio most suitable for combustion, and the combustion proceeds while the fuel injected later is supplied to the flame generated by the self-ignition combustion. Thus, the high octane fuel spray injected into the combustion chamber is diffusely burned. FIG. 3 (e) shows a state in which a mixture of high octane fuel (represented with fine hatching) is diffusely burned. In addition, like FIG.3 (d), in FIG.3 (e), combustion gas is represented with rough hatching. Due to the diffusion combustion of the high octane fuel, the pressure in the combustion chamber becomes higher, and as a result, the piston 144 is pushed down with a stronger force.

  When the piston 144 is lowered to the bottom dead center by the pressure in the combustion chamber, the piston 144 starts to rise. At this time, the exhaust valve 134 is opened and the exhaust stroke is started. The combustion gas in the combustion chamber is discharged from the exhaust valve 134 so as to be pushed out by the piston 144. FIG. 3F shows a state in which combustion gas (shown with hatching) is exhausted from the exhaust valve 134. When the piston 144 rises to the top dead center and exhausts most of the combustion gas, the exhaust valve 134 is closed, and the intake stroke shown in FIG.

  FIG. 4 is an explanatory diagram schematically showing an example of fuel injection control of the engine 100 in the first embodiment. In FIG. 4, the abscissa indicates the crank angle, and shows the transition of the fuel injection amount of the low octane fuel and the transition of the fuel injection amount of the high octane fuel. BDC represents bottom dead center and TDC represents top dead center.

  As shown in FIG. 4, the engine 100 according to the first embodiment injects low-octane fuel in the intake stroke before the bottom dead center (BDC). Further, after the low-octane fuel is self-ignited and burned near the top dead center (TDC), the high-octane fuel is injected.

  By performing such fuel injection control, as described above with reference to FIG. 3, the low-octane fuel is compressed by self-ignition combustion near the top dead center, and the high-octane fuel is diffused after the low-octane fuel is self-ignited. Burn.

  When the low-octane fuel is subjected to compression auto-ignition combustion, it is possible to obtain the effect of reducing the emission amount of air pollutants (nitrogen oxides, carbon monoxide, hydrocarbons) and fuel consumption. The reason why such an effect is obtained by the compression auto-ignition combustion is considered to be due to three factors such as an improvement in isovolume, an increase in excess air ratio, and an increase in specific heat ratio. This will be described in detail below.

  First, the improvement of the equal volume will be described. The isovolume is an index representing how quickly the air-fuel mixture in the combustion chamber can be combusted. When the air-fuel mixture burns before top dead center, the piston compresses the air-fuel mixture whose pressure has started to increase, and the work that can be taken out as power decreases. Similarly, when the air-fuel mixture burns after top dead center, the piston starts to descend without the pressure in the combustion chamber becoming sufficiently high, so the work that can be taken out as power is reduced. Therefore, the amount of work that can be taken out as power increases as the air-fuel mixture in the combustion chamber is quickly burned and approaches combustion at the top dead center of the theoretical cycle.

  In this regard, in the premixed compression self-ignition combustion method, all of the air-fuel mixture can be self-ignited and combusted almost simultaneously. Therefore, the spark ignition combustion method in which the air-fuel mixture in the combustion chamber is combusted by flame propagation, the fuel liquid Combustion can be completed in a much shorter time compared to the diffusion combustion method in which fuel is burned while evaporating from the surface of the droplets. As a result, the premixed compression auto-ignition combustion method can improve the isovolume, and even if the mixture of the same fuel amount is burned, more work can be taken out, and fuel consumption is correspondingly increased. Can be reduced.

  Next, an increase in the excess air ratio will be described. The excess air ratio is an index indicating the ratio between the amount of air and the amount of fuel contained in the air-fuel mixture, and the excess air ratio of “1” means that the air and fuel contained in the air / fuel mixture are not excessive or insufficient. It means that it is a burning ratio. The combustion speed of the air-fuel mixture becomes maximum when the excess air ratio is near “1”, and the combustion speed decreases as the excess air ratio increases. In the spark ignition combustion method, in order to shorten the time from the start of combustion of the entire air-fuel mixture to the completion of combustion, it is necessary to increase the combustion speed of the combustion portion, and the excess air ratio cannot be set too large. Further, in the diffusion combustion method, combustion is performed in a portion near the excess air ratio “1” that is most likely to self-ignite. On the other hand, in the premixed compression self-ignition combustion method, the temperature of the mixture is sufficiently raised and the air-fuel mixture in the combustion chamber is self-ignited and combusted almost simultaneously, so that the combustion of the entire air-fuel mixture can be completed in a short time. The excess air ratio can be set as large as possible.

  When the excess air ratio is set to a large value, the combustion temperature of the combustion portion is lowered, so that the emission amount of nitrogen oxide generated when the air-fuel mixture is locally exposed to a high temperature can be greatly reduced. In addition, when the excess air ratio is set to a large value, it is possible to greatly reduce the amount of carbon monoxide emitted by burning under conditions where oxygen is insufficient with respect to the fuel. Therefore, in the premixed compression auto-ignition combustion method, the emission amount of these air pollutants can be greatly reduced.

  Next, an increase in the specific heat ratio will be described. As described above, in the premixed compression auto-ignition combustion method, the excess air ratio can be set to a large value. A large excess air ratio means that the proportion of air in the air-fuel mixture in the combustion chamber is large. Therefore, the specific heat ratio of the air-fuel mixture in the combustion chamber can be increased.

  Here, the efficiency of an internal combustion engine that operates by repeatedly performing suction, compression, expansion (combustion), and exhaust becomes a better value as the specific heat ratio of the air-fuel mixture increases. Therefore, the fuel consumption is reduced as the specific heat ratio is larger. Thus, in the premixed compression auto-ignition combustion system, the fuel consumption can be reduced by increasing the specific heat ratio.

  Further, the low-octane fuel is given sufficient time to be mixed with air from the time it is supplied into the combustion chamber until the self-ignition combustion. Therefore, it is possible to reduce the amount of smoke generated due to the fuel being heated without being in contact with air.

  Furthermore, the effect of reducing smoke and combustion noise can be obtained by diffusion combustion of the high-octane fuel. That is, the high octane fuel used for the engine 100 in this embodiment has a low boiling point and is easily vaporized. Therefore, when the high octane fuel is injected into the combustion chamber, it is immediately vaporized and sufficiently mixed with the surrounding air, so that the amount of smoke generated is reduced. In addition, since high-octane fuel is self-ignited and burned near the top dead center, the low-octane fuel is injected into the combustion chamber and diffusely burned, so there is a time difference between low-octane fuel combustion and high-octane fuel combustion. Thus, the combustion noise of the engine is reduced.

  In FIG. 4, the fuel injection start timing of the high octane fuel is shown to be within the expansion stroke after the top dead center (TDC), but the injection start timing of the high octane fuel is the self-ignition of the low octane fuel. It may be after combustion and may be before top dead center. From the viewpoint of thermal efficiency, it is preferable that the injection start timing of the high-octane fuel is at most 20 degrees after the top dead center.

  On the other hand, in FIG. 4, the injection start timing of the low octane number fuel is shown to be within the intake stroke, but the injection start timing of the low octane number fuel may be any time when the intake valve 132 is open. . However, the earlier the injection start timing of low-octane fuel (advanced side), the longer the time from fuel injection to self-ignition combustion, the more the fuel and air are mixed, and the greater the amount of air pollutant emissions and smoke generated. Since it can reduce more, it is preferable.

  As described above, the engine 100 can control the combustion mode and the combustion timing in the combustion chamber by performing fuel injection control. In the present specification, an engine operation method including a combustion mode in the combustion chamber, a combustion timing, and the like performed in one operation region is also referred to as an “operation mode”.

  The operation mode is preferably switched according to the engine load. FIG. 5 is a map showing an example of an operation mode of the engine 100 in the first embodiment. In the example of FIG. 5, an operation mode in which operation is performed only by self-ignition combustion of low-octane fuel at the time of low load operation is adopted. That is, in FIG. 4, the fuel injection control is performed so that the low octane fuel injection is performed but the high octane fuel injection is not performed. During low-load operation, it is necessary to perform stable self-ignition combustion, and the amount of fuel supplied into the combustion chamber is relatively small, so there is little risk of intense combustion noise due to premature ignition. Autoignition combustion is performed only with octane fuel.

  On the other hand, during high-load operation, in addition to self-ignition combustion of low-octane fuel, an operation mode is adopted in which operation is performed by diffusion combustion of high-octane fuel. That is, in FIG. 4, the fuel injection control is performed so that both low-octane fuel injection and high-octane fuel injection are performed.

  During high load operation, the amount of fuel supplied into the combustion chamber increases, and the amount of air also increases accordingly, so the pressure in the combustion chamber increases. Therefore, the premixed gas in the combustion chamber is likely to cause self-ignition combustion with less compression. For this reason, if an operation mode in which operation is performed only by self-ignition combustion of low-octane fuel during high-load operation is employed, there is a risk of causing intense combustion noise due to premature ignition.

  Therefore, during high-load operation, an amount of low octane fuel that does not cause pre-ignition is supplied to obtain combustion energy by stable self-ignition combustion, and the remaining necessary combustion energy is excellent in knock resistance. Obtained by diffusion combustion of high octane fuel. By adopting such an operation mode, even during high-load operation, the merit of the premixed compression auto-ignition combustion method can be maximized without generating intense combustion noise due to pre-ignition. You can drive.

  As described above, the engine 100 according to the present embodiment suppresses the combustion noise during high load operation without impairing the advantages of the premixed compression autoignition combustion method, and the premixed compression autoignition combustion method in a wide operation range. Can be operated.

B. Second embodiment:
FIG. 6 is an explanatory diagram schematically showing an example of fuel injection control of the engine 100 in the second embodiment. In FIG. 6, as in FIG. 4, the abscissa represents the crank angle, and shows the transition of the fuel injection amount of the low octane fuel and the transition of the fuel injection amount of the high octane fuel. The difference from the first embodiment shown in FIG. 4 is that the high-octane fuel injection is performed also in the intake stroke, and the others are the same as the first embodiment.

  The high-octane fuel injected in the intake stroke is mixed with the low-octane fuel injected in the intake stroke, stirred in the combustion chamber, and dispersed with a substantially uniform density in the combustion chamber to form a premixed gas. This premixed gas is compressed by the piston 144 and self-ignited and combusted, as in the first embodiment. Here, since this premixed gas contains a low octane fuel and a low octane fuel, it has better knock resistance and self-ignition combustion than a premixed gas formed only by a low octane fuel. It is difficult to do. Therefore, when the combustion chamber is at a higher temperature and pressure, the self-ignition condition is reached and self-ignition combustion occurs. In this way, by changing the ratio of the low octane number fuel and the high octane number fuel, the knock resistance of the premixed gas in the combustion chamber can be changed, and the self-ignition timing of the premixed gas can be controlled.

  FIG. 7 is a map showing an example of an operation mode of the engine 100 in the second embodiment. In the example of FIG. 7, at the time of low load operation, the operation mode in which the operation is performed only by the self-ignition combustion of the low octane fuel is adopted as in the first embodiment. That is, in FIG. 6, the fuel injection control is performed so that only the low octane fuel injection is performed.

  On the other hand, during medium load operation, in addition to self-ignition combustion of low-octane fuel, an operation mode in which operation is performed by self-ignition combustion of high-octane fuel is adopted. That is, in FIG. 6, the fuel injection control is performed so that the high-octane fuel injection is performed in addition to the low-octane fuel injection in the intake stroke.

  As described above, when the load increases, the premixed gas in the combustion chamber is likely to cause self-ignition combustion with less compression. Therefore, when the operation mode in which the operation is performed only by the self-ignition combustion of the low-octane fuel when the load is increased is employed, there is a risk of causing intense combustion noise due to premature ignition as in the first embodiment. Further, the timing of self-ignition of the premixed gas is most desirably in the vicinity of the top dead center, and it is not preferable in terms of thermal efficiency that the self-ignition occurs at a certain advance side or retard side from the top dead center.

  Therefore, during medium load operation, it is preferable to perform low-octane fuel injection and high-octane fuel injection in the intake stroke, and to change the ratio between the low-octane fuel injection amount and the high-octane fuel injection amount according to the load. That is, it is preferable to increase the ratio of the injection amount of the high octane fuel as the load increases. In this way, since the knock resistance of the premixed gas in the combustion chamber changes according to the load, it becomes possible to always generate self-ignition of the premixed gas near the top dead center. Therefore, in a wider operating range, it is possible to perform an operation that takes advantage of the advantages of the premixed compression auto-ignition combustion method without generating intense combustion noise due to premature ignition.

  In addition, during a higher load operation, in addition to the self-ignition combustion of the low-octane fuel and the high-octane fuel, an operation mode is adopted in which the operation is performed by diffusion combustion of the high-octane fuel as in the first embodiment. In the present embodiment, the proportion of combustion energy by self-ignition combustion in the total combustion energy can be increased as compared with the first embodiment. Therefore, more advantages of the compression auto-ignition combustion method can be obtained.

C. Third embodiment:
FIG. 8 is an explanatory diagram schematically showing an example of fuel injection control of the engine 100 in the third embodiment. In FIG. 8, as in FIG. 4, the horizontal axis shows the crank angle, and shows the transition of the fuel injection amount of the low octane fuel and the transition of the fuel injection amount of the high octane fuel. The difference from the first embodiment shown in FIG. 4 is that the high-octane fuel injection is performed also in the latter half of the compression stroke, and the others are the same as the first embodiment.

  In the latter half of the compression stroke, the injected high octane fuel is immediately vaporized and mixed with the surrounding air. Immediately after that, the piston 144 rises to near the top dead center (TDC), so that the high-octane fuel mixture does not have enough time to mix with the low-octane fuel premix that is uniformly formed in the combustion chamber. The self-ignition temperature is reached, and self-ignition combustion occurs near the center of the combustion chamber. That is, self-ignition combustion of high-octane fuel injected in the latter half of the compression stroke is a combustion method in which an air-fuel mixture having a higher fuel concentration is locally formed in the combustion chamber, and is also referred to as “stratified combustion”.

  By stratifying combustion of the high octane fuel near the center of the combustion chamber, the cooling loss from the cylinder wall surface is reduced, the thermal efficiency of the internal combustion engine is improved, and the effect of reducing fuel consumption can be obtained.

  FIG. 9 is a map showing an example of an operation mode of the engine 100 in the third embodiment. In the example of FIG. 9, at the time of low load operation, an operation mode in which operation is performed only by self-ignition combustion of low-octane fuel is employed as in the first embodiment. That is, in FIG. 8, fuel injection control is performed so that only low octane fuel injection is performed.

  On the other hand, during medium load operation, an operation mode is employed in which stratified combustion of high-octane fuel is performed in addition to self-ignition combustion of low-octane fuel. That is, in FIG. 8, the fuel injection control is performed so that the low-octane fuel injection is performed in the intake stroke and the high-octane fuel injection is performed in the latter half of the compression stroke.

  If an operation mode in which only low-octane fuel is self-ignited and combusted during medium-load operation is employed, there is a risk of causing intense combustion noise due to pre-ignition as in the first embodiment. Thus, during medium load operation, an amount of low-octane fuel that does not cause pre-ignition is supplied to perform stable self-ignition combustion, and the remaining required combustion energy is obtained by stratified combustion of high-octane fuel. In this way, it is possible to perform the operation by the compression ignition combustion up to the operation region where the load is higher. Further, the stratified combustion of the high-octane fuel reduces the cooling loss from the cylinder wall surface, improves the thermal efficiency of the internal combustion engine, and reduces the fuel consumption.

  In addition, in the case of a higher load, in addition to the self-ignition combustion of the low octane fuel and the stratified combustion of the high octane fuel, the operation mode is also employed in which the diffusion combustion of the high octane fuel is performed as in the first embodiment.

D. Fourth embodiment:
FIG. 10 is an explanatory view showing an enlarged cross section of a cylinder of the engine 100 in the fourth embodiment. The difference from the first embodiment shown in FIG. 2 is that a recess (cavity) 145 is formed on the top surface of the piston 144. The other configuration is the same as that of the first embodiment.

  FIG. 11 is an explanatory diagram schematically showing an example of fuel injection control of the engine 100 in the fourth embodiment. In FIG. 11, as in FIG. 8, the horizontal axis shows the crank angle, and shows the transition of the fuel injection amount of the low octane fuel and the transition of the fuel injection amount of the high octane fuel. The difference from the third embodiment shown in FIG. 8 is that the high octane fuel that was injected in the second half of the compression stroke in the third embodiment is injected in the first half of the compression stroke in this embodiment. Others are the same as the third embodiment.

  The high-octane fuel injection in the first half of the compression stroke is performed directly into the cylinder by the high-octane fuel injection valve 72, so that the injected high-octane fuel reaches the recess 145 provided on the top surface of the piston 144. And retained well in the recess 145. In addition, since the high-octane fuel has a low boiling point, it is immediately vaporized and mixed with the surrounding air to form a high-octane fuel mixture in the recess 145. When the piston 144 rises to near the top dead center (TDC), the high-octane fuel mixture in the recess 145 reaches the auto-ignition temperature and self-ignites and burns in the recess 145. That is, also in this embodiment, as in the third embodiment, the high octane fuel injected in the first half of the compression stroke stratifies.

  Further, in this embodiment, since there is a relatively long time from the injection of the high octane fuel in the first half of the compression stroke to the stratified combustion of the high octane fuel in the vicinity of the top dead center, the mixing of the fuel and air further proceeds. .

  Therefore, in the present embodiment, the high octane fuel injected in the first half of the compression stroke stratifies in the recess 145, so that the effect of reducing the fuel consumption can be obtained as in the third embodiment, and the cycle It is possible to obtain the effect of reducing the fluctuations in smoke and reducing the smoke.

E. Example 5:
FIG. 12 is an explanatory diagram showing an enlarged cross section of a cylinder of the engine 100 in the fifth embodiment. The difference from the first embodiment shown in FIG. 2 is the position of the low-octane fuel injection valve 82. That is, in the present embodiment, the low-octane fuel injection valve 82 is provided in the cylinder head 130 so that the low-octane fuel can be directly injected into the combustion chamber. The other configuration is the same as that of the first embodiment.

  FIG. 13 is an explanatory diagram schematically showing an example of fuel injection control of the engine 100 in the fifth embodiment. In FIG. 13, similarly to FIG. 4, the abscissa indicates the crank angle, and shows the transition of the fuel injection amount of the low octane fuel and the transition of the fuel injection amount of the high octane fuel. The difference from the first embodiment shown in FIG. 4 is that the low-octane fuel injected in the intake stroke in the first embodiment is injected in the compression stroke in this embodiment, and the others are the first. The same as the embodiment.

  In this embodiment, since the low-octane fuel injection valve 82 is provided at a position where the low-octane fuel can be directly injected into the combustion chamber, the low-octane fuel is burned even in the compression stroke where the intake valve 132 is closed. It can be injected indoors. Therefore, the degree of freedom of the fuel injection timing of the low octane number fuel can be improved.

F. Variation:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

F1. Modification 1:
In each embodiment, the operation mode map of the engine 100 is shown and described. However, these are merely examples, and the operation region can be classified into various other categories, and the operation mode can be various other than these. The operation mode can be adopted.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which showed notionally the structure of the engine 100 as 1st Example of this invention. Explanatory drawing which expands and shows the cross section of the cylinder of the engine 100 in 1st Example. Explanatory drawing which showed notionally an example of operation | movement of the engine 100 in 1st Example. Explanatory drawing which shows roughly an example of the fuel-injection control of the engine 100 in 1st Example. The map which shows an example of the operation mode of the engine 100 in 1st Example. Explanatory drawing which shows roughly an example of the fuel-injection control of the engine 100 in 2nd Example. The map which shows an example of the operation mode of the engine 100 in 2nd Example. Explanatory drawing which shows roughly an example of the fuel-injection control of the engine 100 in 3rd Example. The map which shows an example of the operation mode of the engine 100 in 3rd Example. Explanatory drawing which expands and shows the cross section of the cylinder of the engine 100 in 4th Example. Explanatory drawing which shows roughly an example of the fuel-injection control of the engine 100 in 4th Example. Explanatory drawing which expands and shows the cross section of the cylinder of the engine 100 in 5th Example. Explanatory drawing which shows roughly an example of the fuel-injection control of the engine 100 in 5th Example.

Explanation of symbols

12 ... Intake passage 16 ... Exhaust passage 20 ... Air cleaner 22 ... Throttle valve 24 ... Electric actuator 26 ... Catalyst 32 ... Crank angle sensor 34 ... Accelerator opening sensor 36 ... In-cylinder pressure sensor 50 ... supercharger 52 ... turbine 54 ... compressor 56 ... shaft 60 ... surge tank 62 ... intercooler 72 ... fuel injection for high octane fuel Valve 74 ... Fuel pump 76 ... High octane fuel tank 82 ... Fuel injection valve for low octane fuel 84 ... Fuel pump 86 ... Low octane fuel tank 100 ... Engine 130 ... Cylinder Head 132 ... Intake valve 133 ... Intake port 134 ... Exhaust valve 135 ... Exhaust port 136 ... Spark plug 140 ... Cylinder block 142 ... Cylinder 144 ... Piston 145 .. .Recess 146 ... Connecting rod 148 ... Clan Shaft 162, 164 ... electric actuator

Claims (3)

  An internal combustion engine capable of premixed compression self-ignition operation,
  A combustion chamber composed of a cylinder and a piston;
  An intake valve and an exhaust valve provided in the combustion chamber;
  A first fuel injection valve for injecting low octane fuel;
  A second fuel injection valve that directly injects high octane fuel into the combustion chamber;
  A control unit for controlling the operation of the internal combustion engine;
With
  The control unit forms a premixed gas in the combustion chamber by the first fuel injection by the first fuel injection valve, and after the compression auto-ignition of the premixed gas, the control unit performs the first fuel injection by the second fuel injection valve. In the combustion chamber by performing the first fuel injection using both the first and second fuel injection valves during the opening period of the intake valve and the first operation mode in which the second fuel injection is performed. And a third operation mode in which a second fuel injection by the second fuel injection valve is performed after the pre-mixed gas is compressed and self-ignited.   An internal combustion engine capable of premixed compression self-ignition operation,
  A combustion chamber composed of a cylinder and a piston;
  An intake valve and an exhaust valve provided in the combustion chamber;
  A first fuel injection valve for injecting low octane fuel;
  A second fuel injection valve that directly injects high octane fuel into the combustion chamber;
  A control unit for controlling the operation of the internal combustion engine;
With
  The control unit forms a premixed gas in the combustion chamber by the first fuel injection by the first fuel injection valve, and after the compression auto-ignition of the premixed gas, the control unit performs the first fuel injection by the second fuel injection valve. And the second fuel injection valve in the second half of the compression stroke while performing the first fuel injection by the first fuel injection valve during the opening period of the intake valve. A second fuel injection is performed to form a premixed gas in the combustion chamber, and a third fuel injection by the second fuel injection valve is performed after compression autoignition of the premixed gas. An internal combustion engine having an operation mode.   An internal combustion engine capable of premixed compression self-ignition operation,
  A combustion chamber composed of a cylinder and a piston;
  An intake valve and an exhaust valve provided in the combustion chamber;
  A first fuel injection valve for injecting low octane fuel;
  A second fuel injection valve that directly injects high octane fuel into the combustion chamber;
  A control unit for controlling the operation of the internal combustion engine;
With
  A recess is formed on the piston top surface,
  The control unit forms a premixed gas in the combustion chamber by the first fuel injection by the first fuel injection valve, and after the compression auto-ignition of the premixed gas, the control unit performs the first fuel injection by the second fuel injection valve. The first fuel injection is performed by the first fuel injection valve in the first operation mode in which the fuel injection of 2 is performed and the intake valve is open, and the second fuel injection valve is in the first half of the compression stroke. The second fuel injection is performed to form a premixed gas in the combustion chamber, and after the compression auto-ignition of the premixed gas, the third fuel injection is performed by the second fuel injection valve. An internal combustion engine having an operation mode.

Images