JP4007310B2 - 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. This technology uses a low-octane fuel with excellent ignitability and a high-octane fuel with excellent knock resistance, and lowers the octane number of the fuel supplied in the combustion chamber by increasing the supply ratio of the low-octane fuel in the low-load operation range. On the other hand, in the high load operation region, the supply ratio of the high octane fuel is increased to increase the octane number of the fuel supplied in the combustion chamber. According to this technology, stable self-ignition combustion operation can be performed in the low load operation region, while premature ignition can be suppressed in the high load operation region.

JP 2000-179368 A JP 2001-254660 A JP 11-315733 A

  However, in the technology for variably controlling the octane number of the fuel supplied in the combustion chamber as described above, the high octane number fuel also exists in the low octane number fuel region supplied into the combustion chamber, and there is a region where the fuel concentration is locally high. appear. In the region where the fuel concentration is high, the combustion speed increases, the combustion portion locally becomes very hot, and the amount of nitrogen oxide emissions increases. In the region where the fuel concentration is high, the amount of fuel that is heated without being in contact with air increases, and the amount of smoke discharged also increases. Therefore, in the above-described technique for performing the premixed compression auto-ignition combustion system in a wide operation region, there has been a problem that the emission amount of nitrogen oxides and smoke increases.

  The present invention has been made to solve the above-described conventional problems, and does not increase the emission amount of nitrogen oxides and smoke, and operates an internal combustion engine by a premixed compression auto-ignition combustion system in a wide operation range. The purpose is to provide a technology that makes it possible.

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;
A fuel injection mechanism for directly injecting a low octane fuel and a high octane fuel into the combustion chamber;
With
In the compression stroke, the fuel injection mechanism performs fuel injection so that the low-octane fuel and the high-octane fuel do not substantially overlap each other in the combustion chamber.

  In this internal combustion engine, the octane number of the supplied fuel in the combustion chamber can be changed according to the load, and a region having a high fuel concentration can be prevented from existing in the combustion chamber. Therefore, it is possible to operate the internal combustion engine by the premixed compression auto-ignition combustion method in a wide operation region without increasing the emission amount of nitrogen oxides and smoke.

  In the internal combustion engine, the fuel injection mechanism injects one of the low octane number fuel and the high octane number fuel so that the fuel spray has a hollow cone shape having a large apex angle, and the other one is a hollow cone shape having the large apex angle. The fuel spray may be injected into the hollow portion of the fuel spray so that the fuel spray has a conical shape with a small apex angle.

  In this way, it is possible to easily prevent the low-octane fuel and the high-octane fuel from substantially overlapping each other.

In the internal combustion engine, the fuel injection mechanism includes a first fuel injection valve that injects low-octane fuel and a second fuel injection valve that injects high-octane fuel,
The first fuel injection valve is a fuel injection valve having a small spray angle for injecting fuel toward a central portion of the combustion chamber,
The second fuel injection valve may be a hollow spray fuel injection valve having a large spray angle for injecting fuel toward the periphery of the combustion chamber.

  According to this configuration, the low-octane fuel and the high-octane fuel can be prevented from substantially overlapping with each other, and the low-octane fuel having a relatively high boiling point is placed in the center of the combustion chamber having a relatively high temperature. The high-octane fuel, which has a relatively low boiling point, is distributed in the periphery of the combustion chamber at a relatively low temperature, so that fuel vaporization is promoted and smoke emissions can be further reduced. The problem of dilution can be suppressed.

Further, in the internal combustion engine, a recess is formed on the top surface of the piston,
The fuel injection of the low octane fuel by the first fuel injection valve may be performed in the first half of the compression stroke, and the fuel injection of the high octane fuel by the second fuel injection valve may be performed in the second half of the compression stroke.

  According to this configuration, since the low-octane fuel injected in the first half of the compression stroke is held in the recess, a state in which the high-octane fuel and the low-octane fuel do not substantially overlap each other more easily and reliably is formed. And variation between cycles can be reduced. Furthermore, since a relatively long time can be secured from the fuel injection of the low octane fuel to the self-ignition combustion in the vicinity of the top dead center, the mixing of the fuel and air further proceeds, and the smoke emission is further reduced. Can do.

In the internal combustion engine, the fuel injection mechanism includes a fuel injection valve for two types of fuel capable of injecting both a low octane fuel and a high octane fuel.
The fuel injection valve for type 2 fuel injects low-octane fuel at a small spray angle toward the center of the combustion chamber and hollows high-octane fuel at a large spray angle toward the periphery of the combustion chamber. It may be sprayed on.

  According to this configuration, since both the high-octane fuel and the low-octane fuel are injected from one fuel injection valve, the high-octane fuel spray and the low-octane fuel spray can be more easily separated from each other in the combustion chamber. It can be made not to overlap. Furthermore, since only one fuel injection valve needs to be provided, the mountability of the fuel injection valve can be improved, and the design freedom of the cylinder head can be improved.

In the internal combustion engine, the low-octane fuel is light oil,
The high octane fuel is gasoline;
The ratio of light oil to gasoline may be set so that the ratio of the heat generated by light oil to 30% or less of the heat generated by all fuel supplied into the combustion chamber during one cycle of the internal combustion engine. .

  In this way, smoke emission can be further reduced by keeping the ratio of light oil that is difficult to vaporize due to its high boiling point below a certain level.

  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. 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. 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, and a high octane fuel within the combustion chamber. A fuel injection valve 72 for high-octane fuel that injects the fuel spray and a fuel injection valve 82 for low-octane fuel that injects fuel spray of low-octane fuel into the combustion chamber are 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 the high-octane fuel stored in the high-octane fuel tank 76 by the fuel pump 74. 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.

  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 and the accelerator opening degree θac, and executes control of the opening degree of the throttle valve 22, fuel injection control of the fuel injection valves 72 and 82, and control of the fuel pumps 74 and 84 based on these. To do. 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.

  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.

  FIG. 2 is an explanatory diagram showing an enlarged cross section of a cylinder of the engine 100 in the first embodiment. A high-octane fuel injection valve 72 and a low-octane fuel injection valve 82 are provided at substantially the center of the cylinder head 130.

  The high-octane fuel injection valve 72 directly injects high-octane fuel into the combustion chamber. The low-octane fuel injection valve 82 directly injects low-octane fuel into the combustion chamber. In FIG. 2, the high-octane fuel spray injected from the high-octane fuel fuel injection valve 72 is shown with thin hatching, and the low-octane fuel spray injected from the low-octane fuel fuel injection valve 82 is concentrated. Shown with hatching.

  FIG. 3 is an explanatory diagram schematically showing an example of the fuel injection timing of the engine 100 in the first embodiment. In FIG. 3, the abscissa indicates the crank angle, and shows the transition of the fuel injection amount of the high octane number fuel and the low octane number fuel. BDC represents bottom dead center and TDC represents top dead center.

  As shown in FIG. 3, in the engine 100 in the first embodiment, both the high octane number fuel and the low octane number fuel are injected at substantially the same time in the compression stroke. The high-octane fuel and the low-octane fuel injected in the compression stroke form an air-fuel mixture in the combustion chamber, are compressed by the piston 144, reach the self-ignition temperature near the top dead center, and self-ignite and burn. As described above, the engine 100 extracts power by causing the high-octane fuel and the low-octane fuel to self-ignite and burn in the combustion chamber.

  The engine 100 can change the supply ratio of the high-octane fuel and the low-octane fuel by individually controlling the high-octane fuel amount and the low-octane fuel amount supplied into the combustion chamber. That is, the octane number of the fuel supplied into the combustion chamber can be changed by changing the supply ratio of the high octane fuel and the low octane fuel according to the load.

  Therefore, for example, by increasing the supply ratio of the low-octane fuel excellent in ignitability in the low-load operation region, the octane number of the supplied fuel in the combustion chamber can be lowered, and stable self-ignition combustion operation can be performed. On the other hand, by increasing the supply ratio of the high-octane fuel having excellent knock resistance in the high-load operation region, the octane number of the supplied fuel in the combustion chamber can be increased and pre-ignition can be suppressed. In this manner, engine 100 can be operated by the compression auto-ignition combustion method in a wide operation region.

  As shown in FIG. 2, in this embodiment, the high-octane fuel injection valve 72 is a hollow spray fuel injection valve having a large spray angle for injecting fuel toward the periphery of the combustion chamber. The high-octane fuel spray is guided to the periphery of the combustion chamber in the form of a hollow cone with a large apex angle. On the other hand, the low-octane fuel injection valve 82 is a fuel injection valve having a small spray angle, and injects low-octane fuel into the hollow portion of the high-octane fuel spray that has a hollow cone shape with a large apex angle. The low-octane fuel spray is guided to the center of the combustion chamber in a conical shape with a small apex angle.

  Therefore, the high octane fuel spray injected from the high octane fuel injection valve 72 and the low octane fuel spray injected from the low octane fuel injection valve 82 do not substantially overlap each other in the combustion chamber. That is, in the vicinity of the fuel injection valves 72 and 82, there may be a portion where the high-octane fuel and the low-octane fuel immediately after the injection overlap each other, but the air-fuel mixture is obtained through vaporization of both fuels and mixing with air. In this stage, the mixture of high-octane fuel is formed in the periphery of the combustion chamber, and the mixture of low-octane fuel is formed in the center of the combustion chamber. .

  In the present specification, the “vertical angle” of a cone means the vertical angle of an isosceles triangle obtained by horizontally projecting the cone. Further, the “hollow cone” means a shape obtained by hollowing out a cone having the same apex and height as the cone and having a smaller apex angle than the cone.

  Further, since the high octane number fuel and the low octane number fuel are injected into the combustion chamber in the compression stroke, the time from the fuel injection to the vicinity of the top dead center is very short. For this reason, the high-octane fuel spray guided to the periphery of the combustion chamber and the low-octane fuel spray guided to the center of the combustion chamber have little time to diffuse and substantially overlap each other even near the top dead center. It keeps the state that should not be. Therefore, a region having a high fuel concentration does not exist in the combustion chamber near the top dead center.

  Thus, if the region having a high fuel concentration does not exist in the combustion chamber, it is possible to prevent the emission of nitrogen oxides and smoke from increasing. The reason will be described below.

  First, it will be described that the increase in nitrogen oxide emission can be prevented. Nitrogen oxide is considered to be generated by the reaction of nitrogen molecules and oxygen molecules contained in the air. Since the nitrogen molecule is a stable compound, it reacts with oxygen only after being exposed to a considerably high temperature to form nitrogen oxides.

  Here, if there is a region having a high fuel concentration in the combustion chamber, the amount of heat generated in that portion increases, and the portion that is burning positively in the air-fuel mixture becomes extremely hot. As a result, a temperature at which nitrogen molecules and oxygen molecules react with each other is reached, and nitrogen oxides are generated.

  On the other hand, if there is no region with a high fuel concentration in the combustion chamber, the amount of heat generated in that portion is small. As a result, the temperature at which nitrogen molecules and oxygen molecules react is not reached, and nitrogen oxides are hardly generated. Therefore, if the region having a high fuel concentration does not exist in the combustion chamber, an increase in the nitrogen oxide emission can be prevented.

  Next, it will be described that the increase in smoke emission can be prevented. Smoke is generated when the fuel supplied into the combustion chamber is heated without being in contact with air.

  Here, if there is a region with a high fuel concentration in the combustion chamber, the fuel in that portion is relatively difficult to come into contact with air, so smoke is likely to occur. On the other hand, if there is no region having a high fuel concentration in the combustion chamber, there is no portion where the fuel in the combustion chamber is relatively difficult to come into contact with air, so that smoke does not easily occur. Therefore, if the region having a high fuel concentration does not exist in the combustion chamber, an increase in smoke emission can be prevented.

  Thus, the engine 100 in the present embodiment can be operated by the premixed compression auto-ignition combustion method in a wide operation region without increasing the emission amount of nitrogen oxides and smoke.

  Further, in this embodiment, the low octane fuel having a relatively high boiling point is distributed in the center of the combustion chamber, and the high octane fuel having a relatively low boiling point is distributed in the periphery of the combustion chamber. Here, since the central part of the combustion chamber is at a higher temperature than the peripheral part of the combustion chamber, the low-octane fuel is vaporized by distributing the low-octane fuel in the central part of the combustion chamber. On the other hand, the high-octane fuel quickly vaporizes even in the vicinity of the combustion chamber at a relatively low temperature. Therefore, in this embodiment, the amount of smoke discharged can be further reduced, and the problem of oil dilution due to bore flushing, which is caused by fuel droplets directly adhering to the inner wall surface of the cylinder, can be suppressed.

  In addition, gasoline is mentioned as a typical example of a high octane fuel, and light oil is mentioned as a typical example of a low octane fuel, respectively. Gasoline is easy to vaporize because of its low boiling point, while light oil is difficult to vaporize because of its high boiling point. Therefore, in order to reduce the amount of smoke emitted, it is preferable that the ratio of light oil (the ratio of the amount of heat generated by the combustion of light oil) to the generated heat amount by the total amount of fuel supplied during one cycle of the engine is small.

  FIG. 4 is an explanatory diagram showing an example of the relationship between the ratio of light oil to the total fuel amount and the smoke emission amount. In FIG. 4, the horizontal axis represents the light oil ratio, and the vertical axis represents the smoke discharge amount.

  From FIG. 4, it is preferable to set the ratio of light oil to gasoline so that the ratio of light oil is 30% or less because the smoke emission amount can be about 0.7 FSN (Filter Smoke Number) or less. Moreover, if the ratio of light oil and gasoline is set so that the ratio of light oil is 27% or less, the smoke emission can be reduced to about 0.5FSN or less, which is more preferable.

  In this embodiment, fuel injection of high octane number fuel and low octane number fuel is performed in the compression stroke, but the earlier the injection timing (advance side), the longer the time from fuel injection to top dead center, High and low octane fuels tend to overlap. On the other hand, the later the injection timing (the retard side), the shorter the time from fuel injection to top dead center, and the mixture of fuel and air tends to be insufficient. From such a point, it is preferable that the injection timing of the high-octane fuel and the low-octane fuel is within a period of 30 degrees before and after 90 degrees after the bottom dead center.

B. Second embodiment:
FIG. 5 is an explanatory diagram showing an enlarged cross section of a cylinder of the engine 100 in the second 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. 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. 3, 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. In this embodiment, the low octane fuel is injected in the first half of the compression stroke, and the high octane fuel is injected in the second half of the compression stroke. FIG. 5 shows a state in which low-octane fuel is injected by the low-octane fuel injection valve 82 in the first half of the compression stroke, and the injected low-octane fuel spray is hatched. Yes.

  The low octane fuel injected into the combustion chamber in the first half of the compression stroke is guided to the center of the combustion chamber as in the first embodiment, and therefore reaches the recess 145 provided on the top surface of the piston 144 and enters the recess 145. Holds well. Therefore, after that, in the latter half of the compression stroke, the high-octane fuel is injected toward the periphery of the combustion chamber, and the low-octane fuel remains in the recess 145 even when the piston 144 rises to near the top dead center. Therefore, also in this embodiment, near the top dead center, the high-octane fuel and the low-octane fuel do not substantially overlap each other, and there is no region where the fuel concentration is high in the combustion chamber. Yes. Therefore, also in the present embodiment, similarly to the first embodiment, it is possible to prevent an increase in the discharge amount of nitrogen oxides and smoke.

  In the present embodiment, since the low octane fuel is held in the recess 145 as described above, the high octane fuel and the low octane fuel do not substantially overlap each other near the top dead center. A state can be formed. Therefore, fluctuations between cycles can be reduced.

  Furthermore, in this embodiment, the low octane fuel can be injected in the first half of the compression stroke, and a relatively long time can be secured from the fuel injection of the low octane fuel to the self-ignition combustion near the top dead center. Therefore, mixing of fuel and air further proceeds, and the smoke discharge amount can be further reduced.

C. Third embodiment:
FIG. 7 is an explanatory diagram showing an enlarged cross section of a cylinder of the engine 100 in the third embodiment. The difference from the first embodiment shown in FIG. 2 is that in this embodiment, the cylinder head 130 is replaced with a fuel injection valve 72 for high octane fuel and a fuel injection valve 82 for low octane fuel in the first embodiment. The fuel injection valve 92 for seed fuel is provided. The other configuration is the same as that of the first embodiment.

  The two-type fuel injection valve 92 can directly inject two types of fuel, a high-octane fuel and a low-octane fuel, into the combustion chamber. In FIG. 7, the high-octane fuel spray injected from the fuel injection valve for type 2 fuel 92 is shown with thin hatching, and the low-octane fuel spray injected from the fuel injection valve for type 2 fuel 92 is also shown. It is shown with dark hatching.

  FIG. 8 is an explanatory view showing an example of the structure of the fuel injection valve 92 for the two types of fuel. FIG. 8A shows an enlarged cross section of the nozzle tip portion (A portion in FIG. 7) of the fuel injection valve 92 for the two-type fuel. FIG. 8B shows a BB cross section of FIG. FIG. 8C shows a front view of the C view of FIG.

  Inside the nozzle of the fuel injection valve 92 for the two types of fuel, a low-octane fuel flow path 922 in the vertical direction is provided near the center, and a needle 921 is inserted into the low-octane fuel flow path 922. ing. Further, one low octane number fuel injection hole 923 is provided at the center of the nozzle tip of the fuel injection valve 92 for the two types of fuel, and the low octane number fuel injection hole 923 is the lower end of the low octane number fuel flow path 922. Connected to the department.

  The needle 921 can open and close the connecting portion between the low-octane fuel channel 922 and the low-octane fuel nozzle hole 923 by the vertical movement thereof, and the flow rate of the low-octane fuel can be adjusted. The low-octane fuel that has flowed out of the low-octane fuel channel 922 to the low-octane fuel injection hole 923 is injected toward the center of the combustion chamber to form a conical spray with a small spray angle.

  Similarly, a high-octane fuel flow path 926 in the vertical direction is provided in the periphery of the nozzle of the fuel injection valve 92 for the two types of fuel, and a needle 925 is provided in the high-octane fuel flow path 926. Has been inserted. Further, a high octane number fuel channel 927 is provided immediately below the high octane number fuel channel 926, and is connected to the lower end of the high octane number fuel channel 926. Furthermore, 10 high-octane fuel injection holes 929 are provided at the periphery of the nozzle tip of the two-type fuel injection valve 92, and each of the high-octane fuel injection holes 929 is provided in a horizontal annular shape. The high-octane fuel channel 928 is connected to the lower end of the high-octane fuel channel 927.

  The needle 925 can open and close the connecting portion between the high-octane fuel flow path 926 and the high-octane fuel flow path 927 by its vertical movement, and the flow rate of the high-octane fuel can be adjusted. The high-octane fuel that has flowed out of the high-octane fuel channel 926, through the high-octane fuel channel 927 and the high-octane fuel channel 928 into the high-octane fuel nozzle 929 is directed toward the periphery of the combustion chamber. Sprayed to form a hollow cone spray with a large spray angle.

  Thus, the fuel injection valve 92 for the two types of fuel can inject the high-octane fuel toward the periphery of the combustion chamber and the low-octane fuel toward the center of the combustion chamber. Therefore, as in the first embodiment, the high-octane fuel and the low-octane fuel can be injected so as not to substantially overlap each other in the combustion chamber.

  Therefore, also in the present embodiment, it is possible to prevent a region having a high fuel concentration from existing in the combustion chamber in the vicinity of the top dead center, and to prevent an increase in emissions of nitrogen oxides and smoke.

  Further, in this embodiment, since the high octane fuel and the low octane fuel are injected from one fuel injection nozzle, the high octane fuel spray and the low octane fuel spray are more easily overlapped with each other in the combustion chamber. It can be avoided.

  In addition, since only one fuel injection valve needs to be provided in the cylinder head 130, the mountability of the fuel injection valve can be improved and the design freedom of the cylinder head can be improved.

D. 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.

D1. Modification 1:
In each example, the high octane number fuel is distributed in the combustion chamber peripheral portion and the low octane number fuel is distributed in the combustion chamber central portion, thereby forming a state in which the two fuels do not substantially overlap each other. As long as the fuel and the low-octane fuel do not substantially overlap each other, both fuels may be distributed anywhere in the combustion chamber. For example, high octane fuel may be distributed in the center of the combustion chamber and low octane fuel may be distributed in the periphery of the combustion chamber. Alternatively, the high octane fuel may be distributed in the right half of the combustion chamber and the low octane fuel may be distributed in the left half of the combustion chamber. However, in order to easily form a state where the high-octane fuel and the low-octane fuel do not substantially overlap each other, and to further reduce the smoke emission amount and suppress the problem of oil dilution due to bore flushing, It is preferable to distribute the octane fuel at the periphery of the combustion chamber and the low octane fuel at the center of the combustion chamber.

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 shows roughly an example of the fuel-injection timing of the engine 100 in 1st Example. Explanatory drawing which shows an example of the relationship between the ratio of the light oil which occupies for the total amount of fuel, and smoke discharge amount. Explanatory drawing which expands and shows the cross section of the cylinder of the engine 100 in 2nd Example. Explanatory drawing which shows roughly an example of the fuel-injection control of the engine 100 in 2nd Example. Explanatory drawing which expands and shows the cross section of the cylinder of the engine 100 in 3rd Example. Explanatory drawing which shows an example of the structure of the fuel injection valve 92 for 2 type fuels.

Explanation of symbols

12 ... Intake passage 16 ... Exhaust passage 20 ... Air cleaner 22 ... Throttle valve 24 ... Electric actuator 26 ... Catalyst 30 ... Engine control unit 32 ... Crank angle sensor 34. Accelerator opening 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 92 ... Fuel injection for two types of fuel Valve 100 ... Engine 130 ... Cylinder head 132 ... Intake valve 133 ... Intake port 134 ... Exhaust valve 135 ... Exhaust port 140 ... Cylinder block 142 ... Cylinder 144 .. .Piston 145 ... Recess 146 ... Connecting lock 148 ... Crankshaft 162,164 ... Electric actuator 921 ... Needle 922 ... Low-octane fuel passage 923 ... Low-octane fuel injection hole 925 ... Needle 926 ... High octane number Fuel channel 927 ... High-octane fuel channel 928 ... High-octane fuel channel 929 ... High-octane fuel nozzle

Claims (3)

  An internal combustion engine capable of premixed compression self-ignition operation,
  A combustion chamber composed of a cylinder and a piston;
  A fuel injection mechanism for directly injecting a low octane fuel and a high octane fuel into the combustion chamber,
  The fuel injection mechanism performs fuel injection so that the low-octane fuel and the high-octane fuel do not substantially overlap each other in the combustion chamber in the compression stroke,
  The fuel injection mechanism injects one of a low octane fuel and a high octane fuel so that the fuel spray has a hollow cone shape with a large apex angle, and the other has a hollow cone-shaped fuel spray hollow shape with a large apex angle. Inject the fuel spray into a cone with a small apex angle,
  The fuel injection mechanism includes a first fuel injection valve that injects low-octane fuel and a second fuel injection valve that injects high-octane fuel,
  The first fuel injection valve is a fuel injection valve having a small spray angle for injecting fuel toward a central portion of the combustion chamber,
  The internal combustion engine, wherein the second fuel injection valve is a hollow spray fuel injection valve having a large spray angle for injecting fuel toward the periphery of the combustion chamber. The internal combustion engine according to claim 1 ,
A recess is formed on the piston top surface,
An internal combustion engine in which fuel injection of low-octane fuel by the first fuel injection valve is performed in the first half of the compression stroke, and fuel injection of high octane fuel by the second fuel injection valve is performed in the second half of the compression stroke.   An internal combustion engine capable of premixed compression self-ignition operation,
  A combustion chamber composed of a cylinder and a piston;
  A fuel injection mechanism for directly injecting a low octane fuel and a high octane fuel into the combustion chamber,
  The fuel injection mechanism performs fuel injection so that the low-octane fuel and the high-octane fuel do not substantially overlap each other in the combustion chamber in the compression stroke,
  The fuel injection mechanism injects one of a low octane fuel and a high octane fuel so that the fuel spray has a hollow cone shape with a large apex angle, and the other has a hollow cone-shaped fuel spray hollow shape with a large apex angle. Inject the fuel spray into a cone with a small apex angle,
  The fuel injection mechanism includes a fuel injection valve for two types of fuel capable of injecting both a low octane fuel and a high octane fuel,
  The fuel injection valve for type 2 fuel injects low-octane fuel at a small spray angle toward the center of the combustion chamber and hollows high-octane fuel at a large spray angle toward the periphery of the combustion chamber. An internal combustion engine that injects into

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