JP6969526B2 - Premixed compression ignition engine - Google Patents

Description

INDUSTRIAL APPLICABILITY According to the present invention, a premixed compression ignition engine that mixes fuel injected into a combustion chamber with air and then compresses and ignites, particularly a non-equilibrium plasma for promoting combustion can be supplied to the combustion chamber. Regarding mixed compression ignition type engine.

The following Patent Document 1 is known as an example of a premixed compression ignition engine using a non-equilibrium plasma. The premixed compression ignition engine of Patent Document 1 supplies ozone as an active species to the combustion chamber by generating an injector that injects fuel containing gasoline into the combustion chamber and non-equilibrium plasma (streamer discharge). It is equipped with an ozone generator.

Further, the following Patent Document 2 is also known as disclosing an engine similar to the above.

Japanese Patent No. 6237329 Japanese Patent No. 6149759

According to Patent Documents 1 and 2, by supplying ozone as an active species to the air-fuel mixture, the combustion of the air-fuel mixture is promoted and the amount of unburned residue is suppressed to be small, which has the advantage of improving fuel efficiency. be.

However, in Patent Documents 1 and 2, since compression ignition combustion is performed in a state where the air-fuel mixture and ozone are totally mixed, if a large amount of ozone is inadvertently supplied, the combustion becomes excessively steep. There was a risk of large combustion noise. On the other hand, when the amount of ozone supplied is reduced in order to suppress combustion noise, there is a problem that the effect of improving fuel efficiency is not sufficiently obtained.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a premixed compression ignition engine capable of improving fuel efficiency while suppressing combustion noise to an appropriate level.

To solve the above problems, the premixed compression ignition engine of the present invention has a cylinder in which a combustion chamber is formed and an injector which is arranged in the central portion of the combustion chamber and injects fuel into the combustion chamber. A piston having a crown surface defining the bottom surface of the combustion chamber and having a cavity formed in the center of the crown surface, an intake port for introducing air into the combustion chamber, and a ceiling of the combustion chamber. An intake valve that opens and closes the opening of the intake port formed on the surface, an exhaust port for drawing out fuel from the combustion chamber, and an opening of the exhaust port formed on the ceiling surface of the combustion chamber are opened and closed. An exhaust valve, a plasma generation plug that has an electrode disposed in the combustion chamber and discharges from the electrode into the combustion chamber so that non-equilibrium plasma is generated from the electrode, and an injector. The injector and a control device for controlling the plasma generation plug are provided so as to realize premixed compression ignition combustion in which fuel is compressed and ignited while being mixed with air, and the intake air is viewed from a direction along the central axis of the cylinder. When the side on which the valve is arranged is the intake side and the side on which the exhaust valve is arranged is the exhaust side, the portion of the opening edge of the cavity located on the intake side and the electrode The plasma generation plug is arranged at a position where the distance is shorter than the distance between the portion of the opening edge of the cavity on the exhaust side and the electrode, and the control device is from the injector. The fuel is injected during the pre-injection and compression strokes, which are the fuel injections performed during the intake stroke so that at least a portion of the injected fuel forms a fuel-air mixture on the outer periphery of the cavity. The injector is made to perform the post-stage injection to be injected into the combustion chamber, and the plasma generation plug is directed toward the outer peripheral portion of the ceiling surface of the combustion chamber during the period from the end of the pre-stage injection to the execution of the post-stage injection. non-equilibrium plasma is discharged Te, and, after the succeeding injection, before the air-fuel mixture is ignited, as non-equilibrium plasma toward the opening edge of the cavity from the plasma generation plug is discharged, the plasma It is characterized in that it controls a generation plug (claim 1).

According to the present invention, a discharge is performed between the plasma generation plug and the opening edge of the cavity in a state where a mixture of fuel and air is formed on the outer peripheral side of the cavity. Therefore, active species such as ozone and OH generated from the action of the non-equilibrium plasma can be supplied to the portion on the outer peripheral side of the cavity, and the combustion of the air-fuel mixture in this portion can be promoted.

Here, the outer peripheral portion of the combustion chamber tends to have a lower temperature than the central portion of the combustion chamber. Therefore, if the active species is not supplied to the outer peripheral portion of the combustion chamber, the air-fuel mixture in the outer peripheral portion ignites with a considerable delay with respect to the air-fuel mixture in the central portion of the combustion chamber, and combustion after ignition. The speed will also be considerably slowed down. On the other hand, in the present invention, by supplying the active species to the outer peripheral portion of the combustion chamber as described above, the ignition delay of the air-fuel mixture in the outer peripheral portion can be shortened by the action of the active species, and the air-fuel mixture can be reduced. Combustion can be promoted to increase the combustion rate (that is, the combustion rate in the latter half of combustion). At this time, since the combustion speed of the air-fuel mixture in the central portion of the combustion chamber that ignites first does not change, the pressure increase that occurs in the first half of the combustion does not become remarkable. Therefore, the entire air-fuel mixture can be burned in a short period of time while suppressing the combustion noise to an appropriate level, and a sufficiently high thermal efficiency can be obtained.

Moreover, in the present invention, the distance between the electrode and the portion of the opening edge of the cavity located on the intake side is shorter than the distance between the portion of the opening edge of the cavity located on the exhaust side and the electrode. Has been done. Here, the exhaust valve is maintained at a relatively high temperature by passing high-temperature exhaust gas, while the intake valve is kept at a relatively low temperature by passing low-temperature air. Therefore, the temperature of the intake side region of the outer peripheral portion of the combustion chamber is lower than that of the exhaust side region, and the air-fuel mixture existing in the intake side region tends to be difficult to burn. On the other hand, in the present invention, by being configured as described above, more electric energy and thus more active species can be supplied to the intake side region in the outer peripheral portion of the combustion chamber. .. Therefore, the combustion of the air-fuel mixture in the outer peripheral portion of the combustion chamber can be promoted more effectively.

In addition, the fuel injected from the injector and the non-equilibrium plasma are discharged by discharging during the period from the end of the first stage injection to the execution of the second stage injection and after the second stage injection, that is, after the fuel injection by the injector. Can be prevented from coming into contact with each other, and it is possible to avoid the generation of substances such as formaldehyde that suppress the combustion of the air-fuel mixture due to this contact.

Further, in the present invention, the control device causes the implement and the rear stage injection for injecting fuel into the combustion chamber to the first stage injection in the compression stroke is a fuel injection performed during inspiratory stroke to said injector, said from the plasma generation plug after succeeding injection Ru is non-equilibrium plasma discharge.

Therefore , it is possible to form an air-fuel mixture having a relatively high fuel concentration in the cavity by the rear-stage injection while forming an air-fuel mixture in the entire combustion chamber by the first-stage injection, thereby reliably igniting the air-fuel mixture in the cavity. , The air-fuel mixture of the entire combustion chamber can be reliably burned. Then, after the post-stage injection performed during the compression stroke, the piston is discharged from the plasma generation plug at a timing close to the ceiling surface of the combustion chamber, so that the plasma generation plug is directed toward the opening edge of the cavity. It is possible to discharge more reliably, and the active species can be more reliably supplied to the outer peripheral portion of the combustion chamber, particularly the portion on the intake side.

Further, in the present invention, the control device, Ru discharges non-equilibrium plasma toward from the plasma generation plug during a period from the preceding injection to the succeeding injection at the periphery of the ceiling surface of the combustion chamber.

Therefore , the non-equilibrium plasma is discharged from the plasma generation plug when the pressure in the combustion chamber is relatively low, so that more active species can be generated in the combustion chamber. Moreover, since the non-equilibrium plasma is discharged from the plasma generation plug configured as described above toward the outer peripheral portion of the ceiling surface of the combustion chamber, more active species are discharged to the outer peripheral portion of the combustion chamber, especially the intake side portion. Can be supplied.

In the above configuration, preferably, the plasma generation plug has an insulator provided so as to cover the surface of the electrode facing the ceiling surface of the combustion chamber (claim 2 ).

According to this configuration, it is possible to prevent the discharge from the electrode of the plasma generation plug toward the portion of the ceiling surface of the combustion chamber facing the electrode, and more reliably from the electrode toward the opening edge of the cavity. It can be discharged.

As described above, according to the premixed compression ignition engine of the present invention, it is possible to improve fuel efficiency while suppressing combustion noise to an appropriate level.

It is a schematic plan view which shows the structure of the premixed compression ignition type engine which concerns on one Embodiment of this invention. It is sectional drawing along the intake / exhaust direction of an engine body. It is sectional drawing along the cylinder row direction of an engine body. It is a top view which shows the shape of the crown surface of a piston. It is a schematic diagram for demonstrating the tumble flow formed in a combustion chamber. It is an enlarged view which shows the tip part of the plasma generation plug, (a) is a side view, (b) is a bottom view. It is sectional drawing of a single injector. It is sectional drawing which shows the combustion chamber and its peripheral part enlarged. It is a top view which shows the ceiling surface of a combustion chamber. It is a block diagram which shows the control system of an engine. It is a graph for demonstrating the generation condition of the non-equilibrium plasma. It is a time chart which shows the application pattern of the voltage to the plasma generation plug. It is a map diagram for demonstrating the difference of control according to the operating condition of an engine. It is a time chart for explaining the contents of the combustion control executed at the time of operation in a high load low speed region of an engine. It is a time chart for explaining the contents of the combustion control executed when the engine is operated in a high load high speed range. It is a figure for demonstrating the behavior of the fuel injected from an injector at the time of operation in a high load region, (a) is the situation during execution of the front-stage injection, (b) is the situation during execution of the rear-stage injection. (C) shows the situation near the compression top dead center, respectively. It is a figure which shows typically the situation in the combustion chamber when the main discharge is carried out. It is a figure which shows typically the situation in the combustion chamber when the additional discharge is carried out. It is a graph of the heat generation rate for demonstrating the effect of the said embodiment. It is a figure for demonstrating the modification of the plasma generation plug. It is a figure for demonstrating the modification of the structure of the opening edge of a cavity. It is a schematic plan view corresponding to FIG. 21. It is a figure for demonstrating the modification of the arrangement of the plasma generation plug, and the structure of the opening edge of a cavity. It is a figure for demonstrating the modification of the arrangement of the plasma generation plug, and the structure of the opening edge of a cavity. It is a figure for demonstrating the modification of the plasma generation plug.

(1) Overall Configuration FIG. 1 is a schematic plan view showing the configuration of a premixed compression ignition engine (hereinafter, also simply referred to as an engine) according to an embodiment of the present invention. The engine shown in this figure is a four-cycle gasoline direct injection engine mounted on a vehicle as a power source for driving, and is an in-line multi-cylinder engine body 1 including four cylinders 2 arranged in a row and an engine. The intake passage 50 through which the intake air introduced into the main body 1 flows, the exhaust passage 60 through which the exhaust gas discharged from the engine main body 1 flows, and a part of the exhaust gas flowing through the exhaust passage 60 are returned to the intake passage 50. It is equipped with an EGR device 70.

The engine body 1 is provided with an intake valve 11 described later on one side thereof and an exhaust valve 12 described later on the other side of the surface P passing through the central axis X of the cylinder 2. In the present embodiment, the intake valve 11 and the exhaust valve 12 are provided on one side and the other side, respectively, with the surface P along the arrangement direction of the cylinders 2 (hereinafter referred to as the cylinder row direction). Hereinafter, the direction orthogonal to the surface P is referred to as an intake / exhaust direction, and in this intake / exhaust direction, the side where the intake valve 11 is provided is referred to as the intake side, and the side where the exhaust valve 12 is provided is referred to as the exhaust side.

FIG. 2 is a diagram schematically showing a cross section of the engine body 1 along the intake / exhaust direction, and FIG. 3 is a diagram showing a cross section of the engine body 1 along a direction orthogonal to the intake / exhaust direction (cylinder row direction). It is a figure shown schematically. In FIG. 2, IN indicates the intake side and EX indicates the exhaust side. As shown in FIGS. 2 and 3, the engine body 1 is attached to the cylinder block 3 in which the four cylinders 2 are formed internally and the upper surface of the cylinder block 3 so as to close each cylinder 2 from above. It has a cylinder head 4 and a piston 5 inserted into each cylinder 2 so as to be slidable back and forth.

Above the piston 5, a combustion chamber 6 is formed, which is surrounded by the peripheral surface of the cylinder 2, the crown surface S of the piston 5, and the lower surface of the cylinder head 4. The ceiling surface 28, which is a portion of the lower surface of the cylinder head 4 that covers the combustion chamber 6, is formed in a so-called pent roof shape (triangular roof shape). That is, in the cross-sectional view shown in FIG. 2 (that is, the cross-sectional view along the intake / exhaust direction), the height of the ceiling surface 28 of the combustion chamber 6 becomes lower as it is farther from the cylinder axis X (central axis of the cylinder 2) to the intake side. It has an inclined surface, and an inclined surface whose height becomes lower as the distance from the cylinder axis X toward the exhaust side increases.

Fuel containing gasoline as a main component is supplied to the combustion chamber 6 by injection from an injector 15, which will be described later. Then, the supplied fuel is burned by compression ignition while being mixed with air in the combustion chamber 6, and the piston 5 pushed down by the expansion force due to the combustion reciprocates in the vertical direction. The fuel injected into the combustion chamber 6 may contain gasoline as a main component, and may contain an auxiliary component such as bioethanol in addition to gasoline, for example.

Below the piston 5, a crank shaft 7, which is an output shaft of the engine body 1, is provided. The crank shaft 7 is connected to the piston 5 via a connecting rod 8 and is rotationally driven around the central axis in response to the reciprocating motion (vertical motion) of the piston 5.

The cylinder block 3 is provided with a crank angle sensor SN1 that detects the rotation angle (crank angle) of the crank shaft 7 and the rotation speed (engine rotation speed) of the crank shaft 7.

The geometric compression ratio of the cylinder 2, that is, the ratio of the volume of the combustion chamber 6 when the piston 5 is at the top dead center and the volume of the combustion chamber when the piston 5 is at the bottom dead center, predicts the fuel containing gasoline. The value suitable for mixed compression ignition combustion is set to 15 or more and 30 or less.

FIG. 4 is a plan view showing the crown surface S of the piston 5 together with the tip end portion (discharge electrode 33) of the plasma generation plug 16 described later. As shown in FIG. 4 and the like, the cylinder head 4 has an intake port 9 for introducing air supplied from the intake passage 50 into the combustion chamber 6 for each cylinder 2, and an exhaust gas generated in the combustion chamber 6. The exhaust port 10 for leading out to the exhaust passage 60, the intake valve 11 that opens and closes the opening of the intake port 9 on the combustion chamber 6 side, and the exhaust valve 12 that opens and closes the opening of the exhaust port 10 on the combustion chamber 6 side. Each is provided. Two intake ports 9 and two exhaust ports 10 are provided for one cylinder, and two intake valves 11 and two exhaust valves 12 are provided for each cylinder. The intake valve 11 and the exhaust valve 12 are driven to open and close in conjunction with the rotation of the crank shaft 7 by a valve operating mechanism (not shown) including a pair of camshafts and the like arranged on the cylinder head 4.

FIG. 5 is a diagram schematically showing the inside of the combustion chamber 6 when the intake valve 11 is opened. The intake port 9 is formed so as to extend upward from the ceiling surface 28 of the combustion chamber 6, and a tumble flow is formed in the combustion chamber 6 as the intake valve 11 opens. In the present embodiment, the intake port 9 is connected to the ceiling surface 28 of the combustion chamber 6 at an angle close to a right angle (the inner peripheral surface of the opening portion of the intake port 9 on the combustion chamber 6 side and the ceiling of the combustion chamber 6). The angle formed with the surface 28 is closer to 90 degrees). Further, the area of the opening portion of the intake port 9 on the combustion chamber 6 side is increased. As a result, the vortex diameter of the tumble flow becomes relatively small. Specifically, as shown by the arrow Y1, the main intake flow toward the exhaust side portion in the combustion chamber 6 after flowing into the combustion chamber 6 from the intake port 9 is more downward (toward the crown surface S of the piston 5). ). Further, as shown by the arrow Y2, a relatively large amount of intake air flows from the intake port 9 to the intake side portion. The main intake flow Y1 tends toward the intake side of the combustion chamber 6 near the crown surface S of the piston 5, but this flow is obstructed by the flow indicated by the arrow Y2. As a result, in the present embodiment, the tumble flow formed in the combustion chamber 6 becomes a vortex having a small diameter passing near the center of the combustion chamber 6. Along with this, the gas flow near the outer peripheral edge of the ceiling surface 28 of the combustion chamber 6 is suppressed to be small during the opening of the intake valve 11 and immediately after the closing of the intake valve 11. In FIG. 5, the broken line arrow Y11 is connected to the ceiling surface 28 of the combustion chamber 6 in a state where the intake port 9 is laid down more than the state shown by the solid line in FIG. 5, and is on the combustion chamber 6 side of the intake port 9. This is an example of the tumble flow according to the comparative example when the area of the opening portion of the above is smaller than that of the present embodiment.

As shown in FIG. 4 and the like, the crown surface S of the piston 5 defining the bottom surface of the combustion chamber 6 has a planar reference surface 21 located on the outer peripheral edge thereof and above the reference surface 21 (on the cylinder head 4). It has a raised portion 20 that rises on the approaching side). The height of the raised portion 20 increases as it approaches the cylinder axis X in the cross-sectional view of FIG. 2 (that is, the cross-sectional view along the intake / exhaust direction) so as to be along the ceiling surface 28 of the pent-roof-shaped combustion chamber 6. It is formed. A cavity C that is recessed downward (on the side opposite to the cylinder head 4) is formed in the central portion of the raised portion 20, in other words, the central portion of the crown surface S of the piston 5.

The cavity C has a flat bottom surface portion 22 having a substantially circular shape in a plan view, and a peripheral surface portion 23 rising from the outer peripheral edge of the bottom surface portion 22 while being inclined upward and radially outward. The opening edge C1 of the cavity C, which is the upper end of the peripheral surface portion 23, is formed so as to form an substantially elliptical shape in a plan view, and is in the cylinder row direction (direction orthogonal to the intake / exhaust direction) rather than the dimension in the intake / exhaust direction. It is formed so that the dimensions are longer.

The raised portion 20 has an intake side inclined surface 24 formed on the intake side of the cavity C and an exhaust side inclined surface 25 formed on the exhaust side of the cavity C. The intake side inclined surface 24 is formed so that the height becomes lower toward the intake side (diameterally outside) from the opening edge C1 on the intake side of the cavity C, and the exhaust side inclined surface 25 is formed of the cavity C. The height is formed so as to be farther from the opening edge C1 on the exhaust side toward the exhaust side (outward in the radial direction).

A pair of peaks 26 are formed in a region located outside the cavity C in the cylinder row direction and between the intake side inclined surface 24 and the exhaust side inclined surface 25. The pair of peaks 26 are formed in a substantially planar shape at the highest position in the crown surface S.

Here, the region (that is, the intake side / exhaust side inclined surfaces 24 and 25, the peak portion 26, and the reference surface 21) on the crown surface S of the piston 5 that is radially outside the opening edge C1 of the cavity C is defined as the “crown surface S. The "diametrically outer region", the region radially inside the opening edge C1 of the cavity C in the crown surface S of the piston 5 (that is, the formed surfaces 22 and 23 of the cavity C) is referred to as the "diametrically inner region of the crown surface S". In the present embodiment, since the cavity C is formed so as to be recessed on the side opposite to the ceiling surface 28 of the combustion chamber 6, naturally, the radial outer region of the crown surface S and the ceiling surface of the combustion chamber 6 facing the radial outer region thereof. The vertical distance (piston sliding direction) from 28 is smaller than the vertical distance between the radial inner region of the crown surface S and the ceiling surface 28 of the combustion chamber 6 facing the inner region. Therefore, when the piston 5 approaches the top dead center, a squish flow, which is a gas flow from the radial outer side to the inner side, is formed in the space between the radial outer region of the crown surface S and the ceiling surface 28. Will be done. In the following, the portion of the combustion chamber 6 where the squish flow is formed, that is, the portion between the radial outer region of the crown surface S (the region radially outer of the opening edge C1 of the cavity C) and the ceiling surface 28. Is referred to as a squish area.

As shown in FIGS. 1 to 3, the cylinder head 4 has an injector 15 that injects fuel (mainly gasoline) into the combustion chamber 6 and a plasma generation plug 16 that discharges unbalanced plasma into the combustion chamber 6. One set is provided for each cylinder 2. The non-equilibrium plasma is a plasma in which the energies of electrons, ions, molecules, etc. are not uniform (the energy of electrons is larger than the energy of ions, molecules, etc.) and is thermally unbalanced. Non-equilibrium plasma is also called low temperature plasma because it does not involve a temperature rise. The supply of non-equilibrium plasma having such a property hardly raises the gas temperature in the combustion chamber 6, but leads to reforming the gas component in the combustion chamber 6 (details will be described later).

6 (a) and 6 (b) are enlarged views showing the tip of the plasma generation plug 16. FIG. 7 is a cross-sectional view of the injector 15 alone. FIG. 8 is an enlarged cross-sectional view showing the combustion chamber 6 and its peripheral portion.

As shown in FIGS. 6A and 6B, the plasma generation plug 16 extends radially from the cylindrical plug body 31, the center electrode 32 inserted inside the plug body 31, and the tip of the center electrode 32. It has a plurality of (here, four) discharge electrodes 33. In the present embodiment, these discharge electrodes 33 correspond to the "electrodes" of the claims. When viewed from the direction along the central axis of the center electrode 32, the discharge electrodes 33 are arranged so as to be separated from each other by 90 degrees around the center axis of the center electrode 32. Each discharge electrode 33 has the same shape.

As shown in FIGS. 4 and 8, the plasma generation plug 16 has a center electrode 32 in a region where the discharge electrode 33 overlaps the bottom surface portion 22 of the cavity C in a plan view (viewed from the direction along the cylinder axis X). The tip portion of the cylinder head 4 and the entire discharge electrode 33 are attached to the cylinder head 4 in a state of being exposed to the combustion chamber 6. The plasma generation plug 16 is attached to the cylinder head 4 so that the tips of the four discharge electrodes 33 face the substantially centers of the valve surfaces of the two intake valves 11 and the two exhaust valves 12, respectively. That is, the four discharge electrodes 33 extend in directions intersecting the intake / exhaust direction and the cylinder row direction at an angle of about 45 degrees, respectively.

The plasma generation plug 16 is attached at a position closer to the intake side. Specifically, in the cylinder row direction, the position of the central axis X2 of the plasma generation plug 16 and the cylinder axis X are substantially the same position. On the other hand, in the intake / exhaust direction, the central axis X2 of the plasma generation plug 16 is located on the intake side with respect to the cylinder axis X. That is, the central axis X2 of the plasma generation plug 16 is located on the first reference line Z1 that intersects the cylinder axis X and extends in the intake / exhaust direction in a plan view, and intersects the cylinder axis X in the cylinder row direction. It is located in the region on the intake side of the second reference line Z2 extending to. In the illustrated example, the plasma generation plug 16 is arranged so that the entire discharge electrode 33 is in the region on the intake side of the second reference line Z2.

Here, the opening edge C1 of the cavity C has a shape that is substantially symmetrical with respect to the second reference line Z2 in a plan view. From this, because the plasma generation plug 16 is arranged as described above, the distance between the discharge electrode 33 of the plasma generation plug 16 and the opening edge C1 of the cavity C is shorter on the intake side than on the exhaust side. It has become. That is, the tip of the discharge electrode 33 extending toward the intake side (the electrode extending from the central axis X2 of the plasma generation plug 16 toward the intake valve 11, hereinafter may be referred to as the intake side electrode 33i) and facing the tip thereof. The distance d1 of the cavity C from the opening edge C1 is the electrode extending toward the exhaust side (the electrode extending from the central axis X2 of the plasma generation plug 16 toward the exhaust valve 12, hereinafter may be referred to as the exhaust side electrode 33e). The distance between the tip and the opening edge C1 of the cavity C facing the tip is shorter than the distance d2.

Further, as shown in FIG. 7, the four discharge electrodes 33 of the plasma generation plug 16 are downward (the crown surface S of the piston 5) from the position corresponding to the central axis of the plasma generation plug 16 toward the outer peripheral side of the combustion chamber 6. The amount of separation between each discharge electrode 33 and the ceiling surface 28 of the combustion chamber 6 is larger toward the tip end side (outer peripheral side of the combustion chamber 6) of the discharge electrode 33.

As shown in FIG. 6A, the center electrode 32 is covered with an insulator 34 (insulator) made of alumina or the like. Further, the upper surface of each discharge electrode 33 (the surface of the combustion chamber 6 on the ceiling surface 28 side) is also covered with an insulator 34 (insulator) made of alumina or the like.

When a predetermined pulse voltage is applied to the center electrode 32 (details will be described later), discharge is performed from each discharge electrode 33 toward the ground side electrode provided in the combustion chamber 6 according to the applied voltage. As a result, non-equilibrium plasma is generated along the discharge path connecting the discharge electrode 33 and the ground side electrode. Then, collide with gas molecules by the action of plasma particles with an electric charge (ions and electrons) is the electric field, together with the ozone (O ₃₎ and active species such as OH is produced, the earth these active species from the discharge electrode 33 A flow (induced flow) that moves toward the side electrodes is formed.

As shown in FIG. 3, the injector 15 is attached so that the tip end portion where the fuel ejection port (nozzle port 44 described later) is formed is located near the center of the ceiling surface 28 of the combustion chamber 6. In the present embodiment, the injector 15 is arranged so that the tip portion thereof is located on the cylinder axis X in the cross-sectional view of FIG.

As shown in FIG. 7, the injector 15 is a so-called externally open injector, and corresponds to a cylindrical valve body 41, a needle valve 42 inserted into the valve body 41 so as to be able to advance and retreat, and an applied voltage. It has a drive unit 43 including a piezo element that is deformed. The needle valve 42 has a substantially truncated cone-shaped tip portion 42a whose outer diameter becomes smaller toward the tip side.

When the injector 15 is closed, the needle valve 42 is housed in the valve body 41 in a state where the peripheral surface of the maximum diameter portion of the tip portion 42a is in close contact with the inner peripheral surface of the tip portion of the valve body 41. In such an externally open injector 15, the needle valve 42 is driven in the protruding direction at the time of valve opening, so that the needle valve 42 is driven from a continuous ring-shaped slit between the tip portion 42a of the needle valve 42 and the valve body 41. Nozzle opening 44 is formed. Therefore, when the injector 15 is opened, the fuel is injected into a cone shape (specifically, a hollow cone shape) through the nozzle port 44. In addition, in this specification, such a cone-shaped fuel injection is also an aspect of injecting fuel radially.

The lift amount of the needle valve 42 varies depending on the magnitude of the voltage applied to the piezo element and the application period. According to such a change in the lift amount, the spread of the fuel spray injected from the nozzle port 44 and the penetration force of the spray can be adjusted.

As shown in FIG. 8, each wall surface for partitioning the combustion chamber 6, that is, the peripheral surface of the cylinder 2, the crown surface S of the piston 5, the ceiling surface 28 of the combustion chamber 6, and each of the intake valve 11 and the exhaust valve 12. A heat shield layer 19 is provided on the lower surface of the valve head, respectively. The heat shield layer 19 provided on the peripheral surface of the cylinder 2 is limited to a position above the piston ring 5a (cylinder head 4 side) when the piston 5 is at top dead center, and the piston ring 5a is located. It is designed not to slide on the heat shield layer 19.

The heat shield layer 19 is made of a material having a lower thermal conductivity and volume specific heat than any of the cylinder block 3, the cylinder head 4, the piston 5, and the intake / exhaust valves 11 and 12. This is to suppress the heat of the combustion gas generated in the combustion chamber 6 from being released to the outside of the combustion chamber 6 and to reduce the cooling loss of the engine. As the heat shield layer 19, a silicone-based main material containing silica-based porous particles can be preferably used.

As described above, the heat shield layer 19 covers almost the entire combustion chamber 6 when the piston 5 is at top dead center, but a part D of the ceiling surface 28 of the combustion chamber 6 and the piston. The heat shield layer 19 is not formed on the opening edge C1 of the cavity C of 5. The heat shield layer 19 has higher insulating properties than the piston 5 made of, for example, an aluminum alloy. Therefore, the insulating property between the region D and the opening edge C1 of the cavity C is lower than that of the other regions on the wall surface of the combustion chamber 6. Hereinafter, the region D having low insulation properties formed on the ceiling surface 28 of the combustion chamber 6 is referred to as a ceiling-side non-insulation region D. From this, when the discharge is made from the discharge electrode 33 of the plasma generation plug 16, this non-equilibrium plasma is guided to the ceiling-side non-insulated region D or the opening edge C1 of the cavity C which is not covered by the heat shield layer 19. .. Specifically, the piston 5 is located relatively downward, and the distance between the tip of the discharge electrode 33 and the ceiling-side non-insulated region D is larger than the distance between the tip of the discharge electrode 33 and the opening edge C1 of the cavity C. When it is also short, the non-equilibrium plasma is basically guided to the ceiling-side non-insulated region D, the piston 5 is located relatively upward, and the distance between the tip of the discharge electrode 33 and the ceiling-side non-insulated region D is closer. When is longer than the distance between the tip of the discharge electrode 33 and the opening edge C1 of the cavity C, the unbalanced plasma is basically guided to the opening edge C1 of the cavity C. As described above, during plasma discharge, the discharge electrode 33 functions as an anode, and the ceiling side non-insulated region D or the opening edge C1 of the cavity C functions as a cathode, that is, a ground side electrode.

FIG. 9 is a schematic plan view showing the ceiling surface 28 of the combustion chamber 6. As shown in FIG. 9, the ceiling-side non-insulated region D is provided in a ring shape centered on the cylinder axis X and the central axis of the plasma generation plug 16. In the present embodiment, the ceiling-side non-insulated region D is configured to pass near the center of each valve surface of the intake valve 11 and the exhaust valve 12, and is formed on a part of the valve surface of the intake valve 11 and the exhaust valve 12. Regions with low insulation are formed in each. When the piston 5 is located from the vicinity of the center of the top dead center and the bottom dead center to the top dead center, the distance between the tip of the discharge electrode 33 of the plasma generation plug 16 and the opening edge C1 of the cavity C However, the ceiling-side non-insulated region D is provided at a position that is shorter than the distance between the tip of the discharge electrode 33 and the ceiling-side non-insulated region D.

Returning to FIG. 1, the intake / exhaust system of the engine will be described. The intake passage 50 is connected to four independent intake passages 51 communicating with each intake port 9 of the four cylinders 2 and an upstream end portion (upstream end portion in the intake flow direction) of each independent intake passage 51. It has a surge tank 52 and a single tubular common intake passage 53 extending upstream from the surge tank 52. An openable / closable throttle valve 54 for adjusting the flow rate of the intake air introduced into the engine body 1 is provided in the middle of the common intake passage 53. The surge tank 52 is provided with an air flow sensor SN2 that detects the flow rate of the intake air introduced into the engine body 1.

The exhaust passage 60 has four independent exhaust passages 61 communicating with each exhaust port 10 of the four cylinders 2 and one downstream end (downstream end in the exhaust gas flow direction) of each independent exhaust passage 61. It has a gathering portion 62 gathered in the above and a single tubular common exhaust passage 63 extending downstream from the gathering portion 62. The common exhaust passage 63 is provided with a catalytic converter 65 for purifying the exhaust gas. The catalyst converter 65 includes, for example, an oxidation catalyst that oxidizes HC and CO contained in the exhaust gas to make them harmless, and a GPF (gasoline particulate) that collects particulate matter (PM) contained in the exhaust gas.・ It has a built-in filter).

The EGR device 70 includes an EGR passage 71 that connects the common exhaust passage 63 and the surge tank 52, an EGR cooler 72 that cools the exhaust gas (EGR gas) that is recirculated to the intake passage 50 through the EGR passage 71, and an EGR gas. It has an EGR valve 73 that can be opened and closed in the EGR passage 71 in order to adjust the flow rate.

(2) Engine control system FIG. 10 is a block diagram showing an engine control system. The PCM 100 shown in this figure is a microprocessor for comprehensively controlling an engine, and is composed of a well-known CPU, ROM, RAM, and the like. The PCM 100 corresponds to an example of the "control device" according to the claim.

Detection signals from various sensors are input to the PCM100. For example, the PCM100 is electrically connected to the crank angle sensor SN1 and the airflow sensor SN2 described above, and the information detected by these sensors (that is, the crank angle, engine rotation speed, intake air flow rate, etc.) is used as an electric signal for the PCM100. It is designed to be input sequentially to.

Further, the vehicle is provided with an accelerator sensor SN3 that detects the opening degree of the accelerator pedal (not shown) operated by the driver who drives the vehicle, and the detection signal by the accelerator sensor SN3 is also input to the PCM 100. ..

The PCM 100 controls each part of the engine while executing various determinations and calculations based on the input signals from the various sensors. That is, the PCM 100 is electrically connected to the injector 15, the plasma generation plug 16, the throttle valve 54, the EGR valve 73, etc., and outputs a control signal to each of these devices based on the result of the calculation or the like. do.

For example, the PCM50 calculates an engine load (required torque) based on an accelerator opening degree or the like detected by the accelerator sensor SN3, and the calculated engine load, an intake flow rate detected by the airflow sensor SN2, and a crank angle sensor. Based on the engine rotation speed detected by the SN 1, the amount of fuel to be injected into the cylinder 2 (target injection amount) and the fuel injection timing are determined, and the injector 15 is controlled according to the determination.

Further, the PCM 100 determines the timing and discharge period for discharging the non-equilibrium plasma from the plasma generation plug 16 based on the engine load and the engine rotation speed, and controls the plasma generation plug 16 according to the determination.

FIG. 11 is a graph for explaining the generation conditions of the non-equilibrium plasma, and shows the relationship between the conditions of the pulse voltage (pulse width and applied voltage) applied to the plasma generation plug 16 and the type of plasma to be generated. Shows. The horizontal axis of the graph shows the pulse width, the vertical axis shows the peak value of the applied voltage, and the scales of each axis are both logarithmic scales. As shown in the graph of FIG. 11, in order to generate a non-equilibrium plasma, it is necessary to set the pulse width to 0.01 μsec or more and less than 1 μsec. On the other hand, when the pulse width is increased to 1 μsec or more, a thermal equilibrium plasma is generated. As described above, when a pulse voltage having a short pulse width is applied, a non-equilibrium plasma is generated because only electrons react and ions and molecules hardly react under the condition where the pulse width is short.

From the above findings, in the present embodiment, the PCM 100 controls the voltage applied to the plasma generation plug 16 under the conditions shown in FIG. That is, in the PCM 100, the power from the power supply unit (not shown) to the center electrode 32 is applied so that the pulse voltage having a peak voltage of 10 kV and a pulse width of 0.1 μsec is applied to the center electrode 32 of the plasma generation plug 16. Control the supply. At this time, the PCM 100 repeatedly applies the pulse voltage at a frequency of 100 kHz. As a result, a non-equilibrium plasma is generated between the four discharge electrodes 33 of the plasma generation plug 16 and the open edge C1 of the cavity C of the ceiling side non-insulated region D or the piston 5 having low insulation.

The peak voltage of the pulse voltage for generating the non-equilibrium plasma may be changed in the range of 1 kV to 30 kV depending on the operating conditions. For example, it is conceivable to set the peak voltage higher as the operating condition increases the pressure (in-cylinder pressure) of the combustion chamber 6.

When non-equilibrium plasma is generated in the combustion chamber 6, various substances are generated depending on the environment around the discharge electrode 33 of the plasma generation plug 16. In particular, when the periphery of the discharge electrode 33 was a great lean environment of the air-fuel ratio by the action of the non-equilibrium plasma, as described above, ozone (O ₃₎ of and OH etc., in the combustion chamber 6 Active species (radicals), which are substances that promote the combustion of the air-fuel mixture, are generated.

(3) Control according to operating conditions FIG. 13 is a map diagram for explaining the difference in control according to the operating conditions (load / rotational speed) of the engine. The operation map shown in this figure is roughly classified into a low load region A1 having a predetermined load Ts or less and a high load region A2 having a predetermined load Ts or more. The PCM100 determines whether the engine operating point is included in the low load region A1 or the high load region A2 each time based on the detected values of the sensors SN1 to SN3, and the combustion corresponding to the determined operating region is performed. Control each part of the engine to be realized. For example, when operating in the high load region A2, the PCM 100 is such that an air-fuel mixture is formed over almost the entire combustion chamber 6 (both inside and outside the cavity C) and the air-fuel mixture is burned by compression ignition. It controls the injector 15 and the plasma generation plug 16. On the other hand, during operation in the low load region A1, the PCM 100 controls the injector 15 and the plasma generation plug 16 so that an air-fuel mixture is limitedly formed inside the cavity C and the air-fuel mixture is burned by compression ignition. ..

Specific examples of combustion control in the high load region A2 and the low load region A1 are as follows.

(A) Control in the high load region FIGS. 14 and 15 are time charts for exemplifying the contents of combustion control executed by the PCM 100 during operation in the high load region A2. FIG. 14 shows an example of operation in the high load low speed region A21 in the high load region A2 in which the engine rotation speed is set to a preset reference rotation speed N1 or less. FIG. 15 shows an example of operation in the high load high speed range A22 in which the engine speed is higher than the reference speed N1 in the high load range A2. For example, FIG. 14 shows the timing of fuel injection and plasma discharge executed when the engine load is about 2/3 of the total load (maximum load) and the engine speed is 3000 rpm, which is included in the high load high speed range A21. Shows. As shown in FIGS. 14 and 15, when operating in the high load region A2, the PCM 100 injects fuel from the injector 15 in the intake stroke and the compression stroke, respectively, and discharges the non-equilibrium plasma from the plasma generation plug 16. Let me.

(Control in the high load and low speed range)
In the high load low speed region A21, fuel is injected from the injector 15 in the first half of the intake stroke and the second half of the compression stroke, respectively. In the following, the fuel injection performed in the first half of the intake stroke is referred to as a pre-stage injection, and the combustion injection performed in the latter half of the compression stroke is referred to as a post-stage injection.

The pre-stage injection is executed collectively (without being divided) from the exhaust top dead center (TDC on the left side of FIG. 14), which is the start time of the intake stroke, to the time when 1/2 of the intake stroke has elapsed. .. The intake valve 11 is opened during the entire period of the intake stroke, and the pre-stage injection is performed during the opening of the intake valve 11. For example, the intake valve 11 is closed at about 20 ° CA before the exhaust top dead center to about 60 ° CA after the intake bottom dead center, and the front stage injection is performed when the lift amount of the intake valve 11 is relatively high.

The post-stage injection is executed from the time when 1/4 of the compression stroke has elapsed to the time when 3/4 of the compression stroke has elapsed.

The timing of the post-stage injection will be described in more detail. The point at which 1/2 of the compression stroke has elapsed is the BTDC 90 ° CA advanced by 90 ° from the compression top dead center (TDC on the right side of FIG. 12) (“° CA” represents the crank angle). The time point at which 3/4 of the compression stroke has elapsed is the BTDC 45 ° CA advanced by 45 ° from the compression top dead center. In other words, in the present embodiment, fuel is injected from the injector 15 between BTDC 90 ° CA and BTDC 45 ° CA as the post-stage injection. In the following, the above-mentioned period (the period from BTDC 45 ° CA to BTDC 45 ° CA) in which the post-stage injection is performed may be referred to as “1/2 to 3/4 of the compression stroke”.

FIG. 16 is a diagram for explaining the behavior of the fuel injected from the injector 15 during operation in the high load region A2. In FIG. 16, for convenience, the plasma generation plug 16 is not shown, and the injector 15 located in front of the paper is shown at the original position of the plasma generation plug 16.

As shown in FIG. 16A, the fuel injected in the first half of the intake stroke by the pre-stage injection spreads in a cone shape from the injector 15 arranged near the center of the ceiling surface 28 of the combustion chamber 6. Most of the injected fuel diffuses into the combustion chamber 6. However, since the intake valve 11 is opened during the pre-stage injection, as shown in FIG. 16A, a part of the fuel injected from the injector 15 is sufficiently before and sufficiently spread. It collides with the intake valve 11 before it vaporizes. As a result, a relatively large amount of fuel adheres to the intake valve 11 in a droplet state as compared with the exhaust valve 12. Further, some fuel is scattered on the ceiling surface 28 of the combustion chamber 6 around the intake valve 11 due to the collision with the intake valve 11, and a relatively large amount is also scattered on the ceiling surface 28 of the combustion chamber 6 around the intake valve 11. The fuel will adhere in the form of droplets.

As described above, in the present embodiment, a large amount of fuel adheres to the ceiling surface 28 of the intake valve 11 and the combustion chamber 6 around the intake valve 11 in a droplet state at the time of performing the pre-stage injection. A part of the fuel adhering to the intake valve 11 and the ceiling surface 28 of the combustion chamber 6 around the intake valve 11 travels along the ceiling surface 28 to the intake side portion of the inner peripheral surface of the cylinder 2.

As shown in FIG. 16B, at the time of the latter half of the compression stroke in which the latter stage injection is performed, a mixture of fuel and air related to the first stage injection is formed in various parts of the combustion chamber 6. However, the intake side wall surface of the combustion chamber 6 shown by the dark colored region in FIG. 16B (the intake side portion of the ceiling surface 28 including the valve surface of the intake valve 11 and the intake air on the inner peripheral surface of the cylinder 2). In the vicinity of the side portion), a relatively rich air-fuel mixture (higher fuel concentration than other regions) is formed by the fuel adhering in the droplet state at the time of the previous stage injection as described above. In addition, in FIG. 16B, the region other than the darkly colored region is lightly colored, which indicates that a relatively lean (low fuel concentration) air-fuel mixture is present. Here, the fuel adheres to the exhaust side portion of the inner peripheral surface of the cylinder 2 due to the pre-stage injection, but the amount thereof is suppressed to be smaller than that of the intake side portion.

On the other hand, the fuel injected in 1/2 to 3/4 of the compression stroke by the subsequent injection is introduced into the cavity C of the piston 5 and stays inside the cavity C until the compression top dead center. That is, in the present embodiment, since the injector 15 is arranged near the center of the ceiling surface 28 of the combustion chamber 6 facing the cavity C, the injector 15 is formed into a cone shape at a timing of 1/2 to 3/4 of the compression stroke. When the fuel is injected, the injected fuel is introduced into the cavity C before it is sufficiently expanded radially (see FIG. 13 (b)).

As shown in FIG. 16 (c), most of the fuel once introduced into the cavity C stays inside the cavity C up to the compression top dead center (until just before ignition) without leaking to the outside of the cavity C. It will be. Along with this, the air-fuel mixture above the cavity C is maintained in a relatively lean state near the compression top dead center.

Here, in the process of the piston 5 approaching top dead center, a part of the fuel adhering to the inner peripheral surface of the cylinder 2 is vaporized. Therefore, a relatively rich air-fuel mixture (than the upper portion of the cavity C) is also formed in the squish area located radially outside the opening edge C1 of the cavity C.

As described above, in the present embodiment, in the combustion chamber 6 near the compression top dead center, the relatively rich air-fuel mixture (air-fuel mixture having a high fuel concentration) based on the pre-stage injection is the outer peripheral side portion of the combustion chamber 6, that is, the squish area. Along with being formed (outside the cavity C), a richer air-fuel mixture (air-fuel mixture with a high fuel concentration) based on the post-stage injection is formed inside the cavity C. Further, a particularly rich air-fuel mixture (air-fuel mixture having a high fuel concentration) is formed in the vicinity of the wall surface of the intake side portion of the combustion chamber 6.

As shown in FIG. 14, in the high load low speed region A21, the discharge of the non-equilibrium plasma from the plasma generation plug 16 is executed in the period from the end of the pre-stage injection to the start of the post-stage injection. Hereinafter, the discharge executed during the period from the end of the pre-stage injection to the start of the post-stage injection is referred to as a main discharge.

FIG. 17 is a diagram schematically showing a situation in the combustion chamber 6 when the main discharge is executed. In the present embodiment, the main discharge is executed for a period from the intake bottom dead center (BDC) to a predetermined time near the valve closing time of the intake valve 11, and the pulse voltage is continuously applied to the center electrode 32 during this period. Will be done. As described above, the intake valve 11 is designed to open at a predetermined time before the intake bottom dead center, and the main discharge is started in a state where the intake valve 11 is open.

In the present embodiment, the start time of the main discharge is kept constant regardless of the engine speed. On the other hand, as the engine speed increases, the end time of the main discharge is retarded at the crank angle. That is, when the engine speed is low, the main discharge is carried out during the period shown by the solid line in FIG. 17, and when the engine speed is high, the main discharge is carried out during the period shown by the broken line in FIG.

As described above, when the piston 5 is located from the vicinity of the center position of the top dead center and the bottom dead center to the top dead center, the tip of the discharge electrode 33 of the plasma generation plug 16 and the opening edge C1 of the cavity C. The distance is set shorter than the distance between the tip of the discharge electrode 33 and the ceiling-side non-insulated region D. As a result, in the main discharge, the non-equilibrium plasma is discharged along the line connecting the discharge electrode 33 and the ceiling-side non-insulated region D as shown in FIG. That is, the non-equilibrium plasma is emitted from the tip of the discharge electrode 33 toward the outer periphery of the combustion chamber 6 and guided to the ceiling-side non-insulated region D having a low insulation level.

Main discharge has a low fuel concentration in the combustion chamber 6 a prior succeeding injection, ozone (O ₃₎ and active species such as OH is performed in easily generated state. Further, the main discharge is performed near the bottom dead center of the intake air and when the pressure in the combustion chamber 6 is relatively low. In plasma discharge, than when discharge is higher when the field pressure or atmospheric pressure is low also made, ozone is formed (O ₃₎ and the active species is increased, such as OH. Therefore, when the main discharge is carried out at the above timing, many active species are generated in the combustion chamber 6.

Ozone (O ₃₎ such as activated species is as described above, are generated on the discharge path, flows to the ground side electrode side from the discharge electrode 33. Therefore, the main discharge, and active species such as ozone (O ₃₎ in line around connecting the discharge electrodes 33 of the plasma generating plug 16 and a ceiling-side non-insulating region D is generated, the ceiling-side non-insulating region from the discharge electrode 33 This active species flows toward D. In the present embodiment, the ceiling side non-insulated region D is formed on each valve surface of the intake valve 11 and the exhaust valve 12, and each discharge electrode (intake side electrode 33i and exhaust side electrode 33e) is the intake valve 11 and the exhaust. Since it is arranged so as to extend toward the center of each valve surface of the valve 12, the active species is supplied around the intake valve 11 and the exhaust valve 12.

Further, as described above, in the present embodiment, the plasma generation plug 16 is arranged closer to the intake side, and the distance between the intake side portion of the ceiling side non-insulated region D and the discharge electrode 33 (in other words, intake air). The distance between the side electrode 33i and the ceiling side non-insulated region D) is the distance between the exhaust side portion of the ceiling side non-insulated region D and the discharge electrode 33 (in other words, the exhaust side electrode 33e and the ceiling side non-insulated region D). Distance from region D). Therefore, the electricity applied to the center electrode 32 is more likely to flow between the intake side electrode 33i and the ceiling side non-insulated region D than between the exhaust side electrode 33e and the ceiling side non-insulated region D, and is discharged. The electrical energy flowing from the electrode 33 (intake side electrode 33i) to the intake side region in the ceiling side non-insulated region D is in the ceiling side non-insulated region D from the discharge electrode 33 (exhaust side electrode 33e). The electric energy flowing toward the area on the exhaust side of the is larger. As a result, in the main discharge, the active species generated around the line L1 connecting the intake side electrode 33i and the ceiling side non-insulated region D is the line L2 connecting the exhaust side electrode 33e and the ceiling side non-insulated region D. More active species are supplied around the intake valve 11 (compared to around the exhaust valve 12), more than the active species produced around.

Here, a tumble flow is formed in the combustion chamber 6 with the opening of the intake valve 11. However, as shown by the broken line and the solid line in FIG. 5 and the broken line Y1 in FIG. 17, the tumble flow is mainly a flow downward from the intake valve 11, and is a flow on the ceiling surface of the combustion chamber 6 in which the ceiling-side non-insulated region D is located. The flow near the outer periphery is suppressed relatively weakly. In particular, in the present embodiment, as described above for the solid line in FIG. 5, the flow near the outer peripheral edge of the ceiling surface of the combustion chamber 6 is very weak. Therefore, the generated active species heads from the discharge electrode 33 toward the ceiling-side non-insulated region D, and then stays in the vicinity of this region D, that is, in the vicinity of the outer peripheral edge of the ceiling surface of the combustion chamber 6.

After the main discharge, as described above, the post-stage injection is performed to form a rich air-fuel mixture in the cavity C. After that, in the vicinity of the compression top dead center, the air-fuel mixture existing in the cavity C far from the wall surface of the combustion chamber 6 having a high fuel concentration and a relatively low temperature ignites and burns. Following this, the air-fuel mixture existing in the outer peripheral side portion of the combustion chamber 6, that is, the squish area, ignites and burns. At this time, the active species remaining near the outer peripheral edge of the combustion chamber 6 promote ignition and combustion of the air-fuel mixture existing in the squish area. Specifically, the ignition of the air-fuel mixture present in the squish area starts earlier than in the case where there is no active species, and the combustion rate of this air-fuel mixture is accelerated.

In the present embodiment, as described above, more active species are supplied around the intake valve 11, so that the active species are formed in the vicinity of the wall surface on the intake side of the combustion chamber 6 due to the pre-stage injection. Even a mixture with a very high fuel concentration will be properly burned by the action of the active species. Further, the exhaust valve 12 is maintained at a higher temperature than the intake valve 11 through which the low temperature air flows due to the circulation of the high temperature exhaust gas. Therefore, the temperature of the squish area on the intake side tends to be lower than that of the squish area on the exhaust side, and the air-fuel mixture in the squish area on the intake side tends to be harder to burn than the air-fuel mixture in the squish area on the exhaust side. It is in. On the other hand, by supplying more active species to the squish area around the intake valve 11, that is, the intake side, combustion of the air-fuel mixture in the squish area on the intake side is effectively promoted.

(Control in the high load and high speed range)
As shown in FIG. 15, even in the high load high speed region A22, fuel is injected from the injector 15 in the first half of the intake stroke and the second half of the compression stroke, respectively, as in the high load low speed region A21. This fuel injection control is the same for the high load high speed region A22 and the high load low speed region A21, and the description thereof is omitted here.

On the other hand, as shown in FIG. 15, in the high load high speed region A22, in addition to the main discharge executed in the period from the end of the pre-stage injection to the start of the post-stage injection as the discharge from the plasma generation plug 16, the rear stage After the end of the injection, an additional discharge is performed over a predetermined period including the compression top dead center. The control content of the main discharge is the same for the high load high speed range A22 and the high load low speed range A21, and the description thereof is omitted here.

In the present embodiment, the additional discharge is performed from a predetermined time in the latter half of the compression stroke when the squish flow begins to weaken until the air-fuel mixture ignites. In the case of the present embodiment, the squish flow formed in the squish area (the region located radially outside the opening edge C1 of the cavity C) as the piston 5 rises, that is, the gas flow from the radial outside to the inside , BTDC 10 ° CA advanced by 10 ° from compression top dead center begins to weaken. Along with this, the earliest time to start additional discharge is BTDC 10 ° CA. Further, in the present embodiment, during operation in the high load high speed range A22, the air-fuel mixture ignites up to ATDC 10 ° CA, which is retarded by 10 ° from the compression top dead center, at the latest. Therefore, the latest time to end the plasma discharge is set to ATDC 10 ° CA. In other words, in the present embodiment, the plasma discharge is started and terminated between the BTDC 10 ° CA at which the squish flow begins to weaken and the ATDC 10 ° CA, which is the latest time of the air-fuel mixture ignition. In the example of FIG. 12, the discharge of non-equilibrium plasma from the plasma generation plug 16 is continuously performed between BTDC 5 ° CA and ATDC 5 ° CA. In the present specification, the ignition time of the air-fuel mixture is the start time of the thermal flame reaction of the fuel. The start time of this hot flame reaction can be defined as the time when about 10% by mass of all the supplied fuel burns (MFB 10%).

FIG. 18 is a diagram schematically showing a situation in the combustion chamber 6 when the additional discharge is executed. In the present embodiment, since the additional discharge is performed after BTDC 10 ° CA, the distance between the tip of the discharge electrode 33 and the opening edge C1 of the cavity C is the tip of the discharge electrode 33 when the additional discharge is performed. It is shorter than the distance between the ceiling side and the non-insulated region D on the ceiling side. Therefore, in the additional discharge, the non-equilibrium plasma is mainly discharged from the discharge electrode 33 toward the opening edge C1 of the cavity C. That is, the non-equilibrium plasma flows along the line connecting the discharge electrode 33 and the opening edge C1 of the cavity C from the tip of the discharge electrode 33 toward the opening edge C1 of the cavity C toward the outer periphery of the combustion chamber 6 and downward. , Non-equilibrium plasma is generated around this line. Note that some non-equilibrium plasma may flow from the discharge electrode 33 to the ceiling-side non-insulated region D.

As shown in FIG. 16 (c), in the vicinity of the compression top dead center, a relatively rich air-fuel mixture is formed in the squish area and the inside of the cavity C by the front-stage injection and the rear-stage injection. On the other hand, the discharge paths L11 and L12 connecting the tip of the discharge electrode 33 and the opening edge C1 of the cavity C are located between the two air-fuel mixture regions (between the squish area and the cavity C). The air-fuel mixture present here is relatively lean. Further, as described above, the fuel related to the post-stage injection stays in the cavity C, and the air-fuel mixture existing above the cavity C is relatively lean. Therefore, by adding a discharge, a discharge path L11, L12 around the non-equilibrium plasma ozone (O ₃₎ and active species such as OH is generated which connects the opening edge C1 of the tip and the cavity C of the discharge electrode 33.

Here, as described above, in the plasma generation plug 16, the distance d1 between the tip of the intake side electrode 33i and the opening edge C1 of the cavity C is larger than the distance d1 between the tip of the exhaust side electrode 33e and the opening edge C1 of the cavity C. It is shorter than the distance d2, and the distance between the intake side portion of the opening edge C1 of the cavity C and the discharge electrode 33 is larger than the distance between the exhaust side portion of the opening edge C1 of the cavity C and the discharge electrode 33. short. Therefore, the electric energy flowing from the discharge electrode 33 (intake side electrode 33i) toward the intake side region of the opening edge C1 of the cavity C is more from the discharge electrode 33 (exhaust side electrode 33e) to the opening edge of the cavity C. The electric energy flowing toward the exhaust side region of C1 becomes larger. As a result, in the additional discharge, the active species generated around the line L11 connecting the intake side electrode 33i and the opening edge C1 of the cavity C is the line L12 connecting the exhaust side electrode 33e and the opening edge C1 of the cavity C. More active species are supplied around the intake valve 11 (compared to around the exhaust valve 12) even in the additional discharge.

In this way, the piston 5 starts to descend while the active species is additionally supplied to the air-fuel mixture near the compression top dead center. When the piston 5 begins to descend, a reverse squish flow that flows from the inside to the outside in the radial direction begins to be formed in the squish area. Therefore, most of the active species generated around the line connecting the discharge electrode 33 and the opening edge C1 of the cavity C move to the squish area on the reverse squish flow.

In this way, in the high-load high-speed range A22, in addition to the active species generated by the main injection, the active species generated by the additional discharge are supplied to the squish area, and the mixture existing in the squish area is ignited and burned. Be promoted. In particular, by supplying more active species around the intake valve 11, that is, in the squish area on the intake side, the air-fuel mixture having a high fuel concentration and a relatively low temperature existing in the squish area on the intake side is appropriately burned. become.

In this embodiment, the air-fuel mixture ignites almost at the same time as the end of the additional discharge (that is, in the vicinity of ATDC 5 ° CA). For example, the air-fuel mixture ignites at about ATDC 5 to 10 ° CA, and compression ignition combustion is started.

(Control of intake air)
As described above, during operation in the high load region A2, an air-fuel mixture is mainly formed inside the cavity C and in the squish area (that is, fuel is distributed over a wide range in the combustion chamber 6). On the other hand, the amount of air introduced into the combustion chamber 6 is considerably increased, and as a result, the air-fuel ratio (A / F) in the combustion chamber 6 is significantly leaner than the theoretical air-fuel ratio (14.7). Is set to. Specifically, in the high load region A2, the average air-fuel ratio in the entire combustion chamber 6, that is, the ratio (mass ratio) between the amount of fuel injected from the injector 15 and the amount of air in the combustion chamber 6 during one cycle is. , It is set to a value that is more than twice as large as the theoretical air-fuel ratio. In other words, in the high load region A2, the throttle valve 54 is opened to a sufficiently high opening so that the excess air ratio λ becomes larger than 2 (air corresponding to λ> 2 is introduced into the combustion chamber 6). .. Further, in the high load region A2, the EGR valve 73 is opened except at least in the vicinity of the maximum load, and a predetermined amount of EGR gas is introduced into the combustion chamber 6. For example, in the high load region A2, the gas-fuel ratio (G / F), which is the ratio between the amount of fuel injected from the injector 15 and the total amount of gas in the combustion chamber 6 (total amount of air and EGR gas), is determined. It is set to 30 or more. Even if an attempt is made to secure an air amount equivalent to λ> 2 in the high load region A2, there is a possibility that the air amount will be insufficient only by naturally aspirated engine. In such a case, a supercharger may be added.

As described above, in the high load region A2, the excess air ratio λ in the combustion chamber 6 is in a very lean state, which is larger than 2, but due to the presence of the above-mentioned active species, the air-fuel mixture in the squish area (in other words). And the combustion of the air-fuel mixture in a lower temperature environment than the inside of the cavity C) is promoted, so that the combustion speed of the air-fuel mixture is accelerated and relatively short despite the lean environment of λ> 2. Combustion will end in time.

(B) Control in the low load region Although detailed illustration is omitted, in the low load region A1 where the engine load is lower (that is, the required amount of fuel is reduced) than the high load region A2, the fuel injection from the injector 15 is performed. The non-equilibrium plasma is discharged from the plasma generation plug 16 between the end of the combustion injection and the compression top dead center, which is executed only in the latter half of the compression stroke.

For example, in the low load region A1, fuel is injected from the injector 15 in a plurality of times in 1/2 to 3/4 of the compression stroke. As a result, in the low load region A1, the air-fuel mixture is formed only inside the cavity C. That is, all or most of the air-fuel mixture is formed inside the cavity C, and almost no air-fuel mixture is formed outside the cavity C.

Further, in the low load region A1, discharge is performed from the plasma generation plug 16 after the 3/4 elapse of the compression stroke (BTDC 45 ° CA) and between the end of fuel injection and the compression top dead center. By discharging at this timing, non-equilibrium plasma and active species are generated around the line connecting the tip of the discharge electrode 33 and the opening edge C1 of the cavity C in the low load region A1 as in the above-mentioned additional injection. At the same time, active species are mainly supplied to the squish area. As a result, the combustion speed of the air-fuel mixture in the squish area, which tends to be lower than that of the central portion of the cavity C, becomes faster, and the combustion period of the air-fuel mixture is shortened. In particular, as described above, the additional discharge supplies a large amount of active species to the squish area on the intake side, so that the combustion speed of the air-fuel mixture in the squish area on the intake side, which is lower in temperature than the exhaust side, is effective. Be enhanced.

The air-fuel ratio (A / F) of the air-fuel mixture of the entire combustion chamber 6 is set to a value that is more than twice as large as the stoichiometric air-fuel ratio (that is, λ> 2). As described above, in the present embodiment, the control of compression ignition combustion of the air-fuel mixture is executed in a lean environment of λ> 2 in both the high load region A2 and the low load region A1 (in all the operating regions of the engine). ..

(4) Action and effect As described above, in the present embodiment, the plasma generation plug 16 capable of generating non-equilibrium plasma is provided, and the plasma generation plug 16 is provided near the intake side to open the cavity C. The distance between the portion of the edge C1 located on the intake side and the discharge electrode 33 is shorter than the distance between the portion of the opening edge C1 of the cavity C located on the exhaust side and the discharge electrode 33. There is. Then, when the engine is operated in the high load high speed range A22, the pre-stage injection is performed and the air-fuel mixture is generated inside the cavity C and in the squish area radially outside the cavity C, that is, the outer peripheral portion of the combustion chamber 6. The injector 15 is controlled so as to be formed, and an additional discharge is performed after the injection of the front stage and the injection of the rear stage, after the fuel is injected from the injector 15, and before the air-fuel mixture ignites. A discharge is made from the electrode 33 toward the opening edge C1 of the cavity C. Therefore, there is an advantage that the combustion speed can be increased while suppressing the combustion noise to an appropriate level during the operation of the high load high speed range A22 in the premixed compression ignition type engine. Further, the additional discharge is similarly carried out in the low load region A1 as well, and the combustion speed can be increased while suppressing the combustion noise to an appropriate level even during the operation of the low load region A1.

Specifically, it is possible to generate active species such as a non-equilibrium plasma and ozone (O ₃₎ into the combustion chamber 6 by a discharge from a plasma generation plug 16 is made. Here, since the distance between the discharge electrode 33 and the opening edge C1 of the cavity C is set as described above, many of the discharge electrodes 33 toward the intake side region of the opening edge C1 of the cavity C. Electrical energy is supplied. As a result, the number of active species such as ozone (O ₃₎ is generated in the squish area on the intake side. Therefore, the combustion of the air-fuel mixture in the squish area on the intake side can be promoted by the action of the active species, the combustion speed of the air-fuel mixture can be increased, and the combustion period can be shortened.

Here, the temperature in the squish area located on the outer periphery of the combustion chamber 6 is lower than the temperature in the cavity C located in the center of the combustion chamber 6. Further, the temperature of the squish area on the intake side where the intake valve 11 is arranged tends to be lower than the temperature of the squish area on the exhaust side where the exhaust valve 12 maintained at a high temperature is arranged, and the temperature of the squish area on the intake side is likely to be lower. The temperature tends to be particularly lower than in other regions within the combustion chamber 6. Further, the front stage injection is performed while the intake valve 11 is open, and a part of the fuel collides with the intake valve 11, so that the squish area on the intake side (more specifically, the vicinity of the wall surface on the intake side of the combustion chamber 6). ) Form an air-fuel mixture with a very high fuel concentration. Therefore, if the active species is not supplied to the squish area on the intake side, the air-fuel mixture in the squish area on the intake side ignites with a considerable delay with respect to the air-fuel mixture in the cavity C, and combustion after ignition. The speed will also be considerably slowed down. On the other hand, in the above embodiment, since a large amount of active species is supplied to the squish area on the intake side, the ignition delay of the air-fuel mixture in the squish area on the intake side can be shortened, and the combustion speed of the air-fuel mixture (that is, that is). The combustion speed in the latter half of combustion) can be increased.

Further, in the above embodiment, the active species is also supplied to the squish area on the exhaust side, although the amount is smaller than that on the intake side. Therefore, it is possible to promote the combustion of the air-fuel mixture in the exhaust side squish area, which is suppressed to a lower temperature than in the cavity C.

Moreover, since the combustion speed of the air-fuel mixture in the cavity C that ignites first does not change, the pressure increase that occurs in the first half of the combustion does not become remarkable. Therefore, the entire air-fuel mixture can be burned in a short period of time while suppressing the combustion noise to an appropriate level, and a sufficiently high thermal efficiency can be obtained.

FIG. 19 is a diagram for explaining the above-mentioned action and effect. In FIG. 19, the waveform of the heat generation rate when the air-fuel mixture is burned by the method of the above embodiment is shown by W1. As shown in this waveform W1, when the combustion rate of the air-fuel mixture in the squish area is increased by using the non-equilibrium plasma (active species) (that is, when the method of the above embodiment is used), the combustion noise is taken into consideration. Below the "combustion noise limit" line, which is the upper limit of heat generation rate (that is, within the range where excessive combustion noise does not occur), it is possible to obtain a sufficiently peaky combustion waveform that rises and falls relatively rapidly. .. As a result, it is possible to realize near-ideal combustion without a short combustion period, excellent thermal efficiency, and excessive combustion noise.

The waveform W2 in FIG. 15 shows the waveform of the heat generation rate when the active species based on the non-equilibrium plasma is not supplied. As shown in this waveform W2, when the active species is not supplied to the squish area, a high combustion rate can be obtained in the first half of combustion, which is the stage where the air-fuel mixture in the cavity C having a high temperature burns. In the latter half of combustion, which is the stage where the air-fuel mixture in the squish area where the temperature is low burns, the combustion speed drops significantly, and the combustion period becomes longer as a whole. That is, in the latter half of the combustion, the piston 5 is lowered (expansion of the combustion chamber 6), so that the temperature in the squish area is originally low, and the combustion of the air-fuel mixture in the squish area is combined with the fact that the temperature is originally low. The speed has to be significantly reduced. In this way, it is understood that if plasma discharge (supply of active species) is not performed, the combustion of the air-fuel mixture in the squish area will be slowed down, resulting in a longer combustion period as a whole and a decrease in thermal efficiency. Will be done.

If the active species is supplied to the entire combustion chamber 6 to promote the combustion of both the air-fuel mixture in the squish area and the air-fuel mixture in the cavity C, for example, the waveform shown in FIG. As shown by W3, it becomes possible to further shorten the combustion period and increase the thermal efficiency. However, in this case, the combustion of the air-fuel mixture in the cavity C, which tends to be steep because of its high temperature, becomes steeper, and the heat generation rate at the initial stage of combustion rises sharply as the combustion noise limit is exceeded. Become. In this case, even if it is excellent in terms of thermal efficiency, the combustion noise becomes too large and it becomes impossible to maintain the commercial value. Similarly, if a large amount of active species is supplied to both the intake side and the exhaust side squish area, combustion in the exhaust side squish area is excessively promoted, so that the air-fuel mixture in this portion becomes the cavity C. It burns at the same time as the air-fuel mixture inside, and the combustion noise becomes excessive. On the other hand, in the above-described embodiment, only the combustion of the air-fuel mixture in the squish area is promoted (high speed), and the combustion of the air-fuel mixture in the squish area on the intake side is effectively promoted. The combustion speed can be increased as much as possible within a range that does not become excessive, and it is possible to achieve both commercial value and thermal efficiency at a high level.

Further, in the above embodiment, since the excess air ratio λ in the combustion chamber 6 is made larger than 2 during operation in the high load region A2, the combustion temperature of the air-fuel mixture can be significantly lowered, which accompanies combustion. The amount of NOx generated can be sufficiently suppressed. Here, the "NOx limit" line in FIG. 19 shows the lower limit heat generation rate at which the amount of NOx generated can be suppressed to the extent that a catalyst for reducing NOx (NOx catalyst) is unnecessary. As is clear from the comparison between the NOx limit line and the waveform W1, according to the above-described embodiment in which the air-fuel mixture is burned in a significantly lean environment of λ> 2, high-temperature combustion exceeding the NOx limit is performed. It can be avoided to occur, and the amount of NOx generated can be reduced to the extent that the NOx catalyst can be unnecessary.

In the above embodiment, in the high load region A2, in addition to the pre-stage injection in which fuel is injected from the injector 15 during the intake stroke, the post-stage injection in which fuel is injected from the injector 15 during the compression stroke is performed. Therefore, it is possible to form an air-fuel mixture having an appropriately high fuel concentration inside the cavity C located in the central portion of the combustion chamber 6. Therefore, the air-fuel mixture in the central portion of the combustion chamber 6 can be reliably ignited, whereby the air-fuel mixture in the entire combustion chamber can be reliably burned. Then, as described above, the air-fuel mixture existing in the outer peripheral portion of the combustion chamber, which is relatively difficult to ignite, can be burned at an early stage by the action of the non-equilibrium plasma.

Further, in the above embodiment, in the high load low speed region A21, the main discharge is carried out during the period from the end of the pre-stage injection carried out during the intake stroke to the start of the post-stage injection carried out during the compression stroke. Will be done. That is, the main discharge is performed when the pressure in the combustion chamber is relatively low. Therefore, a large amount of active species can be more reliably supplied to the squish area.

Further, by setting the timing of the main discharge and the additional discharge and the timing of the fuel injection so as not to overlap with each other, it is possible to surely promote the combustion of the air-fuel mixture depending on the active species. Specifically, when the fuel and the non-equilibrium plasma come into contact with each other, a substance that suppresses combustion such as formaldehyde (hereinafter referred to as a suppressive species) is likely to be generated. On the other hand, the main discharge was carried out during the period until the latter stage injection was started, and the additional discharge was carried out after the end of the latter stage injection, so that the injection was injected from the injector 15 into the combustion chamber 6. Contact between the fuel and the non-equilibrium plasma can be avoided. Therefore, it is possible to prevent the combustion of the air-fuel mixture from being hindered by a suppressive species such as formaldehyde.

Further, in the above embodiment, the post-stage injection is carried out from the time when 1/2 of the compression stroke has elapsed to the time when 3/4 of the compression stroke has elapsed (between BTDC 90 ° CA and BTDC 45 ° CA). Will be done. Therefore, the fuel injected from the injector 15 by the post-stage injection can be retained inside the cavity C up to the compression top dead center, and the air-fuel mixture in the cavity C can be more reliably ignited and the entire air-fuel mixture can be reliably burned. can. Further, the fuel concentration of the air-fuel mixture above the cavity C can be kept small. Therefore, when the additional discharge is carried out, the formation of suppressed species such as formaldehyde can be suppressed, and the combustion of the air-fuel mixture can be appropriately promoted.

Further, in the above embodiment, the heat shield layer 19 is provided on the wall surface of the combustion chamber 6. Therefore, it is possible to prevent the heat energy generated by the combustion of the air-fuel mixture in the outer peripheral portion of the combustion chamber 6 from being released to the outside through the wall surface of the combustion chamber 6. In particular, as described above, high thermal energy is generated by combustion of the air-fuel mixture having a high fuel concentration in the vicinity of the wall surface on the intake side of the combustion chamber 6, but this thermal energy can be prevented from being released to the outside and cooling is performed. The loss can be kept small and the fuel efficiency can be further improved.

(5) Modification example In the above embodiment, the injector 15 is arranged near the center of the ceiling surface 28 of the combustion chamber 6, and the squish area and the inside of the cavity C are relatively relative to each other during operation in the high load region A2. Fuel was injected from the injector 15 in the first half of the intake stroke and 1/2 to 3/4 of the compression stroke so that a rich air-fuel mixture was formed, but the position of the injector 15 and the timing of fuel injection were changed. Not limited to this. That is, the position of the injector 15 and the injection timing of the fuel from the injector 15 may be appropriately changed. However, in order to form a rich air-fuel mixture inside the cavity C, it is desirable to inject fuel after 1/4 of the compression stroke (135 ° CA before compression top dead center).

In the above embodiment, the case where only the main discharge is performed in the high load low speed region A21 and the main discharge and the additional discharge are performed in the high load high speed region A22 has been described, but also in the high load low speed region A21 in addition to the main discharge. Additional discharge may be performed. Further, in the high load low speed region A21 and the high load high speed region A22, the main discharge may be omitted and only the additional discharge may be performed.

In the above embodiment, in addition to the opening edge C1 of the cavity C, the insulation of the ceiling-side non-insulated region D, which is a part of the ceiling surface 28 of the combustion chamber 6, is lowered, and the ceiling-side non-insulated region D is subjected to plasma discharge. Although it is made to function as the ground side electrode of the above, only the opening edge C1 of the cavity C may be made to function as the ground side electrode. Further, even when the combustion chamber 6 is provided with a portion that functions as a ground side electrode, the position is not limited to the position including the valve surface of the intake and exhaust valves 12 as described above. However, if a part of the valve surface of the intake valve 11 functions as a ground side electrode, a large amount of active species can be supplied around the intake valve 11 and the air-fuel mixture having a high fuel concentration around the intake valve 11 is surely burned. be able to. Further, in the above embodiment, the case where the opening edge C1 of the cavity C is not covered with the heat shield layer 19 to function as the ground side electrode has been described, but the opening edge C1 of the cavity C is also the heat shield layer 19. You may cover it with. Even in this case, the opening edge C1 of the cavity C protrudes upward (the ceiling surface 28 side of the combustion chamber 6), and the discharge electrode 33 of the plasma generation plug 16 in the crown surface S of the piston 5 With the shortest distance, the unbalanced plasma discharged from the discharge electrode 33 will be guided to the opening edge C1 of the cavity C. However, it is more reliable if the opening edge C1 of the cavity C is not covered with the heat shield layer 19 (highly insulating) or the thickness of the heat shield layer 19 covering the opening edge C1 of the cavity C is reduced. In addition, the non-equilibrium plasma can be guided to the opening edge C1 of the cavity C.

Further, as shown in FIG. 20, the upper surface 33b (the surface of the combustion chamber 6 on the ceiling surface 28 side) of each discharge electrode 33 may be covered with an insulator (insulator) made of alumina or the like. By doing so, it is possible to prevent the unbalanced plasma from being discharged from the upper surface of each discharge electrode 33 toward the upper side, that is, toward the central portion of the ceiling surface 28 of the combustion chamber 6, and the outer periphery of the combustion chamber 6 is prevented from being discharged from the discharge electrode 33. The active species can be more reliably supplied to the side.

Further, in the above embodiment, the case where the opening edge C1 of the cavity C has a shape substantially symmetrical with respect to the second reference line Z2 in a plan view has been described, but the opening edge C1 of the cavity C is shown in FIGS. 21 and 22. It may be configured as shown. Specifically, in the example shown in FIGS. 21 and 22, in the plan view, two portions C1_a facing each intake side electrode 33i in the intake side portion of the opening edge C1 of the cavity C are the combustion chambers 6. It is configured to bulge toward the center side of the. That is, the rising edge of the portion of the peripheral surface portion 23 of the cavity C facing each intake side electrode 33i is configured to be steeper than the other portions. According to this configuration, the distance d1 between the intake side portion of the opening edge C1 of the cavity C and each intake side electrode 33i can be further shortened, and more active species are supplied to the intake side squish area. It becomes possible. FIG. 22 shows the peripheral surface portion 23 when the rising angle of the peripheral surface portion 23 on the intake side with respect to the bottom surface portion 22 is the same as that of the peripheral surface portion 23 on the exhaust side by a chain line. Further, in FIG. 22, the heat shield layer 19 of the cavity C is omitted for the sake of clarity. Further, in FIG. 20 and FIGS. 22 and 23 described later, the injector 15 and the plasma generation plug 16 are shown by solid lines for the sake of clarity.

Further, as shown in FIG. 23, the peripheral surface portion 23 and the opening edge C1 of the cavity C are inside the combustion chamber 6 with the opening edge C1 on the intake side as shown in FIGS. 21 and 22 than the opening edge C1 on the exhaust side. The plasma generation plug 16 may be arranged at the center of the combustion chamber 6 at a position where the central axis of the plasma generation plug and the cylinder axis X coincide with each other. Also in this case, the portion of the opening edge C1 of the cavity C facing the intake side electrode 33i is radially inside the combustion chamber 6 than the portion of the opening edge C1 of the cavity C facing the exhaust side electrode 33e. The distance d1 between the opening edge C1 of the cavity C and the intake side electrode 33i can be made shorter than the distance d2 between the opening edge C1 of the cavity C and the exhaust side electrode 33e. Therefore, even in this configuration, more active species can be supplied to the squish area on the intake side. That is, instead of the above embodiment, the plasma generation plug 16 is arranged in the center of the combustion chamber 6, while the opening edge C1 of the cavity C is located in the intake side portion of the combustion chamber 6 rather than in the exhaust side portion. By configuring the cavity C so as to be located inside in the radial direction, the distance between the portion of the opening edge C1 of the cavity C located on the intake side and the discharge electrode 33 is located on the exhaust side of the opening edge C1 of the cavity C. It may be shorter than the distance between the portion to be discharged and the discharge electrode.

Further, as shown in FIG. 24, as the discharge electrode 33, the plasma generation plug 16 is orthogonal to the discharge electrode 33i extending to the intake side and the discharge electrode 33e extending to the exhaust side along the first reference line Z1 in the intake / exhaust direction. The plasma generation plug 16 may be arranged so as to include two discharge electrodes 33c extending in the direction. Further, as shown in FIG. 24, such a plasma generation plug 16 is arranged in the center of the ceiling surface of the combustion chamber 6, and the portion C1_c on the first reference line Z1 of the opening edge C1 of the cavity C is the combustion chamber 6. It may be made to bulge inward in the radial direction of the.

Further, in the above embodiment, as the plasma generation plug 16, a plasma generation plug 16 having a plurality of discharge electrodes 33 radially protruding from the tip of the center electrode 32 is used (see FIG. 5), but instead of this, for example, FIG. 25 (see FIG. 5). A plasma generation plug 116 having a shallow dish-shaped discharge electrode 133 as shown in a) and (b) may be used.

More specifically, the plasma generation plug 116 according to the modification is a tubular plug body 131, a center electrode 132 inserted inside the plug body 131, and a shallow surface extending radially outward from the tip of the center electrode 132. It has a dish-shaped discharge electrode 133, and an insulator 134 provided between the end surface of the plug main body 131 and the discharge electrode 133. The discharge electrode 133 is formed in a circular shape centered on the tip of the center electrode 132 in the bottom view, and is formed so that the height becomes lower toward the outer side in the radial direction in the cross-sectional view. The insulator 134 is formed so as to cover almost the entire back surface of the discharge electrode 133 (the surface on the cylinder head 4 side, that is, the surface facing the ceiling surface of the combustion chamber 6).

In the above embodiment, as the injector 15, an externally open type injector in which a ring-shaped nozzle opening 44 is formed at the time of valve opening is used (see FIG. 7), but instead of this, a circumferential shape is provided at the tip of the injector. A multi-injection type having a plurality of side-by-side injection holes may be used.

In the above embodiment, an example in which the present invention is applied to a premixed compression ignition type gasoline engine in which a fuel containing gasoline as a main component is mixed with air and compressed and ignited has been described. The present invention may be applied to a premixed compression ignition type diesel engine in which compression ignition is performed while mixing with air.

1 Engine body 5 Piston 6 Combustion chamber S (Piston) Crown surface C (Piston) Cavity C1 (Cavity) Opening edge 15 Injector 16, 116 Plasma generation plug 33, 133 Discharge electrode 100 PCM (Control device)

Claims (2)

The cylinder in which the combustion chamber was formed and
An injector disposed in the central portion of the combustion chamber and injecting fuel into the combustion chamber,
A piston having a crown surface that defines the bottom surface of the combustion chamber and having a cavity formed in the center of the crown surface.
An intake port for introducing air into the combustion chamber,
An intake valve that opens and closes the opening of the intake port formed on the ceiling surface of the combustion chamber, and
An exhaust port for deriving exhaust from the combustion chamber,
An exhaust valve that opens and closes the opening of the exhaust port formed on the ceiling surface of the combustion chamber, and
A plasma generation plug having an electrode disposed in the combustion chamber and discharging non-equilibrium plasma from the electrode into the combustion chamber.
A control device for controlling the injector and the plasma generation plug so as to realize premixed compression ignition combustion in which the fuel injected from the injector is compressed and ignited while being mixed with air is provided.
When the side where the intake valve is arranged is the intake side and the side where the exhaust valve is arranged is the exhaust side when viewed from the direction along the central axis of the cylinder, the opening edge of the cavity is The plasma generation plug is arranged at a position where the distance between the portion located on the intake side and the electrode is shorter than the distance between the portion located on the exhaust side and the electrode in the opening edge of the cavity. It is set up and
The control device is
Fuel during the pre-injection and compression strokes, which are fuel injections performed during the intake stroke, so that a portion of the fuel injected from the injector forms a mixture of fuel and air on the outer peripheral side of the cavity. The injector is made to carry out the post-stage injection that injects the fuel into the combustion chamber .
During the period from the end of the pre-stage injection to the execution of the post- stage injection, the unbalanced plasma is discharged from the plasma generation plug toward the outer peripheral portion of the ceiling surface of the combustion chamber, and after the post-stage injection. the before the air-fuel mixture is ignited, as non-equilibrium plasma toward the opening edge of the cavity from the plasma generation plug is discharged, for controlling said plasma generation plug, it HCCI, wherein Expression engine. In the premixed compression ignition engine according to claim 1,
The plasma generation plug is a premixed compression ignition engine characterized by having an insulator provided so as to cover a surface of the electrode facing the ceiling surface of the combustion chamber.

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