JP6943229B2 - Premixed compression ignition engine - Google Patents

Description

The present invention is a premixed compression ignition engine that mixes the fuel injected into the combustion chamber with air and then compresses and ignites it, and in particular, it is possible to supply a non-equilibrium plasma for promoting combustion 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, there is an advantage that combustion at a particularly low temperature is promoted and compression ignition combustion is stabilized.

However, in Patent Documents 1 and 2, compression ignition combustion is performed in a state where the air-fuel mixture and ozone are totally mixed. Therefore, when 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 the combustion noise, there is a problem that the combustion speed becomes slow especially in the latter half of the combustion when the temperature of the combustion chamber becomes low, and the thermal efficiency is lowered.

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 sufficiently increasing the combustion speed while suppressing combustion noise to an appropriate level. do.

To solve the above problems, the premixed compression ignition engine of the present invention includes an injector that injects fuel into a combustion chamber, a piston having a crown surface that defines the bottom surface of the combustion chamber, and the combustion chamber. A plasma generation plug that has an electrode near the center of the ceiling and discharges unbalanced plasma from the electrode, and premixed compression ignition combustion that compresses and ignites the fuel injected from the injector while mixing it with air. The injector and the control device for controlling the plasma generation plug are provided, and the distance in the piston sliding direction from the radial outer region of the crown surface of the piston to the ceiling surface of the combustion chamber is the radial direction of the crown surface. By making the distance smaller than the distance in the piston sliding direction from the inner region to the ceiling surface of the combustion chamber, a squish flow is generated that flows from the outer side to the inner side in the radial direction as the piston approaches the top dead point. An area is formed on the outer peripheral portion of the combustion chamber, the piston has a cavity in the central portion of the crown surface, and the squish area is a region of the crown surface of the piston that is radially outer of the cavity. The injector is formed between the ceiling surface of the combustion chamber and the control device so that a part of the air-fuel mixture injected from the injector is formed in the squish area. While controlling, the non-equilibrium plasma is discharged from the electrode of the plasma generation plug toward the opening edge of the cavity from a predetermined time in the latter half of the compression stroke when the squish flow begins to weaken until the air-fuel mixture is ignited. As described above, the plasma generation plug is controlled, and the electrodes of the plasma generation plug are formed so as to extend radially from a position corresponding to the central axis of the plasma generation plug, and the piston is at the top dead point. The line connecting the tip of the electrode and the opening edge of the cavity is formed so as to be substantially parallel to the extending direction of the electrode (claim 1).

According to the present invention, an air-fuel mixture is formed in the squish area of the combustion chamber, and the squish flow (gas flow from the outer side to the inner side in the radial direction) that flows through the squish area begins to weaken. Before the qi ignites, the non-equilibrium plasma is discharged toward the opening edge of the cavity (the radial inner end of the squish area ) , so active species such as ozone and OH generated from the action of the non-equilibrium plasma are discharged. It can be moved to the squish area on the reverse squish flow (gas flow from the inside to the outside in the radial direction) generated by the descent of the piston after the compression top dead center. Then, the transferred active species promotes the combustion of the air-fuel mixture in the squish area, so that the combustion speed of the air-fuel mixture can be increased and the combustion period can be shortened.

Here, the temperature of the squish area located on the outer peripheral portion of the combustion chamber tends to be lower than that in the central portion of the combustion chamber. Therefore, if the active species were not supplied to the squish area, the air-fuel mixture in the squish area would ignite with a considerable delay with respect to the air-fuel mixture in the central part of the combustion chamber, and the combustion rate after ignition would be considerably slow. turn into. On the other hand, in the present invention, since the active species is supplied to the squish area, the ignition delay of the air-fuel mixture in the squish area can be shortened, and the combustion rate of the air-fuel mixture (that is, the combustion rate in the latter half of combustion) can be reduced. You can speed it up. Moreover, since the combustion speed of the air-fuel mixture in the central portion of the combustion chamber that ignites first does not change in particular, the pressure increase that occurs in the first half of combustion does not become significant. 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.
Further, in the present invention, when the piston is at the top dead center, the line connecting the tip of the electrode of the plasma generation plug and the opening edge of the cavity is substantially parallel to the extending direction of the electrode. The discharge path of the unbalanced plasma to be generated can be shortened as much as possible. As a result, non-equilibrium plasma can be efficiently generated, and a sufficient amount of active species can be supplied to the squish area.

The time when the squish flow begins to weaken can be BTDC 10 ° CA advanced by 10 ° from the compression top dead center. In this case, the control device may discharge the non-equilibrium plasma to the plasma generation plug after BTDC 10 ° CA (claim 2).

In the above configuration, more preferably, the control device forms a part of the air-fuel mixture in the squish area and the non-equilibrium when the engine is operated in a high load region where the engine load is equal to or higher than a predetermined load. The control for generating plasma is performed ( claim 3 ).

Since the required fuel injection amount is larger in the high load region of the engine than in the low load region, the amount of the air-fuel mixture formed in the squish area tends to be large. Therefore, the configuration of the present invention capable of increasing the combustion speed in the squish area can be more preferably applied during operation in such a high load region.

In the above configuration, more preferably, the injector radially injects fuel from the vicinity of the center of the ceiling of the combustion chamber toward the cavity, and the control device performs the intake stroke and the latter half of the compression stroke. Fuel is injected into each of the injectors ( claim 4 ).

According to this configuration, an air-fuel mixture can be appropriately formed in the squish area and the inside of the cavity, respectively, and these air-fuel mixture can be burned in a short period of time by utilizing the plasma discharge described above.

In the above configuration, more preferably, the engine further comprises a throttle valve that regulates the flow rate of air introduced into the combustion chamber, and the control device is equipped with air in the combustion chamber during operation in the high load region. The throttle valve and the injector are controlled so that the excess rate is greater than 2 ( claim 5 ).

According to this configuration, the combustion temperature of the air-fuel mixture during operation in a high load region can be significantly lowered, so that the amount of NOx generated during combustion can be sufficiently reduced so that the NOx catalyst becomes unnecessary. Can be done.

As described above, according to the premixed compression ignition engine of the present invention, the combustion speed can be sufficiently increased while suppressing the 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 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 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 combustion control executed at the time of operation in a high load region of an engine. 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. (C) shows the situation near the compression top dead center, respectively. It is a figure which shows typically the state of the combustion chamber when the non-equilibrium plasma is discharged from the plasma generation plug. 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 which changed the arrangement place of the plasma generation plug used in the said embodiment. It is a figure for demonstrating the modification of the plasma generation plug used in the said embodiment, (a) is a side view, (b) is a bottom view.

(1) Overall Configuration of Engine 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 traveling, and includes 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. The EGR device 70 is provided.

FIG. 2 is a cross-sectional view of the engine body 1 along the intake / exhaust direction, and FIG. 3 is a cross-sectional view of the engine body 1 along a direction orthogonal to the intake / exhaust direction (cylinder row direction). 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 inside 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 ceiling surface 28 of the combustion chamber 6 is lower in height 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 decreases 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 crankshaft 7, which is an output shaft of the engine body 1, is provided. The crankshaft 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 crankshaft 7 and the rotation speed (engine rotation speed) of the crankshaft 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. A value suitable for mixed compression ignition combustion is set to 15 or more and 30 or less.

As shown in FIGS. 1 and 2, the cylinder head 4 has an intake port 9 for introducing the air supplied from the intake passage 50 into the combustion chamber 6 for each cylinder 2, and is generated in the combustion chamber 6. An exhaust port 10 for leading the exhaust gas to the exhaust passage 60, an intake valve 11 for opening and closing the opening on the combustion chamber 6 side of the intake port 9, and an exhaust valve 12 for opening and closing the opening on the combustion chamber 6 side of the exhaust port 10. And are provided respectively.

The intake valve 11 and the exhaust valve 12 are opened and closed and driven in conjunction with the rotation of the crankshaft 7 by a valve operating mechanism (not shown) including a pair of camshafts and the like arranged on the cylinder head 4.

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 FIGS. 2 and 3 above, the crown surface S of the piston 5 that defines the bottom surface of the combustion chamber 6 is a flat reference surface 21 located on the outer peripheral edge thereof and the reference surface 21. It has a raised portion 20 that rises above (the side closer to the cylinder head 4). 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 recessed downward (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 as the distance from the intake side opening edge C1 of the cavity C toward the intake side (diameter outside), 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 on the crown surface S of the piston 5 that is radially inner than the opening edge C1 of the cavity C (that is, the forming 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 radial 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 (see FIGS. 13 and 14 described later).

As shown in FIGS. 1 to 3, the cylinder head 4 includes 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).

5 (a) and 5 (b) are enlarged views of the tip of the plasma generation plug 16. As shown in this figure, the plasma generation plug 16 includes a cylindrical plug body 31, a center electrode 32 inserted inside the plug body 31, and a plurality of plasma generation plugs 16 (here, a plurality of plasma generating plugs) that project radially from the tip of the center electrode 32. It has four) discharge electrodes 33. The discharge electrode 33 is provided so as to be exposed to the combustion chamber 6 at a position corresponding to the central portion of the ceiling surface 28 of the combustion chamber 6. The tip of the center electrode 32 protruding toward the combustion chamber 6 with respect to the plug body 31 is covered with an insulator 34 (insulator) made of alumina or the like.

In the plan view shown in FIG. 4, the plasma generation plug 16 is arranged at a position where the center (the central axis of the center electrode 32) substantially coincides with the cylinder axis X and the discharge electrode 33 overlaps the bottom surface portion 22 of the cavity C. Has been done. The four discharge electrodes 33 are formed so as to extend in a direction non-parallel to both the intake / exhaust direction and the cylinder row direction, more specifically, in a direction intersecting the intake / exhaust direction and the cylinder row direction at an angle of about 45 degrees. Has been done.

Further, as shown in FIG. 14 described later, the four discharge electrodes 33 of the plasma generation plug 16 are lines connecting the tip of each electrode 33 and the opening edge C1 of the cavity C in a state where the piston 5 is at the top dead center. Is formed so as to be substantially parallel to the extending direction of each electrode 33. Although details will be described later, a predetermined pulse voltage is applied to the center electrode 32, and each discharge electrode 33 is directed toward the combustion chamber 6 (opening edge C1 of the cavity C) according to the applied voltage. The unbalanced plasma is discharged.

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. The tip of the injector 15 is slightly offset from the cylinder axis X to one side in the cylinder row direction in the cross-sectional view of FIG. 3, and is arranged at a position overlapping the cavity C in the plan view. In other words, the tip of the injector 15 is arranged so as to be arranged close to the tip (discharge electrode 33) of the plasma generation plug 16 located at the center of the ceiling surface 28 of the combustion chamber 6 in the cylinder row direction. ..

FIG. 6 is a cross-sectional view of the injector 15 alone. As shown in this figure, the injector 15 is a so-called externally open injector, and corresponds to a tubular 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 deforms. The needle valve 42 has a substantially truncated cone-shaped tip portion 42a whose outer diameter becomes smaller toward the tip end 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 when the valve is opened, 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 this specification, such a cone-shaped fuel injection is also an aspect of injecting fuel radially.

The lift amount of the needle valve 42 changes 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 (penetration force) of the spray can be adjusted.

FIG. 7 is an enlarged cross-sectional view of the combustion chamber 6 and its peripheral portion. As shown in this figure, 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 the intake valve 11 and the exhaust valve 12 are each. 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 (FIG. 14 described later). (See), the piston ring 5a does not 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 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 the heat shield layer is limited to the opening edge C1 of the cavity C of the piston 5. 19 is not formed. The heat shield layer 19 has a higher insulating property than the piston 5 made of, for example, an aluminum alloy. Therefore, when the non-equilibrium plasma is discharged from the discharge electrode 33 of the plasma generation plug 16, the non-equilibrium plasma is naturally guided to the opening edge C1 of the cavity C which is not covered by the heat shield layer 19 (described later). See FIG. 14). As described above, at the time of plasma discharge, the anode and the cathode are configured by the discharge electrode 33 and the opening edge C1 of the cavity C. That is, the discharge electrode 33 functions as an anode, and the opening edge C1 of the cavity C functions as a cathode.

The opening edge C1 of the cavity C that functions as a cathode corresponds to the radial inner end of the squish area described above. In other words, in this embodiment, the non-equilibrium plasma is discharged from the discharge electrode 33 of the plasma generation plug 16 toward the radial inner end of the squish area.

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 and detoxifies HC and CO contained in the exhaust gas, 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 communicates 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 to adjust the flow rate.

(2) Engine control system FIG. 8 is a block diagram showing an engine control system. The PCM 100 shown in this figure is a microprocessor for controlling an engine in an integrated manner, 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 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, and the like, and outputs control signals to these devices based on the results of the above calculation and the like. do.

For example, the PCM50 calculates the engine load (required torque) based on the accelerator opening degree and the like detected by the accelerator sensor SN3, and the calculated engine load, the intake flow rate detected by the airflow sensor SN2, and the crank angle sensor. Based on the engine rotation speed detected by the SN1, 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. 9 is a graph for explaining the generation conditions of 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. Shown. The horizontal axis of the graph shows the pulse width, the vertical axis shows the peak value of the applied voltage, and the scale of each axis is a logarithmic scale. As shown in the graph of FIG. 9, 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 thermodynamic 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.

Based on the above findings, in this 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 a 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, the non-equilibrium plasma is discharged from the four discharge electrodes 33 of the plasma generation plug 16 toward the combustion chamber 6 (opening edge C1 of the cavity C of the piston 5).

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, ozone (O ₃₎ or OH and the like, the combustion of the mixture in the combustion chamber 6 Active species (radicals), which are substances that promote, are generated.

(3) Control according to operating conditions FIG. 11 is a map diagram for explaining a difference in control according to engine operating conditions (load / rotational speed). The operation map shown in this figure is roughly divided 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 operating point of the engine 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 PCM100 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 FIG. 12 is a time chart for exemplifying the contents of the combustion control executed by the PCM 100 during operation in the high load region A2, and is a typical example included in the high load region A2. It shows the timing of fuel injection and plasma discharge performed at the operating point (eg 2/3 load, 3000 rpm). As shown in this figure, during operation in the high load region A2, the PCM100 injects fuel from the injector 15 into the intake stroke and the compression stroke, respectively, and the air-fuel mixture is discharged after the fuel injection in the compression stroke is completed. Before ignition, the non-equilibrium plasma is discharged from the plasma generation plug 16.

Specifically, in the high load region A2, 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, fuel injection performed in the first half of the intake stroke is referred to as pre-stage injection, and combustion injection performed in the latter half of the compression stroke is referred to as post-stage injection. The post-stage injection is executed in a plurality of times (for example, two or three times) from the time when 1/2 of the compression stroke elapses to the time when 3/4 of the compression stroke elapses. The pre-stage injection is collectively (without being divided) from the exhaust top dead center (TDC on the left side of FIG. 12), which is the start time of the intake stroke, to the time when 1/2 of the intake stroke has elapsed. ..

The timing of the post-stage injection will be described in more detail. The time when 1/2 of the compression stroke has passed 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, as the post-stage injection, fuel is injected from the injector 15 in a plurality of times between BTDC 90 ° CA and BTDC 45 ° CA. The first post-stage injection starts after BTDC 90 ° CA, and the final post-stage injection ends by BTDC 45 ° CA. In the example of FIG. 12, the number of divisions of the second-stage injection is set to two, the start time of the first second-stage injection is slightly retarded from the BTDC 90 ° CA, and the end time of the second second-stage injection is from the BTDC 45 ° CA. It is set on the slightly advanced side. In the following, the above-mentioned period (the period from BTDC 90 ° CA to BTDC 45 ° CA) in which the subsequent injection is performed may be referred to as “1/2 to 3/4 of the compression stroke”.

The discharge of the non-equilibrium plasma from the plasma generation plug 16 is executed for a predetermined period including the compression top dead center after the end of the post-stage injection. More specifically, in this embodiment, the non-equilibrium plasma is discharged 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. Therefore, the earliest time to start the plasma discharge is BTDC 10 ° CA. Further, in the present embodiment, during operation in the high load region A2, the air-fuel mixture ignites at the latest by ATDC 10 ° CA, which is retarded by 10 ° from the compression top dead center. Therefore, the latest time to end the plasma discharge is set to ATDC 10 ° CA. In other words, in this 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 at 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 executed between BTDC 5 ° CA and ATDC 5 ° CA, almost at the same time as the end of plasma discharge (that is, in the vicinity of ATDC 5 ° CA). ) The air-fuel mixture is ignited. 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. 13 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. 13, 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. 13A, the fuel injected in the first half of the intake stroke by the pre-stage injection becomes a spray that spreads in a cone shape from the injector 15 arranged near the center of the ceiling surface 28 of the combustion chamber 6 and burns. It diffuses into the chamber 6. As a result, as shown in FIG. 13B, at the time of the latter half of the compression stroke in which the post-stage injection is performed, a state in which the fuel is dispersed and exists in various parts of the combustion chamber 6 can be obtained. However, as shown by the dark colored region in FIG. 13B, in the outermost peripheral portion of the combustion chamber 6, the fuel adhering to the peripheral surface of the cylinder 2 in the state of droplets is sprayed by the evaporated fuel that has evaporated. And the spray left behind in the region (stagnation region) where the main flow of the tumble flow (longitudinal vortex) formed in the combustion chamber 6 does not flow, and are relatively rich (fuel concentration is higher than in other regions). A dense) air-fuel mixture is formed. In addition, in FIG. 13B, the region other than the dark colored region is lightly colored, indicating that a relatively lean (low fuel concentration) air-fuel mixture is present.

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 arranged at a relatively late timing of 1/2 to 3/4 of the compression stroke ( That is, when fuel is injected from the injector 15 in a cone shape (with the injector 15 relatively close to the piston), the injected fuel is introduced into the cavity C before it is sufficiently expanded in the radial direction (FIG. 13 (FIG. 13). b) See). Moreover, since the post-stage injection is executed in a plurality of times, the penetration (penetration force) of the spray by the post-stage injection of each time is weakened. Therefore, as shown in FIG. 13 (c), most of the fuel once introduced into the cavity C does not leak to the outside of the cavity C and reaches the compression top dead center (until immediately before ignition). It will stay inside.

Here, in the process of the piston 5 approaching the top dead center, the squish area located radially outside the opening edge C1 of the cavity C is moved from the radial outside to the inside as shown in FIG. 13 (b). A flowing squish flow is formed. Therefore, at the time of the compression top dead center shown in FIG. 13C, the relatively rich air-fuel mixture originally existing in the outermost peripheral portion of the combustion chamber 6 (or the outermost outer peripheral portion of the squish area) is squished. It moves inward radially in the area and the air-fuel mixture becomes present over a relatively wide area in the squish area. As described above, in the present embodiment, in the combustion chamber 6 near the compression top dead center, a relatively rich air-fuel mixture based on the pre-stage injection is formed in the squish area (outside of the cavity C), and is based on the post-stage injection. A relatively rich air-fuel mixture is formed inside the cavity C.

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 degree 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 air-fuel ratio (G / F), which is the ratio of the amount of fuel injected from the injector 15 to 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, the air amount may be insufficient only by naturally aspirated engine. In such a case, a supercharger may be added.

FIG. 14 is a diagram schematically showing a situation in the combustion chamber 6 when the non-equilibrium plasma is discharged from the plasma generation plug 16. As shown in this figure, the non-equilibrium plasma discharged from the discharge electrode 33 of the plasma generation plug 16 is guided to the opening edge C1 of the cavity C having low insulation because it is not covered by the heat shield layer 19. Here, in the high load region A2, as described above, it is not between BTDC 10 ° CA and ATDC 10 ° CA near the compression top dead center (in the example of FIG. 12, between BTDC 5 ° CA and ATDC 5 ° CA). Since the equilibrium plasma is discharged, at the time of this discharge, a relatively rich air-fuel mixture is formed inside and outside the non-equilibrium plasma in the radial direction, that is, the squish area and the inside of the cavity C, respectively. On the other hand, on the discharge path connecting the discharge electrode 33 and the opening edge C1 of the cavity C, the mixture is located between the two air-fuel mixture regions (between the squish area and the cavity C), and the mixture exists here. Qi is pretty lean. Thus, since the environment of the discharge path of the non-equilibrium plasma is fairly lean, the non-equilibrium plasma, exerts an effect of generating ozone (O ₃₎ and active species such as OH.

As described above, the piston 5 starts descending at the same time that the active species is generated near the compression top dead center. When the piston 5 starts descending, a reverse squish flow that flows from the inside to the outside in the radial direction starts to be formed in the squish area. Therefore, most of the active species generated by the non-equilibrium plasma move to the squish area by riding the reverse squish flow. The transferred active species promotes ignition and combustion of the air-fuel mixture present in the squish area.

After the plasma discharge by the plasma generation plug 16, the air-fuel mixture reaches ignition with almost no time interval (for example, at about ATDC 5 to 10 ° CA), and compression ignition combustion is started. At this time, the presence of the above-mentioned active species promotes combustion of the air-fuel mixture in the squish area (in other words, the air-fuel mixture in an environment lower than the inside of the cavity C), so that the environment is lean with λ> 2. Nevertheless, the combustion rate of the air-fuel mixture is increased, and the combustion is completed in a relatively short 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 only in the latter half of the compression stroke and between the end of the combustion injection and the compression top dead center.

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, the non-equilibrium plasma is discharged from the plasma generation plug 16 from the time when 3/4 of the compression stroke (BTDC 45 ° CA) elapses to the compression top dead center. In this way, the non-equilibrium plasma discharged from immediately after the combustion injection to the compression top dead center acts on the region outside the air-fuel mixture in the cavity C (the region where almost no fuel exists), and ozone or Generate active species such as OH. At least a part of the generated active species is supplied to the outer peripheral portion of the air-fuel mixture in the cavity C to promote ignition and combustion of the outer peripheral portion. As a result, the combustion speed of the air-fuel mixture in the outer peripheral portion of the cavity C, which tends to be lower than that in the central portion of the cavity C, becomes faster, and the combustion period of the air-fuel mixture is shortened.

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 compressing, igniting and burning the air-fuel mixture in a lean environment of λ> 2 is executed 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, when the engine is operated in the high load region A2, the inside of the cavity C and the squish area radially outside the cavity C are mixed. The injector 15 is controlled so that the air is formed, and the opening of the cavity C from the discharge electrode 33 of the plasma generation plug 16 between the predetermined time (BTDC 10 ° CA) in the latter stage of the compression stroke and the ignition of the air-fuel mixture. The plasma generation plug 16 is controlled so that the non-equilibrium plasma is discharged toward the edge C1. According to such a configuration, in the premixed compression ignition type engine, there is an advantage that the combustion speed can be sufficiently increased while suppressing the combustion noise to an appropriate level.

That is, in the above embodiment, the ceiling surface 28 of the combustion chamber 6 is located between the BTDC 10 ° CA where the squish flow (the gas flow from the outside to the inside in the radial direction of the squish area) begins to weaken until the air-fuel mixture ignites. Since the non-equilibrium plasma is discharged from the plasma generation plug 16 located at the center toward the opening edge C1 of the cavity C, active species such as ozone and OH generated from the action of the non-equilibrium plasma are discharged after the compression top dead center. It can be moved to the squish area on the reverse squish flow (gas flow from the inside to the outside in the radial direction) generated as the piston 5 descends. Then, the transferred active species promotes the combustion of the air-fuel mixture in the squish area, so that the combustion speed of the air-fuel mixture can be increased and the combustion period can be shortened.

Here, the temperature of the squish area located on the outer peripheral portion of the combustion chamber 6 tends to be lower than that in the central portion (inside the cavity C) of the combustion chamber 6. Therefore, if the active species were not supplied to the squish area, the air-fuel mixture in the squish area would ignite with a considerable delay with respect to the air-fuel mixture in the cavity C, and the combustion rate after ignition would also be considerably slowed down. It ends up. On the other hand, in the above embodiment, since the active species is supplied to the squish area, the ignition delay of the air-fuel mixture in the squish area can be shortened, and the combustion rate of the air-fuel mixture (that is, the combustion rate in the latter half of combustion). Can be accelerated. Moreover, since the combustion speed of the air-fuel mixture in the cavity C that ignites first does not change in particular, 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. 15 is a diagram for explaining the above-mentioned action and effect. In FIG. 15, 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 is not generated), 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 with a short combustion period, excellent thermal efficiency, and no 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 rate drops significantly, and the combustion period becomes longer as a whole. That is, in the latter half of 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 way, 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 the thermal efficiency is excellent, the combustion noise becomes too loud and the commercial value cannot be maintained. On the other hand, in the above embodiment, since only the combustion of the air-fuel mixture in the squish area is basically promoted (high speed), the combustion speed can be increased as much as possible within the range where the combustion noise is not excessive. , 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. 15 indicates 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 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.

Further, in the above embodiment, a plurality of (four) discharge electrodes 33 provided in the plasma generation plug 16 connect the tip of each electrode 33 and the opening edge C1 of the cavity C with the piston 5 at the top dead point. Is formed so as to be substantially parallel to the extending direction of each electrode 33, so that the discharge path of the non-equilibrium plasma discharged at the above timing (timing including the compression top dead point) can be as much as possible. Can be shortened. As a result, non-equilibrium plasma can be efficiently generated, and a sufficient amount of active species can be supplied to the squish area.

Further, in the above embodiment, from the injector 15 arranged near the center of the ceiling surface 28 of the combustion chamber 6, the first half of the intake stroke and the time corresponding to 1/2 to 3/4 of the compression stroke (from BTDC 90 ° CA). Since the fuel is injected in a cone shape (radial) at (up to BTDC 45 ° CA), an air-fuel mixture can be properly formed in the squish area and the inside of the cavity C, respectively. Can be burned in a short period of time by utilizing the above-mentioned plasma discharge.

(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 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. Is not limited to this. That is, as long as the above-mentioned distribution of the air-fuel mixture can be obtained, the position of the injector 15 and the injection timing of the fuel from the injector 15 may be appropriately changed.

In the above embodiment, the plasma generation plug 16 is arranged at the center of the ceiling surface 28 of the combustion chamber 6, and the position slightly offset from the position of the plasma generation plug 16 (center of the ceiling surface 28) to one side in the cylinder row direction. The injector 15 was placed in the center of the ceiling surface 28 (see FIG. 3), but conversely, the injector 15 was placed in the center of the ceiling surface 28, and the plasma generation plug 16 was placed at a position offset from the center of the ceiling surface 28. You may. Alternatively, both the injector 15 and the plasma generation plug 16 may be arranged at positions offset from the center of the ceiling surface 28. In this case, the position of the plasma generation plug 16 is preferably offset from the center of the ceiling surface 28 (cylinder axis X) to the intake side. When the position of the plasma generation plug 16 is offset to the intake side, the unbalanced plasma discharged from the discharge electrode 33 of the plasma generation plug 16 can be further strengthened on the intake side. As a result, in the combustion chamber 6 where the temperature on the intake side tends to be lower than that on the exhaust side, the combustion speed of the air-fuel mixture is increased in a well-balanced manner (the combustion speed becomes the same on the intake side and the exhaust side), and the combustion period Can be expected to have the effect of shortening.

On the other hand, if the amount of offset of the plasma generation plug 16 to the intake side is large, the amount of active species supplied to the intake side increases too much, and the combustion speed is reversed between the intake side and the exhaust side (the intake side is faster). There is a risk. When such a reversal phenomenon of the combustion speed is a concern, it is effective to make the upper and lower gaps of the squish area smaller on the exhaust side than on the intake side, as shown in FIG. 16, for example. That is, the separation distance between the intake side inclined surface 24 and the ceiling surface 28 facing the intake side inclined surface 24 is defined as the first gap dimension G1, and the separation distance between the exhaust side inclined surface 25 and the ceiling surface 28 facing the exhaust side inclined surface 25 is defined as the second gap dimension G2. Then, the crown surface S of the piston 5 may be formed so that the relationship G2 <G1 is established. As a result, the strength of the reverse squish flow generated by the lowering of the piston 5 becomes stronger on the exhaust side, so that the supply amount of the active species tends to decrease on the exhaust side because the radial distance from the plasma generation plug 16 is large. In the squish area of the above, the supply amount of the active species can be corrected in the increasing direction, and the reversal phenomenon of the combustion speed as described above can be avoided while the plasma generation plug 16 is largely offset to the intake side.

Even when the plasma generation plug 16 is offset in the cylinder row direction (direction orthogonal to the intake / exhaust direction), it is possible to correct the imbalance in combustion speed due to the shape of the piston 5. For example, when the plasma generation plug 16 is arranged at a position offset to one side in the cylinder row direction from the center (cylinder axis X) of the ceiling surface 28 of the combustion chamber 6, a pair of peaks 26 of the piston 5 (FIGS. 3 and 3). 4) and the ceiling surface 28 may be made smaller on the other side than on one side in the cylinder row direction. Alternatively, the same effect can be obtained by increasing the area of the pair of peaks 26 on the other side rather than on one side in the cylinder row direction.

In the above embodiment, almost the entire surface of the combustion chamber 6 excluding the opening edge C1 of the cavity C in the crown surface S of the piston 5 is covered with the heat shield layer 19, so that the heat shield layer 19 is not covered (exposed). ) The opening edge C1 of the cavity C is made to function as a cathode at the time of plasma discharge, but if the discharge of non-equilibrium plasma is performed between the electrode 33 of the plasma generation plug 16 and the radial inner end of the squish area, Well, as long as it is, various modifications are possible. For example, the ring-shaped region corresponding to the radial inner end of the squish area in the ceiling surface 28 (lower surface of the cylinder head 4) of the combustion chamber 6 is set as a region not covered by the heat shield layer 19. The region (a part of the ceiling surface 28) may be made to function as a cathode.

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. 17 (a). A plasma generation plug 116 having a shallow dish-shaped discharge electrode 133 as shown in (b) may be used.

More specifically, the plasma generation plug 116 according to the above modification has a tubular plug body 131, a center electrode 132 inserted inside the plug body 131, and a shallow port 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 face of the plug body 131 and the discharge electrode 133. The discharge electrode 133 is formed in a circular shape centered on the tip end portion 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 (the surface on the cylinder head 4 side) of the discharge electrode 133.

In the above embodiment, as the injector 15, an externally open type injector in which a ring-shaped nozzle port 44 is formed at the time of valve opening is used (see FIG. 6), but instead, the injector 15 has a circumferential shape at the tip of the injector. A multi-injection type having a plurality of aligned 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 compressed and ignited while being mixed with air 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 54 Throttle valve 100 PCM (Control device)
A2 high load range

Claims (5)

An injector that injects fuel into the combustion chamber and
A piston having a crown surface that defines the bottom surface of the combustion chamber,
A plasma generation plug having an electrode near the center of the ceiling of the combustion chamber and discharging non-equilibrium plasma from the electrode.
It is provided with 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.
The distance in the piston sliding direction from the radial outer region of the crown surface of the piston to the ceiling surface of the combustion chamber is the distance in the piston sliding direction from the radial inner region of the crown surface to the ceiling surface of the combustion chamber. A squish area is formed on the outer peripheral portion of the combustion chamber to generate a squish flow that flows from the outside in the radial direction to the inside as the piston approaches the top dead point.
The piston has a cavity in the center of the crown surface and has a cavity.
The squish area is formed between a region of the crown surface of the piston that is radially outer of the cavity and the ceiling surface of the combustion chamber.
The control device controls the injector so that a part of the air-fuel mixture injected from the injector is formed in the squish area, and the squish flow begins to weaken in a compression stroke. The plasma generation plug is controlled so that the non-equilibrium plasma is discharged from the electrode of the plasma generation plug toward the opening edge of the cavity between a predetermined time in the latter period and the ignition of the air-fuel mixture .
The electrode of the plasma generation plug is formed so as to extend radially from a position corresponding to the central axis of the plasma generation plug, and the tip of the electrode and the opening edge of the cavity are in a state where the piston is at top dead center. A premixed compression ignition type engine characterized in that the line connecting the electrodes is formed so as to be substantially parallel to the extending direction of the electrodes. In the premixed compression ignition engine according to claim 1,
The control device is a premixed compression ignition engine characterized in that the non-equilibrium plasma is discharged to the plasma generation plug after BTDC 10 ° CA advanced by 10 ° from the compression top dead center. In the premixed compression ignition engine according to claim 1 or 2.
The control device executes the control of forming a part of the air-fuel mixture in the squish area and generating the non-equilibrium plasma when the engine is operated in a high load region where the engine load is equal to or higher than a predetermined load. A premixed compression ignition engine that is characterized by its ability to do so. In the premixed compression ignition engine according to claim 3,
The injector radially injects fuel from the vicinity of the center of the ceiling of the combustion chamber toward the cavity.
The control device is a premixed compression ignition engine characterized in that fuel is injected into the injectors in the intake stroke and the latter half of the compression stroke, respectively. In the premixed compression ignition engine according to claim 3 or 4.
Further equipped with a throttle valve for adjusting the flow rate of air introduced into the combustion chamber,
The control device controls the throttle valve and the injector so that the excess air ratio in the combustion chamber becomes larger than 2 when operating in the high load region. The premixed compression ignition engine. ..

Images