JP2019218881A - Premixed compression ignition type engine - Google Patents

Abstract

To provide a premixed compression ignition type engine which has a metal discharge electrode part facing a combustion chamber on the ceiling surface of the combustion chamber at its position near a fuel injection port of a fuel injection valve, for improving its thermal efficiency by reducing unburned fuel loss and cooling loss in an operation region where a load is equal to or higher than predetermined one.SOLUTION: In the operation region where the load is equal to or higher than the predetermined one, fuel injection is performed separately in an intake stroke and in a compression stroke. In the compression stroke, the fuel injection is performed over at a plurality of times in a specific period for the compression stroke (from when a quater of the compression stroke passes to when three-quater thereof passes).SELECTED DRAWING: Figure 10

Description

  The present invention belongs to the technical field of a homogeneous charge compression ignition engine.

  BACKGROUND ART Conventionally, there has been known a premixed compression ignition type engine in which a mixture of fuel and air is self-ignited (HCCI combustion) in a combustion chamber (for example, see Patent Document 1). Further, in Patent Document 1, by providing a heat shield layer (heat insulating layer) on the wall surface of the combustion chamber of the engine, the release of combustion heat from the wall surface is suppressed, and the cooling loss is reduced. To improve.

JP-A-2005-081527

  Meanwhile, in a homogeneous charge compression ignition engine, fuel may be injected into the combustion chamber during the intake stroke in order to mix the fuel and air well. However, when fuel is injected into the combustion chamber during the intake stroke, the injected fuel flows into the intake flow (here, a tumble flow) flowing into the combustion chamber from the intake port, and easily adheres to the cylinder wall surface. Become. Part of the fuel adhering to the cylinder wall is lifted up by the piston ring during the compression stroke.However, in an operation region where the amount of injected fuel is large, such as a high-load operation region, a large amount of fuel is accumulated on the cylinder wall. The remaining fuel remains between the peripheral side surface of the piston (the part closer to the crown than the piston ring), and the remaining fuel does not burn, and the unburned loss increases accordingly.

  Therefore, in an operating region of a predetermined load or more where such unburned loss becomes large, in order to reduce the unburned loss, it is conceivable to separately perform the fuel injection into the intake stroke and the compression stroke. Then, in order to satisfactorily burn the fuel injected in the compression stroke and reduce the unburned fuel, the fuel must be injected after the time when 3/4 of the compression stroke has elapsed (45 ° before the compression top dead center in crank angle). Injecting is preferred.

  Here, a discharge plug may be provided on the ceiling wall of the combustion chamber such that the metal discharge electrode portion faces the combustion chamber from the ceiling surface of the combustion chamber. This discharge plug may generate non-equilibrium plasma (also called low-temperature plasma) or generate thermal equilibrium plasma (also called high-temperature plasma) at the discharge electrode portion by discharging at the discharge electrode portion. You may. When there is air or a fuel-lean mixture (essentially air) with a considerably large air-fuel ratio around the discharge electrode, when the non-equilibrium plasma is generated by the discharge at the discharge electrode, the air Thus, substances (for example, ozone, OH, etc.) that promote self-ignition and combustion of the air-fuel mixture are generated. On the other hand, when a non-equilibrium plasma is generated by the discharge at the discharge electrode when a fuel or a relatively fuel-rich mixture exists around the discharge electrode, the fuel automatically ignites the mixture. And substances that suppress combustion (eg, formaldehyde, nitrogen dioxide, etc.). As described above, by generating the non-equilibrium plasma in accordance with the air-fuel ratio around the discharge electrode portion, the combustion of the air-fuel mixture can be controlled. In addition, the thermal equilibrium plasma can be used as an ignition source to assist the self-ignition of the air-fuel mixture, and generates the thermal equilibrium plasma in an operating region where the self-ignition of the air-fuel mixture becomes unstable, such as a low-load operation region. Thereby, the self-ignition of the air-fuel mixture can be assisted.

  When the discharge electrode portion of the discharge plug as described above is provided near the fuel injection port of the fuel injection valve, if fuel is injected after a time that has passed 3/4 of the compression stroke, the mixture will self-ignite. At a point in time (near the compression top dead center), there is a relatively fuel-rich mixture immediately adjacent to the discharge electrode, and the discharge electrode is made of a metal having a high heat transfer coefficient. However, it is particularly easy to escape to the outside of the combustion chamber via the discharge electrode portion, and as a result, the cooling loss increases.

  The present invention has been made in view of the above, and it is an object of the present invention to provide a premixed compression ignition type engine in which a fuel injection valve is disposed near a fuel injection valve of a fuel injection valve on a ceiling surface of the combustion chamber. In the case of having a metal discharge electrode portion facing the above, it is intended to improve the thermal efficiency of the homogeneous charge compression ignition type engine by reducing the unburned loss and the cooling loss in an operation region of a predetermined load or more. is there.

  In order to achieve the above object, the present invention is directed to a premixed compression ignition engine that includes an engine body having a cylinder in which a combustion chamber is formed and that self-ignites a mixture of fuel and air in the combustion chamber. As a fuel injection valve, the fuel injection port faces the combustion chamber from substantially the center of the ceiling surface of the combustion chamber, and injects fuel from the fuel injection port toward the crown of the piston. A metal discharge electrode portion facing the combustion chamber from the vicinity of the fuel injection port, and fuel injection valve control means for controlling the operation of the fuel injection valve; When the operating state is in the operating region of a predetermined load or more, the fuel injection valve is caused to perform fuel injection separately into an intake stroke and a compression stroke, and in the compression stroke, during a specific period of the compression stroke, Multiple Divided is configured to carry out fuel injection in said specific period is a period from the time after the elapse of 1/4 of the compression stroke up to the time that has elapsed 3/4, has a structure that.

  According to the above configuration, in the operation region where the load is equal to or more than the predetermined load, the fuel injection is performed separately in the intake stroke and the compression stroke, so that the fuel injected in the intake stroke and flown into the intake flow (tumble flow) and adheres to the cylinder wall surface And the amount of fuel remaining between the cylinder wall surface and the peripheral side surface of the piston and not combusted is reduced, and as a result, unburned loss can be reduced.

  In addition, since the fuel is injected by the time when 3/4 of the compression stroke has elapsed in the compression stroke, at the time when the air-fuel mixture self-ignites, around the fuel injection port of the fuel injection valve and the discharge electrode portion, There is no longer a relatively fuel-rich mixture.

  Further, since the fuel is injected after the time when 1/4 of the compression stroke has elapsed in the compression stroke, the pressure in the combustion chamber increases after the time, so that it becomes difficult for the fuel to fly far. Further, during the specific period, the ascending speed of the piston increases, so that it is difficult for the fuel to fly far away due to the ascending flow generated above the piston due to the ascent of the piston.

  In addition, since the fuel is dividedly injected during the specific period, it is difficult for the fuel to fly farther. The fuel injected at the beginning of the specified period may reach the cylinder wall surface, but even if it reaches the cylinder wall surface, the fuel is sprayed in the vicinity of the cylinder wall surface as a fuel spray due to split injection. And does not adhere to the cylinder wall in a large amount. As a result, even during fuel injection during the compression stroke, the amount of fuel adhering to the cylinder wall surface can be reduced, and unburned loss can be reduced. Then, the fuel spray floating near the cylinder wall surface rises by the upward flow, reaches the ceiling wall surface of the combustion chamber, and then heads toward the center of the combustion chamber. Thus, at the time when the air-fuel mixture self-ignites, there is no relatively fuel-rich air-fuel mixture near the cylinder wall.

  Therefore, since there is no relatively fuel-rich mixture near the periphery of the discharge electrode portion, the emission of combustion heat from the discharge electrode portion can be suppressed, and the cooling loss can be reduced. Furthermore, since there is no relatively rich fuel-fuel mixture near the cylinder wall surface where combustion is difficult, unburned loss can be further reduced, and emission of combustion heat from the cylinder wall surface can be suppressed. it can.

  Therefore, in the operating range of a predetermined load or more, the unburned loss and the cooling loss can be reduced, and the thermal efficiency of the homogeneous charge compression ignition engine can be improved.

  In the homogeneous charge compression ignition engine, it is preferable that a heat shield layer is provided on a ceiling surface of the combustion chamber.

  Thus, emission of combustion heat from the ceiling surface of the combustion chamber can be favorably suppressed. Even when the heat shield layer is provided on the ceiling surface, the heat shield layer cannot be provided on the portion of the ceiling surface where the discharge electrode portion faces the combustion chamber, and when the heat treatment layer has passed 3/4 of the compression stroke, When fuel is subsequently injected, heat radiation from the discharge electrode is inevitable. However, as described above, fuel is injected during a specific period of the compression stroke, so that the fuel is relatively rich around the discharge electrode. The mixture no longer exists, and the release of combustion heat from the discharge electrode can be suppressed.

  In the homogeneous charge compression ignition engine, it is preferable that a geometric compression ratio of the engine body is 16 or more and 30 or less.

  In the case of such a high compression ratio, the fuel injected during a specific period of the compression stroke becomes more difficult to fly, and hardly adheres to the crown surface of the piston. Therefore, the cooling loss can be further reduced.

  In the case of the high compression ratio as described above, it is preferable that the fuel pressure of the fuel injected from the fuel injection port of the fuel injection valve is set to 15 MPa or more and 60 MPa or less.

  As a result, in the operating range of the predetermined load or more, the fuel can be appropriately injected into the high-pressure combustion chamber in the compression stroke while preventing the fuel from flying far.

  In the above-described homogeneous charge compression ignition engine, it is preferable that the fuel injection valve is configured to inject fuel from the fuel injection port so as to spread in a substantially conical shape toward a crown surface of the piston.

  Thus, the penetration of the fuel spray injected from the fuel injection valve can be reduced, and the fuel can be prevented from adhering to the cylinder wall surface as much as possible.

  As described above, according to the homogeneous charge compression ignition engine of the present invention, the fuel injection port faces the combustion chamber from substantially the center of the ceiling surface of the combustion chamber of the engine body, and the fuel is injected from the fuel injection port to the crown of the piston. A fuel injection valve for injecting the fuel into the combustion chamber, a metal discharge electrode section facing the combustion chamber from the vicinity of the fuel injection port on the ceiling surface of the combustion chamber, and fuel injection valve control means. The valve control means causes the fuel injection valve to perform the fuel injection separately into an intake stroke and a compression stroke when the operation state of the engine body is in an operation range of a predetermined load or more, and during the compression stroke. Is that the fuel injection is performed in a plurality of times during a specific period of the compression stroke (from the time when 1/4 of the compression stroke has elapsed to the time when 3/4 has passed), so that the predetermined load is increased. More luck In the region, it is possible to reduce the unburned fuel loss and cooling loss and improve the thermal efficiency of the HCCI engine.

FIG. 1 is a diagram illustrating a schematic configuration of a premixed compression ignition engine according to an embodiment of the present invention. It is sectional drawing which expands and shows the principal part of the said engine. It is sectional drawing which shows the periphery of the fuel injection opening in the fuel injection valve of an external opening type | formula, (a) shows the state in which the fuel injection opening is closed by the external opening valve, (b) shows fuel injection. This shows a state where the mouth is opened and fuel is being injected. It is sectional drawing which shows the periphery of the injection hole in the fuel injection valve of a multi injection hole type | mold, (a) shows the state by which the injection hole is closed by the core valve, (b) shows the state in which the injection hole was opened and fuel was supplied. Shows the state of injection. It is sectional drawing which expands and shows the heat shielding layer provided in the ceiling surface of the combustion chamber of the said engine, and the crown surface of a piston. FIG. 2 is a block diagram illustrating a control system of the engine. It is a figure which shows the kind of plasma produced | generated by the discharge in a discharge electrode part according to the pulse width and the peak value of the pulse voltage applied to the discharge electrode part of the said discharge plug. 5 is a graph illustrating an example of a pulse voltage waveform when generating non-equilibrium plasma. FIG. 3 is a diagram illustrating an example of a map of a fuel injection mode of a fuel injection valve according to an operation state of an engine body. 5 is a time chart showing the timing of fuel injection in an operation region (operation region A in a fuel injection mode map) in which the load is equal to or more than a first predetermined load. FIG. 7 is a diagram showing a fuel distribution in a combustion chamber at a time when a fuel-air mixture self-ignites in an operation region of a first predetermined load or more. It is a figure which shows a mode of the fuel spray when collectively injecting fuel by the fuel injection valve of an external valve opening type. Examine the relationship between the fuel injection start timing (in the case of split injection, the first injection start timing) and the CO concentration and the THC concentration in the exhaust gas when the fuel is injected all at once or in the divided injection during the compression stroke. 9 is a graph showing the results. 5 is a time chart showing the timing of fuel injection in an operation region on a lower load side than a first predetermined load (operation region B in a fuel injection map). FIG. 4 is a diagram showing a fuel distribution in a combustion chamber at a time when an air-fuel mixture self-ignites in an operation region on a lower load side than a first predetermined load.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a homogeneous charge compression ignition type engine 1 (hereinafter, referred to as engine 1) according to an embodiment of the present invention. In the present embodiment, the engine 1 includes an engine main body 1a having four cylinders 2 (cylinders) each having a combustion chamber 6 formed therein. It is a self-igniting engine.

  The engine 1 is an in-line four-cylinder engine in which four cylinders 2 of an engine body 1a are arranged in series in a direction perpendicular to the plane of FIG. The engine 1 is mounted on a vehicle and used as a drive source for the vehicle. In the present embodiment, the engine 1 is driven by receiving a supply of fuel containing at least gasoline. The fuel may contain, for example, bioethanol in addition to gasoline.

  The engine body 1a has a cylinder block 3 provided with four cylinders 2 and a cylinder head 4 arranged on the cylinder block 3. In each cylinder 2, a piston 5 that partitions a combustion chamber 6 between the cylinder 2 and the cylinder head 4 is reciprocally movable (up and down). The piston 5 of each cylinder 2 is connected via a connecting rod 8 to a crankshaft (not shown) extending in the cylinder row direction.

  The combustion chamber 6 is of a so-called pent roof type, and the ceiling surface of the combustion chamber 6 formed by the lower surface of the cylinder head 4 has a triangular roof shape having two inclined surfaces on the intake side and the exhaust side.

  A cavity 5b is formed in the crown surface 5a of the piston 5 by recessing the center of the crown surface 5a on the opposite side (lower side) to the cylinder head 4. A plurality of (three in this embodiment) piston rings 5c (see FIG. 2) are fitted near the crown surface 5a on the side peripheral surface of the piston 5.

  In the present embodiment, the geometric compression ratio of the engine main body 1a, that is, the volume of the combustion chamber 6 when the piston 5 is at the top dead center, and the volume of the combustion chamber 6 when the piston 5 is at the bottom dead center. The volume ratio is set to 16 or more and 30 or less (more preferably, 20 or more and 25 or less).

  The cylinder head 4 has an intake port 9 for introducing air supplied from an intake passage 20 into the cylinder 2 (combustion chamber 6), and an exhaust gas generated in the cylinder 2 to an exhaust passage 30. Exhaust port 10 is formed. In the present embodiment, two intake ports 9 and two exhaust ports 10 are formed for each cylinder 2. In the present embodiment, a tumble flow T (see FIG. 2) of the air drawn into the combustion chamber 6 from the intake port 9 is generated in the combustion chamber 6 due to the shape of the intake port 9.

  The cylinder head 4 is provided with an intake valve 11 that opens and closes an opening of each intake port 9 on the combustion chamber 6 side, and an exhaust valve 12 that opens and closes an opening of each exhaust port 10 on the combustion chamber 6 side. ing.

  The intake valve 11 opens and closes at a predetermined timing by an intake valve operating mechanism. The intake valve operating mechanism is a variable valve operating mechanism that changes valve timing and / or valve lift. In the present embodiment, the variable valve mechanism has an intake electric S-VT (Sequential-Valve Timing) 17. The intake electric S-VT 17 is configured to continuously change the rotation phase of the intake camshaft within a predetermined angle range. Thereby, the valve opening timing and the valve closing timing of the intake valve 11 change continuously. The intake valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

  The exhaust valve 12 opens and closes at a predetermined timing by an exhaust valve mechanism. The exhaust valve operating mechanism is also a variable valve operating mechanism that changes valve timing and / or valve lift. In the present embodiment, the variable valve mechanism has an exhaust electric S-VT 18. The exhaust electric S-VT 18 is configured to continuously change the rotation phase of the exhaust camshaft within a predetermined angle range. Thereby, the valve opening timing and the valve closing timing of the exhaust valve 12 change continuously. The exhaust valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

  Further, as shown in FIG. 2, the cylinder head 4 is provided with a fuel injection valve 14 for injecting fuel toward the crown 5 a of the piston 5 for each cylinder 2. The fuel injection valve 14 is attached substantially at the center of the ceiling wall of the combustion chamber 6 of each cylinder 2. The fuel injection valve 14 has a fuel injection port (a fuel injection port 61 or an injection port 66 described later) for injecting fuel at a tip end thereof, and the fuel injection port is used to burn from substantially the center of the ceiling surface of the combustion chamber 6. I'm facing room 6. The fuel pressure of the fuel injected from the fuel injection port of the fuel injection valve 14 is set to 15 MPa or more and 60 MPa or less.

  The fuel injection valve 14 may be an external valve type or a multi-injection type. When the fuel injection valve 14 is of an external valve type, as shown in FIG. 3, the fuel injection valve 14 has an external valve 62 that opens and closes a fuel injection port 61. The fuel injection port 61 is formed in a tapered shape whose diameter increases toward the tip end. The distal end side of the outer valve 62 protrudes outside the fuel injection port 61, and the protruding portion contacts (seizes) the fuel injection port 61 so as to close the fuel injection port 61. When the outer valve 62 is lifted from the state in which the fuel injection port 61 is closed (see FIG. 3A) to the outside of the fuel injection port 61 (toward the combustion chamber 6), the fuel injection port 61 is opened. The fuel is injected from the opened fuel injection port 61 so as to spread in a substantially conical shape (specifically, a hollow cone shape) toward the crown surface 5a of the piston 5 (see FIG. 3B). The taper angle of this cone is, for example, 90 ° to 100 ° (the taper angle of the inner hollow portion is about 70 °).

  On the other hand, when the fuel injection valve 14 is of a multi-injection type, the fuel injection valve 14 is, as shown in FIG. (For example, 10 to 20) injection holes 66 (fuel injection holes) formed inside the nozzle hole forming member 65 and having a diameter smaller than the plurality of injection holes 66 at the bottom of the injection hole forming member 65. A core valve 67 that abuts (sits) on the outer side in the direction to close the plurality of injection holes 66 at the same time. The plurality of injection holes 66 extend toward the tip of the fuel injection valve 14 so as to radially expand from the central axis of the fuel injection valve 14. When the core valve 67 is lifted from the state in which the plurality of injection holes 66 are closed (see FIG. 4A) to the side opposite to the combustion chamber 6, all of the plurality of injection holes 66 are opened, and these opened. Fuel is injected from the plurality of injection holes 66 toward the crown surface 5a of the piston 5 so as to spread in a substantially conical shape over the plurality of injection holes (see FIG. 4B). The taper angle of this cone is also, for example, 90 ° to 100 ° (the taper angle of the inner hollow portion is about 70 °).

  The cylinder head 4 is provided with a discharge plug 13 attached to the ceiling wall of the combustion chamber 6 for each cylinder 2. In the present embodiment, the discharge plug 13 is provided in a portion between the two exhaust ports 10 near the fuel injection valve 14 on the ceiling wall of the combustion chamber 6. It may be provided in a portion between the two intake ports 9 in the vicinity of 14. The discharge plug 13 has a metal discharge electrode portion 13a. The discharge electrode portion 13a faces the combustion chamber 6 from between the openings of the two exhaust ports 10 near the fuel injection port on the ceiling surface of the combustion chamber 6 (near the center of the ceiling surface).

  The discharge electrode portion 13a includes a metal center electrode 13b and a ground electrode 13c that face each other in the center axis direction of the discharge plug 13. The center electrode 13b is connected to a voltage application circuit 91 (see FIG. 6) for applying a predetermined voltage for generating plasma between the center electrode 13b and the ground electrode 13c (that is, the discharge electrode portion 13a). When the predetermined voltage is applied between the center electrode 13b and the ground electrode 13c by the application circuit 91, a discharge occurs between the center electrode 13b and the ground electrode 13c, and plasma is applied to the discharge electrode portion 13a by the energy of the discharge. (In the present embodiment, non-equilibrium plasma) is generated.

  An intake passage 20 is connected to the intake port 9. An air cleaner 21 for filtering intake air is disposed at an upstream end of the intake passage 20. The intake air filtered by the air cleaner 21 is supplied to the combustion of each cylinder 2 through the intake passage 20 and the intake port 9. It is supplied to the chamber 6.

  An air flow sensor SN2 that detects the amount of intake air sucked into the intake passage 20 is provided near the downstream side of the air cleaner 21 in the intake passage 20. In addition, a surge tank 25 is disposed near the downstream end of the intake passage 20. The intake passage 20 downstream of the surge tank 25 is an independent passage branched for each cylinder 2, and the downstream end of each independent passage is connected to the intake port 9 of each cylinder 2.

  Further, a throttle valve 22 for opening and closing the intake passage 20 is provided between the air flow sensor SN2 and the surge tank 25 in the intake passage 20. In the present embodiment, during operation of the engine 1, the throttle valve 22 is basically maintained at a full opening or an opening close thereto, and is closed only under limited operating conditions such as when the engine 1 is stopped. To shut off the intake passage 20.

  An exhaust passage 30 for discharging exhaust gas from the combustion chamber 6 of each cylinder 2 is connected to the exhaust port 10. The upstream portion of the exhaust passage 30 is constituted by an exhaust manifold that has an independent passage branched for each cylinder 2 and connected to the exhaust port 10 and a collecting portion where the independent passages gather.

  An exhaust gas purification device 31 that purifies exhaust gas is provided in the exhaust gas passage 30 (portion downstream of the exhaust manifold). In the present embodiment, the exhaust gas purification device 31 includes a three-way catalyst.

  The engine 1 includes an EGR passage 41 for returning a part of the exhaust gas from the exhaust passage 30 to the intake passage 20 as EGR gas. The EGR passage 41 is connected to a portion of the exhaust passage 30 upstream of the exhaust gas purification device 31 and downstream of the exhaust manifold, and a portion of the surge tank 25 in the intake passage 20 so as to communicate with the two portions. It is connected to the.

  The EGR passage 41 is provided with an EGR valve 42 for opening and closing the EGR passage 41 and an EGR cooler 43 for cooling EGR gas passing through the EGR passage 41. The EGR gas is returned to the intake passage 20 after being cooled by the EGR cooler 43.

  In the present embodiment, the engine 1 does not include a supercharger, but may include a supercharger.

  A heat shield layer 7 is provided on the ceiling surface of the combustion chamber 6 and the crown surface 5 a of the piston 5. The heat shield layer 7 is a low heat conductive layer having a lower thermal conductivity than the base material of the cylinder head 4 and the piston 5 (both are aluminum alloys in the present embodiment). In the present embodiment, as shown in FIG. 5, the heat shield layer 7 includes a binder material 7a such as a silicone resin and a number of hollow particles 7b dispersed therein. As the hollow particles 7b, for example, a glass balloon, a shirasu balloon, a silica balloon, or the like is employed. The heat shield layer 7 suppresses the heat of the combustion gas in the combustion chamber 6 from being released through the ceiling surface of the combustion chamber 6 and the crown surface 5 a of the piston 5. It is preferable that the thickness of the heat shield layer 7 is 75 μm or more and 100 μm or less.

  Further, it is preferable that the heat shield layer 7 has a smaller specific heat of volume than the base materials of the cylinder head 4 and the piston 5. That is, it is preferable that the heat capacity of the heat shield layer 7 is reduced and the temperature of the ceiling surface of the combustion chamber 6 and the temperature of the crown surface 5 a of the piston 5 change following the fluctuation of the gas temperature in the combustion chamber 6. By doing so, the difference between the temperature of the combustion gas and the temperature of the ceiling surface of the combustion chamber 6 and the temperature of the crown surface 5a of the piston 5 is reduced, and as a result, the heat of the combustion gas is reduced to the ceiling surface of the combustion chamber 6 and the piston 5 Through the crown surface 5a.

  The heat shielding layer 7 applies a heat shielding material containing a binder material 7a and hollow particles 7b to the ceiling surface of the combustion chamber 6 and the crown surface 5a of the piston 5, and then hardens the binder material 7a by a heat treatment. Can be formed.

  The heat shield layer 7 is not always necessary and may not be provided. Further, of the crown surface 5 a of the piston 5 and the ceiling surface of the combustion chamber 6, the heat shield layer 7 may be provided only on the ceiling surface of the combustion chamber 6. Because the temperature of the crown 5a of the piston 5 is relatively high, the amount of combustion heat released from the crown 5a of the piston 5 is smaller than the amount of combustion heat released from the ceiling of the combustion chamber 6.

  As shown in FIG. 6, the engine 1 is controlled by an ECU (Engine Control Unit) 100. The ECU 100 is a controller based on a known microcomputer. The ECU 100 includes a CPU 101, a memory 102, an input / output bus 103, and the like. The CPU 101 is a central processing unit that executes a computer program (including a basic control program such as an OS and an application program activated on the OS to realize a specific function). The memory 102 includes a RAM and a ROM. The ROM stores various computer programs (particularly, control programs for controlling the engine 1), data including a map described later used when the computer programs are executed, and the like. The RAM is a memory provided with a processing area used when the CPU 101 performs a series of processes. The input / output bus 103 inputs and outputs electric signals to and from the ECU 100.

  Various sensors such as a crank angle sensor SN1, an air flow sensor SN2, and an accelerator opening sensor SN3 are electrically connected to the ECU 100. The crank angle sensor SN1 is provided in the cylinder block 3 and detects the rotation angle of the crank shaft. The accelerator opening sensor SN3 is attached to the accelerator pedal mechanism of the vehicle, and detects an accelerator opening corresponding to the operation amount of the accelerator pedal. These sensors SN1 to SN3 output detection signals to the ECU 100.

  The ECU 100 determines the operating state of the engine 1 based on the input signals from the sensors SN1 to SN3 and the like, and further includes a voltage application circuit 91, a fuel injection valve 14, an intake electric S-VT17, an exhaust electric S-VT18, and a throttle valve. 22, a control signal is output to each device of the engine 1, such as the EGR valve 42, to control each device. The ECU 100 constitutes fuel injection valve control means for controlling the operation of the fuel injection valve 14.

  In the present embodiment, in the combustion cycle of the engine body 1a, non-equilibrium plasma (also called low-temperature plasma) is generated by discharge at the discharge electrode portion 13a of the discharge plug 13 to control combustion in the combustion chamber 6. Like that. The non-equilibrium plasma refers to plasma in which electrons in the combustion chamber 6 and ions and molecules of the gas in the combustion chamber 6 are not in a thermal equilibrium state without increasing the gas temperature in the combustion chamber 6. .

  The non-equilibrium plasma can be generated by setting the pulse width and the peak value of the pulse voltage applied to the discharge electrode portion 13a (between the center electrode 13b and the ground electrode 13c) of the discharge plug 13 to appropriate values. FIG. 7 shows the types of plasma generated by the discharge at the discharge electrode unit 13a according to the pulse width and peak value of the pulse voltage. The horizontal axis in FIG. 7 is the pulse width of the pulse voltage, which is shown on a logarithmic scale. On the other hand, the vertical axis in FIG. 7 is the peak value of the pulse voltage, which is shown on a logarithmic scale. As shown in FIG. 7, when the pulse width is shortened (specifically, when the pulse width is 0.01 μsec or more and less than 1 μsec), it is found that non-equilibrium plasma is generated. This is because with a pulse voltage having a short pulse width, only electrons react and ions and molecules hardly react. On the other hand, it is understood that when the pulse width is increased (when the pulse width is set to 1 μsec or more), thermal equilibrium plasma (also called high-temperature plasma) is generated. Non-equilibrium plasma is not an ignition source for igniting the mixture, while thermal equilibrium plasma is an ignition source for igniting the mixture.

  In the present embodiment, as shown in FIG. 8, the predetermined voltage applied to the discharge electrode portion 13a of the discharge plug 13 by the voltage application circuit 91 is a pulse voltage having a peak value of 10 kV and a pulse width of 0.1 μsec. Yes, the pulse voltage generates a non-equilibrium plasma. When generating the non-equilibrium plasma, the ECU 100 operates the voltage application circuit 91 to cause the voltage application circuit 91 to repeatedly apply the pulse voltage to the discharge electrode section 13a at a frequency of 100 kHz. In FIG. 8, the pulse voltage is a triangular wave, but may be a square wave.

  Note that the peak value of the pulse voltage applied to the discharge electrode portion 13a when generating the non-equilibrium plasma does not need to be fixed to 10 kV, and is based on, for example, the pressure in the combustion chamber 6 (detected by the pressure sensor). , May be changed in the range of 1 kV to 30 kV. Specifically, the higher the pressure in the combustion chamber 6, the higher the peak value of the pulse voltage may be set.

When non-equilibrium plasma is generated in the discharge electrode section 13a, a substance generated in the combustion chamber 6 differs depending on an air-fuel ratio around the discharge electrode section 13a. That is, when air or a fuel-lean mixture (basically air) having a first predetermined air-fuel ratio or more exists around the discharge electrode portion 13a, non-equilibrium plasma is generated in the discharge electrode portion 13a. Then, the non-equilibrium plasma is radiated to the air or the fuel-lean mixture to cause self-ignition and combustion of the air-fuel mixture in the combustion chamber 6 such as ozone (O ₃ ) and OH. An active species is generated that is a promoting substance. On the other hand, in the vicinity of the discharge electrode portion 13a, the fuel or the second predetermined air that is smaller than the first predetermined air-fuel ratio is added to the fuel-rich mixture that is smaller than the first predetermined air-fuel ratio and smaller than the second predetermined air-fuel ratio. If a non-equilibrium plasma is generated in the discharge electrode portion 13a when a fuel-rich mixture having a fuel ratio less than the fuel ratio is present, the fuel or the fuel-rich mixture is irradiated with the non-equilibrium plasma, and the Then, a suppression species such as formaldehyde (CH ₂ O) or nitrogen dioxide (NO ₂ ), which is a substance that suppresses the self-ignition and combustion of the air-fuel mixture in the combustion chamber 6, is generated.

  Therefore, basically, when non-equilibrium plasma is generated in the discharge electrode portion 13a while fuel is being injected from the fuel injection valve 14 located near the discharge electrode portion 13a, the suppression species is generated. When the non-equilibrium plasma is generated when the fuel is not being injected and the intake is being performed in the intake stroke, active species are generated. By generating active species and / or suppressing species in the combustion chamber 6 in this way, the combustion is controlled by speeding up or delaying the combustion of the air-fuel mixture.

  In the present embodiment, compression ignition combustion (CI combustion) is performed in the entire operation region of the engine body 1a. Specifically, fuel is injected into the combustion chamber 6 from the fuel injection valve 14 before the compression top dead center during the operation of the engine body 1a, and a temperature rise is caused by compressing a mixture of the fuel and air. Then, the mixture is self-ignited near the compression top dead center.

  In the operation region B described later, the discharge plug 13 may assist the self-ignition of the air-fuel mixture. In this case, a voltage (peak voltage: 1 kV to 30 kV) having a pulse width of 1 μsec or more is applied to the discharge electrode portion 13 a of the discharge plug 13 to generate a thermal equilibrium plasma, and the self-ignition of the air-fuel mixture is assisted by the thermal equilibrium plasma. .

  FIG. 9 is an example of a map of the fuel injection mode of the fuel injection valve 14 according to the operation state of the engine body 1a. This map is stored in the memory 102 of the ECU 100. In this map, an operation region A having a first predetermined load L1 or more and an operation region B having a load lower than the first predetermined load L1 are set according to the rotation speed and the load of the engine body 1a. The operating region B is divided into three operating regions B1, B2, and B3, as described in detail later.

  The line indicated by RL in FIG. 9 is a load load line, and here, the fuel injection mode is not set in a region where the load is smaller than the load load line RL.

  The first predetermined load L1 changes according to the rotation speed of the engine body 1a. When the rotation speed is equal to or lower than the first predetermined rotation speed N1, the higher the rotation speed is, the higher the rotation speed is, and the rotation speed is higher than the first predetermined rotation speed N1. At a high value and equal to or lower than the second predetermined rotation speed N2 (a rotation speed higher than the first predetermined rotation speed N1), the rotation speed becomes a constant value. Further, the first predetermined load L1 becomes a load on the load load line RL when the rotation speed is higher than the second predetermined rotation speed N2.

  In the operation region A, as shown in FIG. 10, the ECU 100 causes the fuel injection valve 14 to perform the fuel injection separately into the intake stroke and the compression stroke, and during the compression stroke, during a specific period of the compression stroke. The fuel injection is performed a plurality of times (in this embodiment, three times). Note that the crank angle on the horizontal axis in FIG. 10 is such that the compression top dead center is 0 ° and the value before the compression top dead center is a negative value.

  The specific period is a period from the time when 1/4 of the compression stroke has passed to the time when 3/4 has passed. It is desirable that the fuel injection be on the retard side in the specific period in relation to the timing of fully closing the intake valve 11. However, if the rotation speed of the engine body 1a increases (for example, exceeds 4000 rpm), it becomes difficult to perform divided injection in a narrow period, and therefore, injection may be performed anywhere during the specific period. It is preferable that the fully closed timing of the intake valve 11 is substantially the same as the timing after a quarter of the compression stroke has passed, or it is more advanced than the timing.

  In the operation region A where the load is equal to or more than the first predetermined load L1, the amount of fuel to be injected is large. However, if the fuel is injected only in the intake stroke, the amount of fuel that is injected in the intake stroke and flows in the intake flow (here, the tumble flow T) and adheres to the cylinder wall surface of each cylinder 2 increases. Part of the fuel adhering to the cylinder wall surface is lifted up by the piston ring 5c during the compression stroke. However, since a large amount of fuel adheres to the cylinder wall surface, a large amount of fuel is transferred to the cylinder wall surface and the peripheral side surface of the piston 5 (piston side). (The portion closer to the crown surface 5a than the ring 5c), the remaining fuel does not burn, and the unburned loss increases accordingly.

  In the present embodiment, in the operating region A, the fuel injection is performed separately in the intake stroke and the compression stroke, so that the fuel is injected in the intake stroke and flows into the intake flow (tumble flow T) and adheres to the cylinder wall surface of each cylinder 2. The amount of fuel used is reduced. Thereby, the unburned loss is reduced.

  In addition, since the fuel is injected by the time when 3/4 of the compression stroke has elapsed in the compression stroke, a relatively rich air-fuel mixture is stored in the area 51 shown in FIG. A relatively fuel-rich mixture does not exist around the fuel injection port of the fuel injection valve 14 and the discharge electrode portion 13a of the discharge plug 13. A relatively fuel-lean mixture, which is a mixture of fuel and air injected during the intake stroke, exists around the fuel injection port of the fuel injection valve 14 and the discharge electrode portion 13a.

  Further, since the fuel is injected after the time when one-fourth of the compression stroke has elapsed in the compression stroke, the pressure in the combustion chamber 6 increases after the time, so that it becomes difficult for the fuel to fly far. Further, during the above-described specific period, the rising speed of the piston is increased, so that it is difficult for the fuel to fly far away even by the upward flow generated above the piston 5 by the rising of the piston 5.

  In addition, since the fuel is dividedly injected during the specific period, it is difficult for the fuel to fly farther. The fuel injected at the beginning of the specific period may reach the cylinder wall surface, but even if it reaches the cylinder wall surface, the fuel is sprayed in the vicinity of the cylinder wall surface as fuel spray by being dividedly injected. It is in a state and does not adhere to the cylinder wall surface in a large amount. As a result, even during fuel injection during the compression stroke, the amount of fuel adhering to the cylinder wall surface can be reduced, and unburned loss can be reduced. Then, the fuel spray floating near the cylinder wall surface rises by the upward flow, reaches the ceiling wall surface of the combustion chamber 6, and then heads toward the center of the combustion chamber 6. Thus, at the time when the air-fuel mixture self-ignites, there is no relatively fuel-rich air-fuel mixture near the cylinder wall. In the vicinity of the cylinder wall surface, a relatively fuel-lean mixture exists, as in the vicinity of the fuel injection port of the fuel injection valve 14 and the discharge electrode portion 13a.

  As described above, in the operation region A, at the time when the air-fuel mixture self-ignites, the portion of the combustion chamber 6 except for the vicinity of the fuel injection port of the fuel injection valve 14 and the discharge electrode portion 13a and the vicinity of the vicinity of the cylinder wall surface is relatively formed. There will be a fuel-rich mixture.

  In the operation region A, near the compression top dead center, the air-fuel mixture self-ignites at the center of the relatively fuel-rich air-fuel mixture, and the combustion spreads to the surroundings. Here, if the fuel is injected after the lapse of ／ of the compression stroke, a relatively rich fuel-air mixture immediately flows between the fuel injection valve 14 and the discharge electrode portion 13a at the time when the air-fuel mixture self-ignites. Since the discharge electrode 13a is located close to the discharge electrode 13a and is made of a metal having a high heat transfer coefficient, the combustion heat of the air-fuel mixture can easily escape to the outside of the combustion chamber 6 through the discharge electrode 13a.

  However, in the present embodiment, at the time when the air-fuel mixture self-ignites, there is no relatively fuel-rich air-fuel mixture around the fuel injection valve 14 and the discharge electrode 13a, so the combustion heat from the discharge electrode 13a Can be suppressed and the cooling loss can be reduced.

  In addition, since there is no relatively fuel-rich mixture in the vicinity of the cylinder wall surface where combustion is difficult, unburned loss can be further reduced, and emission of combustion heat from the cylinder wall surface can be suppressed. it can.

  Furthermore, in the present embodiment, since the heat shield layer 7 is provided on the ceiling surface of the combustion chamber 6 and the crown surface 5a of the piston 5, the cooling loss can be further reduced.

  As the fuel injection timing in the compression stroke, for example, the first injection starts at 90 ° before the compression top dead center at the crank angle and ends at 86 ° before the compression top dead center. The second injection starts 70 ° before top dead center and ends 63 ° before top dead center. The third injection starts at 49 ° before compression top dead center and ends at 45 ° before compression top dead center. The fuel injection timing in the compression stroke shown in FIG. 10 is adjusted to these injection timings. In addition, the lift amount of the outer opening valve 62 or the core valve 67 at the time of the first injection is 1/5 of the maximum lift amount, and the second lift amount is 1/3 of the maximum lift amount. The same lift amount for the first time is 1/5 of the maximum lift amount.

  As described above, the injection period at the time of the second injection is longer than the injection period at the time of the other injection, and the lift amount at the time of the second injection is larger than the lift amount at the other times. That is, the injection amount at the time of the second injection is larger than the injection amount at the time of the other injections. This is because the pressure in the combustion chamber 6 is higher during the second injection than during the first injection, so that even if more fuel is injected, the fuel will not fly far. Because it can be. On the other hand, in the third injection, although the pressure in the combustion chamber 6 becomes higher, the possibility that the first and second injections and the floating fuel spray are pushed in the advancing direction becomes higher. The injection amount is substantially the same.

  Here, the reason why it is difficult for the fuel to fly far when the fuel is dividedly injected will be described by comparing the divided injection of FIG. 3B and the collective injection of FIG. FIG. 3B shows a state of fuel spraying when fuel is divided into three divided injections, and FIG. 12 shows a state in which the same amount of fuel as the total injection amount at the time of divided injection of FIG. The state of fuel spray is shown.

  As shown in FIG. 12, in the case of the batch injection, the fuel (fuel spray) injected earlier is pushed by the fuel injected later, and is likely to fly far. In addition, at the tip of the previously injected fuel spray, a vortex that winds up the fuel spray is generated along with the progress of the fuel spray, and a part of the fuel spray is wound up by the vortex, but the vortex, It functions to push the fuel injected later in the direction of travel, which also makes it easier for the fuel spray to fly away.

  On the other hand, as shown in FIG. 3B, in the case of the split injection, since the injection amount of each injection is small, the fuel spray is likely to be in a floating state immediately after the injection, which is similar to the case of the batch injection. Swirl is unlikely to occur. Further, the fuel spray injected earlier is less likely to be pushed in the traveling direction by the fuel spray injected immediately thereafter. Therefore, in the case of split injection, it becomes difficult for the fuel to fly far.

  FIG. 13 shows the fuel injection start timing (in the case of split injection, the first injection start timing) when the fuel is injected collectively and in the split injection in the compression stroke, and the CO concentration and THC concentration in the exhaust gas. The result of examining the relationship is shown. THC concentration is the concentration of total hydrocarbons, that is, the concentration of methane and non-methane hydrocarbons.

  In FIG. 13, the horizontal axis represents the fuel injection start timing and the crank angle with the compression top dead center set to 0 °. Here, the crank angle before the compression top dead center is a positive value. The vertical axis is the CO concentration or the THC concentration in the exhaust gas.

  In the engine examined for the above relationship, the fully closed timing of the intake valve is 135 ° before the compression top dead center. In the batch injection, the lift amount of the external valve is set to the maximum lift amount, and the injection period is set to 4 ° in crank angle. In the split injection, the total injection amount is set to be the same as the injection amount of the batch injection, and the injection is performed three times as much as possible so that each injection is performed within the specific period (injection start timing is delayed. If three injections are not possible within the specified period, two injections are performed), and the total injection amount is set to be the same as the injection amount of the batch injection. In the case of split injection, the first injection start timing was delayed until injection could not be performed twice within the above specified period.

  From FIG. 13, it can be seen that, in the case of the batch injection, if the injection is performed during the above-described specific period, the CO concentration and the THC concentration increase (that is, the unburned fuel remains much). On the other hand, even in the case of the batch injection, if the fuel is injected after the time when 3/4 of the compression stroke has elapsed, the fuel is satisfactorily burned (oxidized) and the unburned fuel is reduced. However, if the fuel is injected after the elapse of 3/4 of the compression stroke, the combustion heat of the air-fuel mixture easily escapes to the outside of the combustion chamber 6 particularly through the discharge electrode portion 13a as described above. Therefore, the fuel is dividedly injected during the specific period.

  From FIG. 13, it can be seen that when the fuel is dividedly injected in the specific period, the CO concentration and the THC concentration are considerably reduced (that is, the unburned fuel remains less). In particular, by injecting the fuel after the fully closed timing of the intake valve (135 ° before the compression top dead center), the CO concentration and the THC concentration are further reduced. This is because the pressure in the combustion chamber increases due to the full closing of the intake valve, making it difficult for fuel to fly.

  Therefore, even if the fuel is injected during the specific period, the fuel injected during the specific period is easily burned by performing the split injection, and the unburned fuel of the fuel injected during the specific period can be reduced. .

  In the case of the split injection, the ratio of the air-fuel mixture having an excess air ratio of less than 5 (combustible air-fuel mixture) to the air-fuel mixture in the entire combustion chamber and contacting the cylinder wall surface was examined. The more the starting time was delayed, the lower the proportion. Thus, by injecting as late as possible during the specific period, the release of combustion heat from the cylinder wall surface can be suppressed.

  In the operating region B, the ECU 100 separates from the ceiling surface of the combustion chamber 6 and the crown surface 5a of the piston 5 when the air-fuel mixture self-ignites, so that the air-fuel mixture layer 54 (see FIG. 15) is formed. The fuel injection valve 14 is caused to perform the fuel injection in the middle stage when the compression stroke is divided into three equal stages of the initial stage, the middle stage, and the latter period (see FIG. 14). In the operation region B, fuel injection is not performed in the intake stroke.

  In the present embodiment, in the operation region B, the fuel injection valve 14 is caused to perform the fuel injection in a plurality of times in the middle stage of the compression stroke. The number of injections in the middle stage of the compression stroke by the fuel injection valve is set for each of the three operation regions B1, B2, and B3 in the operation region B.

  The operation region B1 is a region where the rotation speed of the engine main body 1a is equal to or lower than the first predetermined rotation speed N1 and the load of the engine main body 1a is equal to or higher than the second predetermined load L2 and lower than the first predetermined load L1. In the operation region B1, the number of injections in the middle stage of the compression stroke by the fuel injection valve 14 is set to three times. Note that the second predetermined load L2 increases as the rotation speed increases.

  The operation region B2 is a region in which the rotation speed of the engine main body 1a is equal to or less than the first predetermined rotation speed N1, and the load of the engine main body 1a is equal to or more than the load of the load load line RL and less than the second predetermined load L2. In the operation region B2, the number of injections in the middle stage of the compression stroke by the fuel injection valve 14 is set to two.

  The operation region B3 is such that the rotation speed of the engine main body 1a is higher than the first predetermined rotation speed N1 and equal to or lower than the second predetermined rotation speed N2, and the load of the engine main body 1a is equal to or more than the load on the load line RL and the first predetermined load. This is an area that is less than L1. In the operation region B3, the number of injections in the middle stage of the compression stroke by the fuel injection valve 14 is set to three times.

  Therefore, the number of injections in the middle stage of the compression stroke by the fuel injection valve 14 is set to be larger when the load on the engine body 1a is high than when the load is low. In addition, the number of injections in the middle stage of the compression stroke by the fuel injection valve 14 is set to be larger when the rotation speed of the engine body 1a is low than when the rotation speed is high.

  In the operation region B, fuel is injected in the middle stage of the compression stroke. As a result, as shown in FIG. 15, at the time when the air-fuel mixture self-ignites, a relatively fuel-rich air-fuel mixture layer 54 is separated from the ceiling surface of the combustion chamber 6 (particularly, the discharge electrode portion 13a of the discharge plug 13). Is formed, and air (or air and EGR gas) is provided between the ceiling surface of the combustion chamber 6 and the air-fuel mixture layer 54, including around the fuel injection port of the fuel injection valve 14 and the discharge electrode portion 13a. Is formed. Further, the ascending flow due to the rise of the piston 5 and the split injection cause the air-fuel mixture layer 54 to separate from the crown surface 5a of the piston 5 as well. That is, the gas layer 55 is also formed between the crown surface 5a of the piston 5 and the mixture layer 54.

  In the operating region B, the split injection does not always have to be performed. Also in this case, the fuel injection amount is small and the high compression ratio makes it difficult for the fuel injected in the middle stage of the compression stroke to fly, so that the air-fuel mixture layer 54 is formed on the ceiling surface of the combustion chamber 6 and the piston 5. It can be separated from the crown surface 5a.

  Here, in the operating region B, if the number of injections when the load on the engine body 1a is high is the same as the number of injections when the load is low, each injection amount when the load is high becomes less than when the load is low. It is larger than the injection amount of each time. When the injection amount in each time increases, the fuel injected in each time tends to fly far. However, in the present embodiment, by increasing the number of injections when the load is high (the number of injections in the operation region B1) compared to the number of injections when the load is low (the number of injections in the operation region B2), the load is increased. Even when the load is low, the fuel injected each time can be made less likely to fly. Therefore, in the operating region B, the cooling loss can be reduced regardless of the level of the load on the engine body 1a.

  In addition, if the number of injections when the engine body 1a is low in rotation speed is the same as the number of injections when the rotation speed is high, each fuel injected when the rotation speed is low becomes high when the rotation speed is high. As compared with the fuel injected each time, the fuel is more likely to fly toward the crown surface 5a of the piston 5 without being affected by the upward flow due to the rise of the piston 5. However, in the present embodiment, the number of injections when the rotation speed of the engine body 1a is low (the number of injections in the operation region B1) is made larger than the number of injections when the rotation speed is high (the number of injections in the operation region B3). In this way, the injection amount at each time when the rotation speed is low is made smaller than the injection amount at each time when the rotation speed is high, and even if the upward flow due to the rise of the piston 5 is weak, the same as when the upward flow is strong In addition, the fuel injected each time can be made harder to fly. Therefore, in the operating region B, the cooling loss can be reduced regardless of the rotational speed of the engine body 1a.

  Therefore, in the present embodiment, when the operating state of the engine body 1a is in an operating region (operating region A) where the load is equal to or more than a predetermined load, the fuel injection is performed separately in the intake stroke and the compression stroke, and in the compression stroke, During the specific period of the compression stroke (from the time when 1/4 of the compression stroke has elapsed to the time when 3/4 has passed), the fuel injection is performed in a plurality of times. The fuel efficiency can be improved by reducing the fuel loss and the cooling loss.

  The present invention is not limited to the above embodiment, and can be substituted without departing from the scope of the claims.

  The above embodiments are merely examples, and the scope of the present invention should not be interpreted in a limited manner. The scope of the present invention is defined by the claims, and all modifications and changes that fall within the equivalent scope of the claims are within the scope of the present invention.

  INDUSTRIAL APPLICABILITY The present invention is useful for a premixed compression ignition engine that includes an engine body having a cylinder in which a combustion chamber is formed and in which a mixture of fuel and air is self-ignited in the combustion chamber.

DESCRIPTION OF SYMBOLS 1 Premixed compression ignition type engine 1a Engine main body 2 Cylinder 5 Piston 5a Crown surface 6 Combustion chamber 13 Discharge plug 13a Discharge electrode part 14 Fuel injection valve 100 ECU (fuel injection valve control means)

Claims (5)

A premixed compression ignition engine that includes an engine body having a cylinder in which a combustion chamber is formed, and self-ignites a mixture of fuel and air in the combustion chamber,
A fuel injection valve in which a fuel injection port faces the combustion chamber from substantially the center of the ceiling surface of the combustion chamber, and injects fuel from the fuel injection port toward the crown of the piston;
A metal discharge electrode portion facing the combustion chamber from near the fuel injection port on the ceiling surface of the combustion chamber,
Fuel injection valve control means for controlling the operation of the fuel injection valve,
The fuel injection valve control means, when the operating state of the engine body is in an operating region of a predetermined load or more, causes the fuel injection valve to perform fuel injection separately into an intake stroke and a compression stroke, In the compression stroke, during a specific period of the compression stroke, the fuel injection is configured to be performed a plurality of times,
The premixed compression ignition engine according to claim 1, wherein the specific period is a period from a time when 1/4 of the compression stroke has elapsed to a time when 3/4 has passed. The homogeneous charge compression ignition engine according to claim 1,
A premixed compression ignition engine, wherein a heat shield layer is provided on a ceiling surface of the combustion chamber. The premixed compression ignition engine according to claim 1 or 2,
A premixed compression ignition engine, wherein a geometric compression ratio of the engine body is 16 or more and 30 or less. The premixed compression ignition engine according to claim 3,
A premixed compression ignition engine, wherein a fuel pressure of fuel injected from a fuel injection port of the fuel injection valve is set to 15 MPa or more and 60 MPa or less. A premixed compression ignition engine according to any one of claims 1 to 4,
A premixed compression ignition engine, wherein the fuel injection valve is configured to inject fuel from the fuel injection port so as to spread substantially conically toward the crown surface of the piston.