JP2019218883A - Premixed compression ignition type engine - Google Patents

Abstract

To provide a premixed compression ignition type engine capable of stabilizing combustion at the late stage of the combustion while delaying a timing for starting the self-ignition of air-fuel mixture from a compression top dead center, by utilizing non-equilibrium plasma.SOLUTION: In an intake stroke, at least one discharge electrode part 13a of plasma generation means is used for executing first discharge so that air or fuel-lean air-fuel mixture having an air-fuel ratio equal to or higher than first predetermined one is irradiated with non-equilibrium plasma. In a compression stroke, a discharge electrode part 13a of the plasma generation means, which is the same as or different from the discharge electrode part 13a used for executing the first discharge, is used for executing second discharge so that fuel or fuel-rich air-fuel mixture having an air-fuel ratio lower than second predetermined one smaller than the first predetermined one is irradiated with non-equilibrium plasma.SELECTED DRAWING: Figure 7

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). There is also known a high compression ratio engine having a geometric compression ratio of 15 or more and 40 or less (for example, see Patent Document 2).

  Further, for example, Patent Literature 3 discloses an engine in which non-equilibrium plasma (also called low-temperature plasma) is generated in the discharge electrode unit by discharging at the discharge electrode unit by applying a voltage to the discharge electrode unit. ing. In this engine, a non-equilibrium plasma state is formed between a spark plug (discharge plug) in which a discharge occurs at a discharge electrode portion (between the center electrode and the ground electrode) constituted by a center electrode and a ground electrode, and a center electrode and a ground electrode. A short-pulse circuit capable of generating a short-pulse electric field; and the short-pulse circuit generates a short-pulse electric field between the center electrode and the ground electrode, thereby generating a non-equilibrium plasma in the discharge electrode portion.

JP-A-2005-081527 JP 2013-194712 A JP 2014-141919 A

  By the way, the present inventors have made intensive studies and found that when air or a fuel-lean mixture (basically air) having a considerably large air-fuel ratio exists around the discharge electrode portion of the discharge plug, When the non-equilibrium plasma is generated by the discharge in the part, the air is irradiated with the non-equilibrium plasma, and from the air, active species (eg, ozone, OH, etc.) which are substances that promote self-ignition and combustion of the air-fuel mixture ) Was generated. On the other hand, when a non-equilibrium plasma is generated by the discharge at the discharge electrode portion when a fuel or a relatively fuel-rich gas mixture exists around the discharge electrode portion, the fuel or the relatively fuel-rich mixed gas is generated. It has been found that irradiation of the gas with the non-equilibrium plasma generates a suppressing species (for example, formaldehyde, nitrogen dioxide, etc.) which is a substance that suppresses the self-ignition and combustion of the air-fuel mixture from the fuel. As described above, it has been found that the combustion of the air-fuel mixture can be controlled by generating the non-equilibrium plasma according to the air-fuel ratio around the discharge electrode portion.

  Here, in the premixed compression ignition type engine with a high compression ratio, the self-ignition of the air-fuel mixture starts from the center of the combustion chamber near the compression top dead center in the compression stroke, and the combustion spreads, thereby increasing the pressure in the combustion chamber. Increases rapidly, and the maximum pressure becomes extremely high. As a result, the combustion noise tends to increase and the reliability of the engine tends to decrease. Further, the temperature in the combustion chamber becomes extremely high, and the generation amount of RawNOx tends to increase.

  Therefore, it is conceivable that the start timing of self-ignition is delayed to be after the compression top dead center by the above-described suppression species. By delaying the start time of the self-ignition after the compression top dead center as described above, it is possible to suppress the sudden increase in the pressure in the combustion chamber and to suppress the maximum pressure and the temperature in the combustion chamber from becoming too high. it can.

  However, if the start of self-ignition is delayed after the compression top dead center, heat will be generated slowly in the outer peripheral area of the combustion chamber, thus lowering the thermal efficiency of the engine and causing combustion by lowering the piston. There is a problem that the combustion in the latter half of the combustion becomes unstable due to the pressure drop and the temperature drop in the room.

  The present invention has been made in view of such a point, and the purpose thereof is to use a non-equilibrium plasma to delay the start time of the self-ignition of the air-fuel mixture after the compression top dead center, An object of the present invention is to provide a homogeneous charge compression ignition engine capable of stabilizing combustion in the latter stage of combustion.

  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. The engine body has a geometric compression ratio of 16 or more, has a fuel injection valve for injecting fuel into the combustion chamber, and one or more discharge electrode portions, and discharges at the discharge electrode portions. A plasma generating means for generating a non-equilibrium plasma at the discharge electrode portion, and a control means for controlling the operation of the plasma generating means. The control means performs the combustion during the intake stroke during operation of the engine body. The above-mentioned non-reacted air-fuel mixture, which is formed in the combustion chamber by air injected into the combustion chamber by the fuel injection valve or fuel injected by the fuel injection valve and has a first predetermined air-fuel ratio or higher. A first discharge is performed at at least one discharge electrode portion of the plasma generating means so as to irradiate a balanced plasma, and the fuel injected into the combustion chamber by the fuel injector during the compression stroke or the fuel Irradiating the non-equilibrium plasma with a fuel-rich mixture formed in the combustion chamber and having a smaller than the second predetermined air-fuel ratio and less than the second predetermined air-fuel ratio. The configuration is such that the second discharge is performed at the same or different discharge electrode unit as the discharge electrode unit that performed the first discharge.

  More specifically, the control means performs the first discharge in the intake stroke to generate an active species that is a substance that promotes the combustion of the air-fuel mixture in the combustion chamber. By executing the second discharge, a suppression species that is a substance that suppresses combustion of the air-fuel mixture in the combustion chamber is generated.

  According to the above configuration, by performing the first discharge in the intake stroke, the non-equilibrium plasma is irradiated to the air or the fuel-lean mixture having the first predetermined air-fuel ratio or more, whereby active species are generated from the air. . In addition, by performing the second discharge in the compression stroke, the non-equilibrium plasma is irradiated to the fuel injected into the combustion chamber or the fuel-rich mixture less than the second predetermined air-fuel ratio, so that the suppressed species is removed from the fuel. Generated. The fuel injected in the compression stroke forms a relatively fuel-rich mixture layer in the center of the combustion chamber near the compression top dead center. The suppression species generated from the fuel during the compression stroke will basically be present in a fuel-rich mixture at the center of the combustion chamber. In the vicinity of the compression top dead center, around the fuel-rich mixture layer, air sucked into the combustion chamber during the intake stroke, or a mixture mixture layer containing the air and leaner than the mixture layer. Exists. The active species generated from the air during the intake stroke will be present in the fuel-lean mixture.

  Here, if the suppressing species does not exist in the fuel-rich gas-fuel mixture layer, since the compression ratio is high, the self-ignition of the gas mixture is started near the compression top dead center in the compression stroke. Further, the self-ignition of the air-fuel mixture is started from a central portion where the temperature becomes highest in the combustion chamber and a fuel-rich air-fuel mixture layer is formed. On the other hand, if the suppression species is present in the fuel-rich mixture layer, the suppression species can delay the start of the self-ignition of the mixture after the compression top dead center.

  Then, after the self-ignition of the air-fuel mixture has started after the compression top dead center, the combustion spreads to around the fuel-rich air-fuel mixture layer, where active species are present. Is promoted. As a result, even if the start time of the self-ignition of the air-fuel mixture is delayed after the compression top dead center, the combustibility in the later stage of combustion is improved, and the combustion in the latter stage of combustion becomes stable. In addition, compared with the case where no active species are generated, the combustion can be accelerated to end the combustion earlier (the combustion period can be shortened). Will be able to Therefore, it is possible to stabilize the combustion in the latter half of the combustion while delaying the start time of the self-ignition of the air-fuel mixture after the compression top dead center.

  In one embodiment of the homogeneous charge compression ignition engine, a tumble flow of the sucked air is generated in the combustion chamber, and the plasma generating means is provided near a center of a ceiling surface of the combustion chamber. And a discharge electrode portion that faces the combustion chamber from above and performs both the first discharge and the second discharge.

  Accordingly, when a tumble flow of intake air is generated in the combustion chamber, the first discharge at the discharge electrode portion facing the combustion chamber from near the center of the ceiling surface of the combustion chamber during the intake stroke causes the gas to enter the combustion chamber. Non-equilibrium plasma can be applied to the air immediately after inhalation. In the compression stroke, non-equilibrium plasma is irradiated to the fuel or the fuel-rich mixture injected into the combustion chamber by the second discharge at the same discharge electrode as the discharge electrode that performed the first discharge. can do.

  In another embodiment of the homogeneous charge compression ignition engine, a swirl flow of the sucked air is generated in the combustion chamber, and the plasma generation means includes an outer periphery of a ceiling surface of the combustion chamber. A discharge electrode section facing the combustion chamber from the section and performing the first discharge; and a discharge electrode section facing the combustion chamber from near the center of the ceiling surface of the combustion chamber and performing the second discharge. Have.

  With this, when a swirl flow of the intake air is generated in the combustion chamber, the first discharge at the discharge electrode portion facing the combustion chamber from the outer peripheral portion of the ceiling surface of the combustion chamber during the intake stroke causes the gas to enter the combustion chamber. Non-equilibrium plasma can be applied to the inhaled air. Further, in the compression stroke, the non-equilibrium plasma is applied to the fuel or the fuel-rich mixture injected into the combustion chamber by the second discharge at the discharge electrode portion facing the combustion chamber from near the center of the ceiling surface of the combustion chamber. Can be irradiated.

  As described above, according to the premixed compression ignition engine of the present invention, the self-ignition of the air-fuel mixture can be delayed after compression top dead center by the suppression species generated from the fuel, and the air can be cooled from the air. The generated active species can stabilize the combustion in the latter half of the combustion even if the start time of the self-ignition of the air-fuel mixture is delayed after the compression top dead center.

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. FIG. 2 is a schematic plan view of a certain cylinder of the engine. 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. 5 is a time chart showing execution timings of a first discharge and a second discharge and timings of fuel injection. FIG. 4 is a diagram showing a fuel distribution in a combustion chamber near a compression top dead center. It is a graph which shows the PV diagram of the homogeneous charge compression ignition type engine which concerns on this embodiment, and the homogeneous charge compression ignition type engine which self-ignites near compression top dead center. It is a graph which shows the change of the heat release rate (dQ / d (theta)) in an Example and a comparative example. It is a graph which shows the change of the pressure rise rate (dP / d (theta)) in the said Example and the said comparative example. It is a figure equivalent to FIG. 2 which shows a modification. FIG. 4 is a diagram corresponding to FIG. 3, showing the modification. FIG. 11 is a diagram corresponding to FIG. 3, showing still another modification.

  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. The geometric compression ratio of the engine body 1a is preferably set to 16 or more and 30 or less, and more preferably set to 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 has an intake valve 11 that opens and closes an opening 9a of each intake port 9 on the combustion chamber 6 side (see FIG. 3), and an opening 10a of each exhaust port 10 on the combustion chamber 6 side (see FIG. 3). ) Are provided.

  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 FIGS. 2 and 3, 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 at the tip thereof for injecting fuel. The fuel injection port faces the combustion chamber 6 from substantially the center of the ceiling surface of the combustion chamber 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.

  In the present embodiment, the fuel injection valve 14 is an external valve-type fuel injection valve having an external valve that opens and closes a fuel injection port. The fuel injection port is formed in a tapered shape whose diameter increases toward the tip. Then, the fuel injection valve 14 injects the fuel in a substantially conical shape (specifically, a hollow cone shape) from the fuel injection port toward the crown surface of the piston 5. The taper angle of this cone is, for example, 90 ° to 100 ° (the taper angle of the inner hollow portion is about 70 °). The penetration of the fuel injected from the fuel injection valve 14 is set to a length that does not reach the outer peripheral portion of the combustion chamber 6. In addition, the fuel injection valve 14 is not limited to an external valve-type fuel injection valve, and is a multi-injection type fuel injection valve having a plurality of (for example, 10 to 20) injection holes (fuel injection ports) at a tip portion. It may be. Also in this case, fuel is injected from the plurality of injection holes toward the crown surface 5a of the piston 5 so as to spread in a substantially conical shape across the plurality of injection holes.

  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. 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 10a of the two exhaust ports 10 on the combustion chamber 6 side in the vicinity of the fuel injection port on the ceiling surface of the combustion chamber 6 (near the center of the ceiling surface). In.

  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. 4) 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 ends of the independent passages are connected to the two intake ports 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.

  As shown in FIG. 4, 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 discharge electrode section 13a of the discharge plug 13 and the voltage application circuit 91 constitute a plasma generating means for generating non-equilibrium plasma in the discharge electrode section 13a by the discharge at the discharge electrode section 13a. Further, the ECU 100 constitutes control means for controlling the operation of the plasma generation means.

  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. 5 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. 5 is the pulse width of the pulse voltage, which is shown on a logarithmic scale. On the other hand, the vertical axis in FIG. 5 is the peak value of the pulse voltage, which is shown on a logarithmic scale. As shown in FIG. 5, 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. 6, 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, a non-equilibrium plasma is generated by this pulse voltage. 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. 6, 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. In this embodiment, as will be described later, the air-fuel mixture is self-ignited after the compression top dead center.

  More specifically, as shown in FIG. 7, the ECU 100 causes the fuel injection valve 14 to perform fuel injection near the intake bottom dead center in the intake stroke and in the latter half of the compression stroke. In particular, in the compression stroke, it is preferable to perform the fuel injection in a plurality of times (three times in the present embodiment).

  By such fuel injection, as shown in FIG. 8, near the compression top dead center, a relatively fuel-rich mixture layer 51 (fuel and air injected in the compression stroke) Around the air-fuel mixture layer 51, a fuel-air mixture layer 52 (a fuel-air mixture air-fuel layer injected in the intake stroke) than the air-fuel mixture layer 51 is formed. It is formed.

  Further, the ECU 100 causes the discharge electrode portion 13a of the discharge plug 13 to perform the first discharge so as to irradiate the air immediately after being sucked into the combustion chamber 6 with non-equilibrium plasma in the intake stroke. That is, as shown in FIG. 7, before the fuel injection in the intake stroke (when the fuel injection valve 14 is not operated), the voltage application circuit 91 is operated to apply the predetermined voltage to the discharge electrode portion 13a of the discharge plug 13. By applying the (pulse voltage), non-equilibrium plasma is generated in the discharge electrode portion 13a. During the execution of the first discharge, immediately after air flows into the combustion chamber 6 from the opening 9a of each intake port 9 on the combustion chamber 6 side, the air passes through the vicinity of the discharge electrode portion 13a. On the other hand, non-equilibrium plasma is irradiated. Thereby, the active species are generated from the air.

  The active species generated from air as described above basically exist in the gas mixture layer 52. Particularly, when the rotation speed of the engine body 1a increases, the generated active species easily diffuses. Therefore, the first discharge is performed in the middle and late stages of the intake stroke. Middle and late stages when equally divided) are preferred.

  Further, the ECU 100 performs the fuel injection in the subsequent compression stroke (specifically, in the latter half of the compression stroke, in this embodiment, during the period from the start of the second split injection to the end of the third split injection). The discharge electrode portion 13a (in the present embodiment, the same discharge electrode as the discharge electrode portion that caused the first discharge, so that the fuel injected into the combustion chamber 6 by the valve 14 is irradiated with non-equilibrium plasma. ), The second discharge is performed. That is, as shown in FIG. 7, during the period from the start of the second split injection to the end of the third split injection in the compression stroke, the voltage application circuit 91 is continuously operated to discharge the discharge electrode of the discharge plug 13. By applying the predetermined voltage (the pulse voltage) to the portion 13a, non-equilibrium plasma is generated in the discharge electrode portion 13a. During the execution of the second discharge, the fuel injected by the fuel injection valve 14 exists around the discharge electrode portion 13a. Even during the non-injection of fuel between the second split injection and the third split injection, the fuel injection basically exists around the discharge electrode portion 13a because the interval is short and the fuel penetration is short. Non-equilibrium plasma is irradiated to the fuel existing around the discharge electrode portion 13a, and the above-described suppression species is generated from the fuel.

  Note that the fuel-rich mixture layer 51 may be located around the discharge electrode 13a. If the air-fuel ratio of the mixture layer 51 is lower than the second predetermined air-fuel ratio, the fuel-air mixture layer 51 is lower than the second predetermined air-fuel ratio. The non-equilibrium plasma can also be irradiated to the fuel-rich mixture to generate the above-described suppressed species. In this case, the voltage application circuit 91 may be continuously operated from the start of the second split injection in the compression stroke to the start of the self-ignition of the air-fuel mixture. Further, the start of the operation of the voltage application circuit 91 may be the start of the first split injection.

  The suppressive species generated from the fuel as described above basically exists in the gas mixture layer 51. Therefore, near the compression top dead center, the suppressed species exists in the center of the combustion chamber (air-fuel mixture layer 51), and the active species exists around it (the air-fuel mixture layer 52).

  Here, if the suppressing species does not exist in the gas mixture layer 51, the self-ignition of the gas mixture is started near the compression top dead center in the compression stroke because the compression ratio is high. Further, the self-ignition of the air-fuel mixture is started from a central portion where the temperature is highest in the combustion chamber 6 and a fuel-rich air-fuel mixture layer 51 is formed.

  However, in the present embodiment, since the suppression species is present in the mixture gas layer 51, the start time of the self-ignition of the mixture can be delayed after the compression top dead center by the suppression species. The start timing of the self-ignition of the air-fuel mixture is preferably in the vicinity of the compression top dead center in the expansion stroke (for example, 5 ° to 10 ° after the compression top dead center at the crank angle) in consideration of the subsequent combustibility. Accordingly, it is possible to suppress a sudden increase in the pressure in the combustion chamber 6 and to suppress an increase in the maximum pressure and the temperature in the combustion chamber 6.

  Then, after the self-ignition of the air-fuel mixture has started after the compression top dead center, if the combustion spreads to the periphery of the air-fuel mixture layer 51, active species are present there. Is done. As a result, even if the start time of the self-ignition of the air-fuel mixture is delayed after the compression top dead center, the combustibility in the later stage of combustion is improved, and the combustion in the latter stage of combustion becomes stable. In addition, compared with the case where no active species are generated, the combustion can be terminated earlier by promoting the combustion (the combustion period can be shortened). This also makes it possible to stabilize the combustion at the latter stage of the combustion. become able to.

  FIG. 9 shows PV lines of the engine 1 according to the present embodiment and a premixed compression ignition type engine (hereinafter, referred to as a conventional engine) that self-ignites near compression top dead center without generating suppressed and active species. The figure is shown. In the engine 1, the start time of the self-ignition of the air-fuel mixture is set to 5 ° to 10 ° after the compression top dead center. In the conventional engine, the pressure increase rate (dP / dt), which is a change in the pressure in the combustion chamber 6 with respect to a change in the maximum pressure (Pmax) and time in the combustion chamber 6, becomes excessively large, particularly during abnormal combustion (FIG. 9). Dashed line). On the other hand, in the engine 1, the values of Pmax and dP / dt can be reduced (see the solid line in FIG. 9).

  FIG. 10 shows a change in the heat release rate (dQ / dθ), which is a change in the amount of heat generated with respect to a change in the crank angle, in the engine 1 (example) according to the present embodiment. In the embodiment, the start time of the self-ignition of the air-fuel mixture is 5 ° to 10 ° after the compression top dead center. For comparison, FIG. 10 also shows a change in dQ / dθ when the self-ignition of the air-fuel mixture is delayed as much as that of the engine 1 in the conventional engine (comparative example).

  FIG. 11 shows a pressure rise rate (dP / dθ) which is a change in the pressure in the combustion chamber 6 with respect to the crank angle in the above embodiment. For comparison, a change in dP / dθ in the comparative example is also shown in FIG.

  As shown in FIG. 10, in the engine 1 according to the present embodiment, dQ / dθ increases more than the comparative example due to the active species, and then dQ / dθ drops sharply, and the combustion ends early. . In the engine 1, dP / dθ increases due to an increase in dQ / dθ. However, even if dP / dθ increases, the piston 5 moves down to some extent and the pressure in the combustion chamber 6 decreases. Since dP / dθ rises at a certain stage, there is room for dP / dθ to reach a level at which combustion noise is a concern.

  Therefore, in the present embodiment, by delaying the start time of the self-ignition of the air-fuel mixture after the compression top dead center, it is possible to suppress a rapid increase in the pressure in the combustion chamber 6 and to increase the maximum pressure and the maximum pressure in the combustion chamber 6. An increase in temperature can be suppressed. As a result, it is possible to reduce combustion noise, improve the reliability of the engine body 1a, and reduce the amount of RawNOx generated. Even if the start time of the self-ignition of the air-fuel mixture is delayed after the compression top dead center, the combustion in the latter half of the combustion can be stabilized.

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

  For example, in the above-described 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, but instead or additionally. May be provided in a portion between the two intake ports 9 in the vicinity of the fuel injection valve 14 on the ceiling wall of the combustion chamber 6. The discharge electrode portion 13a of the discharge plug 13 provided at a portion between the two intake ports 9 is located between the openings 9a of the two intake ports 9 on the combustion chamber 6 side near the center of the ceiling surface of the combustion chamber 6. As with the above embodiment, both the first discharge and the second discharge are executed facing the combustion chamber 6.

  Further, a plurality of discharge plugs 13 are provided, and a discharge electrode portion 13a of at least one of the plurality of discharge plugs 13 performs the first discharge, and a discharge electrode portion 13a of the remaining discharge plugs 13 The second discharge may be performed. When a tumble flow T of the sucked air is generated in the combustion chamber 6, for example, as shown in FIGS. 12 and 13, a discharge plug 13 (see FIG. 12) having a discharge electrode portion 13a for performing a first discharge. In FIG. 13, the reference numeral 13A denotes a discharge electrode portion that is disposed between the two exhaust ports 10 near the fuel injection valve 14 on the ceiling wall of the combustion chamber 6 and that performs the second discharge. The discharge plug 13 having 13 a (in FIG. 12 and FIG. 13, the reference numeral is 13 B) is disposed on the ceiling wall of the combustion chamber 6 near the fuel injection valve 14 and between the two intake ports 9. That is, the discharge electrode portion 13a of the discharge plug 13A faces the combustion chamber 6 from a portion between the two openings 10a near the center of the ceiling surface of the combustion chamber 6, and the discharge electrode portion 13a of the discharge plug 13B From the center of the ceiling surface between the two openings 9a. The first discharge may be performed by using the discharge plug 13B shown in FIGS. 12 and 13 together with the discharge plug 13A.

  Further, in the above embodiment, the tumble flow T of the sucked air is generated in the combustion chamber 6, but the swirl flow S of the sucked air is generated in the combustion chamber 6. It may be as follows. In this case, as shown in FIG. 14, the swirl valve 16 is provided in the independent passage (in FIG. 14, denoted by reference numeral 20 a) connected to one of the two intake ports 9 of each cylinder 2. When the swirl valve 16 is closed, air flows from the other intake port 9 into the combustion chamber 6.

  When the swirl flow S is generated in the combustion chamber 6 as described above, a plurality of discharge plugs 13 are provided, and a discharge electrode portion of at least one of the plurality of discharge plugs 13 (discharge plug 13A). 13a performs the first discharge, and the discharge electrode portions 13a of the remaining discharge plugs 13 (discharge plugs 13B) perform the second discharge. As shown in FIG. 14, the discharge plug 13 </ b> A is arranged on the outer peripheral portion of the ceiling wall of the combustion chamber 6. In FIG. 14, the discharge plugs 13 </ b> A are arranged at two positions on a straight line L passing through the center of the cylinder 2 and extending in the cylinder row direction on the outer peripheral portion of the ceiling wall of the combustion chamber 6 when viewed from the center axis direction of the cylinder 2. ing. The discharge plug 13A may be disposed at any one of the two positions. In this case, it is preferable that the discharge plug 13A is disposed at a position near the other intake port 9. The discharge plug 13B is arranged near the fuel injection valve 14 on the ceiling wall of the combustion chamber 6, as in the above embodiment. The discharge electrode portion 13a of the discharge plug 13A is adjacent to the outer peripheral portion of the ceiling surface of the combustion chamber 6 (for example, the opening 9a of the other intake port 9 and the flow direction of the swirl flow S with respect to the opening 9a). The discharge electrode portion 13a of the discharge plug 13B faces the combustion chamber 6 from near the center of the ceiling surface of the combustion chamber 6 (the portion between the two openings 9a). Will be.

  When the swirl flow S is generated in the combustion chamber 6, when the discharge electrode 13a of the discharge plug 13A facing the combustion chamber 6 is performing the first discharge, the fuel is injected from the fuel injection valve 14. You may inject. In this case, the vicinity of the discharge electrode portion 13a performing the first discharge is fuel-lean at or above the first predetermined air-fuel ratio due to the air sucked into the combustion chamber 6 and the fuel injected from the fuel injection valve 14. If the air-fuel mixture is a natural gas mixture (air-fuel mixture having a considerably large air-fuel ratio that can be basically regarded as air), active species can be generated by executing the first discharge.

  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.

  The present invention includes an engine body having a cylinder in which a combustion chamber is formed and having a geometric compression ratio of 16 or more, and a self-mixing compression ignition type in which a mixture of fuel and air is self-ignited in the combustion chamber. Useful for engines.

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 (plasma generating means)
14 Fuel injection valve 91 Voltage application circuit (plasma generation means)
100 ECU (control means)

Claims (4)

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,
The engine body has a geometric compression ratio of 16 or more;
A fuel injection valve for injecting fuel into the combustion chamber,
A plasma generating means having one or a plurality of discharge electrode units, and generating non-equilibrium plasma in the discharge electrode unit by discharging at the discharge electrode unit;
Control means for controlling the operation of the plasma generation means,
The control means includes:
During an intake stroke during operation of the engine body, a fuel lean of at least a first predetermined air-fuel ratio due to the air sucked into the combustion chamber or the air and fuel injected into the combustion chamber by the fuel injection valve. A first discharge is performed by at least one discharge electrode unit of the plasma generation means so as to irradiate the non-equilibrium plasma to the air-fuel mixture;
In the compression stroke, the fuel injected into the combustion chamber by the fuel injection valve or a fuel-rich mixture of the air and the fuel, which is smaller than the second predetermined air-fuel ratio and smaller than the second predetermined air-fuel ratio, is smaller than the first predetermined air-fuel ratio. In order to irradiate the non-equilibrium plasma with respect to the discharge electrode, the plasma generating means is configured to execute the second discharge at the same or different discharge electrode as the discharge electrode which caused the first discharge. A premixed compression ignition engine characterized by being made. The homogeneous charge compression ignition engine according to claim 1,
The control means performs the first discharge in the intake stroke to generate an active species that is a substance that promotes the combustion of the air-fuel mixture in the combustion chamber, and generates the second discharge in the compression stroke. A premixed compression ignition engine characterized in that the engine is configured to generate a suppression species that is a substance that suppresses combustion of an air-fuel mixture in the combustion chamber when the engine is executed. The premixed compression ignition engine according to claim 1 or 2,
In the combustion chamber, a tumble flow of the sucked air is generated,
The plasma generation means has a discharge electrode portion facing the combustion chamber from near the center of the ceiling surface of the combustion chamber and executing both the first discharge and the second discharge. Premixed compression ignition engine. The premixed compression ignition engine according to claim 1 or 2,
A swirl flow of the sucked air is generated in the combustion chamber,
The plasma generating means faces the combustion chamber from an outer peripheral portion of a ceiling surface of the combustion chamber and performs the first discharge, and a discharge electrode portion which faces the combustion chamber from near the center of the ceiling surface of the combustion chamber. And a discharge electrode unit for performing the second discharge.

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