JP7001002B2 - Premixed compression ignition engine - Google Patents

Description

The present invention belongs to the technical field relating to a premixed compression ignition engine.

Conventionally, a premixed compression ignition engine that self-ignites a mixture of fuel and air in a combustion chamber (HCCI combustion) has been known (see, for example, Patent Document 1). Further, an engine having a high compression ratio having a geometric compression ratio of 15 or more and 40 or less is also known (see, for example, Patent Document 2).

Further, for example, Patent Document 3 discloses an engine in which a non-equilibrium plasma (also referred to as low temperature plasma) is generated in the discharge electrode portion by discharging at the discharge electrode portion by applying a voltage to the discharge electrode portion. ing. This engine forms an unbalanced plasma state between the ignition plug (discharge plug) in which a discharge occurs in the discharge electrode portion (between the center electrode and the ground electrode) composed of the center electrode and the ground electrode, and the center electrode and the ground electrode. A short pulse circuit capable of generating a short pulse electric field is provided, and the short pulse circuit generates a short pulse electric field between the center electrode and the ground electrode to generate a non-equilibrium plasma in the discharge electrode portion.

Japanese Unexamined Patent Publication No. 2015-081527 Japanese Unexamined Patent Publication No. 2013-194712 Japanese Unexamined Patent Publication No. 2014-141919

By the way, as a result of diligent research by the present inventors, when air or a fuel lean air-fuel mixture (basically air) having a considerably large air-fuel ratio exists around the discharge electrode portion of the discharge plug, the discharge electrode is used. When non-equilibrium plasma is generated by the discharge in the part, the air is irradiated with the non-equilibrium plasma, and the active species (for example, ozone, OH, etc.) which are substances that promote the self-ignition and combustion of the air-fuel mixture from the air. ) Was generated. On the other hand, when a fuel or a relatively fuel-rich mixture is present around the discharge electrode portion and a non-equilibrium plasma is generated by the discharge at the discharge electrode portion, the fuel or a relatively fuel-rich mixture is generated. It was found that by irradiating the air with non-equilibrium plasma, suppressed species (for example, formaldehyde, nitrogen dioxide, etc.), which are substances that suppress self-ignition and combustion of the air-fuel mixture, are generated from the fuel. As described above, it was 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 a premixed compression ignition engine with a high compression ratio, self-ignition of the air-fuel mixture starts from the center of the combustion chamber near the compression top dead point in the compression stroke, and the combustion spreads, resulting in pressure in the combustion chamber. As the engine rises sharply, the maximum pressure becomes very high, which tends to lead to an increase in combustion noise and a decrease in engine reliability. In addition, the temperature in the combustion chamber becomes very high, and the amount of RawNOx generated tends to increase.

Therefore, it is conceivable to delay the start time of self-ignition by the above-mentioned inhibitory species so that it is after the compression top dead center. By delaying the start time of self-ignition after the compression top dead center in this way, it is possible to suppress the rapid rise in pressure in the combustion chamber and to prevent the maximum pressure and temperature in the combustion chamber from becoming too high. can.

However, if the start time of self-ignition is delayed after the compression top dead center, heat will only be generated slowly in the outer peripheral region of the combustion chamber, which will reduce the thermal efficiency of the engine and burn due to the lowering of the piston. There is a problem that combustion becomes unstable, especially in the latter stage of combustion, due to a decrease in indoor pressure and temperature.

The present invention has been made in view of these points, and an object thereof is to delay the start time of self-ignition of the air-fuel mixture after the compression top dead center by using a non-equilibrium plasma. It is an object of the present invention to provide a premixed compression ignition type engine capable of stabilizing combustion in the late combustion stage.

In order to achieve the above object, the present invention is intended for a premixed compression ignition type engine provided with an engine body having a cylinder in which a combustion chamber is formed and self-igniting a mixture of fuel and air in the combustion chamber. As a result, the geometric compression ratio of the engine body is 16 or more, the fuel injection valve for injecting fuel into the combustion chamber, and one or more discharge electrode portions are provided, and the discharge in the discharge electrode portion is provided. The discharge electrode portion is provided with a plasma generation means for generating non-equilibrium plasma and a control means for controlling the operation of the plasma generation means, and the control means is used for the combustion in the intake stroke during operation of the engine body. The non-equilibrium plasma is applied to a fuel lean air-fuel mixture having a first predetermined air fuel ratio or more formed in the combustion chamber by the air sucked into the chamber or the fuel injected into the combustion chamber by the fuel injection valve. The first discharge is executed by at least one discharge electrode portion of the plasma generation means so as to irradiate the fuel, and the fuel injected into the combustion chamber by the fuel injection valve or the fuel in the compression stroke burns the fuel. The first of the plasma generating means so as to irradiate the fuel-rich air-fuel mixture formed in the room with a fuel-rich mixture smaller than the first predetermined air fuel ratio and less than the second predetermined air fuel ratio. The configuration is such that the discharge electrode portion that is the same as or different from the discharge electrode portion that has executed the discharge is configured to execute the second discharge.

More specifically, the control means produces the active species, which is a substance that promotes the combustion of the air-fuel mixture in the combustion chamber, by executing the first discharge in the intake stroke, and also in the compression stroke. By executing the second discharge, it is configured to generate a suppression species which is a substance that suppresses the combustion of the air-fuel mixture in the combustion chamber.

With the above configuration, the execution of the first discharge in the intake stroke causes the active species to be produced from the air by irradiating the non-equilibrium plasma to the air or a fuel lean air-fuel mixture having a fuel lean ratio equal to or higher than the first predetermined air-fuel ratio. .. In addition, by executing the second discharge in the compression stroke, the fuel injected into the combustion chamber or the fuel-rich mixture having a fuel-rich air-fuel ratio less than the second predetermined air-fuel ratio is irradiated with non-equilibrium plasma, so that the suppressed species are released from the fuel. Generated. The fuel injected in the compression stroke forms a relatively fuel-rich air-fuel mixture layer in the center of the combustion chamber near the compression top dead center. The suppressor species produced from the fuel during the compression stroke will basically be present in the fuel-rich mixture layer in the central part of the combustion chamber. Further, in the vicinity of the compression top dead center, around the fuel-rich air-fuel mixture layer, the air sucked into the combustion chamber in the intake stroke or the air-fuel mixture leaner than the air-fuel mixture layer containing the air. Exists. The active species produced from the air during the intake stroke will be present in the fuel lean air-fuel mixture layer.

Here, if there is no inhibitory species in the fuel-rich air-fuel mixture layer, since the compression ratio is high, self-ignition of the air-fuel 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 the central portion where the temperature is the highest in the combustion chamber and the fuel-rich air-fuel mixture layer is formed. On the other hand, if the suppression species are present in the fuel-rich air-fuel mixture layer, the suppression species can delay the start time of self-ignition of the air-fuel mixture after the compression top dead center.

Then, after the self-ignition of the air-fuel mixture is started after the compression top dead center, when the combustion spreads to the periphery of the fuel-rich air-fuel mixture layer, active species exist there. Is promoted. As a result, even if the start time of self-ignition of the air-fuel mixture is delayed after the compression top dead center, the combustibility in the latter stage of combustion is improved and the combustion in the latter stage of combustion becomes stable. Moreover, compared to the case where no active species is produced, by promoting combustion, combustion can be terminated earlier (combustion period can be shortened), which also stabilizes combustion in the latter stage of combustion. Will be able to. Therefore, it is possible to stabilize the combustion in the latter stage of combustion while delaying the start time of self-ignition of the air-fuel mixture after the compression top dead center.

In one embodiment of the premixed compression ignition engine, a tumble flow of sucked air is generated in the combustion chamber, and the plasma generating means is near the center of the ceiling surface of the combustion chamber. It has a discharge electrode portion that faces the combustion chamber and executes both the first discharge and the second discharge.

As a result, when a tumble flow of intake air is generated in the combustion chamber, in the intake stroke, the first discharge at the discharge electrode portion facing the combustion chamber from the vicinity of the center of the ceiling surface of the combustion chamber causes the combustion chamber to enter the combustion chamber. Non-equilibrium plasma can be applied to the air immediately after inhalation. Further, in the compression stroke, the fuel or the fuel-rich mixture injected into the combustion chamber is irradiated with the non-equilibrium plasma by the second discharge in the same discharge electrode portion as the discharge electrode portion in which the first discharge is executed. can do.

In another embodiment of the premixed compression ignition engine, a swirl flow of sucked air is generated in the combustion chamber, and the plasma generating means is the outer periphery of the ceiling surface of the combustion chamber. A discharge electrode portion that faces the combustion chamber and executes the first discharge from the unit, and a discharge electrode portion that faces the combustion chamber and executes the second discharge from the vicinity of the center of the ceiling surface of the combustion chamber. Have.

As a result, when a swirl flow of intake air is generated in the combustion chamber, in the intake stroke, 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 causes the combustion chamber to enter the combustion chamber. Non-combustion plasma can be applied to the inhaled air. Further, in the compression stroke, the non-equilibrium plasma with respect to the fuel injected into the combustion chamber or the fuel-rich mixture due to the second discharge at the discharge electrode portion facing the combustion chamber from the vicinity of 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 suppression species generated from the fuel can delay the start time of self-ignition of the air-fuel mixture after the compression top dead center and from the air. Depending on the active species produced, even if the start time of self-ignition of the air-fuel mixture is delayed after the compression top dead center, the combustion in the late combustion stage can be stabilized.

It is a figure which shows the schematic structure of the premixed compression ignition type engine which concerns on embodiment of this invention. It is sectional drawing which shows the main part of the said engine in an enlarged manner. It is a schematic plan view of a certain cylinder of the said engine. It is a block diagram which shows the control system of the said engine. It is a figure which shows the kind of plasma generated by the discharge in the discharge electrode part, according to the pulse width and the peak value of the pulse voltage applied to the discharge electrode part of the discharge plug. It is a graph which shows an example of the waveform of the pulse voltage at the time of generating a non-equilibrium plasma. It is a time chart which shows the execution timing of the first discharge and the second discharge, and the timing of fuel injection. It is a figure which shows the fuel distribution in the combustion chamber near the compression top dead center. It is a graph which shows the PV diagram of the premixed compression ignition type engine which concerns on this embodiment, and the premixed compression ignition type engine which self-ignites near the compression top dead center. It is a graph which shows the change of the heat generation rate (dQ / dθ) in an Example and a comparative example. It is a graph which shows the change of the pressure rise rate (dP / dθ) in the said Example and the said comparative example. FIG. 2 is a diagram corresponding to FIG. 2 showing a modified example. It is a figure corresponding to FIG. 3 which shows the said modification. It is a figure corresponding to FIG. 3 which shows still another modification.

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

FIG. 1 shows a premixed 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 body 1a having four cylinders 2 (cylinders) in which a combustion chamber 6 is formed, and mixes fuel and air in the combustion chamber 6 in each cylinder 2. It is an engine that self-ignites.

The engine 1 is an in-line 4-cylinder engine in which the four cylinders 2 of the engine body 1a are arranged in series in the direction perpendicular to the paper surface of FIG. The engine 1 is mounted on a vehicle and used as a drive source for the vehicle. In this embodiment, the engine 1 is driven by being supplied with 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. A piston 5 for partitioning the combustion chamber 6 from the cylinder head 4 is fitted in each cylinder 2 so as to be reciprocating (vertically moving). The piston 5 of each cylinder 2 is connected to a crankshaft (not shown) extending in the cylinder row direction via a connecting rod 8.

The combustion chamber 6 is 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 composed of two inclined surfaces, an intake side and an exhaust side.

The crown surface 5a of the piston 5 is formed with a cavity 5b in which the central portion of the crown surface 5a is recessed on the opposite side (lower side) of the cylinder head 4. A plurality of (three in this embodiment) piston rings 5c (see FIG. 2) are fitted in the vicinity of the crown surface 5a on the side peripheral surface of the piston 5.

In the present embodiment, the geometric compression ratio of the engine 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 even more preferably 20 or more and 25 or less.

The cylinder head 4 has an intake port 9 for introducing air supplied from the intake passage 20 into the cylinder 2 (combustion chamber 6) and an exhaust gas generated in the cylinder 2 to be led out to the exhaust passage 30. The exhaust port 10 of the above 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, due to the shape of the intake port 9, a tumble flow T (see FIG. 2) of air sucked into the combustion chamber 6 from the intake port 9 is generated in the combustion chamber 6.

Further, the cylinder head 4 has an intake valve 11 that opens and closes an opening 9a (see FIG. 3) on the combustion chamber 6 side of each intake port 9, and an opening 10a (see FIG. 3) on the combustion chamber 6 side of each exhaust port 10. ) Are provided with an exhaust valve 12 for opening and closing each.

The intake valve 11 is opened and closed at a predetermined timing by the intake valve mechanism. The intake valve mechanism is a variable valve mechanism that makes the valve timing and / or the valve lift variable. In the present embodiment, this variable valve mechanism has an intake electric S-VT (Sequential-Valve Timing) 17. The intake electric S-VT17 is configured to continuously change the rotational phase of the intake camshaft within a predetermined angle range. As a result, 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 is opened and closed at a predetermined timing by the exhaust valve mechanism. The exhaust valve mechanism is also a variable valve mechanism that makes the valve timing and / or the valve lift variable. In the present embodiment, this variable valve mechanism has an exhaust electric S-VT18. The exhaust electric S-VT18 is configured to continuously change the rotational phase of the exhaust camshaft within a predetermined angle range. As a result, 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 surface 5a of the piston 5 for each cylinder 2. The fuel injection valve 14 is attached to substantially 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 for injecting fuel at the tip thereof, and 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 externally open type fuel injection valve having an externally open valve that opens and closes the fuel injection port. The fuel injection port is formed in a tapered shape having a larger diameter toward the tip side. Then, the fuel injection valve 14 injects fuel from the fuel injection port toward the crown surface of the piston 5 in a substantially conical shape (specifically, a hollow cone shape). 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 have a length that does not reach the outer peripheral portion of the combustion chamber 6. The fuel injection valve 14 is not limited to the externally open type fuel injection valve, but is a multi-injection type fuel injection valve having a plurality of (for example, 10 to 20) injection holes (fuel injection ports) at the tip. May be. Also in this case, the 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 over the entire plurality of injection holes.

Further, 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 the portion between the two exhaust ports 10 in the vicinity of 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 on the combustion chamber 6 side of the two exhaust ports 10 in the vicinity of the fuel injection valve port on the ceiling surface of the combustion chamber 6 (near the center of the ceiling surface). I'm out.

The discharge electrode portion 13a is composed of a metal center electrode 13b and a ground electrode 13c facing each other in the central axis direction of the discharge plug 13. The center electrode 13b is connected to a voltage application circuit 91 (see FIG. 4) that applies 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, the voltage is discharged between the center electrode 13b and the ground electrode 13c, and the energy of the discharge causes plasma to the discharge electrode portion 13a. (In this embodiment, non-equilibrium plasma) is generated.

An intake passage 20 is communicated with the intake port 9. An air cleaner 21 for filtering intake air is disposed at the upstream end of the intake passage 20, and the intake air filtered by the air cleaner 21 burns in each cylinder 2 via the intake passage 20 and the intake port 9. It is supplied to the room 6.

An air flow sensor SN2 for detecting the amount of intake air sucked into the intake passage 20 is arranged in the vicinity of the downstream side of the air cleaner 21 in the intake passage 20. Further, a surge tank 25 is arranged near the downstream end of the intake passage 20. The intake passage 20 on the downstream side of the surge tank 25 is an independent passage that branches for each cylinder 2, and the downstream end of each independent passage is connected to each of 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, the throttle valve 22 is basically maintained at a fully open position or an opening close to the throttle valve 22 during operation of the engine 1, and is closed only under limited operating conditions such as when the engine 1 is stopped. The intake passage 20 is shut off.

An exhaust passage 30 for discharging the exhaust gas from the combustion chamber 6 of each cylinder 2 is communicated with the exhaust port 10. The upstream portion of the exhaust passage 30 is composed of an exhaust manifold having an independent passage branched for each cylinder 2 and connected to the exhaust port 10 and an collecting portion where the independent passages gather.

An exhaust purification device 31 for purifying exhaust gas is provided in the exhaust passage 30 (a 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 communicates with a portion upstream of the exhaust purification device 31 in the exhaust passage 30 and downstream of the exhaust manifold and a portion of the surge tank 25 in the intake passage 20. 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 the EGR gas passing through the EGR passage 41. The EGR gas is cooled by the EGR cooler 43 and then returned to the intake passage 20.

In the present embodiment, the engine 1 is not provided with a supercharger, but may be provided with 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 well-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 that is started on the OS and realizes a specific function). The memory 102 is composed of a RAM and a ROM. The ROM stores various computer programs (particularly, a control program for controlling the engine 1), data including a map to be described later used when the computer program is executed, and the like. The RAM is a memory provided with a processing area used when the CPU 101 performs a series of processing. The input / output bus 103 inputs / outputs an electric signal to / from the ECU 100.

Various sensors such as a crank angle sensor SN1, an airflow 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 crankshaft. The accelerator opening sensor SN3 is attached to the accelerator pedal mechanism of the vehicle and detects the accelerator opening corresponding to the operation amount of the accelerator pedal. These sensors SN1 to SN3 and the like output a detection signal 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 also determines the operating state of the engine 1, the voltage application circuit 91, the fuel injection valve 14, the intake electric S-VT17, the exhaust electric S-VT18, and the throttle valve. A control signal is output to each device of the engine 1 such as 22, EGR valve 42, etc. to control each device.

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

In the present embodiment, in the combustion cycle of the engine body 1a, combustion in the combustion chamber 6 is controlled by generating non-equilibrium plasma (also referred to as low temperature plasma) by discharging at the discharge electrode portion 13a of the discharge plug 13. I am doing it. The non-equilibrium plasma refers to a plasma in which the electrons in the combustion chamber 6 and the ions and molecules of the gas in the combustion chamber 6 are not in a thermal equilibrium state without an increase in the gas temperature in the combustion chamber 6. ..

The non-equilibrium plasma can be generated by setting the pulse width and 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 portion 13a according to the pulse width and the peak value of the pulse voltage. The horizontal axis of FIG. 5 is the pulse width of the pulse voltage, which is shown on a logarithmic scale. On the other hand, the vertical axis of FIG. 5 is the peak value of the pulse voltage and is shown on a logarithmic scale. As shown in FIG. 5, it can be seen that when the pulse width is shortened (specifically, when it is 0.01 μsec or more and less than 1 μsec), a non-equilibrium plasma is generated. This is because at a pulse voltage with a short pulse width, only electrons react and ions and molecules hardly react. On the other hand, it can be seen that when the pulse width is lengthened (1 μsec or more), thermal equilibrium plasma (also called high temperature plasma) is generated. The non-equilibrium plasma is not the ignition source for igniting the air-fuel mixture, while the thermal equilibrium plasma is the ignition source for igniting the air-fuel 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, this pulse voltage produces a non-equilibrium plasma. When the unbalanced plasma is generated, the ECU 100 operates the voltage application circuit 91 so that the voltage application circuit 91 repeatedly applies the pulse voltage to the discharge electrode unit 13a at a frequency of 100 kHz. In FIG. 6, the pulse voltage is a triangular wave, but it may be a square wave.

The peak value of the pulse voltage applied to the discharge electrode portion 13a when generating the unbalanced plasma does not need to be fixed at 10 kV, and is based on, for example, the pressure in the combustion chamber 6 (detected by the pressure sensor). It 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 the non-equilibrium plasma is generated in the discharge electrode portion 13a, the substance generated in the combustion chamber 6 differs depending on the air-fuel ratio around the discharge electrode portion 13a. That is, when air or a fuel lean air-fuel mixture (basically air) of air and fuel having a first predetermined air-fuel ratio or more exists around the discharge electrode portion 13a, the discharge electrode portion 13a When a non-equilibrium plasma is generated in the air, the air or fuel lean air-fuel mixture is irradiated with the non-equilibrium plasma, and the air-fuel mixture such as ozone ₍ O3) or OH in the combustion chamber 6 is irradiated. Active species, which are substances that promote self-ignition and combustion of air, are produced. On the other hand, when there is a fuel-rich mixture of fuel or air and fuel, which is smaller than the first predetermined air-fuel ratio and less than the second predetermined air-fuel ratio, around the discharge electrode portion 13a. When the non-equilibrium plasma is generated in the discharge electrode portion 13a, the non-equilibrium plasma is irradiated to the fuel or the fuel-rich air-fuel mixture, and the fuel is used as a base for formaldehyde (CH ₂ O) and nitrogen dioxide (NO ₂ ). Etc., which are substances that suppress self-ignition and combustion of the air-fuel mixture in the combustion chamber 6, are produced.

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 in the vicinity of the discharge electrode portion 13a, the suppression species is generated. When the non-equilibrium plasma is generated when the fuel is being sucked in the intake stroke and the fuel is not injected, the active species will be generated. By generating active species and / or suppressed species in the combustion chamber 6 in this way, combustion is controlled by accelerating or delaying the combustion of the air-fuel mixture.

In the present embodiment, compression ignition combustion (CI combustion) is performed in the entire operating 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 operation of the engine body 1a, and the temperature rises by compressing the air-fuel mixture. Then, the air-fuel 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 inject fuel in the vicinity of 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 inject fuel in a plurality of times (three times in this embodiment).

By injecting such fuel, as shown in FIG. 8, in the vicinity of the compression top dead center, a relatively fuel-rich air-fuel mixture layer 51 (fuel and air injected in the compression stroke) is located in the center of the combustion chamber 6. Along with the formation of the air-fuel mixture layer), an air-fuel mixture layer 52 (fuel-fuel mixture injected in the intake stroke) that is leaner than the air-fuel mixture layer 51 is formed around the air-fuel mixture layer 51. It is formed.

Further, in the intake stroke, the ECU 100 causes the discharge electrode portion 13a of the discharge plug 13 to execute the first discharge so as to irradiate the air immediately after being sucked into the combustion chamber 6 with the non-equilibrium plasma. That is, as shown in FIG. 7, before the fuel injection in the intake stroke (when the fuel injection valve 14 is not operating), the voltage application circuit 91 is operated to cause the discharge electrode portion 13a of the discharge plug 13 to have the predetermined voltage. By applying (the pulse voltage), a non-equilibrium plasma is generated in the discharge electrode portion 13a. At the time of executing this first discharge, immediately after the air flows into the combustion chamber 6 from the opening 9a on the combustion chamber 6 side of each intake port 9, the air passes near the discharge electrode portion 13a, so that the air is charged. On the other hand, non-equilibrium plasma will be irradiated. This produces the active species from air.

The active species produced from air as described above will basically be present in the air-fuel mixture layer 52. In particular, when the rotation speed of the engine body 1a is high, the generated active species are likely to diffuse, so that the execution of the first discharge is performed in the middle and late stages of the intake stroke (the intake stroke is in the early, middle and late stages and 3). The middle and late stages when divided into equal parts) are preferable.

Further, the ECU 100 further injects fuel in the subsequent compression stroke (specifically, the latter half of the compression stroke, in the present embodiment, the period from the start of the second split injection to the end of the third split injection). The discharge electrode unit 13a (in the present embodiment, the same discharge electrode unit as the discharge electrode unit that executed the first discharge) so as to irradiate the fuel injected into the combustion chamber 6 by the valve 14 with the non-equilibrium plasma. Part), the second discharge is executed. That is, as shown in FIG. 7, the voltage application circuit 91 is continuously operated during the period from the start of the second divided injection in the compression stroke to the end of the third divided injection, and the discharge electrode of the discharge plug 13 is operated. By applying the predetermined voltage (the pulse voltage) to the unit 13a, a non-equilibrium plasma is generated in the discharge electrode unit 13a. At the time of executing this second discharge, the fuel injected by the fuel injection valve 14 exists around the discharge electrode portion 13a. Even when the fuel is not injected between the second split injection and the third split injection, the fuel is basically present around the discharge electrode portion 13a because the interval is short and the fuel penetration is short. The fuel existing around the discharge electrode portion 13a is irradiated with non-equilibrium plasma, and the suppressed species are generated from the fuel.

The fuel-rich air-fuel mixture layer 51 may be located around the discharge electrode portion 13a, and if the air-fuel ratio of the air-fuel mixture layer 51 is less than the second predetermined air-fuel ratio, it is less than the second predetermined air-fuel ratio. The above-mentioned suppressed species can be produced by irradiating the fuel-rich air-fuel mixture with non-equilibrium plasma. 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 time of the self-ignition of the air-fuel mixture. It is also possible to start the operation of the voltage application circuit 91 at the start of the first divided injection.

The inhibitory species produced from the fuel as described above will basically be present in the air-fuel mixture layer 51. Therefore, in the vicinity of the compression top dead center, the suppressed species are present in the central portion of the combustion chamber (air-fuel mixture layer 51), and the active species are present in the surroundings (air-fuel mixture layer 52).

Here, if there is no inhibitory species in the air-fuel mixture layer 51, since the compression ratio is high, self-ignition of the air-fuel 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 the central portion where the temperature is the highest and the fuel-rich air-fuel mixture layer 51 is formed in the combustion chamber 6.

However, in the present embodiment, since the inhibitory species are present in the air-fuel mixture layer 51, the suppression species can delay the start time of self-ignition of the air-fuel mixture after the compression top dead center. The start time of self-ignition of the air-fuel mixture is preferably near 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. As a result, it is possible to suppress a sudden rise in pressure in the combustion chamber 6, and it is also possible to suppress an increase in the maximum pressure and temperature in the combustion chamber 6.

Then, after the self-ignition of the air-fuel mixture is started after the compression top dead center, when the combustion spreads to the periphery of the air-fuel mixture layer 51, the active species are present there, and the combustion is promoted by the active species. Will be done. As a result, even if the start time of self-ignition of the air-fuel mixture is delayed after the compression top dead center, the combustibility in the latter stage of combustion is improved and the combustion in the latter stage of combustion becomes stable. Moreover, compared to the case where active species are not produced, combustion can be terminated earlier by promoting combustion (the combustion period can be shortened), and this also makes it possible to stabilize combustion in the latter stage of 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 the compression top dead center without generating suppressed species and active species. The figure is shown. In the engine 1, the self-ignition start time of the air-fuel mixture is set to 5 ° to 10 ° after the compression top dead center. In a conventional engine, the pressure rise rate (dP / dt), which is the change in pressure in the combustion chamber 6 with respect to the maximum pressure (Pmax) in the combustion chamber 6 and the change in time, becomes too large especially during abnormal combustion (FIG. 9). See the dashed line in). 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 generation 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 self-ignition start time of the air-fuel mixture is set to 5 ° to 10 ° after the compression top dead center. For comparison, in the conventional engine, the change in dQ / dθ when the self-ignition of the air-fuel mixture is delayed to the same extent as that of the engine 1 (comparative example) is shown with reference to FIG.

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

As shown in FIG. 10, in the engine 1 according to the present embodiment, dQ / dθ increases significantly depending on the active species as compared with the comparative example, and then dQ / dθ sharply decreases, and combustion ends early. .. Further, in the engine 1, dP / dθ increases due to the increase in dQ / dθ, but even if dP / dθ increases, the piston 5 decreases to some extent and the pressure in the combustion chamber 6 decreases. Since it is rising at the stage where it is, there is a margin before dP / dθ reaches a level at which combustion noise is a concern.

Therefore, in the present embodiment, by delaying the start time of 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 also to suppress the maximum pressure in the combustion chamber 6 and the maximum pressure in the combustion chamber 6. It is possible to suppress the temperature from rising. 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. Further, even if the start time of self-ignition of the air-fuel mixture is delayed after the compression top dead center, the combustion in the latter stage of combustion can be stabilized.

The present invention is not limited to the above embodiment, and can be substituted as long as it does not deviate from the gist of the claims.

For example, in the above embodiment, the discharge plug 13 is provided in the portion between the two exhaust ports 10 in the vicinity of the fuel injection valve 14 on the ceiling wall of the combustion chamber 6, but in place of or in addition to this. , May be provided in the 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 in the portion between the two intake ports 9 is located between the openings 9a on the combustion chamber 6 side of the two intake ports 9 near the center of the ceiling surface of the combustion chamber 6. Facing the combustion chamber 6, both the first discharge and the second discharge are performed in the same manner as in the above embodiment.

Further, a plurality of discharge plugs 13 are provided, the discharge electrode portion 13a of at least one of the plurality of discharge plugs 13 executes the first discharge, and the discharge electrode portion 13a of the remaining discharge plugs 13 is provided. A second discharge may be performed. When a tumble flow T of sucked air is generated in the combustion chamber 6, for example, as shown in FIGS. 12 and 13, a discharge plug 13 having a discharge electrode portion 13a for executing a first discharge (FIG. 12). And in FIG. 13, reference numeral 13A) is arranged in the portion between the two exhaust ports 10 in the vicinity of the fuel injection valve 14 on the ceiling wall of the combustion chamber 6 and is a discharge electrode portion that executes a second discharge. The discharge plug 13 having 13a (reference numeral 13B in FIGS. 12 and 13) is arranged in the 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. That is, the discharge electrode portion 13a of the discharge plug 13A faces the combustion chamber 6 from the 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 faces the combustion chamber 6. The combustion chamber 6 faces the combustion chamber 6 from the portion between the two openings 9a near the center of the ceiling surface. The discharge plug 13B shown in FIGS. 12 and 13 may be used to perform the first discharge 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 like this. In this case, as shown in FIG. 14, the swirl valve 16 is provided in the independent passage (reference numeral 20a in FIG. 14) connected to the intake port 9 of the two intake ports 9 of each cylinder 2. Is provided, and air is allowed to flow into the combustion chamber 6 from the other intake port 9 by closing the swirl valve 16.

When a swirl flow S is generated in the combustion chamber 6 as described above, a plurality of discharge plugs 13 are provided, and the discharge electrode portion of at least one of the plurality of discharge plugs 13 (discharge plug 13A) is provided. 13a executes the first discharge, and the discharge electrode portion 13a of the remaining discharge plug 13 (discharge plug 13B) executes the second discharge. As shown in FIG. 14, the discharge plug 13A is arranged on the outer peripheral portion of the ceiling wall of the combustion chamber 6. In FIG. 14, the discharge plugs 13A are arranged at two locations on the outer peripheral portion of the ceiling wall of the combustion chamber 6 on a straight line L that passes through the center of the cylinder 2 and extends in the cylinder row direction when viewed from the central axis direction of the cylinder 2. ing. The discharge plug 13A may be arranged at any one of the two locations, and in this case, it is preferable that the discharge plug 13A is arranged at a location closer to the other intake port 9. The discharge plug 13B is arranged in the vicinity of 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 opening 9a on the flow direction advancing side of the swirl flow S. The portion between the opening 10a and the combustion chamber 6 faces the combustion chamber 6, and the discharge electrode portion 13a of the discharge plug 13B faces the combustion chamber 6 from the vicinity of the center of the ceiling surface of the combustion chamber 6 (the portion between the two openings 9a). It will be.

Further, when the swirl flow S is generated in the combustion chamber 6, fuel is supplied from the fuel injection valve 14 when the discharge electrode portion 13a facing the combustion chamber 6 of the discharge plug 13A is executing the first discharge. It may be sprayed. In this case, the periphery of the discharge electrode portion 13a executing the first discharge is a fuel lean of the first predetermined air-fuel ratio or more due to the air sucked into the combustion chamber 6 and the fuel injected from the fuel injection valve 14. Any air-fuel mixture (air-fuel mixture with a fairly large air-fuel ratio that can be basically regarded as air) can generate active species by executing the first discharge.

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

The present invention is a premixed compression ignition type that 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 self-ignites a mixture of fuel and air in the combustion chamber. Useful for engines.

1 Premixed compression ignition engine 1a Engine body 2 Cylinder 5 Piston 5a Crown surface 6 Combustion chamber 13 Discharge plug 13a Discharge electrode part (plasma generation means)
14 Fuel injection valve 91 Voltage application circuit (plasma generation means)
100 ECU (control means)

Claims (4)

A premixed compression ignition engine having an engine body having a cylinder in which a combustion chamber is formed and self-igniting a mixture of fuel and air in the combustion chamber.
The geometric compression ratio of the engine body is 16 or more.
A fuel injection valve that injects fuel into the combustion chamber and
A plasma generation means having one or a plurality of discharge electrode portions and generating non-equilibrium plasma in the discharge electrode portion by discharging at the discharge electrode portion.
A control means for controlling the operation of the plasma generation means is provided.
The above control means
In the intake stroke during operation of the engine body, the fuel lean of the first predetermined air-fuel ratio or more due to the air sucked into the combustion chamber or the air and the fuel injected into the combustion chamber by the fuel injection valve. The first discharge is executed by at least one discharge electrode portion of the plasma generation means so as to irradiate the non-equilibrium plasma with respect to the air-fuel mixture.
In the compression stroke, the fuel injected into the combustion chamber by the fuel injection valve, or the fuel-rich mixture of the air and the fuel, which is smaller than the first predetermined air-fuel ratio and less than the second predetermined air-fuel ratio. On the other hand, so as to irradiate the non-equilibrium plasma, the second discharge is executed at the same or different discharge electrode portion of the plasma generation means as the discharge electrode portion where the first discharge is executed. A premixed compression ignition engine characterized by being fueled. In the premixed compression ignition engine according to claim 1,
The control means generates the active species, which is a substance that promotes the combustion of the air-fuel mixture in the combustion chamber, by executing the first discharge in the intake stroke, and also causes the second discharge in the compression stroke. A premixed compression ignition engine characterized by being configured to generate an inhibitory species, which is a substance that suppresses the combustion of the air-fuel mixture in the combustion chamber by being executed. In the premixed compression ignition engine according to claim 1 or 2.
A tumble flow of inhaled air is generated in the combustion chamber.
The plasma generating means is characterized by having a discharge electrode portion that faces the combustion chamber from the vicinity of the center of the ceiling surface of the combustion chamber and executes both the first discharge and the second discharge. Premixed compression ignition engine. In the premixed compression ignition engine according to claim 1 or 2.
A swirl flow of inhaled air is generated in the combustion chamber.
The plasma generating means faces the combustion chamber from the outer peripheral portion of the ceiling surface of the combustion chamber and faces the combustion chamber from the vicinity of the discharge electrode portion that executes the first discharge and the center of the ceiling surface of the combustion chamber. A premixed compression ignition engine characterized by having a discharge electrode portion for executing the second discharge.

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