JP7010141B2 - Engine combustion control method and combustion control device - Google Patents

Description

The techniques disclosed herein belong to the technical fields relating to engine combustion control methods and combustion control devices.

Conventionally, an engine provided with a plasma generating means for generating plasma in a combustion chamber by applying a voltage between electrodes has been known.

For example, Patent Document 1 describes an ignition plug (plasma generating means) in which a discharge is generated between the center electrode and the ground electrode, a first current meter for measuring the current flowing through the center electrode, and a current flowing through the ground electrode. When a short pulse electric field that has a second current to be measured and forms a low temperature plasma state (non-equilibrium plasma state) is generated between the electrodes, the current value measured by the first current meter and the second current meter An engine (internal engine) that measures the flow velocity of the gas flowing between the electrodes is disclosed from the current value measured in.

Japanese Unexamined Patent Publication No. 2014-141919

By the way, as a result of diligent research by the present inventors, when a voltage is applied between the electrodes of the plasma generating means so as to generate a non-equilibrium plasma in the combustion chamber, a substance that promotes combustion of the air-fuel mixture in the vicinity of the electrodes (for example, ozone). It was found that (O3) and OH) were generated, and the decomposition (lowering) of the fuel was promoted in the vicinity of the electrodes, so that the combustion stability of the engine was improved. In particular, when the ignitability of the air-fuel mixture is required, if non-equilibrium plasma is generated in the latter stage of the compression stroke, the air-fuel mixture becomes easy to ignite and the ignitability of the engine is improved.

However, the pressure in the combustion chamber is high in the latter stage of the compression stroke, and a large amount of ions and molecules are present between the electrodes of the plasma generating means. When a large amount of ions or molecules are present between the electrodes, it becomes difficult for electrons to move between the electrodes, discharge is not generated between the electrodes, and non-equilibrium plasma is difficult to be generated. Therefore, there is room for improvement from the viewpoint of improving the combustion stability of the engine by generating non-equilibrium plasma in the latter stage of the compression stroke.

The technique disclosed herein has been made in view of these points, and its purpose is to efficiently generate non-equilibrium plasma even in the latter half of the compression stroke to improve the combustion stability of the engine. There is something in it.

In order to solve the above problems, in the technique disclosed here, the cylinder in which the combustion chamber is formed, the crank shaft that is rotationally driven by the reciprocating movement of the piston inserted in the cylinder, and the combustion chamber are faced. A plasma generation means for generating plasma in the combustion chamber by discharging by applying a voltage between the electrodes and a fuel supply means for supplying fuel to the combustion chamber are provided, and the fuel is supplied by the fuel supply means. For the combustion control method of the engine in which the air-fuel mixture formed by the fuel is compressed, ignited and burned in the combustion chamber, the first pulse voltage is periodically applied between the electrodes of the plasma generating means in the latter half of the compression stroke. Immediately after the completion of the heat equilibrium plasma generation step of generating the heat equilibrium plasma by applying and discharging the heat equilibrium plasma, and immediately after the end of the heat equilibrium plasma generation step, the voltage is the same as the first pulse voltage between the electrodes of the plasma generation means. It includes a first non-equilibrium plasma generation step of generating a non-equilibrium plasma by periodically applying a two-pulse voltage to discharge the fuel.

According to this configuration, by generating thermal equilibrium plasma in the latter stage of the compression stroke, thermions are emitted from the electrodes of the plasma generation means, and free electrons are separated from the ions and molecules between the electrodes. As a result, the number of free electrons existing between the electrodes increases, so that even if a large amount of ions or molecules are present between the electrodes, discharge can be performed between the electrodes. Therefore, by executing the first non-equilibrium plasma generation step after executing the thermal equilibrium plasma generation step, the non-equilibrium plasma can be efficiently generated even in the latter stage of the compression stroke. As a result, a substance (hereinafter referred to as an active species) that generates non-equilibrium plasma in the latter half of the compression stroke to promote the decomposition (lowering) of the fuel in the vicinity of the electrodes and promotes the combustion of the air-fuel mixture in the combustion chamber is introduced. It can be generated to improve the combustion stability of the engine.

In one embodiment of the engine combustion control method, the first pulse voltage is a pulse voltage having a pulse width of the first predetermined value or more , and the second pulse voltage has a pulse width larger than the first predetermined value. It is a pulse voltage that is smaller than the second predetermined value and less than the first predetermined value.

That is, in general, non-equilibrium plasma and thermal equilibrium plasma can be separately generated by controlling the pulse width of the pulse voltage applied between the electrodes of the plasma generating means. Therefore, with the above configuration, non-equilibrium plasma and thermal equilibrium plasma can be efficiently generated according to the purpose. As a result, the combustion stability of the engine can be further improved.

In the combustion control method of the engine, in a period prior to the thermal equilibrium plasma generation step in the compression stroke, the second pulse voltage is repeatedly applied between the electrodes of the plasma generation means to discharge the plasma, thereby causing non-equilibrium. A second non-equilibrium plasma generation step of generating plasma may be further included.

That is, for example, in the early stage of the compression stroke, the in-cylinder pressure is not so high, and it is possible to generate a non-equilibrium plasma even after the thermal equilibrium plasma is generated. Therefore, by generating the non-equilibrium plasma before the thermal equilibrium plasma is generated and at the time when the non-equilibrium plasma can be generated, the active species can be generated in the combustion chamber. This makes it easier for the air-fuel mixture to burn in the combustion chamber, and the combustion stability of the engine can be further improved.

In the combustion control method of the engine, the first non-equilibrium plasma generation step may be a step executed within 5 ° in the crank angle after the completion of the thermal equilibrium plasma generation step.

That is, in the compression stroke, since the air-fuel mixture is flowing in the combustion chamber, the electrons emitted in the thermal equilibrium plasma generation step move from between the electrodes of the plasma generation means due to the flow of the air-fuel mixture. Therefore, after the thermal equilibrium plasma generation step, the first non-equilibrium plasma generation step is executed within 5 ° in the crank angle to generate the non-equilibrium plasma while the electrons do not move much from between the electrodes. As a result, non-equilibrium plasma can be efficiently generated in the latter stage of the compression stroke, and combustion of the air-fuel mixture in the combustion chamber can be promoted. As a result, the combustion stability of the engine can be further improved.

In the combustion control method of the engine, the engine may be an engine having a geometric compression ratio of 15 or more.

That is, when the geometric compression ratio of the engine is 15 or more, the in-cylinder pressure tends to increase in the latter stage of the compression stroke of the piston. Therefore, it is difficult to generate non-equilibrium plasma in the combustion chamber in the latter stage of the compression stroke. Therefore, if the geometric compression ratio of the engine is 15 or more, the non-equilibrium plasma is generated in the latter half of the compression stroke by executing the thermal equilibrium plasma generation step before executing the first non-equilibrium plasma generation step. By making it easier, the effect of improving the combustion stability of the engine can be more appropriately exhibited.

Another aspect of the technique according to the present disclosure is the technique according to the combustion control device of the engine. Specifically, it includes a cylinder in which a combustion chamber is formed, a crank shaft that is rotationally driven by the reciprocating movement of a piston inserted in the cylinder, and a fuel supply means for supplying fuel to the combustion chamber. The combustion control device of the engine that compresses, ignites and burns the air-fuel mixture formed by the fuel supplied by the fuel supply means in the combustion chamber is arranged so as to face the combustion chamber, and a voltage is applied between the electrodes. Further, a plasma generation means for generating plasma in the combustion chamber by electric discharge and a control means for controlling the operation of the plasma generation means are further provided, and the control means is used between the electrodes of the plasma generation means in the latter stage of the compression stroke. In addition, the thermal equilibrium plasma generation control for generating the thermal equilibrium plasma is executed by periodically applying the first pulse voltage to discharge the battery, and immediately after the end of the thermal equilibrium plasma generation control, between the electrodes of the plasma generation means. In addition, the first non-balanced plasma generation control for generating a non-balanced plasma is executed by periodically applying a second pulse voltage , which is the same voltage as the first pulse voltage, to discharge the battery. Yes, it was supposed to be.

Even in this configuration, by generating thermal equilibrium plasma in the latter stage of the compression stroke, thermions are emitted from the electrodes of the plasma generation means, and free electrons are separated from the ions and molecules between the electrodes. As a result, non-equilibrium plasma can be efficiently generated even in the latter stage of the compression stroke. As a result, the combustion stability of the engine can be improved.

In one embodiment of the combustion control device of the engine, the first pulse voltage is a pulse voltage having a pulse width of the first predetermined value or more , and the second pulse voltage has a pulse width larger than the first predetermined value. It is a pulse voltage that is smaller than the second predetermined value and less than the first predetermined value.

According to this configuration, non-equilibrium plasma and thermal equilibrium plasma can be efficiently generated according to the purpose. As a result, the combustion stability of the engine can be further improved.

In the combustion control device of the engine, the control means repeats the second pulse voltage in a period prior to executing the thermal equilibrium plasma generation control in the compression stroke in addition to the first non-equilibrium plasma generation control. It may be configured to apply and perform a second non-equilibrium plasma generation control to generate a non-equilibrium plasma.

According to this configuration, by generating the non-equilibrium plasma before the thermal equilibrium plasma is generated and at the time when the non-equilibrium plasma can be generated, the active species that promotes the combustion of the air-fuel mixture is generated in the combustion chamber. Can be done. This makes it easier for the air-fuel mixture to burn in the combustion chamber, and the combustion stability of the engine can be further improved.

In the combustion control device of the engine, the control means may be configured to execute the first non-equilibrium plasma generation control within 5 ° in the crank angle after the end of the thermal equilibrium plasma generation control.

According to this configuration, non-equilibrium plasma can be generated while the electrons do not move much from the electrodes of the plasma generating means. As a result, non-equilibrium plasma can be appropriately generated in the latter stage of the compression stroke, and combustion of the air-fuel mixture in the combustion chamber can be promoted. As a result, the combustion stability of the engine can be further improved.

In the combustion control device of the engine, the engine may be an engine having a geometric compression ratio of 15 or more.

According to this configuration, by executing the thermal equilibrium plasma generation step before executing the non-equilibrium plasma generation step, it is easy to generate the non-equilibrium plasma in the latter half of the compression stroke, and the combustion stability of the engine is improved. The effect can be exerted more appropriately.

In the combustion control method of the engine including the second non-equilibrium plasma generation step, the period of the second non-equilibrium plasma generation step is longer than the period of the thermal equilibrium plasma generation step and the period of the first non-equilibrium plasma generation step. , May be the configuration.

In the combustion control device of the engine that executes the second non-equilibrium plasma generation control, the period of the second non-equilibrium plasma generation control is larger than the period of the thermal equilibrium plasma generation control period and the period of the first non-equilibrium plasma generation control. It may be long.

As described above, according to the technique disclosed here, by generating the non-equilibrium plasma after generating the thermal equilibrium plasma, it becomes easy to generate the non-equilibrium plasma even in the latter stage of the compression stroke. As a result, non-equilibrium plasma can be generated in the latter half of the compression stroke to improve the combustion stability of the engine.

It is a schematic block diagram of the engine system to which the combustion control device which concerns on an exemplary embodiment is applied. It is a schematic diagram which shows the periphery of the electrode of a discharge plug. It is a block diagram which shows the control system of an engine. It is a map which shows the generation condition of the non-equilibrium plasma and the thermal equilibrium plasma. 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 graph which shows an example of the waveform of the pulse voltage at the time of generating a thermal equilibrium plasma. It is a figure which shows typically the distribution of an ion, a molecule and an electron between the electrodes of a discharge plug in the latter part of a compression stroke, and shows the state before the generation of a thermal equilibrium plasma. It is a figure which shows typically the distribution of an ion, a molecule and an electron among the electrodes of a discharge plug in the latter part of a compression stroke, and shows the state after the generation of a thermal equilibrium plasma. It is a conceptual diagram which shows typically the state in the combustion chamber when the non-equilibrium plasma is generated after the thermal equilibrium plasma is generated. It is a conceptual diagram which shows an example of the generation time of a non-equilibrium plasma and a thermal equilibrium plasma. It is a flowchart which shows the processing operation of PCM at the time of executing the non-equilibrium plasma generation control and the thermal equilibrium plasma generation control.

Hereinafter, exemplary embodiments will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of the engine 1 to which the combustion control device according to the present embodiment is applied. The engine 1 of the present embodiment is an engine mounted on a vehicle. The engine 1 includes an engine main body 1a, an intake passage 20 for introducing combustion air into the engine main body 1a, and an exhaust passage 30 for discharging the exhaust generated by the engine main body 1a.

The engine body 1a is an in-line 4-cylinder type, and the four cylinders 2 are arranged in series in a direction orthogonal to the paper surface of FIG. The engine body 1a is used as a drive source for the vehicle.

The engine body 1a includes a cylinder block 3 in which a cylinder 2 is formed, a cylinder head 4 provided on the upper surface of the cylinder block 3, and a piston fitted to the cylinder 2 so as to be able to reciprocate (here, move up and down). Has 5 and.

Cylinder 2 is a cylinder in which a combustion chamber 6 is formed. Specifically, the combustion chamber 6 is formed above the piston 5 in the cylinder 2. 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. In the combustion chamber 6, the combustion cycle of the engine 1, that is, each of the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke is repeated in this order. In the following description, the space formed between the upper surface of the piston 5 and the ceiling surface of the combustion chamber 6 in the inner space of the cylinder 2 regardless of the position of the piston 5 and the combustion state of the air-fuel mixture is referred to as a combustion chamber 6.

A water jacket 3a through which engine cooling water flows is formed around the cylinder 2 in the cylinder block 3. The water jacket 3a is formed in the cylinder block 3 so as to surround the four cylinders 2.

The piston 5 is connected to the crankshaft 7 via a connecting rod 8 in the cylinder block 3. The crankshaft 7 is rotationally driven by the reciprocating motion of the piston 5. On the upper surface of the piston 5, a cavity is formed in which a region including the central portion thereof is recessed on the opposite side (lower side) of the cylinder head 4.

The geometric compression ratio of the engine body 1a, that is, the ratio of the volume of the combustion chamber 6 when the piston 5 is at the bottom dead center and the volume of the combustion chamber 6 when the piston 5 is at the top dead center is the present implementation. In the form, it is set to 15 or more, particularly 15 to 25 (for example, about 17).

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 a mixture of fuel and air burns in the combustion chamber 6. An exhaust port 10 for leading the exhaust generated by the above to the exhaust passage 30 is formed. Two intake ports 9 and two exhaust ports 10 are formed for each cylinder 2.

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

The cylinder head 4 is provided with an injector (fuel supply means) 14 for supplying (injecting) fuel into the combustion chamber 6. The injector 14 is attached so that the tip end portion on which the injection port is formed is located near the center of the ceiling surface of the combustion chamber 6 and faces the center of the combustion chamber 6. The injector 14 has a plurality of nozzles at its tip, and has a cone shape (specifically, a hollow cone shape) centered on the central axis of the cylinder 2 from the vicinity of the center of the ceiling surface of the combustion chamber toward the crown surface of the piston 5. It is configured to inject fuel. The taper angle (spraying angle) of the cone is, for example, 90 ° to 100 °. The specific configuration of the injector 14 is not limited to this, and may be a single injector.

The injector 14 injects fuel pumped from a high-pressure pump (not shown) into the combustion chamber 6. The injection pressure of the injector 14 is increased up to about 70 MPa.

The cylinder head 4 is provided so as to face the combustion chamber 6 and is provided with a discharge plug 13 for generating plasma in the combustion chamber 6. As shown in FIG. 2, a center electrode 13a and a ground electrode 13b are formed at the tip of the discharge plug 13. The center electrode 13a has a rod shape, and the portion other than the tip is covered with the insulator 13c. The ground electrode 13b has a cylindrical shape concentric with the center electrode 13a. The center electrode 13a is connected to a power source (not shown), and when a voltage is applied from the power source, a discharge is made between the center electrode 13a and the ground electrode 13b. Then, when a discharge is made between the center electrode 13a and the ground electrode 13b, plasma is generated in the combustion chamber 6 by the energy of the discharge. From this, the discharge plug 13 corresponds to a plasma generation means for generating plasma in the combustion chamber 6 by discharging by applying a voltage between the electrodes 13a and 13b.

The intake passage 20 is provided with an air cleaner 21 and a throttle valve 22 for opening and closing the intake passage 20 in order from the upstream side. 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.

The exhaust passage 30 is provided with a purification device 31 for purifying the exhaust gas. The purification device 31 has, for example, a built-in three-way catalyst.

The exhaust passage 30 is provided with an EGR device 40 for returning a part of the exhaust gas passing through the exhaust passage 30 to the intake passage 20 as EGR gas. The EGR device 40 opens and closes the EGR passage 41 and the EGR passage 41 that communicate the portion of the intake passage 20 downstream of the throttle valve 22 and the portion of the exhaust passage 30 upstream of the purification device 31. It has an EGR valve 42.

The engine 1 according to the present embodiment is not provided with a supercharger. However, the technology according to the present disclosure does not exclude application to an engine equipped with a turbocharger.

FIG. 3 shows the control system of the engine 1. The engine 1 according to the present embodiment is collectively controlled by a powertrain control module 100 (hereinafter referred to as PCM100) as a control device. The PCM 100 is composed of a CPU, a memory, a counter timer group, an interface, and a microprocessor having a path connecting these units.

The vehicle is equipped with various sensors. The PCM 100 is electrically connected to these sensors, and a detection signal from each sensor is input to the PCM 100. For example, the engine 1 detects an engine temperature sensor SN1 that detects the temperature of the engine body 1a, an airflow sensor SN2 that detects the intake flow rate flowing into the intake passage 20, and the pressure of the intake air supplied to the combustion chamber 6. An intake pressure sensor SN3, a crank angle sensor SN4 that detects the rotation angle of the crankshaft 7, and an accelerator opening sensor SN5 that detects the opening (accelerator opening) of an accelerator pedal (accelerator opening) that is not shown and is operated by the driver. One is provided for each cylinder 2, and an in-cylinder pressure sensor SN6 for detecting the pressure in each cylinder 2 is provided.

The engine temperature sensor SN1 detects the temperature of the engine body 1a by detecting, for example, the temperature of the engine cooling water flowing through the water jacket 3a. The engine temperature sensor SN1 may be a sensor that detects the temperature of the engine body 1a by detecting the exhaust temperature, and detects the temperature of the engine body 1a by detecting the oil temperature of the engine oil. It may be a sensor.

The PCM100 calculates the rotation speed (engine rotation speed) of the engine body 1a from the detection result of the crank angle sensor SN4. The PCM 100 calculates the engine load from the detection result of the accelerator opening sensor SN5. The PCM 100 calculates the heat generation rate in the combustion chamber 6 from the detection result of the in-cylinder pressure sensor SN6.

The PCM 100 executes various calculations based on the input signals from the sensors SN1 to SN6 and the like to control each part of the engine 1 such as the discharge plug 13, the injector 14, the throttle valve 22, and the EGR valve 42.

<Generation of plasma>
In the present embodiment, the combustion stability of the engine 1 is ensured by generating the non-equilibrium plasma and the thermal equilibrium plasma in the combustion cycle of the engine 1. 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. .. Further, the thermal 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 in a thermal equilibrium state as the gas temperature in the combustion chamber 6 rises. ..

In the present embodiment, the non-equilibrium plasma and the thermal equilibrium plasma are tailored to the purpose by controlling the pulse voltage applied between the electrodes 13a and 13b of the discharge plug 13, and particularly by controlling the pulse width of the pulse voltage. , Generate each. 4 to 6 show the generation conditions of the non-equilibrium plasma and the thermal equilibrium plasma. The horizontal axis of FIG. 4 is the pulse width, which is shown on a logarithmic scale. On the other hand, the vertical axis of FIG. 4 is the peak value of the applied voltage and is shown on a logarithmic scale. As shown in FIG. 4, it can be seen that when the pulse width is shortened, non-equilibrium plasma is generated, and when the pulse width is lengthened, thermal equilibrium plasma is generated. This is because ions and molecules are considerably larger than electrons, and at a pulse voltage with a short pulse width, only electrons react and ions and molecules hardly react.

In the present embodiment, the non-equilibrium plasma and the thermal equilibrium plasma are generated according to the purpose, mainly by changing the pulse width. Specifically, as shown in FIG. 5, when the PCM100 generates a thermal equilibrium plasma, the PCM100 applies a first pulse voltage having a peak voltage of 10 kV and a pulse width of the first predetermined value or more to the electrodes 13a of the discharge plug 13. It is applied between 13b. Further, when the thermal equilibrium plasma is generated, the PCM 100 repeatedly discharges a pulse voltage having a pulse width of 10 μsec or less at a frequency of 100 kHz and a pulse voltage having a pulse width of more than 10 μsec at a frequency as large as possible. As shown in FIGS. 4 and 5, the first predetermined value is, for example, 1 μsec. More specifically, when the PCM100 executes the thermal equilibrium plasma generation control described later, it basically applies a first pulse voltage having a peak voltage of 10 kV and a pulse width of 1 μsec between the electrodes 13a and 13b of the discharge plug 13. I am trying to apply it. From the viewpoint of extending the life of the discharge plug 13, it is preferable to make the pulse width of the first pulse voltage as short as possible.

On the other hand, as shown in FIG. 6, when the PCM100 generates a non-equilibrium plasma, the peak voltage is 10 kV, the pulse width is smaller than the first predetermined value, the second predetermined value is equal to or more than the second predetermined value, and the pulse width is less than the first predetermined value. A pulse voltage is applied between the electrodes 13a and 13b of the discharge plug 13. Further, when the non-equilibrium plasma is generated, the PCM 100 repeatedly discharges the above pulse voltage at a frequency of 100 kHz. As shown in FIGS. 4 and 6, the second predetermined value is, for example, 0.01 μsec. More specifically, when the PCM100 executes the first and second non-equilibrium plasma generation control described later, it basically discharges a second pulse voltage having a peak voltage of 10 kV and a pulse width of 0.1 μsec. The voltage is applied between the electrodes 13a and 13b of 13.

As shown in FIG. 4, the peak voltage in the first pulse voltage in the thermal equilibrium plasma generation control and the second pulse voltage in the first and second non-equilibrium plasma generation control is in the range of 1 kV or more and 30 kV or less. Then, it may be changed based on the in-cylinder pressure or the like.

<Combustion control>
In the present embodiment, compression ignition combustion (CI combustion) is performed in the entire operating region of the engine 1. Specifically, fuel is injected into the combustion chamber 6 from the injector 14 before the compression top dead center, and the mixture of the fuel and air is compressed in the combustion chamber 6 to raise the temperature and perform compression. Self-ignite the air-fuel mixture near dead center.

Here, it is the mass ratio of gas and fuel in the air-fuel mixture in the combustion chamber 6 when the amount of fuel supplied to the intake air is small (lean), such as in a low load operating region where the engine load is a predetermined load or less. The air-fuel mixture is in an operating condition where the G / F is 25 or more, or when the EGR ratio, which is the ratio of the amount of EGR gas (exhaust) in the gas to the total amount of gas in the combustion chamber 6, is 20% or more. It is difficult to self-ignite and the combustion stability tends to decrease. Therefore, in the present embodiment, the combustion stability of the engine 1 is improved by generating non-equilibrium plasma in the latter stage of the compression stroke. In this specification, the first half and the second half of the compression stroke are the first half of the compression stroke (the period at the crank angle) when the execution period (the period at the crank angle) is evenly divided into two. The latter period (the period on the retard side) corresponds to the latter period.

That is, when the non-equilibrium plasma is generated, the decomposition (lowering) of the fuel is promoted in the combustion chamber 6 (the low temperature oxidation reaction proceeds). As a result, the temperature rise of the air-fuel mixture in the combustion chamber 6 is promoted, ignition and combustion are facilitated, and the combustion stability of the engine 1 is improved. Further, when a non-equilibrium plasma is generated, a substance (for example, ozone (O3), OH, etc., hereinafter referred to as an active species) that promotes combustion of the air-fuel mixture in the combustion chamber 6 is generated in the combustion chamber 6. Will be done. As a result, after the air-fuel mixture is ignited in the combustion chamber 6, the flame is easily propagated, and the air-fuel mixture is easily burned.

However, in the latter half of the compression stroke, the in-cylinder pressure is high and it is difficult to generate non-equilibrium plasma. Therefore, in the present embodiment, the PCM 100 executes the thermal equilibrium plasma generation control for generating the thermal equilibrium plasma before executing the non-equilibrium plasma generation control for generating the non-equilibrium plasma. Specifically, in the latter half of the compression stroke, the PCM 100 generates a heat-balanced plasma by applying a first pulse voltage such that a heat-balanced plasma is generated in the combustion chamber 6 between the electrodes 13a and 13b of the discharge plug 13 to discharge the plasma. Immediately after the thermal equilibrium plasma generation control is completed, a second pulse voltage is applied between the electrodes 13a and 13b of the discharge plug 13 so as to generate unbalanced plasma in the combustion chamber 6. By discharging, the first non-equilibrium plasma generation control for generating non-equilibrium plasma is executed.

FIG. 7 schematically shows the distribution of ions, molecules, and free electrons between the electrodes 13a and 13b of the discharge plug 13 before the thermal equilibrium plasma is generated. As shown in FIG. 7, the in-cylinder pressure is high in the vicinity of the compression top dead center, and a large amount of ions and molecules forming an air-fuel mixture are formed between the center electrode 13a and the ground electrode 13b of the discharge plug 13. exist. Therefore, even if a voltage is applied between the electrodes 13a and 13b, it is difficult for free electrons to move between the electrodes 13a and 13b and it is difficult for them to be discharged. Therefore, it is difficult to generate non-equilibrium plasma.

When the thermal equilibrium plasma generation control is executed from the state of FIG. 7, the number of free electrons between the electrodes 13a and 13b increases as shown in FIG. This is because the thermal equilibrium plasma generation control causes thermions to be emitted from the electrodes 13a and 13b of the discharge plug 13, and free electrons to be separated from the ions and molecules between the electrodes 13a and 13b. If the number of free electrons between the electrodes 13a and 13b increases and the number density of free electrons increases, even if a large amount of ions or molecules are present between the electrodes 13a and 13b, they can be discharged between the electrodes 13a and 13b. Is possible. This makes it possible to generate non-equilibrium plasma.

FIG. 9 schematically shows the state in the combustion chamber 6 when the thermal equilibrium plasma generation control is executed in the latter half of the compression stroke. In FIG. 9, the crank angle of the compression top dead center is set to 0 °, whereas the advance angle side (the time earlier than the compression top dead center) is represented by a minus, and the retard side (later than the compression top dead center) is shown. Time) is shown as a plus. The compression stroke is a period of −180 ° to 0 °.

As shown in FIG. 9, when the thermal equilibrium plasma generation control is executed in the latter stage of the compression stroke, a region S having a high number density of free electrons is formed around the electrodes 13a and 13b of the discharge plug 13. Immediately after the end of the thermal equilibrium plasma generation control, if the first non-equilibrium plasma generation control is executed, the decomposition of the fuel is promoted (the low temperature oxidation reaction proceeds) and the active species is produced in the region S. It is formed. As a result, the flame propagates from around the electrodes 13a and 13b, and the air-fuel mixture burns in the combustion chamber 6. Therefore, the combustion stability of the engine 1 is improved.

When the in-cylinder pressure becomes 4 MPa or more, it becomes difficult to generate the thermal equilibrium plasma itself. Therefore, the thermal equilibrium plasma generation control is executed in the latter half of the compression stroke when the in-cylinder pressure is less than 4 MPa. Further, the period for executing the thermal equilibrium plasma generation control is set to be considerably shorter than the period for executing the first non-equilibrium plasma generation control. Specifically, in the present embodiment, the thermal equilibrium plasma generation control is executed only for a period in which flame nuclei are not formed around the electrodes 13a and 13b of the discharge plug 13, for example, a period of about 5 ° at the crank angle .

In the present embodiment, the end time of the first non-equilibrium plasma generation control is set to a time near the start of the low temperature oxidation reaction in the combustion chamber 6. Specifically, the end time of the first non-equilibrium plasma generation control is set to 10 ° to 30 ° before the compression top dead center (in FIGS. 9 and 10, when the end time is 30 ° before the compression top dead center. Is illustrated). Further, the period for carrying out the first non-equilibrium plasma generation control is basically set to a period of about 15 ° in terms of the crank angle. The period for executing the first non-equilibrium plasma generation control and the timing for ending the first non-equilibrium plasma generation control may be changed depending on the engine load and the engine speed. For example, the higher the engine load, the earlier the end time of the first non-equilibrium plasma generation control may be set (the time on the advance angle side).

Here, in the latter stage of the compression stroke, the air-fuel mixture is flowing in the combustion chamber 6. Therefore, if the period from the execution of the thermal equilibrium plasma generation control to the execution of the non-equilibrium plasma generation control is long, the free electrons emitted by the thermal equilibrium plasma generation control are discharged by the flow of the air-fuel mixture. It moves from between the electrodes 13a and 13b of 13. Therefore, in the present embodiment, the PCM 100 is configured to execute the first non-equilibrium plasma generation control within 5 ° in the crank angle after the end of the thermal equilibrium plasma generation control. That is, the above-mentioned "immediately after the end of the thermal equilibrium plasma generation control" means a period within 5 ° in terms of the crank angle. The period within 5 ° of the crank angle after the end of the thermal equilibrium plasma generation control includes the same time as the end of the thermal equilibrium plasma generation control.

If the first non-equilibrium plasma generation control is executed within a period of 5 ° or less in the crank angle after the end of the thermal equilibrium plasma generation control, free electrons emitted by the thermal equilibrium plasma generation control are emitted from between the electrodes 13a and 13b. A non-equilibrium plasma can be generated before it has moved much. As a result, non-equilibrium plasma can be efficiently generated in the latter stage of the compression stroke. As a result, the combustion stability of the engine 1 can be further improved.

In the present embodiment, when the thermal equilibrium plasma generation control and the first non-equilibrium plasma generation control are not continuous, that is, the first non-equilibrium plasma generation control is started at the same time as the end of the thermal equilibrium plasma generation control. When not, the application of the voltage to the discharge plug 13 is not stopped from the end of the thermal equilibrium plasma generation control to the start of the first non-equilibrium plasma generation control. Specifically, from the end of the thermal equilibrium plasma generation control to the start of the first non-equilibrium plasma generation control, a pulse voltage to the extent that non-equilibrium plasma is not generated is applied. As a result, after the completion of the thermal equilibrium plasma generation control, the discharge state between the electrodes 13a and 13b of the discharge plug 13 can be maintained, and the process can smoothly shift to the first non-equilibrium plasma generation control.

Here, in the present embodiment, as shown in FIG. 10, the PCM100 is described in detail in a period prior to executing the thermal equilibrium plasma generation control in the compression stroke in addition to the first non-equilibrium plasma generation control. Is to execute the second non-equilibrium plasma generation control for generating non-equilibrium plasma by repeatedly applying the second pulse voltage between the electrodes 13a and 13b of the discharge plug 13 in the first half of the compression stroke to discharge the voltage. It is configured. That is, in the early stage of the compression stroke, the in-cylinder pressure is not so high, and it is possible to generate a non-equilibrium plasma even after the thermal equilibrium plasma is generated. Therefore, by generating the non-equilibrium plasma in the early stage of the compression stroke, the active species can be generated in the combustion chamber 6. As a result, the air-fuel mixture becomes easier to burn in the combustion chamber 6, and the combustion stability of the engine 1 can be further improved. Further, by generating the active species in the early stage of the compression stroke, the generated active species diffuse into the combustion chamber 6 by the flow of the air-fuel mixture. This makes it easier for the flame to propagate after the air-fuel mixture is ignited. Therefore, the combustion stability of the engine 1 can be further improved.

From the viewpoint of improving the combustion stability of the engine 1, it is preferable to perform the second non-equilibrium plasma generation control for as long as possible. Therefore, in the present embodiment, as shown in FIG. 10, the PCM100 is the second non-equilibrium plasma over a period of more than half of the period in the first half of the compression stroke (that is, a period of 1/4 or more of the entire compression stroke). Execute generation control. More specifically, the PCM 100 executes the second non-equilibrium plasma generation control from a period before half of the first half of the compression stroke to just before entering the second half of the compression stroke. As a result, as many active species as possible can be produced in the combustion chamber 6, and the combustion stability of the engine 1 can be further improved.

Next, the processing operation of the PCM 100 when the non-equilibrium plasma generation control and the thermal equilibrium plasma generation control are executed will be described with reference to the flowchart of FIG. The processing operation based on this flowchart is executed every one combustion cycle while the engine 1 is operating.

First, in step S1, the PCM 100 reads information from each sensor SN1 to SN6.

In the next step S2, the PCM 100 determines whether or not the compression stroke has been entered. When YES in the compression stroke, the PCM 100 proceeds to step S3, while when NO in the compression stroke, the determination in step S2 is repeated until the compression stroke is entered.

In step S3, the PCM 100 starts the second non-equilibrium plasma generation control.

Next, in step S4, the PCM 100 determines whether or not the compression stroke has entered the latter stage. When YES in the latter half of the compression stroke, the PCM 100 proceeds to step S5, while in the case of NO which has not yet entered the compression stroke, the determination in step S2 is repeated until the latter half of the compression stroke is entered, and the second non-equilibrium is described. The plasma generation control is continuously executed.

In step S5, the PCM 100 ends the second non-equilibrium plasma generation control.

In the next step S6, the PCM 100 sets a period for executing the thermal equilibrium plasma generation control and the first non-equilibrium plasma generation control. In step S6, the PCM 100 sets a period for executing the thermal equilibrium plasma generation control and the first non-equilibrium plasma generation control based on the engine load and the engine speed.

In the following step S7, the PCM 100 starts the thermal equilibrium plasma generation control. Then, when the period set in step S6 (basically, about 5 ° in the crank angle) has elapsed, the thermal equilibrium plasma generation control is terminated in the next step S8.

In the next step S9, the first non-equilibrium plasma generation control is started. Then, when the period set in step S6 (basically, about 15 ° in the crank angle) has elapsed, the first non-equilibrium plasma generation control is terminated in the next step S10. After the above step S10, it returns.

Therefore, in the present embodiment, in the latter half of the compression stroke, the thermal equilibrium plasma generation control for generating the thermal equilibrium plasma by applying the first pulse voltage into the combustion chamber 6 between the electrodes 13a and 13b of the discharge plug 13 to discharge the electric discharge. Is executed, and immediately after the end of the thermal equilibrium plasma generation control, a second pulse voltage is applied between the electrodes 13a and 13b of the discharge plug 13 to discharge the unbalanced plasma, so that the first non-equilibrium plasma generation control is generated. To execute. As a result, non-equilibrium plasma can be efficiently generated in the combustion chamber 6 even in the latter stage of the compression stroke, and the combustion stability of the engine 1 can be improved.

Further, in the present embodiment, since the second non-equilibrium plasma generation control is executed in the period prior to the thermal equilibrium plasma generation control in the compression stroke, the in-cylinder pressure is not so high and the non-equilibrium plasma can be generated. Also, the above active species are produced in the combustion chamber 6. As a result, the air-fuel mixture becomes easier to burn in the combustion chamber 6, and the combustion stability of the engine 1 can be further improved.

Further, in the present embodiment, the first non-equilibrium plasma generation control is executed within 5 ° in the crank angle after the end of the thermal equilibrium plasma generation control, so that the air-fuel mixture flows in the combustion chamber 6. Even in such a situation, non-equilibrium plasma can be generated while the free electrons emitted by the thermal equilibrium plasma generation control do not move much from between the electrodes 13a and 13b. As a result, non-equilibrium plasma can be efficiently generated in the latter stage of the compression stroke, and combustion of the air-fuel mixture in the combustion chamber 6 can be promoted. As a result, the combustion stability of the engine 1 can be further improved.

The technique disclosed herein 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-described embodiment, the pulse width of the first pulse voltage is set to the first predetermined value or more (1 μsec or more), but the present invention is not limited to this, and the pulse width of the first pulse voltage is set to be less than the first predetermined value. You may. In this case, the peak voltage of the first pulse voltage may be made larger than 10 kV (for example, 20 kV). Further, the pulse width of the second pulse voltage is set to be less than the first predetermined value (less than 1 μsec), but the pulse width of the second pulse voltage is not limited to this, and the pulse width of the second pulse voltage is set to be equal to or more than the first predetermined value in the range of less than 10 μsec. You may. In this case, the peak voltage of the first pulse voltage may be set to less than 10 kV (for example, 8 kV).

Further, in the above-described embodiment, the supercharger is not provided, but in the case of an engine including the supercharger, the first in the thermal equilibrium plasma generation control is based on the supercharging pressure of the supercharger. The peak voltage of the pulse voltage and the peak voltage of the second pulse voltage in the first and second non-balanced plasma generation control may be changed.

Further, in the above-described embodiment, the pulse voltage applied between the electrodes 13a and 13b of the discharge plug 13 in the first non-equilibrium plasma generation control and the electrode 13a of the discharge plug 13 in the second non-equilibrium plasma generation control. The pulse voltage applied between 13b and 13b is the same as the pulse voltage, but different pulse voltages may be used as long as the pulse width is 0.01 μsec or more and less than 1 μsec and the peak voltage is 1 kV or more and less than 30 kV. In particular, since the pulse voltage in the second non-balanced plasma generation control is executed in the first half of the compression stroke, even if the pulse width and the peak voltage are made smaller than the pulse voltage in the first non-balanced plasma generation control, it is not. It is possible to generate a balanced plasma.

Further, the period for executing the second non-equilibrium plasma generation control may be changed according to the engine speed and the engine load as long as the period is more than half of the period in the first half of the compression stroke. Specifically, the higher the engine speed, the longer the period for executing the second non-equilibrium plasma generation control may be set. Further, the lower the engine load, the longer the period for executing the second non-equilibrium plasma generation control may be set.

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

The technology disclosed herein includes a cylinder in which a combustion chamber is formed, a crank shaft that is rotationally driven by the reciprocating motion of a piston inserted in the cylinder, and a fuel supply means that supplies fuel to the combustion chamber. It is useful for an engine that burns an air-fuel mixture formed by the fuel supplied by the fuel supply means in the combustion chamber.

1 Engine 5 Piston 6 Combustion chamber 7 Crankshaft 13 Discharge plug (plasma generation means)
13a Center electrode (electrode of plasma generation means)
13b Ground electrode (electrode of plasma generation means)
14 Injector (combustion supply means)
100 PCM (control means)

Claims (12)

A cylinder in which a combustion chamber is formed, a crank shaft that is rotationally driven by the reciprocating movement of a piston inserted in the cylinder, and a discharge that is arranged so as to face the combustion chamber and applies a voltage between electrodes. A plasma generating means for generating plasma in the combustion chamber and a fuel supply means for supplying fuel to the combustion chamber are provided, and an air-fuel mixture formed by the fuel supplied by the fuel supply means is compressed and ignited in the combustion chamber. It is a combustion control method for the engine to be burned.
In the latter stage of the compression stroke, a thermal equilibrium plasma generation step of generating a thermal equilibrium plasma by periodically applying a first pulse voltage between the electrodes of the plasma generating means to discharge the plasma.
Immediately after the end of the thermal equilibrium plasma generation step , a second pulse voltage, which is the same voltage as the first pulse voltage, is periodically applied between the electrodes of the plasma generation means to discharge the non-equilibrium plasma. A method for controlling combustion of an engine, which comprises a first non-equilibrium plasma generation step of generating. In the engine combustion control method according to claim 1,
The first pulse voltage is a pulse voltage having a pulse width equal to or larger than the first predetermined value.
The second pulse voltage is a combustion control method for an engine, wherein the pulse voltage is a pulse voltage having a pulse width equal to or more than a second predetermined value smaller than the first predetermined value and less than the first predetermined value. In the engine combustion control method according to claim 1 or 2.
In the period prior to the thermal equilibrium plasma generation step in the compression stroke, the second non-equilibrium plasma is generated by repeatedly applying the second pulse voltage between the electrodes of the plasma generation means to discharge the plasma. An engine combustion control method comprising further a plasma generation step. In the engine combustion control method according to any one of claims 1 to 3.
A combustion control method for an engine, wherein the first non-equilibrium plasma generation step is a step executed within 5 ° in a crank angle after the completion of the thermal equilibrium plasma generation step. In the engine combustion control method according to any one of claims 1 to 4.
The engine is a combustion control method for an engine, characterized in that the engine has a geometric compression ratio of 15 or more. It is provided with a cylinder in which a combustion chamber is formed, a crank shaft that is rotationally driven by the reciprocating movement of a piston inserted in the cylinder, and a fuel supply means for supplying fuel to the combustion chamber, and is supplied by the fuel supply means. It is a combustion control device of an engine that compresses, ignites and burns the air-fuel mixture formed by the produced fuel in the combustion chamber.
A plasma generating means that is arranged so as to face the combustion chamber and generates plasma in the combustion chamber by electric discharge by applying a voltage between the electrodes.
Further provided with a control means for controlling the operation of the plasma generation means,
The control means executes thermal equilibrium plasma generation control to generate thermal equilibrium plasma by periodically applying a first pulse voltage between the electrodes of the plasma generation means to discharge the plasma in the latter stage of the compression stroke. Immediately after the end of the thermal equilibrium plasma generation control , a second pulse voltage, which is the same voltage as the first pulse voltage, is periodically applied between the electrodes of the plasma generation means to discharge the non-equilibrium plasma. A combustion control device for an engine, characterized in that it is configured to perform a first non-equilibrium plasma generation control to generate. In the combustion control device for the engine according to claim 6.
The first pulse voltage is a pulse voltage having a pulse width equal to or larger than the first predetermined value.
The second pulse voltage is a combustion control device for an engine, wherein the pulse voltage is a pulse voltage having a pulse width equal to or more than a second predetermined value smaller than the first predetermined value and less than the first predetermined value. In the combustion control device of the engine according to claim 6 or 7.
In addition to the first non-equilibrium plasma generation control, the control means repeatedly applies the second pulse voltage in a period prior to executing the thermal equilibrium plasma generation control in the compression stroke to generate the non-equilibrium plasma. A combustion control device for an engine, characterized in that it is configured to perform a second non-equilibrium plasma generation control to generate. The engine combustion control device according to any one of claims 6 to 8.
The control means is a combustion control device for an engine, characterized in that the first non-equilibrium plasma generation control is executed within 5 ° in a crank angle after the end of the thermal equilibrium plasma generation control. The engine combustion control device according to any one of claims 6 to 9.
The engine is an engine combustion control device, characterized in that the engine has a geometric compression ratio of 15 or more. In the combustion control method of the engine according to claim 3,
A combustion control method for an engine, wherein the period of the second non-equilibrium plasma generation step is longer than the period of the thermal equilibrium plasma generation step and the period of the first non-equilibrium plasma generation step. In the combustion control device for the engine according to claim 8.
The combustion control device for an engine, characterized in that the period of the second non-equilibrium plasma generation control is longer than the period of the thermal equilibrium plasma generation control and the period of the first non-equilibrium plasma generation control.

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