JP2010216463A - Method for igniting internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for igniting an internal combustion engine, performing ignition with less energy than normal spark discharge, achieving the low consumption of the discharge electrode of an ignition plug, improving fuel economy, and reducing the amount of NOx emitted and the amount of CO<SB>2</SB>emitted. <P>SOLUTION: In this method for igniting the internal combustion engine, under the presence of combustible gas containing combustible material and combustion-supporting gas under positive pressure higher than atmospheric pressure, burst is generated by causing pulse streamer discharges repeatedly for a plurality of times at intervals of 100 μs or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ignition method for an internal combustion engine capable of igniting with less energy.

  An internal combustion engine is a machine that takes out power by burning fuel in a combustion chamber, and is classified into a kind of heat engine that converts thermal energy into mechanical energy. For example, a piston engine corresponds to this. A gasoline engine, which is a kind of piston engine, is also called a gasoline engine. It is an internal combustion engine that reciprocates a piston by igniting, burning, and expanding a mixture of combustible gas gasoline and air after it is compressed by the piston. is there.

  The combustion of a gasoline engine is usually started by using an ignition plug having a role of igniting (igniting) an air-fuel mixture containing gasoline by spark discharge. This spark discharge is mainly used for ignition of combustible gas. Spark discharge is excellent in that it can be ignited using a simple discharge circuit. However, since the discharge region is limited to the vicinity of the electrode of the spark plug, flame nucleation is performed in a region where heat is taken away by heat conduction in the immediate vicinity of the electrode. During lean operation or dilution operation, the nucleation region of the flame is further reduced, and thus there is a disadvantage that misfire often occurs after ignition until the flame propagates.

  In automobile gasoline engines, in order to avoid such inconvenience, the electrode volume is minimized by using a highly durable material such as iridium as the discharge electrode, and the heat absorption and heat dissipation by the electrode is reduced to reduce the cooling of the flame. It is preventing. In addition, in order to ensure flame propagation, an attempt has been made to apply a large energy for spark discharge and maintain the discharge.

  However, since it is necessary to flow a large current from the spark plug, it is necessary to increase the storage capacity. For this reason, it takes about 1 ms to store electricity. Further, the concentration of the air-fuel mixture may change near the discharge part of the spark plug due to the influence of the airflow. For this reason, when the air-fuel mixture in the vicinity of the discharge portion is in a lean state at the time of ignition, there is a risk of misfire. In order to solve these problems, attempts have been made to ensure ignition by performing spark discharge a plurality of times for each ignition (for example, see Patent Document 1). On the other hand, attempts have been made to promote flame propagation itself. For example, an ignition method using a laser (see, for example, Patent Document 2) and attempts to ignite a discharge without applying a large current by applying a high pulse voltage.

JP 2004-79458 A JP-T 8-505676

The air-fuel mass ratio (air-fuel ratio, A / F) in a conventional gasoline engine is approximately 14.7, which is close to the stoichiometric air-fuel ratio at which oxygen and fuel burn without excess or deficiency. Therefore, it is difficult to employ oxygen-rich lean burn in order to make the three-way catalyst to remove the three types of harmful gases (hydrocarbon, carbon monoxide, and nitrogen oxide) generated. Met. However, recently developed automobiles are required to improve fuel economy and reduce the amount of carbon dioxide (CO ₂ ) emitted to prevent global warming, and to satisfy these requirements. Lean burn engines are getting attention again.

  On the other hand, a three-way catalyst is necessary to remove the three types of harmful gases (hydrocarbon, carbon monoxide, and nitrogen oxide) that are generated. An exhaust gas composition having a low oxygen partial pressure is essential. Therefore, in lean burn operation where the air-fuel ratio is not large enough, the combustion temperature is still high, so nitrogen oxide is generated, and because it is rich in oxygen, it cannot be reduced with only a three-way catalyst, improving fuel efficiency. In addition, it is difficult to employ a lean burn (lean combustion) engine because there is a problem that the catalyst must be mounted in excess in an oxidizing atmosphere and the cost becomes high.

  However, if the air-fuel ratio can be sufficiently increased (equivalent ratio is sufficiently reduced) and the combustion temperature can be greatly reduced, not only the fuel consumption can be improved, but also the generation of nitrogen oxides can be suppressed, and a reduction catalyst becomes unnecessary. Therefore, it is only necessary to install a three-way catalyst for purifying the exhaust gas near the stoichiometric air-fuel ratio used at high torque and high rotation, and the cost can be reduced.

  In the conventional arc discharge ignition, the air-fuel mixture is burned by strongly swirling or tumbling the air-fuel mixture and mainly devising flame propagation. That is, since the temperature of the air-fuel mixture has to be increased to prevent the disappearance of combustion, there is a problem that the flame becomes high temperature and a large amount of nitrogen oxide is generated.

  In the arc discharge ignition, the gas is activated with a slight discharge just before the arc discharge. However, since the rise of the pulse is slow, the active state is often not reached, and the effect is almost negligible. For this reason, it is thought that the ignition by arc discharge is governed by how much current can flow. Further, according to the method of performing spark discharge a plurality of times for each ignition as disclosed in Patent Document 1, it takes about 1 ms on average for charging to supply an arc discharge current. For this reason, it has been extremely difficult to repeatedly perform arc discharge twice or more at the optimal ignition timing. In addition, since the current value is large in the arc discharge ignition, the discharge electrode of the spark plug was also consumed heavily.

The present invention has been made in view of the above-described problems of the prior art, and the object of the present invention is to ignite with less energy than a normal spark discharge, and to a discharge electrode of a spark plug. It is an object of the present invention to provide an ignition method for an internal combustion engine that consumes less, improves fuel consumption, and emits less nitrogen oxides and carbon dioxide (CO ₂ ).

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that the above-described problems can be achieved by adopting the following configuration, and have completed the present invention.

  That is, according to the present invention, the following ignition method for an internal combustion engine is provided.

[1] Burst by repeatedly causing pulse streamer discharge satisfying the following condition (1) at an interval of 100 μs or less in the presence of a combustible gas containing a combustible substance and a combustion-supporting gas under a positive pressure of atmospheric pressure or higher. An internal combustion engine ignition method to be generated (hereinafter also referred to as “first ignition method”).
[Condition (1)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, the third inflection point from the second second inflection point counted from the start of discharge among the inflection points at which either the peak electric field strength or the peak current density changes rapidly. Pulse discharge that occurs until the third inflection point.

[2] The ignition method for an internal combustion engine according to [1], wherein a fine pulse streamer discharge and / or a glow discharge satisfying the following condition (2) is caused before causing the pulse streamer discharge.
[Condition (2)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, the second inflection point from the first inflection point counted from the start of discharge among the inflection points at which either the peak electric field strength or the peak current density changes rapidly. Pulse discharge generated up to the second inflection point.

[3] A fine pulse streamer discharge satisfying the following condition (2) is repeatedly generated at intervals of 100 μs or less in the presence of a flammable gas containing a flammable substance and a combustion-supporting gas under a positive pressure of atmospheric pressure or higher, and a burst is generated. An internal combustion engine ignition method (hereinafter also referred to as “second ignition method”).
[Condition (2)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, the second inflection point from the first inflection point counted from the start of discharge among the inflection points at which either the peak electric field strength or the peak current density changes rapidly. Pulse discharge generated up to the second inflection point.

[4] When a fine pulse streamer discharge satisfying the following condition (2) is repeatedly caused at an interval of 100 μs or less in the presence of a combustible gas including a combustible substance and a combustion-supporting gas under a positive pressure of atmospheric pressure or higher. At the same time, an ignition method for an internal combustion engine that causes a pulse streamer discharge that satisfies the following condition (1) in accordance with the ignition timing to generate a burst (hereinafter also referred to as “third ignition method”).
[Condition (1)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, the third inflection point from the second second inflection point counted from the start of discharge among the inflection points at which either the peak electric field strength or the peak current density changes rapidly. Pulse discharge that occurs until the third inflection point.
[Condition (2)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, the second inflection point from the first inflection point counted from the start of discharge among the inflection points at which either the peak electric field strength or the peak current density changes rapidly. Pulse discharge generated up to the second inflection point.

[5] One or more fine pulse streamer discharges satisfying the following condition (2) in the presence of a combustible gas including a combustible substance and a combustion-supporting gas under a positive pressure of atmospheric pressure or higher, and the fine pulse streamer discharge: An ignition method for an internal combustion engine that causes one or more combinations with one or more pulse streamer discharges that satisfy the following condition (1) to generate a burst (hereinafter also referred to as “fourth ignition method”).
[Condition (1)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, the third inflection point from the second second inflection point counted from the start of discharge among the inflection points at which either the peak electric field strength or the peak current density changes rapidly. Pulse discharge that occurs until the third inflection point.
[Condition (2)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, the second inflection point from the first inflection point counted from the start of discharge among the inflection points at which either the peak electric field strength or the peak current density changes rapidly. Pulse discharge generated up to the second inflection point.

  [6] The electric field intensity of the electric pulse that causes the pulse streamer discharge is 3 to 15 kV / mm, and the voltage increase rate (dV / dt) at the rise of the pulse streamer discharge is 50 kV / μs or more. ] The ignition method for an internal combustion engine according to any one of [2], [4], and [5].

  [7] The internal combustion engine ignition method according to [6], wherein an electric field intensity of the electric pulse causing the pulse streamer discharge is 5 to 10 kV / mm.

  [8] The ignition method for an internal combustion engine according to [6], wherein the electric field intensity of the electric pulse causing the pulse streamer discharge is 7 to 10 kV / mm.

  [9] The ignition method for an internal combustion engine according to any one of [2] to [6], wherein an electric field intensity of an electric pulse causing the fine pulse streamer discharge is 5 to 13 kV / mm.

  [10] The ignition method for an internal combustion engine according to [9], wherein an electric field intensity of an electric pulse causing the fine pulse streamer discharge is 7 to 13 kV / mm.

  [11] The ignition method for an internal combustion engine according to [9], wherein an electric field intensity of an electric pulse causing the fine pulse streamer discharge is 7 to 11 kV / mm.

  [12] The ignition method for an internal combustion engine according to any one of [1] to [11], wherein an electric pulse is generated and discharged by a pulse power source using an electrostatic induction thyristor as a switching device.

  [13] The internal combustion engine ignition method according to [12], wherein the pulse power supply is an inductive energy storage type power supply circuit.

  [14] The ignition method for an internal combustion engine according to [12] or [13], wherein a voltage of an electric pulse generated using the pulse power source is controlled by an induction energy storage time.

  [15] The voltage according to any one of [12] to [14], wherein the voltage, interval, number of times, and a combination thereof of the electric pulse generated using the pulse power source are controlled by an engine control unit (ECU). Ignition method for internal combustion engine.

  [16] Any one of [1] to [15], wherein the combustible substance is at least one selected from the group consisting of methane, propane, gasoline, light oil, plant-derived fuel, hydrogen, and synthetic chemical fuel. The ignition method of the internal combustion engine as described.

  [17] The combustible gas may be air and / or oxygen, and at least one dilution gas selected from the group consisting of nitrogen, carbon dioxide, and combustion exhaust gas may be included in the combustible gas. ] The ignition method for an internal combustion engine according to any one of [16] to [16].

The ignition method for an internal combustion engine of the present invention can be ignited with less energy than ordinary spark discharge, consumes less discharge electrodes of the spark plug, improves fuel consumption, and emits nitrogen oxides and carbon dioxide There is an effect that the amount of (CO ₂ ) is small.

It is a conceptual diagram which shows typically one Embodiment of the 1st ignition method of this invention. It is a conceptual diagram which shows typically other embodiment of the 1st ignition method of this invention. It is a conceptual diagram which shows typically one Embodiment of the 2nd ignition method of this invention. It is a conceptual diagram which shows typically one Embodiment of the 3rd ignition method of this invention. It is a conceptual diagram which shows typically one Embodiment of the 4th ignition method of this invention. It is a circuit diagram which shows the structure of an IES circuit. It is a schematic diagram which shows operation | movement of an IES circuit. It is a schematic diagram which shows the state of discharge. It is a graph which shows the relationship between peak electric field strength and peak current density. It is a graph which shows a time-dependent change of the peak electric field strength and peak current density at the time of pulse streamer discharge generation. It is a graph which shows a time-dependent change of the peak electric field strength and the peak current density at the time of arc discharge generation. It is a schematic diagram which shows the form of the 1st electrical connection with a pulse power supply and the electrode pair of a plug. It is a schematic diagram which shows the form of the 2nd electrical connection with a pulse power supply and the electrode pair of a plug. It is a schematic diagram which shows the form of the 2nd electrical connection with a pulse power supply and the electrode pair of a plug. It is the graph which plotted IMEP fluctuation rate (%) with respect to the air fuel ratio (A / F).

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described below, but the present invention is not limited to the following embodiment, and is based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention. It should be understood that modifications and improvements as appropriate to the following embodiments also fall within the scope of the present invention.

[1] Ignition method for internal combustion engine:
[1-1] First ignition method:
FIG. 1 is a conceptual diagram schematically showing an embodiment of the first ignition method of the present invention. In the first ignition method, the pulse streamer discharge PS is performed a plurality of times at an interval of 100 μs or less in the presence of a combustible gas containing a combustible substance and a combustion-supporting gas under a positive pressure of atmospheric pressure or higher (for example, 1 MPa or less). A burst is generated by repeatedly causing the internal combustion engine to ignite. 1 to 5, “T” indicates an ignition interval (ms). For example, when the internal combustion engine is an engine having a rotation speed N (rpm), the ignition interval T = (1000 / N) × 2 × 60 = 120,000 / N (ms) can be calculated.

  The pulse streamer discharge is a non-equilibrium discharge that satisfies the following condition (1). By applying an electric pulse (pulse voltage) between electrodes arranged opposite to each other in a combustion chamber of an internal combustion engine to repeatedly cause pulse streamer discharge at a predetermined interval, high-energy electrons are efficiently generated, and a combustible gas is generated. A certain air-fuel mixture can be excited and the generation of active species radicals can be promoted.

  [Condition (1)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, the third inflection point from the second second inflection point counted from the start of discharge among the inflection points at which either the peak electric field strength or the peak current density changes abruptly. Pulse discharge that occurs between the inflection points.

  The interval between the plurality of pulse streamer discharges in the first ignition method is 100 μs or less, preferably 10 to 90 μs, more preferably 30 to 50 μs. If the energy injection is insufficient or the interval between pulse streamer discharges is less than 10 μs, the pulse power supply may be destroyed when the mis-arc current is energized.

  FIG. 2 is a conceptual diagram schematically showing another embodiment of the first ignition method of the present invention. As shown in FIG. 2, in the first ignition method, it is preferable to cause fine pulse streamer discharge FPS or glow discharge that satisfies the following condition (2) before causing pulse streamer discharge PS. It is also preferable to cause a combination of fine pulse streamer discharge and glow discharge as appropriate. This makes it possible to optimize the input energy and extend the life of the electrode.

  [Condition (2)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, inflection points where either the peak electric field strength or the peak current density changes rapidly, the second second from the first inflection point counting from the start of discharge. Pulse discharge that occurs between the inflection points.

[1-2] Second ignition method:
FIG. 3 is a conceptual diagram schematically showing an embodiment of the second ignition method of the present invention. In the second ignition method, non-equilibrium discharge satisfying the above condition (2) is performed under a positive pressure of atmospheric pressure or higher (for example, 1 MPa or lower) and in the presence of a flammable gas including a flammable substance and a combustion-supporting gas. A certain fine pulse streamer discharge FPS is repeatedly generated at intervals of 100 μs or less to generate bursts, and the internal combustion engine is ignited.

  By applying electrical pulses (pulse voltage) between electrodes facing each other in the combustion chamber of an internal combustion engine to repeatedly cause fine pulse streamer discharge at a predetermined interval, high energy electrons are efficiently generated, and a combustible gas is generated. It is possible to excite the gas mixture, and to promote the generation of active species radicals.

  The interval between a plurality of fine pulse streamer discharges in the second ignition method is 100 μs or less, preferably 10 to 90 μs, more preferably 30 to 50 μs. If the energy injection is insufficient or the interval between fine pulse streamer discharges is less than 10 μs, the pulse power supply may be destroyed when the misarc current is applied.

[1-3] Third ignition method:
FIG. 4 is a conceptual diagram schematically showing an embodiment of the third ignition method of the present invention. In the third ignition method, non-equilibrium discharge satisfying the above condition (2) in the presence of a combustible gas including a combustible substance and a combustion-supporting gas under a positive pressure of atmospheric pressure or higher (for example, 1 MPa or lower). The fine pulse streamer discharge FPS is repeatedly caused at intervals of 100 μs or less, and at the same time, the pulse streamer discharge PS, which is a non-equilibrium discharge that satisfies the above condition (1), is caused to occur in accordance with the ignition timing to generate a burst and ignite the internal combustion engine. To do. That is, in the third ignition method, the fine pulse streamer discharge FPS is always caused at a predetermined interval. Then, a pulse streamer discharge PS is caused at an arbitrary timing to ignite.

  By always causing fine pulse streamer discharge at a predetermined interval, high-energy electrons can be generated efficiently, and the mixture that is a flammable gas can be excited, and the generation of active species radicals can be promoted. Can do. In addition, if the fine pulse streamer discharge is always in the background as described above, plasma can be generated efficiently without applying the high voltage required to cause arc discharge, and can be ignited at an arbitrary timing. Can do.

  The interval between fine pulse streamer discharges repeatedly caused in the third ignition method is 100 μs or less, preferably 10 to 90 μs, more preferably 30 to 50 μs. If the energy injection is insufficient or the interval between fine pulse streamer discharges is less than 10 μs, the pulse power supply may be destroyed when the misarc current is applied.

[1-4] Fourth ignition method:
FIG. 5 is a conceptual diagram schematically showing an embodiment of the fourth ignition method of the present invention. In the fourth ignition method, at least once satisfying the condition (2) in the presence of a combustible gas including a combustible substance and a combustible gas under a positive pressure of atmospheric pressure or higher (for example, 1 MPa or lower). One or more combinations of the fine pulse streamer discharge FPS and one or more pulse streamer discharges PS satisfying the condition (1) following the fine pulse streamer discharge FPS are caused to generate a burst and ignite the internal combustion engine.

  In the case where the fine pulse streamer discharge is caused a plurality of times, the interval between the plurality of fine pulse streamer discharges is preferably 100 μs or less, more preferably 10 to 90 μs, and particularly preferably 30 to 50 μs. preferable. If the energy injection is insufficient or the interval between fine pulse streamer discharges is less than 10 μs, the pulse power supply may be destroyed when the misarc current is applied.

  In the case where the pulse streamer discharge is caused a plurality of times, the interval between the plurality of pulse streamer discharges is preferably 100 μs or less, more preferably 10 to 90 μs, and particularly preferably 30 to 50 μs. preferable. If the energy injection is insufficient or the interval between pulse streamer discharges is less than 10 μs, the pulse power supply may be destroyed when the mis-arc current is energized.

[2] Pulse power supply:
In the ignition method for an internal combustion engine of the present invention, an electric pulse indicating a pulse voltage waveform having a predetermined pulse width is applied between electrodes to generate a specific type of discharge. An inductive energy storage type power supply circuit using an electrostatic induction thyristor (hereinafter also referred to as “SIThy”) as a switching device to generate an electric pulse having a pulse voltage waveform having a predetermined pulse width and apply it between electrodes. It is preferable to employ a pulse power source (hereinafter also referred to as “IES circuit”). The IES circuit turns off using an opening switching function in addition to the closing switch function of SIThy, and this turn-off generates a high voltage between the gate and the anode of SIThy. Details of the IES circuit are described in Katsuji Iida, Ken Sakuma: “Inductive energy storage type pulse power supply”, 15th SI Device Symposium (2002).

The configuration of the IES circuit (pulse power supply) will be described with reference to FIG. The IES circuit 13 includes a low voltage DC power supply 131. The voltage E of the low-voltage DC power supply 131 is allowed to be significantly lower than the peak value of the electric pulse voltage generated by the IES circuit 13. For example, even if the peak value V _LP of the voltage _VL generated at both ends of the inductor 133 described later reaches several kV, the voltage E of the low voltage DC power supply 131 is allowed to be several tens of volts. The lower limit of the voltage E is determined by a latching voltage equal to or higher than the SIThy 134 latching voltage described later. Since the IES circuit 13 can use the low voltage DC power supply 131 as an electrical energy source, it can be constructed in a small size and at a low cost.

  The IES circuit 13 includes a capacitor 132 connected in parallel to the low voltage DC power supply 131. The capacitor 132 enhances the discharge capability of the low voltage DC power supply 131 by apparently reducing the impedance of the low voltage DC power supply 131.

  Further, the IES circuit 13 includes an inductor 133, a SITy 134, a MOSFET (Metal Oxide Field Effect Transistor) (hereinafter also referred to as “FET”) 135, a gate drive circuit 136, and a diode 137. In the IES circuit 13, the positive electrode of the low-voltage DC power supply 131 and one end of the inductor 133 are connected, the other end of the inductor 133 and the anode of the SIThy 134 are connected, the cathode of the SIThy 134 and the drain of the FET 135 are connected, The source and the negative electrode of the low voltage DC power supply 131 are connected. In the IES circuit 13, the gate of the SIThy 134 and the anode of the diode 137 are connected, and the cathode of the diode 137 and one end of the inductor 133 (the positive electrode of the low-voltage DC power supply 131) are connected. A gate drive circuit 136 is connected to the gate and source of the FET 135.

  The SIThy 134 can be turned on and off in response to a gate signal.

The FET 135 is a switching element in which the conduction state between the drain and the source changes in response to the gate signal V _c supplied from the gate drive circuit 136. It is desirable that the on-voltage or on-resistance of the FET 135 is low. Further, the withstand voltage of the FET 135 needs to be higher than the voltage E of the low voltage DC power supply 131.

  The diode 137 is provided in order to prevent a current flowing when a positive bias is applied to the gate of the SIThy 134, that is, to prevent the SIThy 134 from being driven by current when a positive bias is applied to the gate of the SIThy 134.

  The inductor 133 functions as an inductive element having self-inductance, and a load 139 (here, an electrode pair) is connected in parallel to both ends thereof. If the load 139 is connected to both ends of the secondary side of the step-up transformer using the primary side of the step-up transformer as the inductor 133, an electric pulse having a higher voltage peak value can be obtained.

Next, the operation of the IES circuit will be described with reference to FIG. In FIG. 7, in order from the top, the gate signal V _c applied to the FET, the conduction state of SIThy, the current I _L flowing through the inductor, the voltage V _L generated at both ends of the inductor, and the voltage V _AG between the anode and the gate of SIThy The change of (vertical axis) with respect to time (horizontal axis) is shown.

First, when the gate signal V _c is switched from OFF to ON at time t ₀ , the drain and source of the FET 135 become conductive. Thus, the gate of the SIThy134 is positively biased relative to the cathode, the anode-cathode of SIThy134 becomes conductive ( "A-K-conducting" in the figure), the current I _L begins to increase.

When current I _L time t ₁ to the gate signal V _c per peaking value I _LP is switched to OFF from ON, the drain-source of the FET135 is rendered non-conductive, and conductive state between the anode and gate of SIThy134 ("AG conduction" in the figure). As a result, from time t ₂ to time t ₃ , in synchronization with the expansion of the depletion layer in SIThy 134 (“depletion layer expansion” in the figure), the current I _L decreases and the voltage V _L and the voltage V _AG suddenly increase. To rise.

Then, the voltage V _L and the voltage V _AG at time t ₃ is, after the inverted direction of the current I _L respectively reached the peak value V _Lp and the peak value V _AGP, and from time t ₃ to time t _4, in SIThy134 In synchronization with the reduction of the depletion layer (“depletion layer reduction” in the figure), the current I _L increases and the voltage V _L and the voltage V _AG rapidly decrease.

When SIThy134 is turned off at time t ₄ ( "non-conducting" in the figure), the current I _L decreases towards the time t _5, the voltage V _L and the voltage V _AG becomes zero.

  By adopting a configuration in which an electrical pulse is generated and discharged by the IES circuit, the pulse waveform and pulse frequency of the applied electrical pulse can be appropriately changed. For this reason, discharge conditions can be optimized according to the pressure change of a combustible gas, a temperature change, or a composition change. Therefore, ignition can be performed in a state in which the concentration of the active species radical having a finite lifetime in the combustion chamber of the internal combustion engine is increased as much as possible. Note that the IES circuit is a circuit that can be configured extremely small. Specifically, since the volume of the IES circuit is as small as about 100 to 1000 ml, it is also suitable as an in-vehicle pulse power source.

  Further, the pulse power supply of the IES circuit has a short time required to store energy necessary for discharging, and is approximately 10 μs or less. In other words, since the number of discharges per unit time can be increased as compared with the conventional circuit, ignition can be performed at an optimal timing, and the certainty of ignition can be improved. The voltage of the electric pulse generated by the IES circuit is controlled by the induction energy storage time in the inductor 133 which is an inductive element, that is, the on time of the FET 135.

  Note that the voltage, interval, number, and combination of electric pulses generated using the pulse power source can be arbitrarily changed according to the discharge conditions. That is, it is possible to apply a pulse voltage train having an optimum waveform according to a signal from an engine control unit (ECU) in accordance with an operation condition of the internal combustion engine according to a preprogrammed algorithm.

[3] Discharge type:
Both pulse streamer discharge and fine pulse streamer discharge are non-equilibrium discharges with excellent discharge uniformity. For this reason, if the number of repetitions of these discharges is controlled, non-thermal equilibrium plasma containing a large amount of active species radicals can be produced without increasing the temperature of the combustible gas (air mixture) to the ignition temperature in the conventional ignition method. It can be efficiently generated without applying a high voltage required to cause arc discharge. Specific examples of the electrode include a center electrode that is an electrode constituting a general spark plug, an outer (ground) electrode, and the like.

If the ignition method for an internal combustion engine according to the present invention is employed, lean combustion can be performed in a stable state even when an air-fuel mixture with a large air-fuel ratio (A / F) is ignited. Therefore, the ignition method for an internal combustion engine of the present invention is suitable as an ignition method for an internal combustion engine such as a lean burn engine, and contributes to an improvement in fuel consumption and a reduction in the amount of carbon dioxide (CO ₂ ) emitted. is there.

  FIG. 8 is a schematic diagram showing a state of discharge caused by application of an electric pulse to the electrode pair.

  As shown in FIG. 8, when the pulse width of the electric pulse reaches a predetermined value, a glow discharge is generated in which new positive ions are generated by secondary electrons emitted when the positive ions collide with the cathode 82.

  On the other hand, when the rate of increase of the voltage V (voltage increase rate (dV / dt)) at the rise of the electric pulse is approximately 30 to 500 kV / μs, the growth of the streamer 83 from the anode 81 to the cathode 82 starts. The growth of the streamer 83 ends at the initial stage where the short streamer 83 is scattered between the anode 81 and the cathode 82. On the other hand, when the pulse width is further increased, the streamer 83 grows in earnest, and a long streamer 83 branched between the anode 81 and the cathode 82 exists. In the internal combustion engine ignition method of the present invention, the discharge is stopped at the initial stage of the streamer 83 growth so that the streamer 83 does not grow and the anode 81 and the cathode 82 do not conduct.

  If the pulse width is further expanded, local current concentration occurs, and finally arc discharge is caused.

  In the above description, the range of the voltage increase rate (dV / dt) is “substantially” because these are specific configurations of the spark plug such as the distance between the anode 81 and the cathode 82 and the structure of the anode 81 and the cathode 82. It is because it changes depending on. Therefore, whether or not the fine pulse streamer discharge is performed should be determined by observing not only the rate of voltage increase (dV / dt) at the time of rising but also the actual discharge.

  FIG. 9 is a graph showing the relationship between peak electric field strength and peak current density. The discharge state usually changes under the influence of the length of the pulse width, the temperature level, the voltage level, the current level, and the atmospheric pressure level. The graph shown in FIG. 9 is created by performing discharge under the conditions of metal electrode discharge gap: 1.5 mm, plug anode area: φ2 mm, plug cathode area: 2 × 3 mm, pressure: 10 atm, temperature: 60 ° C. It is a thing. As shown in FIG. 9, when a voltage is applied between the electrodes, a current due to glow discharge gradually starts to flow from a certain peak electric field intensity. When the voltage is further increased, the peak current density is increased to a fine pulse streamer discharge through an inflection point (first inflection point) at which the peak current density rapidly rises, and the increase rate of the peak current density is increased. When the voltage is further increased, the peak electric current density increases through the inflection point (second inflection point) at which the peak electric field intensity begins to gradually decrease, and then shifts to pulse streamer discharge. When the voltage is further increased, the peak electric field intensity hardly changes, and the arc current is shifted to an arc discharge through an inflection point (third inflection point) in which only the peak current density is increased.

  In this specification, the discharge generated between the start of discharge and the first inflection point is referred to as “glow discharge”, and the discharge generated between the first inflection point and the second inflection point is referred to as “fine pulse streamer”. Discharge ", discharge generated between the second inflection point and the third inflection point is referred to as" pulse streamer discharge ", and discharge generated after the third inflection point is referred to as" arc discharge ".

FIG. 10 is a graph showing temporal changes in peak electric field strength and peak current density when a pulse streamer discharge is generated. Further, FIG. 11 is a graph showing temporal changes in peak electric field strength and peak current density when arc discharge occurs. As shown in FIGS. 10 and 11, at any discharge occurrence, the peak voltage density increases as the peak electric field strength increases. However, the maximum value of the peak voltage density reaches several 10 A / cm ² in the case of arc discharge, but is 0. 0 in the case of pulse streamer discharge. It is about several to several A / cm ² . Also, at any discharge occurrence, the peak voltage density decreases as the peak electric field strength decreases. However, in the case of arc discharge, the peak current density continues to be observed after the disappearance of the peak electric field strength, whereas in the case of pulse streamer discharge, the peak current density is not observed (disappears) before the peak electric field strength disappears. ). Comparing the full width at half maximum of the peak current density, the arc discharge is several μs to several ms, whereas the pulse streamer discharge is as short as 200 ns or less.

  In the ignition method for an internal combustion engine of the present invention, the pulse current stream discharge or the fine pulse streamer discharge in which the half value (disappearance tailing) of the peak current density is extremely shorter than the arc discharge is used, and the temperature of the air-fuel mixture is increased. Is not generated up to the ignition temperature in the conventional ignition method, and non-thermal equilibrium plasma containing a large amount of active species radicals is efficiently generated without applying a high voltage required to cause arc discharge.

  The electric field intensity of the electric pulse causing the pulse streamer discharge is preferably 3 to 15 kV / mm, more preferably 5 to 10 kV / mm, and further preferably 7 to 10 kV / mm. By setting the electric field intensity of the electric pulse within the above range, highly efficient radical generation can be realized.

  Further, the voltage increase rate (dV / dt) at the time of rising of the pulse streamer discharge is preferably 50 kV / μs or more, more preferably 100 to 500 kV / μs, and more preferably 200 to 300 kV / μs. Particularly preferred. By setting the voltage increase rate (dV / dt) within the above range, highly efficient radical generation can be realized.

  The electric field intensity of the electric pulse that causes fine pulse streamer discharge is preferably 5 to 13 kV / mm, more preferably 7 to 13 kV / mm, and particularly preferably 7 to 11 kV / mm. By setting the electric field intensity of the electric pulse within the above range, highly efficient radical generation can be realized.

[4] Flammable substances:
The combustible gas (air mixture) burned by the internal combustion engine contains a combustible substance and a combustion-supporting gas. As the combustible substance, a conventionally known substance that is combusted in a general internal combustion engine can be adopted. Specific examples of the combustible substance include at least one selected from the group consisting of methane, propane, gasoline, light oil, plant-derived fuel, hydrogen, and synthetic chemical fuel.

[5] Combustion gas:
As the combustion-supporting gas contained in the combustible gas (air mixture), a conventionally known gas that may be contained in the combustible gas burned in a general internal combustion engine can be employed. Specific examples of the combustion-supporting gas include air, oxygen, and a mixed gas thereof.

[6] Dilution gas:
The combustible gas (air mixture) may contain a diluent gas as a component other than the combustible substance and the combustion-supporting gas. As the dilution gas, a conventionally known gas that may be contained in a combustible gas burned in a general internal combustion engine can be employed. Specific examples of the dilution gas include at least one selected from the group consisting of nitrogen, carbon dioxide, and combustion exhaust gas. In the ignition method for an internal combustion engine according to the present invention, when the exhaust gas is circulated (exhaust gas circulation (EGR)), an inert dilution gas rich in nitrogen or carbon dioxide is contained in the air-fuel mixture. Even if it exists, there exists an advantage that it can be set as the stable ignition state.

[7] Electrical connection between pulse power source and spark plug electrode pair:
FIGS. 12, 13 and 14 are schematic views showing a form of electrical connection between the pulse power source and the electrode pair of the spark plug.

  In the first form of electrical connection shown in FIG. 12, pulse power supply 1000 and electrode pair 1012 of spark plug 1006 are directly connected. For example, the positive output end 1002 of the pulse power source 1000 is connected to the anode 1008 of the spark plug 1006, and the negative output end 1004 of the pulse power source 1000 is connected to the cathode 1010 of the spark plug 1006. The negative output terminal 1005 of the pulse power supply 1000 and the cathode 1010 of the spark plug 1006 may be grounded.

  However, the first electrical connection configuration shown in FIG. 12 is liable to generate arc discharge shown in FIG. Therefore, in order to suppress the arc discharge shown in FIG. 11 and exclusively generate the pulse streamer discharge shown in FIG. 10, it is desirable that the second electrical connection configuration shown in FIG. 13 or the third electrical connection shown in FIG. A typical connection form is adopted.

  In the second electrical connection mode shown in FIG. 13 and the third electrical connection mode shown in FIG. 14, the pulse power sources 1100 and 1200 and the electrode pairs 1112 and 1212 of the spark plugs 1106 and 1206 are in resistance. Connected through. For example, the positive output terminals 1102 and 1202 of the pulse power supplies 1100 and 1200 are connected to the anodes 1108 and 1208 of the spark plugs 1106 and 1206 via resistors 1114 and 1214, and the negative output terminals 1104 and 1204 of the pulse power supplies 1100 and 1200 are ignited. Connected to the cathodes 1110 and 1210 of the plugs 1106 and 1206. The negative output terminals 1104 and 1204 of the pulse power supplies 1100 and 1200 and the cathodes 1110 and 1210 of the spark plugs 1106 and 1206 may be grounded.

  The resistors 1114 and 1214 may be built in a connection cable that connects the pulse power source 1100 and the spark plug 1106 as shown in FIG. 13, or are built in the spark plug 1206 as shown in FIG. Also good.

  The “resistance” only needs to include a resistance component, and need not be a pure resistance that does not include a reactance component. The resistance value of the resistance component is preferably 500 to 2000 ohms, and more preferably about 1000 ohms. This is because if the resistance value falls below this range, it becomes difficult to obtain an effect of suppressing arc discharge, and if the resistance value exceeds this range, the loss becomes too large.

  The “ignition plug” is an electrode structure that includes at least an anode and a cathode, and preferably includes a base that fixes the anode and the cathode. In the ignition method for an internal combustion engine of the present invention, a known spark plug can be adopted, but a spark plug having a structure different from that of the known spark plug can also be employed.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

Example 1
Using a spark ignition (SI) engine equipped with a spark plug, the rotation speed is fixed at 1000 rpm and the air-fuel ratio (air / fuel mass ratio, A / F) according to the following ignition condition (1) (PRD) Was made variable within the range of the theoretical air-fuel mass ratio (A / F = 14.7 to 26.7), and the ignition timing was set to Minimum Advance for Best Torque (MBT). In addition, both the operation mode (1) and the operation mode (2) shown below were performed.

<Ignition condition (1) (PRD)>
-Total input energy: Variable-Electric pulse input energy control method: Accumulated energy control by gate time width-Electric pulse input pattern: Voltage pulse with gate pulse width of 3 μs (half width = 200 ns) is applied between electrodes 8 times This caused a pulse streamer discharge. Next, a voltage pulse having a gate pulse width of 5.5 μs (half width = 200 ns) was applied between the electrodes twice to cause a pulse streamer discharge. The interval between the pulse streamer discharges was 40 μs.
・ Primary input voltage of power supply: 150V
・ Spark gap (distance between the center electrode and the outer (ground) electrode): 1.5 mm

<Operation mode (1)>
In this operation mode, the operation is performed while maintaining the suction pressure at 70 kPa, and the operation is performed while controlling the total amount of suction air.

<Operation mode (2)>
This is an operation mode in which the average effective pressure (IMEP) is maintained at 440 kPa, and the operation is performed while controlling the engine load.

(Comparative Example 1)
Ignition was performed by the same operation as in Example 1 except that the following ignition condition (2) (CIC) was followed.

<Ignition condition (2) (CIC)>
・ Conventional circuit ignition was performed.
・ Spark gap (distance between the center electrode and the outer (ground) electrode): 0.5 mm

(Evaluation result (1))
From the results shown in FIG. 15, in Comparative Example 1, the maximum air-fuel ratio (A / F) that can be ignited (operated) in a stable region where the IMEP fluctuation rate is less than 5% is 20, whereas in Example 1, It is clear that ignition (operation) can be stably performed up to the maximum air-fuel ratio (A / F) 23.

  That is, it has been found that the ignition method for an internal combustion engine of the present invention is effective not only when igniting an actual internal combustion engine (engine) but also an experimental container. However, it is well known that even the conventional ignition method can extend the lean limit if high energy is applied. Therefore, when the supply energy to the circuit used in Example 1 was estimated by measuring the instantaneous voltage and current in this circuit, it was about 140 mJ / cycle, which is almost equivalent to the energy supplied by the conventional ignition method. It turned out to be.

  The present invention is suitable as an ignition method for an internal combustion engine such as a gasoline engine.

81: Anode, 82: Cathode, 83: Streamer, 13: IES circuit, 131: Low voltage DC power supply, 132: Capacitor, 133: Inductor, 134: SIThy, 135: FET,
136: Gate drive circuit, 137: Diode, 139: Load, PS: Pulse streamer discharge, FPS: Fine pulse streamer discharge

Claims (17)

An internal combustion that generates a burst by repeatedly causing a pulse streamer discharge satisfying the following condition (1) at an interval of 100 μs or less in a presence of a combustible gas including a combustible substance and a combustion-supporting gas under a positive pressure of atmospheric pressure or higher. How to ignite the engine.
[Condition (1)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, the third inflection point from the second second inflection point counted from the start of discharge among the inflection points at which either the peak electric field strength or the peak current density changes rapidly. Pulse discharge that occurs until the third inflection point. The ignition method for an internal combustion engine according to claim 1, wherein a fine pulse streamer discharge and / or a glow discharge satisfying the following condition (2) is caused before the pulse streamer discharge is caused.
[Condition (2)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, the second inflection point from the first inflection point counted from the start of discharge among the inflection points at which either the peak electric field strength or the peak current density changes rapidly. Pulse discharge generated up to the second inflection point. An internal combustion engine that repeatedly generates fine pulse streamer discharge satisfying the following condition (2) at intervals of 100 μs or less under a positive pressure higher than atmospheric pressure and in the presence of a flammable gas containing a flammable substance and a combustion-supporting gas. Ignition method.
[Condition (2)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, the second inflection point from the first inflection point counted from the start of discharge among the inflection points at which either the peak electric field strength or the peak current density changes rapidly. Pulse discharge generated up to the second inflection point. In the presence of a combustible gas containing a combustible substance and a combustion-supporting gas under a positive pressure of atmospheric pressure or higher, a fine pulse streamer discharge satisfying the following condition (2) is repeatedly caused at intervals of 100 μs or less, and ignition is performed. A method for igniting an internal combustion engine that causes a pulse streamer discharge that satisfies the following condition (1) in accordance with the timing to generate a burst.
[Condition (1)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, the third inflection point from the second second inflection point counted from the start of discharge among the inflection points at which either the peak electric field strength or the peak current density changes rapidly. Pulse discharge that occurs until the third inflection point.
[Condition (2)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, the second inflection point from the first inflection point counted from the start of discharge among the inflection points at which either the peak electric field strength or the peak current density changes rapidly. Pulse discharge generated up to the second inflection point. One or more fine pulse streamer discharges that satisfy the following condition (2) in the presence of a combustible gas containing a combustible substance and a combustion-supporting gas under a positive pressure of atmospheric pressure or higher, and the following following the fine pulse streamer discharge: An ignition method for an internal combustion engine that causes one or more combinations with one or more pulse streamer discharges that satisfy the condition (1) to generate a burst.
[Condition (1)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, the third inflection point from the second second inflection point counted from the start of discharge among the inflection points at which either the peak electric field strength or the peak current density changes rapidly. Pulse discharge that occurs until the third inflection point.
[Condition (2)]: A pulse voltage is applied between the electrodes of the spark plug in a state where the pulse width, temperature, voltage, current, and atmospheric pressure are constant, the peak electric field strength is plotted on the horizontal axis, and the peak current density is plotted on the vertical axis. In the graph obtained by plotting each of the above, the second inflection point from the first inflection point counted from the start of discharge among the inflection points at which either the peak electric field strength or the peak current density changes rapidly. Pulse discharge generated up to the second inflection point. The electric field intensity of the electric pulse causing the pulse streamer discharge is 3 to 15 kV / mm,
The ignition method for an internal combustion engine according to any one of claims 1, 2, 4, and 5, wherein a rate of voltage increase (dV / dt) at the rise of the pulse streamer discharge is 50 kV / µs or more.   The ignition method for an internal combustion engine according to claim 6, wherein the electric field intensity of the electric pulse causing the pulse streamer discharge is 5 to 10 kV / mm.   The ignition method for an internal combustion engine according to claim 6, wherein the electric field intensity of the electric pulse causing the pulse streamer discharge is 7 to 10 kV / mm.   The ignition method for an internal combustion engine according to any one of claims 2 to 6, wherein an electric field intensity of an electric pulse that causes the fine pulse streamer discharge is 5 to 13 kV / mm.   The ignition method for an internal combustion engine according to claim 9, wherein the electric field intensity of the electric pulse causing the fine pulse streamer discharge is 7 to 13 kV / mm.   The ignition method for an internal combustion engine according to claim 9, wherein the electric field intensity of the electric pulse causing the fine pulse streamer discharge is 7 to 11 kV / mm.   The ignition method for an internal combustion engine according to any one of claims 1 to 11, wherein an electric pulse is generated and discharged by a pulse power source using an electrostatic induction thyristor as a switching device.   The internal combustion engine ignition method according to claim 12, wherein the pulse power source is an inductive energy storage type power source circuit.   The internal combustion engine ignition method according to claim 12 or 13, wherein a voltage of an electric pulse generated by using the pulse power source is controlled by an induction energy storage time.   The ignition of the internal combustion engine according to any one of claims 12 to 14, wherein the voltage, interval, number of times, and a combination thereof of the electric pulse generated by using the pulse power source are controlled by an engine control unit (ECU). Method.   The internal combustion engine according to any one of claims 1 to 15, wherein the combustible substance is at least one selected from the group consisting of methane, propane, gasoline, light oil, plant-derived fuel, hydrogen, and synthetic chemical fuel. Ignition method. The combustion-supporting gas is air and / or oxygen;
The ignition method for an internal combustion engine according to any one of claims 1 to 16, wherein the combustible gas contains at least one dilution gas selected from the group consisting of nitrogen, carbon dioxide, and combustion exhaust gas.

Images