JP2018132032A - Ignition device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably operate an internal combustion engine by maintaining and promoting ignition in accordance with atmosphere pressure inside a combustion chamber of the internal combustion engine.SOLUTION: An ignition device 100 for an internal combustion engine includes: a first ignition plug 20 for forming a low-temperature plasma; and a second ignition plug 22 for forming thermal plasma with a translation temperature higher than the low-temperature plasma. The first ignition plug 20 is disposed upstream of an air flow relative to the second ignition plug 22 to generate low-temperature plasma with the first ignition plug 20 and then generate thermal plasma with the second ignition plug 22.SELECTED DRAWING: Figure 1A

Description

  The present invention relates to an ignition device for an internal combustion engine.

  An internal combustion engine ignition device (ignition plug) that includes a center electrode (ignition electrode) that is insulated and held by an insulator and a ground electrode, and generates a spark by applying a voltage between the center electrode and the ground electrode is known. ing.

  When the gas mixture is spark-ignited when the gas density is relatively high, ignition by low temperature plasma generated by corona discharge reduces ignition delay time compared to ignition by thermal plasma generated by arc discharge can do. Therefore, an ignition device for an internal combustion engine that ignites by generating at least low-temperature plasma under an operating condition in which the gas density in the combustion chamber at the ignition timing is a predetermined value or more is disclosed (Patent Document 1).

JP 2013-238129 A

  By the way, when performing ignition with low-temperature plasma, there is a problem that the ignition performance (reduction rate of ignition delay time) decreases because the electron temperature of the plasma decreases as the pressure in the combustion chamber increases.

  One aspect of the present invention is an ignition device for an internal combustion engine that ignites fuel in a combustion chamber, and includes a first spark plug that forms a low-temperature plasma and a first plasma that forms a thermal plasma having a higher translation temperature than the low-temperature plasma. An ignition device for an internal combustion engine, comprising: two ignition plugs, wherein low temperature plasma is generated by the first ignition plug and then thermal plasma is generated by the second ignition plug.

  Here, it is preferable that the first spark plug is disposed on the upstream side of the airflow from the second spark plug.

  In addition, it is preferable to control at least one of a voltage and a time applied to the first spark plug according to the pressure in the combustion chamber.

  Further, it is preferable to increase the voltage applied to the first spark plug as the pressure at the ignition timing of the fuel in the combustion chamber increases, or to increase the application time of the voltage to the first spark plug. is there.

  Another aspect of the present invention is an ignition device for an internal combustion engine that ignites fuel in a combustion chamber, and includes an ignition plug having an ignition electrode and a ground electrode separated by an insulator, and low temperature plasma is generated by the ignition plug. An ignition apparatus for an internal combustion engine, characterized in that after being generated, thermal plasma is generated by the ignition plug.

  Here, after generating a low temperature plasma by applying a first voltage to the ignition electrode over a first time or intermittently, a second voltage higher than the first voltage is applied to the ignition electrode. It is preferred to generate the thermal plasma for a second time longer than one hour.

  In addition, it is preferable to generate a low temperature plasma by applying a high frequency voltage to the ignition electrode, and then generate a thermal plasma by applying a DC voltage to the ignition electrode.

  In addition, it is preferable that a convex portion or a concave portion is provided on the ignition electrode or the ground electrode.

  According to the present invention, ignition can be maintained and promoted according to the atmospheric pressure in the combustion chamber of the internal combustion engine, and the internal combustion engine can be operated stably.

It is a permeation | transmission side view which shows the structure of the ignition system of the internal combustion engine in 1st Embodiment. It is a top view which shows the structure of the ignition system of the internal combustion engine in 1st Embodiment. It is a figure which shows the relationship between a pressure, electron temperature, and an ignition delay time reduction rate. It is a figure which shows the chemical reaction formula used for an electron collision reaction calculation. It is a figure which shows the relationship between a pressure and an electric field strength by using electronic temperature as a parameter. It is a figure which shows the relationship between time and an electronic mole fraction by using a pressure as a parameter. It is a figure for demonstrating the control method of the ignition system of the internal combustion engine in 1st Embodiment. It is a figure which shows the structure of the ignition system of the internal combustion engine in 2nd Embodiment. It is a figure for demonstrating the control method of the ignition system of the internal combustion engine in 2nd Embodiment. It is a figure for demonstrating the generation | occurrence | production state of the low temperature plasma in the ignition system of the internal combustion engine in 2nd Embodiment. It is a figure for demonstrating the generation state of the thermal plasma in the ignition system of the internal combustion engine in 2nd Embodiment. It is a figure which shows the structure of the ignition system of the internal combustion engine in 3rd Embodiment. It is a figure for demonstrating the control method of the ignition system of the internal combustion engine in 3rd Embodiment. It is a figure which shows another example of a structure of the ignition system of the internal combustion engine in 3rd Embodiment. It is a figure which shows another example of a structure of the ignition system of the internal combustion engine in 3rd Embodiment.

[First Embodiment]
As shown in FIG. 1 (FIGS. 1A and 1B), an ignition system 100 for an internal combustion engine in the first embodiment includes a piston 12, a cylinder 14, a cylinder head 16, a combustion chamber 18, a first spark plug 20, and a first spark plug 20. Two ignition plugs 22, a pressure sensor 24, an ignition circuit 26 and a control unit 28 are included.

  The combustion chamber 18 is formed by the piston 12, the cylinder 14, and the cylinder head 16 that is the top of the cylinder 14. The piston 12 is accommodated in the cylinder 14 so as to be reciprocally movable. The cylinder head 16 is provided with a first spark plug 20, a second spark plug 22, an intake valve (not shown) and an exhaust valve (not shown). The combustion chamber 18 is connected to an intake port (not shown) via an intake valve, and is connected to an exhaust port (not shown) via an exhaust valve.

  1A shows a transparent side view of the first spark plug 20 and the second spark plug 22 arranged on the cylinder head 16 as seen from the side, and FIG. 1B shows the first view of the combustion chamber 18 seen from the cylinder head 16 side. The arrangement of the first spark plug 20 and the second spark plug 22 is shown. As shown in FIGS. 1A and 1B, the first spark plug 20 and the second spark plug 22 are disposed close to the combustion chamber 18.

  In the intake step, intake gas is introduced into the combustion chamber 18 from the intake port by opening the intake valve and lowering the piston 12. At the same time, fuel is injected into the intake port from a fuel injection valve (not shown) disposed at the intake port and mixed with intake gas, whereby the air-fuel mixture is introduced into the combustion chamber 18. In the compression process, the intake valve is closed and the air-fuel mixture is compressed as the piston 12 rises. The air-fuel mixture compressed in the combustion chamber 18 is ignited and burned by the sparks generated by the first spark plug 20 and the second spark plug 22. The burned gas is discharged from the combustion chamber 18 to the exhaust port by opening the exhaust valve in the exhaust process.

  The first spark plug 20 and the second spark plug 22 are connected to the ignition circuit 26. The ignition circuit 26 generates a spark in the combustion chamber 18 by applying a voltage to each of the first spark plug 20 and the second spark plug 22. The ignition circuit 26 is controlled by the control unit 28. The control unit 28 receives the pressure in the combustion chamber 18 measured by the pressure sensor 24, and controls the ignition circuit 26 according to the pressure.

  In the internal combustion engine ignition system 100 according to the present embodiment, a low temperature plasma of fuel (air mixture) is generated by the first spark plug 20, and a thermal plasma having a higher translation temperature than the low temperature plasma is generated by the second spark plug 22. Thus, the ignition reaction of the fuel is maintained and promoted.

  Plasma is a state in which gas molecules are ionized and electrons and cations move independently. For this reason, there are four types of temperatures: an electron temperature representing the energy of electrons, a vibration temperature and a rotational temperature representing the vibration energy and rotational energy between atoms, and a translation temperature corresponding to a normal gas temperature. The energy supplied to the plasma is transmitted in the order of electrons, vibration, rotation, and translation. Since the exchange of energy is easy between rotation and translation, the temperatures of both are at the same level. Low-temperature plasma is non-thermally balanced and has different temperatures for electrons, vibration, and rotation (translation). Low temperature plasma includes streamer discharge, nanopulse discharge, and high frequency discharge. On the other hand, thermal plasma is in thermal equilibrium and has the same temperature of electron, vibration, and rotation (translation). There is a spark discharge as the thermal plasma.

The ignition delay time during the formation of the low temperature plasma is determined by a function of the atmospheric pressure and the electron temperature. That is, as shown in FIG. 2, since the electron temperature decreases as the atmospheric pressure increases, the ignition delay time reduction rate also decreases. Here, the ignition delay time reduction rate is expressed by Equation (1).

The ignition delay time reduction rate can be obtained in advance by the following procedure. (1) For a given electric field strength, atmospheric pressure, and gas mixture composition (for example, gas composition CH ₄ / O ₂ / H ₂ = 1: 2: 8, equivalence ratio 1, initial gas temperature 1200 K), the electron Boltzmann equation To obtain the average electron temperature in the steady state (parallel state). (2) An electron collision reaction calculation is performed under the obtained average electron temperature, and a time history of each radical, ion, and electron concentration during voltage application is obtained. The electron collision reaction calculation is performed based on the chemical reaction formula shown in FIG. (3) A combustion reaction calculation is performed using the gas composition obtained at the end of voltage application as an initial condition, and an ignition delay time is calculated. (4) The reduction rate with respect to the ignition delay time when no voltage is applied is obtained.

  Therefore, when the low temperature plasma is formed by the first spark plug 20, the control unit 28 according to the present embodiment performs control to change the electric field strength according to the atmospheric pressure and maintain the electron temperature above a certain level. The control unit 28 receives the measured value of the atmospheric pressure in the combustion chamber 18 from the pressure sensor 24 and performs control to increase the voltage applied from the ignition circuit 26 to the first spark plug 20 as the atmospheric pressure increases. Do.

  For example, under a condition where a voltage is applied to the center electrode of the first spark plug 20 and an electric field of 0.5 kV / mm is applied, the ignition delay time reduction rate at an atmospheric pressure of 0.5 MPa (5 atm) is 50%. The electron temperature at that time is 5000K. When the electric field is maintained at 0.5 kV / mm, when the atmospheric pressure is increased to 0.8 MPa (8 atm), the electron temperature becomes 3000 K, and the ignition delay time reduction rate becomes 0%. Thus, as the atmospheric pressure increases, the electron temperature decreases and the ignition delay time reduction rate also decreases. Therefore, the voltage applied to the first spark plug 20 is controlled based on the relationship between the combination of the atmospheric pressure and the electric field strength shown in FIG. For example, when the atmospheric pressure is increased to 0.6 MPa (6 atm), in order to maintain the electron temperature at 5000 K and the ignition delay time reduction rate at 50%, the first spark plug is set so that the electric field strength is 0.6 kV / mm. Control is performed to increase the voltage applied to 20.

  Further, as shown in FIG. 5, the electron mole fraction (electron concentration) saturates in a certain time after voltage application (electric field formation) to the first spark plug 20. Therefore, the control unit 28 of the present embodiment performs control to change the time width in which the electric field is formed according to the atmospheric pressure when the low temperature plasma is formed by the first spark plug 20. The control unit 28 receives the measured value of the atmospheric pressure in the combustion chamber 18 from the pressure sensor 24, and lengthens the time for applying the voltage from the ignition circuit 26 to the first spark plug 20 as the atmospheric pressure increases. Take control.

  For example, saturation of the electron mole fraction (electron concentration) when the atmospheric pressure is 0.3 MPa (3 atm) under the condition that a voltage is applied to the center electrode of the first spark plug 20 and an electric field of 0.5 kV / mm is applied. The time is 500 μs, and the saturation time of the electron mole fraction (electron concentration) when the atmospheric pressure is 0.5 MPa (5 atm) is 250 μs. Therefore, when the atmospheric pressure is 0.5 MPa, a voltage pulse of 250 μs is applied to the first spark plug 20 in a plurality of times. Since electrons that have reached a certain concentration move downstream of the first spark plug 20 due to the influence of the airflow, it is preferable to apply the voltage pulse in multiple times.

  The relationship between the atmospheric pressure and the electron temperature and the relationship between the atmospheric pressure and the electron mole fraction vary depending on the configuration and size of the ignition system 100 of the internal combustion engine. Therefore, the relationship between the atmospheric pressure and the electron temperature and the relationship between the atmospheric pressure and the electron mole fraction are determined in advance through experiments and analysis in accordance with the configuration and size of the ignition system 100 of the internal combustion engine, and control is performed based on the characteristics. Is preferably performed.

  Furthermore, the control unit 28 of the present embodiment performs control so that thermal plasma is formed by the second spark plug 22 after the low temperature plasma is formed by the first spark plug 20. Specifically, as shown in FIG. 6, after applying a voltage pulse for forming a low temperature plasma to the first spark plug 20, a voltage for forming a thermal plasma to the second spark plug 22. Apply a pulse. Thereby, in addition to the electron temperature, the translation temperature is increased to promote the growth of the initial flame.

  At this time, it is preferable that the first spark plug 20 is disposed on the upstream side of the airflow with respect to the second spark plug 22 (the airflow is indicated by an arrow in FIG. 1). When the thermal plasma (spark discharge) is formed, electrons having a constant concentration are present in the vicinity of the second spark plug 22, so that the dielectric breakdown voltage decreases. As a result, the formation of thermal plasma by the second spark plug 22 is promoted and maintained stably.

[Second Embodiment]
In the first embodiment, the mode in which the low temperature plasma and the thermal plasma are generated using the two plugs of the first spark plug 20 and the second spark plug 22 has been described, but the present invention is not limited to this. In the second embodiment, a power source 30, a switching element 32, and a spark plug 34 are used as shown in FIG.

  As shown in the cross-sectional view of FIG. 7, the spark plug 34 includes a center electrode 34a, a ground electrode 34b, and an insulator 34c. The center electrode 34a is an electrode to which a voltage is applied to the ground electrode 34b. In the present embodiment, the center electrode 34a is formed from a cylindrical conductive material. The ground electrode 34b is an electrode that is electrically grounded. In the present embodiment, the ground electrode 34b is formed from a cylindrical conductive material. The center electrode 34a and the ground electrode 34b are electrically insulated by an insulator 34c. The ground electrode 34b is formed of a disk-shaped insulating material provided with a hole through which the center electrode 34a passes in the center. The ground electrode 34b is disposed so as to surround the periphery of the insulator 34c. As a result, the center electrode 34a and the ground electrode 34b are arranged coaxially, and a gap X is formed between the center electrode 34a and the ground electrode 34b.

  In the present embodiment, the center electrode 34a and the ground electrode 34b are arranged coaxially. However, a structure in which flat plates are arranged in parallel may be used.

  The power supply 30 and the switching element 32 are included in the ignition circuit 26. The power source 30 can be a DC power source that outputs a predetermined voltage. The switching element 32 is switched between a conduction state (on state) and a cutoff state (off state) under the control of the control unit 28.

  As shown in FIG. 8, after the fuel is supplied to the combustion chamber 18, the control unit 28 energizes the ignition plug 34 for a short time from the power source 30 once or intermittently. As a result, as shown in FIG. 9, low temperature plasma is formed in the gap X between the center electrode 34a and the ground electrode 34b. The time width of the energized voltage pulse is preferably 10 μs or more and less than 1 ms. After forming the low temperature plasma, a voltage pulse having a pulse width longer than the voltage pulse applied when forming the low temperature plasma is applied to the spark plug 34. The time width of the energized voltage pulse is preferably 0.1 ms to 1 ms. As a result, as shown in FIG. 10, a spark is generated between the tip of the center electrode 34a and the tip of the ground electrode 34b, and thermal plasma is formed around the spark.

  When forming a low temperature plasma, it is preferable to perform the same control as the control by the control unit 28 in the first embodiment. That is, the control unit 28 receives the measured value of the atmospheric pressure in the combustion chamber 18 from the pressure sensor 24 and performs control to increase the voltage applied from the ignition circuit 26 to the ignition plug 34 as the atmospheric pressure increases. It is preferred to do so. In this case, the ignition circuit 26 may be provided with a booster circuit that boosts the output voltage of the power supply 30. Further, the control unit 28 receives the measured value of the atmospheric pressure in the combustion chamber 18 from the pressure sensor 24, and lengthens the time for applying the voltage from the ignition circuit 26 to the ignition plug 34 as the atmospheric pressure increases. It is preferable to perform control.

  Note that the atmospheric pressure in the combustion chamber 18 can be estimated from the dielectric breakdown voltage at the start of low-temperature plasma formation without providing the pressure sensor 24 as in the first embodiment. The controller 28 estimates the atmospheric pressure based on the voltage when dielectric breakdown occurs after applying a voltage to the spark plug 34. For example, it is possible to estimate the atmospheric pressure corresponding to the measured dielectric breakdown voltage by storing a map in which the relationship between the dielectric breakdown voltage and the atmospheric pressure is obtained in advance.

  Further, in the first embodiment, the spark plug 34 in the present embodiment may be applied instead of the first spark plug 20.

  According to the present embodiment, ignition is maintained and promoted by the single spark plug 34 without using the two spark plugs of the first spark plug 20 and the second spark plug 22, and the internal combustion engine is stably operated. Can be made.

[Third Embodiment]
In the second embodiment, the mode using one power supply 30 and one switching element 32 has been described, but the present invention is not limited to this. As shown in FIG. 11, the third embodiment includes a spark plug 34, a first power supply 40, a first switching element 42, a second power supply 44, and a second switching element 46.

  The first power supply 40 is a high frequency power supply. The first power supply 40 is used for generating low temperature plasma. The first switching element 42 is switched between a conduction state (on state) in which a high-frequency voltage is applied from the first power supply 40 to the spark plug 34 and a cutoff state (off state) in which the first switching element 42 is not applied. The second power source 44 is a DC power source or a power source having a frequency lower than that of the first power source 40. The second power supply 44 is used for generating thermal plasma. The second switching element 46 is in a conductive state (on state) in which a DC voltage (or low frequency voltage) is applied from the second power source 44 to the spark plug 34 under the control of the control unit 28 and in a disconnected state (off state) in which it is not applied. And can be switched.

  As shown in FIG. 12, the controller 28 switches the first switching element 42 from the off state to the on state by the pulse A after the fuel is supplied to the combustion chamber 18. As a result, a high frequency voltage is applied from the first power supply 40 to the spark plug 34. Therefore, as shown in FIG. 9, low temperature plasma is formed in the gap X between the center electrode 34a and the ground electrode 34b. After forming the low-temperature plasma, the first switching element 42 is returned to the off state. The control unit 28 switches the second switching element 46 from the off state to the on state by the pulse B. As a result, a DC voltage (or low frequency voltage) is applied to the spark plug 34 from the second power source 44. Therefore, as shown in FIG. 10, a spark is generated between the tip of the center electrode 34a and the tip of the ground electrode 34b, and thermal plasma is formed around the spark.

  As shown in FIGS. 13 and 14, the shape of the center electrode 34a of the spark plug 34 may be changed. In the spark plug 34 shown in FIG. 13, a protrusion 34d is provided near the tip of the center electrode 34a toward the ground electrode 34b. Moreover, in the spark plug 34 shown in FIG. 14, the recessed part 34e is provided in the tip part vicinity of the center electrode 34a. This facilitates discharge when generating thermal plasma.

  12 piston, 14 cylinder, 16 cylinder head, 18 combustion chamber, 20 first spark plug, 22 second spark plug, 24 pressure sensor, 26 ignition circuit, 28 control unit, 30 power source, 32 switching element, 34 spark plug, 34a Center electrode, 34b Ground electrode, 34c Insulator, 34d Convex part, 34e Concave part, 40 1st power supply, 42 1st switching element, 44 2nd power supply, 46 2nd switching element, 100 Ignition system (ignition device).

Claims (8)

An internal combustion engine ignition device for igniting fuel in a combustion chamber,
A first spark plug for forming a low temperature plasma;
A second spark plug for forming a thermal plasma having a higher translation temperature than the low temperature plasma;
With
An ignition device for an internal combustion engine, wherein low temperature plasma is generated by the first spark plug and then thermal plasma is generated by the second spark plug. An ignition device for an internal combustion engine according to claim 1,
The ignition device for an internal combustion engine, wherein the first spark plug is disposed on the upstream side of the airflow from the second spark plug. An ignition device for an internal combustion engine according to claim 1 or 2,
An ignition device for an internal combustion engine, wherein at least one of a voltage and a time applied to the first spark plug is controlled in accordance with a pressure in the combustion chamber. An ignition device for an internal combustion engine according to claim 3,
As the pressure at the ignition timing of the fuel in the combustion chamber increases, the voltage applied to the first spark plug is increased, or the voltage application time to the first spark plug is increased. Engine ignition device. An internal combustion engine ignition device for igniting fuel in a combustion chamber,
Comprising a spark plug having an ignition electrode and a ground electrode separated by an insulator;
An ignition apparatus for an internal combustion engine, wherein low temperature plasma is generated by the spark plug and then thermal plasma is generated by the spark plug. An ignition device for an internal combustion engine according to claim 5,
After generating a low-temperature plasma by applying a first voltage to the ignition electrode over a first time or intermittently, a second voltage higher than the first voltage is applied to the ignition electrode from the first time. An ignition device for an internal combustion engine, characterized by generating thermal plasma over a long second time. An ignition device for an internal combustion engine according to claim 5,
An ignition apparatus for an internal combustion engine, wherein a low temperature plasma is generated by applying a high frequency voltage to the ignition electrode, and then a thermal plasma is generated by applying a DC voltage to the ignition electrode. An ignition device for an internal combustion engine according to claim 7,
An ignition device for an internal combustion engine, wherein the ignition electrode or the ground electrode is provided with a convex portion or a concave portion.