JP2010185317A - Plasma igniter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma igniter capable of improving the ignitibility of a fuel/gas mixture by increasing the surface area of a plasma jet injected from an injection hole compared with the conventional configuration. <P>SOLUTION: A coil 6 is provided for generating a magnetic field necessary for applying a Lorentz force to a plasma jet P injected from a jetting hole radially with respect to the injection direction central axis C. The magnitude of the Lorentz force is made larger in the case the ignition timing is on the lag angle side than the set timing compared with the case with the ignition timing on the lead angle side than the set timing. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a plasma ignition device.

  In an internal combustion engine, it is necessary to reliably ignite a homogeneous mixture in the entire cylinder or a mixture existing in a part of the cylinder by an ignition device. However, a general ignition device that generates a spark in the ignition gap ignites one point of the air-fuel mixture and does not have a very high ignitability.

  As an ignition device excellent in ignitability, a plasma ignition device that injects a plasma jet has been proposed. The plasma ignition device includes a chamber formed by an insulator side wall, a center electrode disposed on one end side of the chamber, and a ground electrode disposed on the other end side of the chamber. The gas in the chamber is turned into plasma by the discharge generated by applying a voltage between them, and thus the high-temperature and high-pressure plasma in the chamber is injected as a plasma jet from the nozzle hole communicating between the chamber and the cylinder, Since the air-fuel mixture is simultaneously ignited in a portion in contact with the substantially cylindrical plasma jet having a relatively large surface area immediately after injection, high ignitability can be realized.

  By the way, a cylindrical chamber is extended in the axial direction of the plasma ignition device, a central electrode is disposed on the proximal end side of the chamber, a ground electrode is disposed on the distal end side of the chamber, and the inner diameter of the ground electrode is the same as the inner diameter of the chamber. And a spiral groove is formed in the side wall of the chamber, and the peripheral portion of the plasma jet ejected from the nozzle hole is swung around the axis by the spiral groove in the chamber side wall, that is, around the central axis in the injection direction. In this way, it has been proposed to stabilize the injection direction of the plasma jet by the gyro effect (see, for example, Patent Document 1).

JP2008-184964 JP 09-317621 A JP 2008-177142 A JP2008-186743

  According to the above-described plasma ignition device, the plasma jet ejected from the nozzle hole spreads in a substantially conical shape by swirling the peripheral portion. However, in the plasma jet spreading in a substantially conical shape in this manner, the spiral groove on the side wall of the chamber acts as a resistance when the plasma jet is ejected to reduce the ejection energy of the plasma jet. The generatrix length of the conical plasma jet is shortened, and the surface area of the substantially conical plasma jet immediately after injection does not increase so much from the conventional substantially cylindrical plasma jet, and the injection direction can be stabilized by the gyro effect. However, the ignitability of the air-fuel mixture cannot be improved as compared with the conventional plasma ignition device.

  Accordingly, an object of the present invention is to provide a plasma ignition device capable of improving the ignitability of the air-fuel mixture by increasing the surface area of the plasma jet ejected from the nozzle holes as compared with the conventional art.

  According to a first aspect of the present invention, there is provided a plasma ignition device comprising a coil for generating a magnetic field necessary for causing a Lorentz force to act radially on a central axis in an injection direction of a plasma jet injected from an injection hole. It is characterized by.

  A plasma ignition device according to a second aspect of the present invention is the plasma ignition device according to the first aspect, wherein the plasma ignition device injects a plasma jet toward the top surface of a piston, and the Lorentz force is large. This is characterized in that when the ignition timing is retarded from the set timing, the ignition timing is made larger than when the ignition timing is advanced before the set timing.

  According to the plasma ignition device of the first aspect of the present invention, there is provided a coil for generating a magnetic field necessary for causing a Lorentz force to act radially on the central axis in the injection direction on the plasma jet injected from the injection hole. Therefore, the plasma jet is expanded in a conical shape by the Lorentz force, and the jet energy is not reduced at that time. Therefore, the arrival distance of the plasma jet immediately after injection is not shortened, and the plasma jet immediately after injection is not shortened. The surface area can be increased sufficiently, and the ignitability of the air-fuel mixture can be improved as compared with the conventional plasma ignition device.

  According to the plasma ignition device of the second aspect of the present invention, in the plasma ignition device of the first aspect, the plasma ignition device injects a plasma jet toward a piston top surface. The magnitude of the acting Lorentz force is larger when the ignition timing is retarded than the set timing, compared to when the ignition timing is advanced before the set timing. As a result, when the ignition timing is retarded from the set timing, the apex angle of the conical shape of the plasma jet is increased, and the tip of the plasma jet reaches the piston and cools, contributing to ignition of the air-fuel mixture It is possible to suppress the failure. In this way, by controlling the magnitude of the Lorentz force acting on the plasma jet, the conical shape of the plasma jet having an increased surface area in order to improve the ignitability can be easily changed to a desired shape.

It is a schematic longitudinal cross-sectional view which shows embodiment of the plasma ignition apparatus by this invention. It is AA sectional drawing of the plasma ignition apparatus of FIG. It is a schematic sectional drawing which shows the advance side ignition timing of an internal combustion engine provided with the plasma ignition apparatus by this invention. FIG. 4 is a schematic cross-sectional view showing a retard side ignition timing of the internal combustion engine of FIG. 3. It is a schematic sectional drawing which shows the advance side ignition timing of another internal combustion engine provided with the plasma ignition apparatus by this invention. It is a schematic sectional drawing which shows the retard side ignition timing of the internal combustion engine of FIG.

  FIG. 1 is a schematic longitudinal sectional view showing an embodiment of a plasma ignition device according to the present invention. In the figure, 1 is a cylindrical chamber that is formed by a side wall of an insulator 2 so as to extend in the axial direction of the ignition device and generates plasma, and 3 is a center disposed on the base end side of the chamber 1. An electrode 4 is a ground electrode integrated with the housing located on the front end side of the chamber 1. Of course, the ground electrode 4 may be electrically and mechanically integrated with the housing as a separate member from the housing. An injection hole 5 communicates the chamber 1 and the inside of the cylinder. In this embodiment, the nozzle hole 5 has the same diameter as the chamber 1 and is formed on the ground electrode 4 and is chamfered on the outside.

  The center electrode 3 and the ground electrode 4 can be made of a metal having heat resistance and high conductivity, for example, an iron-based metal such as stainless steel, a nickel-based metal, an iridium-based metal, or an iridium alloy. The material of the insulator 2 for insulating the ground electrode 4 from the center electrode 3 is preferably ceramics (for example, alumina ceramics).

  In order to turn the gas in the chamber 1 into plasma, first, a high voltage is applied between the center electrode 3 and the ground electrode 4 to generate a creeping discharge S 1 on the inner surface of the side wall of the insulator 2. Thus, when the gas (air mixture) in the vicinity of the creeping discharge in the chamber 1 is turned into plasma and ions and electrons are generated, air discharge at a relatively low voltage becomes possible through the plasmaized gas, Next, this air discharge S2 is generated.

  Thus, when most of the gas in the chamber 1 is converted into plasma by the air discharge S2, the gas in the chamber 1 becomes high temperature and pressure and is injected as a plasma jet from the nozzle hole 5 to ignite the air-fuel mixture in the cylinder. Let Of course, instead of using the creeping discharge and the air discharge in combination as described above, the gas in the chamber 1 may be converted into a plasma by only the creeping discharge or the air discharge.

  In general, the plasma jet is ejected from the nozzle hole 5 as a substantially cylindrical shape substantially equal to the diameter of the nozzle hole 5, and the air-fuel mixture is simultaneously ignited at a portion in contact with the substantially cylindrical plasma jet. Thereby, if the surface area of the plasma jet immediately after injection is increased, the ignitability of the air-fuel mixture can be improved.

  In the plasma ignition device of this embodiment, a plurality of coils 6 are radially arranged at equal intervals in the circumferential direction in the side wall of the insulator 2 around the chamber 1, and plasma is generated in the chamber 1 by discharge. By energizing each coil 6 in the same direction during the operation, a magnetic field B passing through each coil 6 in the clockwise direction in a plan view is formed as shown by a dotted line in FIG. A radial Lorentz force acts on the generated plasma with respect to the central axis C of the chamber 1 as indicated by an arrow in FIG.

  In the present plasma ignition device, the central axis of the chamber 1 coincides with the central axis C in the injection direction of the plasma jet injected from the nozzle hole 5, whereby the plasma jet P is expanded in a conical shape by Lorentz force, In this case, since the ejection energy is not reduced, the reach distance of the plasma jet P immediately after the injection is not shortened (that is, in the plasma jet, the length of the cylindrical bus before being expanded by the Lorentz force is It is possible to improve the ignitability of the air-fuel mixture by sufficiently increasing the surface area of the plasma jet P immediately after the injection.

  In order to obtain this effect, the present plasma ignition device may be arbitrarily disposed in the cylinder, and the plasma injection direction can also be arbitrarily set. In the plasma ignition device of the present embodiment, the coil 6 that generates the magnetic field B necessary for causing the Lorentz force to act radially on the central axis C in the injection direction on the plasma jet P injected from the nozzle hole 5 is: Although divided into a plurality of parts, of course, an integral triidal coil may be used.

  3 and 4 are schematic cross-sectional views showing an internal combustion engine equipped with a plasma ignition device according to the present invention. In these figures, reference numeral 10 denotes the plasma ignition device shown in FIGS. Reference numeral 11 denotes a pair of exhaust ports that communicate with the cylinder via a pair of exhaust valves 12, and reference numeral 13 denotes a pair of intake ports that communicate with the cylinder via a pair of intake valves 14. Reference numeral 15 denotes a fuel injection valve disposed between the two intake ports 13 around the upper part of the cylinder. 16 is a piston.

  This internal combustion engine injects fuel in the intake stroke by the fuel injection valve 15, forms a homogeneous mixture in the cylinder by the latter half of the compression stroke, and performs homogeneous combustion in which this homogeneous mixture is ignited and combusted. In the present internal combustion engine, the plasma ignition device 10 is disposed substantially at the center of the upper part of the cylinder and injects plasma toward the substantially center of the top surface of the piston 16. Thereby, the central part of the homogeneous mixture can be simultaneously ignited by the plasma jet and burned radially, and good homogeneous combustion with a high combustion rate can be realized.

  FIG. 3 shows a state in which the plasma jet P1 is being injected from the plasma ignition device 10 when the ignition timing of the compression stroke is on the advance side before the set timing (set crank angle). At this time, the energization current to each coil 6 during the generation of plasma in the chamber 1 by creeping discharge or air discharge is set to a predetermined value or less, and the generated magnetic field B is made relatively weak so that the inside of the chamber 1 The Lorentz force acting radially on the plasma in the jet direction central axis is made relatively small. As a result, the apex angle of the conical plasma jet P1 ejected from the nozzle hole 5 is relatively small, but the surface area is increased and the ignitability can be improved as compared with the conventional cylindrical shape.

  Further, when the plasma jet is injected toward the piston top surface as in the internal combustion engine, the plasma jet P1 is formed into a conical shape so that the cylindrical plasma jet having the same busbar length (the same reach distance) is obtained. In comparison, it is difficult for the tip to reach the top surface of the piston immediately after injection, thereby preventing the tip from colliding with the piston top surface and being cooled, thereby preventing the tip from contributing to the ignition of the air-fuel mixture. Compared with a cylindrical plasma jet that is almost the same as the nozzle hole diameter, the central part of the homogeneous mixture can be ignited over a wide range at the same time. The combustion speed can be increased.

  FIG. 4 shows a state where the plasma jet P2 is being injected from the plasma ignition device 10 when the ignition timing of the compression stroke is retarded from the set timing. At this time, the energizing current to each coil 6 during the generation of plasma in the chamber 1 by creeping discharge or air discharge is made larger than the set value, and the magnetic field B to be generated is made relatively strong to increase the inside of the chamber 1. The Lorentz force acting radially on the central axis of the injection direction is relatively increased. Thereby, the apex angle of the conical plasma jet P2 ejected from the nozzle hole 5 becomes larger than that shown in FIG.

  Thereby, due to the retard of the ignition timing, the piston position of the ignition timing becomes closer to the cylinder head than in the case shown in FIG. 3, and the conical plasma shown in FIG. 3 having the same bus length (the same reach distance). In the jet P1, the tip reaches the top surface of the piston and is cooled, so the tip does not contribute to the ignition of the air-fuel mixture, but this is suppressed by increasing the cone-shaped apex angle of the plasma jet P2. Further, a homogeneous air-fuel mixture can be burned well in a radial manner by igniting a wider central portion at the same time.

  In this way, by controlling the magnitude of the Lorentz force acting on the plasma jet, the conical shape of the plasma jet having an increased surface area in order to improve the ignitability can be easily changed to a desired shape. In this internal combustion engine, the magnitude of the Lorentz force may be increased as the ignition timing is retarded.

  5 and 6 are schematic sectional views showing another internal combustion engine provided with the plasma ignition device according to the present invention. In these figures, 10 'is the plasma ignition device shown in FIGS. Reference numeral 11 denotes a pair of exhaust ports that communicate with the cylinder via a pair of exhaust valves 12, and reference numeral 13 denotes a pair of intake ports that communicate with the cylinder via a pair of intake valves 14. Reference numeral 15 'denotes a fuel injection valve disposed substantially at the center of the upper part of the cylinder. 16 'is a piston.

  The internal combustion engine injects fuel in the intake stroke by the fuel injection valve 15 ′ at the time of high engine load, forms a homogeneous mixture in the cylinder by the latter half of the compression stroke, and ignites and burns this homogeneous mixture. To implement. On the other hand, at the time of low engine load, fuel is injected in the compression stroke by the fuel injection valve 15 ′ to form a stratified mixture in a part of the cylinder, and stratified combustion is performed to ignite and burn this stratified mixture. . The fuel injection valve 15 'injects the fuel into a hollow conical shape, and the fuel injected in this manner is vaporized well by friction with the high-pressure intake air during the compression stroke, and reaches the piston top surface. A stratified mixture can be formed in a part of the cylinder.

  In the present embodiment, the plasma ignition device 10 'is disposed on the intake port side in the vicinity of the fuel injection valve 15' and injects plasma toward the center of the top surface of the piston 16 '. Thereby, at the time of homogeneous combustion, the same effect as the internal combustion engine of FIGS. 3 and 4 can be obtained by controlling the conical shape of the plasma jet similar to the internal combustion engine of FIGS.

  FIG. 5 shows a state in which the plasma jet P1 'is injected from the plasma ignition device 10' when the ignition timing of the compression stroke at the time of stratified combustion is on the advance side before the set timing (set crank angle). At this time, the energization current to each coil 6 during the generation of plasma in the chamber 1 by creeping discharge or air discharge is set to a predetermined value or less, and the generated magnetic field B is made relatively weak so that the inside of the chamber 1 The Lorentz force acting radially on the plasma in the jet direction central axis is made relatively small. Thereby, the apex angle of the conical plasma jet P1 ′ ejected from the nozzle hole 5 is relatively small, and at the ignition timing when the plasma jet P1 ′ is ejected, the tip of the conical plasma jet P1 ′ is It can be immediately before the piston top surface at the ignition timing on the advance side.

  During stratified combustion, when the ignition timing is on the advance side before the set timing, a relatively large amount of fuel is injected immediately before this ignition timing, and the stratified mixture F1 with the tip near the piston top surface at the ignition timing. The conical plasma jet P1 ′ formed as described above can contact the stratified mixture F1 over a wide range and ignite and burn the stratified mixture F1 satisfactorily.

  FIG. 6 shows a state in which the plasma jet P2 'is injected from the plasma ignition device 10' when the ignition timing of the compression stroke during stratified combustion is retarded from the set timing. At this time, the energizing current to each coil 6 during the generation of plasma in the chamber 1 by creeping discharge or air discharge is made larger than the set value, and the magnetic field B to be generated is made relatively strong to increase the inside of the chamber 1. The Lorentz force acting radially on the central axis of the injection direction is relatively increased. As a result, the apex angle of the conical plasma jet P <b> 2 ′ ejected from the nozzle hole 5 is larger than that shown in FIG. 5. Thereby, at the ignition timing at which the plasma jet P2 'is injected, the tip of the conical plasma jet P2' can be immediately before the piston top surface at the retarded ignition timing.

  When the ignition timing is retarded from the set timing during stratified combustion, a relatively small amount of fuel is injected immediately before the ignition timing, and a stratified mixture F2 having a tip near the top surface of the piston is formed at the ignition timing. In addition, the conical plasma jet P2 ′ described above can contact the stratified mixture F2 over a wide range and ignite and burn the stratified mixture F2 well.

  In this way, by controlling the magnitude of the Lorentz force acting on the plasma jet, the conical shape of the plasma jet having an increased surface area in order to improve the ignitability can be easily changed to a desired shape. In this internal combustion engine, the magnitude of the Lorentz force during stratified combustion may be increased as the ignition timing is retarded, that is, as the fuel injection amount decreases and the fuel injection timing is retarded. good.

DESCRIPTION OF SYMBOLS 1 Chamber 2 Insulator 3 Center electrode 4 Ground electrode 5 Injection hole 6 Coil

Claims (2)

  A plasma ignition device comprising a coil for generating a magnetic field necessary for causing a Lorentz force to act radially on a central axis of an injection direction on a plasma jet injected from an injection hole.   The plasma ignition device injects a plasma jet toward the top surface of the piston, and the magnitude of the Lorentz force is such that when the ignition timing is retarded from the set timing, the ignition timing is advanced before the set timing. The plasma ignition device according to claim 1, wherein the plasma ignition device is larger than that at the corner side.

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