Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T13/00—Sparking plugs
  • H01T13/40—Sparking plugs structurally combined with other devices
  • H01T13/44—Sparking plugs structurally combined with other devices with transformers, e.g. for high-frequency ignition
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T13/00—Sparking plugs
  • H01T13/50—Sparking plugs having means for ionisation of gap

Definitions

• the present invention relates generally to the generation of plasma in a gas, and more particularly to inductively coupled plasma generation devices.
• Plasma generation is used in particular for the controlled ignition of internal combustion engines by the electrodes of a candle, but can also be used, for example, for sterilization in an air conditioning process or pollution control systems.
• the invention relates to a plasma generating device comprising two electrodes, a series resonator having a resonance frequency greater than 1 MHz and comprising a capacitor provided with two terminals, and an inductive winding surrounded by a shield, the capacitor and the coil being arranged in series, the electrodes being connected to the respective terminals of the capacitor.
• Such a device is in particular described in the form of a candle in the document FR 2 859 830.
• This type of candle has reduced internal parasitic capacitances and forms a series resonator having a high overvoltage coefficient.
• this device makes it possible to maintain a radiofrequency voltage between its electrodes for the generation of a plasma, its optimization has hitherto been problematic.
• the object of the invention is to provide an even more efficient radiofrequency plasma generation device.
• the device of the present invention also in accordance with the definition given in the preamble above, is essentially characterized in that the ratio of the winding radius r int to the shield radius r ext is between 0.5 and 0.6 and preferably 0.56.
• FIG. 1 represents a diagrammatic representation in section of an example of a candle that can be used in the plasma generation system
• FIG. 2 represents a graph representing a study of the overvoltage coefficient (y) as a function of the ratio r int / r ext (x).
• FIG. 1 illustrates details of the structure of a radiofrequency plasma generation device of the prior art, in the form of a surface spark plug, for which the application of radiofrequency excitation is particularly advantageous.
• the spark plug 110 may be fixed on the cylinder head 104 of an internal combustion engine 105 of a motor vehicle.
• the surface effect spark plug 110 comprises a low voltage cylindrical electrode which serves as a metal base 103 intended to be screwed into a recess made in a motor cylinder head and opening inside the combustion chamber.
• the base 103 is intended to be electrically connected to ground.
• the base 103 surrounds a cylindrical high voltage electrode 106 arranged in a central position.
• the electrode 106 is isolated from the base 103 via an insulating sleeve 100.
• the insulating sleeve consists of a material whose relative permittivity is greater than 1, for example a ceramic.
• the spark plug has a gap 105 between the dielectric 100 and one end of the electrode 103.
• Electrodes and insulation having materials and geometry adequate to initiate combustion in a mixture at a combustion density and to resist the plasma thus formed.
• Figure 1 also shows a sectional view of a candle advantageously incorporating a series resonator as described in the document of the prior art mentioned above.
• the spark plug 110 has a connection terminal 131, connected to a first end of an inductive winding 112.
• the second end of the inductive winding 112 is connected to an inner end of the high voltage electrode 106. This end is also in contact with an insulating element 111 forming the capacitor.
• the electrodes 103 and 106 are in this example separated by the dielectric material 100.
• the series resonator integrated in the spark plug 110 comprises the inductive winding 112 and the insulating element 100 also forming the capacitor between the electrodes 103 and 106.
• the capacitor and the inductive winding 112 are arranged in series.
• the serial capacitance of the series resonator is formed of the capacitor and internal parasitic capacitances of the candle. This capacitance is arranged in series with an inductor to form the series resonator. When the length of the connection between the inductor and the capacitor is reduced, we reduce the parasitic capacitances in the candle.
• the candle 110 is thus used to maintain the alternating voltage between the electrodes 103 and 106, in the desired frequency range, preferably from 1 Mhz to 20 Mhz.
• the integrated series resonator in the candle preferably has a single inductive coil 112, facilitating the manufacture of such a candle.
• the single inductive winding 112 preferably has an axis (identified by the dashed line) and consists of a plurality of turns superimposed along its axis. It is thus understood that the projection of a turn is identical to the projection of all the turns along this axis.
• the parasitic capacitances are then limited by not superimposing turns radially.
• the spark plug furthermore advantageously comprises a shield 132 connected to a ground and surrounding the inductive winding 112. The field lines are thus closed inside the shielding 132.
• the shielding 132 thus reduces the parasitic electromagnetic emissions of the spark plug 110.
• coil 112 can indeed generate intense electromagnetic fields with the radiofrequency excitation that is intended to apply between the electrodes. These fields may notably disrupt embedded systems of a vehicle or exceed thresholds defined in emission standards.
• the shield 132 is preferably made of a non-ferrous material of high conductivity, such as copper or silver. We can in particular use a conductive loop as shielding 132.
• the coil 112 and the shield 132 are preferably separated by an insulating sleeve 133 of a suitable dielectric material, having a dielectric coefficient greater than 1, and preferably a good dielectric strength to further reduce the risk of breakdown or breakdown. effluvia, causing energy dissipation.
• a suitable dielectric material having a dielectric coefficient greater than 1, and preferably a good dielectric strength to further reduce the risk of breakdown or breakdown. effluvia, causing energy dissipation.
• the dielectric material may for example be one of the silicone resins sold under the references Elastosil M4601, Elastosil RTV-2 or Elastosil RT622 (the latter having a breakdown voltage of 20 kV / mm and a dielectric constant of 2.8).
• the outer surface of the sleeve 133 is metallized to form the shielding 132 above.
• a plasma formed using such a device has many interests in the context of automotive ignition such as a significant decrease in the rate of misfires in a stratified lean mixture system, a reduction of wear of the electrodes or an adaptation of the ignition initiation volume as a function of density.
• Radiofrequency excitation is also suitable for a plasma deposition application in a gas having a density of between 2 mol / l ICT and 5 * 1 CT 2 mol / l.
• the gas used in this application can typically be nitrogen or air, especially ambient air.
• the radiofrequency excitation is further adapted to an application for the depollution of a gas having a density of between 2 mol / l ICT and 5 * 1 CT 2 mol / l.
• the radio frequency excitation is furthermore suitable for a lighting application using a gas having a molar density of between 0.2 mol / l and 1 mol / l.
• the current which passes the son of the coil 112 will be distributed between the inner surface and the outer surface of the son in the ratio of magnetic fields.
• the magnetic field is homogeneous in the winding support and in the space between the winding and the shielding.
• the flux in the space between the winding and the shielding is therefore substantially equal to the flux in the winding support, and the magnetic fields are therefore in the ratios of the sections, which gives:
• the self L can be calculated as follows:
• the quality coefficient is equal to:
• This parameter thus makes it possible for any type of radiofrequency plasma generating device, for example an engine spark plug, to optimize their overvoltage coefficient.

Landscapes

• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Ignition Installations For Internal Combustion Engines (AREA)
• Spark Plugs (AREA)
• Air Filters, Heat-Exchange Apparatuses, And Housings Of Air-Conditioning Units (AREA)
• Transplanting Machines (AREA)
• Electron Sources, Ion Sources (AREA)
• Chemical Vapour Deposition (AREA)
• Electron Tubes For Measurement (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)

Priority Applications (5)

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Citations (2)

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• 2006
  • 2006-10-17 FR FR0609081A patent/FR2907269B1/fr not_active Expired - Fee Related
• 2007
  • 2007-07-03 ES ES07823538T patent/ES2342987T3/es active Active
  • 2007-07-03 AT AT07823538T patent/ATE461544T1/de not_active IP Right Cessation
  • 2007-07-03 EP EP07823538A patent/EP2080254B1/fr not_active Not-in-force
  • 2007-07-03 DE DE602007005395T patent/DE602007005395D1/de active Active
  • 2007-07-03 US US12/445,636 patent/US8278807B2/en not_active Expired - Fee Related
  • 2007-07-03 JP JP2009532852A patent/JP5108892B2/ja not_active Expired - Fee Related
  • 2007-07-03 WO PCT/FR2007/051582 patent/WO2008047013A1/fr not_active Ceased

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