Electromagnetic ignition--an ignition system producing a large size and intense capacitive and inductive spark with an intense electromagnetic field feeding the spark

• US 4,774,914 A
• Filed: 07/15/1986
• Issued: 10/04/1988
• Est. Priority Date: 09/24/1985
• Status: Expired due to Fees

• Current Assignee: Combustion Electromagnetics Incorporated
• Original Assignee: Combustion Electromagnetics Incorporated
• Inventors: Ward, Michael A. V.
• Primary Examiner(s): Wolfe, Jr., Willis R.
• Application Number:
  US06/885,961
• Time in Patent Office: 812 Days
• Field of Search: 123/143 B, 123/143 C, 123/162, 123/169 EL, 123/169 MG, 123/210, 123/536, 123/596, 123/598, 123/604-608, 123/620, 123/621, 123/633, 123/634, 123/636 , 123/637, 123/661, 313/134, 336/221, 336/222
• US Class Current: 123/162
• CPC Class Codes: F02B 1/04 with fuel-air mixture admission into cylinder
• CPC Class Codes: F02B 3/06 with compression ignition compression ignition engines using air or gas for blowing fuel into compressed air in cylinder F02B13/02
• CPC Class Codes: F02P 15/04 one of the spark electrodes being mounted on the engine working piston
• CPC Class Codes: F02P 15/08 having multiple-spark ignition, i.e. ignition occurring simultaneously at different places in one engine cylinder or in two or more separate engine cylinders
• CPC Class Codes: F02P 23/045 using electromagnetic microwaves

Abstract

An Electromagnetic Ignition system suitable for adaptation to standard automobile engines including diesel engines, which has been improved by means of a high efficiency RF capacitive spark plug with a projecting antenna tip used for forming very large spark gaps to the plug shell and piston face as well as for coupling high electric fields to the local initial flame plasma, preferably used in combination with shielded high voltage cable including series inductive choke elements and a Capacitive Discharge ignition system incorporating an input capacitor, a SCR switch, an ignition coil with an optimized high current and high output voltage, and preferably a synchronous DC-DC power converter providing "boost power" during ignition so that substantial capacitive, inductive, and electromagnetic energy is supplied to the air-fuel mixture. Preferably the coil has a turns ratio of 50 with the input capacitor having a capacitance between 5 and 10 microfarads and a 400 volts rating. Large output capacitance is provided naturally by existing coil and shielded cable capacitance, supplemented with large plug capacitance of 50 to 250 picofarads, which are charged up to between 15 and 30 Kilovolts prior to breakdown of the wide variable spark gap producing: high frequency capacitive sparks, large inductive spark of several amps; and high pulsed local EM electric field strength of thousands of volts/cm providing a practical, highly efficient ignition system capable of igniting very lean air-fuel mixtures for reducing exhaust emissions and increased engine efficiency.

Claims

1. An electrical ignition system comprising a high voltage ignition coil capable of producing a voltage Vs greater than 20 Kilovolts for igniting air-fuel mixtures contained in a combustion chamber of an internal combustion engine, the chamber being defined by at least an outer fixed chamber member and an inner chamber member, at least one spark plug mounted on said outer chamber member to produce an ignition spark inside said combustion chamber, a secondary winding of said coil in combination with said plug and interconnecting cable comprising secondary circuit capacitance Cs to ground, and means defining a spark plug firing end including a high voltage igniting tip constructed and arranged to electrically break down the air-fuel mixture gap between said igniting tip and said inner or outer combustion chamber member under conditions enabling an effective breakdown over a length of at least 0.1 inch (0.25 cm) to produce a spark of at least 0.1 inch (0.25 cm) under at least one condition of operation of said engine, so as to provide under all normal operating conditions of said engine a high breakdown voltage and corresponding high secondary capacitive stored energy just prior to breakdown given by 1/2*Cs*Vs**2 which is greater than five millijoules for delivery of said energy immediately after breakdown of said gap.

2. The system defined in claim 1 wherein said outer chamber member is a cylinder head and said inner member is the top face of a piston of a reciprocating internal combustion engine.

3. The system defined in claim 1 wherein said inner chamber member is the rotor of a rotary type internal combustion engine.

4. The system defined in claim 1 wherein said inner chamber member is a movable compression means used for compressing air-fuel mixture prior to ignition and wherein said system comprises means providing a total output capacitance of at least 50 picofarads connected to output of said high voltage coil and wherein said high voltage coil is a low turns ratio high efficiency coil with a turns ratio between 40 and 60 which is part of a capacitive discharge (CD) circuit with a discharge capacitor of capacitance greater than 3 microfarads which is charged to a voltage of approximately 350 volts and wherein said high voltage coil provides at least 30 kilovolts output voltage and a spark current with a first current peak of at least 1 amp.

5. The system defined in claim 4 wherein said coil is a very high efficiency coil with a primary winding being made up of No. 8 to No. 14 wire and a coil turns ratio between 20 and 30 and wherein said discharge capacitor has a capacitance of at least two microfarads which is charged to a voltage of approximately 700 volts.

6. The system defined in claim 4 or 5 wherein said CD circuit comprises a bistable semiconductor switch including reverse recovery diode for controlling spark firing, and said discharge capacitor is connected to said bistable semiconductor switch so as to be fired during ignition to be able to produce a long duration discharge by keeping said bistable semiconductor switch ON for several oscillations of said discharge circuit.

7. The system defined in claim 1 wherein said inner chamber member comprises a cyclically movable member, and wherein said ignition coil secondary capacitance is of at least 50 picofarads, and said spark plug capacitance is of at least 20 picofarads, and the plug firing end is constructed and arranged to produce an ignition spark gap of at least about 0.1" (0.25 cm) under all operating conditions of said internal combustion engine except when the cyclically movable member is within 15 degrees of TDC when the gap may be smaller.

8. The system defined in claim 7 wherein said high voltage ignition coil has connected in series with its secondary winding high voltage output an inductive choke of inductance between 5 and 400 microhenry to limit very high frequency current produced by the discharge of said coil secondary capacitance during spark formation, which is responsible for radio frequency interference (RFI).

9. The system defined in claim 7 or 8 wherein said plug firing end and said movable member are dimensioned and designed so as to form a spark between said firing end and said movable member such that under all normal operating conditions of the engine the breakdown voltage forming said spark is within the range of 10 to 33 KV, wherein said ignition coil has a turns ratio between 40 and 60 and is part of a CD circuit including a discharge capacitor of capacitance greater than 3 microfarads charged to a voltage of approximately 350 volts, and wherein the system further includes multiple pulsing circuit for producing closely spaced multiple spark pulses.

10. The system defined in claim 7 or 8 wherein a discharge circuit including the ignition coil and discharge capacitors, bistable switching means and a recovery diode is contained in a grounded metallic enclosure, and wherein the coil secondary wire comprising the central conductor of high voltage coaxial cable with grounded outer conductor is connected to shielded intermediary components connected to coaxial shielded plugs such that RFI is supressed.

11. The system defined in claim 7 wherein central high voltage conductor of said sprak plug has at least one diameter not less than 0.4 inches (1.0 cm) and a spark plug tip of the plug firing end constructed to fire either back upon the circular edge of the plug shell surrounding said plug tip or across to said movable member, and wherein said minimum 0.4 inch (1.0 cm) diameter conductor is surrounded by high purity alumina dielectric insulating material of thickness about 0.1 inch (0.25 cm) and of relative dielectric constant of approximately nine.

12. The system defined in claim 11 wherein said dielectric material is low RF loss material with dielectric constant greater than 10.

13. The system defined in claim 11 wherein said spark plug tip comprises a protruding central electrical conductor of length at least 0.2 inches (0.5 cm) surrounded by an insulating material of at least one thickness greater than 0.060 inches (0.15 cm), said spark plug being disposed to ignite said mixture by making a spark either to said movable member in said chamber or to said fixed member of said chamber by firing backwards, wherein said fixed and movable member and tip are dimensioned and disposed such that the spark gap breakdown voltage varies within the range of 10 to 30 Kilovolts under normal operating conditions of said internal combustion engine.

14. The system defined in claim 13 wherein site at which tip of said spark plug is located is the edge of an air-squish zone.

15. The system defined in claim 1 wherein said high voltage igniting tip is constructed and arranged to electrically break down the air-fuel mixture gap between said igniting tip and said outer and/or said inner combustion chamber member with voltage in excess of 10 Kilovolts to supply said minimum 5 millijoules capacitive spark energy under all normal operating conditions of said IC engine without use of a series gap, and enabling an effective breakdown over a length of at least 0.16 inch (0.4 cm) to produce a spark of at least 0.16 inch (0.4 cm) under at least one condition of operation of said IC engine.

16. The system defined in claim 15 wherein said high voltage coil is constructed with primary and secondary windings to produce a voltage greater than 30 Kilovolts into a capacitive load greater than 100 pf and an initial capacitive spark peak breakdown current in excess of 100 amps.

17. The system defined in claim 16 wherein said combustion chamber outer fixed member is a cylinder head and said inner member is the top face of an air-fuel mixture compressing means of an IC engine, wherein compressing means moves to and from a top dead center, TDC, position of closest proximity to the outer member whereby minimizing chamber volume as defined, and wherein the sum of spark plug capacitance Csp and capacitance Cs'"'"' at the coil secondary side including externally added capacitors is greater than 100 pf and wherein said current peak in excess of 100 amps is produced by discharge of plug capacitance Csp.

18. System in accordance with claim 17 wherein said spark plug firing end central conductor tip is within and insulated from a spark plug shell with insulation length extending beyond plug shell end of length between 0.16" and 0.32" (0.4 cm and 0.8 cm) and defining a gap between said spark plug tip and said inner compressing means of at least 0.04 inches (0.1 cm) at TDC, and wherein spark formation of said plug tip defines an electrical breakdown "Firing Envelope" with a minimum voltage of 10 Kilovolts and a maximum voltage of 30 Kilovolts.

19. The system defined in claim 18 wherein said plug firing end defines an antenna tip with base diameter 2b" approximately equal to 1/4" (5/8 cm) and base gap "go" equal to 0.04" (0.1 cm).

20. System in accordance with claim 18 constructed and arranged so that immediately upon breakdown at the spark plug tip, the capacitance Csp discharges electrical charge producing EM current oscillations of frequency between 50 and 500 MHz and with peak currents in excess of 200 amps, and the capacitance Cs'"'"' discharges producing capacitive current oscillations of frequency between 2 and 20 MHz with peak currents in excess of 20 amps, and wherein a choke inductor Ls with inductance value between 1 and 400 microhenries is interposed between high voltage terminal of secondary winding of said coil and said high voltage tip of spark plug to tune frequency of said capacitive current corresponding to discharge of capacitor Cs'"'"' to below 10 MHz.

21. The system defined in claim 20 wherein said high voltage coil is a low turns ratio high efficiency coil with a turns ratio in between 45 and 55 which is part of a capacitive discharge (CD) circuit with a 400 volt rated discharge capacitor of capacitance value of 4 to 20 microfarads providing an inductive spark current with a current peak greater than 2 amps.

22. The system defined in claim 4 or 21 wherein said coil is a high efficiency coil with primary and secondary turns wound on the arms of a closed magnetic core of cross sectional area approximately one square inch, said primary winding made up of No. 8 to No. 14 wire and secondary winding made up of No. 22 to 26 wire.

23. The system defined in claim 21 including a spark plug lead connecting coil high voltage to plug and wherein low voltage wire of coil secondary winding is isolated from low voltage primary winding and said low secondary wire defines a shield for said spark plug lead, which shield is grounded to the IC engine block.

24. The system defined in claim 23 including ferrite material which begins to absorb EMI above 10 MHz which is placed around said spark plug central wire.

25. The system defined in claim 24 including distributor means to distribute high voltage to several spark plugs wherein all the spark plugs are shielded with metallic shielding material grounded at or near each respective spark plug shell and other ends of said shields are all connected together to an end of shield surrounding King lead which finds its ground through each spark plug shield and is connected to the isolated low side of coil secondary.

26. The system defined in claim 25 wherein spark plug contain in their body a choke inductor of inductance 0.25 to 5 microhenries.

27. The system of claim 25 wherein in addition to said two choke inductors there is a choke inductor mounted on rotor arm of distributor used for distributing high voltage to the spark plugs.

28. The system defined in claim 26 wherein said spark plug includes plug capacitance in excess of 20 pf made up of electrically conducting plating placed on outer and inner surfaces of the plug insulator and wherein said inductor is interposed between said inner plating and plug means used for connecting plug to high voltage means.

29. The system defined in claim 18 wherein said plug is part of a CDC ignition system producing multiple ignition pulses per ignition pulse firing train and wherein said antenna plug tip defines an EM Control Volume characterized by the sequential production of ignition spark pulses and high electric fields.

30. The system defined in claim 29 wherein duration of said firing train varies from approximately 3 msecs at 1000 RPM down to 1 msec at 3000 RPM, and wherein time between pulses at 1000 RPM is greater than time between pulses at 3000 RPM.

31. Combustion ignition system comprising in combination:

(a) means defining a spark plug for mounting in a combustion chamber and for acting as a first anchor of a sparking discharge extending therefrom to a spaced portion of a combustion chamber wall, which effectively provides a ground return to an ignition circuit through said chamber wall,

(b) means defining said ignition circuit, said circuit being connected to said spark plug for effecting at least one space firing period having an initial VHF to UHF current oscillation lasting for at least about one microsecond, whereby an electrical self resonance is induced in the combustion chamber by the circulation of said VHF-UHF current along the chamber wall to establish an oscillating EM field which enhances said spark discharge and flame kernel, while each such spark firing period further includes high capacitive and inductive spark energy transfer from the circuit to the spark.

32. The ignition system of claim 31 in combination with an internal combustion engine comprising a movable wall which moves relative to to a fixed wall to cyclically change the combustion volume, the spark plug being mounted in said fixed wall for sparking to the movable wall in an orientation which enables said self resonant chamber effect, and wherein said ignition circuit is further constructed and arranged for effecting multiple of pulses with OFF periods between them establishing repetitions of the initial VHF-UHF oscillations with EM energy components followed by inductive lower frequency sparks.

33. The ignition system of claim 32 wherein the spark plug has a capacitance in the range of 20 to 200 picofarads whereby a lean air-fuel mixture is excess of 20 to 1 can be fired under normal cruise engine operating conditions.

34. Ignition system in accordance with claim 33 including an external EM energy source connected to said combustion chamber for resonantly exciting said chamber during formation of said sparking discharge.

35. Ignition system in accordance with claim 33 wherein said movable wall is the rotor of a rotary engine with a central TDC contoured surface constructed and arranged such that as spark timing is advanced the spark gap between said movable wall and spark plug increases, for at least 50 degrees BTDC, and wherein the product of spark gap length and intake manifold pressure is within a range of four for timing of up to 50 degrees BTDC and provides a spark breakdown voltage which is within the range of 10 to 30 kilovolts.

36. Internal combustion engine apparatus comprising:

(a) a combustion chamber formed of a cylinder;

(b) a piston disposed in said cylinder for compressing air-fuel mixture by moving in successive cycles to and from a TDC position defining a minimum combustion volume;

the improvement comprising a combustion ignition system comprising at least one high voltage high capacitance electrode mounted in a central zone of the top of said cylinder and constructed and arranged as part of a CD ignition circuit to effect oscillations of sparking to the face of said piston during a spark firing period to generate essentially entirely internally to said combustion chamber and said high capacitance electrode circuit a VHF to UHF self resonant electrical oscillation and wherein the capacitance of high capacitance electrode is at least 20 picofarads and said spark firing period includes inductive component of at least two oscillations during a single engine cycle.

37. The system defined in claim 36 wherein said piston face at site of said electrode is contoured to provide a smaller change in said main spark gap relative to change in piston position about TDC.

38. The system defined in claim 36 wherein said high voltage capacitance electrode comprises a center conductor of a spark plug having a capacitance contained in the body of said spark plug between said center conductor and an outer shell and said system including an ignition coil and an inductor interposed between said center conductor and said ignition coil to confine said self resonance to within said plug and said chamber.

39. The system defined in claim 38 wherein the value of inductance of said inductor in units of microhenries is within a factor of five of the value of the output capacitance of said ignition coil in units of picofarads.

56. System in accordance with any of claims 4, 36, and 41 in combination with means for providing an air-fuel mixture to said combustion chamber of at least 22:

1 air-fuel ratio excepting under starting and high load conditions.

40. In a combustion apparatus comprising an enclosed combustion volume, a spark ignition and fuel and air feeding means, and an improved ignition system comprising means for generating an initial capacitive high frequency spark discharge of high initial breakdown voltage within the range of 3 MHz to 600 MHz oscillating internally within said combustion volume at an initial field strength in excess of 500 volts/cm/atmosphere for a duration of at least of the order of magnitude of one microsecond, through ignition circuit controlled conversion from a power supply of essentially DC frequency, i.e. frequency less than 1 MHz, the ignition system being constructed and arranged to repetitively render such spark discharges in repetitive combustion cycles.

41. The apparatus of claim 40 wherein said ignition system includes means for generating at least one follow on spark discharge within said volume, the initial and follow on discharges comprising a total ignition cycle corresponding to a single combustion cycle, the system further being constructed and arranged with low RF loss and to prevent misfire (failure to discharge) as the volume and discharge length increases within the preselected TDC range for said discharge, and wherein said apparatus includes means for changing said volume, the latter means comprising a cylinder with a fixed cylinder head, a movably reciprocatable piston face for approaching and receding from said fixed cylinder head, a spark plug firing end located essentially centrally in said head and insulated and impedance mismatched to force said discharges to be made to said piston face, with a ground return path comprising the piston, the wall of said cylinder, and said cylinder head.

42. The apparatus of claim 41 including a ceramic annulus communicating with said combustion volume so that said high frequency discharge currents flow around said annulus and effectively lower the oscillation frequency of said discharge currents.

43. The apparatus of claim 42 wherein said cylinder includes a sleeve and a gasket-type member sandwiched between said cylinder head and sleeve, said annulus being contained in said gasket-type member.

44. The apparatus of claim 41 including a high voltage ignition coil and an inductor interposed between said spark plug and said high voltage ignition coil so that approximately oscillation in the range between 100 and 600 MHz is produced by discharge of capacitive energy stored in said plug and approximately between 2 MHz and 20 MHz by discharge of capacitive energy stored in the capacitance of said coil discharging through said inductor.

45. In an electrical ignition system used for igniting air-fuel mixtures contained in a combustion chamber of an IC engine including at least one spark plug with a central high voltage conductor and an outer ground conductor containing a dielectric ceramic material interposed between said central conductor and said outer ground conductor, the improvement comprising means for providing maximum plug capacitance and minimum resistance to EM current in said spark plug by plating with high electrical conductivity material the ceramic surfaces of the portion of the said ceramic section interposed between said central and outer conductors.

46. The system defined in claim 45 wherein said high electrical conductivity material is from the group consisting of silver and copper, and the thickness of the plating on the outer ceramic surface is between 0.0002" (0.0005 cm) and 0.010" (0.025 cm).

47. The system of claim 45 wherein IC engine is a motor vehicle engine including at least one cylinder and piston with said spark therein, and said plug central conductor comprising a tip constructed and arranged such that under at least one normal cruise conditions of said vehicle the spark forms both to the back of the plug or plug shell and to the piston face during one spark plug firing.

48. The system defined in claim 45 wherein said central high voltage conductor of said spark plug has at least one diameter not less than 0.35" (7/8 cm) which is surrounded by dielectric insulating material of thickness between 0.1" and 0.12" (0.25 and 0.30 cm) and with relative dielectric constant greater than 8.0.

49. The system defined in claim 48 wherein said spark plug has protruding out of an outer shell ground conductor a central electrical conductor high voltage tip insulated along its length excepting for a bare metallic tip, i.e. an antenna plug tip, said insulated section of central conductor extending at least 0.2" (0.5 cm) beyond the outer shell ground conductor and wherein said spark plug tip and said outer plug ground conductor are further dimensioned and disposed such that the plug tip breakdown voltage is within the range of 8 to 32 Kilovolts under normal operating conditions of IC engine, and the system further including a multiple plusing CDC ignition for operating said plug wherein said plug tip defines a EM control volume characterized by the sequential production of spark pulses and high electric field pulses.

50. In an ignition system containing at least one spark plug, each such spark plug comprising means defining a conductive shell and a protruding central antenna conductor tip extending substantially beyond the spark plug shell of greater than 0.070" (0.175 cm) diameter and surrounded along part of its length with insulator of thickness about equal to tip diameter, the foregoing structure further defining a base gap "go" of at least 0.04" (0.1 cm), wherein said spark plug is mountable in a combustion chamber of an IC engine to define therein an EM Control Volume characterized by formation of both ignition spark and long duration high electric fields of strengths of at least 5000 volts/cm over at least a one cubic cm volume around said antenna tip.

51. The system defined in claim 50 including a CDC ignition system for producing multiple ignition pulses per ignition firing and said plug is mounted in a combustion chamber of an IC engine to ignite lean or other difficult to ignite mixtures, said CDC ignition designed to produce a train of sparking pulses including an initial ringing or closely spaced pulses followed by pulsus with larger spacings.

52. The system defined in claim 51 wherein said IC engine is a reciprocating IC engine and said plug tip defines a gap to the reciprocating member of said engine such that upon ignition firing sparks are formed to said plug shell and/or to said reciprocating member, and wherein the duration of said pulse train is reduced with engine RPM and wherein said pulse train includes "non-firing" pulses producing high electric fields within said EM Control Volume.

53. The system defined in claim 51 wherein said tip diameter is approximately 0.08" (0.2 cm), said insulator thickness is approximately 0.08" (0.2 cm) and said tip extends at least 0.2" (0.5 cm) beyond said shell to define "go" equal to approximately 0.05" (0.125 cm).

54. In an IC engine including at least one combustion chamber to which is mounted at least one spark plug and wherein each of said spark plugs are connected to at least one ignition coil, which ignition coil is part of a CD circuit with total secondary circuit high voltage capacitance Cs, the improvements comprising spark plug firing ends designed to provide a minimum spark breakdown voltage Vsm under normal operating engine conditions such that at least 5 millijoules are stored in Cs prior to breakdown and choke inductor interposed between high voltage terminal of said coil and high voltage terminal of said plug to control and tune discharge of secondary capacitances making up Cs and wherein inductance of said choke inductor is between 5 and 400 microhenries.

55. The system of claim 54 wherein said plug is a capacitance plug with capacitance greater than 20 pf and wherein in addition to said choke inductor there is a plug choke inductor disposed immediately at the high voltage connecting terminal of said spark plug.

57. An ignition system for cyclically firing internal combustion engine with a varying combustion volume comprising

(a) means for generating sequentially within said volume in each cycle of firing the following:

(i) rapid, large gap electromagnetic energy current pulses of magnitude greater than 100 amps and delivering approximately 50 KWatts to the large gap at an operating frequency between 50 and 500 MHz,

(ii) less rapid capacitive energy derived ignition pulses of magnitude greater than 20 amps and delivering approximately 10 KWatts to the large gap at an operating frequency between 1 and 50 MHz,

(iii) much less rapid ignition pulses of approximately 4 amps peak current and delivering approximately 1 KWatt to the large gap at a frequency of approximately 10 KHz,

(b) antenna means for coupling said electromagnetic current pulses and high electric field pulses within an EM Control Volume of at least one cubic cm;

(c) means defining a large gap spark anchor of 0.16" to 0.32" (0.4 to 0.8 cm) relative to said antenna means contained within said EM Control Volume.

58. The system defined in claim 57 voltage required to form said large gap spark defines a "firing envelope" with voltage between 10 and 30 Kilovolts.