Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02P—IGNITION, OTHER THAN COMPRESSION IGNITION, FOR INTERNAL-COMBUSTION ENGINES; TESTING OF IGNITION TIMING IN COMPRESSION-IGNITION ENGINES
  • F02P3/00—Other installations
  • F02P3/06—Other installations having capacitive energy storage
  • F02P3/08—Layout of circuits
  • F02P3/0876—Layout of circuits the storage capacitor being charged by means of an energy converter (DC-DC converter) or of an intermediate storage inductance
  • F02P3/0884—Closing the discharge circuit of the storage capacitor with semiconductor devices
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02P—IGNITION, OTHER THAN COMPRESSION IGNITION, FOR INTERNAL-COMBUSTION ENGINES; TESTING OF IGNITION TIMING IN COMPRESSION-IGNITION ENGINES
  • F02P9/00—Electric spark ignition control, not otherwise provided for
  • F02P9/002—Control of spark intensity, intensifying, lengthening, suppression
  • F02P9/007—Control of spark intensity, intensifying, lengthening, suppression by supplementary electrical discharge in the pre-ionised electrode interspace of the sparking plug, e.g. plasma jet 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
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
  • F02B1/00—Engines characterised by fuel-air mixture compression
  • F02B1/02—Engines characterised by fuel-air mixture compression with positive ignition
  • F02B1/04—Engines characterised by fuel-air mixture compression with positive ignition with fuel-air mixture admission into cylinder

Definitions

• the present invention relates to fuel ignition systems, and particularly to such systems for forming electrical field dischar ⁇ ges at the flame front of burning hydrocarbon fuels, particularly in internal combustion engines.
• EM stimula ⁇ tion can be made to occur in the entire combustion volume by high frequency electric fields resonantly stored in the combustion chamber with field strengths of order of 1000 volts/cm/atmosphere, exciting intermediate molecular levels at the flame front plasma.
• Other prior art of the applicant herein is disclosed in U.S patent application Serial No. 885,961, based on U.S. patent appli ⁇ cation Serial No.779,790, where EM flame-front stimulation occurs near the spark plug site by means of a system designated as "EM Ignition".
• the present invention generally is based on having taken what is believed to be a new and different perspective on "ignition” by extending existing ignition principles and the new EM Ignition concepts to include the high density chemically produced hydro ⁇ carbon flame plasma as an intrinsic part of the ignition process, with the result that a more general and unified approach to igni ⁇ tion is attained. From this new ignition perspective, new opti ⁇ mized ignition systems have been invented, and answers found to hitherto unresolved ignition controversies.
• the ignition spark, the initial flame (plasma), and the electric field at the spark plug site are viewed as interrelated, coexisting aspects or characteristics of a much more general, overall ignition process.
• the degree to which one usefully harnesses these interrelated ignition processes is what- leads to a greater or lesser effective ⁇ ness of the overall ignition system.
• the approach one takes to more optimally harness these various interrelated igni ⁇ tion processes depends strongly on the physical conditions or environment one is dealing with, and the result one is attempting to achieve.
• the current state-of-the-art in ignition systems is believed to be the recently disclosed EM.
• Ignition system which is designed to incorporate in a more optimal way the capacitive and inductive spark components within a very large ignition volume.
• the present invention builds upon these characteristics — by taking the new perspective and including in a self-consistent way the electrical spark discharge characteristics, the associated electric field, and the behavior of the resulting flame plasma in the electric field environment of the spark discharge.
• This new perspective has led to the invention of new ignition systems designated as ECDI and PFDI, and to the invention of a more optimized fuel for such systems, designated as EMT fuel.
• the first of these new systems is a modification to the stan ⁇ dard ignition system which provides "enhanced conventional spark ignition” (hereinafter sometimes referred to as the ECDI system), with the intention to attain optimal coupling of. the naturally occurring electric field (associated with the spark discharge) to the initial flame front plasma forming at the spark plug site.
• This system can use either a high efficiency, high energy conven ⁇ tional coil to drive it, or a modification to be described and referred to hereinafter as ECDCC, which stores more energy per firing and delivers it to the "spark” with a very high efficiency of 70% to 80%, many times that of a standard ignition.
• the ECDI system preferably uses such an ECDCC system.
• PFDI pulsed flame discharge ignition
• the pulsed flame discharge ignition version of the present invention has as its practical basis the high efficiency voltage doubling coil with its high energy and very high efficiency, as described in copending U.S. patent application SN 688,030 (desig- nated as the CDCC system), and the concept of a large "EM Control Volume" defined at the antenna type plug tip of the EM Ignition system described in copending U.S. patent application SN 885,961.
• This invention is based upon the recognition of the criticality of certain ignition parameters (such as but not limited to combi- nations of the spark plasma temperature and recombination coeffi ⁇ cient, the lean hydrocarbon-air mixture flame plasma density and the electron neutral collision frequency, the ignition operating frequency, the flame speed and engine speed (RPM), the ignition pulse train temporal characteristics, the structure of the spark plug tip and the structure to which it is mounted, and the orien ⁇ tation of the structure and plug tip to the " piston motion and more generally to the fluid motion at the plug tip) which define the pre and post breakdown spatial electric field intensity (both the magnitude and direction).
• certain ignition parameters such as but not limited to combi- nations of the spark plasma temperature and recombination coeffi ⁇ cient, the lean hydrocarbon-air mixture flame plasma density and the electron neutral collision frequency, the ignition operating frequency, the flame speed and engine speed (RPM), the ignition pulse train temporal characteristics, the structure of the spark plug tip and the structure to which it is mounted, and the orien ⁇ tation of the structure and plug tip to the "
• pulsed flame discharge ignition (hereinafter sometimes referred to as PFDI) can be attained and ignition energy can be dumped, across the flame front, depositing up to hundreds of watts of electrical power at the flame front to produce intense electrical excitation energy to allow very lean mixtures to burn.
• the fuel selected for use in the present invention is prefer ⁇ ably tailored to generate a plasma with a high or boosted density at the flame front and a lower density elsewhere, i.e. it gene ⁇ rates the plasma chemically.
• Such boosting is achieved by modi- fying the carbon to hydrogen or C/H ratio of the fuel (increasing the ratio) and simultaneously eliminating additives which reduce the plasma recombination coefficient and increase the tail plasma
• additives such as low ionization potential metals are preferably not used except in very small amounts significantly lower than used heretofore for generating high density plasmas.
• Such trace additives may be desirable to provide a slight boosting of the density across the entire flame profile, especially along the front edge, provided that the tail density is much lower than the flame front density.
• the fuel as described above When used as a fuel in an internal combustion engine, the fuel as described above generates a flame plasma density profile which is suitable for stimulation by an intense electric field maintained in the combustion chamber, preferably in the region of the initial burn.
• the electrical energy is coupled at the flame front plasma, and marginally at the tail, to generate intense molecular internal excitation at the flame front to help the lean burning flame burn faster and more completely. More important, with respect to the novel ignition systems proposed herein, such fuel will further enhance their effectiveness to allow the burning of extremely lean mixtures.
• ignition is viewed not simply as the electrical breaking down of air, but rather as the formation of electrical discharges which are coupled to the flame front itself which becomes the ignition spark (essentially a moving "spark"), to lesser or greater extent depending whether one is implementing an ECDI or PFDI approach, characterized in part by high to very high electrical power delivery to the mixture (of about 100 and 500 watts respectively).
• ECDI or PFDI approach characterized in part by high to very high electrical power delivery to the mixture (of about 100 and 500 watts respectively).
• the interaction of the electric field with the spatial and time varia- tions of the plasma discharges of the spark and moving flame are considered in detail from a new unified perspective. This is done in part with the objective of using the powerful new ignition technologies and approaches developed by the applicant in U.S.
• Another object of the present invention is to use the high plasma generating properties of hydrocarbon flames in combination with an ignition system including a spark ignition,means which provides ignition energy in which a significant part of the igni ⁇ tion energy is delivered to the flame; and to provide such a system in which the flame front from such a spark moves initially in a direction in which the electrical field intensity parallel to the flame front increases.
• a high efficiency (low turns ratio) voltage doubling ignition coil of the CDCC type which has the major part of its length perpendicular to the electrical field intensity at the spark plug tip, and in which the flame propagating from the spark moves in a
• SUBSTITUTE SHEET current (e.g. 50 ma to 200 ma) to improve the coupling of such field to the flame plasma; to provide such a system in which the discharge current is in the form of sine-waves with peak ampli ⁇ tudes in the range of 100 to 400 ma; to provide such a system which includes a large spark gap of about 0.1 inches of a projec ⁇ ting type spark plug tip providing a significant normal component of electric field to the spark orientation, and a button at the end of the plug tip providing a long ignition duration correspon ⁇ ding to a longer flame path so that the discharge electric field is coupled to the flame plasma over the larger volume defined by the button and the plug shell.
• Yet another object of this invention is* to provide such a fuel in which are present low ionization potential materials in trace amounts sufficient, when a mixture of air and such fuel is ignited, to boost the plasma density across the entire flame pro ⁇ file or flame zone without unduly increasing the density in the tail zone; and to provide such a fuel having no more than trace amounts of alkali earth metals and optionally one or more addi ⁇ tional compounds in amounts sufficient so that upon ignition, the resulting flame plasma density is boosted with the plasma profile still exhibiting a sharply dropping plasma tail characteristic of pure hydrocarbon fuel-air combustion.
• a conti- nuous flow combustion system e.g. a turbine or burner
• SUBSTITUTE SHEET Another object of the present invention is to use such a fuel with an EM Ignition system featuring sequentially pulsed ignition “firings" and an antenna type plug tip contoured to produce a pre-breakdown electric field distribution at the tip with electric field components distributed largely perpendicular to the spark and largely parallel to the flame as it propagates away from the tip (and is still contained in the EM Control Volume).
• Another object of the present invention is to use such a fuel with a system providing a spark energy delivery efficiency greater than 50%, ' i.e. the CDCC system using a low turns ratio voltage doubling coil with primary circuit capacitor charged to preferably between 360 and 660 volts, and secondary circuit capacitance of about 200 picofarads contained in part in a "boot" mounted on a spark plug (or in the plug itself) which has a projecting tip for producing a large ignition volume and a large arc burning voltage of at least two hundred volts under typical operating conditions.
• Another object of the present invention is to use such a fuel with an EM Ignition system with an ignition "sparking profile" characterized by the sequential generation of single sine wave sparks with a large capacitance component and a large oscillating sine wave inductive component, wherein such closely spaced single sine wave sparks are formed to the spark plug shell and/or the piston face to create high, longer duration pre-breakdown local electric fields followed by some degree- of electrical discharge across the flame front around the spark plug tip.
• Another object of the present invention is to use a spark plug with a partially insulated center electrode nose end which is contoured to provide focussing of the electric field which exists during all stages of the plug firing so that the plug nose becomes essentially a cylindrical electric field lens resembling a hyperboloid of one sheet for focussing the electric field to a small toroidal region surrounding the cylindrical plug end for reducing the breakdown voltage and for further guiding and coup ⁇ ling of the electrical spark energy to the initial flame as it propagates away from the initial spark site and into the chamber and around the large toroidal gap surrounding the plug nose end.
• Another object of the present invention is to provide such a focussing lens plug with a firing end button tip made of small diameter, erosion resistant material with its maximum diameter projecting just beyond the ceramic insulator tube end of the plug nose and contoured to be part of the plug lens to further improve the electric field focussing and thus provide a more optimized electric field focussing lens plug (or EFFL plug).
• Another object of the present invention is to further contour the plug nose of such an EFFL plug in conjunction with contouring of the plug shell end and positioning with respect to the cylinder head to improve the focussing to the surrounding ground surfaces comprised of the plug grounding shell end and/or edge of cylinder head around said plug shell end so as to reduce the breakdown voltage between the plug tip and said surrounding ground surfaces to further improve coupling to the initial flame front.
• Another object of the present invention is to provide such an EFFL plug for the industry standard 14 mm threaded shell plug •which has an insulator of approximately 0.1 to 0.12 inch thick ⁇ ness surrounding a 0.09 to 0.12 inch diameter center high voltage conductor at the region where the gap between the insulator and the plug grounding shell is a minimum, providing an overall insu ⁇ lator diameter of approximately 0.30 to 0.36 inches inside the shell near the plug firing end, and a smaller overall diameter between 0.22 and 0.26 inches for the insulator section located at the plug firing tip,- and a diameter of approximately equal to and slightly greater than 0.25 inches for the high voltage metallic firing end button.
• Another object of the present invention is to use such an EFFL plug with a CDCC ignition system, preferably including a smaller capacitive boot of about 50 picofarads capacitance and with spark plug wire of preferably high inductance and low resistance, where the capacitive discharge system of the CDCC system is contained along with the ignition coil in an insulating enclosure to provide high ignition system efficiency by minimizing the coil primary current path, and where EMI may be reduced by using a further enclosure of a conducting material grounded to the engine block and thus defining a further improved or optimized CDCC ignition.
• HEET Another object of the present invention is to provide a high efficiency capacitive discharge ignition system using low forward drop SCRs as the spark pulsing switches, preferably of one volt forward drop at 100 amp current, and capable of producing closely ' spaced multiple spark pulses of short duration of 80 to 100 usec, brought about by a speed-up shut-off circuit which naturally and simply applies a negative bias to the SCR trigger gate during SCR firing to shorten the SCR's recovery time and provide an optimized ignition pulse train for the present invention.
• Another object of the present invention is to optimize said improved CDCC ignition system by including said speed-up SCR shut -off circuit so that the ignition can have a minimum pulse firing time without the SCR latching (80 usecs for current low forward voltage SCRs) and can thus have many spark pulses per ignition firing, say ten at low engine RPM and at least three at high RPM, and by further adjustment and refinement of the ignition system parameters to provide an optimized PDI system, defined as the CEI Ignition system.
• Another object of the present invention is to provide a some- what higher peak current (i.e. about 1 amp) ECDI system with a shorter spark pulse period of about 100 usecs and a low primary coil turns, i.e. 10 to 30 turns depending on the primary voltage used, and preferably a recharge circuit for supplementing the lower energy stored in the discharge capacitor of the modified ECDI system (i.e. 100 to 300 millijoules versus 300 to 500 milli- joules for the standard PDI system).
• a some- what higher peak current (i.e. about 1 amp) ECDI system with a shorter spark pulse period of about 100 usecs and a low primary coil turns, i.e. 10 to 30 turns depending on the primary voltage used, and preferably a recharge circuit for supplementing the lower energy stored in the discharge capacitor of the modified ECDI system (i.e. 100 to 300 millijoules versus 300 to 500 milli- joules for the standard PDI system).
• FIG. 1 depicts an idealized, partial, cross-sectional view of a standard spark plug tip defining a spark gap, and showing various spark characteristics.
• FIG.la depicts a partial, cross-sectional view of an antenna type spark plug tip of an EM Ignition system mounted near the end of an internal combustion engine chamber, depicting the electric field distributions around the tip.
• FIG. lb is a graphical representation of the typical voltage- current discharge characteristic of a standard spark plug such as is shown in FIG. 1.
• FIG.2 is an idealized, longitudinal cross-sectional, partial view of a projecting type spark plug tip, particularly useful in the ECDI system and embodying the principles of the present inve ⁇ - tion, which view also includes a showing of an electric fLeld distribution defined by the plug tip structure with respect to both the initial spark or arc and a propagating flame front.
• FIG. 2a is a cross-section taken along the plug tip of FIG. 2 including lobes for controlling the position of the initial spark.
• FIGS. 2b, 2c are graphical representations of preferred dis ⁇ charge current-voltage curves used in conjunction with the igni ⁇ tion ignition system having the plug tip of FIGS. 2 and 2a.
• FIG.2d is an idealized, longitudinal cross-sectional partial view of a projecting type spark plug tip embodying principles of the present invention and particularly useful in the PFDI system, depicting the electric field perpendicular to the spark and more parallel to the propagating flame front plasma.
• FIG. 3 is a graphical representation of a typical heat- release, plasma density, and temperature spatial distributions across the flame front of a model one dimensional flame.
• FIG. 3a is a graphical representation of flame plasma density distributions n(0,phi,f) versus fuel-air equivalence ratio phi of a standard fuel and a preferred fuel of the present invention.
• FIG. 4 is a graphical representation of the initial arc density-time distibution of a single initial short duration spark, and the flame density distributions for four equivalence ratio flames started by the spark.
• FIG. 5 is a graphical representation of the plasma density profile as a function of time of a multi-sparking arc and ensuing flame plasma in an ignition system of the present invention using an antenna type tip and a very lean flame of the preferred fuel.
• FIG. 7 is an idealized, cross-sectional view of a preferred spark plug for use either alone or with the boot of FIG. 8 and suitable for use in either of the PFDI or ECDI systems.
• FIG. 8 is an idealized, cross-sectional partial view of a preferred plug with a preferred capacitive boot particularly suitable for use in the PFDI system.
• FIG. 8a is a schematic diagram of the equivalent circuit of the embodiment of FIG. 8.
• FIG. 9 is a graphical representation of the spark and flame plasma distributions as a function of time resulting from igni ⁇ tion firing in a PFDI system preferably of a multi-sparking CDCC system with a very lean hydrocarbon fuel-air mixture, showing the various time dependent plasma build-ups and decays with time.
• FIGS. 9ab to 9af inclusive shows a sequence of partial sectional views of a PFDI spark plug tip of FIG. 2d showing the magnitude and position of the spark and flame plasmas (relative to the electric field direction) as a function of time with each successive ignition firing.
• FIG. 9b is a graphical representation of the relative magni ⁇ tude and direction of the spark and flame front plasmas as a func ⁇ tion of time with each successive ignition firing (represented by FIGS. 9, 9a, of a system exemplified by FIG. 10) with the direc- tion of the average electric field superimposed on each front.
• FIG. 10 is an idealized view, partially in block diagram and partially schematic, of a preferred embodiment of the complete PFDI system of the present invention suitable for use in a multi- cylinder internal combustion engine, including a capacitive dis- charge circuit with EM interference supressing circuitry and cables.
• FIG. 10 is an idealized view, partially in block diagram and partially schematic, of a preferred embodiment of the complete PFDI system of the present invention suitable for use in a multi- cylinder internal combustion engine, including a capacitive dis- charge circuit with EM interference supressing circuitry and cables.
• FIG. 11 is a longitudinal cross-sectional partial view of an electric field focussing lens (EFFL) spark plug end defining a toroidal gap and contoured such that it embodies the principle of focussing of the electric field to the vicinity of the cylinder head edge region into which, and around which, the initial flame propagates and thus improves coupling of the electric energy to the initial propagating flame front while simultaneously reducing the size of the end button and keeping the initial spark pulse away from the surface of the insulator.
• FIG. 11a is a longitudinal cross-sectional partial view of the plug end of an EFFL spark plug, of a variant design compared to FIG. 11, based on an 18 mm plug with the shell end further contoured to both act as the approximate focal point circular edge and to provide a gradual transition from an initial spark pulse formed in the interior to the subsequent spark pulses of a single ignition system firing.
• EFFL electric field focussing lens
• FIG. lib is a half longitudinal cross-sectional partial view of an EFFL plug, of a variant design compared to FIG. 11, wherein the insulator end is further contoured to provide a somewhat larger end diameter for assisting in keeping the initial spark pulse away from the insulator surface.
• FIG.lie is a longitudinal cross-sectional partial view of an EFFL plug, of a variant design compared to FIG. 11, with the plug nose end and shell end contoured so that the nose end lens focus- ses directly onto the edge of the shell end so as to reduce the breakdown voltage and provide a larger spark gap for a given maximum output voltage.
• FIG. lid is a longitudinal cross-sectional partial view of an
• EFFL plug of a variant design compared to FIG. 11, with the plug end and shell end contoured so that the nose end lens focusses somewhat beyond the shell end and near the cylinder head edge and such the interior end surface of the shell forms a gradual slope so that in combination with the electric field focussing effect the spark pulses are encouraged to move outwards and around the toroidal gap defined by the plug end.
• FIG. lie is a longitudinal cross-sectional partial view of an EFFL plug, of a variant design compared to FIG. 11, with the interior end surface of the shell further contoured so that it in turn becomes a partial electic field lens which in combination with the plug nose lens helps intensify the electric field between the plug end button and the plug shell edge.
• FIG. llf is a longitudinal cross-sectional partial view of an EFFL plug, of a variant design compared to FIG. 11, located near a sidewall of an engine cylinder which is contoured along with the plug shell interior to produce further electric field focussing to the spark plug end button.
• FIG. llf is a longitudinal cross-sectional partial view of an EFFL plug, of a variant design compared to FIG. 11, located near a sidewall of an engine cylinder which is contoured along with the plug shell interior to produce further electric field focussing to the spark plug end button.
• llff is a longitudinal cross-sectional fragmentary view of an idealized EFFL plug with an overly extended shell end with interior surfaces contoured to form an electic field lens which, in combination with the plug nose lens, further intensifies the electric field between the plug end button and an interior point of the plug shell.
• FIG. 12 is an idealized, cross-sectional partial view of an EFFL plug which is of particularly simple construction with a preferred particularly simple, flexible, low EMI, moderately low capacitance (30 to 50 picofards) capacitive boot to which is connected a preferred high inductance, low resistance, low EMI spark plug wire.
• FIG. 13 is an idealized view, partially in block diagram and partially schematic, of a preferred embodiment of an optimized form of ignition of the present invention, referred to as the CEI Ignition, suitable for use in a multi-cylinder internal combus ⁇ tion engine. -
• the "low" current or ECDI version of the present invention employs a somewhat projecting special type spark plug tip with a gap of about 0.1" for a large flame path.
• a more projecting plug tip approximately 0.2 inches long is used, and is shaped such that the initial spark forms mainly perpendi ⁇ cular to the electrical field intensity so that on subsequent ignition pulses the coupling to the decaying ignition spark plasma is very poor, but the coupling to the flame propagating from the initial spark is strong because the flame front becomesprogressively sively parallel to the electrical field and is able to absorb the electrical power.
• the flame front itself becomes the ignition spark, and the ignition circuit is completed through it.
• EMT fuel Such a fuel has been designated as EMT fuel.
• EMT fuel is characterized by having, during combustion, a higher than normal electron plasma density at the flame front produced by the phenomenon of chemi-ionization.
• the fuel - has a C/H ratio near one, and more generally in the range of .5 to 2.
• Trace amounts of alkali earths may be used in combination with fuels of appropriate C/H ratios (from. " 5 to 2) and/or preferably with an overall plasma recombination coefficient that forces the tail plasma to decay rapidly.
• Effective stimulation of the flame is achieved " by using such an EMT fuel in IC engines where the ignition can be pulsed ON and OFF during an ignition firing, generating successively high and low electric fields in the region of the flame front.
• electrical energy is coupled at the flame front plasma where it is needed, and to a lesser extent to the successive spark plasmas and to the tail plasma behind the flame, i.e. pulsing insures that the spark and tail plasmas are allowed to decay during the electric field OFF periods while the chemically pro ⁇ claimed flame front plasma grows progressively in volume and inten ⁇ sity, absorbing progressively more of the electrical energy on successive pulses while the flame is within the "EM Control Volume” (the volume over which the air-fuel flame plasma is influenced).
• the modified fuel of the present invention can be used in all internal combustion (IC) engines, from gas turbines where the fuel can be used in conjunction with an EM field reso ⁇ nantly stored in the combustion zone, to lean burn reciprocating and rotary engines where the fuel may be used in conjunction with EM Ignition using a projecting spark plug tip for producing a large EM Control Volume with mainly perpendicular and parallel
• Such a fuel is also applicable to burners, with operation similar to turbines.
• FIG. 1 is a longitudinal, cross-section partial view of a nose end of a prior art type of spark plug 10, including center metal electrode 11 of diameter "2a", surrounded on its sides by nose insulator 18. Electrode 11 has one uninsulated end defining a spark gap 17 of width "h" with respect to ground electrode 13.
• spark 14 Shown also is the spark 14 as defined by the applicant to include the initial capacitive component formed upon the breakdown of the dielectric in gap 17 and subsequent discharge of the high voltage secondary capacitance, followed by the "inductive” component resulting typically from the delivery of the magnetic energy stored in the coil of a standard inductive ignition system, and the electromagnetic (EM) electric field component 16 (solid lines with arrows pointing in the field direction); such field is now claimed by the applicant to exist (co-exist) in all phases of the ignition process.
• EM electromagnetic
• FIG. la is a longitudinal, cross-section partial view of a prior art "antenna type" spark plug tip recently disclosed by the applicant in pending U.S. patent application SN 885,961 depicting the enlarged region over which the electric field lines 16a, 16aa have their influence, namely the EM Control Volume 19.
• the plug tip 11a is generally pointed, as shown, to be able to focus the electric field to more readily form spark 14aa to the piston 13b (as well as to the plug shell 13a - spark 14a).
• spark 14a can have its direction largely normal to the electric field E but the resulting flame 15a (shown cross-hatched) is also largely normal to the electric field, having a large component En versus a large tangential component Et, the latter preferably.
• the conical shape of the tip 11a and insulator tip 18a with pointed end extending outwardly reduces the field intensity of the elec ⁇ tric field (lines 16a) because of the large bowed path length between the surface of tip 11a and surface 12a of the cylinder head 12.
• spark 14aa which is parallel to the E- field, no effect at all of the present invention is achieved. Spark plugs similar to the one disclosed in U.S.
• patent appli ⁇ cation SN 885,961 (excepting for the tip 11a which protruded less and had same diameter as the main wire 11) were installed in a 1.3 litre 1985, Ford Escort engine. Using a high octane unleaded fuel, the engine produced excellent lean burn results. However, since the engine is of the hemi-head type with the spark plug located near a curved surface near one end of the combustion chamber similar to that shown in FIG.la, the plug thread tip necessarily projected well beyond the cylinder surface to achieve best results (contrary to the teachings of the present invention since it reduces the E-field converging onto the cylinder surface).
• the tip itself and conical shape of the insulator tip further reduced the electric field intensity over what is now seen to be preferred, as already pointed out with reference to FIG. la. Furthermore, whenever a spark was formed at the left side of the cylinder head (see FIG.la), the E-field coupling to the flame front propagating from that spark would be poor because the E- field is largely normal to it.
• FIG. lb depicts typical Voltage-Current discharge character- istics of the plug of FIG. 1, further showing the three principal regions of interest for the present purposes, the glow discharge region I defined as that portion of the curve up to about 50 ma (and a potential of about 500 volts); the transitional region II defined as that portion of the curve between a current of about 50 ma (voltage of about 500 volts) and a current of about 2 amps (voltage of 50 volts); and the arc discharge region III defined by an approximately constant voltage of 40 volts for currents greater than 2 amps.
• the glow discharge region I defined as that portion of the curve up to about 50 ma (and a potential of about 500 volts)
• the transitional region II defined as that portion of the curve between a current of about 50 ma (voltage of about 500 volts) and a current of about 2 amps (voltage of 50 volts)
• the arc discharge region III defined by an approximately constant voltage of 40 volts for currents greater than 2 amps.
• TGD transitional glow discharge
• TAD transitional arc discharge
• the voltage across spark gap 17 (in air or in a typical air-fuel mixture) is approximately 500 volts, represen ⁇ ting a field strength of 5000 volts/cm for a gap width h of 0.040 inches (1.0 mm).
• E-field flame stimulation it will be seen that this statement implies that along with the ignition spark there exists an E-field of the required strength (1000 volts/cm/atmosphere) to stimulate the hydrocarbon fuel-air mixture flame in the spark gap 17 under almost all conditions of operation of an engine or burner.
• the increased time as the mixture is made leaner is consistent, since it is known that flame speed drops with air-fuel ratio.
• the flame speed of 2.4 mm/msec is six times the gasoline flame speed of 40 cm/sec, corresponding to the six-fold expansion effect of the initial flame, i.e.” the flame temperature is six times the gas temperature.
• the present invention therefore serves to optimize a standard ignition system by, in addition to increasing the gap size (but not to the point where the E-field falls below 800 v/cm/a) increa ⁇ sing the electrode gap area, thus increasing the E-field enhanced flame travel length and the duration of the spark correspondingly.
• the spark current typically starts at a value of about 300 ma corresponding to about 200 volts discharge voltage, and progressively drops, increasing the voltage and increasing the E-field stimulating effect.
• this enhancement can be extended to an unlimited path length, the practical limitation being however the E-field strength that one can maintain.
• FIG. 2 is a cross-section longitudinal partial view of a spark plug suitable for more optimally employing the low current E-field enhanced conventional discharge ignition, or ECDI version of the present invention.
• This plug differs substantially from the prior art plug shown in FIG. 1 in that it omits any ground electrode per se, and differs significantly from the prior art type plug of FIG. la in that it includes a large erosion resistant metallic plug tip or "button" 21a (having substantially flat outer surface 29b) mounted on an axially disposed conductor 21 typically 0.090 inches in diameter encased by electrically insulating layer 28 of substantially constant thickness of 0.06" to 0.08" for at least a length 2L1 defined hereinafter.
• electrically conductive plug shell 23 Disposed about the outer surface of layer 28 is electrically conductive plug shell 23 which includes projecting cylindrical end portion 23a spaced apart from the central wire 21 by a uniform distance of between .02" to .04".
• Length "LI" defined as the axial distance between the button 21a and the bottom of end portion 23a is in the range of .06" to .12".
• a portion of the cylindrical periphery of button 21a forms conical frustrum 29a at an approximately 45 degree angle to the axis of wire 21 in a direction away from the tip.
• an approximately toroidal gap 27 is created between frustrum 29a and portion 23a providing a large ignition volume as required.
• button 21a as a frustrum serves two further very important advantages, namely to intensify the E-field in the gap 27 and to reduce the detrimental effects of surface erosion from ignition sparks (because of the larger mass of button 21a which is preferably a Nickel alloy).
• FIG. 2a shows the plug of FIG. 2 in cross-section through plane defined by CS of FIG. 2, with center conductor 21b surroun- ded by insulating layer 28a, and several lobes 26a, 26b, 26c, 26d forming smaller gaps gO to the surface of insulator 28a thereby intensifying the field in these gaps.
• the length of its flame path and thus its E-field enhanced volume is significantly greater than that of FIG. 1.
• the E-field enhanced volume can also be increased by adding a large ground electrode across button surface 29a with the additional advantage that the flame path is increased by a relatively lesser amount.
• this advantage is more than off-set by the disadvantage of the large heat absorbing ground electrode, it being further relatively easy to provide a longer spark duration since the power delivery is relatively low. It is also disadvantagous to have the spark and field parallel to each other versus at some angle to each other determined by the present plug tip geometry.
• spark 24 forms through local initial breakdown in a gap gO between shell portion 23a and insu ⁇ lator surface 28 across which almost the full ignition voltage is applied.
• the local discharge plasma then moves along the surface of the insulator (seeking the other electrode) and anchors itself on button 21a defining a spark direction largely perpendicular to the E-field lines 26; flame fronts 25 (shown cross-hatched) move away to become progressively parallel to the E-field lines 26.
• the (ECDI) system thus described is further improved by using a modification to the ignition system of the CDCC type described in U.S. patent application SN. 688,030.
• This proposed modifica ⁇ tion uses approximately five times the number of primary turns used in the prior system and about half the primary energy storage capacitance, to provide a sinewave current with an initial peak current approximately one eighth that of the prior (CDCC) system, or 300 ma, and approximately five times the sine wave period (0.4 msec for example).
• a 3 msec duration ignition discharge can easily be achieved with eight complete oscillations.
• coil turns ratio is 50 and capacitance is 4 ufd which is charged up to about 350 volts providing 0.3 joules stored energy.
• the modified ignition system (sometimes hereinafter referred to as ECDCC) is preferably used in the multi-pulse ignition mode as is depicted in FIGS. 2b, 2c, where the reference numerals 122 and 123 represent the two halves of the sinewave current, and reference numerals 122a, 123a represent the corresponding arc voltage waveforms, with a period of 400 usecs and a time between pulses of 100 usecs (i.e. 0 to 250 usecs), so that the subsequent "sparks" 124/125, 126/127, etc. have a chance to form across the moving flame front plasma for further possible improvement.
• the typical rate of energy delivery of such an ECDI system is 100 watts, or five times the standard ignition, i.e. assuming an average current of 200 ma and an arc burning voltage of 500 volts.
• the independent variables i.e. either increase the spark current or the size of the spark gap. But increasing the spark current (for a constant gap) is accompanied by a reduction in the voltage (for no overall gain) and a reduction of the E-field strength. Increasing the gap size reduces the field strength.
• E-field discharge enhancement (ECDI) is abandoned, and a much larger current of several amps peak is used, which can be provided (in a practical, cost effective way) by the CDCC system of U.S. patent application SN 688,030.
• the relatively low arc burning voltage is then increased (to about 200 volts) by further extending the plug nose end of FIG. 2 to that shown in FIG. 2d., providing a higher power of about 500 watts to the spark, but relatively little to the initial flame front as the E-field is low.
• the E-field lines 26 are mainly perpendicular to the major part of the spark core 24a (the capacitance spark component), which reduces the coupling of the E-field to the existing spark or to the residual spark or spark remnant (depending on the situation).
• the E-field asso ⁇ ciated ' With the spark discharge provides the flame enhancement, but rather a "pulsed flame discharge ignition", wherein the flame front plasma itself becomes the ignition plasma.
• the flame front shown typically at 25a, 25b, 25c in cross-hatched lines, has much more of its front parallel to the E-field than does the spark 24a, and since the spark is a very high density plasma which tends to exclude the field, namely the normal compo ⁇ nent En, which is the predominant one here, little electrical energy can be coupled to the spark after the initial breakdown, while effective coupling can occur to the flame.
• the discharge E-field is low (for the higher peak currents of 1 - 3 amps)
• PFDI alternative
• a preferred embodiment of the plug tip of FIG. 2d has preferably center conductor 21 with diameter 0.09" terminating in a button 21a with a surface 29a representing essen ⁇ tially a 90 degree arc of a circle.
• the plug shell is preferably recessed 1/32 to 3/32 of an inch from the cylinder head surface 22a, defining a length shown "L r " which is approximately 2/3 of length "L2".
• Insulator 28 has its surface essentially vertical (i.e. parallel to conductor 21) and its thickness is between 0.06 to 0.09 inches. Gap gl is in the range of 0.02 to 0.06 inches, preferably 0.04 inches. With such a geometry, spark formation 24a occurs with its major part normal to the E-field. First flame front 25a results from the inductive plume 24b which surrounds spark core 24a at the end of the first spark discharge.
• Flame fronts 25b and 25c are spaced apart by one mm on the scale shown, representing the flame front position 1/4 and 1/2 msecs later assuming moderate (1000 RPM) engine speed induced air flow which doubles the flame speed.
• flame front 25c very strongly couples to the E-field since its front is almost totally parallel to the E-field, which has a relatively high intensity because of the geometry shown, i.e. path length "Lg” is only a fraction longer than length "L”, and the E-field magnitude "E” is given by E - V/Lg, where V is the voltage on conductor 21a.
• FIG. 3 depicts the various spatial distributions across a one dimensional hydrocarbon (HC) fuel-air flame front. Shown is the flame front identified by reference numerals 31 defining its front edge, and further defined by the heat release curve 33 (in dotted line), the temperature curve 34 (in dashed line), and the flame plasma concentration curve 32 or density n(x) (in solid line). Flame plasma width 36 (x(0)) corresponds to the width of the reaction zone. What is illustrated here is the "chemi-ionization" nature of the HC fuel-air flame, which dictates that the density concentration curve n(x) will have its front edge coincide with the front edge of the heat release rate curve 33.
• n(x) which is more completely designated as n(x,phi,f)
• phi equivalence fuel-air ratio
• chemi-ionization is an unusual chemical ionization phenomenon characteristic of all HC fuel-air combustion, which was discovered about three decades ago and was found to depend on the existence of the C-H bond in the fuel. Furthermore, it was found that the peak value of the HC fuel-air flame plasma density n(0,phi,f) (or n(0) for short) is six orders of magnitude greater than the value dictated on thermal grounds, because it is chemically produced. For the present purposes, the flame plasma density is sufficiently high to be of important con ⁇ sideration in the ignition and combustion process. It is claimed here that it is an inherent part of ignition, that when properly viewed and implemented, becomes a key factor to the solution of the Lean Burn problem. It is the missing factor in the Electrical Theory of Ignition.
• x(l) a tail width defined as the value at which curve
• N(xl) J n ⁇ x is ⁇ e tota l plasma (electron) count o across the flame front.
• AFR gasoline air-fuel ratio
• PR of a fuel is obviously an arbitrary one, but one that permits the making of comparisons among fuels from
• EMT fuel PR rating of 100 or greater
• the fuel described by the value of n(0,.6,f) shown here is of marginal use for the present purpose (represen ⁇ ting a PR value of about 96).
• n(0,.6,f) shown here is of marginal use for the present purpose (represen ⁇ ting a PR value of about 96).
• n(0,.6,fl) 4*10**10 as indicated by point 39a, and the profile factor PF is unchanged at 1.0.
• FIG. 4 shows the logarithm of temporal density distribution of a single spark 42 designated as n(arc,t), corresponding to the case of a spark formed by a CDCC system (with an oscillation period of approximately 80 usecs) , and the postulated temporal density development of four flame plasmas 43, 44, 45, 46 with equivalence ratios phi of 1.0, 0.8, 0.7, 0.6 respectively.
• ⁇ (t) n(0)/[l + n(0)*alpha*t]
• alpha which increases inversely with the temperature cubed, is taken as 2*10**(-7) cubic cm/sec, corresponding to the value for the temperature of flames and low current (1 - 10 amp) arcs.
• T is the time expressed in units of 50 usecs, (which is one quarter the typical time between ignition pulses of the CDCC ignition system and much less than the time corresponding to the typical flame speed time scale of one to three msecs)
• a very lean flame of phi 0.7
• the density curve 45 meets the tail 47 in about 2.0 T
• the extremely lean flame of phi 0.6 the density curve 46 never reaches the spark tail 47.
• FIG. 5 depicts the temporal log density distributions of the spark and flame plasma of a multi-pulsing ignition of the CDCC type, pulsed every 300 usec (assuming a spark duration of 80 usec) with an EM Ignition type spark plug of FIG. la, in a combustion chamber with a typical HC fuel of phi ratio of 0.7, i.e. a gaso ⁇ line AFR of 21 to one.
• the time begins with the end of the first spark showing its decay 52 and the build-up of the flame plasma at 56. The latter occurs as a result of the build-up of the E- field after the end of the sine-wave spark, which couples E-field energy (within the EM Control Volume shown of FIG. la).
• the flame plasma density increases upon retriggering of the ignition to a peak 56a because of the initial high E-field prior to and during the initial stages of the subsequent spark formation 53.
• the process continues, with the flame plasma growing as shown at curve 57 prior to the next spark 54.
• FIG. 6 depicts the spatial plasma density profiles of a stan ⁇ dard HC flame 61 and others achievable by modifying the fuel.
• the simplest and most useful modification is to increase the C/H ratio of the fuel to as close to one as practical since the flame plasma density of the fuel is known to be maximum at a C/H ratio of one since chemi-ionization is based on reactions involving the C-H bond, which is maximum for the aromatic fuel family (benzene derivatives), which have the general formula CnH2n-6.
• an inexpensive low octane fuel is taken with typically 0.45 C/H ratio (representing a fuel with on the average 8 Carbon atoms to 18 Hydrogen atoms), and there is added approximately 20% of an aromatic methyl benzene (with very high octane) with formula C7H8, and there is obtained a fuel with a C/H ratio just greater than 0.5 (and with a very high octane), which would classify as an EMT fuel useful for high compression ratio, lean burn engines,.
• Curve 62 represents an expected density profile n2 for a fuel » with a C/H ratio close to unity and is an excellent EMT fuel with a PR rating around 108.
• Curve 63 is a density profile of a flame seeded with a low ionization potential alkali metal such as Cesium or Potassium, in amounts of several parts per million (or p.p.m.). While the peak ionization is very high (leading to otherwise a PR rating of about 120) the tail is so large because of the very low recombination coefficient, that the PR rating is an unacceptable value below 50.
• a low ionization potential alkali metal such as Cesium or Potassium
• Lithium and Sodium have a recom ⁇ bination coefficient ten time greater than Cesium and Potassium, so that (in the form of trace amounts of their salts or organic compounds in the fuel) they will produce a curve such as 64 with density profile n4 and a PR rating of between 60 and 100.
• some further tailoring in terms of using some aromatics (which incidently also boosts Octane Rating) and using only trace amounts (of order one p.p.m. or less) of the compounds of metals selected from the group of the alkali metals Lithium and Sodium, and the alkaline earth metal Calcium one can achieve a PR rating of 116 as in curve 65 of density n5.
• the latter PR value is very high, and represents an ideal EMT fuel for use in burning extremely lean mixtures with the systems of the present invention.
• Ne the electron density expressed in units of 10**12/cc
• Wp the plasma frequency expressed in units of 10**9
• Nu the electron-neutral collision frequency, which can be taken as 3*10**11 at one atmosphere
• f the operating frequency
• Kr the imaginary part (lossy part) of the generallized, complex, relative dielectric constant
• Wp 2*pi*9*J[Ne]
• the spark remnant has a very high field (the one initiating the spark) applied at the (spark initiating) gap 30a, which will tend to produce local ionization, and twist the E-field in favor of the spark remnant, producing a larger effective field along the major length of the spark remnant than is inferred from En (which requires gap gl be kept as large as practical within other con ⁇ straints, namely the electrical breakdown constraints). Also, the spark will have some Et component along its main length, which while small relative to Es, is significant. These factors imply that the field En in the spark remnant must be adjusted (raised) by a factor which ultimately is experimentally determined, and which for the present purposes is estimated at five (in the range of three to eight), modifying En to Enl:
• the location of the flame 165 usecs after the ' spark must be considered (following the proceedure that was carried out earlier with reference to flame fronts 25a, 25b ⁇ 25c of FIG. 2d).
• the spark of the CDCC system itself with its typical initial 2 to 3 amp peak current and, say, two initial full sine-wave oscil ⁇ lations, will tend to bloom outward as the plume 24b and move the first flame front to a more favorable site 25a, while the flame speed Vf, cited as 1.6 mm/msec, will take on a higher value in an engine as a result of of air-flow induced by the piston motion.
• 25c correspond to the second spark pulse at 1800 RPM and 3600 RPM respectively (for a typical value of Cl of 1/2). Therefore, at
• the third ignition pulse is the one most likely to form a discharge across the flame front (for the conditions which we have been discussing), and at 3600 RPM it is the second pulse.
• alpha the critical assumption made regarding the value of the spark plasma recombination coefficient "alpha" must now be reassessed in the light of the information developed.
• the value of alpha was assumed to correspond to about 2000 degrees C, the peak flame front temperature. It is postulated for the ignition strategy proposed here that this is a good assumption.
• the temperature of the neutral and ion species are close to the gas temperature.
• the ion temperature rises, taking on values from 1,000 to 10,000 degrees C at currents in the range of 1 amp to 1,000 amps. It is evident in terms of maintaining a maximum value of the (spark related) recombination coefficient alpha, that preferably the peak arc currents be kept low. But for the CDCC ignition (of the PFDI system under discussion) this is the case, with the main spark energy being delivered within the current range of 1 to 3 amps.
• SUBSTITUTE SHEET 7 increasing the time between pulses to 4T or 5T (200 or 250 usecs) for low to moderate engine RPM to both give the flame front more time to move to a more favorable position and to reduce the spark remnant density, although this is of limited use since in turn it reduces the average power delivery to the spark plug end;
• FIGS. 7 and 8 depict designs of actual plugs and a practical capacitive boot for optimally achieving the effects mentioned, and substantially include the plug tip designs of FIGS. 2 and 2d, where once again like numerals denote like parts.
• the tips of the plugs of FIGS. 7 a t nd 8 have been arbitrarily chqsen to correspond to tips of FIGS. 2d and 2 respectively.
• the plug shown in FIG. 7 is a detailed drawing of an example of a plug usable in FIG. 8, excepting for the center electrode structure, which is designed for minimizing electrical resistance and maximizing electrical capacitance and heat transfer.
• FIG. 7 which is based on a 14 mm standard plug, includes central or axial wire made up of an upper portion 71b of large diameter 0.25" terminating in connector 74, intermediate series portions 71a of large diameter 0.32" and 71 of diameter 0.15", and lower portion 21 of small diameter 0.09" terminating in 0.32" diameter button 21a. Diameter of portion 21 is made small to allow for better PFDI effect (to provide small overall diameter of the plug tip), although not so small so as to seriously limit the high amplitude, high frequency (MHz range) capacitive current.
• Upper portions 71/71a (and 71b) are of large diameter to provide low resistance to the capacitive current and maximum plug capacitance defined with respect to insulating layers 78/78a surrounding portions 71/71a respectively, which in turn are surrounded by plug shell conducting portions 23/73 respectively.
• Small diameter wire 21 is preferably made of copper to reduce its electrical resistance as much as practical and provide good heat transfer capability for cooling button 21a r which is preferably made of highly erosion resistant material such as Nickel alloy.
• Wires 71, 71a, 71b can be made of other metals, preferably copper plated to provide low resistance to the capacitive current.
• At least a portion of the cylindrical periphery of button 21a forms conical frustrum 29a at an approximately 45 degree angle to the axis of wire 21, for focussing the E-field onto the shell end 23a (and cylinder head surface 22a) as discussed with reference to FIG. 2d.
• toroidal gap 30 is created between frustrum 29a and shell end 23a (and cylinder surface 22a shown with reference to FIG. 8) along whose periphery flame discharges can occur as part of the PFDI system to ignite the entire toroidal gap during the ignition ON period.
• a preferable dimensioning of the end section based on a 14 mm plug is shown with shell ID 23b taken as 0.38" along major part of 14 mm threaded, 0D of tip firing end of insulator 28 taken as 0.25", and shell end interior diameter 23c taken as 0.32" (provi ⁇ ding gap size gl equal to 0.035 inches).
• Spark plug insulator 78/78a/78b preferably has its seat at the bottom end region 80 of the largest diameter section 73 of the plug shell, and not in the base junction 76 where insulator section 78 first communicates with the combustion chamber, which must be free of sharp points as to not cause local ionization from high voltage, leading to eventual damage of the spark plug.
• Junction volume 76 is used in part to prevent insulator tracking, and in part (in this application) to diffuse the electrical shor ⁇ ting out effect of the flame front as it moves up the junction.
• Top insulator portion 78b has preferably an 0D of approxi ⁇ mately 1/2 inch to conform to the ID of boot insulator 90 of FIG. 8, which has preferably a inside diameter 2d of 1/2 inch. The large diameter is also chosen to provide a maximum capaci ⁇ tance in the plug itself as defined by the layers 73/78a/71a, as already mentioned. Insulator 78b also provides clearance (0.045" shown) to inner conductor 71b to accommodate sealing cement 75.
• Shell region 73 accommodates preferably 3/4" hex, and a threaded section 72 with preferably 13/16-20 UNEF thread for use with the capacitive boot 90 to form ground contact of outer metallic tube 86 of the capacitive boot.
• FIG. 8 depicts a minor variant (a simplification) of the plug of FIG. 7 in which center conductor sections 21/71 of FIG. 7 are combined into one section 21b, and sections 71a/71b (FIG. 7) are combined into one section 71c, and on which is mounted a novel capacitive boot 90.
• the boot is formed of elongated insulator tube 85, one end of which is seated in contact with and extends from the upper end of metallic cylinder 84 forming essentially a hollow extension of conductor 71c.
• spark plug wire 87 Connected to the upper end of cylinder 84 is spark plug wire 87 with preferably EMI suppressing
• SUBSTITUTESHEET inductive winding 87a formed as a helix of low resistance wire, preferably wound around a core of magnetic material preferably loaded with resistive material which begins to absorb at the very high frequency end of the spectrum where EMI is a problem, i.e. above 30 MHz.
• Wire 87 is connected to end 84 preferably by means of a crimp (representing a unitary section whose distributor end
• V'-' of spark plug wire 87 is slid into insulator tube 85 from its bottom end prior to distributor end of wire 87 having its distri ⁇ butor boot installed).
• the outside diameters of cylin ⁇ der 84 and upper portion 78b of spark plug insulator are the same, e.g. 1/2 inch, and the resistance is preferably equal to or less than one ohm/foot resistance for the PFDI system and of the order of 10 ohms/foot for the ECDI system.
• the spark plug boot is formed of elongated insulator tube 85, one end of which is seated in contact with and extends from the- upper end of portion 72 of shell 73.
• the internal diameter of the insulator tube 85 is dimensioned to provide a snug sliding fit over both the insulator portion 78b and the tube 84.
• Upper end of tube 85 is provided with a top section 90a preferably approxi ⁇ mately 1/2 inches long, which forms shoulder 90b to which top end 86b of outer metallic tube section 86 seats, where end 86b is of greater thickness to reduce the field intensity at its top extre ⁇ mity and to form a crimp there to hold metallic tube 86 in place.
• Metallic tube 86 surrounds cylinder 85 for its entire length except for section 90a, bottom end of tube 86 being preferably threaded to screw onto threaded portion 72 of spark plug shell.
• the relative dielectric constant of the material of which insulator tube 85 is formed is preferably in the range of 6 to 30 to provide a capacitance in the range of 50 to 200 picofarads.
• the insulator material preferably has a low loss factor in the 10 to 100 MHz range, a breakdown voltage greater than 300 volt/mil, and an operating temperature of at least 300 degrees F.
• Thickness "tb" of the insulator (85) is preferably approximately 1/8 inch.
• Minimum diameter 2d' which captures top end of tube 84 is somewhat less than major interior diameter 2d.
• the equivalent circuit of FIG. 8 is shown in FIG. 8a, where like numerals again denote like parts.
• Capacitance 79 is formed in the embodiment of FIG.8 by plug shell 73 and metallic tube 86 which form the outer plate of a coaxial capacitor, metallic cylinder 84 (and conductor 71c to a lesser extent) which forms the inner plate, and insulator tube 85 which provides the necessary high dielectric constant between the capa ⁇ citor plates.
• capacitor 79 Upon breakdown of gap 30, capacitor 79 discharges its energy very rapidly (in about one usec) through the ionized gap as moderately high magnitude currents of 50 and 400 amps at ' 20.to 50 MHz range frequencies, while inductor 87a provides very high i pedence to the parallel path for discharging capacitor 79.
• inductance of wire 87a is of the order of 50 uH/foot, serving the second function of (while minimizing EMI) presenting a very low resistance, "low" (from the EMI perspective) frequency tuned circuit with the output capacitance 9 (which typically will have a cpacitance in the range of 20 to 100 pfd).
• FIG. 9 depicts spark and flame plasma density distributions of a preferred ignition pulsing sequence (of the CDCC ignition) of the PFDI system using, for example, the plug tip structure of FIGS. 2d or 7, and more particularly that of FIG. 2d, shown in FIG. 9a below. Shown are ignition sparks of period of about 100 usecs, and a time between pulses of (the minimum of) approximately 150 usec. The shapes 92, 93.
• phi 0.6
• PR rating for example, a high octane unleaded fuel using aromatics to boost the octane.
• Of interest is the gra ⁇ dual build-up of flame plasma density on the first two pulses 96, 97 although most the energy is delivered to the spark as evidenced by the peaked shapes 92, 93.
• the first "arcing" of the flame front plasma occurs, producing a density distribution at the peaked shape 98 with a higher peak level than the spark remnant pulsed plasma peaked shape 94, since the flame is now in a position where the E-field strongly couples to its front. Thereafter, energy continues to be coupled to the flame front, producing further successive peaked shapes 99, 100, and the flame is launched, while the the spark remnant decays to a small last tiny peak 95 and " then continues to decay.
• FIG. 9a depicts five partial cross-sectional views of the spark plug tip of FIG. 2d (as an example of a preferred structure of the PFDI system) able to produce the density-time shapes shown in FIG. 9 through electrical action of the five ignition pulses delivering energy to the plug tip.
• the drawings represent the same plug tip viewed at 250 usecs intervals with like numerals denoting like parts with respect to FIG. 2d. Shown are the center conductor 21, a preferred button 21a, tip insulator 28, spark plug shell 23 (somewhat recessed from the surface 22a of cylinder head 22), and (four of) the electric field lines represented by 26..
• Each view represents an ignition pulsing at a time where the ignition energy (current) is maximum (at a peak of either of the two half sine-wave curves).
• FIG. 9ab shows the initial spark 92a and flame front 96a with mainly perpendicular E-field components; followed 250 usecs later by FIG. 9ac showing a weaker spark 93a (thin line) at the same location and flame front 97a with a par- tially parallel E-field component; followed 250 usecs later by FIG. 9ad showing a greatly diminished spark 94a (dashed line) and flame front 98a mainly parallel to the E-field and absorbing most of the energy (conducting most of the "spark” current); followed 250 usecs later by FIG.
• FIG. 9ae showing a further diminished spark 95a (dotted line) and a now larger flame front 99a parallel to the E- field; followed finally 250 usecs later by FIG. 9af showing the absence of the remnant of the initial spark 92a and a flame front 100a, moving away and growing in size, with its upper part lOOaa moving outside the influence of the E-field and its lower portion lOObb growing sideways; that is, following the fourth pulsing (after 750 us ' ecs), flame front 99a preferably will move sideways along the periphery of the circular edge of the plug/cylinder interface where the E-field coupling is strongest, forming flame discharges along the periphery, igniting the entire toroidal gap.
• FIG. 9af shows the absence of the remnant of the initial spark 92a and a flame front 100a, moving away and growing in size, with its upper part lOOaa moving outside the influence of the E-field and its lower portion lOObb growing sideways; that is
• FIG. 9b depicts schematically in the form of bars the spark and flame plasma intensities and their average orientation refe ⁇ renced to FIG. 9a, and located to coincide in a vertical perspec ⁇ tive with their position shown in FIG. 9a, on the same time basis defined in FIG. 9.
• the direction of the E-field relative to the spark and flame front is shown as an arrow drawn through the bars (representing an average ralative direction). It is seen that the spark gradually decays from position 92b to 93b to 94b (with the E-field always normal to its front) while the flame plasma slowly grows from position 96b through position 98b with the E-field becoming progressively parallel, as shown and described in FIG.9a.
• FIG. 10 depicts a preferred circuit of the CDCC type compri ⁇ sing a high efficiency (preferably 70% - 80%) DC-DC converter 102 intended to be connected to battery 8 of voltage VB, typically of 12 or 24 volts. One output terminal from DC-DC converter 102 is grounded, the other being connected to the anode of diode 7.
• the circuit is controlled to produce an ignition pulse train upon receipt of a trigger at input terminal 101 of power supply and controller 103 (connected to battery 8 to be powered thereby) which also regulates the output voltage by being connected to the junction of series divider resistors 104a, 104b connected across the output terminals of converter 102.
• Isolation power supply diode 7 has its cathode connected to cathode of diode 6 whose anode is connected to ground.
• Capacitor 4, SCR 5, diode 6, and primary winding 1 of special CDCC coil 3 comprise a capacitive discharge (CD) circuit in which SCR 5 is connected across diode 6 and the gate of the SCR is connected to output of controller 103.
• Capacitor 4 is connected to between cathode of diode 7 and high side of primary winding 1 of transformer 3, the other side of the primary winding being grounded.
• the transformer (coil) 3 has a closed ferrite core 3a with secondary winding 2 and capacitance 9.
• active snubbing network formed of series-connected capacitor 4a and inductor 4b.
• High or hot side of secondary winding 2 of transformer 3 is connected to input of conventional distributor 107 via King lead 108a which, like spark plug wire 108b (or 87 of FIG. 8), is a low resistance, highly inductive wire.
• the output of the distributor is connected to spark plug 109 which may be of any of the types disclosed here ⁇ inbefore, including the further modification shown where inductor 108c is added to tune down the discharge of the boot capacitance - (not shown) already mentioned.
• Such modification is further use ⁇ ful in the embodiment shown where a moderate capacitance of, say, approximately 40 pfd is built into the plug to produce moderately intense but low energy capacitive spark for ignition, with induc ⁇ tor 108c forming a continuous inductor with 108b to limit EMI.
• Capacitive boot (of the type 90 disclosed in FIG. 8) may be omitted if sufficient capacitance is built into the spark plug.
• a trigger pulse is received at terminal 101 and the subsequent output from controller 103 turns SCR 5 "ON", placing a high voltage Vs between the dis ⁇ tributor rotor 107a and a point therein.
• the rotor tip gap is preferably as small as is practical, e.g.
• the rotor tip is preferably made of erosion resistant material such as Nickel.
• the output voltage at the distributor rises and breaks down the gap at the tip of rotor 107a and at the plug end 109a.
• the capacitor 4 is charged to a voltage Vp of 350 volts and has a value of approximately 8 microfarad (ufd).
• the leakage inductance, Lpe, of primary winding 1 is approximately 20 microhenries (uH) to give an oscillation period of 80 usecs (dictated by the reco ⁇ very period of SCR 5).
• Snubber capacitor 4a is approximately 4% the value of capacitor 4, and inductor 4b takes on a value from zero (no inductance) up to approximately the value of Lpe.
• capacitor 4a delivers its energy to the spark as a continuously ringing, decaying oscillation with a period of 15 to
• the snubbing network also serves to protect SCR 5.
• PFDI effect is achieved when SCR 5 is trigerred in a sequence every, say, 240 usecs (for a duration of one to three msecs) and some ECDI effect is also achieved by the discharge of energy from capacitor 4a, especially when the spark gap length "L" is kept at a minimum value for the PFDI system of approximately 0.12 inches.
• controller 103 senses the engine RPM and adjusts not just the ignition pulse train width as disclosed in U.S. patent application SN 688,036 (reducing the width with RPM), but also adjusts the period between firings so that it is reduced with RPM, from say 400 usecs for up to 1500 RPM, to say 300 usecs
• SUBSTITUTESHEET at 3000 RPM to say 200 usecs at 4500 RPM and higher.
• a preferred way to accomplish this is to use a voltage tunable oscillator adjusted so that the period between firings increases from an initial value of say 200 usecs to 400 usecs in say 3 rasecs, and the pulse train width varies from 3 msecs at 1500 RPM, to 2 msecs at 3000 RPM, to 1 msec at 4,500 RPM, providing an average pulse width falling with RPM as desired.
• the time between pulses may be increased in some proportion to the pulse width.
• variable (longer) ignition period at lower engine speeds is that the flame is given time to ignite the entire toroidal gap while still influenced by the ignition, i.e. multiple flame discharges of the PFDI system can be formed around the plug periphery (within the toroidal gap 30) as the flame burns its way around, especially at the low speeds where the air motion is small and the mixture is more difficult to ignite.
• EFF Pare/[Pare + Pscr + Pcoil + Protor]
• Varc average plug tip arc burning voltage
• Vrotor average rotor tip arc burning voltage
• Vscr average forward voltage drop of the SCR during the current conduction stage
• EFF 67%, which is an extremely high efficiency considering power is being delivered at a rate of several hundred watts to the plug end (ten times greater than standard ignition).
• Pcoil is small, whereas in prior art ignition systems Pcoil is generally the principal contributor to the system inefficiency.
• PFDI is clearly applicable to all combustion systems including "spark" ignited diesel engines where the application is of particular interest. In such applications, one is dealing with fuel spray velocities (where the fuel contains entrained air) one order of magnitude greater than the fluid/flame velocities associated with gasoline engines.
• PFDI is based on providing electrical "ignition" means for air-fuel mixtures during a period of time Tign when the ignition is still active and the flame is still at its initial growth stage and in the region of influence of the ignition system.
• the flame launched by the initial ignition spark is progressively favored in terms of absorbing the ignition energy provided during Tign, over the energy absorbed by the plasma at the previous spark site (i.e. by the spark remnant).
• the present PFDI invention provides a small gap defined by two opposed electrodes, one of which is partially insulated; across the gap between the electrodes the full voltage is applied creat ⁇ ing a very high E-field region causing an initial ionizing plasma.
• the plasma forms into a spark channel by being dragged and bent by the E-field to an exposed part of the otherwise insulated electrode (which preferably forces the major part of the spark length to form perpendicular to the originally ionizing E-field).
• the plasma is thus anchored to form a stable electrical spark discharge — in a way that reduces the electrical coupling to the spark remnant upon subsequent turn-off of the ignition and its refiring (as part of a multiple pulsing ignition having a train of pulses making up one ignition firing).
• FIG. 2d depicts an optimum way to accom ⁇ plish this.
• the end button is appropriately contoured and the plug shell recessed from an appro- priately contoured cylinder head, one can get such a strong focus- sing of the electric field onto the cylinder head edge, that even without the presence of the ionizing flame (and just from the pre ⁇ sence of plasma from the outward moving spark plume) the secondary discharges form outwards and away from the spark plug insulator surface between the plug tip and the cylinder head.
• the subsequent ignition pulses discharge across the flame front to ignite the entire toroidal gap.
• a movable element e.g. a piston of a conven- tional engine, or a rotor of a Wankel engine
• a movable element can be designed to move so that coupling to the spark (or spark remnant) is reduced and coupling to the flame improved, all at slightly later times following the ignition spark, and when the flame is at a slightly different location; i.e. the gap which defined the initial spark increases in size, while the gap which defines the positions to which the flame moves decreases in size.
• the structure and position of the plug shell end relative to the mounting cylinder surface i.e. recessed from it, is important in achieving the best PFDI effect.
• the principle of operation can be used with moderate effectiveness even with spark plugs with ground electrodes, by modifying their construction; for example, taking a spark plug with an extended insulator nose of say 1/8" and extended center conductor wire of say 1/4" beyond the insulator, one can add multiple ground electrodes (typically two to four) which surround and run parallel to the center conduc ⁇ tor, and are bent near their ends to partially cover the center conductor tip and form an axial spark gap of approximately 0.08"; the ground electrodes also alternatively joined together to form a closed nest around the center conductor, and the center conduc ⁇ tor preferably dimensioned to.
• Cl is one); in this way by using the principles disclosed herein of the ECDI system in conjunction with the high efficiency ECDCC ignition operated in a pulsed mode for long durations (of up to 5 msecs), one can guarantee ignition of a large volume around the plug end of a spark plug, which is a simple modification to exis ⁇ ting spark plugs, having multiple ground electrodes.
• SUBSTITUTE SHEET such as the older 18 mm plugs still in use in some applications; and generally to scale up some of the parts from between 10% to the full 40%, say 20% for the center conductor wire to a 0.11" diameter, 10% for the insulator tip thickness to say 0.09", which would leave a substantial edge on the plug shell end of approxi ⁇ mately 3/16" (for a 0.04" radial coaxial gap), allowing for a contouring of the edge to, say, a concave surface for improving the electric field focussing within the toroidal gap defined by the gap between the edge and the button at the end of the center electrode.
• FIG. 11 to llff reveal embodiments of the electric field focussing lens plug end, or "EFFL" plug, as it will be sometimes referred to hereinafter.
• FIG. 11 in which like numerals denote like parts (with respect to FIG. 2, 2d, and 7) there is shown a longitudinal cross-sectional partial view of an electric field focussing lens
• the spark plug nose is contoured such that it embodies the principle of focussing of the electric field, in this case in the vicinity of the cylinder head edge region 119b/119c around which the initial flame propagates.
• the insulator end is made up of three sections, a large diameter section 118, a converging sec ⁇ tion 117 which typically converges at an angle between 30 and 50 degrees to the vertical, and an essentially straight section 28 as disclosed earlier»
• the "lens” is made up of the surface 28a of insulator section 117 with the electric field line or ray 110 normal to its surface ("normal ray 110"), the surface 28b of the end insulator section 28 with a normal ray 111, and surface 29a of the end button 21a/114, which makes an angle between 15 and 45 degrees to the vertical, with a normal ray 112, the rays 110, 111, and 112 converging to a focus point F designated by numeral 116 and defined as the "lens focus” F. Since the "lens" defined by surface 113 is an electric field lens it is influenced by the surrounding electrical conducting grounding surfaces 22/23d to form a "ground focus” F' somewhat shifted in position from point
• an essentially electrostatic lens 113 which focusses the electric field to a region 116/ll6a where later spark pulses such as 25 of a multiple spark pulsing ignition train occur.
• the focussing region is far away from the plug end surfaces 28a/28b and at the far reaches of the toroidal volume 30 to enable significantly improved coupling of the elec ⁇ tric field energy to the initial flame front propagating outwards and away from the inital spark 24. This is accomplished while simultaneously reducing the size of the end tip 21a/114, which is shown made up of an erosion resistant hollow button 114 which is crimped onto the center conductor 21 by means of the crimp 115.
• SUBSTITUTE SHEET The relatively sharp changes in angle of the surfaces making up lens 113 help keep the initial spark 24 away from the surface of the insulator while the relatively thick insulating region 118 helps prevent damage to the insulator portion around the spark initiating auxiliary partially insulated gap 30a defined by shell surface 119a and the insulating surface across it.
• the plug end design shown is approximately six times scale and is based on a 14mm plug shell, which is shown recessed into the cylinder head as disclosed earlier. However, in this design the protecting junction volume 76 is built into the shell, simpli ⁇ fying the insulator end 118/117/28 design (but reducing the spark tracking surface), i.e. the shell end has the shape 23d cut into its end, forming both the junction volume 76 and one surface (119a) of the spark initiating gap 30a.
• the diameter of the center wire 21 is somewhat larger than previously disclosed * to conform to the somewhat larger diameter D2 of the insulator end.
• the initial spark pulse 24 and some of the follow on spark pulses generally end at the junction 29b of the base edge of the surface 29a of button 114 and the outer edge of the insulator 28 so there is not much advantage to having a button much larger in diameter than D2 except as it pertains to contributing to the formation of lens 113.
• wire and insulator diameters DI, D2 somewhat larger than disclosed earlier, and a button diameter only 10% to 20% larger than D2 to conform to the end dia ater D2.
• DI center conductor diameter
• the other dimensions D3, D4, D5 are given so as to provide a gap width 30a and junction volume 76 consistent with what was disclosed earlier for a 14 mm plug.
• Nose length L2 is divided in an approximately 2/3 ratio for the two lengths L22 and L21 corres- ponding to insulator section 117 and 28, i.e. 0.08" and 0.12" for L2 equal to 0.2".
• the ratio of L22/L21 will be in the range of 0.3 to 0.4, and L2 will be in the range of 0.15" to 0.30".
• FIG. 11a is a longitudinal cross-sectional partial view of an EFFL spark plug end based on an 18 mm plug, with like numerals denoting like parts with respect to FIG. 11, and with the shell end section 23e further contoured to act both as an "ideal ground focus" F" (116b), defined as a focus where F and F' coincide, as well as to provide a tapered spark or arc "runner” section 119d along which the spark pulses 25a, 25b, 25c, can form and "run” as the flame front moves away from the initial spark 24.
• the lens focussing effect can be so strong that under some or all ignition operating conditions, * the spark forms across the large gap designated by the spark 25c rather than initiating across the much smaller auxiliary gap 30a. This results in the formation of a very large initial spark well away from the plug nose insulator surfaces 28a/28b.
• Such spark formation is more readily accomplished by advanta ⁇ geously using the much larger plug end dimensions available from the larger diameter 18 mm plug which provides greater flexibility in contouring surface 28a/28b/29a to form, for example, a curved surface approximating a section of a parabola which will provide a more intense and well defined focus F" (point 116b), i.e. the approximately parabolic lens 113 will focus the electric field normal rays 110b, 111b, 112b to the extremity of the shell edge (point 116b) or just beyond point 116b.
• the diameter D2' of base edge 29b of button 114 may be of somewhat larger (i.e. 10% to 30%) than the diameter D2 of the end of insulator 28 to reduce the distace L3 (along ray 112b) to a (nonetheless large) 0.1" to 0.2" distance.
• the diameter of the center conductor wire 21 can be increased to a large diameter 71d of say 0.3" relatively close to the shell end as shown so that with an inside diameter of 0.53" of the shell 23 a relatively large capacitance per unit length is formed with the insulating layer 78, which is preferably of high purity alumina (93% to 99.9%) with a dielectric constant of approximately nine.
• a plug capacitance of about 30 picofarads is attainable with a shell length of one to two inches.
• tip 115 may also be shaped and dimensioned so that under ignition firing conditions where ignition timing is near TDC and the engine cylinder pressure is maximum, ignition firing may occur to the piston face from tip 115 which may form a relatively' small gap of say 0.060" to 0.12".
• the scale of FIG. 11a is approximately five times full scale.
• FIG. lib is a half longitudinal cross-sectional partial view of an EFFL plug based on the design of the 14 mm plug of FIG. 11, with like numerals denoting like parts with respect to FIG. 11.
• the main difference shown here is a further contouring of the insulator nose to add a section 28d with surface 28c, providing a somewhat larger end insulator diameter for assisting in keeping the initial spark pulse away from the insulator surface, i.e. section 28d increases the path the initial spark would take if it w as to form on a path along surfaces 28c, 28b, 28a, and then across gap 30a, versus along the depicted path 24.
• lens 113 is also a somewhat more symmetric lens with rays 110a, Ilia, 112a, and 112b focussing to the ground focus F' (point 116a).
• FIG.lie is a longitudinal cross-sectional partial view of an EFFL plug based on the design of the 14 mm plug of FIG. 11, with like numerals denoting like parts with respect to FIG. 11, with the main difference being the dimensioning and contouring of the insulator sections 117/28 and the shell end 23f so that the lens 113 focusses its normal rays 110c, 111c, 112c directly onto the edge of the shell to produce an ideal ground focus F" (point 116b) as also achieved in the larger 18 mm plug embodiment of FIG. 11a.
• the portion 23f especially the end portion 23ff, behaves as a ground for the initial and/or follow on spark pulses represented by 25, and section 23f behaves as an arc runner should the initial spark form at the inside location indicated by curve 24.
• Lengths L2, L21, L22, and L3 are approximately 0.16", 0.1", 0.06", and 0.12" respectively, with L3 representing the preferred length for the ECDI case.
• L21 and L22 are taken in conjunction with shell end section 23f of length L4, shown as approximately 0.1", to focus the electric field at point F" (116b), the inside edge of the shell.
• the initial spark may form either along path 25 (as a result of the intense electric field at F" which.initiates the ionization), or either along 24 or 24a due to ionization in gap 30b, although as already stated curve 24 represents the preferred path versus the " substantially longer surface path 24a which would ordinarily be the preferred path were it not for the shaping of the insulator nose 118/117/28.
• the dimensions DI through D5 are essentially similar to those listed with reference to FIG. lie, as are dimensions L4 and L22, while lengths L2 and L21 are somewhat longer, about 0.18" and about 0.12" respectively, to form a focus F (116) somewhat beyond the shell edge 23gg, and
• FIG. lie is a longitudinal cross-sectional partial view of an EFFL plug based on the design of the 14 mm plug of the previous figure (FIG. lid), with like numerals denoting like parts with respect to FIG. lid, the main difference being the dimensioning and contouring of the inside surface 119e of the shell end 23h so that it in effect becomes a ground focussing lens to reinforce the plug nose lens 28a/28b/29a and concentrate the electric field lines to the spark plug end outer regions, i.e. to the plug end button 114 and the shell edge 23hh.
• the diameter of the center conductor 21 is made somewhat smaller (0.9" shown) as well as the diameter of the back portion 118 of the insulator to provide a thicker, shell end section 23h for forming the ground lens 119d.
• the ground lens 119e can be viewed as a refinement of the runner surface 119d of FIG. lid and FIG. 11a (the 18 mm plug).
• ground lens 119e For ease of visualization and as a way of defining the ground lens 119e, it is shown with its normal rays 112c focussing onto edge 29b as if it is the source of the electric field, with the edge 29b designated as focus Fl, point 114a, i.e. these rays are drawn independent of the plug nose (as if it was not present) as a way of defining the shape 119e, recognizing that the plug nose clearly distorts the rays 112c.
• ground lens 119e is similar to that of FIG. lid, except that it is somewhat curved and makes a larger angle to the vertical to form an inclu ⁇ sive angle thetal equal to approximately ninety degrees.
• FIG. llf is a longitudinal cross-sectional partial view of a more optimized 14 mm EFFL plug based, more particularly, on the designs of the plug ends of FIG. lid and FIG. lie, with like nume ⁇ rals denoting like parts with respect to FIG. lid and FIG. lie.
• the plug end is located near the perimeter 22b of a curved surface 119f, such as an engine cylinder head end section, which in effect behaves as a ground lens 119f already disclosed with reference to FIG. lie, focussing electric field lines 112d onto plug end button 114 shown somewhat extending beyond the dia- meter of insulator 28 to form a focus Fl (114a).
• the plug nose itself forms the usual ground focus F" (116a) from the field lines 110a/llla/112a.
• the two foci Fl and F" encourage the spark pulses to form along a curve joining them, such as curve 25, launching a flame front which moves outwards and into regions of high electric fields so that the initial flame front becomes bathed from all sides with electric field energy which feeds the flame as it moves into the unburnt gas (including along the perimeter of the shell).
• the shell edge 119b is not protruding and is directly across insulator edge 118a as disclosed earlier as one preferred embodiment of the design of the gap 30b.
• FIG. llff The fragmentary partial view FIG. llff, based on FIG. llf, which like FIG. llf is also approximately six times full scale, has like numerals denoting like parts with respect to FIG. llf, and serves to show an alternative preferred embodiment of a plug end showing the formation of the two foci Fl (114a) and F" (116a) with the spark 25 joining the foci, as in FIG. llf.
• volume 76 is in effect eliminated and replaced by 76', which is defined by surfaces 28a and 119g, and the entire plug nose is in effect contained inside the elongated shell 23i, which can either be a solid cylinder or an axially segmented cylinder.
• the main advantage of this design over other similar designs is the formation of the foci Fl, F", which allow for a very large spark (gap) 25 and which provide an electric field distribution which bathes the spark/flame in a strong electric field to stimu- late the initial flame front propagating from the spark pulses 25 formed along the toroidal volume contained between the two foci.
• a very large spark (gap) 25 and which provide an electric field distribution which bathes the spark/flame in a strong electric field to stimu- late the initial flame front propagating from the spark pulses 25 formed along the toroidal volume contained between the two foci.
• FIG. 12 is an idealized, cross-sectional partial view of an EFFL plug which is of particularly simple construction and with a preferred particularly simple, flexible, low EMI, moderate capa ⁇ citance capacitive boot 90 to which is connected a preferred high inductance low EMI spark plug wire 87.
• like numerals denote like parts with respect to FIGS. 8 t and 11.
• the main feature of this embodiment versus that of FIG. 8 is the use of an internally flexible boot 90 made possible by using a flexible, lower dielectric constant material 85, such as a lightly (30%) loaded silicone rubber, with relative dielectric constant of 5 to 10 to provide a boot capacitance between 30 and 50 picofards.
• a flexible, lower dielectric constant material 85 such as a lightly (30%) loaded silicone rubber
• relative dielectric constant of 5 to 10 to provide a boot capacitance between 30 and 50 picofards.
• the use of a lower secondary plug/boot capacitance is based on the recent recognition that having a large capacitive initial spark is not desirable as it intensifies the initial spark plasma remnant.
• lower overall capacitive energy is preferred, delivered in a very short time to produce a very intense but lower overall energy capacitive spark, attained by building 10 to 20 picofarads (pf) in the plug shell section and 30 to 50 pf in the boot, and providing very low resistance at high frequencies (i.e. 100 MHz) in center conductor 71d/21 (e.g. by silver plating it).
• pf picofarads
• center conductor 71d/21 e.g. by silver plating it.
• a lower dielectric constant material 85 which is flexible, and contained in a casing 86 which may also be flexible (e.g. of braid, as in ground strap), and in turn the boot can be made to fit snuggly over the spark plug insulator 78b by allowing the elastomer 85 to stretch out and over the upper insulator 78b of the plug.
• plug boot 90 is similar to that of FIG. 8, except that in this embodiment it is designed to fit a 5/8 inch spark plug hex of a 14 mm plug shell and thus has a smaller outer diameter and an elastomer 85 outer diameter of about 9/16 inches.
• a spark plug wire crimping element 84a of typical length 1" to 2" which also acts as the inner conductor of the capacitor defined by layers 84a/85/86.
• the elongated section 78 of the spark plug to provide a preferred 15 to 20 picofarads of plug capacitance in conjunction with the large diameter (0.18") center wire section 71d and outer shell sections 23/73.
• 86c can be used to add capacitance and further suppress EMI.
• the entire structure has a capa ⁇ citance of about 60 pf, about 15 pf in the plug section contained in the spark plug shell 23/73, about 10 pf in the upper portion of the plug (along upper insulator section 78b), and about 35 pf along the layer between the crimping element 84a and the metallic casing 86.
• the plug upper insulator section 78b and crimp element 84a preferably have the same outside diameter to accomodate a constant inside diameter of (preferably elastic) dielectric material 85.
• FIG. 13 is an idealized view, partially in block diagram and partially schematic, of a preferred embodiment of the optimized CEI Ignition suitable for use in a multi-cylinder internal combus- tion engine.
• the ignition is based on that of FIG.10 and operates as disclosed there, and the drawing follows that of FIG. 10, with like numerals denoting like parts with respect to FIG. 10.
• DC-DC converter 102a includes output diode means and voltage regulating means internal to it (explicitely shown in FIG. 10).
• the ignition system depicted in FIG. 13 represents the optimized system developed based on the principal disclosed herein and in other related patents and patent applica ⁇ tions, and is sometimes referred to henceforth as the CEI Ignition.
• the CEI ignition preferably uses the more optimized plug and boot 109 disclosed in FIG. 12, and as already disclosed provides multiple spark pulses per ignition firing approximately every 250 to 400 usecs with a typical spark firing period of 80 - 100 usecs. This period is in part determined by the recovery time of the SCR, which is typically 35 to 40 usecs for a low forward drop standard recovery SCR.
• CEI Ignition it is preferable to have more short duration (single sinusoid) spark pulses rather than fewer longer duration ones in order to be able to influence the initial flame front over an overall longer duration, i.e. for about three milliseconds (msec) at low engine speeds and one msec at high engine speeds. This is accomplished by using, in part, two further improvements.
• the first is a speed-up turn off circuit which reduces the SCR turn-off time by 5 to 10 usecs by applying a negative bias voltage to the " gate 5a of the SCR 5.
• This voltage is obtained from point P (the high voltage end of the coil primary winding 1) which has a negative electrical polarity during the first and last quarter cycles of the capacitor 4 discharge cycle.
• resistor 138a order of magnitude 5 Kohms resistance
• capacitor 138c of about 0.2 uFarads
• point PI intersection of resistor 138a and capacitor 138c
• resistor 138b of order of 100 ohms
• Resistor 5b is typically 50 ohms and for the typical SCR used in this application, such as the Motorola MCR265-8, is built into the SCR.
• the SCR used in conjunction with the fast turn-off circuit has a low forward drop of 1 volt at 120 amps peak current of coil primary winding 1, achievable by improving the SCR design over existing state-of-the-art parts such as the MCR265 by using a larger die, larger leads, etc., and by taking advantage of how the part is used in the present application (e.g. not requiring reverse hold-off voltage, etc).
• the second improvement relates to modifying the CDCC dis ⁇ charge circuit (already disclosed) by either reducing the size of the discharge capacitor 4 (from, say, 8 to 5 uFarads) and retain ⁇ ing the voltage doubling feature disclosed in the recently issued U.S. patent number 4,677,960, or reducing the operating voltage (from, say, 350 volts to 200 volts) while retaining or increasing capacitance of discharge capacitor 4 (from, say, 8 to 12 uFarad).
• the voltage recharge circuit 4c/4e/4f - is used.
• Capacitor 4c preferably has a value about equal to that of capa ⁇ citor 4, or about equal to a value by which discharge capacitor 4 is reduced, e.g. about 3 uFarads for the case where capacitor 4 is reduced from, say, 8 to 5 uFarads.
• Inductance value of choke 4e is determined such that upon firing of SCR 5 it will oscillate (with choke inductor 4e, capacitor 4, and coil primary winding 1) through one half of a cycle just prior to SCR refiring (typically 250 to 400 usecs), delivering charge to capacitor 4 and preventing SCR latching.
• the choke inductance 4e has a value of about 10 millihenries for the typical CDCC ignition disclosed herein.
• a ferrite or other low loss.core with cross-sectional area of approximately one square inch (or less if practical) and with high saturation flux density, and preferably a winding window opening three inches long by one inch wide with about 25 turns of primary wire, and a coil turns ratio N of about 50 (for 400 volt rating capacitor 4).
• a coil leakage inductance 20 to 30 uHenries (uH) to provide the preferred discharge period of 80 to 100 usecs for a 6 to 10 uF discharge capacitor 4.
• ECDI ECDI
• PDI PDI
• a peak spark current of one amp and a frequency of operation of, say, 10 KHz one could use a lower voltage system of, say, 200 volts (250 volt capacitors) with a high capacitance of 8 to 12 uF for capacitor 4 (allowing for a relatively low coil leakage inductance to obtain the 10 KHz frequency).
• a turns ratio of about 100 is dictated, only 15 turns of primary winding are required (for a one inch square core), and so the core size is actually reduced because of the smaller primary winding because of the fewer turns of smaller primary winding wire and smaller size secondary wind ⁇ ing because of the similar turns of smaller size secondary wire.
• the CDCC coil for the CEI Ignition with the primary 1 and secondary 2 windings wound colinear as shown in FIG. 13, but with the three legs of the core 3a exterior to the windings eliminated.
• the single (open) core interior to the windings provides fairly tight coupling between the coil windings so that the peak voltage is reduced by only 5% (for a ferrite core), which is easily com ⁇ pensated for by increasing the turns ratio by 3%.
• the efficiency is hardly reduced, and any reduction in discharge period may be compensated for by using a slightly larger discharge capacitor 4 or by other methods already disclosed.
• capacitor 4c may still be kept as a lower value 0.1-0.2 uFarad second snubbing capacitor (with resistor 4d set at a low value of 1 to 10 ohms, or zero).
• capacitor 4a will also work with capacitor 4a to deliver high frequency, lower peak (ECDI) current spark energy to the spark discharge following the SCR shut-off, as disclosed with reference to FIGS. 2b. 2c, and 10.
• CEI Ignition Another main feature of the more optimized CEI Ignition is the placement of the the coil and entire discharge circuit in the same enclosure 130 made of non-magnetic material including prefer ⁇ ably an insulator casing 133 and an open metalic casing 132 for providing electrical shielding while not absorbing useful elec ⁇ trical energy. This helps to both minimize EMI and optimize the electrical capacitive discharge ignition efficiency by minimizing the length of primary wire 1. Further improvement in EMI (and other forms of interference, including conductive interference), is achieved by placing a Faraday shield 135 (an open loop) between the coil windings 1 and 2, and connecting it with the low side of the secondary wire at a convenient point 136.
• EMI and other forms of interference, including conductive interference
• CEI Ignition in terms of obtaining the value of (boot) capa'citance Csb of about 50 pf near the spark plug is to use a shield 86c such as metallic braid over the spark plug wires 108b, which in this case would be straight, large diameter metallic wires providing very low inductance Lsb (0.1 to 1 uH), very low resistance, and the required capacitance to produce an intense but relatively low energy capacitive spark upon initial breakdown (spark formation).
• Lsb very low inductance
• Lsb very low resistance
• the required capacitance to produce an intense but relatively low energy capacitive spark upon initial breakdown (spark formation).
• the source impedance Zsb is given by:
• the spark plug wire can be designed to provide a range of values of capacitance and inductance (per unit length) by adjusting the center conductor diameter and dielectric constant and thickness of the insulator.
• the King lead 108a preferably would be of highly inductive absorptive wire with very low capacitance to ground.
• the concept of source impedance is useful in disclosing and defining the parameters of the CDCC ignition to be used with the EFFL plug which make up in part the CEI Ignition.
• the equivalent arc resistance is at least an order of magnitude higher while Zs is not equivalently as high, so that in this case the system has been designed to make use of the high electric field that naturally exists across the preferred toroidal gap to couple electrical energy to the flame front plasma.
• a range of hybrid systems can be designed based on the CDCC system and EFFL plug disclosed herein (and the hydrocarbon fuel used) to produce variants of the optimized CEI ignition system all falling within the scope of this disclosure of this invention.
• CEI Jgnition is a system which redefines ignition, both in terms of what should be achieved, and how it should be achieved, providing.a practical and highly effective ignition of unprecedented capability.
• the CEI Ignition takes the initial flame into account in a systematic way as part of the more complete "ignition process" in order to most effectively influence it. Equally important, practical ways to achieve this optimal lean mixture ignition have been disclosed herein.

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• Engineering & Computer Science (AREA)
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• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
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• 1987
  • 1987-12-11 AU AU10881/88A patent/AU1088188A/en not_active Abandoned
  • 1987-12-11 WO PCT/US1987/003346 patent/WO1988004729A1/en not_active Application Discontinuation
  • 1987-12-11 JP JP88500803A patent/JPH02502661A/ja active Pending
  • 1987-12-11 EP EP19880900648 patent/EP0339043A4/de not_active Withdrawn
  • 1987-12-18 CA CA000554843A patent/CA1311795C/en not_active Expired - Lifetime

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