Note: Descriptions are shown in the official language in which they were submitted.
~ 3~79~
--1
FORM~TION OF ELECTRIC FIELD DISCI-IARGES ~r THE FL~ME ERONT PLASMA IN
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BURNING IIYDROCARBON ~UELS BASED ON A UNIFIED APPROACII TO IGNITION
BACKGROUND OF THE INVENTION AND PRIOR ART
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.
Considerable research has been conducted on ignition systems
and on fuels for internal combustion engines with the objective
of improving the combustion of the air-fuel mixture. More speci-
fically, during the past thirty years there has been work done on
improving the ability of ignition systems for igniting the fuel,
especially of the inherently cleaner and more efficiently burning
lean air-fuel mixtures, and also for improving thc anti-knock
characteristics of the fuel itself so that higher engine compres-
sion ratios can be used for higher internal combustion engine
efficiency.
The prior art work on ignition has focussed on improving the
ignition voltage and the spark's energy content, and on sustaining
-~ 20 high electromagnetic (EM) fields at the flame front. Little atten-
tion, however, appears to have been given to actually improving~
the electrical coupling to the flame front, and to using the
hydrocarbon air-fuel flame front plasma as a source of ignition
plasma for absorbing electrical (discharge) energy.
2~ Prior work on hydrocarbon fuels appears to have been largely
limited to work on improving the fuel's anti-knock characteristic~
or octane rating and on the fuel's volatility, Little or no atten-
tion seems to have been given towards using the fuel's combustion
plasma generating properties (or plasma rating as described here-
inafter) as an approach for improving the ignition and combustion.
; The limited work on fuels appears to have occurred because, with
few exceptions~ no practical proposals were made to use the fuel's
flame plasma generating properties in the internal combustion
engine to electrically stimulate the combustion to improve `lean
mixture combustion.
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Prior art work on spark ignition aspects are numerous, and
for example, are summari~ed in Edward F. Obert's book, "Internal
Combustion Engines and Air Pollution", pp. 532 to 566, Spark-
Ignition Engines, Intext Educational Publishers, 1973. The work
reported by Ohert, and most the work since then, does not discuss
the plasma properties of the flame. Earlier work by the
applicant herein has been limited principally to the very high
frequency (microwave) coupling to the flame plasma, F~r example,
work on generating and maintaining a high electromagnetic field
in the combustion chamber is disclosed in U.S. Patent Nos.
3,934,566 and 4,138,980, where the concept of electromagnetically
stimulated combustion is introduced. In these cases, F~ 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 Seria] No.779,790, where EM flame-front stimulation occurs
near the spark plug site by means of a system designated as "EM
Ignition".
In all these cases, while the concept of interacting with
the flame plasma is either important or helpful, there is actu-
ally no discussion of redesigning the "ignition" system to either
~5 enhance or maximize to whatever extent flame discharge ignition
naturally occurs, or to force the flame front to become an elec-
trical discharge path for the ignition spark circuit. The closest
prior art known is that of the applicant herein, namely the above
referenced EM Ignition, wherein EM flame-front stimulation occurs
by using a large antenna type plug tip which couples to the flame
; front: 1) the pre-breakdown electric fields associated with the
high voltage r1se of secondary pulses, and 2) the high frequency
(of MHertz range) EM fields at the spark plug site arising from
grounding the spark to the piston face. These electrical fields
persist for up to a few microseconds (usecs). In neither case is
the present invention contemplated.
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Moreover, careful inspection of the antenna type plug tips
of the EM Ignition system disclosed show insulator ends which are
generally converging and metallic end tips which are either poin-
ted or surrounded at the sides by insulating material. Such struc-
tures are of opposing shape to that of the present invention, and
furthermore produce electric field lines whicll are bowed outwards
from the spark plug end, significantly reducing the electric field
intensity from that which is disclosed with reference to the
present invention.
Furthermore, in the previous cited cases, and in all the
prior art work known to the applicant, there is no discussion of
modifying the fuel itself to improve its flame plasma properties
for preferentially absorbing electrical energy at the flame front.
A large amount of prior art work on the fuel was largely
concerned with the use of lead to increase the octane rating, and
is incidently related prior art in that lead reduces the electron-
ion recombination coefficient to sustain a higher density plasmaat the post-combustion ~one or '~tail" region of the flame profile
which is detrimental to the present invéntion. Similarly 9 addi-
tion of alkali earth metals (with low ionization potential) tathe fuel does produce a large volume, high density plasma during
ignition, but since the plasma is generated principally by heating
of the fuel, the density profile of the plasma follows the flame
temperature profile, once again producing the main plasma in the
tail region of the flame.
Other related prior art work is in the area of continuous
flowing plasma jet igniters, for example by Hilliard and Weinberg~
Nature 259 (1976), where additional fuel is fed to a plasma jet
cavity to feed chemical energy to the plasma by the locally rich
; 30 burning flame. Such systems are of the dual fuel type with all
the associated problems of handling of two fuels.
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SUMMARY _ THE INVENTION
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.
In this new unified approach to ignition, 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. Moreover, the approach one
takes to more optimally harness these various interrelated igni-
tion processes depends strongly on the physical conditions or
~o 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
~5 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 P~DI, and to the invention of a more optimized fuel for
such systems, designated as EMT fuel.
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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 ~odification to be described and
referred to hereinafter as ECDCC, which stores more energy per
firing and delivers it to the "spark" with a very hlgh efficiency
of 70% to 80%, many times that of a standard ignition. The ECDI
system preferably uses such an ECDCC system.
Another version of the present invention which follows from
the new unified approach employs repeated discharge of electrical
energy across the plasma in the flame as it propagates away from
the initial spark site while still in the vicinity of the spark
plug tip. Such a version is termed hereinafter as "pulsed flame
discharge ignition" (PFDI). More specifically, this latter ver-
sion of the present invention provides an optimi~ed lean mixture
ignition system by combining the space-time spark and flame plasma
discharge characteristics and behavior with a special ignition
energy delivery system and with a plug structure so as to form
~ "ignition" sparks or discharges across the initial moving flame
;~ front or flame plasma. The system can be further improved by
including an improved plasma generating property of the flame in
an ignited mixture of air and a hydrocarbon fuel selected to have
a higher "plasma rating" or "PR" rating of the fuel as hereinafte~
described.
It should be noted, with regard to the improved (EMT) fuel,
that the use of lead in the fuel is undesirable since it produces
a large "tail" plasma behind the flame front which robs electrical
excitation energy from the front edge of the flame front plasma.
Similarly, the use of alkali earth metal additives in the fuel in
the present invention is undesirable if its presence produces the
main plasma in the tail region of the flame, and thus tends to
rob the incipient flame of electrical excitation energy.
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The pulsed flame discharge ignition version of the present
invention has as its practical basis the lligh efficiency voltage
doubling coil with its high energy and very high eEEiciency, as
described in copending [J.S. patent application SN 688,030 (desig-
nated as the CDCC system), and the concept of a 1arge "EM ControlVolume" defined at the antenna type plug tip of the EM Ignition
system described in copending U.S. patent application S~ 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 hy~rocarbon-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). When these parameters and structures
are selected in the context of the present disclosure, then
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 densit~
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 (increasingthe ratio) and simultaneously eliminating additives which reduce
the plasma recombination coefficient and increase the tail plasma.
Generallyi 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.
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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.
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 hely 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.
To recapitulate, in the present invention 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 del:ivery to the mixture
; (of about 100 and 500 watts respectively). To achieve this, 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.
patent applications SN 688,030 and 885,961, to impose conditions
so that these heretofore apparently unrelated ignition processes
can be harnessed from the present new perspective to make ignition
a process where electrical energy is delivered, not primarily to
(the remnant of) the initial spark kernel or spark channel, but
to the incipient flarne front plasma.
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OBJECTS OF T11E INVENTION
It is a principal object of the present invention to provide
a new and improved ignition system for a fuel-air mixture and
including a plug structured so that a major portion of the length
of the spark discharges therefrom extend into the mi~ture approxi
mately perpendicularly to the electric field around the plug tip
and the resulting initial flame front propagates into the air-
fuel mixture with its Eront progressively parallel to the elec-
trical field while still in the influence of the field.
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.
It is another object of this invention to provide a multiple
pulsed flame discharge ignition such that an ini~ial intense spark
with a moderately large capacitive component is formed ~preferabl~
in conjunction with 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
; 25 spark moves in a way that its direction becomes increasingly
parallel to the electrical field intensity defined by the plug
structure and mounting surface, so that on further pulsing of the
(CDCC) ignition, electrical "spark'7 discharges are formed across
the flame front, pumping up to hundreds of watts of electrical
power into the flame front, versus the energy being delivered
into the spark which forms at the same initial (spark remnant)
site providing little or no assistance to the propagating flame.
It is another object of this invention to provide a system
which uses the electrical field of the high discharge voltage of
approximately ~00 volts associated with a low spark discharge
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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 oE sine-waves with peak ampli-
tudes in the range of lO0 to 400 ma; to provide such a system
which includes a large spark gap oE about O.l 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.
It is another object of this invention to provide a hydro-
carbon fuel the composition of which is modified such that the
ratio of carbon to hydrogen (C/H) in the fuel is in the range of
0.5 to 2.0 to provide a high plasma rating or PR of the fuel to
improve the ability of coupling electrical energy to it.
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 pIasma 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 dropplng plasma tail characteristic of; ~ pure hydrocarbon fuel-air combustion.
It is another object of this invention to increase the flame
~; front plasma density generating properties in an ignited fuel-airmixture as described above in conjunct~ion with a high octane
rating of the fuel, preferably by increasing the relative content
of "aromatic" fuel components to the remainder of the fuel.
It lS another obJect of this invention to provide a combina-
tion of such a high plasma density generating fuel with a conti-
nuous flow combustion system, e.g. a turbine or burner, that usestechniques to electromagnetically~stimulate combustion of the fuel.
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~31~L795
Another object oE 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"
; characteri~ed 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 ~or focussing the elec~ric 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.
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Another object of the present invention is to provide such a
focussing ]ens 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 t:o 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 sheIl 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 overa]l 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 systemj 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 deEining a further improved or optimized CDCC ignition.
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Another ob~ect of the present invention is
to provide a high efficiency capacitive discharge
ignition system using low forward drop SCRs as the
spark pulsing swi-tches, 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 ingnition 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 somewhat 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.
1~ 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 millijoules for the standard PDI
system).
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Other objects of the invention will in part
be obvious and will in part appear hereinafter. I'he
invention accordingly comprises the apparatus
possessing -the construction, combinations of elements
5 and arrangements of parts, and the process including
the several steps and relation of one or more of such
steps wi-th respect to each of the others, all of
wnich will be exemplified in the following detailed
disclosure and the scope of the application of which
will be indicated in the claims.
In accordance wi-th one embodiment of the
invention there is provided a high efficiency, high
output electrical ignition system for igniting
air-fuel mixtures in a combustion chamber of an
internal comhustion, or IC engine, which includes
means defining a spark plug and spark plug boot of
combined capacitance Cspb to ground between 30 and 80
pf, the spark plug including a plug firing and having
a central electrode and second electrode means
disposed about the central electrode so as to provide
a spark gap of at least 0.06" between the electrodes,
across which gap one or more spark pulse discharges
and electrical fields arise upon application of
electrical energy to the plug. An ignition firing
circuit means is provided for energizing the plug.
The ignition firing circuit means includes a
capacitive discharge ignition means including
ignition coil means with primary and secondary
winding of turns ratio N, input capacitor means of
capacitance Cp connected to the power converter means
for charging to a peak voltage Vp and the other side
of the capacitor connected to the hot side of the
; coil primary winding, switch means S for discharging
primary energy stored in the input capacitor Cp to
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12b 13~L79~
energize the coil, the coil secondary to primary
turns ratio N defined approximately by the formula
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N = [Vs/(2*Vp)]*[l+(~)*(Cs/Cp)*(Vs/Vp)**2],
wherein Cs is total secondary circuit capacitance,
including Cspb, and Vs is the peak output voltage of
the coil whose secondary winding is connected to the
central electrode of the spark plug. Means defining
an IC engine portion include at least one combustion
chamber with a movable compressing member therein
creating air motion inside the combustion chamber
including at least one of microscale -turbulence,
squish, or swirl, wherein the spark gap is exposed to
the air motion such that under normal operation of
the IC engine the spark discharges provide an arc
burning voltage Varc substantially greater than that
produced in still air. In the typical operation of
the IC engine the ignition provides ignition spark
discharge power output Parc greater than lO0 watts at
a discharge system efficiency EFF greater than 40%
and at an overall ignition system efficiency EFFtot,
including the powe~r converter means, greater than
30%.
In accordance with a further embodiment
there is provided an ignition system for an internal
combustion device having a combustion chamber with
spark plug means mounted on a mounting structure
with an interior surface with a ground firing edge
or ground electrode defined as the region between and
including the spark plug means outer second elec-trode
or shell end and the interior surface region adjacent
the shell end. A central firing end or nose
comprises a partially insulated end section of the
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12c
central electrode of the spark pluy means further
comprising a ceramic nose with a metal.lic firing tip
or but-ton set at its end forming a coaxial gap with
the firing edge. Sparking means are provided by the
spark plug means for igniting an air-fuel mixture in
the combus-tion chamber. Means are provided for
delivering electrical energy to the sparking means to
ignite the mixture. The sparking means produces one
or more spark pulse discharges and electrical fields
upon application of the electrical energy to the
spark plug means to ignite t.he toroi.dal volume
defined by the coaxial gap. I.n accordance with the
invention, the improvement in the ignition system
includes a shaping and disposing of the firing end
and firing edge such that they form an essentially
electric field or electrostatic focussing lens or
EFFL, for focussing the electric field onto or near
the firing edge. The coaxial gap between the button
and the ground electrode is greater than 0.06", the
EFFL feature~of the plug means substantially reducing
:~ the voltage required to electrically break down the
coaxial gap to form spar]c discharges relative to an
equal gap formed between infinite coaxial uniform
cylinders.
In a still further embodiment there is
provided a spark ignition combustion system for
igniting and combusling a hydrocarbon fuel-air
mixture. The system includes means for initiating
and maintainlng a spark ignited combustion in~
;~ 30 repetitive cycles in a compression/expansion combus-
tion volume and for feeding a hydrocarbon fuel-air
mixture of high~flame-front plasma density thereto.
Each such cycle comprises a spark ignition period
comprising an initial and follow-on ignition stage
where:in combustion lS lnitiated. Spark ignition
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means create an initial spark/flame kernel during the
initial spark ignition period which includes an
ini-tial breakdown spark of the ignition means and
also produce from the kernel during the follow-on
stages of operation of the spark ignition means at
least one outwardly moving flame-front into the
volume and an electrical field capable of sustaining
a plasma discharge in the outwardly moving flame-
front. T~e system is constructed and arranged such
that the ou-twardly moving flame-front propaga-tes into
the fuel-air mixture during the follow-on ignition
stage such that under normal operation of the combus-
tion system the electric field is sufficiently
parallel to the outwardly moving flame-front, and the
plasma density at the flame-front of the moving flame
-is sufficiently high such that an increasing fraction
oE the electrical energy available in the follow-on
ignition stage is coupled to the moving flame
relative to that which is coupled to the spark
remnant of the initial kernel. Thus, the combustion
reactions of the outwardly moving flame-fronts of
lean hydrocarbon fuel-air mixtures and of otherwise
difficult to ignite hydocarbon fuel-air mixtures are
enhanced.
For a fuller understanding of the nature
and objects of *he present invention reference
should be had to the following detailed description
taken in connection with the accompanying drawings.
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-13-
BRIEF DESCRIPTION OF THE DRAWINGS
_
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 inven-
tion, which view also includes a showing of an electric fielddistribution 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 system9
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 d1mensional flame.
FIG. 3a is a graphical representation of flame plasma density
distributions n(O,phi,f) versus fuel-air equivalence ratio phi of
a standard fuel and a preferred fuel of the present invention.
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FIG. 4 is a graphical representation of the initial arc
density-time distibution of a single initlal 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 flarne of the preferred fuel.
FIG. 6 is a graphical representation of the density distri-
butions n(x,phi=l,f) as a function of the flame position for a
range of fuels treated according to the present invention refer-
enced to a standard 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 C~CC
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~oE 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-
3S tion of the average electric field superimposed on each front.
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FIG. 10 is an idealiæed view, partial:Ly ln 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. ll 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. 1la 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.
FIG. 11b is a half longitudinal cross-sectional partial view
~ of an EFFL plug, of a variant design compared to FIG. ll, 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.llc is a longi~udinal cross-sectional partial view of an
EFFL plug, of a variant design compared to FIG. ll, 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. lld is a longitudinal cross-sectional partial view of an
EFFL plug, of a variant design compared to FIG. ll, 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
,.. ,., . ,, . - -
.
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-16-
so that in combination with the electric f:ield focussing effect
the spark pulses are encouraged to move outwards and around the
toroidal gap defined by the plug end.
FIG. lle 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 Eurther 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.
10FIG. 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.
15FIG. llff is a longitudinal cross-seotional fragmentary view
of an idealized EFFL plug with an overly extendcd 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.
`.`", :":
-17- ~31179~
DESCRIPTION OF PREFERRED EMBODIMENTS
With the advent of EM combustion stimulation, and recently
with the advent of the more practical EM Ignition technology, the
idea has been introduced of viewing ignition systems for hydro-
carbon Euel-air mixtures, not as electrically isolated or indepen-
dent spark generators, but as a more general system which includes
the flame plasma properties of the fuel-air combusting mixture as
part of the ignition system or electrical circuit. When viewed
in the further light of the space-time properties of the spark
discharge plasma, substantially improved systems (embodying the
present invention) have been developed -- a lower power version
based on Standard Ignition providing typically 100 watts spark
power (FCDI), and a higher power version based on EM Ignition
prov~ding typically 500 watts (PFDI).
For both systems there is a restructuring of the tip of the
spark plug with respect to the surface on which it is mounted.
By using such a restructured plug tip in conjunction with a high
energy/high efficiency ignition (a CDCC system) operating either
with currents of several hundred milliamps of the "transitional
2~ glow discharge" or of one to two amperes of the "transitional arc
discharge", substantial ignition energy can be coupled to the
flame front either through the high field that exists for currents
in the range of about 50 ma to 200 ma, or through forcing the
initial flame front itself to b~come an intense spark discharge
2~ plasma absorbing up to hundreds of watts of electrical power (in
the amps current range), and thus greatly improving the Lean Burn
capability of the system.
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. In the "high" current
or PFDI version which typically uses up to several amps of current,
a more projecting plug tip approximately 0.2 inches long is used,
and is shaped such that the initial spark forms mainly perpendi-
cuIar to the electrical field intensity so that on subsequent
ignition pulses the coupling to the decaying ignition spark plasma
is very poorj but the coupling to the flame propagating from the
. . ... ..
~:
13~79t~
18-
initial spark is strong because the flame front becomes progres-
sively parallel to the electrical field and is able to absorb the
electrical power. The Elame front itself becomes the ignition
spark, and the ignition circuit is completed through it.
One can further enhance these effects to realize an even
leaner burn by modifying the fuel itself so that E-field energy
can be more easily coupled to its air-fuel mixture flame front
plasma. Such a fuel has been designated as E~r fuel. Such modi-
fied 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. Preferably, 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/~ ratios (from.5 to 2) and/or preferably
19 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
2a low electric fields in the region of the flame front. In this
way 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
2~ during the electric field OFF periods while the chemically pro-
duced flame front plasma grows progressively in volume and inten-
sity, absorbing progressively more of the electrical energy on
succesive pulses while the flame is within the 'tEM Control Volume'3
(the volume over which the air-fuel flame plasma is influenced).
The modified fuel of the present invention (EMT fuel) 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 æone, 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
.... .. . .
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--19--
electric fields referenced to the inltial spark and the p~opaga-
ting flame front respectively. Such a fuel is also applicab:Le 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.
Shown also i3 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
lg 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.
FIG. la is a longitudinal, cross-section partial view of a
2a 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 o~er which the electric field lines 16a, 16aa
have their influence, namely the EM Control Volume 19. In this
design, the plug tip lla is generally pointed, as shown, to be
29 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).
Sometimes the spark (namely spark 14a) produced by this plug 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. Furthermore, the
conical shape of the tip lla 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 lla and surface 12a of the cylinder
head 12. In the case of spark 14aa, which is parallel to the E-
field, no effect at all of the present invention is achieved.
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-20- ~ 9 ~
Spark plugs similar to the one disclosed in U.S. patent appli-
cation SN 885,961 (excepting for the tip lla wllich pro~ruded 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 en8ine 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 ~o 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 coùpling 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
2g 50 ma ~voltage of about 500 volts) and a current of about 2 amps
(voltage bf 50 volts); and the arc discharge region III defined
by an approximately constant voltage of 40 volts for currents
greater than 2 amps.
For the purposes of describing the two major versions of the
system of the present invention (ECDI and PFDI), there are two
sub-regions in region II, designated as TGD for transitional glow
- discharge, and TAD for transitional arc discharge. Region TGD
spans the current range of 40 ma to 400 ma, and region TAD spans
the current range of 400;ma to 2 amps. The ECDI and PFDI systems
are defined by (operate within) the TGD and TAD regions respecti-
veIy, as will be seen in the later discussions.
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.
.
~3~79~
-21-
Referring again to FIG. 1, for the typical prior art spark
current of 50 ma, 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). As now viewed from the perspective of electric
field or E-field flame stimulation, it will be seen that this
statement implies that along with the ignition spark there exists
an E-field o~ 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.
It is here asserted that electric field stimulation of the flame
is a hitherto unrecognized key characteristic of low current (less
than 200 ma) spark ignition~ Indeed, it is hypothesized here
that not only is this the case, but that once this is accepted~
several long standing ignition controversies become resolved and
help confirm the Electrical versus Thermal Theory of Ignition.
One such controversy is that relating to the role of current
magnitude in ignition. It has been shown Bosch Technical Report
5, 1977 that when the current is increased from 25 mat to 50 ma,
to 100 ma, the igniting capability for lean mixtures improves
progressively, and then only marginally if at all in further cur-
rent increase to 200 ma and to 400 ma. As can be seen with refe-
rence to FIG. lb, as the current increases from 100 ma, the field
strength progressively drops, until at above 200 ma it becomes of
a marginal value for enhancing the flame. That is, as the current
increases, field enhancement is traded off against the size of
the ignition kernel tcurrent). Such a trade-off is very favorable
up to lOO to 200 ma as a sufficient electric~field can still be
maintained to~enhance the combustion reactions in the spark gap.
Beyond 400 ma electric field enhancement is lost, consistent with
observations on igniting ability with current. Furthermore, at
about~ 1 amp of peak current the ignition capability of a system
has in some cases been observed to be less than that at 100 ma.
Since at 1 ampere, the E-field in the spark gap is 50 ~olts for a
standard gap, representing the same energy delivery to the gap as
st 100 ma, one can conclude that the difference is due to the
loss of field enhancement at the 1 ampere current level.
,
.
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-22-
Another hitherto unresolved question relates to measurements
by ~lancock et al, SAE paper 860321, 1986, which gives the optimal
minimum ignition durations as 0.4 msec and 0.6 msec respectively
for stoichiometric and lean flames. For a flame speed of 2.4 mm
per msec and a radius of 1.0 mm of gap 17, the time of traversal
is then 0.4 msec, equal to what was measured by Hancock as the
time beyond which one obtains no further ignition improvement by
extending the spark duration (for quiescent combustion where
there is very little fluid motion through the spark gap). It is
submitted that this is a further confirmation of the view that the
flame is electrically enhanced while in the gap. 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.
Finally, ~lancock et al diagram dif~erences in cycle-by-cycle
variation (CBCV) as a function of ignition timing and gap width.
Particularly, a dramatic difference is seen both in shape and mag-
nitude of the CBCV-arc duration curves corresponding to ignition
timings of 32 and 55 degrees before top dead center (Bl~C) for a
gap width of 3.0 mm (versus 0.9 mm where no difference is seen).
It is here asserted that the difference is due to the E-field
enhancement effect, i.e. that at the approximate 1/3 load setting
of the 7.5 compression ratio engine, at 32 and 55 degrees BTDC
the air density corresponds to applied pressures in the cylinder
of approximately two and one atmospheres pressure respectively.
For a gap width of 3.0 mm and an assumed arc voltage of 500 volts,
this further corresponds to a field strength of 750 and l,500
volts/cm/atmosphere (v/cm/a) respect1vely. But this is precisely
consistent with the present teaching, namely that at the value of
750 v/cm/a, E-field enhancement is marginally effective in stimu-
lating the flame within the gap, producing a relatively flat
CBCV-arc duration curve with a poor CBCV of 20%; while at 1,500
v/cm/a E-field enhancement is fully operative, showing a sharp
drop in CBC~ to 10% in 0.5 msecs, corresponding to the time that
the flame is within the gap (and subject to E-field stimulation).
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For a gap width oE 0.9 mm, no difference in behavior of the CBCV-
arc duration curve is shown with ignit:ion timing at 32 and 55
degrees BTDC, which is now explained since the E-field is very
high in both cases, i.e. 2,500 and 5000 v/cm/a, which produces
strong stimulation in both cases.
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 Ealls 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.
In such a case, 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. In principle this enhancement can
lS 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
2b 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 2Ll defined hereinafter. Disposed about the outer
surface oE 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 "Ll", 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. Thus, an apprvximately
~!
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13~79~
-24-
toroidal gap 27 is created between frustrum 29a and portion 23a
providing a large ignition volume as required. The geometry
provided by form:ing the periphery of button 21a as a frustrum
serves two further very important advantages, namely to intensify
the Æ-field in the gap 27 and to reduce the detrimental effects
of surface erosion from ignition sparks (because of the larger
mass of buttorl 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.
Inspecting the plug tip of FIG. 2, it can be seen that thelength of its flame path and thus its E-field enhanced vol~lme 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. However,
this ndvnntagc is more th~n of-set by the disndvantsg~ of th~
large heat absorbing ground electrode, it being further relatively
easy to provide a longer spark dllration s~nce the power delivery
i9 relatively low. It is ~lso disadvantagous to have the spark
and field parallel to each other versus a~ some ~ngle to each
other determined by the present plug tip geometry.
In the preferred design shown, 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.
Because the spark 24 is principally perpendicular to the E-field,
a higher initial (transient) arc voltage Varc is a~tained, 1 1~2
the normal 500 volts at 0.1 amp, thus providing a higher E-field
for a given gap length "Lg" during part of the discharge cycle.
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Furthermore, as will be discussed more fully with reference
to FIG. 2d, the coupling to the flame fronts 25 is improved since
the E-field lines 26 become progressively more parallel to the
fronts (away from the spark). Additionally, in automotive appli-
cations where a distributor is used, the over-all efficiency will
be improved, as discussed with reference to FIG. 10, by the even
higher spark gap voltage Varc (over the rotor gap voltage Vrotor).
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. 68~,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 oE the prior (CDCC) system,
or 300 ma, and approximately five times the sine wave period (0.4
msec for example). Thus a 3 msec duration ignition discharge can
easily be achieved with eight complete oscillations. Preferably
coil turns ratio is 50 and capacitance is 4 ufd which is charged
up to about 350 volts providing 0.3 joules stored energy.
An actual design for such a modified coil would preferably
use a standard U core/I bar combination of 1 square inch cross-
section and 2.5 inch winding length, with approximately 100-tùrns
of #14 primary wire (#13 to #15) and 5000 secondary turns of #28
wire, providing an overall very high efficiency of 60% to 80%.
Such a system would be of special interest in retrofit applica-
tions where moderate leanness of operation is required, e.g. 20:1
to 21:1 ~FR, and where cost is more important (versus the PFDI
system to be described which is more suited to OEMs).
The modified ignition system (sometimes hereinafter referred
to as EGDC~) is preferably used in the multi-pulse ignition ~ode
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.
.,:
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.
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~26-
Clearly, 300 ma was chosen as the first peak to provide a strong
initial spark kernel, while the sinusoidal nature of the current
provides signif-icant time durations at less than 200 ma, wherein
E-field enhancement is strong as the voltages 122a/123a are high.
~s tlle current peaks of successive half-waves progressively decay
to 200 ma, the E-field enhancement maximizes since the voltage
achieves the maximum value and is approximately flat (constant)
at that value, i.e. the voltage waveforms 122a, 123a, 124a, 125a,
126a, 127a become progressively flatter, with greater arc time
spent near the peak voltage for maximum enhancement of the flame.
With reference to FIG. lb, the llOW defined ECDI system is seen to
be operated within the defined TGD region as req~ired.
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.
In order to increase the power delivery rate~ one can attempt to
modify the independent variables, i.e. either increase the spark
current or the si~e 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.
The implication is that some other approach must be taken to
increase the energy delivery rate, which has led to the other
aspect of the present invention, namely the PFDI aspect. In this
aspect, 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 GDCC 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 Elame front as the E~field is low.
As a result, another (and most significant) step was taken (in
arriving at the PFDI version of the invention), namely that of
forming actual plasma discharges across the flame front by repeti-
tively pulsing the ignition in conjunction with parameter adjust-
ments including but not limited to the plug structure, the fuel
.
. .
- . .
.
:
~31~79~
-27-
combustion properties, the spark dlscharge properties, and the
ignition system properties. Below follows a description of such
preEerred embodiment of the PFDI version of the present invention
and analyses necessary to understand its principles of operation.
5Referring to FIG. 2d in which like numerals denote like parts
(with respect to FIG. 2) there is shown plug nose 30 considerably
extended beyond shell 23 by a length L2 which typically equals
0.2 inches. Since nose 30 is long relative to gap 30a (width gl)
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 R-field to the existing spark or to
the residual spark or spark remnant (depending on the situation).
In this configuration is established some of the necessary (but
not sufficient) conditions for producing enhanced ignition, but
not of the ECDI type described earlier wherein 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. That is, since
the flame front, shown typically at 25a, 25b, 2Sc 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. However, since
the discharge E-fleld is low (for the higher peak currents of 1 -
3 amps), then there is employed the alternative (PFDI) approach
where the ignition is pulsed in a way that the flame front itself
becomes the discharge plasma. In other words, the plas~a ~hysics
of the spark, the flame plasma, the ignition, and the E-field
(governed in part by the geometry of the plug and mounting struc-
ture) is used to lnsure that with a CDCC ignition system desi8nedfor this application and pulsed in a precise manner, ignition
discharges can be made to occur across the flame front to deliver
hundreds of watts of electrical power to the weak, very lean flame,
providing flame stimulation of major proportions.
, , .
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-28-
More specifically, 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
S recessed 1/32 to 3/32 of an inch from the cylinder head surface
22a, defining a length shown "L"' 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. Thus 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. Furthermore,
as is seen, there is a somewhat focussing of the E-field lines
(a crowding of lines 26) at the location of flame front 25c to
further assist in the formation of a discharge across this front.
Thus, it is asserted that if the ignition is repetitively pulsed
ON and OFF, say every 1/4 msec, 50 that an ON pulsing occurs when
the front is at the site represented by 25c, a discharge will be
formed through front 25c. To what extent this is made to happen
can be more precisely defined once the flame front plasma and
other characteristics are studied, which is advantageously done
with reference to the preferred fuel, described with reference to
FIGS. 3 to 6, and then, in turn, with reference to the ignition
system characteristics. It can then be demonstrated that by
proper design and selection of parameters, a highly effective
PFDI system can be developed for use in most combustion systems.
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-29-
FIG. 3 depicts the various spa~ial distributions across a one
dimensional hydrocarbon (I~C) 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 .i9 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. The back edge
of these curves also initially coincide, and then diverge to form
a tail 32a of the density curve n(x) governed by the electron~ion
recombination process to be discussed with reference to FIG. 4.
The density fùnction n(x), which is more completely designated as
n(x,phi,f), depends in addition on the equivalence fuel-air ratio
"phi" of the fuel-air mixture and on the type of HC-fuel "f".
It should be recognized that 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(O,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.
The following can be defined as follows with reference to FIG.3:
x(l) = a tail width defined as the value at which curve
3Za has diminished to some predetermined low value.
N(xl) = ~ n~dx is the total plasma (electron) count
across the flame front.
.. . A~ .,
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-30-
A flame p1asma rating designation, analogous to the octane
rating parameter of a fuel, can be defined as the Plasma Rating
parameter "PR(f)" of a fuel "f" in terms of a profile factor P~
and density factor DF:
PR(f) = [Profile Factor PF] * [Density Factor DF]
PF = [2*n(0)*x(0)/N(Xl)]
DF = lO*log[n(O,phi=.6,f)],
where log means "log to the base 10".
It has been tacitly assumed here that a typical or standard HC
fuel i9 one with a C/H ratio of 0.5, which has no a~ditives, and
which has a profile factor of 1.0, (i.e. as much plasma resides
in the flame front as in the tail); and its peak density 35, at
an equivalence ratio phi = 0.6, or 24 to one gasoline air-fuel
ratio (AFR) is 10**10, where "**" means exponentiation. Thus its
g plasma rating PR equals 100.
The definition of PR of a fuel is obviously an arbitrary one,
but one that permits the making of comparisons among fuels from
the perspective of tlle present inYention, and contributes to the
characterization of ideal fuels. What the above equation says is
2d that in terms of the profile factor PF, the more plasma that is
within the reaction ~one 26 (versus the tail) the better, since
the purpose is to electrically stimulate the flame front and not
the tail (the back part of the flame). In terms of the density
factor DF, the higher the peak density (referenced to 10**10) the
2~ better, the objective being to preferably have an HC fuel with a
PR rating of 100 or greater (referred to herinafter as an EMT fuel).
FIG. 3a depicts the flame plasma density curve 37 as a
function of air-fuel ra~io phi at atmospheric pressure of a fuel
f among several measured, showing the density falling from 10**12
at stoichiometry to less than 10**10 at phi = 0.6 (point 39).
As will be apparent, 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). To improve the fuel property, one
either has to be content to work with a higher phi value of say
0.66 (or 22 to one AFR), or one needs to treat the fuel (only
slightly if one is content to work within the limit of phi = 0.6).
. .
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.
-31- ~3~79~
Curve 38 represents an EMT fuel f1, with a "boosted" flame
plasma density five times the average, and a PR rating of 106,
(i.e. n(Ot.6,fl) = 4*10**lO as indicated by point 39a, and the
profile factor PF is unchanged at 1.0). The usefulness of such a
fuel modification will be discussed with reference to the temporal
plasma decay characteristics of the spark, which in the present
invention is the characteristic with which the flame plasma
competes following the striking of the first ignition spark.
FIG. 4 shows the logarithm of temporal density distribution
of a single spark 42 designated as n(arc,t), corresponding to tlle
case of a spark ~ormed by a CDCC system (with an oscillat:ion
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. It is
assumed that the plasma decay rate of the arc is governed by the
following recombination equation, which is a key concept:
n(t) = n(O)/[] ~ n(O)*alpha*t]
where 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.
Making a change in variable from t to T, where 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), the above equation then becomes:
n(T~ - n(O)/[l ~ n~O)*(10**-ll)*T]
A spark plasma at one atmosphere pressure with an intense
capacitive spark component is expected to have an initial arc
density of 10**18/cubic cm (cc), so the abo~e equation reduces to:
n(T) - (10**11)/T, where T is in 50 usec units of time.
Thus on the time scales of interest, a density value of 10**11/cc
becomes the density scale, or value with which the flame plasma
must compet~, which is a key concept of the present invention.
The curves in FIG. 4 show the flame plasma density 43 for a
stoichiometric HC-air flame rising to meet the decaying arc plasma
density tail 47 in a fraction of the above defined time scale T;
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and for the moderately lean flame of phi = 0.8 the plasma density
curve 44 meets the tail 47 in about 1.0 T; ~nd for a very lean
flame of phi = 0u7 the density curve 45 meets the tail 47 in
about 2.0 T; and for the extremely lean flame of phi - 0.6 the
density curve 46 never reaches the spark tail 47. In a very
general way one can inEer a relationship between effect:ive spark
ignition and the plasma density of the flame, as will be made
more precise with reference to FIG. 5 .
FIG. 5 depicts the temporal log densi~y 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. Ihe 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 ~he 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.
Now if the flame kernel is still within the EM Control Volume
during the spark pulsing process7 then it can occur that instead
of the spark plasma 55 and flame plasma 58, a discharge can take
place across the flame front producing a much lower spark plasma
55a (at the previous spark site) and a much higher "spark" flame
plasma density 58a. This process can be enhanced if the the fuel
is modified to provide a high fuel-air flame plasma rating (PR);
or if the plug tip is redesigned along principles which were dis-
cussed with reference to FIG. 2d. Thus, even with a standard
unmodified HC fuel, by carefully designing the system (to a PDFI
system of FIG. 2d) one can produce ~he "flame ignition" effect
shown by curve 58a, delivering up to hundreds of watts to the
flame front~ greatly stimulating the flame.
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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 modiEication is to increase the C/~l
ratio of the fuel to as close to one as practical since the flame
plasma density of the Euel is known to be maximum at a C/~l ratio
of one since chemi-ioni~ation is based on reactions involving the
C-H bond, which is maximum for the aromatic fuel family (benzene
derivatives), which have the general formula Cnll2n-6.
As a specific examyle of an EMT fuel which can be currently
made, an inexpensive low octane Euel 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 benæene (with very high octane) with formula C7H8,
and there i9 obtained a fuel with a C/H ratio just sreater than
0.5 (and with a very high octane), which would classify as an EMT
fuc1 useful for h~gh comprcssion r~tio, 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 ioni~ation 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. On the other hand 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. With
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 Sodium9 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.
.
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~.3~179~
-~4-
With this understandin~ of the ft~el (flame plasma) aspects of
the present invention, an analysis is now performed with respect
to the PFDI system to integrate the remaining parts of the system
To begin with, relationships for the tangential component Et and
normal component En are developed in terms of the electric field
Es, assuming that the side surfaces of the insulating layer 28 of
of the plug tip of FIG. 2d (with which the PFDI system is defined
and will be referred to in the discussion that follows) are
substantially parallel to the axis of wire 21, and where:
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*1~**11 at one atmosphere;
f = the operating frequency;
Kr = the imaginary part (lossy part) of the generallized,
complex, relative dielectric constant;
Then:
Kr = ~[tWp**2)/W*Nu]
Wp = 2*pi*9* ~Ne]; W = 2*pi*f
Et = Es
En = Es/Kr, since Kr**2 is very large in the present cases.
It is useful to consider the practical case where:
f = 100 KHz; Ne = 3*10**10 electrons/cc; which gives
Kr = 10; En = Es/10,
or a normal component of electric field En one tenth that of the
tangential component Et. Based on the earlier equation for the
decay of the spark plasma:
n(T) = (10**11)/T,
it is noted that the value of n(T) corresponding to Ne = 3*10**10
is 3.3*T or 165 usecs. From FIG. 3a, this val~e of Ne is seen to
correspond to an AFR of 21:1 for a standard HC fuel. From these
values it can be inferred that, neglecting the E-field strength
; and direction for now, the spark is equally likely to form at the
old spark site as at the flame front if the ignition is refired
after a delay of 165 usecs from the end of the previous spark, in
an air-fuel mixture of ratio 21:1 (equivalence ra~io phi = 0.7).
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i3~79~
In actual fact it may be necessary to ignite even leaner air-
fuel mixtures of approximately 24:1 ~FR tphi = 0.6), where for
o~her than an ideal EMT fuel not currently available, the flame
plasma density is significantly lower than the spark density after
165 usecs. But what has been described above in terms of the E-
field components permits this to happen, because the flame can,
in principle, have a fie]d of the order of ten times greater
coupled to its front than is coupled to the spark remnant.
The situation is not quite as favorable as indicated above,
because the above analysis is somewhat of an over simplification.
The spark remnant has a very high field (the one lnitiating 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 F.n (which
requires gap gl be kept as large as practical within other con-
straints, name:Ly 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:
Enl = En/k = ~s~k*Kr where l/k = 5 (or 3 to 8)
With reference to FIG. 2d, the geometry of the tip is seen
to provide a length Lg (corresponding to the most favorable flame
front site 25c) approximately equal to the length of the spark
core 24a, implying that the ratio of the field strength in the
flame front versus the core is given by:
Es/En = k*Kr
In turn, the conservative assumptivn can be made that an ignition
pulse occurring t usecs after the last spar~ will for~ at the
initial flame front or spark remnant, depending on whether the
above ratio multiplied by the corresponding square root of the
plasma density ratio is greater or less than unity (assuming
power absorption controls the discharge of the electrical energy)
. .
. ~ . : . .
~ 3 1 1 7 9 ~ !
-36-
e ratio, designated as FSR for flame/spark ratio, is given by:
ESR = [k*Kr] * ~[n(flame,phi,t)/n(arc,t)]
where the above density designations are given in EIG. 4.
To Eirst order, the flame density can be taken as a constant (for
a given equivalence ratio) and the expression for the spark decay
substituted to give:
FSR = [k*Kr] * ~[n(O,phi,f)*T]
where n(O,phi,f) is expressed in units of 10**11.
For example, for: k = 0.2, Kr = 10, T = 4 (200 usecs),
n(0,0.6,f) = 0.1 (in units of 10**11),
FSR = [0.2*10] * ~ 0.1*4] = 2*0.63 = 1.3
implying that the spark is 30% more likely to form at the flame
site than at the previous spark site under these conditions.
Clearly, the above expression is not an exact theory, and
must eventually be tailored on the basis of experimentation, but
serves as a very useful and important guide in providing direction
for the (PFDI~ system design of the present invention.
Finally, 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.
That is, assuming a piston stroke o ~ cms, at an engine speed of
600 RPM, the average piston velocity is equal to the above quoted
flame speed of 1.6 mm/msec (and to the piston speed at 45 degrees
BTDC, corresponding to a typical advanced ignition timing for lean
mixture engine operation). Thus, we can take the initial engine
flame speed VEfi to increase approximately proportional to engine
speed S plus one, or more conservatively S ~in units of 600 RPM):
VEfi = C1 * S * Vf
where ~1 is between 0 and 1, and represents the component of the
~ piston induced ~luid motion along the flame direction.
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~311 ~7~
This implies that the flame positions represented by 25b,
25c correspond to the second spark pulse at 1800 RPM and 3600 RPM
respectively (for a typical value of C1 of 1/2). Therefore, at
1800 RPM 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.
Under conditions of highly turbulent flows or intense squish or
swirl at the spark plug site, the speed VEfi can clearly be
higher since these flows can impart a velocity in the direction
of motion of the flame front greater than ~he piston velocity,
making for a value of Cl greater than one.
It is to be noted that the above expression for FSR assumes
the restriking of the spark at a time when the flame front is at
a favorable position defined by having its front mainly parallel
to the E-field near the spark plug tip upon the ignition refiring
From the above discussion clearly the flame motion can be expli-
citely included in the expression for FSR through a multiplica-
tive Eactor on the right hand side of the equation of the form:
1/[1 + C2/(S*T)]
where C2 is a constant in the range of one to five.
Finally, the critical assumption made regarding the value o~
the spark plasma recombination coefficient "alphal' 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.
For the glow discharge, the temperature of the neutral and
ion species are close to the gas temperature. As the transition
is made to the arc discharge, 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
alphat that preferably the peak arc currents be kept low. But for
the CDCC ignition (of the PFDI system under discussion) this is
the caset with the main spark energy being delivered within the
current range of 1 to 3 amps.
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-38- ~31~ 9~
Therefore, all that remains is to insure that the high peak
capacitive currents, which would ordinarily be maximized to opti-
mize the igniting ability of the initial spark kernel, be kept to
values in the 10 - 200 amps range, which is done as will be seen
with reference to FIGS. 7 and 8 (rather than at 1000 amps quoted
by others). This implies that since the predominant temperature
in the plug tip vicinity is the flame temperature, which is of a
similar value to the arc current temperature of a low current arc,
and since the PFDI effect typical;Ly will occur several hundred
microseconds after the initial peak capacitive current (giving
the initial capacitive spark channel time to cool), then it is an
appropriate assumption to choose the value of alpha as was done.
Factors which enhance the formation of the discharge across
the flame front to optimize the PFDI effect are summarized below:
1) raising the PR rating of a hydrocarbon fuel to about 100 or
above (so that it becomes a good EMT fuel);
2) increasing the fluid dynamical coefficient Cl somewhat so that
greater velocity is imparted to the initial flame front twithout
impeding its motion around the plug) by the introduction of swirl,
squish, or preferably microscale turbulence at the spark plug site~
3) increasing C1 by having the axis of the spark plug form a
significan~ angle to the axis of motion of the piston (so that a
significant component of the piston induced fluid motion appears
in the direction normal to the initial flame front);
?~ 4) minimizing the diameter of the plug tip protruding from the
plug shell, so that the PFDI effect is relatively insensitive to
the location around the periphery of the plug where the initial
spark is formed relative to the plug's location in the combustion
chamber and in the fluid flow field of the air-fuel mixture;
5) using asymmetrical lobes (see FIG. 2a), e.g. on one side only
of the spark initiating gap, and orienting the plug so that the
spark is formed in the most favorable orientation with respect to
formation of PFDI eEfect;
6) designing the high voltage ignition circuit to provide mode-
rately high inital capacitive current to insure ignition while
minimizing the size of the spark remnant it leaves;
,....
,
: .
-39- ~3il~9~
7) increasing the time between pulses to 4T or ST (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 oE limited use since in
turn it reduces the average power delivery to the spark plug end;
8) reducing the frequency f (which increases Kr and reduces Enl)
by using a high output capacitance oE say 250 pfd (say 100 pfd in
the coil, 100 pfd in the boot, and 50 pfd in the plug) which redu-
ces f from the above assumed value of 100 K~lz to 50 KHz or less;
9) designing the spark plug tip as sllown particularly in FIGS~ 2d
and 7, and adjusting parameters to further reduce coupling to the
spark remnant and increasing coupling to the flame front plasma.
~IGS. 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 and 8 have been arbitrarily chosen 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.
The pre~erred embodiment of FIGo 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 0.09'1
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 linlit 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 surro~lnding portions 71/71a respectively, which in turn are
surrounded by plug shell conducting portions 23i73 respectively.
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~,o ~3i~79~
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, 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.
Also (as described in connection with FIG. 2) at least a
portion of the cylindrical periphery of button 21a forms conical
~rustrum 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,
Thus, as previously discussed, toroidal gap 30 is created between
frustrum 29a and shell end 23a (and cylinder surface 22a shown
with reference to FIG. ~) 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, OD 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). These dimensions, taken
with others shown, provide thicknesses of insulators the 78 and
78a of 0.11" to 0.12" for sufficient hold-off voltage and maximum
capacitance of the plug, which can be further raised by increasing
the length of the insulator section 78a sandwiched between center
conductor 71a and shell 73 from the approximate value of 1/2 inch
shown to approximately 1 inch, and also by using an insulating
ceramic material of higher dielectric constant. Length L of insu-
lator protrusion beyond shell end 23a, which is set between 0.12"
to 0.24'i for the PFDI system (and half that for the FCDI system),
is shown as 0.16" (corresponding to the PFDI case).
With regard to the above dimensions, it is emphasized that
they are chosen to conform to an overall spark plug size suitable
to existing engines, where the spark plug "well" diameter may be
only 7/8 inch. Clearly most of the dimensions can be sized up or
down as long as the principles introduced herein are adhered to.
r ~a~
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-41- 13~7 9~
With regard to the si~es quoted herein, they are taken gene-
rally as plus or minus lO~, and where the term "approximate" and
"about" are used preceding the si~e dimension, they are taken to
imply larger ranges; for example "approximately" may mean plus or
5 minus 25~, and "about" may mean plus or minus 50%. The term "of
the order of (magnitude of)" has the ususal meaning of within a
factor of ten either side of the number quoted.
Spark plug insulator 78/78at78b 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 OD 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
2~ section 72 with preferably 13/16-20 ~NEF 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 sec~ions 21/71 of FIG. 7 are
30 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 gO. 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
35 hollow extension of conductor 71c. Connected to the upper end of
cylinder 84 is spark plug wire 87 with preferably EMI suppressing
.~. ., :
,
.
~L3~179~
-42-
inductiYe 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 Erequency end of the spectrum where EMI is a problem, i.e.
above 30 Mllz. Wire 87 is connected to end 84 preferably by means
of a crimp (representing a unitary section whose distrib~tor end
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).
In the preferred embodiment, the outsicle 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 oE 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 Mnlz 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.
13~ 79~
-43-
The equivalent circuit of FIG. 8 is shown in FIG. 8a, where
like numerals again denote like parts. Central to the schematic
of FIG. 8a is wire 71c one end of which is connected to plug tip
21a separated by gap 30 from shell 23a. Wire 71c is connected
through capacitance 79 to ground and through inductor 87a to
terminal 77 to a source of h:igh voltage (secondary of an ignition
coil), across which the coil output capaci~ance 9 is connected.
Capacitance 79 is formed in the embodiment of FIG.8 by plug shell
73 and meta1lic tube 86 which form the outer plate of a coaxia]
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. 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 impedence to the parallel path for discharging capacitor 79.
Preferably, 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 perspective3 frequency
tuned circuit with the output capacitance 9 (which typically will
have a cpacitance in the range of 20 to 100 pfd). Thus capacitor
9 will discharge its energy in the low (non-EMI producing) 1 to 5
MHz frequency range providing to the spark in gap 30 peak current
of the order of 10 amps lasting for several usecs, and thus provi-
ding useful igniting energy to the initial spark without unduly
raising the spark channel temperature (as previously discussed
with reference to the spark recombination coefficient alpha).
Finally, it may be further advantageous from the EMI and the
recombination coefficient (alpha) perspectives to "tune down" the
discharge of the capacitive energy stored in the plug boot, which
can be advantageously done by replacing large diameter central
plug conductor 71c with a coil (shown in FIG. 10) of, say, induc-
tance of 4 uHenry, which with a 100 pfd capacitance boot, will
produce relatively lower frequency oscillations of approximately
10 M~lz with peak currents in the range of 20 to 100 amps.
. /.; I
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-44-
EIG. 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 9 and more particularly that of FIG. 2d, shown in
EIG. 9a below. Shown are ignlt:Lon sparks o~ p~rlo(l o~ about 100
usecs, and a time between pulses oE (the ~linimum of) approximately
150 usec. ~he shapes 92, 93. 94, 95 are thc spnrk den~lty dlstri-
butions on a logarithmic scale, and the shapes 96, 97, 98, 99,
and 100 represcnt the corrcspondillg flame plasmn density dLstri-
butlons for a very lean flame (phi = 0.6) of an exLsting gasolinefuel with a good 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. On the third pulse, 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, lOO, 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 Eive partial cross-sectional views of the
9park plug tip of FIG. 2d (a8 an ex~mp1e 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 ig~ition pulses
delivering energy to the plug tip. The drawings represent the
same plug tip vlewed at 250 usecs intervals with like numerals
denoting like parts wlth respect to ~IG. 2d. Shown are the center
conductor 21, a preferred button 21a, tip insulator 28, spark
plug shell 23 (somewhat recessed from the surface 22a oE 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).
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-45-
Moving leEt to right, 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-
S tially p~rallel 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. 9ae showin~ a further diminished spark 95a
~0 (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
lOOa, moving away and growing in si~e, with its upper part IOOaa
moving outside the influence of the E-field and its lower portion
100bb growing sideways; that is, following the fourth pulsing
(after 750 usecs), 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.
2a 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.
The flame plasma begins to dominate at position 98b over the spark
at position 94b, and even more so at position 99b tover the spark
at position 95b). Thereafter the spark at the original spark plug
site (92a of FIG. 9a) disappears altogether and the flame plasma
at position lOOb intensifies with a strong E-field parallel to it
and forms new fronts along the plug periphery as discussed above.
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~3~79~
-46-
FIG. 10 depicts a preferred circuit of the CDCC type compri-
sing a high efficiency (preferab]y 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 terrninal 101 of power supply and
controller 103 (connected to battery 8 to be powered thereby)
which also regulates the output vo:Ltage 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.
Connected across primary winding 1 is active snubbing network
formed of series-connected ca~acitor 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 sufficlent capacitancc i9 built into the spnrk plug.
~'' .
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-47-
In operation (say of the PFDI system), a trigger pulse is
received at terminal 101 and the subse~uent 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 practica1, e.g. 1/64" and 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 lO9a. Preferably
the capacitor 4 is charged to a voltage Vp of 350 volts and has a
value oE 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 talces on a value from
zero (no inductance) up to approximately the value of Lpe.
Thus, upon breakdown, primary and secondary spark currents
oscillate with an 80 usec period, with the spark current having
an initial maximum current of two to three amps for an assumed
turns ratio N of transformer 3 between 45 and 50. At the end of
the oscillation period (assuming SCR 5 has recovered and is not
retriggered), capacitor 4a delivers its energy to the spark as a
continuously ringing, decaying oscillation with a period of 15 to
usecs and a peak current of 1/10 to 1/5 of the main 80usec
oscillation peak, or typically 200-300 ma of initial peak current,
thus producing strong (ECDI) E-field enhancement effects. 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 tfor 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.
Preferably 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
- ,-
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:
-48- ~3~i79~
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 msecs, and
the pulse train width varies from 3 ~secs 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. Alternatively~ the time between
pulses may be increa~sed in some proportion to the pulse width.
The advantage of the 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.
The total CD system efficiency EFF can be assessed as follows:
EFF = Parc/[Parc ~ Pscr + Pcoil ~ Protor]
where:
Parc = power delivered to the spark (plug end lO9a);
Pscr = power dissipated in SCR 5 (and diode 6);
Pcoil = power dissipated in transformer 3;
Protor = power dissipated in the rotor gap in the distributor.
Neglecting Pcoil, which can be held to 10% of Parc, the above
reduces to:
EFF = Varc/[Varc + Yrotor ~ NVscr]
where:
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;
N = coil turns ratio.
For the typical preferred PFDI system:
EFF = 240/[240 -~ 40 + 1.6*50] = 240/360,
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).
'''` ~'1
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13~79~
-49-
Especially noteworthy is the advantage of the lower than
standard turns ratio N (fifty versus one hundred), and the much
larger voltage Varc versus Vrotor brought about by the large gap
(which increases Varc), and the largely normal E-field component
(En) to the spark, which further increases Varc over Vrotor and
N*Vscr in the early stages of the current formation.
For the typical preferred ECDI system:
EFF = 800/[800 + 350 + 1.0*50] = 800/1200
EFF = 67%,
which is about five times higher than the efEiciency of standard
ignitions, delivering also about five times the power, although
employing the same input power level. In both the above cases
Pcoil is small, whereas in prior art ignition systems Pcoil is
generally the principal contributor to the system inefficiency.
While the discussion of the PFDI system has concentrated on
gasoline engine applications, 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
2d entrained air) one order of magnitude greater than the fluid/flame
velocities associated with gasoline engines. Hence, in such
applications one needs to reduce the time between pulses to about
T (50 usecs) and orient the plug tip so that it is in the appro-
priate part of the spray, and optionally use asymmetrically lobed
plugs to appropriately direct the spark relative to the spray.
Additionally, it should be recognized that while the main
application for the PFDI embodiment of the present invention is
in the lean burn engine area, the principle on which PFDI is
based is of a much broader scope. 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. In PFDI, 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).
. .
. . .
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~ 3117~5
-50-
The present P~DI invention provides a sma:Ll gap defined by two
opposed electrodes, one of which is partially ins~llated; across
the gap between the electrodes the full voltage is applied c~eat-
ing a very high ~-field region causing an initial ionizing plasma.
The plasma forms into a spark chahnel 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 tra:in
of pulses making up one ignition firing). On the other hand, the
flame that is launched moves such that for some well defined
early intermediate period of time Tign, the electrical coupling
to the flame is strong. FIG. 2d depicts an optimum way to accom-
plish this. Moreover, with such a design where 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 evenwithout 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. Thereafter,
as the flame moves around the rim, the subsequent ignition pulses
dischar~e across the flame front to ignite the entire toroidal gap.
Further, the invention is not limited to fixed electrodesO
For example, within the time Tign and in conjunction with the
pulse train period, a movable element (e.g. a piston of a conven
tional engine, or a rotor o~ a Wankel engine) can be designed to
move so that coupling to the spark (or spark remnant) is reduced
and coupling to the Elame 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.
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_5l_ 13~17~
It is emphasized that since concepts disclosed herein rela-
ting to P~DI (and ECDI and E~r fuel) differ in part substantial]y
from prior art concepts, and introduce substantially different
perspectives on ignition ~e.g. that delivering large amounts of
energy to the spark channel is wasteful), there then necessarily
follows a whole new range of trade-ofEs which should be made in
optimizing the system. The broad concepts or principles on which
PFDI is based have been presented (and supported by one or more
particular preferred embodirnents), and these support (within the
framework of their disclosure) a range of important trade-offs.
Specifically: 1) In disclosing the dual nature of flow velocity
in both helping the flame move as well as inhibiting its motion
in igniting the entire ~oroidal volume within the ignition period,
it is seen that an intermedite flow velocity (e.g. one having a
low swirl number) is desirable, especially when other factors are
considered. 2) In building capacitance in the secondary circuit,
from among the capacitance of the ignition coil, boot, and plug,
a preferred design is to provide about 20% capacitance in the
~ plug, 40% in the boot~ and 40% in the coil, for approximately 200
2~ pfd total capacitance in order t~ moderate the temperature of the
capacitive spark. 3) In terms of improving the focussing effect
of the electric field for the discharging of the field energy
across the propagating flame front upon repetitive firing of the
ignition system of the PFDI system, the structure and position of
the plug shell end relative to the mounting cylinder surface i.e.
recessed ~rom it, is important in achieving the best PFDI effect.
4) In operating the CDCC ignition system for the PFDI case, given
the preferred 2T to 5T (150 to 250 usec) time between pulses and
the desire to have, say, eight pulses at low RPM, it is not prac-
tical to recharge the CD capacitor between Eirings, so maximizingCDCC system efficiency becomes important to be able to sustain
such eight pulses on one dischargej leading to an ignition coil
design with approximately 24 primary turns (for 350 volts) tighly
wound (coupled) on an approximately 1.2 inch square cross-section
ferrite core with a turns ratio of 45 and a capacitor of approxi-
mately 8 ufd~ ~or highest efficiency and somewhat reduced current
. i
:;
., .
~3~79~
-52-
5) With regard to the ECDI system disclosed, the principle of
operation can be used with moderate e~fectiveness 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 have a somewhat larger diameter of
0.12" to minimize erosion, while maintaining a side clearance of
approximately 0.1" between the parallel sections defined by the
center and ground electrodes by increasing the shell ID to approx-
imately 3~8" for a 14 mm plug; upon firing the ECDCC ignition,
the spark will form axially at the tip, and the flame will then
move in part up along and between the parallel wires wi~h its
front perpendicular to the axis (defined by the center conductor
direction), supported by ~he electric (ECDI) field between the
~,1" gap, and further assisted by the piston induced flow (which
in this case is in the direction of motion of the flame along the
wires for the plug mounted axially with the piston motion, i.e.
Cl is one); in this way by using the principles disclased 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. 6) Finally,
it should be noted that the trend in the automotive industry has
been towards smaller diameter spark plugs with 14 mm thread and
5/8" hex bodies (and even 12 mm plugs); in most cases there is
not a very important reason for this; hence, it would be advanta-
geous, in terms of providing a larger periphery of the plug shell
end, and hence a larger toroidal gap to be ignited twith either
_ ; the ECDI or PDI systems), to use spark plugs with larger diameter,
~'~
.
131~L795
-53-
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 ed8e 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.
In the disclosure that follows there is revealed a further
improvement of the spark plug firing end configuration to produce
improved coupling to the initial flame front, as well as improved
design of the overall ignition system to improve PDI, ECDI, and
EMT fuel effects as they pertain to achieving optimized ignition.
The present disclosure is based in part on the recognition that
the electric field focussing effects discussed earlier can be
significantly improved by contouring not just the spark plug end
button as previously disclosed but by also contouring the insula-
tor nose in conjunction with the end of the spark plug shell and
cylinder head. This can be done to obtain a cylindrical electric
field focussing "lens" with a focus point, or rather focus circle
(since the "lens" herein is a cylindrical lens resembling a hyper-
boloid of one sheet), such that the electric energy can be further
guided for reducing breakdown and improving coupling to t~e mo~ing
initial flame front. An further benefit of such contouring of
the insulator end is that it also leads to a minimum size of the
end electrode or button for minimum physical perturbation of the
combustion chamber and minimum absorption of combustion energy by
it. Also such focussing permits the spark firing of a very large
gap without the need for the small spark initiating partially
insulated auxiliary gap already disclosed. Figures 11 to llff
reveal embodiments of the electric field focussing lens plug end,
or "EFFL" plug, as it will be sometimes referred to hereinafter.
Referring to FIG. 11 in which like numerals denote like parts
(with respect to FIG. 2, 2d, and 7) there is shown a longitudinal
~7 cross-sectional partial view of an electric field focussing lens
d~
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.
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(EFFL) plug end defining a toroidal gap 30 between the center high
voltage portion and the ground shell end portion 23d and cylinder
head 22. 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 ll9b/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 50degrees 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 Eield line or ray 110
normal to its surface ("normal ray 110"), the surface 28b of the
end insulator section 28 w;th 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
2d form a "ground focus" F' somewhat shifted in position from point
116 (lens focus F) to the edge ground conductor surface point 116a.
This occurs because rays 110, 111, 112 are bent (distorted) by
the presence of the electrical conductor surfaces 22/23d to form
new rays llOa, llla, and 112a respectively, terminating at point
2g 116a, the ground focus F'. Clearly, the closer ~' is to F, the
more intense is the normal electric field at the point F'.
There has thus been constructed an essentially electrostatic
lens 113 which focusses the electric field to a region 116/116a
where later spark pulses such as 25 o a multiple spark pulsing
ignition ~rain 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 propagatin~ 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.
... .
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-55- ~3~17~
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 ll9a 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 118/117/2~ 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 dimensions shown for
the various diameters are representative of a t4mm plug, provi-
ding a tip insulator 28 thickness of about 0.05" and an insulator
thickness at the base 118 of 0.09" to 0.12", enabling portion 118
to withstand the full secondary voltage without voltage puncture.
The diameter of the center wire 21 is somewhat larger than
2d previously disclosed to conform to the somewhat larger diameter
D2 of the insulator end. This is because it has been found that
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
2g 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. There is advantage to having a larger insulator diame-
ter D2 of 0.22" to 0.26" as shown to bring surface 29a and edge29b closer to the edge ll9b/119c so that the spark pulses (which
may follow the initial spark pulse 2~) occurring in the preferred
multiple pulsing ignition can more easily reach the surfaces
ll9b/119c. Thus, there is shown wire and insulator diameters Dl,
D2 somewhat larger than disclosed earlier~ and a button diameter
only 10% to 20% larger than D2 to conform to the end diamater D2.
Clearly, it is further advantageous to be using the somewhat
larger center conductor diameter (Dl) wire, in the range of 0.10"
and 0.12t', to improve its electrical and thermal conductivities.
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The other dimensions D3, D4, D5 are given so as to provide a
gap wiclth 30a and junction volume 76 consistent w;th what was
disc]osed 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 e~ual to 0.2". Typically, the ratio of 1.22/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. lla is a longitudinal cross-sectional partial view of
an EFFL spa}k plug end based on an 18 mm p]ug, with like numerals
denoting like parts with respect to FIG. ll, and with ~he 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. Moreover,
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 ùsing 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, lllb, 112b to the extremity of ~he shell edge
(point 116b) or just beyond point 116b. In such a design there iS9
in effect, provided a preference for the spark to follow the flame
moving along the periphery of the shell end, as is also disclosed
with reference to FIG,11c, which may be especially useful for the
ECDI case. In such a design, the diameter D2' of base ed~e 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.
.. . . ~,
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In the 18 mm plug case of FIG. lla it is also particularly
simple to form the seat 120 of the insulator to the shell 23 near
the shell end for better cooling of the plug nose 28. Also, 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. Finally, the tip t15 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. lla is approximately five times full scale.
FIG. 11b 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 sur~ace 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
was to form on a path along surfaces 28c, 28b, 28a, and then
across gap 30a, versus along the depicted path 24. In this design,
lens 113 is also a somewhat more symmetric lens with rays 110a,
111a, 112a, and 112b focussing to the ground focus F' (point 116a).
FIG.11c 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, lllc, 112c directly onto the
edge of the shell to produce an ideal ground focus F" (point 116b)
as also achieved in the larger I8 mm plug embodiment of FIG. 11a.
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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 23E behaves as an arc runner should the initial
spark form at the inside location indicated by curve 24.
This plug design is also approximately six times full scale,
with dimensions Dl through D5 referenced to FIG. 1 given approxi-
mately in this case by Dl = .11", D2 = .23", D3 = .33", D4 = .39",
and D5 = .42". 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 eclge of the shell. Note that as previously
discussed, 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 ioni~ation 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
2d the insulator nose 118ill7/28.
In this plug end design there is shared a feature already
disclosed with reference to FIG. lla, namely the formation of the
seat 120 near the plug end and the increase of the center conduc-
tor diameter 21 from about 0.11" tD about 0.16" (conductor 71d),
along with an increase, in this case, of the shell interior dia-
meter from about 0.33" to about 0.39" along insulator section 78
to provide a moderately high capacitance per unit length while
providing a thickness of insulator 78 of at least 0.11" to prevent
insulator puncture.
FIG. lld is a longitudinal cross-sectional partial view of a
more optimi2ed 14 mm EFFL plug based on the designs of the plug
ends of FIGS. ll, lla, and llc, with like numerals denoting like
parts with respect to FIGS. 11, lla, and llc. The dimensions Dl
through D5 are essentially similar to those listed with reference
to FIG. IIc, as are dimensions L4 and L22, while lengths L2 and
L21 are somewhat longer, abou~ 0.18" and about 0.12" respectively,
to form a focus F (I16) somewhat beyond the shell edge 23gg, and
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.
131~79~ ~
-59-
to produce a somewhat more extensive spark length (which can be
increased by proportionally increasing the length L2 by up to 50%).
In this design, several of the special features disclosed
with reference to FIGS. 11, 11a, and 11c are incorporated herein,
with some of the more pertinent enumerated as follows:
1) formation of a sharp angle of section 117 (about 40 degrees
to the vertical) which both helps push the focus point F further
out for improved coupling to the outwardly moving flame front, as
well as increasing the surface path length 24a (and 24aa) relative
to path length 24 to encourage form3tion of initial sparks along
path 24 (or 25b) which is away from the insulator surface 28a/28b;
2) shaping of the shell end 23g to form a gap 30b between the
inside shell corner 119b and the insulator edge 118a, where the
shell edge point ll9b of the gap 30b is displaced slightly down-
wards (0.01" to 0.03") from edge 118a to further help keep the
initial spark pulse away from the plug nose insulator surface;
3) contouring of the inside surface ll9d of the shell end sec-
tion 23g to form a slope of 6 to 36 degrees to the vertical andan inclusive angle thetal of 36 to 90 degrees with slope line 28a
to improve the focussing of ray llOa onto shell edge 23gg and to
create an arc runner surface 119d which encourages spark pulses
to move sequentially from the path 24 to paths 25a, 25b, 25c, and
other paths further out and around the periphery of the shell edge
23gg and cylinder head edge 116c, designated as a second ground
focus Fl'l (116c) (in addition to the ground focus F" (116a));
4) recessing the shell edge 23gg slightly, e.g. 1/32", from the
cylinder head so as to provide in effect three foci F", Fl", F,
each one further away yet and each one more intense than the other
to encourage spark pulses of a multiple pulsing ignition to move
out and along with the flame front to continually couple spark
energy to the moving flame front; and
5) minimizing the thickness of the insulator layers 78 and 78a
by increasing the diameter of center wire 21 from approximately
0.11" to about 0.18" (diameter D1') to provide maximum capacitance
without puncture of the insulator, and also minimizing the resis-
tance and inductance of center wire 71d, which is preferably made
of copper.
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13~95
-60
These and other features make the plug end especially useful
for the PDI case where large high current sparks are formed which
follow the flame front as it moves out and around the periphery.
It is also to be noted that the indented point 119b may be absent
(diameter D4 = 0.40 for D5 = 0.40) in which case the corner point
ll9b is preferably directly across insulator edge 118a, forming a
minimum horizontal gap, as shown in FIGS. llf and 12.
FIG. 11e 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. lld), with like numerals denoting like parts with
respect to ~IG. lld, the main difference being the dimensioning
and contouring of the inside surface ll9e of the shell end 23h so
that it in effect becomes a ground focussing tens to reinforce
the plug nose lens 28a/28bt29a 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 ll9d.
With an 18 mm plug one already has the necessary thickness of
shell end 23h so that the center conduc~or wire and insulator can
be maintained at a larger diameter. The ground lens ll9e can be
viewed as a refinement of the runner surface ll9d of FIG. lld and
FIG. lla ~the 18 mm plug).
2g For ease of visualization and as a way of defining the ground
lens ll9e, 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 ll9e, recognizing that the plug nose
clear1y distorts the rays 112c. In its simplest form, ground lens
ll9e is similar to that of FIG. lld, 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.
ln the left half of the drawing are shown the actual electric
field lines llOd formed from the plug nose, exhibiting a tendency
of the field to concentrate at the edge point 23hh of the shell
. . , ~ .
~3~79~
-61-
end 23h, namely focus F" point 116a. There is thus a preference
for the spark to form along curve 25 rather than 24, except under
a limited number of conditions, including at higher pressures and
when there is a significant fluid ~elocity normal to the cylinder
head surface 22a. In this way, by selectively dimensioning and
contouring both the plug nose and plug shell end, one can achieve
an optimum degree of foc~ssing of the electric field.
FIG. 11f is a longitudinal cross-sectional partial view of
a more optimi~ed 14 mm EFFI, plug based~ more particularly, on the
designs of the plug ends of FIG. lld and FIG. lle~ with like nume-
rals denoting like parts with respect to FIG. l1d and FIG. 11e.
In this case, 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 ~round lens ll9f already disclosed
15with reference to FIG. 11e, 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).
In this embodiment ~he 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.
- The fragmentary partial view FIG. 11ff, 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. In this embo-
diment, ~olume 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.
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-62-
The main advantage of this design over othe-r similar desigrls
is the formation of the Eoci 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 Eront propagating from the spark pulses 25formed along the toroidal volume contained between the two foci.
In principle, one can ignite the entire enormous volume contained
between the plug nose and plug shell 23i during the time in which
the preferably multiple pu~sing ignition is ON by using the longer
duration ECDI system or a variant of it.
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. In this figure, as before,
like numerals denote like parts with respect to FIGS. 8 and 11.
The main feature of this embodiment versus that of FIG. 8 is
the use of an internally flexible boot 90 made possibie by using a
flexible, lower dielectric constant material 85, such as a lightly
2~ (30%) loaded silicone rubber, with relative dielectric constan~ 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 recog~ition that having a large capacitive initial spark is
not desirable as it intensifies the initial spark plasma remnant.
29 Rather, 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). In this
way, one can use a lower dielectric cons~ant material 85 which is
flexible, and contained in a casing 86 which may also b~ 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 s~retch out and over the upper insulator 78b
of the plug.
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.
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-63-
In other respects plug boot 90 is similar to that of FIG. 8,
except that in this embodiment it is designed to fit a 5/~ 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.
Another simplifying feature of this design is the use of a spark
plug wire crimping element 8~a of typical length 1" to 2" which
also acts as the inner conductor of the capacitor defined by
layers 84a/85/86. Also noteworthy is 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 sèctions 23/73. Optional shield
86c can be used to add capacitance and further suppress EMI.
In a preferred embodiment, 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. Also, as previously disclosed and shown herein, 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 optimi~ed
CEI Ignition suitable for use in a multi-cylinder internal combus-
tion engine. The ignition is based on that of FIG.10 and operatesas 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).
As already stated, the ignition system depicted in FI~. 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.
It has several distinguishing features (improvements) over the
system depicted in FIG.10, in ~he areas of improved efficiency,
improved EMI, improved operation, and improved effectiveness in
igniting lean mixtures.
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-64-
The CEI ignition preferably uses the more optimized plug and
boot 109 disclosed in ~IG. 12, and as already disclosed provides
multiple spark pulses per ignition firing approxlmately every 250
to 400 usecs with a typical spark Eiring 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 .Eor a low Eorward drop standard
recovery SCR. In the more optimized 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 durationt 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. By connecting
diode 138, resistor I38a (order of magnitude 5 Kohms resistance),
capacitor 138c (of about 0.2 uFarads) in series between point P
and ground as shown, and then connecting point Pl (intersection
of resistor 138a and capacitor 138c) to the gate 5a of SCR 5 as
shown through resistor 138b tof order of lO0 ohms), one impresses
29 an average negative voltage of about minus one volt to the gate
5a (for a 4~0 volt capacitive discharge (~DCC) system) and reduces
(improves) the SCR recovery time. 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.
Preferably the SCR used in conjunction with the fast turn~off
circuit has a low forward drop of l volt a~ 120 amps peak current
of coil primary winding l, 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 requirin~
reverse hold-off voltage, etc~.
l3~79~
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).
Preferably in both cases, the voltage recharge circuit 4c/4e/4f
is used. In this way, less energy is delivered per ~0 - 100 usec
spark pulse, while the same total energy is deliverable by using
the recharge circuit comprised of capacitor 4c, choke inductor 4e,
and diode 4f (with resistor 4d eliminated) to deliver more spark
pulses with higher energy in the follow-on spark pulses relative
to the initial spark pulse. This strategy is consistent with the
perspective o~ not delivering much higher (low frequency 10 KH~)
spark energy in the initial pulse versus the follow-on pulses.
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.
; ~ With regard to maintainin8 the voltage doubling feature, an
equation has been developed (based on the disclosure in patent
No. 4,677,960) which specifies the coil turns ratio N in terms of
input voltage Vp, the maximum desired secondary output voltage Vs,
the value Cp of the discharge capacitor 4, and the value Cs of the
~; ~ secondary output capacitor 9 (FIG. 10). It is given by:
N = [(Vp/Vs)*(Cp/Cs)]*[l + ~[1 - (Cs/Cp)*(Vs/Vp)**2]]
and simplifies to:
N = [Vs/(2*Vp)]*~1 ~ (1/4)*(Cs/Cp)*(Vs/Yp)**2]
for the case ~here (Cs/Cp)*(Vs/Vp)**2 is much less than one, the
i ~ condition one works to ~chieve in the CDCC system.
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It is seen that reducing the coil output capacitance Cs, by
lowering the capacitance of the plug and boot (disclosed herein
as an improvement), helps also in reducing the coil turns ratio N
and thus increasing ignition system efficiency. It also permits
a lower value of discharge capacit:or Cp as disclosed above in one
form of the more efficient, more suitable recharge circuit confi-
guration of the ignition where Cp was specified as 5 uFarads (uF)o
By way of example, we take Cp = 5 uF, Cs = 160 pF~ Vp = 350
volts (assuming a 400 volt capaci~:or), Vs - 33 Kvolts, to obtain:
N = [33,000/700]*[1 ~ 0.07] 50
which is a desirably low turns ratio.
With regard to the design of the optimized coil for the PDI
system (of the CEI Ignition), there is preferably used 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).
Such a design (for the case where the primary 1 and secondary 2
windings are wound over the same section of the core 3a) will
give a coil leakage inductance of 20 to 30 uHenries (uH) to
provide the preferred discharge period of 80 to 100 usecs for a 6
to lO uF discharge capacitor 4. For a lower value of discharge
capacitor of, say, 5 uF, one can increase the coil leakage induc-
tance in order to maintain the preferred 80 to 100 usec discharge
period. This is achieved by reducing the length to width ratio
of the core window (from 3:1 to, say, 2.5:1), or by using a lower
inductance (permeability) core, and/or by increasing the number
of turns of the coil windings 1 and 2. A smaller core area can be
incorporated by using materials of higher saturation flux density
of, say, 6 to 12 KiloGauss, such as nickel iron, should the cores
be cost competitive and efficient. Recent improvements in the
technology of low cost iron powder cores (improving efficiency)
may make them ideal candidates for the present application which
preferably uses low to moderate inductance material cores.
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-67-
For the ECDI system, or a variant of it with characteristics
between ECDI and PDI, including say, 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). In such a system, while 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 si~e secondary wind-
ing because of the similar turns of smaller si~e secondary wire.
Since less energy is s~ored in the discharge circuit (250 mjoules)one would need the recharge circuit if more energy is called for.
In applications where size and cost are important, one can
design 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.
To further improve ignition system operation, especially for
ignitions for engines which run at high RPM, one can use two SCRs,
where one is fired on the first pulse and ~he other fired for the
remaining pulses of an ignition pulse train.
If the r~ch~rg~ c:Lrcult i9 not usc(l, c~pncitor 4c m~y ~till
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).
Such a capacitor will also work with capacitor 4a to deliver high
fre~uency, lower peak (ECDI) current spark energy to the spark
discharge following the SCR shut-off, as disclosed wi~h reference
~i ~, to FIGS. 2b. 2c, and 10.
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-68-
Another maln feature of the more opt:imized 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 for5 providing electrical shielding wh:ile not absorbing useful elec-
trical energy. This helps to both minimize EMI and optimize theelectrical capacitive discharge ignition efficiency by minimizlng
the length of primary wire 1. Further improvement in EMI (and
other forms of interference, including conductive interference),
is achieved by placing a Faraclay 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.
Another preferred embodiment of the CEI Ignition in terms of
obtaining the value of (boot) capacitance 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 Esb
(0.1 to 1 ull), very low resistance, and the required capacitance
to produce an intense but relatively low energy capacitive spark
upon initial breakdown (spark formation). For the typical values
of Csb of 60 pf and an assumed value 0.6 uH for Lsb, the source
impedance Zsb is given by:
Zsb = ~ Lsb/Csb = 100 ohms.
But the EFFL plugs disclosed in FIGS. 11 to llff typically have a
breakdown voltage Vb of 8 to 12 Kilovolts at atmospheric pressure
(for the typical 0.12" to 0.20" focussing spark gap), leading to
an initial yeak capacitive current Isb (assuming Vb - 10 KV) oE:
Isb = Vb/Zsb - 100 amps
at atmospheric pressures, which is in the range of values for the
breakdown capacitive spark for the application of this invention.
The spark plug wire can be designed to provide a ran8e of values
of capacitance and inductance (per unit length) by adjusting the
center conductor diameter and dielectric constant and thickness
of the insulator. In this way the desired level of peak current
and capacitive energy can be obtained for best ignition. In such
an embodiment, the King lead 108a preferably would be of highly
; inductive absorptive wire with very low capacitance to ground.
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-69-
The concept of source impedance is useful in ~isclosing and
defining the pararneters of the CDCC ignition to be used with the
EFFL plug which make up in part the CEI Ignition. The source impe-
dances Zp, Zs of the primary and secondary circuits respectively
for current flow during the sparking period can be shown to equal:
Zp = 1/~2*pi*f*Cp)
Zs = N*Zp
with ~he equivalent resistance, Karc, of the spark gap given in
terms of the arc burning voltage Varc and arc current Iarc as:
Rarc = Varc/Iarc
For the disclosed PDI version of the preferred embodi~ent of the
CEI Ignition, f is taken to equal approximately 10 K~lz, Cp to
equal about 8 uF, and N to equal approximately 50, giving:
Zp = 2 ohms
Zs = 100 ohms
leading to a 2 amp value of arc (secondary circuit) current Iarc
for the average primary circuit voltage Vp of 200 volts (where Vp
ranges from 350 down to 100 volts during igni~ion firing):
Iarc = Vp/Zs = 200/100 = 2 amps
But the typical EFFL plug with the 0.1" - 0.2" gap as used in the
PDI system disclosed herein has an arc voltage Varc-of about 200
volts at 2 amps current, leading to an arc resistance Rarc of:
Rarc = Varc/Iarc = 200/2 = 100 ohms
implying perfect matching betweed the CDCC power supply and EEF~
spark plug. Hence, one achieves optimization of energy transfer
while providing the other benefits disclosed herein, especially
and most importantly, direct electrical discharging across the
flame fron~ to produce flame discharge ignition.
For the ECDI system the equivalent arc resistance is at least
an order of magnitude higher while Zs is not e~uivalently 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.
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-70-
It should be recognized that a practical consideration accom-
panying and aiding the development of the CEI Ignit:ion, particu-
larly the more optimal arrangement of parts in the enclosure 130,
is a totally new type of DC-DC converter, called a ~urrent Pump
(disclosed in U.S. patent application S.N. 885,912 and correspon-
ding foreign applications), which has rnany new positive features
including insensitivity to where the load is placed to thus permit
the arrange~ent of parts shown within enclosure 130. Moreover,
the development of the current pump and several other inventions
including the CDCC ignition system of U.S. patent 4,677,960, the
predecessor EM Ignition, and the present invention (which works
to optimally couple electrical energy to the air-fuel mixture and
to the propagating initial flame front) have lead to the optimized
CEI Ignition disclosed herein.
The summarize, the CEI Ignition i5 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. At its basic level, 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. They involve using, in a synergistic way, the develop-
ments disclosed in the present invention, together with earlier
inventions tCDCC, Current Pump, and EM Ignition) to provide ma~or
improvements in lean burn capability (of ~our to five air-fuel
ratios), which have been corroborated by preclse testing both on
current design engines and on next generation engines still under
development.
Finally, with regard to the toroidal gap, and more specifi-
cally with regard to the more general "coaxial gap", it should be
noted that the term "coaxial gap'~ as used herein is intended to
refer to the volume of space between two coaxial electrodes and
should not be construed to include any specific radial or axial
limitation unless expressly stated.
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-71-
Therefore, it is particularly emphasiz,ed with regard to the
present invention, that since certain changes may be made in the
above apparatus and method without departing from the scope oE
the invention herein involved, it is intended that all matter
contained in the above description, or shown in the accompanying
drawings, shall be interpreted in an illustrative and not in a
limiting sense.
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