Note: Descriptions are shown in the official language in which they were submitted.
1 This application is a divisional of application
serial number 273,061 filed March 3, 1977 and relates to spark
plugs employing both corona discharge and arc discharge and to
systems employing the same~
The problem of atomspheric pollutants by combustion
engines has long plagued the automobile indus-try; these pollutants,
o~ course, are mainly hydrocarbons and oxides of nitrogen (N0x).
It has been found, for present purposes, that both pollutants
can be reduced by providing an arc that is substantially longer
than available using spark plugs now in use.
Accordingly, it is an object of the present invention
to provide a spark plug which, in an operating system, can
provide an arc at least the order of 100 mils and longer.
Another object of the invention is to control the arc
o a spark plug in a way that allows some con-trol over the path
followed by the arc.
A further object is to provide a substantially long
arc ancl one that, once initiated, can be moved about to alter the
2~ length of the same to enhance combustion in a system by virtue
of the movement alone.
A still further object is to proviAe a spark plug
whexein the trajectory o~ the arc is aEfectecl by electromagnet;.a
interaation between electr:ic current in the arc and electric
current in the electrodes o~ the spark pluy.
A still ~u.rther object is to provide a spark plug
whose sparkiny surEaces are so positioned and so shaped tha-t
electric l.ines of foxce act, in part, to establish a desired path
~or the arc~
-- 1 --
1 A further object is to provide a spark plug wherein the
role of the lines of force is to couple to the ioniæed species
created during combustion, thereby to affect the nature of flame
propagation.
Another obj~ct is to provide a spark plug wherein
magnetic particulate is employed to enhance such electromagnetic
interaction.
Still another object is to provide a spark plug wherein
the electrodes and/or insulating parts employ low work function
materials to promote corona and arc discharge.
Still another object is to provide a spark plug that acts
to generate active chemical species in the corona discharge
and secondary charged species in the arc discharge to facilit~te
and enhance combustion.
These and still further objects are elaborated upon in
the description that follows.
The foregoing objects are achieved in a spark plug
having two main electrodes with a first sparking surface and a
second sparking surface, respectively, and an i.ntermediate or
floating electrode between the two and capacitively coupled to
one of the main electrodes, there being a first gap formed between
the first sparking surface and the sparking surace o~ the
float.ing electrode and a second gap between the sparking surEace
oE the ~loating electrode and the second sparking surEace. The
~eometx:Les oE the first ~parking surface and the seconcl ~parking
surface are chosen to prov:ide a spark gap that diE;eers at one
location between the surfaces Erom the gap at each other location
therebetween, that is, there is a variahle-length gap between
the sparkin~ surEaces oE the main el.ectrodes; said geometries
are further chosen to serve, together with interacting electric
1 curren-ts in one of the main electrodes and in the arc that
appears between sparking sux~aces of an operational spar~ plug, to
guide said arc and effect spatial movement thereo~. At one
region thereof, the two main electodes are separated from one
another by a distance much less than the shortest length of the
gap between the first sparking surface and the second sparkiny
surface, there being a high dielectric solid insulation there-
between at said region so that, in an ope:rating system, a corona
discharge occurs at said region to initiate arcing between said
sparking surfaces. The electrode configuration is further
selected so that the ionized species created by the combustion
process will be subjected to a high electric field for a ~ime
period following the initiation of combustion.
In one of its aspects, the present invention provides
an elongate spark plug that comprises, in combination, a
conductive body, a first electrode electrically isolated from the
spark plug body, said first electrode extending outward from
the body of the spark plug at one axial end of the plu~ and
extending as well to effect electrical connection to a terminal
at the other axial end of the spark plug, the first electrode
being surrounded by solid insulation from the terminal to an
exposed portion at said one end, a second eleckrod~ connected
to and e~tendiny rom the body o~ the spark pluy to a
xe~ion o~ the. ~irst electrode that is surrounded b~ the solid
insulat.ion, the second electrode b~incl separa-ted ~rom the
first electrode b~ a distance throuyh the solid insulation
that is much less than the gap that exists between the secorld
electrode and said exposed portion of the first electrode,
and at least one intermed.iate floating electrode within said
gap.
-- 3 --
1 The inven-tion is hereinafter described with reEerence
to the accompanying drawing in which:
Fig. 1 is a partial elevation view, partly cutaway,
showing a spark plug having main electrodes with tape~ed sparking
surfaces and a floating electrode with tapered sparking surfaces;
Fig. 2 is a highly diagrammatic representation showing
a part of the combustion system of an automobile and including
a schematic representation of a spark plug similar to the
1 spark plug of Fig. 1;
Fig. 3 shows a voltage curve of an electric potential
that may be applied to the spark plug of Fig. l;
Fig. 4 is a partial side view, partly cutaway, showing
a modi~ication of the spark plug of Fig. l;
Fig. 5 is a partial isometric view of a further modi-
fication;
Fig. 6 is a schematic electric circuit diagram of a
system khat includes a spark plug like that shown in Fig. 1 plus
a power supply to energize the spark plug and a contro:L voltage
means to manipulate the arc;
Fig. 7 is a schematic circuit diagram showing a further
circuit arrangement to energi~e the spark pluy herein disclosed;
Fig. 8 is a schqmatic o~ a spark plug with main
elec-trodes and a plurality of floating electrodes in a ~urther
cixcuit arrangement;
Fi~. 9 is a partial ~ide section view o~ a modi~ication
o~ the spaxk plug oE Fig. 1.
Be~ore going into a detai.led explanation of the
struc-~ure of the present spark plug, there follows first an
overall discussion. The purpose o~ the ignition device herein
disclosed is to create an arc discharge whose length is much
- 4 -
1 longer than ordinarily obtainable and whose length and
disposition can be electronically controlled. Experimental
results indicate that a corona discharge is a precursor to the
arc and that the corona may be used for several purposes.
First it may be used to charge fuel droplets that may be present,
for example, in fuel in~ection engines and to concentrate
the charged fuel droplets so as to affect the air-to-fuel ratio
to enhance the ignition and combustion process. Secondj the
corona will act to generate active radicals which promote the
combustion process. Third, the corona can establish a path
along which an arc discharge is guided or preferably established.
This favorable path can be substantially longer -than ordinarily
obtainable. For example, it was discovered that an arc 0.125
inches long was established repeatedly in a Chrysler 360 CID
engine using their standard ignition system with a complete
set of plugs based on a structure like that shown in Fig. 5.
The length of path of the arc was discovered to be only weakly
dependent on pressure after a certain threshold voltage is
at-tained. Tests have shown that a gap of 0.225 inches between
sparking surfaces with a floating electrode midway between
the two, as shown in Fig. l, can be ~ired in a 360 CID Chrysler
combustion engine, using standard equipment and in a wide range
o~ operating conditions. Furthe~nore, by proper clesign of the
electroc~e conf.i~uratlon and the electrodes, it i~ possible
to control the path and conse~uently the leng-th o~ the arc
discharge. As later explained, this control :is acquired in part
and in appropriate circ~s-tances, by virtue of the repulsion of
two oppositely directed electric currents and in part by
appropriately shap:ing the sparking sur~aces oE the plug. The
duration o~ the corona phase of the plug firing can be controlled
5 _
1 and may vary in time down to the sub-microsecond regime. The
spark pluy has a number of further advantages in an operating
system, as now explained.
The ignition process in a combustion engine depends
on the interplay of several factors. The plug forms part of the
elec-trical circuit of the ignition system. This circuit is
characterized by resistive, inductive and capacitive elements
which can be controlled to affect the magnitude and time
dependence o the voltage across the plug electrodes and the
current through them. In particular, ~oltage and current
rise times, duration and alternation in polarity are of
importance, as is the nature of the energy dissipation in each
plug firing. Another factor is the heat transfer properties of
the spark plug. By proper design, the electrodes can àct
to control the temperature of the initial ignited volume,
which is important because during the initial period com-
bustion tends to attain the highest temperature and to
produce a large part of the N0x pollutants. By properly
designing the electrodes 50 as to heat sink as large a volume
of the initial flame as possible, as is done in the present
plug, an N0x reduction can be achieved. Also, a very important
~actor in controlling ~lame pxopagation and the heat transfer
~rom the ~lame to the plug i5 the nature oE the electric
~ield to which the burning air-fuel m:ixture i.s .subjected
by the energizea spark plucJ. ~he time duration of the voltage
across ~le plug electrodes is from one to severcll hundred
microseconds. The flame Eront moves approximately 1-2 mm in
150 micxoseconds. During this time a considerable number of
charged species are created by the combustion process itself.
-- 6 --
1 They are then subjected to the electric Eield associated with
the energized plug and consequently a substantial force is
exerted upon the flame. The affected combustion volume in
the plug disclosed herein can be of the order of 200 mm3,
whereas the flame volume subjected to a high field in the
conventional plug is only several mm3, i.e., perhaps l/lOOth
that of the present plug. During the first few hundred micro-
seconds the voltage across the plug can oscillate in polarity
producing a correspondingly oscillating force on the propagating
flame. The force on the flame tends to drive it into the
plug electrodes where heat will be extracted. It is further
apparent that in the disclosed spark plug the arc discharge
combined with the electromagnetic forces acting upon the charged
species associated with the combustion process will act to
create turbulence in the burning fuel. A further factor in
the ignition process is the creation of secondary electrons
at the positive plug electrode, and, again, the large sparking
surfaces and the shape and orientation thereof serve to
maximize the desired effect. In the description that now follows,
an attempt is made to apply the same or similar labels to
~tem elements that per~orm the same or similar functions.
With reE~rence now to FicJ 2, a combustion s~stem is
shown ~t lOl comprislnc3 a spark plug lO and high voltacJe supply
means 16 interconnected and the cylinder, labeled 21, and the
piston, labeled 22, of a cornbustion encJlne~ A~ shown in Fig. l,
khe sparlc pluc~ la has a base or body ~ which, as in conventional
plug, is the t~readed metal structure that threads into the
engine block of an~ automobi.le. A hicJh voltacJe axial or central
3~
electrode l extends from an input terminal 11 at a Eirst end
1 of the plug 10 through the plug body ~ and outward to a second
end of the plug axially separated from the first end. The
central elec-trode 1 is surrounded hy an insulator 9 which
isolates the electrode 1 from the conductive plug body 4. The ~-
part labeled lB of the electrode 1 that extends outward from
the base 4 is surrounded by an insulating jacket 3 that is merely
an extension of the insulator 9, and the exposed end of the
electrode 1 at said second end is en electrically conductive cap
lA shaped in the ~orm of the frustum of a cone. ~ ground
electrode 2, attached to the body 4 and also in the shape of
the frustum of a cone, extends inward from the base 4 to the
vicinity of the electrode l; sparking surfaces o~ the electrodes
1 and 2 are labeled lAl and 2Al, respectively. Experimental
results indicate that the electrodes 1 and 2 act in combination
with the high voltage means to create, first, a corona discharge
and, then, an arc dischar~e through the corona, as now discussed
with reference to Fig. 5. ~ -
The electrode l in Fig. 5 is a high voltage elongate
. .
axial electrode which, as above noted, extends outward ~rom
the base or body 4 of the spark plug designated 10~. The
outwardly extending part of the electrode 1 is covered by the
thin ti~e,, ~ 1 mm) insulating jacket 3 except for the exposed
porkion 1~ at its ~ree end, ~Strictl~ speaking, the exposed
portion lA ~hould ~e called the "electrode", ~ut throughout this
sp~ai~.iaation the high voltage electrode includes the electrical
conductor between the ~nput terminal 11 at the first end of the
plug to and including the exposed portion 1~ at the second ~nd
thereo~.) The electrode 2 ~which i9 a ground electrode in the
embodiment shown and or the purposes of this discussion is
,
~ . .
:' ;
,- ` ~ .
1 assumed to be negative with respect to the elec-trode 1) is
disposed adjacen-t the high voltage electrode 1 at a region 5
displaced from the exposed portion lA by a substantial gap (see
the gap numbered G in Fig. 5~ and is separated therefrom at
the reyion 5 by the insulating ~acket 3 so that the distance from
the ground electrode to the axial electrode through the jacket
at the region 5 is much less than the distance from the ground
electrode across the gap 6 to the exposed portion lA ~i.e.,
the distance between the sparking surfaces lAl and 2Al). Hence,
in an operating system, corona discharge ~which can in some
cases be called pre~strike ionization~ can be created between
the high voltage electrode and the ground electrode; the corona
begins in the high electric field region 5 wherein the two
electrodes are closest together and spreads generally along
the insulating jacket toward the sparking surface lAl due to an
axial component of the electric field. When the corona dis-
charge reaches the vicinity of the exposed portion lA, an arc
discharge 30 in Fig. 5 occurs -through the corona between the
sparking surface lAl of the first electrode 1 and the sparking
~ surface 2Al of the second or ground electrode 2 in the air
space surrounding the insulating jacket, with a co~ponent of the
~rc being substantiall~ parallel to the surEace of said jacket:
~he arc 30 is a long arc compared to the 0.30 to 0.~0 inch arc
.in more ~onven-kional spark plugs, being the order o~ 0.100 inohes
or more .in leng-th. Th~ a.rc 30 ~ollow~ a path whose shape and
location are dete.rmined, in part, b~ the corona discharye and,
thexe~ore, b~ the shape and position o:E the active portions o~
th~ electrodes 1 and 2. The arc 30 will tend to occur in close
proximit~ to the electrode 1, thereby tending to cause it
1 initially to contact the surface of the insulator 3. In the
plug lOA, the active portions of the electrode~ l and 2 are
shaped and positioned to provide a configuration wherein the
initial surface discharge nature of the arc is affected by the
electromagnetic interaction between the electric current in the
arc and the electric current carried in the electrodes so that
the arc will tend to lift from the insulator surface by virtue
of said electromagnetic interaction. More specifically, an - -
electric current, say, upward in the electrode l at the stem
portion shown at lB will interact electromagnetically with a
current downward in the arc 30, causing the arc 30 to move
rad}ally outward away from the stem portion lB of the electrode
l, but the present spark plug also affects the arc in another ~-
way, as now explalned, again with reference to Fig. 5.
The sparking surface lAl of the electrode l is in the
form of a frustum of a cone as is, also, the sparking surface ~
; 2Al of the electrode 2. The axes of the cones coincide with ~;
the axis of the first electrode l; the apexes of the two cones
face each other;and the cone angles are chosen so that the `~
; electric lines of force entering or leaving the surfaces of the
; conical conductive sparking sur~aces lAl and 2Al are directed
~o that the electric discharge ~i.e., the arc) of the energized
~park plug lO~ is ~orced radially out~ard ~rom the plug axis; as
now explainqd.
~ h~ aation o~ the tapexed ~parking sux~ace~ and 2
can be understood ~rom the boundary conditions on the electria
~ield that dxlve the arc 30, This ~ield cannot have a tan~ential
aomponent at each metallic, highly conductive sparking surface
but must enter and leave each sparking sur~ace normal thereto.
-- 10 -- .
1 Consequently, the lines of force acting on the charged speeies
in the arc ean be manipulated by proper orienta-tion of the
sparking surfaees lA1 and 2Al to ~oree the arc ou-tward ~rom
the plug axis. The eleetromagnetic foree, as above stated, is
directed normal to each sparking surface and is independen~
of the eleetrie current magnitude in the arc, depending only on
the potential differenee between the sparking surface lAl and
2Al. Hence, by tapering the sparking surfaces in the way done
here, the foree on the are, by virtue of that fact alone, is
lO directed outwardly strongly, thereby affecting the shape of the
discharge even at low values of arc eurrent.
To place matters in some perspective, the electrie
eurrent through the eleetrode 1 and henee through the are 30
initially may be the order of tens of amperes or more. This high
eurrent is determined in part by the eircuitry external to the
plug and some control of the high current pulses through the
are discharge can be attained by proper circuit design. In a
eapaeitative discharge ignition system, without a current limiting
~O series resistanee, eurrent pulses of both polarity have been
observed with maximum current reaehing approximately 60 a~peres
and lasting for 10 8 seeonds. These pulses are reduced if a
ser.ie~ re~istanee is ineluded, ~Iigh eurrents oeeur intermi-ttentl~
~or approximatel~ 10 ~ seeonds and then ~rop to a level oE S~
milliamperes. The low electr:ie eurrent eondit.ion i~ the
prina:ipal ~i~eharge phase o the spark plug and during the
same the interaetion Eoree between the currerlt in the ara 30 ana
-- 11 --
4~
1 the current in the axial high voltage electrode 1 has dropped
sharply from the ~orce present during the initial high current
phase. The drop varies as the square of the ratio of the
currents and, hence, can be a decrease in force by a factor
of 4 x 104; however, the electromagnetic forces associated
with the shape of the sparking surfaces lAl and 2Al continues
even at low electric currents to push the arc outwar~. And,
initially r with several amperes flowing in the system, both
aspects act together to provide the bowed out character of
the arc 30 shown. A large arnount of energy may be dissipated
during the high current phase and this may be a vital part of
the ignition process during which a substantial transfer of
electrical energy could take place to the fuel air mixture.
The outward movement of the arc 30 has a number of felicitous
consequences; it removes the arc from contact with the sur~ace
oE the insulator 3, thereby reducing fouling problems; it CRn
be exploited to lengthen the arc~ thereby increasing the ignition
volume in the system; and it can create a continuously chang.ing
position of the arc which increases the ignition volume an
even greater amount. In addition, the arc thereby formed
is a new type discharge. It is known that the scattering cross
s~c-tion as described by the Born approximation decreases as
the ~uare oE the veloc.ity o the implnginy particle. Thus, the,
probability o~ initia-king a chemical re~ction associated w.ith
the combustion ~orces will decrease i~ the velocities o~ the
charged species in the arc become too high~ Ilhe new type dis-
charge herein gives ri.se to a wide distri~ution o~ energie's,
thereby enhancing the likelihood of correctly matching the
energy o~ at least part o.~ the discharge to the chemical process
3~ to which lt is to couple. E'urthermore, in view o~ the fac-t that
- 12 -
o~
1 the present invention adds two further controllable parameters,
the control of the arc can be very precisely variable. In o ~er
words, in view of recent developments in analysis capability
and in view of the advent of microprocessors and the like (see
United States Letters Patent 3,897,766, Pratt, Jr.~, the arc path
and the eneryy therein can be controlled by an appropriate
electric power source to optimize those conditions of optimization.
Furthermore, as mentioned above, aEter ignition has been started,
a large volume of the burning fuel is subjected to a high
~ electric field. Electric energy is coupled into the burning
gases, affecting the nature of flame propagation.
Turning again to Fig. 1, the spark plug 10 has at
least one floating electrode 7 which has sparking surfaces 7A
and 7B. The corona discharge is initiated at the region 5, as
before, and proceeds upward toward the sparking surface lAl in
Fig. l; an arc 30A forms between the surface 2Al and the surface
7A. The floating electrode 7 is capacitively coupled through
the thin insulating sleeve 3 to the stem portion lB of the
electrode 1 so that for some short delay time while this capaci-
tance charges, only the arc 30A is present; after said shorttime delay, an arc 30B strikes between the tapered sparking
surEace 7B and the tape.red sparking surface lAl It has been
found, ~or present purposes t that -the intermediate electrode 7
permits a laryer total gap than otherwise allowable at the hiyh
pres~ures in internal combus-tion enyines w:ith the above-mentioned
beneEicial results, By wa~ of illustrat:i.on, a total yap o~ 0.225
inche~ can successfully be used in a standard ignition s~s-tem
with a floatiny electrode to divide the gap.
The yap 6 in Fig. 5 consists oE two serial yaps in
the pluy 10 of Fig. 1, one gap between the tapered sparkiny
- 13 -
~ t~
1 surface 2Al and the tapered sparking surface 7A and the other
between the tapered sparking surface 7B and the tapered sparking
lAl. In each instance, the gap increases in length at increasing
radial distances outward from the jacket 3. The electrode 7
is a band or a ring that encircles the jacket 3 so that an arc
can form at any circumferential part thereof.
Mention is made previously herein that the pa-th of
the arc is determined, in part, by the shape of the sparking
surfAces lAl and 2~1 in the plug lOA of Fig. 5; similarly the
path of arc 30B between the floating electrode 7 and the
electrode 1 of Fig. 1 is determined, in part, by the shape of
the sparking surfaces. In addition, it has been observed that
an arc can form directly between the sparking surfaces lAl and
2Al in the spark plug 10 of Fig. 1. Also, it has been observed
that appropriate orientation of the floating electrode 7 can
result in an arc 30A on one side of the jacket 3 of the plug 10
and an arc 30B on the other side thereof. This situation will
effect ignition of the fuel air mixture at substantially
different sites about the jacket. It has been further observed
by microscopic examination of the electrode surfaces of spark
plugs, like the spark plugs 10 and lOA, after the spark plugs
have been used in a combustion engine, that arciny tends ko
oc~ur around kh~ entire annular sparking sur~aces. It is also
~videnk that arc.ing occurs out to the extreme periphery of the
sparking surEace~. In connection with the pre~ent work, sparklng
~urEaces made o~ supexalloys such as Udimet 500 (~rade Mark),
a high-nickel, hlgh-temperature alloy, have proved to be ver~
duxable ~or the sparkiny surfaces 1~1 and 2~1 and the floating
electrode 7. In general, it is necessary to use metals capable
of withstanding high temperatures and resiskant to pitking in
view of the several electric and electrochemical forces present~
- 14 -
~7 ¢
1 The spark plug labeled lOB in E~ig. 4 has many of the
same elements as the plug 10, but the intermediate or floating
electrode labeled 7' in Fig. 4 differs in shape from the
electrode 7. The floating electrode 7', like the electrode 7,
is pre~erentially in the form of a band or ring that encircles
(i.e., is disposed about) the jacket 3, but the sparking surfaces
labeled 7A' and 7B' are disposed radially outward a substantial
distance by a supporting structure 8 so that the arcs shown at
30A' and 30B' orm away from the jacke-t 3. Again the arcs thus
formed are pushed outward by interaction between eleetric
eurrents in the two arcs and electric current in the stem portion
lB of the axial electrode 1. A capacitor plate 15, embedded in
the insulation jacket 3, is capacitively coupled to the stem
portion lB through the insulation.
The eapacitive coupling o~ the floating or intermediate
electrodes is shown schematically in Fig. 8 which shows a
spark plug lOC having a plurality of such floating electrodes 7"
and 7"' (or more) coupled through capacitors 34 and 35 to
; the high voltage electrode 1. Shunting resistors Rl, R2 and R3
(~ one megohm) represent the surface resistance among the several
eleetrodes. The spark gap between the main electrode l and
the ~loaking elec-trode 7" is marked 61, the gap between
~loatincJ eleGkrodes 7" and 7"' is marked 6" and the yap between
the ~loating eleetrode 7"' and the main eleG-krode ~ is marked
6"'. The system labeled lOlC in E'ig. 8 emplo~s th~ multiple
~ap spark plug .LOC whieh has pr:ovision (not shown in FicJ. 8) for
corona diseharcJe as before, as well as a voltage source ].6',
which .is conneetecl through a switch Sl to enerqize the plug lOC.
The switeh Sl is under. the contro.l of a controller~distributor
17.
- 15
1 A few ~urther matters of a general nature are included
in this paragraph~ It has been ~ound to be advantageous if
the sparking surface lAl is so shaped that it has an exposed
rim at the loca-tion labeled 23 in Figs. 1 and 2, by, Eor example,
making the cap lA slightly larger than the jacket 3 where -the
two are in contact. This rim provides a field intensification
which aids in establishing the arc discharge at a lower voltage
than otherwise possible. The sur~ace of the insulating jacket
was found in experimental work done to remain extremely clean
IQ with the incorporation of this ~ield intensification surface
into the sparking surface 1~1. A similar field intensi~ication
por~ion is found in sparking surfaces 2Al shown as 200 in Fig. 4.
The thermal mass of the sparking surfaces lAl and 2Al, and to some
extent those associated with the floating electrodes, will act
to cool the burning gases. Furthermore, the effect of the
electric field on the burning gas will tend to drive the flame
onto one or another of the sparking surfaces. Thus a partial
electromagnetic induced confinement of the flame is achieved.
Consequentl~ some heat sinking or cooling of the flame will
~ kake place as a result of flame interaction with the electrode.
~his will act to suppress NO formation. It is important,
thero~ore, to selec-t the heat transfer eharacteristics oE the
~p~rking ~u~aees, the electrodes, and the plug bocly and to control
khe voltag~ applied to the plug so that total quenching of
th~ ~lame cloes not oeeur but a de~ired and con-trolled degree
of eooling does take place so as to reduce -khe production o~
NOX. Beeau~e oE the very diEferent nature of the multiple arcs
associated with this spark plug and its effect on the burning
mixture, it is essential -that proper t.iminc~ o~ the spark be
3~ carried out.
- 16 ~
t The insulating jacket 3 can be made of conven-tional
ceramic insul.ating material used in spark plugs. The foregoing
electromagnetic interaction can be enhanced, however, by
distributing through the insulating material prior to formation
a small amount of Fe3O4 or some other magnetic particulate
(e.g., the jacket 3 can be a ferrite). The particulate will
increase the magnetic field due to current in the electrode 1
without degrading the insulating properties of tthe jacket 3.
Small magnetic particles in the 100 to 1000~ range of sizes
could act effectively in this regard.
- As above no-ted, corona is believed to begin in the
region 5 and move along the insulating jacket; as it does, it
is subjected to electric lines of force between the ground
electrode 2 and the exposed portion lA of the hiyh voltage
electrode 1 in an operating system 101 in Fig. 2 to provide an
arc. The arc thus formed moves along a path generally parallel
to the stem portion lB of the axial electrode 1 which is
covered by the insulating jacket. ~he path of the arc is,
then, determined in par.t by the corona, and the shape of the
corona is determined to a large extent by the geometry o~ the
electrode 1. Hence, the jacketed high voltage electrode serves
ko gu:ide ~he corona and, thus, the arc di.scharge. It is also
po~lble to guide the co:rona along curved insulat.ing su~:eaces
aoverin~ a curved high volt:age electrode.
The spark pl.uy 10 has a conventional base 4 tha-t
threcads into an eng.ine block at electrical grourlcl, as above
noted. In Fiy. 2, as above inclicated, the elemen-t-c; 21 ancl 22
represent a cylinder and pi.s-ton, respectivel~, of such engine.
The rcyion marked 20 can represent a conEined elongate volume
bounded in part by engine walls which can serve to cool the
. _ 17 -
1 initial combination. The spark plug disclosed herein can also
be used in rotary engines and, in general, in combustion systems
that require spark ignition devices. The high voltage supply
means can be a capacitance discharge system or conventional
automobile coil, or such means can be a supply that furnishes
a waveform to provide timing in connection with both the corona
discharge and the arc discharge. Further, in the irNmediate
vicinity of the spark plug 10 there will be an air-Puel mixture,
and, in this connection, the duration of the corona discharge
can af~ect the composition of said mixture. Also, since the
amount of electrical energy can be dissipated in the arc is a
function of the arc length, the present system introduces great
benefits to ~ny combustion system, particularly in lean
burning engines having a high air-to-fuel ratio. And, it can
now be seen, such energy can be increased as the arc is moved
outward since, as distinguished ~rom prior art systems, in the
present system the arc length is or can be increased. In ~hat
follows, some theories underlying ~he present invention are
given more rigorous treatment than is done in the foreqoing
explanation.
~ or~ done to date indicates that a corona is first
~stablishe~ between the ground elec-trode 2 and the high voltage
elec~rode 1 throu~h thc insulator 3. The charcJed species in
the corolla experierlce an electric Pield having a rad:ial com-
p~nent ~r in ~i~. 5 direc-ted perpendicular to the axially
direated high volta~e elec-trode 1, and an axial component Ez
directed parallel to electrode 1. ~he radial and axial
currents Jr and Jz, respectively are
~r ar ~r
J = ~ E
- 18 -
~ t7
1 where ar is the radial conductivity through the insulating
jacket 3 to the electrode 1 and ~z is the conductivity along
the surface of the jacket 3.
Although Er ~ E , because of the insulating jacket,
az ~'~r An arc can be established in the axial direction
yielding Jz ~ Jr. The current in the arc 30 in Fig. 5 is
essentially equal in magnitude and opposite iII direction to the
current flowing in the insulated high voltage electrode at
lB. These two currents exert a :Eorce on each other in the radial
direction forcing them apart. Since the arc can move in space,
it will lift off the surface of the insulating jacket 3, as
previously mentioned. The radially directed force F per unit
length Q acting on the arc is
F = 2 x 10 (I )2
Q a arc
where F is in newtons, Q and _ are in meters, and IarC in amperes.
The separation between the arc current and that carried by
electrode 1 is given by a. The current IarC is not constant
when the arc discharge occurs. Immediately aEter the arc is
estabLished, IarC can be quite large while the self-capacitance
of the plug is discharged. Values as hlgh as ten amperes
~u~ing noise~suppressing components) can be atta.i.necl OVel. a t:i.me
~c~e' oE 1~ ~ seconds. 'L'h:ls hiyh current quickly drops to a
value of appxoximately 50 mA durlng the dissipation oE the
magne~.ic enerCJy in the coll o~ a convent,ional .ignit:Lon system.
The sel~capac:itance oE the plug can be dellberate.l~ controlled
to a~fect the value oE IarC. The duration of the sel:E-capacitance
discharge can be adjusted b~ manipula-tion of the RC tirne constant
oE said d.ischarge. If, ~or example, IarC is taken to be ten
amperes and the arc 30 has pushed away from the axial electrode 1
-- 19 --
1 ko a distance a of O.l cm, then
F = 2 x lO 7 x lo2 = 2.0 x lO 2 newtons
Q l x lO meter
The force acting on an individual electron or positive ion in
the arc would be the order of
2.0 x lO 2 x lo~lO = 2 0 x lO-2 newtons
This is to be compared with the force Fl on the electron or
positive ion due to the electric field that drives the arc.
If the field in the gap 6 in FigO 5 is 30,000 V/cm, the
corresponding driving force Fl is
Fl = l.6 x lO l9 x 3 x lO~ = 4.8 x lO 13 newtons
Hence, the force F acting to push the arc away from the sur~ace
of the insulator 3 can dominate the electric force Fl that
produces the arc itself during high current pulsations. ~his
tendency to lift the arc off the surface is important because
it can be used to establish the arc away from a surface that
could otherwise quench the combustion process, it allows better
propagation of the combustion process in all directions away
from the arc, and it reduces p~ug fouling since a surface current
is strongly pushed off the surface. The tendency to push the
arc aw~y fr~m the surface is of further importance as it can
h~ us~d -to control the length of the arc~ The lifting ac-tion
can be very ~Eectively assisted by shaping the sparking sur~aces
l~l and 2Al, an~ those ass~ciated with intermediate or floating
~lectrodes, in the manner previously described, hy providing
a sparking surface having a substantial area whos~ outward
normal is directed so that it can initiate or terminate an arc
which is forced outward and away from an electrode of the plug
3~
that carries all or part of the plu~ current. In Fig~ S the
-20 -
1 ou-tward direction is radial and the axial electrode 1 carries
substantially all the plug current.
As pointed out above, the ele~tric current carried by
electrode 1 and, therefore, the arc current, is determined
by nature of the ignition circuit and by the nature of the
discharge. In a capacitive ignition system, it was found that
within the first 500 microseconds large current oscillations
took place with peak amplitudes as high as 50 amperes. Over
a period of 140 microseconds, large current and, in work done
in connection with the present invention, voltage transients
of both polarities were observed. These transients were much
more pronounced in the floating electrode plug disclosed herein
as compared to the conventional spark plug (Champion NY-13)
and more pronounced that those observed in a plug having -the
same structure as that presently disclosed and shown in Fig. 1
and Fig. 2 but with no floating electrode 7. The very large
! current and voltage transients which take place during the first
500 x 10 9 seconds will transfer a substantial amount oE energy
into the fuel-air mixture whose flame ~ront travelling at 800 cm/
second could only move some four microns during this time
interval. Therefore, intense local heating can be expected
over this period. This will produce a local plasma into which
energy can be transferred from the electric ield applied to the
plu~ el.ectrodes. Th.i~ plasma w.ill be ~urther enhanced ~)y the
combust.ion reaction it~el.
The use of low work -~unc-k.ion materiaL in the
elec-trode~ ~i.n the sparking surfaces r for examp:Le) and in the
:insulating jacket 3 oE ~ig. :L can also be of use in faci..Litating
the establishment of thc coron~ discharge and the arc itself.
~qat.erials such as LaB6l for example, have very low work functions
and produce a copious supply of electrons as a result of
elevated -temperatures and electric fields. These electrons
emanate from a combination of thermionic and field emissions.
Electrons liberated in the high field produce and assist in
the production of the corona and arc discharges. These dis-
charges are initiated and maintained at higher pressures and
lower voltages if the supply of electrons in the gas is enhanced.
This is in part due to the ability of electrons accelerated
by the electric fields present from the high voltage source to
produce ionization in the gas. Of course, the insulating quality
of the jacket 3 must be main-tained so that breakdown through
it does not occur.
The high voltage source that creates the initial corona
discharge and establishes the arc can be adapted to perform
several functions. It can supply a corona voltage and limit
the corona current so as to suppress the formation of an arc
until th~ desired instant. A fast rise time pulse as shown in
Fig. 3 can be impressed upon the corona voltage, which might
be in the 5kv range, to create the arc. Multiple fast rise time
arc-forming pulses could be supplied to form ~ sequence of
arc discharges. Further, this sequence of arcs can be used in
the ignition oE a single fuel-air charge. The corona can be
cx~a~e~ simpl~ as a conse~uence o~ the vol~aye inc~easeC~
assoclatcd with t}le vo:L-tage pulse that es-tablishes the arc
discharge. qlhe corona stage of -the discharye may last only for
a very shoxt t:ime. Some technical matters relating to the arc
and an elec-tric system to eE~ect the various electrical ~unc-tions
herein disclosed are now ta]cen up.
The interaction be-tween the current carried in the
arc and tile current ~lowing in the insulated high voltage
electrode can be used to control ~he length of the arc, as is
1 previously noted herein. One means of effec-ting -this control
is to vary the current carried by the arc. This can be done
by using a variable current or voltage source connected across
the plug terminals. When the arc discharge is ofE, the
resistance Roff of the plug is high, e.g., 106 ohms. During the
corona discharge preceeding the arc, the resistance RCorona is
also ~uite high and the corona current is in the 10 5 ampere
range. When the arc is on, the resistance across the plug Ron
is dras-ticall~ decreased from Rof~. Ron will usually be of the
order o~ ten ohms. A variable voltage or current source can
now be used to pass a control current -through the arc and
conse~uently affect the force which tends physically to separate
the arc from the currents flowing in the plug s-tructure; and
by using tapered sparkiny surfaces of the type shown herein,
the length of the arc is further a~fected. An electric circuit
using a control scheme is shown in Fig. 6 for a standard
ignition system.
The electric circuit of Fig. 6 includes a battery 16
and a coil 47. The coil ~7 has two windings, 47A and 47B, as
in a conventional system, one oE which, 47A, is connected
through a resistance 18 and diode 19 to the single spark plug 10
in Fig. 7. The winding 47B is connec-ted throuyh a resistance
1~ to po.ints 13 and parallel condenser 12. Control voltage
means 25 serve~ to con-tro:L the voltage rise -time, -the value
and durakion o~ the arc current, and the vol-tage applied aEter
igni-tion ha~ been ini-tia-ted.
Fig. 7 is an equivalent c:ircuit representa-tion oE
the plug 5 tructure shown :in E`ig. 1. The ~loa-ting or intermediate
electrode 7 i5 coupled by an RC network to the hi~h voltage
3~ electrode 1 through the insuLating jacket 3 and this is
- 23 -
; ` ~
t explicitly represented in Fig. 7 by the capacitor labeled 36
and resistor RSl which represents the resistance between the
high voltage electrode at lA along the insulator surface to the
floating electrode 7. The resistance from the ~loating
electrode 7 to ground is marked RS2. The arc 30B o~ Fig. 1 is
~ormed in the gap shown at 6A in Fig. 7 while the arc 30A of
Fig. 1 is formed in the gap shown at 6B in Fig. 7. An additional
capacitor 66 can be connected across the plug or equivalently
across the high voltage source marked 16" to increase the
effective self-capacitance o~ the plug. ~ resistor 67 connected
in series with the capacitor 66 controls the RC ~ime constant
of the discharge of the capacitor which occurs when the gaps 6A
and 6B are broken down so that the overall impedance between -~
: :
the electrodes 1 and 2 drops to a low value as a result of the
- arc discharge. The energy stored in the capacitor 66 is released
into the arc so that the arc current can be controlled in both
~amplitude and time by variation of the capacitance and resistance,
in particular of elements 66 and 67 of Fig. 7, in the high
voltage source to the plug controls the arc current. This
could be done by a computer using feedback signals from a
variety of sensing elements, such as, for example, torque and
rpm sensors, to optimize performance. During the cold start
conditions and in ai~aumstanaes whexe ~ouling is aggravated,
additional AXC auxrent would be help~ul in in~uring ignitiQn~
Sevexal modes o~ behavior of the circuit o~ Fig. 7 are
po~sible, dependin~ upon the nature o~ ~he signal ~rom the high
vo~tage source 16" and the circuik elements of the plug structure.
If the capacitor 36 is 1arge enough and the volta~e rise tLme
ast enough, then the capacitor 36 will act as a high pass
~ilter and mo~t of the high voltage will appear across gap 6B.
: '
~ ~,
'' ' -.
1 When the gap 6B breaks down, substantially all of the high
voltage will occur across gap 6A, causing it to break down. If
the capacitance 36 is negligible, the resistors R~l which :is
in parallel with the reslstance of gap 6A would act with the
resistance RS2 which is in parallel with gap 6B to divide the
voltage drop between the electrodes 1 and 2. It is apparent
that a fast rise time of the high voltage signal is very desir-
able so that the maximum possible voltage appears across the
gaps during this sequential breakdown.
The floating electrode 7 can be capacitively coupled
by an RC network to ground, that is, it can be coupled to the
plug body, as shown in Fig. g wherein the spark plug is designated
lOD, rather than to the high voltage electrode 1. That would
be equivalent to connecting the capacitor 36 in Fig. 7 to
ground rather than to the high voltage source. This change is
effected in Fig. 9 by connecting the floating electrode 7 to
a cylindrical capacitor plate 31 coaxial with the plug base 4
by conductive support strips 32A and 32B; the cylindrical
capacitor plate 31 is separated from the base 4 by the insulator
~ 9. This arrangement will also serve to heat sink the floating
electrode 7 as well as providlng mechanical support therefor.
The incoming volta~e pulse ~rom a voltage sourcc to the p:lug 100
would see the Elo~ting electrode 7 eE:Eectively at ground i;E
the voltage rise time were East, compared to the RC t.ime constant
o~ the sel~capacitance and selE-resistance of the p:Lug lOD.
This would cause a gap between the e:lec-trodes 2 and 7 oE the
plug lOD t.o breakdown Eirst, :Eollowed by the sequential
breakdown of gap between the electrodes 7 and 1 o~ the plug lOD.
~ multiple Eloating e:Lectrode structure would also be possible
iE the floating electrodes 7" and 7"' shown in Fig. 8 were
- 25 -
1 coupled by RC networks to ~round or to one of the high voltage
electrode and the other to ground or with only one oE them
coupled by a combination of impedances to either the high
voltage electrode or to ground. A different circuit represen-
tation would be required for each of these cases. The basic
concept taught here is a structure employing intermediate or
~loating electrodes however coupled to their electrical en~iron-
ment so that a~ arc wi].l form using the shape, orientation and
position of the floating electrodes to establish a long overall
arc whose current is directed opposite to the discharge current
in at least a portion of the plug structure, resulting in an
electromagnetic repulsion force on at least part of the arc and
acting to force a portion of the arc away from the sur~ace of
the insulator which spaces the floating electrodes, the several
electrode sparking surEaces being so shaped that the ~ield
lines normal to these 5urfaces act to assist in ~he formation
of the arc along one or more paths not contacting the insulator
surface.
The spark plug herein disclosed is particularly useful
2~ in a combustion enyine system which includes a computer capa~le
of rap~d control of the engine operating parameters such as a
~uel-air rati.o, spark timing, and the like, and further adapted
ko control the natu.r~ oE the arc discharge o:E each spa.rk plug
by manipulatin~ the output oE ~ variable voltage or current
source conn~cted to the plug. ~he individual Elrin~s oE each
plug could be con-trolled not only as to the timing o~ the
discharge but its phys:ical nature as well, e.g., amount o~
corona, length o~ the arc discharge and duration oE the arc
discharge (see in this connection, Un.ited States Letters
3~ Patent 3,897,7~6, Prat-t, ~r.). Furthermore, the voltage supplied
1 to a plug after combustion has begun could be controlled so as
to.affect the electromagnetic interaction between the plug
structure and the ionization in the burning fuel-air mixture
for the purpose of controlling the nature of the combus-tion
process and the rate of combustion.
Spaces in the plug structure such as that beneath the
sparking surface 2A1 in Fig. 1, which can trap fuel which does
not burn may be filled.
Further modifications of the invention herein disclosed
will occur to persons skilled in the art and all such moclifi-
cations are deemed to be within the spirit and scope of the
invention as defined by the appended claims.
- 27 -
