Note: Descriptions are shown in the official language in which they were submitted.
S6;~42
,.: .
~ackground of the Invention
This invention relates to an automobile internal,.
combustion engines and particularly, to electric spark-
~ plugs for automobile internal combustion engines. An
; object of this invention is to provide an antipollution
internal combustion engine which is superior in exhaust
gas properties.
To enable the prior art to be described with the aidof drawings, the accompanying drawings will first be listed.
Fig. 1 is a graph s~owing the relationships of the
NOX concentration (by parts per million, i.e., ppm,
graduated on the left ordinate) in the exhaust gas, the
,/ HC concentraticn (by hexane equivalent ppm, graduated on
the left ordinate) therein anu the CO concentration (by ~,
graduated on the right ordinate) therein, respectively,
with respect to the excess air ratio F (abscissa) of the
gas mixture in the internal combustion engine.
Fig. 2 is a graph showing the relationship, in one
example, among the left and right sides of the ignition
theoretical inequality (1) of the inventors and the excess
air ratio F, with V as a parameter.
Fig. 3 is a graph showing the relationship, in one
example, between the ignition limit excess air ratio Fc
and the electrode gap distance Ls, with G of the
inequality (1) as a parameter, being based on the calcula-
tions from Fig. 2, the shaded region being the ignitable
region.
Fig. 4, (a) and (b) are schematic views showing a
: thermal boundary layer and a hydrodynamic boundary layer
formed on the electrode surface by electro-flame-wind,
respectively.
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~ Fig. 5 and Fig. 6 together show one example of the
; conventional thin electrode type spark-plugs, the respective
; parts (a)s and (b)s of Fig. 5 and Fig. 6 showing the
sectional side views and the bottom views, Fig. 6(c)
showing the sectional front view.
; Fig. 7 shows one embodiment of the two-electrode spark-
plug of the present invention, the part (a) of Fis. 7 being
the sectional side view of the two-electrode spark-plug,
the part (b) thereof being the sectional side view of
~i 10 essential parts and the part (c) thereof being the bottom
. .
. view.
Fig. 8 to Fig. 14, Fig. 17 to Fig. 26, Fig. 29, Fig.
32, Fig. 34 to Fig. 36 show the other embodiments of the
.
, two-electrode spark-plug of the present invention, the
respective parts (a) and (c) thereof showing the sectional
side view of the essential parts and the sectional front
.,~ , .
`~ view, the part (b) thereof being the bottom view.
Fig. 15 is a side enlarged view of the electrode
dischargins faces of the spark-plug, the Eo of Fig. 15
showing the conventional spark-plug electrodes, the El, E2
and E3 showing the spark-plug electrodes of the present
invention.
Fig. 27, Fig. 28, Figs. 30, 31 and 33 show the
enlarged views of the electrode essential parts of the
spark-plugs of the present invention, respectively, the
respective parts (a) and (b) of Fig. 27 and Fig. 28 being
the sectional side view and the top view, the part (c) of
Fig. 28 being the sectional front view, and the respective
parts (a), (b) and (c) of Fig. 30, Fig. 31, and Fig. 33
being the sectional side view, the top view, and the
sectional front view.
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;'
Fig. 16 shows one embodiment of three-electrode spark-
plugs of the present invention, the part (a) thereof being
-~ the sectional side view and the part (D) thereof being
the bottom view.
Fig. 37 shows one example of the conventional spark- -
:,.
; plugs of surface creeping discharge type, and Fig. 38 to
Fig. 40 show one embodiment of the spark-plugs of surface
creeping discharge type of this invention, respectively,
tne parts (a) thereof being the sectional side views,
; 10 the parts (b) thereof being the bottom views.
...
Fig. 41, (a) and (a') show the streamlines (in section)
~ of the electro-flame-wind in the conventional thin electrode -
; type spark-plug, and the structure (in section) of the
boundary layers with respect to the electro-flame-wind,
respectively, the parts (b) to (-g) thereof showing the
streamlines (in section) of the electro-flame-wind in
the various spark-plugs of the present lnvention, the parts
(b') to (g') thereof showing the constructions (in section)
of the boundary layers with resepct to the electro-flame-
winds corresponding to the parts (b) to (g), respectively,
any of electrode saps in these spark-plugs being the same
value Ls.
Fig. 42 to Fig. 45 show the experimentally measured
characteristics of the ignition limit excess air ratio FL
of the spark-plugs (ordinate on the left side) and the
electrode gap distance L (abscissa); in any graphs, the
ordinate on the right side showing the ignition limit air
fuel ratio, a horizontal dotted line Xl showing an equivalent
air fuel ratio (F = 1), curves W, W' and Eo showing the
FL-LS characteristic curves of the conventional spark-plugs,
th other curves A, D, El to E6, G2, G3, Kl, 1 3 4 6
- 4 _
1~6242
`; and N7 showing the FL-L5 characteristic curves of the
' spark-plugs of this invention, X2 showing each level of
',~t the air fuel ratio = 19.25, (F = 1.25), the region below
j/~
" the each curve being the ignitable region.
Fig. 46 shows the ignition limit excess air ratio FL
(ordinate on the left side), with the spark gap Ls as a
parameter,in the spark-plug shown in Fig. 7, or shows
' experimentally measured characteristics of dependence of
`~ ignition limit air fuel ratio (ordinate on the right side)
` 10 upon the first electrode projection height Hl (abscissa).
Fig. 47 snows the ignition limit excess air ratio
'~ (ordinate on the left side), with the spark gap Ls as a
parameter in the spark-plug shown in Fig. 12, or shows
experimentally measured characteristics of dependence of
ignition limit air fuel ratio (ordinate on the risht side)
upon the curvature v (abscissa) of the electrode discharging
face.
~ An internal combustion engine provides power through
; the burning operation of a gas mixture of air and hydro-
20 carbon fuels such as gasoline, petroleum gas, etc. As
shown in Fig. 1, the respective concentrations of exhaust
` gas constituents such as nitrogen oxides (NOX), carbon
monoxide (CO) and hydrocarbons (HC),' etc. which are discharged
from the internal combustion engine, vary in accordance
with an excess air ratio F (which means a ratio of an air
fuel ratio to an equivalent air fuel ratio, the air fuel
ratio indicating a ratio of air mass and fuel mass, the
equivalent air fuel ratio indicating an air fuel ratio
provided that H2O and CO2 have been produced sto-ichiometri-
30 cally through reaction of the fuel and the oxygen. Accordingly,
the smaller the value of the excess air ratio F is, the
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1056242
;..
higher the fuel concentration is. The greater the value
of the excess air ratio F is, then the lower the fuel
':'`, ' :
concentration is). For example, the gas mixture in the
range of 0.9<F<1.25 produces a large quantity of IIOx due
to high combustion temperatures (approximately 2,000 K to
3,000 ~). The gas mixture in the range of F<0.9 produces
relatively small quantity of NOx, but an extremely large
amount of CO and ~C. Accordingly, in order to improve the
exhaust gas properties to develop antipollution internal
combustion engines, it is required to burn lean gas
mixture in the range of F>1.25, or to effect exhaust gas
recirculation (EGR) to make fuel concentration lean to lower
the combustion temperature of the gas mixture down to
approximately 1,500 K or less.
In the conventional thin electrode type spark-plug,
for example, a spark-plug shown in Fig. 5 and by Table 1,
line W, which comprises a grounded electrode 1 composed
of wide and long plate and with a high-tension electrode
2 of thin cylinder with flat end face, has, as shown in
Fig. 42, extremely narrow ignitable region (a region below
the curve). Fig. 42 shows the relationship of the
ignition-limit excess air ratio FL of the gas mixture
under 1 atmospheric pressure and room temperature vs. the
electrode gap distance, namely, spark gap Ls. As seen
from Fig. 42, in the conventional spark-plug, the ignition
of the lean gas mixture in the range of the F>1.25 can be
; realized only when the spark gap is greater than Ls = 2.28mm
(the Ls shows a measured ignitable spark gap for an excess
air ratio of ignition-limit of FL = 1.25).
~:;
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1056'~,4Z
i Table 1 (Prior art)
. .. .
Marks of FL-Ls Grounded High-Tension Ls
~ Characteristic Types of Electrode Electrode
:~ Curves Electrodes Dimensions Dimension (mm)
(mm) (mm)
~ W Fig. 5 2.7 width1.0 diameter 2.28
;~` 1.3 thickness
5 length
;
W' Fig. 6 2.7 width1.0 diameter 2.04
1.3 thickness
` 10 5 length
Also, as in the other conventional spark-plug of Fig. 6
and Table 1, line W', according to a thin electrode type
spark-plug which comprises the same high-tension electrode -
2 as that of Fig. 5, and a grounded electrode 1 with U-shaped
~ groove 1' along the lengthwise direction of the discharging
Pj`-` plane on the wide and long plate, the characteristic curves -
between the excess air ratio FL of ignition-limit and the
electrode gap distance Ls are improved as compared with
:.
the curve W, as apparent from the curve W' of Fig. 42.
- 20 However, the ignitable region is so narrow that the ignition
of the lean gas mixture in the range of the F>1.25 can be
` realized only when the electrode gap distance is greater
than Ls = 2.04 mm.
In using an ignition power supply on the market,
dischargeable-limit gap distance Ls for discharge with
two-electrode type plug is about 2 mm for a gas mixture
(gas mixture on heavy loading of the internal combustion
engine with a compression ratio of approximately 10),
which is compressed into molar density as eight times
high as that under one atmospheric pressure. Accordingly,
in the conventional spark-plugs, it has been difficult to
directly ignite the lean gas mixture where F>1.25. In
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~ ~GS6242 ~
order to eli~inate such difficulty, the following three
methods have been proposed.
A torch igniting means has been considered as a first
method, according to which an antipollution internal com-
bustion engine is realized by use of spark-plugs of the
prior art. The torch makes it possible to ignite such
lean gas mixture that has an air fuel ratio at the
explosion limit. Accordingly, by making the gas mixture
; only near the spark-plug high in fuel concentration to
effect the igniting operation, the excessively lean gas
mixture (on the whole) can be burned through the formation
of the torch. However, the disadvantages with the above
torch ignition means are that a combustion subchamber, and
subcarburetor, or extra fuel injection system, etc. are
required to realize the above-described burning operation
, . .
of the lean gas mixture.
Secondly, it is also possible to take measures for
individual operation modes. During starting and warming-up
operations, idling (no-load~ operation and engine-braking
(negative load operation), less NOX are produced independently
of the value of the excess air ratio F, because of the low tem-
perature and low pressure of the gas mixture. However, in such
modes an F value of nearly equal to 1 or smaller is required to
assure ignition operation. Thus, the number of revolutions of
the engine in idling mode has to be high to ensure F~l, ahd
hence, the fuel consumption increases adversely. In the heavy
loading operation mode and the others than the above mentioned
modes, temperature and pressure of the gas mixture is high, and
therefore, the lean gas mixture in the range of approximately
F = 1.2 or smaller can be spark-ignited. Accordingly, the less
NOX is produced with F ~ 1.2 and simultaneously better heat
transfer rate through the cylinder wall of the engine. The
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`` 10~6Z4Z
disadvantage of such individual-operation-mode measure is that
the internal combustion engines should provide a system that the
value of the excess air ratio F is to be adjusted and controlled
in the extremely narrow allowable value range for every opera-
tion mode.
Thirdly, it is possible to provide an internal combustion
engine wherein an excessively rich gas mixture (on the whole) is
ignited to burn at relatively low temperature for preventing the
NOX production and C0 and HC are rear-treated through the use of -
~10 catalyst or thermal reactor. However, in order to realize the
~, .
above requirements, rear-treating system including catalyst,
- thermal reactor, air pump, catalyst antioverheat equipment, etc.
are required, thus resulting in power loss in exhaust system
increased fuel consumption due to excessively rich fuel, sul-
furic acid mist and scattering heavy metal.
The internal combustion engines used in the above-
- mentioned flrst, second and third methods have such
G~ disadvantages as increased weight and cost of the engines,
complicated adjustment of the optimum operation conditions
of the engines, inferior stability of the optimum operation,
difficult mass production controlling, and complicated,
difficult adjustment of the manner of use.
Summary of the Invention
This invention consists of an electric spark-plug for
automobile internal combustion engine comprising: a
metallic screw portion to be engaged with an internal
combustion engine, an electrode terminal part, an electric
insulator for supporting said screw part and said electrode
terminal part in a coaxial relation, keeping them insulated
from each other, and at least a pair of electrodes, the
pair including a first electrode and a second electrode,
said first electrode being supported by a supporter formed
g ~
10562~Z,
on the metallic screw part, said second electrode being
rod-shaped and electrically connected to said electrode
. terminal pa~t by means of a central conductor disposed
on the axis of said screw part and in said insulator, said
first electrode and said second electrode being supported
insulatedly from each other by means of said insulator,
; keeping a given ignition gap between their discharging
`` faces, characterized in that: fluid resistance against -
gas flow of flame nucleus of said electrodes is decreased
in a manner to have an ability of ignition that is defined
by capability to ignite and burn a lean gas mixture of
.: isobutane and air under the conditions of normal temperature :
- (T) of about 20C, the pressure of lean gas mixture equals
1 atmospheric pressure (density index ~1), excess air
~:. ratio (F) of more than 1.25 and electrode gap distance (Ls)
. of less than 2mm, so that the following ignition conditional
.~ inequality applies thereby to decrease the thermal con- :
ductance G from the flame nucleus to the electrodes:
. G ~exp(Eb/RT (n + 4.773 mF)n+m*
~ V l(d - l)B~ n+m* 3.773 n m (Xt - Xi) m F J
: 20 . . . . . . . . . . (1),
~ where J, E and m* are given by
J = ~ Eb (Ts - To) + RTs ] / ~ RTs,
E = [ (760 -p ) / 760] Rc,
m* = (1 + y)m,
wherein V is the nucleating volume size and is represented
by an equation of V=9Ls wherein 9 is a proper constant and
Ls is the electrode gap distance, T is a temperature of the
nucleating volume, To is the temperature of the electrodes, :-
Xi is a molar density in 1 atmospheric pressure of incom-
bustible gases other than nitrogen, F, E, p and Rc are
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.
, . . ~ :. .
1~562~2
excess air ratio, density index of molecules, absolute
value of negative pressure (mm Hg~ in intake pipe and
compression ratio at the time of ignition, respectively,
in the gas mixture, J being practically a constant when
the dependence of the singular point temperature T upon
-. the variable quantities V, G, Xi, F and E are sufficiently
: small, Eb is an activation energy in Arrhenius' equation,
and is a constant inherent to individual fuel, n and m
are the molecularities of reaction of fuel and oxygen,
respectively, y is a parameter showing the participation
degree of nitrogen molecules in reaction process, ~ is a
multiplication factor of chain carriers, R is a gas
constant, B, Xt and ~ are constants, respectively.
The invention also consists of a method of igniting
an automobile internal combustion engine of lean gas
mixture combustion type using the lean gas mixture having
excess air ratio F of F> l in operation modes including
~- idling, engine-braking,-constant speed, acceleration and
deceleration, by means of at least one sprak-plug com-
prising: a metallic screw portion to be engaged with
said internal combustion engine, an electrode terminal
part, an electric insulator for supporting said screw
part and said electrode terminal part in a coaxial
relation, keeping them insulated from each other, and
at least a pair of electrodes, the pair including a first
electrode and a second electrode, said first electrode being
supported by a supporter formed on the metallic screw part,
said second electrode being rod-shaped and electrically
connected to said electrode terminal part by means of
a central conductor disposed on the axis of said screw part
and in said insulator, said first electrode and said second
electrode being supported insulatedly from each other by
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10~ 42
means of said insulator, keeping a given ignition gap
between their discharging faces, the method being char-
acterized in that: a lean mixture of gas is ignited with
a decreasing fluid resistance against gas flow of flame
nucleus of said electrodes in a manner to have an ability
of ignition that is defined by capability to ignite and
burn a lean gas mixture of isobutane and air under con-
, . . .
ditions of normal temperature (T) of about 20C, the
; pressure of lean gas mixture equalling 1 atmospheric
: 10 pressure (density index of about 1), excess air ratio
~. (F) of more than 1.25 and electrode gap distance (Ls) of
; less than 2mm, so that the following ignition conditional :
inequality applies thereby to decrease the thermal
conductance (G) from the flame nucleus to the electrodes:
G ~exp(Eb/RT) (n + 4.773 mF)
V l(d - l)B 3 773rm nnmm (x - Xi)n m F J
. . . . . . . . . . '~1), ~ ,
wherein J, and m* is given by
J = [Eb (Ts ~ To) + RTs ] / ~ RTs
.` = [(760 - p ) / 760~RC,
. 20 m*= (1 + y)m,
wherein V is the nucleating volume size and is represented
by an equation of V=~LS wherein 0 is a proper constant and
Ls is the electrode gap distance, T is a temperature of the
nucleating volume, To is the temperature of the electrodes,
Xi is a molar density in 1 atmospheric pressure of incom-
bustible gases other than nitrogen, F, ~, p and Rc are
; excess air ratio, density index of molecules, absolute
value of negative pressure (mm hg) in intake pipe and
compression ratio at the time of ignition, respectively,
, . .
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;' :. l~t~6'Z42
in the gas mixture, J being practically a constant when
.~ the dependences of the singular point temperature Ts upon
~- the variable quantities V, G, Xi, F and E are sufficiently
. small, Eb is an activation energy in Arrhenius' equation,
i -
and is a constant inherent to individual fuel, n and m
: are the molecularities of reaction of fuel and oxygen,
respectively, y is a parameter showing the participation
: degree of nitrogen molecules in reaction process, ~ is a
multiplication factor of chain carriers, R is a gas
.' lO constant, B, Xt and ~ are constants, respectively.
-. The invention also consists of an automobile internal
combustion engine of lean gas mixture combustion type
including a combustion chamber, a lean gas mixture
producing device for producing lean gas mixture having
. excess air ratio of F of F> l in operation modes including
; idling, engine-braking, constant speed, acceleration and
decleration, a compressing means which compresses said lean
gas mixture containing air and fuel by varying volume of
` said combustion chamber, at least one electric spark-plug
for igniting said compressed lean gas mixture, said spark-
plug comprising a metallic screw portion to be engaged
with an internal combustion engine, an electrode terminal
part, an electric insulator for supporting said screw
.. part and said electrode terminal part in a coaxial
. relation, keeping them insulated from each other, and at
least a pair of electrodes, the pair including a first
electrode and a second electrode, said first electrode
:- being supported by a supporter formed on the metallic
screw part, said second electrode being rod-shaped and
30 electrically connected to said electrode terminal part by r
means of a central conductor disposed on the axis of said
:'
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; -` 1056242
screw part and in said insulator, said first electrode
and said second electrode being supported insulatedly
from each other by means of said insulator, keeping a
given ignition gap between their discharging faces, char~
acterized in that: fluid resistance against gas flow of
flame nucleus of said electrodes is decreased in a manner
to have an ability of ignition that is defined by ~-.
capability to ignite and burn a lean gas mixture of
. .
isobutane and air under the conditions of normal tem-
- 10 perature tT) of about 20C, the pressure of lean gas
mixture equals 1 atmospheric pressure (density index ~
approximately equal to 1), excess air ratio (F) of more
than 1.25 and electrode gap distance (Ls) of less than
2mm, so that the following ignition conditional inequality
applies thereby to decrease the thermal conductance G
from the flame nucleus to the electrodes:
G ~exp(Eb/RT) (n + 4.773 mF)
V l(d - l)B~n+m 3.773~m nnmm (X - X )n+m* Fm*J
; . . . . . . . . . .(1), ~
. wherein J, and m* are given by -
J = ~Eb (Ts ~ To) + RTs ] / ~ RT 2,
~ - [760 - p ) / 760] Rc,
m* = (1 + ~)m,
wherein V is the nucleating volume size and is represented
by an equation of V=~LS wherein ~ is a proper constant and
Ls is the electrode gap distance, T is a temperature of
the nucleating volume, To is the temperature of the
electrodes, Xi is a molar density in 1 atmospheric pressure
of incombustible gases other than nitrogen, F,~ , p and
Rc are excess air ratio, density index of molecules,
., ~ . .
516~
i absolute value of negati~e pressure (mm Hg) in intake pipe
;~ and compression ratio at the time of ignition, respectively,
. .
`; in the gas mixture, J being practically a constant when
....
~;~ the dependences of the singular point temperature Ts upon
.; ,................................................................... .
the variable quantities V, G, Xi, F and ~ are sufficiently
~- small, Eb is an activation energy in Arrhenius' equation,
. "
; and is a constant inherent to individual fuel, n and m
are the molecularities of reaction of fuel and oxygen,
respectively, y is a parameter showing the participation
degree nitrogen molecules in reaction process, ~ is a
multiplication factor of chain carriers, R is a gas constant,
B, Xt and ~ are constants, respectively.
Detailed Disclosure of the Embodiments
A new theory concerning growth or decay of the initial
flame nucleus, which determines the success or failure of
the electric spark ignition of the combustible gas mixture,
is as follows: Namely, the model of micro chain reaction
has been established to analyze the model mathematically.
Not only elements governing the ignition limit, such as
' 20 gas mixture temperature, density index of molecules,
excess air ratio F, incombustible gas density, flame t
nucleus volume, and thermal conductance G to electrodes,
but also the relationships among them have been clarified.
A new concept has been introduced wherein high speed fluid
motion named "electro-flame-wind" is caused at the time
of the spark discharging. As a result, the fluid resis-
tance of the electrodes play a principal part for the
thermal conductance G, and the electrodes, which are
adapted to have small fluid resistances, can ignite the
30 lean gas mixture. This invention is embodied, based
on this theory.
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516'~42
It is an object of this invention to provide electric
spark-plug for automobile internal combustion engines,
based on the above new theory, which is capable of directly
igniting the lean gas mixture, and antipollution automobile
internal combustion engines of lean gas mixture combustion
type which are superior in exhaust gas characteristics.
It is also an object of this invention to provide a
method of igniting an automobile internal combustion engine
of lean gas mixture combustion type, based on the above
new theory, which is the method of directly igniting the
lean gas mixture, thereby easily to realize the anti-
pollution automobile internal combustion engines which are
superior in exhaust gas characteristics.
This invention will be described hereinafter in detail
with reference to the theory and embodiments.
(A) Theory: In the following, the new theory concerning
the electric spark isnition of the combustible gas mixture
will be described in five steps. First, five steps are
summarized:
(1) first step (model of micro chain reaction)
First, th~e model of reaction scheme of the chain
combustion in the initial flame nucleus is made to establish
the equations which determine chain carrier molar density
X in the flame nucleus and the behaviour of the temperature
T.
(2) second step (derivation of ignition conditional
inequality)
The equations obtained in the above step is analyzed
by use of a known Liapunov's stability theorem to derive
the ignition conditional inequality.
(3) third step (derivation of ignition conditional
.. : .
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` 1(:1 S62,~2
,~ .
inequality expressed in the excess air ratio F)
The dependence of ignition conditional inequality
on the mixing ratio obtained in the second step is examined
- about the gas mixture composed of air, fuel, inert gases
except nitrogen to rewrite the ignition conditional
inequality in the expression of the excess air ratio F.
(4) fourth step (examination of dependence of excess
air ratio of ignition limit on each parameter)
In accordance with the ignition conditional inequality
obtained in the third step, the dependence of the ignition
limit excess air ratio, upon the gas mixture temperature T,
upon the density index ~ of molecules thereof, upon the
incombustible gas molar density Xi thereof, upon the flame
? nucleus volume V thereof, and upon the thermal conductance
; G to the electrodes, particularly the dependence upon the
flame nucleus volume V and the thermal conductance G to
the electrodes is examined in detail.
`~ (5) fifth step (relationship between thermal conductance
G and fluid resistance of electrode(s))
Finally, the proportional relationship between the
thermal conductance G and the fluid resistance ~ of the
electrodes is clarified hydrodynamically. As a result,
since the thermal conductance G becomes small proportionally
as the fluid resistance ~ becomes small, accordingly, the
lean gas mixture ignition can be possible. At the same time,
the reasons why the conventional spark-plugs can not ignite
the lean gas mixture are described. Now, the steps are
described in detail.
First Step (model of micro chàin reaction)
There exists a nucleating volume-(volume V, temperature
T), that is, a minute space, in which the enlargement of
.
,, ~ , .
:: .
i(~S6Z4
.
the pre-explosion flame (flame nucleus) formed around dis-
charge channel is limited. In this or smaller volume, no
significant local heating can take place and the molar
density of the chain carrier does not increase so fast
.:
as to cause an explosion. Assume that in the volume, the
molar densities ~mol/cm3) of the chain carrier, fuel, oxygen
and nitrogen are X, ~Xf, ~XOX and ~Xni, respectively.
~; Therein, ~ is a density index of molecules expressed in
the following equation:
; 760 - p
~ . Rc ...................................... (2),
-~ 760
wherein p is an absolute value (mm Hg) of negative pressure
in intake pipe, P~c being a compression ratio at the time
.
; of ignition.
., ~
The reaction scheme of the branched-chain combustion
in the nucleating volume is as follows.
n (fuel) + m (ox) + ym (ni) + (chain carrier) h >
(inactive products) + ~ . (chain carrier) .. (3),
(chain carrier) t > (inactive products) ......... .(4),
wherein ox is oxygen, ni is nitrogen in the air, kb and kt
are the rate constants for branching and termination,
respectively, ~ is a multiplication factor of chain carrier,
n and m are the molecularities of reaction of fuel and
oxygen, respectively (the power indices of the rate terms
of fuel molecule and of oxygen molecule, respectively, in
the rate equation of reaction). The incombustible molecules
such as nitrogen, etc. are also constituents of the
conservation system of kinetic energy and momentum produced
through the collision reaction between the fuel molecules
and the oxygen molecules. Participation of the incombustible
molecules in this conservation system is not always
:
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~s6;~4Z
,.
effected after the reaction of the fuel and the oxygen
has been terminated. Therefore, it is reasonable to
consider that the participation is performed even in the
way to the reaction. The direct participation of the
nitrogen molecules in the combustion process should be
: considered particularly under conditions where NOX, even
if very small in amount, may be produced. The number of
the nitrogen molecules participated in the reaction is
assumed to be above-described ym (ni). Generally, y is
3.773 (a molar concentration ratio of the nitrogen in
the atmosphere to the oxygen therein) or less.
From the reaction formulas (3) and (4), the kinetic
equations concerning the molar density of chain carrier and
the energy conservation equation are expressed in the
following equations (5) and (6), respectively:
dt = ~(~ - 1)( Xt) (EXoX)m(Xni)Ymk-kt~ X .......... (5),
dt pc (d-l)(Xf) (xox) (Xni) Y kaHb+ktaHt} - Vpc (T-To)
.......... (6),
wherein t is time, p is the density of the gas mixture,
CS is average sp~cific heat of the gas mixture, AHb and
aHt are the reaction enthalpy of the chain branching and
chain termination, respectively. The thermal conductance
from the nucleating volume, namely, the flame nucleus
to the spark-plug electrodes (temperature To) iS assumed
to be G. Also, the temperature dependence of k is assumed
to follow the usual Arrhenius' equation k = B exp (- Eb/RT),
(wherein B is a constant, Eb is activation energy for
branching, R is a gas constant), but kt is assumed to be
independent on the temperature.
-- 19 --
. . .
.' ' : . ~ , .;: :. ' , ' :' , : '
.. ~. - , .
-`~
l~S~ 4~
In the actual com~ustion reaction, the chain reaction
shown in the eq. (5) and the thermal reaction shown in the
eq. (6) proceeds simultaneously. Accordingly, we deal
simultaneously with the two equations (5) and (6) to
obtain the conditions of ignition, namely, the conditions
where flame nucleus will not go out. If all of Xf, XOX and
Xni are sufficiently larger than X, and the changes of
' all of Xf, XOX, and Xni are negligible as compared with
the change of X, the reaction becomes a pseudo-first
order reaction. Therefore, in this case by writing
kb = (~-l)B( ~Xf ) ( ~XOX ) ( ~Xni )Y eXP(-Eb/RT) ~ (7)~
~Hb/pCS= hb~ l~Ht/PCs ht
the equations (5) and (6) can be simplified as follows:
= (kb - kt)X ...................................... .(9),
' ldT ( bhb + ktht)X ~ VpG (T - T )
Second Step (derivation of ignition conditional inequality)
~; Since the equations (9) and (10) contain no independent
~, variable explicity on the right side, a phase ( T - X ) plane
.- method can be used to examine the behavior in a phase plane.
, 20 The following equation can be obtained by writing the left
side of the equations (9) and (10) as f and g, respectively,
g = dT = ( b b t t) VPCs ( T To) (11)
The singular points of this equation are obtained by solving
the following simultaneous equations:
~(kb ~ kt)X = 0 ....................................... (12~,
l (kbhb + ktht) X - VpC (T - To) = ~ .,,,,,,,, (13) -
We denote the coordinates of the singular points by (Xs, Ts)
- 20 -
', '~`' i~sl624~:
and X - X and T - T are used as new variables, respectively,
to enable the eq. (11) to be linearized in the neighborhood
of the singular points. So, we transform X - Xs and T - Ts
to X and T, respectively, as f and g to become both O in
the origin of the coordinates (O, O). If the f and g have
second derivatives at the origin, according to the Taylor's
theorem, the following equation should hold:
g(X, T) = g(, ) + gx(~ O)X + gT(O, O)T +
2 f xx gXT ( ~ ~ ~ ) XT + gTT ( ~ ) T 2,3 ........... ( 14 J
wherein gX = ag/aX. gT = ag~aT~ gXX = a2g/aX2. gXT = a2g/aXaT,
gTT = a g/a T , ~, = ~X, ~ T ( O <(~ <1 ) .
Accordingly, in the neighborhood of the origin, namely, in a
location where ¦X¦ and ¦T¦ are small, g(X, T) are approximated
as follows:
f(X, T) = rix + r2T~ wherein rl = gx(O, O), r2 = gT(O' )
.......... (15).
Likewise, f(X, T) is also approximated as follows:
f(X, T) = r3X + r~T, wherein r3 = fx(~ )~ r4 = fT(O, O)
.......... (16).
, . ~
20 Accordingly, the eq. (11) is expressed as follows:
dX = 1 r2T RTS (ktht + kbhb)x + (X kbEbh - ~)T
3 + 4T RTS (kb - kt) X + (XSkbEb)
.......... (17)
wherein ~ = RTS (aT{vpc (T - To)¦~ (T = Ts)
The nature of the signularity is found by examining the
characteristic equation associated with the eq. (17), i.e.,
~ (r2 + r3)~ + r2r3 - rlr4 = O -------............ (18),
21
.~ -`" lOS624;~
,
~ (r +r ) +~(r - r )2 + 4r r
the roots of which are ~ + = 2 3 2 3 1 4
.. ,
(r? + r3) --/(r - r )2- +~4r r
: 2
If ~+ and ~- are both real and differing in sign (i.e. r2r3 -
rlr4<0), that particular signularity is a "saddle point" and
. .
unstable. At this time, the T and X diverge. Physically, the
flame nucleus does not go out and the combustion spreads to
the entire gas mixture. I~amely, it means that the ignition
(explosion) occurs. The condition for this is rlr4>r2r3.
Namely, the following equation is given:
(k h + ktht)XSkbEb ~ (kb ~ kt)(xskbEb b
~5i! This is an inequality expressing the ignition (explosion)
s condition. ~ = RTS2vpGc is substituted into the above
equation and the both sides of the inequality are divided
,.
by RTS to obtain the following inequality:
kbkt(hb + ht)Xs b2 > t b G .......................... (21).
The eq. (7) is substituted into the inequality (21) and the
both sides of the inequality are multiplied by Vpcs to obtain
~- the following inequality.
b t b Ht)XSRT 2 V ~ (kt - kb) G .................... (22)
The inequality (22) can be expressed as
(~Hb + ~Ht)XSRT ~ ~ V-( kb ~ kt) ---................ (23)
One of the singularities which simultaneously satisfy the
equations (12) and (13) is obviously (Xs, Ts) = (0, To).
This is a stable nodal point, but is not a saddle point. The
relationship between Xs and Ts is obtained for another
- 22 -
1~56242
singularity (saddle point). From Xs ~ and the eq. (12)
the following equation is obtained: t
~,...
b t ~ (24)
The equation (24) is substituted into the eq. (13) to hold:
s V kt(~Hb + ~H ) ~ ................................ (25).
~: On the other hand, the termination of the chain carrier is
:
mainly due to collision deactivation against the electrode
face. Chain carriers (particles) reach the electrode face
` and are annihilated, and simultaneously the carried heat
energies are transferred to the electrode. Since the mass
flow and the heat flow are performed through the same
.; molecular mechanism, the rate constant kt of the termination
is proportional to the thermal conductance G. Since the flame
~, nucleus volume V is considered to increase in proportion to
. ~
the spark gap Ls and the electrode annihilation of the chain
carriers grows out of the end of the nucleus volume V near
the electrode face, the decreasing rate of the average
density of chain carrier over the nucleating volume is in
- inverse proportion to Ls, according to V.
The kt is given by
k _ ~ G ............................................. (26)
t V ~-
wherein ~ is a constant.
The equations (25) and (26) are substituted into the inequality
(23) to obtain the following equation:
Eb(rS - rO) + RTS > G
~ RTs V kb -----~ (2
On the other hand, from the equations (7), (24) and (26) and
under the condition of T = Ts, the following equation is
obtained:
.' .
- 23 -
.
:... ::
l~S6Z4~
~ .
exp(Hmb )=V ......................................... (28)
. s (~ - l)B(~Xf) (~XOX) (~ ni~
Although Ts depends upon V or [(~Xf)n(~XoX)m(~Xni)Ym~ 1, the
dependency of the T on them is extremely small. For example,
as typical Eb and Ts in the actual combustion reaction, in
. - the neighborhood of Eb = 50 Kcal/mol, T = 500K, if V or
Xf) (sXc ~m(~X i)Ym~ 1 increases twice, T increases only
by 1.4%. Namely, the left side in the inequality (27) can
be considered to be a constant independent from V or a
mixing ratio, and hence, by writing it as J, the ignition
condition is given by
J V kb (29)
. Considering Xni = 3.773 XOX in the atmosphere, the eq. (7) is
substituted into the inequality (29) to obtain the following
` inequality:
G exp (Eb/RT)
(d-l)B3 773Ym~n+(l+y)mxn X (l+y)m ---- (30)-
ox
Third Step (derivation of the ignition conditional inequality
of the excess air ratio representation)
The gas mixture which consists of air, fuel and incom-
bustible gases other than nitrogen is examined. The entire
molar density of the gas mixture is constant, independently
of the mixing ratio. From this condition, the following
equation is give~
Xf + XOX + Xni + Xi = Xf + 4.773 XOX + Xi Xt Co
.......... (31),
wherein Xi is the molar density of incombustible gases,
other than nitrogen, contained in the nucleating volume when
E = 1. Now, the excess air ratio F is defined as shown in the
- 24 -
. 105624Z
following equation:
F ~A/Mf
(MA/~)st ...................................... (32).
wherein MA/Mf is an air fuel ratio (a mass ratio of air to
fuel), (MA/Mf.)st is an air fuel ratio of an equivalent gas
mixture. The air fuel ratio MA/Mf can be expressed in the
following equation:
. A ox~ox ni~ni _ ox (~ox ~ni) ox ~a
Mf Xf~f Xf~f Xf ' ~f
.......... (33),
wherein the molecular weight of the fuel, oxygen, and nitrogen
are ~f~ ~ox' ~ni' respectively, and ~a = ~ox + 3 773 ~ni
On the other hand, in the equivalent gas mixture, X x/Xf = m/n
is provided, and thus the air fuel ratio of the equivalent
gas mixture is given from the eq. (33) by the following
equation:
MA m ~a
(Mf)st n ~f -------.................................. .......... (34
Resultantly, from the.equations (32), (33) and (34), F is
given by the following equation:
F n ox . ............................................ .......... (35).
Xf and X x are given, from the equations (31) and .(35), -
as the following equation:
n ( t - Xi) m(Xt - Xi)F
Xf n + 4.773 mF' Xox n + 4.773 mF - --- (36)
The eq. (36) is substituted into the inequality (30) to express
the ignition condition by the following inequality:
Gr exp Eb/RT~ (n + 4.773 mF)n+(l+Y.)m
¦(d-l)BE ( Y) 3-773~m nnm(l+l~)m (X -x )n*(l+~)mr(l+~y)mJ
.......... (1').
- 25 -
6;Z4Z
.'.,' .
This ignition conditional inequality means the easier the
ignition becomes as the smaller the right-hand side becomes.
Now, by defining Z(T, E, Y) and Y (F, Xi) as follows:
Z(T ~ Y) = exp ( b/RT) y (37)
Y(F, X ) = (n + 4.773m ~)n+(l+y)m
.773ym nnm(l+y)m(x -X )n+(l+Y)M F(l~Y)m
.......... (38),
the condition of ignition can be simplified as follows:
J > V Z (T, E ~ Y) .................................. (39).
^~ Accordingly, the ignition limit condition given by
J = V Z (T,~ , Y) ................................... (40).
;,
Fourth Step (examination of the dependence of
ignition limit excess air ratio on each parameter)
(a) With regard to parameters G and V of ignition limit
conditional equation (40).
Dependence of F of VZ in the right side of the eq. (40)
is expressed through the Y (F, Xi) in the eq. (38) and the
Z ~T, ~, Y) of the eq. (37). In Fig. 2, curves I to IV show
one example of VZ ~ FL characteristic curve group with
various numerical values of G/V which is optionally selected
to be listed in Table 2. The left side of the eq. (40) is
independent of the value F, and therefore can be expressed
by a horizontal line J. A curve I does not cross the hori-
; zontal line J. In this V = 1.000 case, the ignition is not
effected in any mixing ratio. VZ curve moves downwardly when
V is made small to 0.867, and the curve II and the horizontal
' line J comes to contact with each other at one point, thus
allowing the ignition to be effected only at the excess air
ratio of F = FR2 = FL2. If the V is made smaller to 0.743,
- 26 -
1~56~4Z
.
the V-Z curve moves further downwardly so that the curve may
cross the horizontal line J at two points, F = FR3 and FL3.
Thus, the ignitable region is FR3<F<FL3. In the case where
V = 0.629 (curve IV), the ignitable region is further
enlarged to FR4<F~FL4. Thus, if the parameter V is reduced
under a given limit, the ignitable region can be enlarged
to the lean mixture (and the rich mixture).
Table 2 (relative values of V for various curves)
~ ~.
~ urves in a b c d
\ Fig.3
\ (G=1.000Gl) (G=0.867G ) (G=0.743G ) (G=0.629G )
Curves in \ 1 1 1
_ ._ .
I (-V = 1.000) 1.000 0.867 0.743 0.629
II(V = 0.867) 1.154 1.000 0.857 0.726
- III(V- = 0.743) 1.346 1.167 1.000 0.847
IV(y = 0.629) 1.591 1.379 1.182 1.000
Accordingly, under a condition where G is constant, if
the V is made larger, the excess air ratio FL of the lean
mixture side ignition limit can be made larger and the
excess air ratio FR of the rich mixture side ignition limit
can be made smaller. On the o her hand, under a condition
where the V is constant, if the G is made smaller, the FL
can be made larger and the FR can be made smaller. This
description will be given in detail in the belowmentioned
fifth step.
Then, dependence of the FR and FL upon the V, hence,
dependence upon the electrode gap distance Ls, will be
examined hereinafter. Assume that the nucleating volume
size V is increased in proportion to the electrode gap
distance Ls, namely,
- 27 -
: - . . , -
1056Z4Z
s ....................................... (41),
wherein ~ is a proper constant. The eq. (41), t37~ and (38)
are substituted into the ignition limit conditional equation
. ~ .
~ (40) to rewrite the equation explicitly. Thus, eq. (40) is
~ . ~
rewritten:
:- J_Gz_ G exp( b/RT) (n + 4.773m FC)n+(l+y)m
V ~Ls (d l)B~n+(l+y)m 3.773Y nnm(1+~)m(Xt-Xi) Fc
.:
~ .......... (42),
I
wherein Fc is an ignition limit excess air ratio, and hence
Fc is equal to FR or FL.
Each numeral in the columns under a, b, c and d of
Table 2, shows the relative values of V calculated, respec-
tlvely, corresponding to the curves I to IV of Fig. 2 in the ~
respective cases of G = Gl, G = 0.867 Gl, G = 0.743 Gl, ;
G = 0.629 Gl. The curves a, b, c and d in Fig. 3 are
` obtainable by converting the V values of Table 2 to the
electrode gap distance Ls on the basis of the eq. (41) and
then re-plotting the ignition limit excess air ratios Fc
of Fig. 2 with respect to Ls. Such curves a, b, c and d
in Fig. 3 correspond to the a, b, c and d of Table 2.
These curves apparently shows that either of leaner mixture
gas and richer mixture gas becomes ignitable as the electrode
;~ gap distance Ls, namely nucleating volume V, increases.
Furthermore, if G is made small, the same lean gas mixture
,.:
becomes ignitable even in a narrower electrode gap distance
Ls, and also in case of the same electrode gap distance Ls,
the excess air ratio FL of the lean mixture side ignition
limit can be increased. The ignitable ~egion in the value
of each G is a shaded portion in Fig. 3. When F-0.614
(corresponding to an minimum point of the curve II in Fig. 2)
- 28 -
56Z4Z
; is established in each curve a, b, c and d, the shortest
gap distance of ignition limit Lq is provided. The Lq can
be derived as follows. The excess air ratio F* corresponding
` to the minimum point of the curve II in Fig. 2 is given,
through solving dY=O by the following equation:
F* = 4l7~3 .......................................... t43).
Referring to the eq. (42), since Ls = Lq is established
in F*=(l+y)/4.773, the Lq is expressed by the following
equation:
Lq=G ~ exp( b/RT) ~4.773 l(l+y)m
b~( l)B~n+(l+Y)m3 773 ym nnl(l+y)mJ
~ n+(l+Y)m~ ........................................ - (44)
This is the electrode gap distance corresponding to a so-
called quenching distance, which has been known experimentally.
It is found out from the eq. (44) and Fig. 3 that the gap
distance of ignition limit Lq becomes smaller as the G
becomes smaller.
- It is obvious from Fig. 3 that the ignition limit curve
~ with respect to FL portion moves leftwards and upwards, and
` the ignition limit curve with respect to FR portion moves
leftwards and downwards when G becomes small. Namely, the
ignition of the same lean gas mixture can be realized with
a narrow electrode gap distance Ls if the G is made small.
Also, in the case of the same electrode gap distance Ls,
the excess air ratio FL of the lean mixture ignition limit
can be increased.
As described hereinabove, the lean mixture ignition is
possible when the V is made small. It also is effective for
the lean mixture ignition operation to control the other
- 29 -
1~56Z42
, .
parameters T, and Y in the right side of the eq. (40~,
thereby to make Z (T, E, Y ) small.
(b) with regard to parameters T, E and Y of ignition limit
conditional equation (40)..
.
As apparent from the eq. (37), the higher the ~ of
` the gas mixture is (absolute value p of the negative
pressure in intake pipe is smaller and compression ratio
Rc is larger), or the higher the gas mixture temperature
is, then the smaller Z becomes.
Also, apparent from the eq. (38), Y becomes small as
the incombustible gas amount Xi is small. Accordingly, the
Z becomes small as is clear from the eq. (37). In these
cases, as'the characteristic curve VZ mves downwards in
Fig. 2, a point of right side intersection FL moves right-
wards so that the leaner gas mixture can be ianited.
However, as described hereinafter, the E, T and Xi
are subject to limits, depending upon the actual operating
^ modes of the internal combustion engine. During the engine
brakins operation or negative load, the absolute value of
the negati~e pressure in intake pipe becomes approximately
p = 600 mm Hg, and thus the density index E of molecules
of the gas mixture in the engine of a compression ratio
; RC=6 reaches only E = 1. 26 even at the top dead center
position of the piston. Since the compression ratio of
the internal combustion engine is normally Rc = 6 to 10, the
limit in low density indexes of molecules can be considered
E~l. Since the pressure rise accompanied by adiabatic
process is hardly produced under the condition of providing
E ~1, the limit in the gas mixture pressure, which is
disadvantageous to the ignition of the actual internal
combustion engines, is considered to be equal to 1 atmospheric
- 30 -
- lOS6~2
pressure. Since the temperature of the gas mixture is
approximately equal to atmospheric temperature during the
starting and warming-up operations of the internal combus-
tion engine, the atmospheric temperatures in very cold
districts during the winter are severe temperature conditions
to the igniting operation. However, it is difficult to
limit the conditions numerically. Since the pressure and
the mixing ratio compensate for each other, actually the
approximately 20C (room temperature or normal temperature)
can be considered as a reference temperature. ~lso, as -
.
: described hereinbefore, when the negative pressure in
intake pipe is larger, one portion of the combustion exhaust
gas flows backward (formlng automatic recirculation of
exhaust gases, self EGR) during the overlapping operation
of the exhaust and intake valves. Thus, the molar density
. ~ ,
of the incombustible gases Xi increases. Needless to say,
more Xi is increased when the EGR is used through an
: . :
external recirculation circuit. ~s described hereinbefore,
it is found out that the ~, T and Xi are limited by the
actual conditions of the internal combustion engine and the
condition of the ignition becomes disadvantageous particu-
larly during light load. -
In order to control the production of the NO during
acceleration or heavy load in the driving operation of the
internal combustion engine, namely, under the high tem-
perature of the gas mixture and/or under the high pressure
conditions, the value of F mustIbe larger than around 1.25.
It is sufficient for the antipollution combustion that the
electric spark can ignite the gas mixture of F ~ 1.25 under
30 the severest igniting condition, 1 atmospheric pressure and ;~
normal temperature. The reason why are that the combustion
- 31 -
~, . ..
s~z~;z
temperature of the lean gas mixture (F > 1.25) is low
; regardless of the operation modes of the internal com-
bustion engine and therefore is not suitable for the
condition of the NOX production, and that the excess of
oxygen in the lean gas mixture is not suitable for the
condition of production of CO and hydrocarbons.
Fifth Step (relationship between thermal conductance G and
electrode fluid resistance)
; As described in this step, the high speed fluid motion
which we called "electro-flame-wind" is caused during the
electric spark ignition in the flammable gas mixture. Accord-
ingly, the thermal conductance G from the flame nucleus
of temperature T to the electrodes of temperature To has
to be determined through hydrodynamical process.
(a) with respect to electro-flame-wind
Combustion of the gas mixture certainly accompanies
the fluid motion of gas. The combustion process is not only
a chemical phenomenon, but also a hydrodynamical phenomenon.
The thermodynamical quantities (temperature, pressure,
density, enthalpy, entropy, etc.), which are caused through
the gas fluid velocity and the combustion reaction, are
subject to laws of conservation of mass, momentum and energy.
; In the electric spark ignition, the flame nucleus is
made within the electrode gap, and co-exists with discharge
during the duration time of discharge. Thus, during this
period, the flow of the flame nucleus gases is subject to
the influence from not only the thermodynamical quantities,
but also electric fields. Namely, it has to be kept in
3~ mind that the flow of the flame nucleus gases has influences
from the electro-flame-wind in the form, size and arrangement
:
105~'4;~
.
of the electrode and the cation drag thereof, instead of
simply having normal vector of the flame surface. According
to the experiments of the inventors, voltage across the
spark, obtained from oscillogram of the discharge current
in case of the electrode gap distance Ls = 0.84 mm, is 960 V
at its initial value. Accordingly, the strength of the
electric field is estimated to be 1.27 x 10 V/cm. Using
the value of mobility 1.9 cm /V.s of N2 ion in N2 gas of
1 atmospheric pressure and 20C temperature, considering
the highest partial pressure of N2 in the gas mixture, then,
the drift velocity of N2 ion moving from positive electrode
to negative electrode becomes 217 m per second. Other ions
i have approximately the same drift velocities as the N2 ion
has. Since this drift velocity diffuses even to the neutral
molecules through viscosity, the high speed flow of gases
moving from the positive electrode to the negative electrode
is caused. This flow can not stay within the spark region
due to the continuity and viscosity of the flow.` Thus the
flow of gas phase is caused in a region around the electrode
and the spark.
This is a phenomenon known as electric wind, in
incombustible gas. In the inflammable gas mixture, the
combustion flame itself is weak plasma, and the cation in
the flame before the discharge is terminated also, acts to
strengthen the electric wind. This flow has a vector of
axial direction going from the positive electrode to the
ne~ative electrode. But the flame has a vector in the
normal direction of the flame surface, and hence, has a
radial vector which is perpendicular to a line connecting
the positive electrode and the negative electrode. Hence,
the flow which is expressed in a resultant vector of the
.
~OS6Z4'~
''.
axial vector and the radial vector is considered to ha~e
been produced in the initial stage of the electric spark
ignition, namely, within a period (3.7 ms in the above
experiment) of the current flowing. The inventors call this
flow the "electro-flame-wind". The electro-flame-wind
caused in the inflammable mixture has larger expansion
than the simple electric wind caused in incombustible
mixture has.
,;.
The electro-flame-wind is considered as a unique
high speed flow, which is different from the simple electric
~'
; wind, the torch which is flame without the electric dis-
charge, and a simple overlapping of the simple electric
wind and the torch. According to the calculations which
are based on the experimental data obtained by the inventors,
the flow speed reaches u ~ 33 m per second.
The Nusselt number Nu concerning a plate of width
w = I and length y is given by
Nu = 0.686 (Pr)3 ~ .................................. (45),
wherein Pr is the Prandtl number, ~ being kinematic viscosity.
Considering that the abovementioned equation is applicable
; even to a cylindrical electrode having flat discharge plane
of radius r = 0.05 cm, and assuming that the average tem-
perature of the flame nucleus is 1,000K, then by substituting
the Prandtl number of the air, Pr = 0.702 (at 1,000K),
the kinematic viscosity, ~ = 1.201 cm2/s (at 1,000K), and
the above-described electro-flame-wind velocity u ~ 3.3x103
cm/s into the eq. (45), Nu ~ 7.0 is obtained. Since the
physical meaning of the Nusselt number is a ratio of a
heat transfer rate in fluid to the heat transfer rate in
still fluid, the heat transport in such high speed flow has
- 34 -
.
: - lOS6iZ4Z
:
to be handled hydrodynamically,
(b) with regard to relationship between thermal
conductance G and electrode fluid resistance
(i.e., fluid dra~)
The thermal conductance G mainly depends upon the
fluid drag of the electrodes, namely, the fluid resistance
which is determined by the form, size and arrangement of
, the electrodes. The reason therefor will be described
hereinafter. Since the success or failure of the ignition
is determined by the growth or decay of the flame nucleus
of the nucleating volume V, the words "fluid drag of the
electrodes" used herein is for the flow of the flame nucleus
gas, namely, the electro-flame-wind inside the nucleating
volume.
Generally, fluid drag working upon an object in
viscous fluid is the sum of friction drag ~f and pressure
drag p.
= f + p ......................................... (46)
The pressure drag p is caused through a decrease of
surface pressure of object downstream of the point of
separation, due to boundary layer separation caused on the
object surface. The pressure distribution upstream of the
point of separation can be analyzed theoretically, while no
method of correctly analyzing the pressure distributions
is provided downstream of the point of separation, except
that actual measurement is effected.
First, a case where the electro-flame-wind is a laminar
flow and boundary layer is not separated will be described
about symmetrically opposed electrodes with flat plane. In
this case, the fluid drag of the electrodes is only the
friction drag f and can be handled analytically. As shown
- 35 -
-
. . ~ .
:
: 1056'~4Z
. . .
- in Fig. 4, (a) and (b), an x axis (abscissa) is set in
parallel to the electrode face and a y axis (ordinate~ is
set in a direction vertical to the electrode face (Fig. 4
shows the sectional view of one electrode). For brevity's
sake, assume that the thermal conductance to one electrode
- and the fluid drag due to one electrode are equal for
positive electrode and negative electrode respectively and
are 1/2 of the entire thermal conductance and the entire
fluid drag, respectively (actually, the position of nucleating
volume is not at the center of the negative electrode and
the positive electrode, but is closer to the negative
electrode due to the electro-flame-wind. Accordingly, the
thermal conductance to the negative electrode is greater than
that to the positive electrode). As shown in Fig. 4, (b),
the fluid velocity u = O is given, due to the bonding force
- between the molecule and the solid surface in y = 0 (electrode
surface). Hence, heat flow to one electrode face, namely,
heat flux density q (x), per unit area and per unit time,
is proportional to the temperature gradient (~T/~y)y=0 on the
electrode surface. Assume that k is the thermal conductivity
of the flame nucleus, then the heat flux density q(x) is
given by
q(x) = - K (ay)y=o ............................ ,.,, (47)~ ~
and (aT/ay)y=0 is approximated as follows:
(aay)y=0 X ~ .................................. ......(48),
wherein T is temperature of the flame nucleus gas in the
offing of the electrodes, To is electrode temperature, and
~T(X) is the thickness of a thermal boundary layer (region
in which a temperature gradient exists) as shown in Fig. 4(a).
The ~T(x) is given by the following equation, wherein in the
- 36 -
~, , ' , ' .:
:
~, - lOS6~,4Z
.... . .
laminar flow, the temperature conductivity of the fluid
is x, the fluid viscosity at the offing being u
; Accordingly, from the equations (47), (48) and (49), the
total heat flow Q which flows, per unit time, to the
symmetrically opposed electrodes with flat plane of width
w = 1, and length x = Q is given, by the following equation:
. . .
. Q
. Q = 2 IO q(x)dx ~ -2~ (T-To)lO ~ dx ................. (50).
. On the other hand, the friction drag per unit area
10 a (x) of one~electrode is the flow of momentum per unit area
i and per unit time, and therefore is proportional to the
velocity gradient (au/ay)y 0 on the electrode surface. The
fractional drag a(x) is given by the following equation, wherein
. ~ is the viscosity:
~: ~(x) = -t (a~)y=o --------------.-.................. (51).
. The (a u/ay)y=o is approximated as follows:
' au
(a Y)y=o x ~ - - - - - - - - - .. - ................................... (52).
~ The ~v(x) is the thickness of hydrodynamic boundary layer
(region in which velocity gradient exists) as shown in Fig. 4,
(b) and is given by:
Accordingly, from the equations (51), (52) and (53), the
friction drag f which works upon the opposed electrodes
.` with flat plane of width w = 1, length x = Q is given by the
following equation:
Q Q
= 2lo ~(x)dx ~ -2~ulo ~ ( ) dx ....................................... (54)-
.
- 37 -
. . , . ~
- . . ~ . .
~0~6;~4Z
From the equations (49) and (53), the following equation is
given:
~T(x) ~ ~v(x) = - ~ (x) ............................ (55),
wherein Pr is the Prandtl number. Accordingly, from the
equations (50), (54) and (55), the following equation is
given:
Q ~ r (T To)~ ....................................... (56).
On the other hand, the thermal conductance G iB defined by
Q = G (T-To) (57)
From the equations (56) and (57), the relationship between
the thermal conductance G and the friction drag ~f is given by:
~ u i ........................................... (58).
Even when the electro-flame-wind on the flat plane electrode
is originally turbulent flow, the following relation is
given between the q(x),~and a(x) due to Reynolds analogy, t
q(x) ~ P( )a(x) ..................................... (59),
wherein T and u are the average temperature and average
speed of the turbulent flow, respectively, and Cp is specific
heat at constant pressure. Therefore, even in the turbulent
flow as in the laminar flow, the relationship between the
thermal conductance G and the fraction drag ~f is given by
G ~ Cp ~j ........................................... (60)
Independently of the laminar flow or the turbulent flow,
the thermal conductance G is proportional to the friction :
drag ~f of the electrodes, when the flow velocities u & u
are under a given constant condition and the fluid drag
consists only of the friction drag. By substituting the
- 38 -
.
-- lOti6~
- eq. (53) into the e~. (54) and effecting the integration,
the following equation is giyen:
3 1
.' ~ ~ 4~u2Q2
v 2
It is found out from the above equation that, in the
electrodes with flat discharging plane, as the length Q
decreases, the friction drag ~f with respect to the flow
:
of the flame nucleus gas decreases in proportion to ~-.
.,~
~ As a result, the thermal conductance G is in proportion
-to ~ and thus the condition of the ignition is improved
,10 as can be understood from the inequality (1). Generally
speaking, in the electrode with flat discharging plane,
;~f and G decrease as dimensions, which govern the fluid
resistance with respect to the flow of the flame nucleus
gas, decrease, and therefore, the condition of the ignition
is improved, thus allowing the lean gas mixture to be
ignited and burned effectively. It is too complex precisely
and perfectly to indicate the abovementioned "dimensions".
But, for the electrode arrangement that end face is the
discharging face~ the "dimensions" can be indicated or
represented by diameter for circular cylinder, by length
of diagonal for square section cylinder or by length of
the longest diagonal for polygonal section cylinder.
.
The above description is given only about the frictional
drag ~f in the fluid drag ~ of the electrodes. In the case
of the electrode having flat discharging plane with edges
on the ends of discharge plane of the electrode, the
separation of the boundary layer occurs at the edges.
Thus, wakes of the turbulent flow type are likely to be
caused around the separated boundary layer. Viscosity,
- 39 -
,
~OS~i~4Z
.-
diffusion and thermal conduction are phenomena wherein
momentum, constituent molecules and kinetic energy are
transported by molecular motion, respectively, but the
turbvlence transport, the momentum, the constituent
molecules and the kinetic energy in extremely large scale
(eddy transport). Accordingly, in the turbulence, apparent
coefficient of viscosity, apparent diffusion coefficient
and apparent thermal conductivity which are called as
eddy viscosity, eddy mass diffusivity and eddy thermal
diffusivity, respectively, become extremely large in value.
Thus, when the turbulent flow is caused, the pressure drag
} ~p is produced and is added to the friction drag ~f. There- t
fore, the total fluid drag ~ _ ~f + ~p increases, thus
.~
`~ resulting in remarkable increase of the thermal conductance
G, which remarkably deteriorates the condition of the
ignition.
On the other hand, even in a thick electrode, if the
discharging plane is made convex (streamline shape, without
discontinuous edge such boundary layer separation as
described hereinabove, namely, the turbulent flow occurrence
can be prevented. Since the pressure drag ~p is hardly -
caused, the total fluid drag ~ decreases by the amount of
~p(~=~p+~f~f)/ thereby effectively decreasing the thermal
conductance G. As the thermal conductance G becomes also
small, effectively, the condition of the ignition is
improved remarkably. If the elèctrode is made streamline
and thin in shape, the ~f is further decreased, thus
resulting in further improving igniting conditions.
(c) Reasons why the conventional spark-plug can not
ignite lean gas- mixture./
The streamline of the electro-flame-wind in the
.
- 40 -
.: -- . :
.
- 105~6,'1;:4Z
; conventional type of spark-plug as shown in Fig. 5 is shown
in section, in Fig. 41, (a~ and the structure of the boundary
layers accompanied in this flow is shown in section, in
Fig. 41, (a'). The boundary layer is supposed to be in
;~ such a shape, as in Bl, in the front face of the positive
electrode 21 and in such a shape, as in B2, in the front
face of the negative electrode 22, in accordance with the
equations (49) or (53). As apparent from the above
description, the friction drag ~f increases when the
streamline passes through the boundary layer. As a wide
plate, namely, of large in dimensions Q, is used for the
positive electrode 21, the boundary layer Bl is thick and the
~f is large. Besides, the streamline with a mark * in Fig.
41, (a) shows the wake of turbulent flow type. The
turbulent flow caused on the side face and the rear side of
; the positive electrode 21 is large on scale and the
pressure drag~p also increases remarkably. As a result,
the fluid drag ~=~f+~p~ hence, the thermal conductance G
; from the flame nucleus to the electrode is large, and the
establishment of the ignition limit conditional inequality
(1) becomes hard. Thus, such a conventional type of spark- -
plug as shown in Fig. 5 can not sufficiently ignite the lean
gas mixture as apparent from the curve W of Fig. 42 showing
the ignition limit excess air ratio FL and electrode gap
distance Ls characteristics.
On the other hand, as shown in Fig. 6, the FL ~ Ls
characteristic curve W' of the conventional type of spark
plug lies on the left hand of the curve W, thus resulting
in some improvements. However, W' does not go upwardly,
being different in quality from the behavior of Fig. 3,
wherein the ignition limit characteristic curves displace
.:
~, . . . :
i
''
10~6Z4Z
;'`''' ' '
leftwardly and simultaneously upwardly when G is made small
as shown in Fig. 3. This fact will be described hereinafter.
Namely, the spark-plug of the curves W' is provlded with
uneven grounded-electrode having U-shaped groove on a
rectangular parallelepiped plate hence having many edges as
shown in Fig. 6. Accordingly, these edges are likely to
, .
'-; separate the boundary layer to cause the turbulent flow,
; and therefore the percentage of the pressure drag ~ in the
fluid drag ~ is large. The pressure drag ~ is given by the
following equation, wherein p is fluid density, u is flow
velocity, Q is the "dimensions" of the object and ~ is a
factor related to the shape of the object.
u2Q2 ......................................... (62).
As described hereinbefore the pressure drag ~p increases in
proportion to the square of the flow velocity u (Newton's
i~ law of resistanceJ.
Next, the dependency on spark gap Ls f the electro-
flame-wind velocity u will be described. Discharge current
is shows exponential decay concerning time t as follows:
i = io exp (~T / T), (io: discharge;current in t=O,T:decay
time constant for discharge). T = 2.27 ms for LS=0.84 mm,
and T = 1. 93 ms for IS=1.56 mm have been obtained from the
oscillogram analysis of the is under a given condition of
discharge energy. Namely, as the electrode gap distance Ls
is made larger, the discharging ceases in a shorter time,
and thus the energy consumption rate (speed) increases.
Since one portion of the discharge energy is converted,
into the kinetic energy of the electro-flame-wind, which is
greatly subject to the influences from the cation drag, an
increase in the energy consumption rate causes the increase
in the electro-flame-wind velocity u. Accordingly, an
- 42 -
. ~ ' , .
~ .
` ~os~jz4z
increase of the electrode gap distance Ls causes an increase
of the electric flame fluid velocity u, and therefore in
accordance with the eq. (62) the pressu-e drag ~p, hence,
the thermal conductance G increases. In the conventional
type of spark-plug as shown in Fig. 6, the characteristic
curves of the excess air ratio FL of lean mixture side
ignition limit vs, electrode gap distance Ls of Fig. 3 are
plotted for various G as parameter. Therefore, as Ls
increases, the operation point moves from curve to curve
as d -~ c -~ b -~ a in Fig. 3. As a result, the upward
movement of the FL ~ Ls characteristic curves is prevented
remarkably. Accordingly, the characteristic shown in
,
the curve r~ of Fig. 42 are provided, thus making easy
ignition of the lean gas mixture hard. The result of the
abovementioned theoretical analysïs is as follows. When
the electrodes of the spark-plug has the form, size and
arrangement for decreasing the fluid resistance against the
; electro-flame-wind contained inside the nucleating volume,
then the thermal conductance G can be made small, thus
increasing the excess air ratio FL of the lean mixture
ignition limit in accordance with the relationship of the
inequality (1). In the conventional spark-plug, the fluid
resistance of the electrode with respect to the electro-
flame-wind has not been taken into consideration and the
thermal conductance G has been large, and hence the spark-
plug itself has had a flame-arrestive characteristic so that
the flame nucleus once made has been liable for the
annihilation.
From the theoretical analysis of the above description,
the requirements on the form, size and arrangement of the
electrodes which allow the spark-plug to ignite the'lean gas
- 43 -
:`
" 1~5;6Z42 t
mixture are found as follows;
(1) The positive and negative electrodes shall be thin
and be disposed in coaxial relation so that the axes of
both electrodes may be aligned in line with each other.
For the electrodes of the present invention, thin
electrodes, for instance, rod-shaped or cylindrical
electrodes can be used as elucidated hereinafter referring
to the examples. Hereinafter, the word "rod" is used to
imply a cylinder or analogous one which includes any types
of cylinder, for instance, circular cylinder, square section
cylinder (square prism), polygonal section cylinder, etc.
or slightly tapered cylinders wherein one bottom is slightly
larger than the other.
(2) At least one of the electrodes shall have discharging
~- face made convex surface (in streamline shape) and be
disposed in coaxial.
- (B) Embodiment: ~
: '
First, the condition for experiments to obtain the
excess air ratio Fc of ignition limit (especially, to
obtain the excess air ratio FL of the ignition limit for
the lean mixture side) in each embodiment of the present
invention will be described.
In order to precisely obtain the excess air ratio
FL of ignition limit (degree of leanness of fuel), isobutane
of 100% in degree of vaporization was used. The isobutane
is a component of liquefied petroleum gas (LPG) having the
ignition temperature 673K which is above the ignition
temperature about 523K for gasoline. Accordingly, the
isobutane is usable as sample fuel in this experiment.
For power supply, an apparatus which generates peak
voltage of 35KV at no-load by operating an ignition coil
56Z42
.
(rating: primary coil for 12 V, 4.1A, inductance of 8.58 mH,
- stored energy 72 mJ) by means of a transistor switch was used.
.,
The power supply was connected to the spark-plug from the
positive terminal to the grounded electrode (a first electrode)
, of the spark-plug and from the negative terminal to the
: high-tension electrode (a second electrode).
It is desirable that electrode gap distance is 0.8 mm
.~,.
or less when the ordinary ignition power supply of the
internal combustion engine is used. From measurements and
calculations, the "dimensions" of the electrodes of the
spark-plug, which allows the characteristic curves of the
excess air ratio of ignition limit FL vs. the spark gap
s to cross an equivalent air fuel ratio straight line X
~ when Ls-0.8mm, are obtained as described hereinafter.
i` Namely, for the electrode of which front end is a discharging
face, 1.7 mm of diameter when the cross-sectional view of
the electrode was circular, and 1.7mm of diagonal line when
`~ the cross-sectional view thereof is rectangular are to be
used as the dimensions. For the electrode, of which side
face is the discharging face, 1.2mm width and 2mm of
thickness are to be used as the dimensions. The width used
here is the size of the electrode face measured in the
direction having right angle to the discharging direction
and in the widthwise direction of the electrode, while the
thickness used here is the size of the rod-shaped electrode
along the discharging direction.
Therefore, according to the present invention, in a
rod-shaped electrode, in which the front end is of discharging
face, the diameter should be 1.7mm or less if the cross-
sectional plane of the electrode is circular, and thediagonal line should be 1.7mm or less if the cross-sectional
- 45 -
10~i6Z4Z
.~
plane thereof is rectangular, in the rod-shaped electrode,
in which a side face is of discharging plane, the width
should be 1.2mm or less, and the thickness should be 2mm or
less.
The automobile internal combustion engines of lean gas
mixture combustion type according to this invention comprises
a combustion chamber, a lean gas mixture producing device for
producing the lean gas mixture having F>l in operation modes
including idling, engine-braking, constant speed, acceleration
and deceleration, a compressing means for compressing lean
gas mixture containing air and fuel by varying volume of the
combustion chamber and at least one electric spark-plug for
igniting the compressed lean gas mixture.
The abovementioned spark-plug can be constructed as
described in the following.
The following examples 1 to 4 relate to spark-plugs
comprising a pair of rod-shaped electrodes each with flat
discharging face, for first and second electro`des.
Example 1 (Fig. 7)
As shown in Fig. 7, (a), (b), (c) and Table 3, the
spark-plug 200 of the present invention comprises a
metallic screw part 29 to be engaged with the internal
combustion engine, an electrode terminal part 27, an
insulator 24 for supporting the above-mentioned screw
part and the electrode terminal part in given relative
positions, keeping them insulated from each other, and a
pair of electrodes, namely a first electrode 21 and a second
electrode 22. The first electrode is installed on a
supporter 23 which is mounted on the metal screw part 29.
The second electrode 22 is a rod-shaped member, which is
electrically-connected to the electrode terminal part 27 by
- 46 -
``:
)5~4Z
~' .
means of a central conductor 26, and is arranged in parallel
; with the central axis of the metallic screw part 29 and
~- is supported by means of the insulator 24, so that a given
ignition gap distance is provided between the given part
on the first electrode 21 and the rod-shaped member 22.
' Numeral 28 designate a gasket.
The first electrode 21 is a rod-shaped electrode, which
':
is projected, by a given height hi, e.g. lmm, from the end
of supporter 23 made of heat-resisting nickel alloy, etc.,
towards the second electrode 22, in the direction of the central
axis of the metallic screw part 29 having at its front end,
` a discharging plane normal to the central axis. The first
electrode is installed on the supporter 23 through methods
of welding, driving, forced insertion, or caulking after
insertion, etc. In order to simplify the machining operation,
; it is recommended that the first electrode 21 and the
supporter 23 should be composed of a continuous member.
The above-mentioned structure and machining can be applied
even to the spark-plugs of Examples 2 to 17 given herein-
after. The second electrode 22 is a rod-shaped electrode,
which is projected, by a given height h2, e.g. lmm, from
the end of insulator 24 and has a discharging plane normal
to the central axis. The first and second electrodes 21
and 22 are disposed coaxially with spark gap of, for
example, 1.28mm inbetween.
In the present embodiment, when a rod-shaped electrode
of from 1.7mm to 0.3mm in diameter and preferably, about
; lmm in diameter are used, it is desirable for the sake of
durability, to use noble metals, which are superior in heat
resisting and electro-corrosion resisting properties, such
as Pt, Pd, Au, or alloy thereof.
- 47 -
: ~05~iZ4Z
In the spark-plug in this e~bodiment, both electrodes
have small diameters, respectively. As shown in ~ig. 41,
(b'), both boundary layers Bl and B2 are thin and the
friction drag ~f is small as apparent from the eq. (61).
Therefore, from the equations (58) and (60), the thermal
conductance G from the flame nucleus to the electrodes
becomes small. As a result, the condition of ignition is
improved as is indicated by the inequality (1). The FL-L
characteristic curve A of Fig. 42 (The curve A corresponds
to a case where the projection height of grounded electrode
hl = 1 mm and the raised height of high-tension electrode
h2 = lmm, as shown in the line A of Table 3) of the spark-
plug of this embodiment lies remarkably on the left-upward
position as compared with the characteristic curves W & W'
of the conventional spark-plug.
As described hereinbefore, the condition of ignition is
remarkably improved when both electrodes 21 and 22 are
; projected and raised from the supporter 23 and the insulator
24, resepctively. The degree of the improvements depend
upon the projection height hl and~or h2 as described hereinafter.
The speed (u) of the electro-flame-wind produced in a
position in the electrode gap decreases as the position
departs farther from the gap. Accordingly, the thickness
~3 of a boundary layer which is formed on the surface of
the supporter 23 is considerably large as compared with the
respective thickness ~1 and ~2~of boundary layers Bl and B2.
The influences of ~ at least, on viscosity frictional loss
can be neglected under the condition of hl + ~1 > ~3. There-
fore, only the electrode thickness effect Q should be
considered. Accordingly, the ignition limit air fuel ratio
FL must be almost saturated for above a given critical
,
- 4~ -
: ~5624Z
projection height hl. Inversely, in the projection height
hl under the condition of
hl + ~ 3,
the effect of the viscosity frictional loss due to the thick
boundary layer of ~3 thickness along the supporter 23 exists,
and thus the ignition limit air fuel ratio FL depends upon
the projection height hl. The results of the experiments
by which the above description is proved are shown in Fig.
46 and in Table 3, lines Al to A6. Fig. 46 shows the experi-
mental results measured concerning the relation between the
projection height hl of the first electrode and the ignition
; limit air fuel ratio FL of the spark-plug shown in Fig. 7,
with the spark gap Ls as a parameter. In the experiments,
a metal-plate supporter 2.7mm wide, about 5mm long is used
as the supporter 23, while the cylindrical electrodes of lmm
in diameter are used as the first electrode 21 and the
second electrode 22, respectively. The raised height h2 of
the second electrode is lmm. Also, in Fig. 46, curve Ul
shows the measured results of Ls = 0.85 mm; curve U2, Ls=0.9mm;
curve U3, Ls=l.Omm; curve U4, Ls=1.25mm; curve U5, Ls=l.Smm;
and curve U6, Ls=2.0mm, respectively. As apparent from Fig~
46, in each characteristic curve, the ignition limit excess
air ratio FL i5 almost saturated for the range of hl > 0.25mm.
Namely, the critical value of hl is hl=0.25mm. Thus, it is
desirable for the projection height hl to be larger than 0.25mm
to ignite the lean mixture. Since the end of the supporter
23 (Fig. 41(b')) is retreated from the electrode gap by hl,
the turbulent flow is difficult to be produced on the side
face and the rear side. Accordingly, the pressure drag ~p,
hence thermal conductance G decreases further and the curve
A of Fig. 42 goes further leftwards and upwards with respect
- 49 -
` ~ ~ lOS6~4Z
to the curves W and Wl of Fig 42. Accordingly, the leaner
~as mixture can be ignited.
The effect of projection of the first electrode 21
from the supporter 23 as described hereinbefore is similarly
realized, if the second electrode 22 is raised from the end
of insulator 24.
Examples 2 to 17 which will be described hereinafter
relate to spark-plug, with first electxode 21 and the second
electrode 22 both raised from the supporter 23 and the
insulator 24 by 0.25mm or more, respectively. Accordingly,
in the examples 2 to 17, given hereinafter, the forms,
sizes and arrangements of the electrodes only and effects
thereof will be described, omltting descriptions on common
items.
. . .
~ Referring to the drawings of the spark-plug in all
.:.
examples, the same reference marks and numerals as those
- for Example 1 will be given to all the corresponding
~ components.
.; .
Example 2 (Fig. 8)
~~ 20 The spark-plug in this embodiment shown in Fig. 8, (a)
and (b) has two pairs of electrodes. A pair of first
electrodes 21, and 21 are rod-shaped electrodes, which are - -
projected from the supporters 23 and 23 by a given height
.
~-~ hl, respectively, towards a second electrode 22 and 22, in
the direction normal to the central axis of the metallic
screw part 29. The electrodes have in their front end,
discharging faces in parallel with the axis, respectively.
The second electrodes 22 and 22 are rod-shaped electrodes,
which are raised by a given height h2, from the central axis
` 30 26 in the direction vertical to the axis and have a dis-
charging planes in parallel to the axis, respectively. The
- 50 -
,
,
~OS624Z
first electrodes 21 and 21 and the second electrodes 22
and 22 are disposed to allow their discharging planes to
face each other, respectively, with the electrode gap
distance Ls between each pair of the electrodes 21 and 22.
By providing two pairs of electrodes, the spark-plug of this
embodiment has an advantage, in terms of durability (service
life), of having longer life ~han the spark-plug of Fig. 7
(Example 1). It is also recommendable that three pairs of
electrodes or more should be provided to obtain further
increased service life.
Example 3 (Fig. 9)
. .
In the spark-plug of this embodiment shown in Fig. 9,
a first electrode 21 is a rod-shaped electrode, which is
projected by a given height from a supporter 23 towards
below the second electrode 22 in the direction vertical to
the central axis of the metallic screw part 29, and has
~ ,.
discharging face on its upper side face, while the second
electrode 22 is a rod-shaped electrode, which is raised,
by a given height, from an insulator 24, and has, at its
front end, a discharging face normal to the axis. The
lengthwise axis of the first and the second rod-shaped
electrodes 21 and 22 are disposed at right angle with
each other. As apparent from the value in line B, column
Ls* of Table 3, the effects similar to those of Example 1
are obtained by this spark-plug.
Example 4 (Fig. 10)
As shown in Fig. 10 and Table 3, C line, in the spark-
plug of this embodiment, a first electrode 21 is a rod-
shaped electrode, which is projected, by a given height, from
a supporter 23, towards a second electrode 22, in the
direction parallel to the central axis of the metallic screw
; :
~ lVS6Z4Z
part 29, and has on its side face, a discharging plane which
is parallel to the axis,while the second electrode 22 is a
rod-shaped electrode, which is pro,ected, by a given height,
from an insulator 24 and has, on its side face, a discharging
` plane parallel to the axis. The first and second rod-shaped
electrodes 21 and 22 are disposed in parallel to each other
with their discharging faces of respective given lengths
QQ (for example lmm) opposing to each other. The opposing
lengths QQ of both electrodes are determined through con-
sideration of electro-corrosion-resisting property, namely,
service life. As apparent from the value of Table 3, line
C, column Ls*, the effects similar to those of the Example
~ 1 are obtainable also by this example. In this spark-plug,
-~ area of discharging face increases in proportion to the
opposing lengths QQ of both electrodes. Accordingly, the
spark-plug in this Example 4 is superior, in electro-corrosion
resistivity.
In the rectangular type spark-plug of the Example 3
(Fig. 9), one of the electrodes, or a first electrode is
shaped so as to have its axis having right angle with
sparking lines. Accordingly, the boundary layer Bl shown
in Fig. 41, (b'), spreads, also to the axial direction
of the electrode. Also, in the spark-plug of Example 4
(Fig. 10), both electrodes have their axis at right angles
with the sparking lines, and thus the boundary layers Bl
and B2 spread also in the axial direction of the electrode.
Therefore, the friction drag ~f increases.
Accordingly, from the equations (61), (58), and -
inequality (1) and from the experimental results, it is
generally obvious that establishment of the ignition
condition is more advantageous for the right-angle-arranged
~ .
S6'~,4Z
, rod electrodes type than that of a parallel rod electrodes
type, and further advantageous for coaxial-arranged rod
;, .
electrodes type. The effect of this electrodes arrangements
are also obtainable in the following examples 5 to 17.
.
Table 3 (Examples 1, 3 and 4)
Dimensions Dimensions
Marks of (mm) of (mm) of
; F -Ls Electrodes Grounded High-Tension
C~aracter- Types of Arrange- Electrode Electrode L *
10 istic ~lectrodes ment (First (Second s
Curves Electrode 21) Electrode 22)(mm)
. . _
A Fig. 7coaxial 1.0 diameter 1.0 diameter 1.28
1.0 hl 1.0 h2
(Al) Fig. 7 - 2.7 width 1.0 diameter
1.3 thickness 1.0 h 2.28
5 length 2
:~ O hl
(A2) Fig. 7coaxial 1.0 diameter 1.0 diameter 2.06
0.07 hl 1.0 h2
~:i 20 ( 3) Fig. 7coaxial 1.0 diameter 1.0 diameter
; 0.14 hl 1.0 h2 1.81
(A4) Fig. 7 coaxial 1.0 diameter 1.0 diameter
0.25 hl 1.0 h2 1.59
(A5) Fig. 7 coaxial 1.0 diameter 1.0 diameter
0.5 hl 1.0 h2 1.45
(A8) Fig. 7 coaxial 1.0 diameter 1.0 diameter
2.0 hl 1.0 h2 1.28
(B5) Fig. 9 with right 1.0 width
angle 0.62 thick- 1.0 diameter 1.52
ness
5 length
(C)Fig. 10 parallel 1.0 width 1.0 width
(with 0.62 thick- 1.0 thick-
opposing ness nesS 1.52
lengths 5 length 5 length
QQ=l.Omm)
Note: Curves for (Al) to (A6), (B5) and (C) are almost
analogous to that of A, and therefore, are not shown
in the graphs.
The belowmentioned examples 5 to 11 relate to spark-plugs ,-
each comprising the first and second electrodes, at least one
- 53 -
:: ~
: - 1056Z4J2
of which has convex discharging face.
Example 5 (Figs. 11 to 13 and 15~
As shown in Fig. 11, in the spark-plug of this embodiment,
a first electrode 21 is an electrode, which is projected by
",
a given height hl towards below a second electrode 22 in the
axial direciion, and has at its front end a flat discharging
face with right angle with the axis, while a second
electrode 22 is an electrode, which is projected, by a
given height h2 from an insulator 24 and has at its front
end a convex discharging face. And the first and second
electrodes 21 and 22 are disposed coaxially with each other.
In order to provide further imrpoved ignition char-
'~ acteristics, it is recommended that both electrodes should
have convex discharging faces at respective front end as
shown in Fig. 12, and Fig. 13.
As shown in Fig. 41, (c) and (c'), the boundary layers
Bl and B2 concerning the electro-flame-wind on the electrodes
of the spark-plug of, for instance, Fig. 12 are both
retreated with respect to and from the flame nucleus space,
the dimensions Q effectively become small and friction drag
` ~f decreases. Simultaneously, both electrodes are stream-
lined, thus resulting in smaller occurrence of the turbulent
flow, and the pressure drag ~p is extremely reduced. Accord-
ingly, the fluid drag ~ = ~f + ~p and the thermal conductance
G becomes small, and the FL-LS characteristic curve consider-
ably moves leftward and upward with respect to the curve
W as shown in Fig. 42, curves E3 and E6. Therefore, suf-
ficiently lean gas mixture can be ignited. The above-
mentioned effect of retreating the boundary layer increases
as the curvature v of the discharging plane increases.
The above conclusion is apparent from the F~-LS characteristic
- 54 -
; ~
05;6Z4Z
curves Eo to E3 of Fig. 43 and Fi~. 4 7, which indic~tes
that in the practical range of an electrode gap Ls of less
- than 2mm, the excess air ratio of ignition limit rapidly
increases with the curvature V and saturates in the region ;
~.`' around the numerical value 0.46mm 1 of curvature. Curves
:
Eo to E3 are for the cases of various curvatures Eo to E3
shown by Fig. 15 and in Table 4 lines Eo to E3, column C.
Fig. 43 shows measured characteristic curves indicating
the relationship between the ignition limit excess air ratio
10 FL and the electrode gas distance L , in a case where the
electrodes have diameters fixed at 2. 55 mm, and the curvature
; v only on the discharging face of the electrode front end
is changed variably as shown in Table 4. Fig. 47 shows
measured characteristic curves of dependence the excess
air ratio FL of ignition limit upon the curvature v of the
electrode discharging face with the electrode gap distance
~ Ls for the curves Eo to E3 of Eig. 43 as a parameter. In
; Fig. 43, only the curve E3 lles above the curves Eo~ El
and E2. In the electrode of the curve E3, the front end
20 discharging face is of a hemispherical type and connects
with cylindrical side face smoothly without edge, accordingly
no turbulent flow is produced. On the other hand, as shown
in Fig. 15, in the electrodes of the curves Eo, El and E2,
the convex discharging faces and the electrode side faces t
make edges inbetween, so that a turbulent flow are caused.
Needless to say, it is understood from Fig. 42, curve
D, that the ignition characteristics of the aforementioned
spark-plug of a type shown Fig. 11 and in Table 4, line D
is between those of the spark-plugs represented by the above-
30 mentioned curves E3 and Eo~
From comparison of curves E3 to E6 it is apparent that
- 55 -
- 10~24Z
.: , .
the condition of the ignition is further improved when the
electrode diameter is made small and the curvature v on the
discharging face is made great.
` In this embodiment of Figs. 11 to 13 the first electrode
21 is projectedly secured to the supporter 23 by such a
method described in Example 1.
;:.j
Example 6 (Fig. 14)
As shown in Fig. 14, the spark-plug of this embodiment
is analogous to the spark-plug in Fig. 12 in the Example 5.
That is, a first electrode 21 is an electrode, which is
projected by a given height hl towards below a second electrode
22 in the axial direction, and has at its front end, a
. .
convex discharging face, while a second electrode 22 is an
electrode, which is projected, by a given height h2 from an
. . .
insulator 24 and has at its front end a convex discharging
face. And the first and second electrodes 21 and 22 are
" disposed coaxially with each other.
In this embodiment, the first electrode 21 is projected,
on supporter 23, to form a convex discharging face through
a knock-out method. Accordingly, the present example has
an advantage of easy manufacture.
,:
Example 7 (Figs. 17 to 21)
As shown in Figs. 17 to 21, a first electrode 21 is
projected from a supporter 23 by a given height, towards
below a second electrode 22 vertically-with respect to the
axis, and has on its side face, a convex discharging face,
while a second electrode 22 is projected from an electric
insulator 24 by a given height, and has at its front end,
a convex discharging face. Thus, a tip side face of the
first electrode faces the end of the second electrode and
axes of both electrodes are disposed at right angle with respect
- 56 -
; l~S624Z
to each other. As apparent from ~alues in Table 4, Gl to
- G3 lines, column LS , similar effects to those of Fig. 12
and Fig. 13 (Example 5 with both electrodes with convex
discharging faces) are obtainable. As described hereinbefore,
the spread of the electro-flame-wind is large enough to reach
the rear face of the discharging plane. Accordingly, it is
advantageous to use a streamline-shaped electrode for
preventing occurrence of turbulence and resulting in effective
improvements of the ignition condition. And the streamline-
shaped electrode should have smooth curved convex face,
wherein the discharging face is smoothly connected with the
circumferential side part of the electrode. Similarly, it
is desirable that the front end part and adjacent part of
the electric insulator 24 and screw portion 29, where the
electro-flame-wind or the flame nucleus during its growing
stage contact, should be formed with gently-curved surfaces
as shown in Figs. 13, 20 and 21. The first electrode 21
and the supporter 23 are formed in such continuous shape as
in Fig. 19, and therefore are manufactured easily through
20 a drawing using a drawing die.
Example 8 (Fig. 22)
As shown in Fig. 22, in the spark-plug of this embodi- t
ment, a first electrode 21 is projected, by a given height,
towards a second electrode 22 in a direction parallel to
the central axis of the metallic screw part 29, and has,
on its side face, a convex discharging face, while a second
electrode is projected, by a given height, from an electric
insulator 24, and has, on its side face, a convex discharging
face. The first and second electrodes 21 and 22 are dis-
30 posed in parallel relation with given opposing lengths QQ
(for example, 2mm excepting hemispherical end parts) between
- 57 -
-: : - ~ '' ' . :
- ~
~OS624Z
,.
the electrodes. As apparent from the Ls* value of lines
Hl, H2 of Table 4, the effects similar to those of Figs.
12 and 13 (Example 5) are obtainable. The opposing lengths
QQ of electrodes 21 and 22 should be determined through
consideration of electro-corrosion resisting properties,
i.e., service life.
Example 9 (Fig. 23)
. . .
As shown in Fig. 23, in the spark-plug of this embodi-
,; ment, a first electrode 21 is projected from a supporter 23
.
by a given height, in a direction vertical to the axis
towards below a second electrode 22 and has on its side
` face (actually, upper face), a convex discharging face, while
the second electrode 22 is a rod-shaped electrode projected
from an electric insulator 24 by a given height, and has at
. .
its front end, a flat discharging face, and the axes of the
first and the second electrodes 21 and 22 have right angle
.,: -
~, between each other. The spark-plug of this example is
formed by a combination of a rod-shaped second electrode
22 with small friction drag ~f, and a streamlined first
electrode 21 with small friction drag ~f and pressure drag
~p. As shown in the Ls value of lines Il, I2 of Table 4,
,.
the condition of ignition is improved through combined
operation of the both electrodes.
Example 10 (Fig. 24)
As shown in Fig. 24, in the spark-plug of the embodiment,
a first electrode 21 is a rod-shaped electrode, which is
projected vertically, by a given height,-towards below a
second electrode 22 in a direction vertical to the central
axis of the metallic screw part 29 and has, on its side
face, a flat discharging face having right angle to the
axis, while a second electrode is an electrode, which is
:
- 58 -
. .
~ ;
-` 10~6Z4Z
.: ,
projected, by a given height, from an electric insulator
24, and has at its front end, a convex discharging face.
The first and second electrodes axe disposed at right angle
with each other. In the spark-plug in this embodiment has
a combination of thin first electrode with small friction
; drag ~f and streamlined second electrode with small friction
drag ~f and pressure drag ~p. As shown in the Ls line of
Jl~ J2 of Table 4, the condition of ignition is improved
through the combined operation of the both electrodes.
Example 11 (Fig. 20)
Both electrodes 21 and 22 of the spark-plug in this
embodiment, shown in Eig. 20 and Table 4, line G3, are both
streamlined. The dimensions, such as thickness, of the
positive electrode 21 as a first electrode are smaller
than those of the negative electrode 22 as a second electrode.
The dimensions should be the size measured in the direction
having right angle to the discharging direction, for example,
diameter for circular cylindrical electrode, diagonal line
for square section cylinder electrode. Such structure of
the electrode was determined, based on the new knowledge
of the inventors that a positive electrode is not directly
hit by the electro-flame-wind, and no defacement of the
electrode due to the direct hit is made, and accordingly,
the dimensions of the positive electrode 21 can be smaller
or thinner than those of the negative electrode 22, without
any sacrifice of the spark-plug service life.
As shown in Fig. 41, (d) and (d'), space occupied by
the boundary layer Bl on the positive electrode 21 is small
,:
- 59 -
:, .
~S6Z4Z
and the turbulence is hard to occur~ In addition, the boundary
layer B2 on the negative electrode 22 is retreated from the
flame nucleus space. Accordingly, the fluid drag ~ = ~f 1 ~p
and the thermal conductance G are extremely small. Further-
more, expansion waves due to the electro-flame-wind are hard
to occur in the space ~ on the front face of the positive
electrode 21 and the low density space of molecules are hard
to form. Thus, the establishment of chain combustion is
easy from the inequality (1). Through the above-described
actions, the FL-L characteristic curve G3 of the spark-plug
of a type shown in Fig. 20 lies on the left and above part
of Fig. 44, and therefore the lean gas mixture can be ignited
sufficiently.
In the service life tests, the Ni alloy negative electrode
(2.55 mm in diameter) of the spark-plug of this embodiment
was less in defacement than the conventional negative electrode
(lmm in diameter) of expensive heat-and-defacement resisting
Au-Pd alloy (Fig. 5). Accordingly, the spark-plug of this
embodiment has advantages that the low-priced Ni alloy can
be used and the longer service life is provided.
In order to further improve ignition characteristics,
it is recommended that the negative electrode diameter for -
spark-plug of this embodiment should be as thin as, for
example, 1 mm.
Also, in order to provide increased mechanical firmness
of the thin positive electrode 21, it is recommended that ;
both ends of the positive electrode 21 should be secured to
the screw part 29 as shown in Fig. 21.
- 60 -
.
~ 105~iZ4Z
.
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-- 61 --
~0~6Z4Z
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:: ~ ~ ~ ~ ~ _
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': O O ~ o ~ D~
:~ ~
; ---- ._ ~ O
:
O ~ ~ s a) ~ ~ a) ~I h
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~ ~ ~ 4~ ~o
Ln Ln ~a a)
n o o o o n a) h
Ln ~ ~ S
rO
~ ~
I` O O 1`
o ~ ~ O O o
~I h
O O
.
h ~a h U~ to C~
a) ~ ~ s ~ s ~ s .Y ~ ~ O O
a~ 1 c 0 as
I S ~ rl S O S S
~ _~ 3 .~S~ a ~ 3 ~ ~ 3 ~ ~1
Ln Ln O O
, Ln o o ~r Ln o ~ o ~ ~ ~
. ~ n ~ ~ ~ ~ n ~_1 ~ Ln ~ ~ Ln 0 0
:~
tJ ~
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. ~ ~0a ~ ~0~ ~S~ ~S~ ~S~ ~S ~ 0
~ o s o ~ o s o r~ ~ ~
h ~ ~1~ 3 ~ 3 ~) 3 ~ 3 ~ 0 0
,a s ~t~
3 ~ ~ 3 ~1 ~ h h h h I
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_
-- 62 --
,: .
` 1~56Z4Z
The next Example 12 relates to a spark-plug, wherein
at least one of said electrodes circumferential portion
connected to the discharging face is formed streamlined.
Example 12 (Figs. 25 to 28)
; As shown in Fig. 25 and 27 and in the line Kl of Table 5,
in the spark-plug of this Example, in at least one (having
diameter of d) of a first and a second electrodes 21 and 22,
the end faces are made approximately flat circular (having
radius r) discharging faces Sl- Sl, and the circumferential
part which is connected to the discharging face Sl-Sl has
convex face Sl-S2 connected to the discharging face Sl-Sl,
without edges between its circumferential part and the
discharging face Sl-Sl. Such structure leads to an
advantage that, as shown by Fig. 44, curves Kl for this
Example 12 and A for Example 1, respectively, the ignition
characteristics of this Example 12 are improved in region
for such wide electrode gap Ls>lmm, wherein a turbulent
flow is likely to be produced because of speed-increasing
'~ electro-flame-wind.
Also, the electrode of the spark-plug of this Example
;- can be made by slicing the front end part of the hemispherical
end face shown in Fig. 12, thereby to form circle plane of,
for example, 1 mm in diameter. Thus, in terms of the
igniting characteristics, as shown in Fig. 44, the char-
acteristic curve Kl of this spark-plug is slightly poorer
in the range of Ls qmm than the characteristic curve E3 of
the spark-plug of Fig. 12. However, this E~ample 12 is
remarkably superior in terms of durability, since the dis-
charging spots are not concentrated at one point.
As described hereinbefore, such spark-plugs having the
pair of an electrode with almost flat discharging face of
- 63 -
056242
small area and turbulence-preventing stream-lined (convex
face) circumferential part connected to the discharging
face, both facing each other, has almost superior features
of the FL-LS characteristics of the spark-plugs wherein each
` electrode has turbulence-preventing streamlined discharging
face, and furthermore is superior in durability due to the
construction to prevent the discharging spots from concen-
~` trating in one point.
As apparent from the values of line K2 or K3, column
LS* of Table 5, the effects of the above Example 12 are
obtainable even in a spark-plug shown by Fig. 26 and Table
5, line K2 where both electrodes are disposed at right angle
with each other, and even in a spark-plug of Table 5, line
K3 where both electrodes are disposed in parallel to each
other. Fig. 28 shows a magnified sectional view of the
posi$ive electrode 21 of Fig. 26. Referring to the drawing,
w designates the width of the discharging face Sl-Sl, Sl-S2
designates streamlined convex side face for preventing the
occurring of the turbulence, d designates an electrode
diameter
,
- 64 - ~
. .
- lOS624~
'' @ ~
o ~ 5~ ~ ~ t, o
~o ~ n
.,, ~ ~ ~. ~. (D ~
I ~ ~Q ~u~
~ ~n , ~ Hl
~' ~
., _ ___
~,. It ~
~_ ~~ n~ ~ t
3 1~ ~ ~ ~ ~
_~__ ~D ,~Ul (D
~o .
.`
O ~ o ~ ~ o ~ ~h O 1--0 ~
: ~n u~ ~_ O ~h ~n P' ul 1- 0 ~nn ~h O ~ Vl ~ t~ (D
--~ n t~ C~ ~_
n ~. ~ r~ ~ n ~- n P~ n 1~- ~ :~ ~ tD o
~h~ o ~ o ~ ~ o ~ O ~ ~ (D o ~ ~ g- 0~ n
7~ ~ ~ H~ 4 fD ~ r~ ~ ~ O
I_ ~ D ~ ~ ~t ~ t U~ ~
.,, ~ :
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(D ~n l~ O ~ H~ O 1- 0 ~ ~h O 1- 0
t~ ~ - P~ R) ~ t~
.~ ~h n 1- o ~n no ~n n ~ o ~s
o ~ ~~ ~ ~ ~ ~ ~ n _ ~_~
~- o ~ o 3cr 3 n ~ Q 3 n ~ 3O O ~ ~ .
lD ~ ~ ~Q tD ~ r~ ~ ~ ~ o~ .,
o ~ t '~ ~ S U~ ~ (D
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.,
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6 ~ :
. -, ,
, ~ . . - . : . .
.. . ~. . .
:: :
~`
` `~
`-` lOS6Z4Z
The following Examples 13 to 16 relate to spark-plugs
with electrodes, at least one of the electrodes having a
recess on a part of its fac~ that is facing the other
electrode.
Example 13 (Figs. 29 to 33)
~'
In the spark-plug of this embodiment, as shown in Fig. 29
and 30, a first electrode (diameter d) 21 is projected by a
given height from a supporter 23 vertically towards below a
second electrode 22 in a direction vertical to the central
axis of the metallic screw part 29, while the second electrode
' 22 is projected by a given height from an electric insulator
. .
24, at least one, for example, the first electrode 21, of
, .,
the first and second electrodes 21 and 22 having a recess
on a part of its face that is facing the other electrode 22.
The recess c (depth h, length 1) is formed not in a part
directly facing the discharging face s of the second electrode
:: ~
22, but in another part adjacent to the abovementioned direct-
, facing part. The discharging face of the first electrode 21
and a circumferential part coupling to this discharging face
~,:
form a convex face (streamline type).
j~ The recess serves to prevent the occurrence of turbulence,
'~.'
namely, the pressure drag ~p and to reduce the thickness of
the boundary layer. The prevention of the occurrence of
turbulence is made by inhaling such part of the boundary layer
on the long electrode, that is close to the electrode wall
and hence is liable to separation through losing kinetic
energy due to shearing stress on wall plane. The reducing
. .
of the thickness of the boundary layer is made by retreating
the boundary layer from the flame nucleus space. In addition,
the first electrode has the convex discharging face, and
therefore, the friction drag ~f and the pressure drag ~p
105624Z
.,
are both satisfactorily small. Therefore, the fluid drag
becomes small and the thermal conductance G becomes small
to improve the condition o~ ignition remarkably.
Also, the effect given by the recess c in this spark-
plug electrode is the same as that given by the projection
of electrode described in Example 1. Accordingly, it is
desirable to make the depth of the recess c as deep as t
approximately 0.25mm or more, like the projection height h
and/or h2 of Example 1 being so.
Fig. 31 shows a spark-plug electrode, having a small
flat discharging face s (width w) made by slicing a part of
the convex discharging face of the spark-plug electrode of
Figs. 29 and 30. A spark-plug using this electrode has
similar superior ignition characteristics to those of Figs.
- 29 and 30. Besides, the Example of Fig. 31 is advantageous
in terms of durability, since the discharging spots are not
concentrated in narrow part.
Also, in order remarkably to simplify manufacturing,
as shown in Figs. 32 & 33, and Table 6, line M, a spark-plug
may also be made by using a s~uare rod electrode of width w,
~ thickness z with a recess c (depth h, length i). In Fig.
-~ 33, s is discharging plane). The recess is not in a part
; of a face that is facing the other electrode but in another
part ad~acent to the direct-facing part. This spark-plug
is also improved in the condition of the ignition due to
small pressure drag ~p and friction drag ~f as shown in
the Ls* value of the line M of Table 6.
Example 14 (Figs. 34 and 35)
As shown in Fig. 34 and Table 6, line Nl, in the spark-
plug of this embodiment, a first electrode 21 is projected
by a given height from a supporter 23 vertically towards
~ ~S6Z~Z
below a second electrode 22 in a direction vertical to the
' central axis of the metallic screw part 29. And the dis-
charging face and the circumferential part are forming -
continuous convex face (stream-line shape). The second
electrode 22 is projected by a given height from an
i insulator 24. And the discharging face and the circum-
ferential part are forming continuous convex face (stream-
line shape). At least one electrode of the first and
second electrodes 21 and 22 has a recess c in the dis-
charging face, of the one electrode (for example, first
electrode 21), which is directly facing the discharging
;~ face of the other electrode (for example, the second
` electrode 22).
As shown in Fig. 41, (f) and (f'), in the spark-plug
of this Example, the expansion waves, which caused in the
space ~ of the discharging face of the first electrode due
to the electro-flame-wind are offset by gas molecules
supplied from the recess c as reservoir of gas. Accordingly,
the discharging face of the first electrode 21 is not liable
to become the space of low molecular density. Thus, the E
in the inequality (1) does not become small, and accordingly,
` the establishment of chain combustion becomes easy.
` Furthermore, as shown in Fig. 41, (f'), this spark-plug
has an effect of reducing ~f, since as a result of forming
the recess c the boundary layer Bl formed along the first
electrode 21 becomes thinner than the boundary layer of the
first electrode (for example, Fig. 41 (e')) not equipped
with recess c. Furthermore, since both electrodes are
formed streamlined, the turbulences are hard to form, and
therefore, the ~p becomes small.
Such FL-LS characteristics of the spark-plug of this
, ~
- 68 -
'-'`. 1~516Z4Z~
Example as shown in the curve Ni of Fig. 45 are obtainable,
through the compound efects, of preventing the formation
of the space of low density of molecules, reducing the
boundary layer Bl in thickness and preventing the occurrence
; of the turbulent flow due to streamlined shape. Namely,
not only in a relatively long electrode gap region, but
also in a relatively short electrode gap region, ignition
of lean mixture can be made sufficiently.
Also, in order to provide further improved ignition
characteristics, as shown in Fig. 35 and Table 6, line N3,
. it is recommended coaxially to arrange the first electrode
~; 21 with gas reservoir recess c and the second electrode 22.
~ Through this arrangement, the dimensions Q of the first-.
~ electrode 21 can be made effectively small and the friction
', drag ~f and the thermal conductance G decrease. Accordingly,
as shown in the curve N3 of Fig. 45, easy lean gas ignition'
is further made possible. The same operating effect as
described hereinbefore is obtainable even with a through
hole as the gas reservoir recess c of the first electrode 21.
~;s sh^wn in the Ls* value of line N2 of Table 6, the lean
mixture ignition can be effected sufficiently with such
through hole. This spark-plug has advantages in that the
gas reservoir hole hardly be clogged with dusts, and easier
in cleaning when the reservoir hole is closged with dusts.
It is also recommended to arrange the electrodes 21 and
22, at least one of which electrodes has said recess, in
parallel to each other with their discharging faces of
respective given lengths opposing to each other, in order
to improve the electro-corrosion resistivity.
30 Example 15 tFig. 36) -
As shown in Fig. 36 and in Table 6, line N4, a second
:,
: . ., : . ~ , ,
- lOS62~'Z
,
, electrode 22 as a negative electrode has such gas reservoir
recess c.
. .
In a spark plug of this Example shown in Fig. 41, (g),
; (g), electric field is negligibly small inside the recess c.
.
-` Accordingly, when the electro-flame-wind, which has been
accelerated in the electric field in the electrode gap Ls,
rushes into the recess c and the electro-flame-wind is not
,; .
accelerated any more. Accordingly, the positive ions in the
~ electro-flame-wind lose the momentum, the kinetic energy,
?~
- 10 etc. while colliding against the neutral molecules, and are
sufficiently decelerated before positive ions reach the wall
of the recess c. In other words, the electro-flame-wind
' can effectively deliver its own thermodynamic quantity to
the unburned mixture inside the recess c, and on the other hand
` the collision of the electro-flame-wind against the negative
:,
j~ electrode wall ~ is relieved. Thus, the direct loss of the
:.
~; thermodynamic quantity caused through the collision of the
electro-flame-wind to the negative electrode is reduced
remarkably. Furthermore, this spark-plug has more effect
of thinning boundary layer B2 formed along the negative
electrode 22 (as shown in Fig. 41(g)) than that of the
negative electrode that has no recess (e.g. Fig. 40, (e')),
and hence, the f is also reduced. sesides, the turbulent
flow haxdly occurs because of the streamline shape of both
electrodes 21 and 22, and therefore, p becomes small. As
is seen from the FL-LS characteristics (Fig. 45, curve N4)
i of the spark-plug of this embodiment, through the compound
effects of preventing the direct collision of the electro-
flame-wind against the negative electrode wall ~ by means of
recess c, reducing the boundary layer B2 in thickness, and
preventing the occurrence of the turbulent flow by means of
- 70 -
., ~ .
.. ..
105624Z
...
streamline shape, the lean mixture ignition can be suf-
ficiently effected not only in a relatively long electrode
gap region, but also in a relatively short electrode gap
region.
Also, the ignition characteristics are further improved
as shown in the curve N6 of Fig. 45 if the positive electrode
21 and the negative electrode 22 with the recess c are
disposed coaxially each other as shown in Table 6, line N6.
Even when the gas reservoir recess c in the negative
~, .
~; 10 electrode 22 is made as a through hole, the same operating
- effect as described hereinbefore is provided and thus the
~ lean mixture ignition can be sufficiently effected as shown
-~ in the Ls* value of the line N5 of Table 6. This spark-plug
- has advantages in that the gas reservoir is hardly clogged
- with dusts, etc. and easier in cleaning even if clogged with
the dusts.
Example 16
The spark-plug of this embodiment has a gas reservoir
recess, on both electrodes as shown in Table 6, line N7.
As is seen from the ignition characteristics in Fig. 45,
curve N7, the lean gas mixture ignition can be sufficiently
effected by the spark-plug, of this embodiment by means of
- combined operation between the operating effect of the gas
reservoir recess of the positive electrode 21 and the
; operating effect of the gas reservoir recess of the negative
electrode 22.
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-- 72 --
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The following Example 17 relates to three-electrode
type spark-plug wherein an electrode for trigger discharge
~ . .
is added to the spark-plugs of all the Examples 1 to 16.
Example 17 (Fig. 16¦
A spark-plug of this Example, as shown in Fig. 16, is
formed by adding a trigger electrode 33 (projection height
h3), which has the form, size and arrangement of small
fluid resistance with respect to the electro-flame-wind,
in a position of distance L13 from the positive electrode 21,
! 10 to any of the preceding type of spark-plug, for instance,
in Fig. 12 wherein two-electrodes are provided. The main
electrodes 21 and 22 are disposed to face each other with
the main electrode gap distance L12 inbetween.
In the spark-plug of this construction, the fluid
resistance of the electrodes is small, and therefore the
thermal conductance G is small. The main discharge limit
gap with respect to a given applied voltage pulse can be
enlarged up to approximately 1.75 times the discharge limit
- gap of the above-mentioned two-electrode spark-plugs, so
that the main electrode gap distance Ls, and hencej the
flame nucleus volume V can be selected large. Accordingly,
the condition of the ignition of an inequality (1) is
improved and accordingly very lean mixture can be ignited.
; In case of this three-electrode spark-plug, the spark-
plug can be driven by means of an ordinary ignition power
source for two-electrode spark-plugs without using other
power source, by connecting terminal 34 to the metallic
screw part 29 or to a high tension electrode terminal
through a resistor or a capacitor.
The following Example 18 relates to a spark-plug of
surface creeping discharge type wherein a surface creeping
- 73 -
. . - , -
; `
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discharge path is on the face of an electric insulator 24
between a first electrode 21 and a second electrode 22.
Example 18 (Figs. 38 to 40)
:.
,
As shown in Fig. 38, in the spark-plug of this Example
` 18, the first and second electrodes 21 and 22 are projected
. .
by a given heights hl and h2, respectively, above the face
of the surface creeping discharge path 44. Both of these
projection heights hl and h2 are as low as, for example,
0.3mm or less.
The FL-LS characteristics of this spark-plug are
remarkably enough improved to ignite the sufficiently lean
mixture, as compared with the FL-L characteristics of the
conventional spark-plug of surface creeping discharge type
(Fig. 37) with the first electrode 1 and the second electrode
2 both projected by approximately 0.5mm above the surface
creeping discharging path 4. This effect is obtained through -
the improved condition of the ignition as can be understood
from the inequality (l), since the respective projection
heights hl, h2 of the electrodes 21 and 22 of this spark-plug
have been made small, and thus the dimensions Q of the
.:
discharging faces of the opposing electrodes become effectively
small to reduce the friction drag ~f, hence, the thermal
conductance G.
In order to provide easier ignition of the lean mixture,
it is recommended that as shown in Fig. 39 and Fig. 40, the
electrode projection heights from the surface creeping path
44 should be 0.3mm or less alike the spark-plug of the Fig. 38 !
the shape of the electrodes should be of gentle convex faces,
and the shape of the surface creeping discharge path 44 of
the electric insulator 24 should be, also, of gentle convex
face.
- 74 -
1~5~24Z
;
In addition, in order to widen the main electrode gap
distance, it is also xecommended that a trigger discharge
electrode be added to the surf~ce creeping discharge type
spark-plug of this embodiment to use as a three-electrode
type spark-plug.
: As described elucidating, the abovementioned eighteen
examples, the spark-plugs and engines of this invention have
superior ignition characteristics which ensure positive and
reliable ignition under conditions where combinations of
temperature, pressure and concentration of the gas mixture
- are hard for ignition. The spark-plug and engine make it
possible to ignite and burn the lean gas mixture of 1.25 or
more in excess air ratio F, under the normal temperature,
- 1 atmospheric pressure, and with an electrode gap narrower
than Ls=2mm with which ignition has been impossible with
~ conventional spark-plugs and engines.
:;
.
,:
- 75 -
. .
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