U.S. patent application number 15/400736 was filed with the patent office on 2018-02-22 for krypton-85-free spark gap with cantilevered component.
The applicant listed for this patent is General Electric Company. Invention is credited to Joseph Darryl Michael, Mohamed Rahmane, Timothy John Sommerer, Karim Younsi.
Application Number | 20180054881 15/400736 |
Document ID | / |
Family ID | 61192325 |
Filed Date | 2018-02-22 |
United States Patent
Application |
20180054881 |
Kind Code |
A1 |
Michael; Joseph Darryl ; et
al. |
February 22, 2018 |
KRYPTON-85-FREE SPARK GAP WITH CANTILEVERED COMPONENT
Abstract
Embodiments of the present disclosure relate to a spark gap
device that includes a first electrode having a first surface and a
second electrode having a second surface offset from and facing the
first surface. The spark gap device also includes a cantilevered
component coupled to the first electrode that is configured to
generate a field emission, a corona discharge or both, to emit
light toward at least the first surface such that photons are
incident on the first surface and cause electron emission from the
first surface. The spark gap device may not include a radioactive
component.
Inventors: |
Michael; Joseph Darryl;
(Schenectady, NY) ; Sommerer; Timothy John;
(Ballston Spa, NY) ; Younsi; Karim; (Ballston
Lake, NY) ; Rahmane; Mohamed; (Ballston Lake,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Company |
Schenectady |
NY |
US |
|
|
Family ID: |
61192325 |
Appl. No.: |
15/400736 |
Filed: |
January 6, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62376306 |
Aug 17, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01T 2/00 20130101; H01T
1/20 20130101; F02P 23/04 20130101; F02C 7/266 20130101; H05H 1/52
20130101; H01T 19/00 20130101; F05D 2250/75 20130101; H01T 4/10
20130101 |
International
Class: |
H05H 1/52 20060101
H05H001/52; H01T 19/00 20060101 H01T019/00; H01T 1/20 20060101
H01T001/20; F02P 23/04 20060101 F02P023/04 |
Claims
1. A spark gap device, comprising: a first electrode having a first
surface; a second electrode having a second surface offset from and
facing the first surface; and a cantilevered component coupled to a
third surface of the first electrode, wherein the cantilevered
component is configured to generate a field emission, a corona
discharge, or both to emit light toward at least the first surface
such that photons emitted by the field emission, the corona
discharge, or both when the spark gap is operated are incident on
the first surface and cause electron emission from the first
surface.
2. The spark gap device of claim 1, wherein the cantilevered
component comprises an "L" shape having a first portion and a
second portion.
3. The spark gap device of claim 2, wherein the first portion
extends radially outward from the first electrode a first distance,
and wherein the second portion extends axially from the first
portion a second distance.
4. The spark gap device of claim 3, wherein the first distance is
between 3 millimeters (mm) and 5 mm.
5. The spark gap device of claim 3, wherein the second distance is
between 3 millimeters (mm) and 5 mm.
6. The spark gap device of claim 2, wherein the second portion
extends past a surface of the first electrode.
7. The spark gap device of claim 1, wherein the cantilevered
component comprises a first diameter that is between 1% and 5% of a
second diameter of the first electrode.
8. The spark gap device of claim 1, wherein the first electrode
comprises a cathode and the second electrode comprises an
anode.
9. The spark gap device of claim 1, wherein the spark gap device
does not include a radioactive component.
10. The spark gap device of claim 1, wherein the cantilevered
component is configured to emit the field emission, the corona
discharge, or both to emit the light toward the second surface.
11. An ignition device, comprising: one or more igniters configured
to ignite a fuel stream or vapor during operation; and one or more
exciter components, each connected to a respective igniter, wherein
each exciter component comprises a spark gap having a cantilevered
component configured to generate a field emission, a corona
discharge, or both when the spark gap is operated.
12. The ignition device of claim 11, wherein the spark gap
comprises: a first electrode having a first surface; and a second
electrode having a second surface offset from and facing the first
surface, wherein the cantilevered component is coupled to a third
surface of the first electrode.
13. The ignition device of claim 12, wherein the first electrode is
a cathode and the second electrode is an anode.
14. The ignition device of claim 12, wherein the cantilevered
component comprises a first diameter that is between 1% and 5% of a
second diameter of the first electrode.
15. The ignition device of claim 12, wherein the cantilevered
component comprises an "L" shape having a first portion and a
second portion.
16. The spark gap device of claim 15, wherein the first portion
extends radially outward from the first electrode a first distance,
and wherein the second portion extends axially from the first
portion a second distance.
17. The ignition device of claim 11, wherein the cantilevered
component is disposed within a housing of the spark gap.
18. A method for generating a conductive plasma, comprising:
applying a voltage across a spark gap comprising a first electrode
and a second electrode, wherein the first electrode comprises a
surface facing the second electrode, and wherein a cantilevered
component is coupled to the first electrode; generating free
electrons at a tip portion of the cantilevered component via a
field emission, a corona discharge, or both; and subsequent to
generating the free electrons, generating the conductive plasma
across the spark gap.
19. The method of claim 18, wherein free electrons are not
generated by a radioactive isotope.
20. The method of claim 18, wherein generating the free electrons
at the tip portion of the cantilevered component via the field
emission, the corona discharge, or both, comprises generating a
high intensity electric field at the tip portion.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit and priority of U.S.
Provisional Patent Application Ser. No. 62/376,306, entitled
"KRYPTON85-FREE SPARK GAP USING FIELD-EMISSION OR CORONA
DISCHARGE," filed Aug. 17, 2016, which is herein incorporated by
reference in its entirety.
BACKGROUND
[0002] The subject matter disclosed herein relates to spark gaps
for use in ignition systems or other suitable systems.
[0003] Spark gaps are passive, two-terminal switches that are open
when the voltage across the terminals is low, and then close when
the voltage across the terminals exceeds a design value (e.g., 3
kV). The spark gap then re-opens when the current has fallen to a
low level or when most of the energy from the voltage source is
dissipated. Internally, the current is carried between two metal
electrodes that are separated by a small `gap` (.about.mm) that is
filled with a gas or gas mixture (e.g., Ar--H.sub.2--Kr) near
atmospheric pressure. The gas is ordinarily insulating, but it
becomes a conducting plasma `spark` when the voltage between the
two electrodes exceeds the design value which corresponds to the
breakdown voltage.
[0004] For various applications, one parameter of interest may be
the time between when a sufficient voltage is applied to the spark
gap and the time at which it becomes conducting. This time
corresponds to the `breakdown` processes that initiate the
transition of the gas from an insulator to a conductor.
[0005] There is an idealized but useful view of electrical
breakdown as a two-step process--a `statistical` time for the first
electron to appear, followed by a `formative` time for the
electrons to `avalanche` to a highly conductive state. A free
electron appears at some time and location in the gap, and is
accelerated by the electric field that is created by the potential
difference between the electrodes. Once the electron gains
sufficient energy there is some probability for it to ionize a gas
atom or molecule and release a second free electron. Each electron
is then accelerated and the process repeats, leading to an electron
avalanche that makes the gas highly conducting. The energy gain and
multiplication processes must overcome various energy and particle
loss processes, and the first free electron should be created in
preferred locations (e.g., at or near the negative electrode) for
maximum effectiveness.
[0006] The time required for the second (avalanching) process is
the `formative time lag`. It is generally short and can be
practically ignored. Thus, the time required for the first process
(the initial electron) is the `statistical time lag`, and it is
this `first electron problem` that is of primary interest in
practice. In some devices such as laboratory apparatus or large
electric discharge lamps the `first electron problem` is solved by
doing nothing more than waiting for a cosmic ray to create a free
electron when it collides with a gas atom, gas molecule, or surface
within the device. Electron-ion pairs are always being created at a
given rate in atmospheric air by energetic cosmic rays that can
easily penetrate into gas volumes within devices and structures. A
Geiger counter is an example of a device that detects such
events.
[0007] However, the ubiquitous cosmic-ray process cannot be relied
upon to create effective free electrons within a required timeframe
that may be needed for reliable operation of many devices that
incorporate a spark gap. In particular, for device employing a
spark gap the timeframe is typically too short to rely on a cosmic
ray based process because the interaction volume (the region
between the electrodes) is relatively small.
[0008] Instead, the conventional approach to solving the
first-electron problem in a spark gap context (as well as in other
devices dealing with similar issues, such as small electric
discharge lamps) is to add a source of radioactivity, for example
in the form of radioactive krypton-85 (e.g., .sup.85Kr), which
undergoes beta decay to emit an energetic (687 keV) electron, to
generate seed electrons and reduce statistical time-lag to
acceptable values. Other radioactive materials such as tritium or
thorium are sometimes used. The addition of a radioactive component
is sometimes referred to as `radioactive prompting`.
[0009] However, radioactive materials, even at trace level, are
generally not desirable in a component or product because these
materials add to of the cost of manufacturing, handling, and
shipping.
BRIEF DESCRIPTION
[0010] In one embodiment, a spark gap device includes a first
electrode having a first surface, a second electrode having a
second surface offset from and facing the first surface, and a
cantilevered component coupled to a third surface of the first
electrode, where the cantilevered component is configured to
generate a field emission, a corona discharge, or both, to emit
light toward at least the first surface such that photons emitted
by the field emission, the corona discharge, or both when the spark
gap is operated are incident on the first surface and cause
electron emission from the first surface.
[0011] In another embodiment, an ignition device includes one or
more igniters configured to ignite a fuel stream or vapor during
operation and one or more exciter components, each connected to a
respective igniter, where each exciter component includes a spark
gap having a cantilevered component configured to generate a field
emission, a corona discharge, or both when the spark gap is
operated.
[0012] In still further embodiments, a method for generating a
conductive plasma includes applying a voltage across a spark gap
that includes a first electrode and a second electrode, where the
first electrode includes a surface facing the second electrode, and
where a cantilevered component is coupled to the first electrode,
generating free electrons at a tip portion of the cantilevered
component via a field emission, a corona discharge, or both, and
subsequent to generating the free electrons, generating the
conductive plasma across the spark gap.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0014] FIG. 1 depicts voltage with respect to time in spark gap
operation so as to illustrate concepts related to the present
approach;
[0015] FIG. 2 depicts a spark gap having a cantilevered component
configured to emit light via a field emission, a corona discharge,
or both, in accordance with aspects of the present disclosure;
[0016] FIG. 3 is a schematic of the cantilevered component of FIG.
2, in accordance with aspects of the present disclosure;
[0017] FIG. 4 is a graphical illustration of a performance of spark
gaps that include the cantilevered component of FIG. 2 compared to
a performance of spark gaps that do not include the cantilevered
component, in accordance with aspects of the present disclosure;
and
[0018] FIG. 5 depicts an engine, here a jet engine, employing
ignition components that include a spark gap as discussed herein
and in accordance with aspects of the present disclosure.
DETAILED DESCRIPTION
[0019] One or more specific embodiments will be described below. In
an effort to provide a concise description of these embodiments,
all features of an actual implementation may not be described in
the specification. It should be appreciated that in the development
of any such actual implementation, as in any engineering or design
project, numerous implementation-specific decisions must be made to
achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which may vary
from one implementation to another. Moreover, it should be
appreciated that such a development effort might be complex and
time consuming, but would nevertheless be a routine undertaking of
design, fabrication, and manufacture for those of ordinary skill
having the benefit of this disclosure.
[0020] When introducing elements of various embodiments of the
present invention, the articles "a," "an," "the," and "said" are
intended to mean that there are one or more of the elements. The
terms "comprising," "including," and "having" are intended to be
inclusive and mean that there may be additional elements other than
the listed elements. Furthermore, any numerical examples in the
following discussion are intended to be non-limiting, and thus
additional numerical values, ranges, and percentages are within the
scope of the disclosed embodiments.
[0021] The present approach relates to spark gaps, such as those
used in ignition systems for combustion engines, as well as in
other contexts such as surge protection, power switching, and so
forth.
[0022] By way of introduction to the concepts and terminology used
herein, an illustrative example of the operation of a spark gap is
illustrated in FIG. 1. In this example, if the voltage waveform 10
is a ramp, the rate of voltage rise is 6 kV/s, and the desired
voltage rating is 3.+-.0.05 kV, then the total time from Point 12
(the time sufficient voltage for the spark gap to fire is reached)
to Point 14 (the time when the spark gap is closed) should be no
more than 17 ms. This time corresponds to the `breakdown` processes
that initiate the transition of the gas from an insulator to a
conductor.
[0023] As can be appreciated from FIG. 1, the breakdown voltage 32
depends on the intrinsic properties of the spark-gap, as well as
the voltage ramp 10 that is defined by other portions of the
circuit. If the rate of voltage rise is slower, then the
voltage-rise between Point 12 and Point 14 is reduced, so Point 12
is sometimes referred to as the `intrinsic` breakdown voltage of
the spark gap, because it does not depend on the circuit
properties.
[0024] As noted above, an idealized but useful view of electrical
breakdown is to view it as a two-step process, with a first
component corresponding to a `statistical` time 16 for the first
electron to appear (at time 20), followed by a second component
corresponding to a `formative` time 18 for the electrons to
`avalanche` to a highly conductive state, occurring at time 22 when
the spark gap closes. In this example, the difference between the
voltage 30 sufficient for the spark gap to fire and the voltage 32
at which the spark gap closes is the variation 34 in gap
voltage.
[0025] In terms of the underlying concept, a free electron appears
at some time and location in the gas surrounding the spark gap, and
is accelerated by the electric field that is created by the
potential difference between the electrodes. Once it gains
sufficient energy there is some probability for it to ionize a gas
atom or molecule and release a second free electron. Each electron
is then accelerated and the process repeats, leading to an electron
avalanche that makes the gas highly conducting. The energy gain and
multiplication processes must overcome various energy and particle
loss processes, and first electrons are preferably created in
certain locations (e.g., near the negative electrode or cathode)
for maximum effectiveness.
[0026] As noted above, the time 16 required for the first process
(i.e., the release of the initial electron) is referred to as the
`statistical time lag`, and it is this `first electron problem`
that is addressed in the present approach. The present approach
solves the first-electron problem in the spark gap (i.e., the
statistical time lag) without relying on the traditional approach
of providing a source of ionizing radiation (e.g., .sup.85Kr),
which is generally undesirable, and thus does not employ
`radioactive prompting`. Similarly, the present approach does not
rely solely on the effects of cosmic-rays, for generation of the
initial electrons as such rays typically are insufficient to
generate first electrons at a sufficient rate needed in a spark gap
ignition context (or other industrial or mechanical context).
[0027] With the preceding introduction in mind, in the present
approach .sup.85Kr is eliminated from the spark gap and a
photo-electric effect is instead employed to generate seed
electrons. By way of example, in one implementation, a light source
(e.g., a field emitter and/or a corona discharge) is employed that
emits light (e.g., light energy) at a specific nominal wave length
(or range of wavelengths) at a specific level of emitted flux.
[0028] In the photo-electric process the absorption of a photon by
a material causes the material to emit an electron. The energy of
the photon must exceed the work-function of the material. The
work-function of materials is typically in the range 2-6
electron-volts. The energy .epsilon. of a photon is related to its
wavelength .lamda. through the expression .epsilon.=hc/.lamda.,
where h is Planck's constant, c is the speed of light. In practical
units .epsilon.=1240/.lamda., where .epsilon. is in units of
electron-volts and is .lamda. in units of nanometers. To be
effective for photoelectron emission the wavelength of light
should, therefore, be shorter than a certain value in the range
200-600 nanometers, corresponding to 2-6 electron-volts, with the
exact value depending on the specific material.
[0029] While the present embodiments focus on a spark gap that
includes a light source or emission inside of an envelope (e.g.,
housing) of the spark gap, in some embodiments, the light source or
emission may be outside of the envelope of the spark gap. In such
embodiments, the spectral transmission of the envelope should be
considered. By way of example, borosilicate glass absorbs strongly
at wavelengths less than 300 nanometers, corresponding to an energy
of 4 electron-volts. So if, by way of example, a given material has
a work-function of 3 electron-volts, and a light source is placed
outside the glass envelope to create photoelectrons, then only
photons of energy 3-4 electron volts (300-400 nanometers) will be
effective. Photons with wavelength longer than 400 nanometers will
not have sufficient energy to cause photoemission, and photons with
wavelength shorter than 300 nanometers will be absorbed by the
glass. Thus, the material to be photo-electrically stimulated, the
wavelength of light to be employed, and the transmissive properties
of the envelope are all factors to be considered in the design and
configuration of a spark gap system as discussed herein.
[0030] With the preceding in mind, the light source (e.g., a field
emitter and/or a corona discharge) is located with respect to one
of the electrodes (e.g., the cathode or the anode) of a spark gap
and the emitted photons incident on the surface of the electrode
cause it to emit electrons via the photo-electric effect. These
electrons are then available to initiate the gas discharge or
breakdown event. In accordance with some implementations, the
electrode on which photons from the light source are incident and
which emits electrons is a conventional electrode (e.g., a
conventional conductive metal substrate and surface), as opposed to
an electrode having a coated surface or other emissive coating
(e.g., a special purpose emissive coating) and in contrast to a
photoelectrode (e.g., a photocathode or other an annular electrode
or coil having a coating or composition specifically for the
purpose of emitting electrons in response to light photons).
However, in other embodiments, electrodes having a coated surface
and/or photoelectrodes may be utilized.
[0031] Embodiments of the present disclosure relate to a spark gap
that utilizes a field emission and/or a corona discharge to
generate the photo-electric effect, which eliminates the need for
.sup.85Kr in the spark gap. For example, FIG. 2 is a perspective
view of a cantilevered component 100 (e.g., a component capable of
producing a field emission and/or a corona discharge) coupled to a
first electrode 102 (e.g., an anode or a cathode) of a spark gap
104. The spark gap 104 may also include a second electrode 106
(e.g., an anode or cathode) disposed proximate the first electrode
102 to form a gap 108 between the first electrode 102 and the
second electrode 106. In some embodiments, the cantilevered
component 100 may be coupled to the first electrode 102 by a weld.
In other embodiments, the cantilevered component 100 may be coupled
to the first electrode 102 using another suitable technique (e.g.,
a fastener, an adhesive, or otherwise mechanically coupled to the
first electrode 102). Additionally, as shown in the illustrated
embodiment of FIG. 2, the cantilevered component 100 may be coupled
to a body portion 109 (e.g., on a surface not facing the second
electrode 106) of the first electrode 102 as opposed to an active
portion 110 of the first electrode 102 (e.g., a portion of the
first electrode 102 that establishes a connection with the second
electrode 106). However, in other embodiments, the cantilevered
component 100 may be coupled to the active portion 110. In any
case, the body portion 109 of the first electrode 102 may be
electrically coupled to the active portion 110 of the first
electrode 102.
[0032] In some embodiments, the cantilevered component 100 may
receive a high-voltage, which may form a high intensity electric
field at a tip portion 111 of the cantilevered component 100. The
high intensity electric field at the tip portion 111 may create a
field emission (e.g., by providing seed electrons above a threshold
amount) and/or a corona discharge within an envelope 112 (e.g., a
housing) of the spark gap 104. The field emission and/or corona
discharge may cause a breakdown in the gap 108, thereby causing the
spark gap 104 to close. More specifically, in some embodiments, the
voltage supplied to the tip portion 111 may reach a value
sufficient for a field emission to occur, electrons emitted from
the tip portion 111 due to the field emission may then ionize a gas
mixture 113 present in the envelope to form a corona discharge. The
corona discharge may, in turn, create photons that strike a surface
of the first electrode 102 and/or the second electrode 106, thereby
releasing photo electrons and initiating a plasma and/or spark in
the gap 108. Therefore, in some embodiments, the envelope 112 may
be filled with the gas mixture 113 that may ultimately lead to
breakdown in the spark gap 104.
[0033] The cantilevered component 100 may be configured to form a
field emission and/or a corona discharge at the tip portion 111,
rather than at another location along the cantilevered component.
Accordingly, a threshold electric field for a field emission and/or
a corona discharge should be reached at the tip portion 111 before
another point along the cantilevered component. Generally the
threshold electric field is reduced at the tip portion 111 when
compared to other locations along the cantilevered component 100
because the electric field is concentrated at the tip portion 111.
Conversely, the electric field is spread out along other locations
of the cantilevered component 100 (e.g., a cylindrical wire). In
some cases, it may be desirable to prevent a field emission and/or
a corona discharge at a point along the cantilevered component 100
other than the tip portion 111. Therefore, the cantilevered
component 100 may be disposed within the spark gap 104 so that the
tip portion 111 of the cantilevered component 100 is positioned
nearest the first electrode 102 when compared to other locations
along the cantilevered component 100.
[0034] In some embodiments, the tip portion 111 may include a
relatively small radius and be positioned at a distance sufficient
to block the field emission and/or the corona discharge from
reaching the first electrode 102 and/or the second electrode 106.
For example, a ratio of the distance from the tip portion 111 and
the first electrode 102 (e.g., d) and the radius of the tip portion
111 (e.g., r) may be less than 7, less than 6, or less than 5.85 to
ensure that a corona discharge will occur without reaching the
first electrode 102 and/or the second electrode 106.
[0035] As shown in the illustrated embodiment of FIG. 2, the
cantilevered component 100 may be substantially "L" shaped.
Therefore, the cantilevered component 100 may include a first
portion 114 (e.g., a cantilevered portion) extending radially
outward from the first electrode 102 (e.g., cathode) and a second
portion 116 extending in an axial direction 118 from the first
portion 114. However, in other embodiments, the cantilevered
component 100 may include any suitable configuration, such that the
field emission and/or the corona discharge occur at the tip portion
111 of the cantilevered component 100. In still further
embodiments, the cantilevered component 100 may include an
electronic component 119 (e.g., a resistor, an inductor, and/or a
capacitor) disposed on the first portion 114 and/or the second
portion 116. The electronic component 119 may impede an amount of
current flowing through the cantilevered component 100 to limit a
current of light emitted by the field emission and/or the corona
discharge, while maintaining a high intensity electric field at the
tip portion 111 of the cantilevered component 100. Accordingly, the
electronic component 119 may enable enhanced control of light
emitted by the cantilevered component 100.
[0036] In any case, the cantilevered component 100 may include a
diameter 120 that is substantially less than a diameter 122 of the
first electrode 102. In some embodiments, the diameter 120 of the
cantilevered component 100 (e.g., at least at the tip portion 111)
may be between 0.01% and 20% of the diameter 122 of the first
electrode 102, between 0.1% and 10% of the diameter 122 of the
first electrode 102, or between 1% and 5% of the diameter 122 of
the first electrode 102. Because the tip portion 111 of the
cantilevered component 100 includes a relatively small diameter
when compared to the diameter 122 of the first electrode 102, the
tip portion 111 may be configured to produce the high intensity
electric field. For example, the tip portion 111 may include (e.g.,
receive) the same voltage as the first electrode 102, but because
the tip portion 111 includes a substantially smaller cross
sectional area, the tip portion 111 may generate a large electric
field. Accordingly, the tip portion 111 of the cantilevered
component 100 may generate a field emission, a corona discharge, or
both, during operation of the spark gap.
[0037] In some embodiments, lengths of the first portion 114 and/or
the second portion 116 may determine a performance of the spark gap
104 (e.g., a wavelength, frequency, and/or energy output by the
field emission and/or the corona discharge). For example, FIG. 3 is
a schematic of the cantilevered component 100 extending from the
first electrode 102. As shown in the illustrated embodiment of FIG.
3, the first portion 114 may extend radially outward from the first
electrode 102 a distance 140. The second portion 116 may extend in
the axial direction 118 a distance 142 from the first portion 114.
In some embodiments, the second portion 116 may extend a distance
144 beyond a surface 146 of the first electrode 102 that faces a
second surface 148 of the second electrode 106. However, in other
embodiments, the second portion 116 may be substantially flush with
the surface 146 or be positioned below the surface 146 relative to
the axial direction 118. Additionally, the first portion 114 may be
coupled to the first electrode 102 a distance 150 from the surface
146.
[0038] In some embodiments, the distance 140 may be between 0.5
millimeters (mm) and 10 mm, between 1 mm and 7 mm, between 2 mm and
6 mm, or between 3 mm and 5 mm. In other embodiments, the distance
140 may be approximately (e.g., within 5% or within 10% of) 4 mm.
Similarly, in some embodiments, the distance 142 may be between 0.5
millimeters (mm) and 10 mm, between 1 mm and 7 mm, between 2 mm and
6 mm, or between 3 mm and 5 mm. In other embodiments, the distance
142 may be approximately (e.g., within 5% or within 10% of) 4 mm.
Further, the distance 144 may be between 0.1 mm and 3 mm, between
0.3 mm and 2 mm, or between 0.5 mm and 1.5 mm. Similarly, the
distance 150 may be between 0.1 mm and 10 mm, between 1 mm and 8
mm, or between 2 mm and 4 mm. Further still, in some embodiments,
the gap 108 may include a distance 152 between 0.1 mm and 10 mm,
between 0.5 mm and 5 mm, or between 1 mm and 3 mm. In other
embodiments, the distance 152 may be approximately (e.g., within 5%
or within 10% of) 2 mm.
[0039] As may be appreciated, the temperature environment where the
present approach may be employed may vary. By way of example, in an
ignition system for a jet engine the environmental temperature at
the exciter component where the spark gap 104 is located may be
around 150.degree. C. The operation of the spark-gap does not
depend strongly on temperature, and the cantilevered component 100
may produce the field emission, the corona discharge, or both over
a relatively wide range of temperatures. For example, the spark gap
104 includes a closed volume, such that the field emission and/or
the corona discharge depend on a density of gas in the spark gap
104. Accordingly, pressure in the spark gap 104 may increase as
temperature increases due to the field emission and/or corona
discharge, but a total number of gas atoms may remain substantially
fixed in the closed volume. Therefore, the density of the gas
remains substantially constant, and even though temperature
increases, the field emission and/or the corona discharge are
substantially unaffected.
[0040] FIG. 4 is a graphical illustration of results in terms of
breakdown voltage for the spark gap 104 having the cantilevered
component 100 when compared to a spark gap that does not include
.sup.85Kr or the cantilevered component 100. As shown in the
illustrated embodiment of FIG. 4, three of the spark gaps 104
having the cantilevered component 100 (Runs 7-9) were compared to
six spark gaps that did not include either the cantilevered
component or .sup.85Kr (Runs 1-6). Weibull percentiles of each
spark gap are shown on a y-axis 160 and breakdown voltage is shown
on an x-axis 162. As used herein, Weibull percentiles may refer to
a statistical distribution of a variation in breakdown voltage over
a variety of samples (e.g., 100 samples) for a given spark gap
(e.g., Runs 1-9). As shown in FIG. 4, the spark gaps 104 having the
cantilevered component 100 (Runs 7-9) generally included a smaller
range of breakdown voltages than the spark gaps without the
cantilevered component 100 and/or .sup.85Kr (Runs 1-6). For
example, the spark gaps 104 having the cantilevered component 100
(Runs 7-9) include steeper slopes than the spark gaps without the
cantilevered component 100 and/or .sup.85Kr (Runs 1-6), thereby
indicating a smaller breakdown voltage range.
[0041] With the preceding in mind, FIG. 5 depicts an example of an
engine 170, here a jet engine, in which the spark gap 104 using the
cantilevered component 100 may be employed. For example, the spark
gap 104 may be included as part of a fuel ignition system 172 for
the engine 170 by which a fuel stream or vapor is combusted. In
this example, the spark gap 104 may be provided for one or more
igniters 174. For example, each spark gap 104 may be provided as
part of an exciter component 176 in communication with a respective
igniter 174 via a corresponding lead 178. In this manner, spark
events induced at a given spark gap 104 may correspond to a
conductive flow between the electrodes of the spark gap 104,
causing an ignition event at the corresponding igniter 174 and an
ignition event during operation of the engine 170. Though an engine
170 such as that depicted in FIG. 5 is one possible use for a spark
gap 104 as discussed herein (e.g., as part of an ignition system),
a spark gap 104 as presently disclosed may also be used in other
ignition and non-ignition contexts.
[0042] Technical effects of the invention include an alternative
approach to generating seed electrons at a spark gap, allowing
.sup.85Kr to be eliminated from the gas mixture typically present
at the spark gap while maintaining the same performance and
function of the device. The present approach utilizes the
photo-electric effect, using a cantilevered component coupled to an
electrode to generate light energy with a specific nominal wave
length (or range of wavelengths) at a specific level of emitted
flux to generate seed electrons. The light source (e.g., a
cantilevered component coupled to an electrode that generates a
field emission and/or a corona discharge) is located with respect
to one of the electrodes (e.g., the cathode) of a spark gap and the
emitted photons landing incident on the surface of the electrode
causes it to emit electrons needed to initiate the gas discharge or
breakdown event. The present approach may be retrofit in existing
packaging, such that there would be no major changes in the
manufacturing of the spark gap 104 or the remainder of the ignition
system.
[0043] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal languages of the claims.
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