U.S. patent application number 13/347448 was filed with the patent office on 2013-02-21 for controlled spark ignited flame kernel flow in fuel-fed prechambers.
This patent application is currently assigned to Woodward, Inc.. The applicant listed for this patent is Domenico Chiera, Gregory James Hampson, David C. Petruska. Invention is credited to Domenico Chiera, Gregory James Hampson, David C. Petruska.
Application Number | 20130042834 13/347448 |
Document ID | / |
Family ID | 46063125 |
Filed Date | 2013-02-21 |
United States Patent
Application |
20130042834 |
Kind Code |
A9 |
Chiera; Domenico ; et
al. |
February 21, 2013 |
Controlled Spark Ignited Flame Kernel Flow in Fuel-Fed
Prechambers
Abstract
A pre-chamber spark plug that includes a shell. Additionally,
the pre-chamber spark plug includes an insulator disposed within
the shell. In a particular embodiment, a center electrode has a
first portion surrounded by the insulator, and a second portion
that extends from the insulator into a pre-chamber. The pre-chamber
defined by the shell. In a further embodiment, a ground electrode
is attached to the insulator. In particular embodiments, the ground
electrode is tubular in shape and includes an inner spark surface
ring spaced in surrounding relation to the center electrode to
create a spark gap, an outer ring attached to the shell, and a
plurality of rounded spokes connecting the inner and outer rings.
In a particular embodiment, the ground and center electrodes
accommodate attachment of precious metal alloys to increase
electrode surface life. In another embodiment the ground electrode
and insulator is coaxial to the center electrode.
Inventors: |
Chiera; Domenico; (Fort
Collins, CO) ; Petruska; David C.; (Fort Collins,
CO) ; Hampson; Gregory James; (Boulder, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Chiera; Domenico
Petruska; David C.
Hampson; Gregory James |
Fort Collins
Fort Collins
Boulder |
CO
CO
CO |
US
US
US |
|
|
Assignee: |
Woodward, Inc.
Fort Collins
CO
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20120125287 A1 |
May 24, 2012 |
|
|
Family ID: |
46063125 |
Appl. No.: |
13/347448 |
Filed: |
January 10, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13042599 |
Mar 8, 2011 |
|
|
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13347448 |
|
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61416588 |
Nov 23, 2010 |
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Current U.S.
Class: |
123/254 ;
123/266 |
Current CPC
Class: |
F02P 15/001 20130101;
F02B 19/12 20130101; H01T 13/32 20130101; H01T 13/54 20130101; F02B
19/16 20130101; F02P 13/00 20130101; Y02T 10/125 20130101; F02P
21/02 20130101; F02P 23/04 20130101; F02P 9/007 20130101; Y02T
10/12 20130101 |
Class at
Publication: |
123/254 ;
123/266 |
International
Class: |
F02B 19/12 20060101
F02B019/12; F02B 19/16 20060101 F02B019/16 |
Claims
1. A pre-chamber spark plug comprising: a shell; an end cap of the
shell including a plurality of ventilation holes; an insulator
disposed within the shell; a center electrode coaxially surrounded
by the insulator, and extending into a pre-chamber, the pre-chamber
defined by the shell and the end cap; and a ground electrode
attached to the insulator and surrounding a distal end of the
center electrode comprising: a tubular inner ring spaced in
surrounding relation to the center electrode; and a radial offset
circumferential extension extending axially past the distal end of
the center electrode forming an aerodynamic nose cone.
2. The pre-chamber spark plug of claim 1, wherein the aerodynamic
nose cone is attached to the ground electrode and the ground
electrode is attached to the insulator to form an aerodynamic
ram.
3. The pre-chamber spark plug of claim 1, further comprising a
first stage defined by a cavity formed between the center electrode
and the insulator.
4. The pre-chamber plug of claim 3, further comprising a second
stage defined by a cavity between the insulator and the shell.
5. The pre-chamber plug of claim 4, wherein the insulator has at
least one lateral hole exposing the first stage to the second stage
and configured to allow a flame kernel to exit the first stage and
enter the second stage.
6. The pre-chamber of claim 5, wherein the at least one lateral
hole is angled such that the lateral hole has a longitudinal axis
that is neither perpendicular nor parallel to a longitudinal axis
of the pre-chamber spark plug and does not intersect the
longitudinal axis of the pre-chamber spark plug.
7. The pre-chamber spark plug of claim 1, wherein the shape of the
aerodynamic nose code is configured to facilitate a flow of an
air/fuel mixture through spaces between the ground electrode and
the center electrode.
8. The pre-chamber spark plug of claim 1, wherein the plurality of
ventilation holes are configured to direct a primary flow of an
air/fuel mixture into the aerodynamic nose cone at a velocity
between one and one-hundred meters per second.
9. The pre-chamber spark plug of claim 8, wherein the plurality of
ventilation holes are configured to cause a secondary flow of the
air/fuel mixture into the pre-chamber to swirl about the
pre-chamber.
10. The pre-chamber spark plug of claim 9, wherein the plurality of
ventilation holes are angled such that each hole has a longitudinal
axis that is neither perpendicular nor parallel to a longitudinal
axis of the pre-chamber spark plug and does not intersect the
longitudinal axis of the pre-chamber spark plug.
11. The pre-chamber spark plug of claim 1, further comprising a
fuel injector nozzle in the pre-chamber configured to enrich a fuel
to air ratio of the pre-chamber.
12. The pre-chamber spark plug of claim 1, wherein a surface of the
center electrode and a surface of the ground electrode is selected
from the group consisting of: a nickel allow, a platinum alloy, and
an iridium alloy.
13. The pre-chamber spark plug of claim 1, wherein a distal end of
the center electrode is a flat surface.
14. The pre-chamber spark plug of claim 1, further comprising a
crevice formed between an exterior surface of the insulator and an
interior surface of the shell.
15. The pre-chamber spark plug of claim 14, further comprising a
root of the shell, wherein the shell extends from the root and the
crevice is proximate the root.
16. The pre-chamber spark plug of claim 14, wherein a volume of
space defined by the crevice is 1/5 to 1/10 of a total volume of
the pre-chamber.
17. The pre-chamber spark plug of claim 3, wherein the center
electrode includes a notch and the ground electrode forms a
backwards facing step that faces the notch forming a flame holder
in the first stage.
18. A method of facilitating combustion in an internal combustion
engine comprising: igniting an air/fuel mixture in a pre-chamber of
a pre-chamber spark plug, wherein igniting the air/fuel mixture in
the pre-chamber comprises: providing a plurality of ventilation
holes to permit a primary flow of the air/fuel mixture into a spark
gap of the pre-chamber; igniting the air/fuel mixture, wherein an
ignition event produces a flame kernel; transporting the flame
kernel to a first stage of the pre-chamber wherein the first stage
of the pre-chamber is defined by a cavity disposed between a ground
electrode attached to an insulator that is coaxial to a center
electrode; providing a secondary flow of the air/fuel mixture into
the pre-chamber from the plurality of ventilation holes such that
the secondary flow disperses throughout a second stage of the
pre-chamber defined by a cavity disposed outside of the ground
electrode attached to the insulator; wherein the flame kernel
travels from the first stage to the second stage; and igniting the
secondary flow of the air/fuel mixture causing a flame jet to issue
from the plurality of ventilation holes.
19. The method of claim 18, wherein the flame kernel travels from
the first stage to the second stage through lateral holes in the
insulator.
20. The method of claim 18, wherein providing the secondary flow
comprises providing at least one ventilation hole having a
longitudinal axis that is not parallel with, perpendicular to, and
does not intersect a longitudinal axis of the pre-chamber spark
plug.
21. The method of claim 18, wherein the primary flow of the
air/fuel mixture into the spark gap has a velocity between one and
one-hundred meters per second.
22. The method of claim 18, wherein the primary and secondary flow
of the air/fuel mixture purges residual amounts of fuel from the
spark gap.
23. The method of claim 21, wherein primary flow cools the spark
gap and the ground electrode.
24. The method of claim 18, further comprising: providing a fuel
injector nozzle in the pre-chamber; injecting fuel into the
pre-chamber thereby enriching a fuel to air ratio of the
pre-chamber.
25. The method of claim 18, wherein the primary flow of the
air/fuel mixture flows into an aerodynamic ram surrounding a distal
end of the center electrode.
26. A pre-chamber spark plug comprising: a shell; an end cap
attached to the shell; an insulator disposed within the shell; a
center electrode extending from the insulator into a pre-chamber,
the pre-chamber defined by the shell and the end cap; and a ground
electrode attached to the insulator, the ground electrode
comprising: an inner ring spaced in surrounding relation to the
center electrode forming a spark gap therebetween.
27. The pre-chamber spark plug of claim 26, further comprising a
gas admission valve integrally formed with the shell, wherein the
gas admission valve dispenses fuel from storage chambers into the
shell.
28. The pre-chamber spark plug of claim 27, wherein the insulator,
the center electrode, and the ground electrode are removable from
the gas admission valve and the shell.
29. The pre-chamber spark plug of claim 26, further comprising a
plurality of ventilation holes configured to connect the end cap to
a cylinder chamber.
30. The pre-chamber spark plug of claim 29, further comprising a
first stage of the pre-chamber that is defined by a cavity spaced
between an inner surface of the ground electrode attached to the
insulator and an outer surface of the center electrode.
31. The pre-chamber spark plug of claim 30, further comprising a
second stage of the pre-chamber that is defined by a cavity spaced
between an inner surface of the shell and an outer surface of the
ground electrode attached to the insulator.
32. The pre-chamber spark plug of claim 31, further comprising
lateral holes in the insulator that connect the first stage to the
second stage.
33. The pre-chamber spark plug of claim 32, wherein the plurality
of ventilation holes are configured to direct a primary flow of a
air/fuel mixture into the spark gap and direct a secondary flow of
the air/fuel mixture into the second stage of the pre-chamber.
34. The pre-chamber spark plug of claim 33, wherein the primary
flow of the air/fuel mixture has a velocity between one and
one-hundred meters per second.
35. The pre-chamber spark plug of claim 26, wherein increasing an
axial length of the spark gap increases the usable life of the
spark gap.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This patent application is a Continuation-in-Part of
co-pending U.S. patent application Ser. No. 13/042,599, filed Mar.
8, 2011, which claims the benefit of U.S. Provisional Patent
Application No. 61/416,588, filed Nov, 23, 2010, the entire
teachings and disclosure of which are incorporated herein by
reference thereto.
FIELD OF THE INVENTION
[0002] This invention generally relates to spark plugs for internal
combustion engines, and, more particularly, to spark plugs having a
pre-combustion chamber, or pre-chamber.
BACKGROUND OF THE INVENTION
[0003] Engines operating on gaseous fuels, such as natural gas, are
commonly supplied with a lean fuel mixture, which is a mixture of
air and fuel containing a excess air beyond that which is
"chemically correct" or stoichiometric. The lean fuel mixture often
results in poor combustion such as misfires, incomplete combustion
and poor fuel economy and often efforts to improve combustion lead
to detonation or the use of high energy spark that leads to short
spark plug life. One factor that can lead to such events is the
poor ability of conventional spark plugs to effectively and
consistently ignite a lean fuel mixture in the cylinder of the
operating engine. More effective combustion of lean fuel mixtures
can be achieved using a pre-combustion chamber, or pre-chamber.
[0004] Pre-chamber spark plugs are typically used to enhance the
lean flammability limits in lean burn engines such as natural gas
lean burn engines or automotive lean gasoline engines. In known
pre-chamber spark plugs, such as the pre-chamber spark plug
disclosed in U.S. Pat. No. 5,554,908, the spark gap is confined in
a cavity having a volume that may represent a relatively small
fraction of the total engine cylinder displacement. In some
embodiments, a portion of the cavity is shaped as a dome and has
various tangential induction/ejection holes. During operation, as
the engine piston moves upward during the compression cycle,
air/fuel mixture is forced through the induction holes in the
pre-chamber. The orientation of the holes may determine the motion
of the air/fuel mixture inside of the pre-chamber cavity and the
reacting jet upon exiting the pre-chamber.
[0005] When the burn rate of the air/fuel mixture in the
pre-chamber cavity is increased, the result is more highly
penetrating flame jets into the engine combustion chamber. These
flame jets improve the ability of the engine to achieve a more
rapid and repeatable flame propagation in the engine combustion
chamber at leaner air/fuel mixtures. Many conventional pre-chamber
spark plugs have non-repeatable and unpredictable performance
characteristics which may lead to a higher than desired coefficient
of variation (COV) and misfire, which is a measure of roughness.
Further, many conventional pre-chamber spark plugs are sensitive to
manufacturing variation and suffer from poor burned gas scavenging,
which further leads to increased COV.
[0006] One of the challenges in spark plug design is to create a
plug capable of achieving a repeatable and controllable ignition
delay time during the combustion process, in spite of the fact
that, in internal combustion engines, the fresh charge will not
usually be homogeneous or repeatable from cycle to cycle in many
aspects (e.g., equivalence ratio, turbulence, temperature,
residuals). It is also desirable to have a spark plug that is
relatively insensitive to variations in manufacturing or components
or the assembly thereof.
[0007] Another challenge in spark plug design is premature spark
plug wear. Typically, premature spark plug wear is caused by a high
combustion temperature of the stoichiometric mixture. It is not
uncommon for a spark plug in high BMEP engine applications to last
only 800 to 1000 hours before it needs to be replaced. This can
lead to unscheduled downtime for the engine and therefore increased
operational costs for the engine operator.
[0008] Embodiments of the invention provide a spark plug that
generates high velocity flame jets with very low COV and long
operating life--the benefits of which are faster combustion in the
main chamber leading to improved NOx vs. fuel consumption (or
efficiency) trade-offs. These and other advantages of the
invention, as well as additional inventive features, will be
apparent from the description of the invention provided herein.
BRIEF SUMMARY OF THE INVENTION
[0009] In one aspect, embodiments of the invention provide a
pre-chamber spark plug that includes a shell, and an end cap
attached to the shell, a center electrode and ground electrode.
Additionally, the pre-chamber spark plug includes an insulator
disposed within the shell. In a particular embodiment, the center
electrode has a first portion surrounded by the insulator, and a
second portion that extends from the insulator into a pre-chamber.
The pre-chamber volume is defined by the shell and end cap. In a
further embodiment, the ground electrode is attached to the shell.
In particular embodiments, the ground electrode includes an inner
ring spaced in surrounding relation to the center electrode, an
outer ring attached to the shell, and a plurality of spokes
connecting the inner and outer rings. In a particular embodiment,
the ground electrode has a tubular shape which serves to protect
the incoming central hole flow (primary) passing through the gap
between the center and ground electrode from disturbances from the
flow entering via lateral (secondary) holes. The tubular shape also
directs the lateral hole flow behind the ground electrode at the
periphery to join the spark kernel as it exits the gap.
Additionally, the center electrode has an aerodynamic shape which
improves the flow stream line through the gap from the center
hole.
[0010] In another aspect, embodiments of the invention provide a
method of facilitating combustion in an internal combustion engine.
The method includes igniting an air/fuel mixture in a pre-chamber
of a pre-chamber spark plug. In a particular embodiment, igniting
an air/fuel mixture in a pre-chamber includes providing a first
port to permit the flow of a first amount of air/fuel mixture into
a gap between the center and ground electrode with a predominant
backward flow direction from the front chamber of the pre-chamber,
and igniting the air/fuel mixture in the gap, wherein the ignition
produces a flame kernel. Further, the method includes causing the
flame kernel to be transported to a back chamber of the
pre-chamber, and providing a second port to permit the flow of a
secondary (Lateral) amount of air/fuel mixture into the front
chamber, such that the secondary amount of air/fuel mixture flows
to the back chamber to be ignited by the flame kernel. The
secondary flow may also have swirl which serves to spread the
developing flame in the back chamber in the azimuthal
direction--such that azimuthal uniformity is improved and generate
turbulence within the pre-chamber which further speed combustion.
The ignition of the first and second amounts of air/fuel mixture
creates a pressure rise in the pre-chamber which causes a flame jet
to issue from the first and second ports. The port hole size and
angle can be optimized to maximize the flame jet velocity and
penetration into the main chamber, thus enhancing combustion in the
main chamber. The hole size controls both the inflow and outflow
and thus is optimized to achieve the desired engine specific
ignition delay time, jet velocity, and flame jet penetration and
thus main chamber combustion rates.
[0011] In yet another aspect, embodiments of the invention provide
a pre-chamber spark plug that includes a shell, and an end cap
attached to the shell. Additionally, the pre-chamber spark plug
includes an insulator disposed within the shell. In a particular
embodiment, a center electrode has a first portion surrounded by
the insulator, and a second portion that extends from the insulator
into a pre-chamber. The pre-chamber defined by the shell and end
cap. In a further embodiment, a ground electrode is attached to the
shell. In particular embodiments, the ground electrode includes an
inner ring spaced in surrounding relation to the center electrode,
and a plurality of spokes projecting radially outward from the
inner ring which hold the ring in place. In an embodiment, the end
of each spoke is attached to the shell.
[0012] Further, in another aspect, embodiments of the invention
provide a method of manufacturing a pre-chamber spark plug. The
method includes attaching a ground electrode to the shell. In a
particular embodiment, the ground electrode comprises a tubular
electrode. In at least one embodiment, the tubular electrode has an
inner ring located in surrounding relation to the center
electrode.
[0013] The method also includes attachment of precious metal (or
Noble Metal) to the center electrode and to the ground electrode
which represents the sparking surface. The method also includes the
manufacturing process whereby the gap between the center electrode
and the ground electrode is created with a gapping tool during
manufacturing and assembly such that the gap is determined
accurately during manufacturing and assembly--thus reducing the
need for re-gapping after fabrication. In one embodiment, the
gapping tool is inserted between the center electrode and the
ground electrode prior to final attachment of the ground electrode
to the shell. This gap is best maintained if this is the final
heating step in the process. In another embodiment, the spark gap
is created after attachment of the ground electrode via electron
beam (EB), water jet, or other suitable material removal method to
create a precise high tolerance gap. The ideal new plug gap ranges
from 0.15 mm to 0.30 mm
[0014] The particular arrangement of a tubular ground electrode
with a concentric center electrode having created conditions for
flow through the gap to the back side of the ground electrode can
be accomplished in a pre-chamber in the head design which does not
require the shell of the spark plug, where the cylinder head
pre-chamber takes the place of the spark plug shell wall.
Additionally, fuel may be added to either the pre-chamber spark
plug or the pre-chamber in the head device to further extend the
lean operating limit. These are referred to as "fuel-fed"
devices.
[0015] In another embodiment, a pre-chamber spark plug comprises a
shell, an insulator, a center electrode, and a ground electrode.
The shell includes a plurality of ventilation holes. The insulator
is disposed within the shell. The center electrode is surrounded by
the insulator, and extends into a pre-chamber that is defined by
the shell. The insulator is coaxial around the center electrode.
The ground electrode is attached to the insulator and surrounding a
distal end of the center electrode. The ground electrode comprises
a tubular ring spaced in surrounding relation to the center
electrode, and has a radial offset circumferential extension
extending axially past the distal end of the center electrode
forming a geometry which serves as an aerodynamic ram.
[0016] Another embodiment of the present invention includes a
method of facilitating combustion in an internal combustion engine
comprising several steps. An air/fuel mixture is ignited in a
pre-chamber of a pre-chamber spark plug. Igniting the air/fuel
mixture comprises providing a plurality of ventilation holes to
permit a primary flow of an air/fuel mixture into a spark gap of
the pre-chamber, and igniting the air/fuel mixture, wherein an
ignition event produces a flame kernel. Next, the flame kernel is
transported to a first stage of the pre-chamber wherein the first
stage of the pre-chamber is defined by a cavity disposed between a
ground electrode attached to an insulator that is coaxial to a
center electrode that functions as a "flame holder" by creating a
recirculation zone. After transporting the flame kernel into the
first stage, a secondary flow of the air/fuel mixture is provided
to the pre-chamber from the plurality of ventilation holes such
that the secondary flow disperses throughout a second stage of the
pre-chamber defined by a cavity disposed outside of the ground
electrode attached to the insulator. Finally, the flame kernel
travels from the first stage to the second stage igniting the
secondary flow of the air/fuel mixture causing the flame to spread
through-out the pre-chamber, burning the bulk of fuel in the
pre-chamber, creating a large pressure rise and consequently a
flame jet to issue from the plurality of ventilation holes.
[0017] In another embodiment of the present invention, a
pre-chamber spark plug comprises a shell, an insulator, a center
electrode and a ground electrode. The insulator is disposed within
the shell. The center electrode has a first portion surrounded by
the insulator, and has a second portion that extends from the
insulator into a pre-chamber, which is defined by the shell. The
ground electrode is attached to the insulator and comprises an
inner ring spaced in surrounding relation to the center electrode
forming a spark gap.
[0018] Another embodiment uses a laser light beam focused at a
location between the gap surfaces, instead of an electric spark, to
heat the AFR to ignition temperatures and create a flame kernel
with photons instead of electrons. This embodiment includes a means
to bring the light beam into and focus it into the gap region. The
benefit of laser beam ignition is that it is far less sensitive to
cylinder pressure conditions, where as an electric spark requires
higher voltage to achieve break-down and spark as the pressure
increases. The laser ignition method enables ignition at pressures
above the break-down voltage limits of conventional electric
ignition systems.
[0019] Other aspects, objectives and advantages of the invention
will become more apparent from the following detailed description
when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The accompanying drawings incorporated in and forming a part
of the specification illustrate several aspects of the present
invention and, together with the description, serve to explain the
principles of the invention. In the drawings:
[0021] FIG. 1 illustrates a cross-sectional view of a portion of a
pre-chamber spark plug, according to an embodiment of the
invention;
[0022] FIG. 2 is a perspective view of the tubular electrode,
constructed in accordance with an embodiment of the invention;
[0023] FIG. 3 illustrates an exemplary embodiment of the first and
second electrode surface rings, in accordance with an embodiment of
the invention;
[0024] FIG. 4 is a plan view of the tubular electrode, constructed
in accordance with an alternate embodiment of the invention;
[0025] FIG. 5 is a cross-sectional view of the tubular electrode
having a first electrode surface ring on a substrate material, in
accordance with an embodiment of the invention;
[0026] FIG. 6 is a perspective view of a tubular electrode,
constructed in accordance with another embodiment of the
invention;
[0027] FIG. 7 is an end view of an end cap for the pre-chamber
spark plug, according to a particular embodiment of the
invention;
[0028] FIG. 8 is a cross-sectional view of the end cap of FIG.
7;
[0029] FIG. 9 is a cross-sectional view of a portion of a
pre-chamber spark plug, according to a particular embodiment of the
invention;
[0030] FIG. 10 is a cross-sectional view of a large bore piston
cylinder assembly and a pre-chamber spark plug in accordance with a
particular embodiment of the present invention;
[0031] FIG. 11 is a cross-sectional view of a pre-chamber spark
plug in accordance with a particular embodiment of the present
invention;
[0032] FIG. 12 is a cross-sectional view of a pre-chamber spark
plug illustrating fuel flow into the pre-chamber in accordance with
a particular embodiment of the present invention;
[0033] FIG. 13 is a cross-sectional view of a secondary fuel
injector in the pre-chamber in accordance with a particular
embodiment of the present invention;
[0034] FIG. 14 is a cross-sectional view of a combined gas
admission valve with igniter/spark plug in accordance with a
particular embodiment of the present invention;
[0035] FIG. 15 is a close up cross-sectional view of an
igniter/spark plug of a combined gas admission valve with an
igniter, in accordance with a particular embodiment of the present
invention; and
[0036] FIG. 16 is a close up cross-sectional view of a crevice of a
pre-chamber in accordance with a particular embodiment of the
present invention.
[0037] While the invention will be described in connection with
certain preferred embodiments, there is no intent to limit it to
those embodiments. On the contrary, the intent is to cover all
alternatives, modifications and equivalents as included within the
spirit and scope of the invention as defined by the appended
claims.
DETAILED DESCRIPTION OF THE INVENTION
[0038] To address the issues of a repeatable and controllable
ignition delay time during the combustion process, which results in
both a more efficient combustion process and longer life for the
spark plug, a pre-chamber spark plug has been developed that
incorporates a tubular electrode to control the flame kernel
development, ignition delay time, flame jet evolution, main
combustion chamber burn rate, and consequently improves engine
performance. The delay time is the period between the spark and
that time when the combustion affects a volume sufficient to
increase the pressure in the pre-chamber and in turn the main
combustion chamber.
[0039] FIG. 1 illustrates a cross-sectional view of a portion of a
pre-chamber spark plug 100, according to an embodiment of the
invention. The pre-chamber spark plug 100 has a longitudinal axis
101 and a center electrode 102 that extends along the longitudinal
axis 101, and further extends from an insulator 104 into a
pre-combustion chamber that is divided into a back chamber 106 and
a front chamber 108. A tubular electrode 110, which serves as the
ground electrode, is disposed inside a shell 112. In embodiments of
the invention, the shell 112 is made from a high-strength metal
capable of withstanding exposure to high temperatures. The disk
portion 114 of the tubular electrode 110 separates the back chamber
106 from the front chamber 108. An end cap 116 defines an end of
the pre-chamber volume of the spark plug 100 and also a boundary of
the front chamber 108. As shown in FIG. 1, in a particular
embodiment of the invention, an interior surface 118 of the shell
112 may have a stepped portion 120 such that the tubular electrode
110 can seat on the stepped portion 120 during assembly of the
pre-chamber spark plug 100.
[0040] FIG. 2 is a perspective view of the tubular electrode 110,
constructed in accordance with an embodiment of the invention. The
tubular electrode 110 has an inner ring 130 and an outer ring 132
imbedded within the tubular ground electrode 110. In the embodiment
of FIG. 2, the inner ring 130 and outer ring 132 are connected by
three spokes 134. Extending from the inner ring 130 in the center
portion of the tubular electrode 110 is a tubular inner ring, or
velocity control tube 136. In a particular embodiment of the
invention, as illustrated in FIG. 1, the velocity control tube 136
extends away from the disk portion 114 in one direction into the
front chamber 108. A central opening 138 extends through the inner
ring 130 and the velocity control tube 136.
[0041] Still referring to FIG. 2, in an embodiment of the
invention, the tubular electrode 110 is made from a copper alloy, a
nickel alloy, or some other relatively highly-conductive metal. In
a particular embodiment of the invention, a precious metal is
attached to, or deposited on, an inner surface 140 of the inner
ring 130. Precious metals are typically used on spark plug
electrodes to increase the life of the spark plug and improve
performance. The precious metals chosen for this application
exhibit a high melting point, high conductivity, and increased
resistance to oxidation. In embodiments of the invention, a first
electrode surface ring 142 of, for example, platinum or alloys
thereof, rhodium or alloys thereof, tungsten or alloys thereof,
iridium or alloys thereof lines the inner surface 140 of the inner
ring 130. In alternate embodiments, the inner surface 140 of the
inner ring 130 is lined with an iridium-rhodium alloy or a nickel
alloy. Referring again to FIG. 1, in particular embodiments of the
invention, a second electrode surface ring 144, of the same or
similar material as the first electrode surface ring 142, is
attached to, or deposited on, an exterior surface 146 of the center
electrode 102.
[0042] Referring again to FIG. 2, the spokes 134 may be
square-edged for easy manufacturing or may have a curved contour so
as to provide less resistance to gases flowing through the spaces
between the spokes 134. In alternate embodiments of the invention,
there may be a greater or fewer number of spokes connecting the
inner ring 130 and outer ring 132. In an alternate embodiment of
the invention, the tubular electrode 110 does not have an electrode
surface ring made from a precious metal. In an exemplary
embodiment, the entire tubular electrode 110 is made from a single
material such as a nickel alloy.
[0043] The tubular electrode 110 may be cast or machined
substantially as a single piece, though the first electrode surface
ring may be a separate ring of some type of precious metal or
similarly suitable metal. It is also envisioned that the tubular
electrode 110 can be made from powdered metal, wherein the powdered
metal is sintered or injection molded. Other manufacturing
techniques in which the powdered metal is melted rather than
sintered are also envisioned. In at least one embodiment, the first
and second electrode surface rings 142, 144 are made from, for
example, cylindrical or rectangular bar stock, which is cut to
length and formed into a ring. In an alternate embodiment, the
first and second electrode surface rings 142, 144 are made from
flat sheet stock, and a punch is used to produce a number of
electrode surface rings 142, 144 from a single flat sheet. FIG. 3
shows an exemplary embodiment of the first and second electrode
surface rings 142, 144 in which the two electrode surface rings are
punched in a single operation such that the first and second
electrode surface rings 142, 144 are attached via three tabs 148.
In a particular embodiment, both the first and second electrode
surface rings 142, 144 are assembled to the tubular electrode 110
with tabs 148 in place to maintain the correct spacing between the
electrode surface rings 142, 144. The tabs 148 are removed after
the first electrode surface ring 142 is attached to the tubular
electrode 110, and after the second electrode surface rings 144 is
attached to the center electrode 102. The ring 142 may also be cut
into one or more semi-circular sections to accommodate fabrication,
assembly, attachment and /or thermal expansion.
[0044] An alternate embodiment of the tubular electrode is
illustrated in FIG. 4. In this embodiment, the inner ring 130,
outer ring 132, spokes 134 and velocity control tube 136 are
substantially the same as for tubular electrode 110. However,
tubular electrode 111 includes the second electrode surface ring
144 attached to the first electrode surface ring 142 by three tabs
156. As such, the correct spacing between the first and second
electrode surface rings 142, 144 is maintained until assembly is
completed. After assembly, the tabs 156 can be removed mechanically
or by electron beam or water jet or similar method. However, in a
particular embodiment, the tabs 156 can be made, for example, from
a material with a substantially lower melting point that the other
materials in the tubular electrode 111 or the second electrode
surface ring 144. This allows for the tabs 156 to be removed by
burning or melting after assembly of the tubular electrode 111 to
the pre-chamber spark plug 100.
[0045] There are several methods by which the first electrode
surface ring 142 can be attached to the tubular electrode 110. In a
particular embodiment of the invention, the tubular electrode 110
is cast around the first electrode surface ring 142. In an
alternate embodiment, a separate metal ring with a layer of
precious metal or similarly suitable metal attached to an inner
surface of the metal ring is assembled to the inner ring 130 of the
tubular electrode 110.
[0046] For example, the electrode surface ring material can be
deposited on, for example, a powdered metal substrate, using
physical or chemical vapor deposition. For example, the powdered
metal substrate may be a hollow cylinder and the electrode surface
ring material can be deposited on the interior surface of the
hollow cylinder. The cylinder could be sliced into a number of
first electrode surface rings 142. If the same material is
deposited on the outside of a smaller hollow cylinder, it could be
sliced into a number of second electrode surface rings 144. Made in
this fashion, the first electrode surface rings 142 could be
inserted into the central opening of the tubular electrode 110 and
welded or brazed in place. FIG. 5 shows a cross-sectional view of
tubular electrode 110 having a first electrode surface ring 142
attached or deposited on a substrate material 143, for example a
nickel alloy or highly conductive alloy. In a particular
embodiment, the weld is a tack weld in one spot or a few select
spots to allow for some relative movement due to the differing
rates of thermal expansion for the different materials. Using the
methods described above to add the precious metal to the tubular
electrode 110 allows for the fabrication of the pre-chamber spark
plug 100 with less of the precious metal than typically used in
conventional pre-chamber spark plugs, thus making the pre-chamber
spark plug 100 less expensive to manufacture than many conventional
pre-chamber spark plugs.
[0047] In a further embodiment, the tubular electrode 110 can be
assembled from separate components. The embodiment of FIG. 5 also
shows a cross-sectional view of a particular embodiment of the
tubular electrode 110 having a separate disk portion 114 and
velocity control tube 136. In at least one embodiment, the velocity
control tube 136 has a notched portion 152 at one end, and the
notched portion is press fit into an annular receiving portion 154
in the disk portion 114. In a further embodiment, the annular
receiving portion 154 could be pressed inward into the notched
portion 152 of the velocity control tube 136 holding it in place.
In a further embodiment, the notched portion 152 includes a annular
protrusion about its circumference that fits into a divot in the
annular receiving portion 154 of the tubular electrode 110 to
improve the attachment between the disk portion 114 and velocity
control tube 136. In alternate embodiment, the notched portion 152
is threaded along with an interior surface of the annular receiving
portion 154 such that the velocity control tube 136 can be threaded
into the disk portion 114.
[0048] Referring again to FIG. 1, in operation, the air/fuel
mixture is drawn into the front chamber 108 of pre-chamber spark
plug 100 from the main cylinder of the engine (not shown) through a
center hole 162 (see also FIGS. 7 and 8) in end cap 116, and
through a plurality of periphery holes 164 (see also FIGS. 7 and
8). The air/fuel mixture drawn in through the center hole 162 flows
through the velocity control tube 136 to the spark gap between
center electrode 102 and tubular electrode 110 where it is ignited
by an electric spark. The velocity of the air/fuel mixture causes
the initial flame kernel to be transported into the back chamber
106.
[0049] A key function of the flow through the primary central hole
is that this flow consists of fresh Air-Fuel charge with a low
level of residuals. This primary flow forces its way into the spark
gap region--uniformly--pushing the last combustion event residuals
backwards and out of the spark gap region, effectively purging the
spark gap of residuals, thus "controlling" the residuals within the
pre-chamber. In conventional pre-chamber spark plugs, the residual
gases are not "controlled" well or at all, leading to an unknown
and uncontrolled mixture of fresh charge and left-over residuals at
the time of spark. This represents a key source of shot-to-shot
combustion variation within conventional pre-chamber spark plugs.
Thus it is claimed that this design uniquely and most effectively
purges the residuals backwards (away from the end cap) leading to
exceptionally low COV, via "Residual Gas Control"
[0050] The air/fuel mixture drawn in through periphery holes 164
has a swirling motion due to the angled nature of the periphery
holes 164. The swirling air/fuel mixture flows past the outside of
the velocity control tube 136 toward the back chamber 106 where it
is ignited by the flame kernel from the center hole flow. The
turbulence caused by the swirling motion of the air/fuel mixture
distributes the growing flame kernel around the back chamber 106
predominantly consuming the fuel in the back chamber 106. This
results in a faster burn and a rapid increase in pressure inside
the pre-chamber as combustion of the air/fuel mixture proceeds from
the back chamber 106 to the front chamber 108. The result is a more
complete burn of the air/fuel mixture and, therefore, increased
pressure within the pre-chamber. This results in a high-velocity
jet of flame through the center hole 162 and through the plurality
of periphery holes 164 into the main combustion chamber (not
shown).
[0051] In this manner, ignition is delayed by the flow of the flame
kernel to the back chamber 106. The combustion process starts in
the back chamber 106 and must progress through the front chamber
108 before the resultant flames project into the main combustion
chamber. Because this increased ignition delay time results in a
more complete burn, the process is more repeatable and has less
variation, and therefore a lower COV, than in typical conventional
pre-chamber spark plugs. An additional benefit of the delay in
ignition is that the spark can be initiated sooner in the
combustion cycle when the cylinder pressure is lower than would be
the case without the ignition delay. Initiating the spark when the
cylinder pressure is lower prolongs the life of the pre-chamber
spark plug 100.
[0052] Further, in configuring the pre-chamber spark plug, the
volume of the back chamber 106 behind the tubular electrode 110,
and of the front chamber 108 in front of the tubular electrode 110
can be optimized to control the flame kernel development, and thus
the ignition delay time. The ratio of volume of the front chamber
108 to that of the back chamber 106 controls the size and
penetration of the flame jet that issues from the center hole
162.
[0053] FIG. 6 is a perspective view of a tubular electrode 180,
constructed in accordance with an embodiment of the invention.
Tubular electrode 180 serves as a ground electrode and is similar
to tubular electrode 110, except that tubular electrode 180 has no
outer ring. Tubular electrode 180 includes the inner ring 130 with
a central opening 138. The inner ring 130 extends axially to form
the velocity control tube 136. In the embodiment of FIG. 6, three
spokes 134 extend radially outward from the exterior of the inner
ring 130. In a particular embodiment, the tubular electrode 180 is
assembled to the pre-chamber spark plug 100 by attaching an end 182
of each spoke 134 directly to the shell 112. The attachment may be
made by welding, brazing, or the like.
[0054] FIGS. 7 and 8 show an end view and a cross-sectional view,
respectively, of the end cap 116 for pre-chamber spark plug 100,
according to a particular embodiment of the invention. In a
particular embodiment, the end cap 116 is cup-shaped such that it
protrudes slightly from the end of the shell 112. The end cap 116
has center hole 162 that, in at least one embodiment, is centered
around the longitudinal axis 101 of the pre-chamber spark plug 100.
The center hole 162 is configured to control the rate of flow of
air/fuel mixture into the front chamber 108. The end cap 116
further includes the plurality of periphery holes 164 which may be
drilled or formed in a sidewall 166 of the end cap 116. The
periphery holes 164 are configured to create a swirling motion of
the air/fuel mixture in the pre-combustion chamber. In an
embodiment of the invention, the end cap 116 is attached to the
shell 112 via welding, brazing, and the like. The end cap 116 in
another preferred embodiment may also be flat (perpendicular to the
shell) and or "V" shaped.
[0055] FIGS. 7 and 8 illustrate an embodiment of the end cap 116
having seven periphery holes 164 in the sidewall 166, and seven
periphery hole axes 168. For the sake of simplicity, only one
periphery hole axis 168 is shown in FIG. 7. FIG. 7 shows and end
view of end cap 116 that includes an exemplary swirl angle for the
periphery holes 164, and further includes the longitudinal axis 101
for pre-chamber spark plug 100 as it would be located, in a
particular embodiment, when the end cap 116 is assembled to shell
112. FIG. 8 is a cross-sectional view of the end cap 116 and shows
an exemplary penetration angle for the periphery holes 164.
[0056] Other embodiments of the end cap 116 may have more or less
than seven periphery holes 164. The periphery holes 164 are angled
such that none of the periphery hole axes 168 intersect the
longitudinal axis 101. As stated above, FIG. 7 illustrates a swirl
angle for the periphery holes 164. As shown in FIG. 7, the swirl
angle is defined as the angle between the periphery hole axis 168
and a radial line 169 projecting from the center of the end cap 116
through a point on the periphery hole axis 168 midway between the
ends the cylinder defined by the corresponding periphery hole
164.
[0057] In the embodiment of FIGS. 7 and 8, the swirl angle is 45
degrees but, in alternate embodiments, could be greater or lesser
than 45 degrees. FIG. 8 illustrates a penetration angle for the
periphery holes 164. As shown in FIG. 8, the penetration angle is
defined as the angle between the periphery hole axis 168 and the
longitudinal axis 101 or a line 171 parallel to the longitudinal
axis 101. During engine operation, when an air-fuel mixture is
introduced into the front chamber 108 of the pre-chamber, the
angled nature of the periphery holes 164 produces a swirling effect
on the air-fuel mixture in the pre-chamber. The exact location
(i.e., on the sidewall 166) and configuration (e.g., diameter,
angle) of the periphery holes 164 is dependent on the desired flow
field and air-fuel distribution within the pre-combustion
chamber.
[0058] FIG. 9 is a cross-sectional view of a pre-chamber spark plug
200, constructed in accordance with an embodiment of the invention.
Pre-chamber spark plug 200 has a longitudinal axis 201. The center
electrode 102 that extends along the longitudinal axis 201, and
further extends from the insulator 104 into the pre-chamber,
divided into back chamber 106 and front chamber 108. A tubular
electrode 210, disposed inside shell 112, serves as the ground
electrode. The disk portion 214 of the tubular electrode 210
separates the back chamber 106 from the front chamber 108. The end
cap 116 defines the end of the pre-chamber spark plug 200 and also
a boundary of the front chamber 108. In a particular embodiment of
the invention, an interior surface 118 of the shell 112 may have a
stepped portion 120 such that the tubular electrode 210 can seat on
the stepped portion 120 during assembly of the pre-chamber spark
plug 200.
[0059] In operation, the pre-chamber spark plug 200 operates in a
manner similar to that described above for the operation of
pre-chamber spark plug 100. However, it can be seen in FIG. 9 that
a tubular inner ring, or velocity control tube 236 extends axially
both into the front chamber 108 and into the back chamber 106. By
increasing the length of the velocity control tube 236, i.e.,
adding the portion that extends into the back chamber 106, the
ignition delay time can be further increased. In this case, the
ignition delay time is controlled by the length of the extended
back portion of the velocity control tube 236, and by the flow
velocity in the extended back portion of the velocity control tube
236. The flow velocity in the velocity control tube 236 is a
function of the mass flow through the center port 162. The
increased ignition delay time that results from the extended
velocity control tube 236 allows the spark to be initiated even
earlier than in the case of pre-chamber spark plug 100. Initiating
the spark earlier when cylinder pressure is lower prolongs the life
of the spark plug. Such a design also makes it possible to
fabricate pre-chamber spark plugs having center and ground
electrodes without any precious metal. This reduces the material
cost and simplifies substantially the manufacture and assembly of
the spark plug.
[0060] FIG. 10 illustrates a cross-sectional view of a pre-chamber
spark plug assembly 300 in accordance with another embodiment of
the present invention. The pre-chamber spark plug assembly 300
includes a pre-chamber 304 in the head of large bore piston
cylinder chamber 302. Within the pre-chamber 304, is a spark plug
306 adapted for the configuration of having the pre-chamber 304 in
the head of a large bore piston cylinder 302.
[0061] FIG. 11 illustrates a close up cross-sectional view of the
pre-chamber 304 of the pre-chamber spark plug assembly 300 of FIG.
10. The pre-chamber 304 is bounded by a shell 334 and connected to
the cylinder chamber 302 by an end cap 340 that has a series of
ventilation holes 324. The ventilation holes 324 allow a fuel and
air mixture to enter the pre-chamber 304, and for a flame to exit
the pre-chamber 304 into the cylinder assembly 302. While the
particular embodiment of the invention shown in FIG. 11 shows three
ventilation holes 324, more or less are contemplated. Additionally,
the ventilation holes 324 could be in the form of slots as opposed
to holes.
[0062] The pre-chamber 304 has a longitudinal axis 301 and a center
electrode 310 that extends axially along the longitudinal axis 301
into a pre-combustion chamber 304. Around the center electrode, at
the center electrode's 310 distal end, is the ground electrode 308.
The ground electrode 308 is attached to the insulator 312, which
insulates the center electrode 310 from the ground electrode 308.
In certain embodiments, the center electrode 310 connects to a
voltage source (not shown), and the ground electrode 308 is
grounded through a connection (not shown), through the interior of
the insulator 312, to the shell 334, which is electrically
grounded.
[0063] Further, the ground electrode 308 forms a circular region
around the distal end of the center electrode 310 forming spark gap
314. The spark gap 314 is between the outer surface of the center
electrode 310 and a tubular inner ring of the of the ground
electrode 308 that is spaced in surrounding relation to the center
electrode 310. The insulator 312 extends axially around the center
electrode 310 from above the spark gap 314 up to the top of the
pre-chamber 304 forming a velocity control tube. Additionally,
above the spark gap 314 are two lateral holes 318 drilled into the
insulator, or by another name the velocity control tube 312, which
act to ventilate a flame kernel after an ignition event.
[0064] The area around the center electrode 310, but inside the
insulator 312 is referred to as a first stage 320 of the
pre-chamber 304. The first stage 320 acts to restrict fuel into a
small space such that a flame kernel generated by an ignition event
is protected and controlled as to not cause excessive damage to the
ground electrode 308 and the center electrode 310. While in this
particular embodiment of the invention two lateral holes 318 are
shown in the insulator 312, more or less are contemplated.
[0065] The area outside of the insulator 312 and bounded by the
shell 334 is referred to as a second stage 322 of the pre-chamber
304. The second stage 322 is where the flame kernel begins to
expand prior to exiting from the ventilation holes 324 into the
cylinder chamber 302.
[0066] Additionally, the ground electrode 308 extends further into
pre-chamber 304 than the center electrode 310. As illustrated in
FIG. 11, the ground electrode 308 includes a radial offset
circumferential extension extending axially past the distal end of
the center electrode 310 forming an aerodynamic nose cone or by
another name an aerodynamic ram 316. The aerodynamic ram 316
functions to trap the vapor flow from the main cylinder chamber 302
as it flows into the pre-chamber 304. This trapped vapor is an
air/fuel mixture that is ignited at the spark gap 314.
[0067] As an aside, the spark gap 314 width can be altered to
affect useable life of the spark plug. By increasing the axial
length of the spark gap, the surface area of where a spark is
generated will increase. Therefore, it will take longer for the
material that composes the center electrode 310 and the ground
electrode 308 to erode to the point that the plug itself needs to
be refurbished or replaced. The drawback to increasing the width is
that this shrinks the first stage and thereby makes initial
ignition of the fuel more difficult.
[0068] FIG. 12 illustrates the flow physics of how combustion is
created and managed in the pre-chamber 304. Initially, a primary
mixture of fuel and air will flow into the pre-chamber through the
ventilation holes 324 from the cylinder assembly 302. The flow is
created because of a pressure differential between the cylinder
chamber 302 and the pre-chamber 304 created during the compression
stroke of an associated engine system (not shown). The flow is
composed of a primary and secondary flow 328 and 330 respectively.
As the primary and second flow 328, 330 enter the pre-chamber 304,
the primary and secondary flow 328, 330 purge residual fuel from
previous ignition cycles from the spark gap 314 region toward the
top of the pre-chamber 304. This replaces the fuel in the spark gap
314 and the second stage 322 with fresh evenly dispersed fuel.
[0069] Further, the secondary flow 330 disperses uniformly around
the second stage 322 of the pre-chamber 304, and the primary flow
328 is captured by the aerodynamic ram 316. The aerodynamic ram 316
gathers the primary flow 328 around the spark gap 314. The velocity
of the primary flow 328 into the spark gap is between 1 and 100
meters per second. The fuel that is part of the primary flow 328
will gather around the spark gap 314 thus creating a pressure
differential between the area within the aerodynamic ram 316 and
the first stage 320 causing the fuel to flow into the first stage
320 of the pre-chamber 304. In certain embodiments, a distal end of
the center electrode 310 is flat to facilitate the primary flow 328
into the spark gap 314.
[0070] Additionally, fuel will flow through the lateral holes 318.
The lateral holes 318 are angularly offset such that they are not
perpendicular to the center axis 301. This prevents the air/fuel
mixture from the secondary flow 330 from filling the first stage
320. Therefore, the pressure differential caused by aerodynamic ram
316 is not disturbed by the lateral holes 318.
[0071] Once a spark is generated in the spark gap 314, the fuel in
the spark gap 314 will ignite thus creating a flame kernel. Because
of the pressure differential, the flame kernel travels into the
first stage 320 of the pre-chamber 304 where the flame kernel is
protected from the outside environment by the relatively small size
of the first stage 320. Specifically, the flame kernel moves upward
into a notch 332 located in the center electrode 310. The notch 332
then introduces the flame kernel to a backwards facing step
structure 334 of the ground electrode 308. As the primary flow
enters the first stage 320 the backward facing step creates a
recirculation zone trapping some fuel in this location that allows
the flame kernel to expand slightly while also being protected from
being quenched by primary flow entering the spark gap 314.
Therefore, the notch 332 and the backwards facing step 334 form a
flame holder that protects the flame kernel from the higher
velocity primary flow 328.
[0072] Additionally, because the lateral holes 318 allow only a
minimal amount of the fuel to enter the first stage 320, the flame
kernel remains small. This keeps the temperature inside the first
stage 320 low and minimizes damage to the ground electrode 308 and
the center electrode 310.
[0073] As the flame kernel grows and consumes the fuel in the first
stage 320 it travels out of the lateral holes 318 into the second
stage 322 of the pre-chamber 304. The flame kernel is carried by
the secondary flow 330 and wraps around the insulator 312. At this
point the flame kernel begins to spread and consume the fuel in the
second stage 322. The flame then expands, greatly increasing the
pressure inside the pre-chamber 304, and jets out of the
ventilation holes 324 into the cylinder chamber 302 where it
ignites the fuel in the cylinder chamber 302.
[0074] By controlling the flow of the flame kernel around the
center electrode 310, the usable lifetime of the pre-chamber spark
plug assembly 300 is greatly increased. This is because the first
stage surrounds the center electrode 310 and only allows the small
flame kernel to burn around it, as opposed to traditional systems
that have an exposed spark gap with no protection.
[0075] FIG. 13 illustrates an embodiment of the present invention
that includes a secondary fuel injector 326 in the pre-chamber 304.
The secondary fuel injection 326 specifically injects fuel into the
pre-chamber 304. Another primary fuel injector (not shown) injects
fuel into the main cylinder chamber 302, which travels into the
pre-chamber 304 through the ventilation holes 324. The secondary
fuel injector 326 allows the user to enrich the pre-chamber mixture
beyond what would typically be present from the primary
injection.
[0076] Typically, the fuel to air ratio of the cylinder chamber 302
is stoichiometric, or in other words the fuel and air exist in
equal quantities in the cylinder chamber 302 prior to combustion.
Therefore, the fuel to air ratio within the pre-chamber 304 could
be stoichiometric or less than that (leaner) due to the flow
through ventilation holes 324. To guarantee a properly fuel
enriched environment in the pre-chamber 304 employing the secondary
fuel injector 326, the secondary fuel injector 326 increases the
fuel to air ratio. Typically the increase will be such as to make
the lean mixture coming from the main combustion chamber
stoichiometric, or in other words it would not be a-typical to
enrichen the pre-chamber fuel as air is present in the pre-chamber
304 prior to combustion to more than twice the main chamber
fuel-air ratio. By enriching the pre-chamber 304, the ignition
process will run hotter. However, running the ignition process
hotter will decrease the useable lifetime of the center and ground
electrodes 310, 308. This embodiment enables the fuel-fed
(fuel-enriched) pre-chamber to run leaner with minimal or no
enrichment--thus creating a Fuel-Air ratio in the pre-chamber to be
much closer to the lean mixture found in the main chamber and as
far away from stoichiometric enrichment as possible. Such reduction
in pre-chamber enrichment leads to lower combustion temperatures in
and around the spark surfaces, which leads to extended life of the
spark plug.
[0077] FIG. 14 illustrates a gas admission valve 402, integrally
formed with a shell 416 of a pre-chamber 404, combined with a spark
plug 400. In the particular embodiment illustrated in FIG. 14,
there are three separate gas admission valves 402a, 402b, and 402c.
The gas admission valves 402a, 402b, and 402c supply fuel from
storage chambers 430 to the pre-chamber 404. As discussed in regard
to FIG. 13, the gas admission valve 402 allows the user to adjust
the richness of the fuel/air mixture in the pre-chamber 404.
Further, in certain embodiments, the spark plug 400, which includes
an insulator 414, a center electrode 406, and a ground electrode
408, is removable from the gas admission valve 402 portion such
that quick replacement of the spark plug 400 is facilitated.
[0078] FIG. 15 illustrates a close-up view of the pre-chamber 404
of FIG. 14. The pre-chamber 404 is connected to a cylinder of an
engine (not shown) system by an end cap 440 with ventilation holes
412. Similar to embodiments of the invention discussed above, the
pre-chamber 404 includes a center electrode 406, a ground electrode
408, ventilation holes 412, an insulator 414, and a shell 416. An
aerodynamic ram 428 also exists in this embodiment. Further, the
insulator includes lateral holes or slots 418. Similar to the later
holes 318 (from FIG. 11), the slots 418 provide access from a first
stage 420 that is defined by a cavity formed between the ground
electrode 408 connected to the insulator 414 and the center
electrode 406, and a second stage 422 that is defined by a cavity
between the shell 416 and the ground electrode 408 attached to the
insulator 414.
[0079] A first pressure differential is created by the compression
stroke of an engine system forcing a fuel/air mixture into the
pre-chamber 404 through the ventilation holes 412 at a velocity
between one and one-hundred meters per second and directed
backwards and away from the end cap 440. As this mixture flows into
the pre-chamber 404, it will gather around a spark gap 424 formed
between the center electrode 406 and the ground electrode 408. The
relative small width of the spark gap 424 will facilitate a second
pressure differential between the first stage 420 and the second
stage 422 of the pre-chamber 404. Therefore, when a spark is
generated at the spark gap 424, the second pressure differential
will draw the flame kernel formed by the spark igniting the
fuel/air mixture into the first stage 420, which has an area
expansion which serves to slow the flow and create a recirculation
zone formed between a notch 426 formed in the center electrode 406
and a backward facing step 432 formed in the ground electrode 408.
The recirculation zone holds fuel particles in recirculation loops
and acts effectively as a flame holder--preventing the blow-out of
the flame kernel that is swept out of the spark gap 424 region.
This flame kernel will burn the fuel in the first stage 420 until
it exits through the slots 418 into the second stage 422. In the
second stage 422, the flame kernel grows into a flame by consuming
the fuel in the pre-chamber 404. This greatly increases the
pressure in the pre-chamber 404 and causes the flame to jet from
the ventilation holes 412.
[0080] Removal of the flame kernel from the spark gap region and
into the flame holder, will reduce the temperature of the spark
surfaces, which reduces the primary factor in spark plug loss of
life, being high temperature oxidation of the spark surface in the
presence of high temperature oxidizing environment. Thus the
removal of the high temperature flame kernel from the spark gap 424
after the spark has occurred will extend the spark surface and thus
the spark plug life.
[0081] Another function of the ventilation hole 412 in the form of
central or primary hole flow is to cool the tubular ground
electrode 408 and the spark area during the induction period prior
to spark, since the inducted fresh charge is of a lower temperature
than the residual gases in the pre-chamber 404. This further
extends spark plug surface life but also reduced the surface
temperatures in the pre-chamber 404, keeping temperatures below the
auto-ignition temperature of the fresh charge.
[0082] Similar to the previously described embodiment, by
controlling the flow of the flame kernel around the center
electrode 406, the usable lifetime of the spark plug 400 is greatly
increased. This is because the first stage surrounds the center
electrode 406 and only allows the small flame kernel to burn around
it, as opposed to traditional systems that have an exposed spark
gap with no protection.
[0083] In another embodiment of the present invention, a crevice
536 is created between an exterior surface of a ceramic insulator
512 and an interior surface of a shell 534 near a base or root 538
of the shell 534 and insulator 512, as illustrated in FIG. 16. The
crevice 536 is designed to enhance heat transfer from the hot
residual fuel/gases to the cooler shell region, which is cooled on
the back side by engagement with the threads of the cylinder (not
illustrated) head (presumably water or oil cooled). The crevice 536
has a large surface area to volume ratio, which promotes cooling of
the residual gas and thus "quenching" of the residual gas
reactivity.
[0084] In one embodiment, the crevice 536 volume is designed to be
approximately 1/5 to 1/10 of the pre-chamber 504 volume, such that
if the pre-chamber 504 is full of residual gases, these will be
compressed into the crevice 536 taking up no more space that that
allowed by the compression ratio of the engine. (i.e. a 10:1 CR
engine will reduce the pre-chamber 504 gas volume to 1/10 during
compression).
[0085] A further embodiment may include surface area enhancement of
the crevice region by a means similar to "threading" the shell 534
in the crevice 536 to further enhance the heat removal capability
of the crevice 536 to cool the residual gas.
[0086] All references, including publications, patent applications,
and patents cited herein are hereby incorporated by reference to
the same extent as if each reference were individually and
specifically indicated to be incorporated by reference and were set
forth in its entirety herein.
[0087] The use of the terms "a" and "an" and "the" and similar
referents in the context of describing the invention (especially in
the context of the following claims) is to be construed to cover
both the singular and the plural, unless otherwise indicated herein
or clearly contradicted by context. The terms "comprising,"
"having," "including," and "containing" are to be construed as
open-ended terms (i.e., meaning "including, but not limited to,")
unless otherwise noted. Recitation of ranges of values herein are
merely intended to serve as a shorthand method of referring
individually to each separate value falling within the range,
unless otherwise indicated herein, and each separate value is
incorporated into the specification as if it were individually
recited herein. All methods described herein can be performed in
any suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g., "such as") provided herein, is
intended merely to better illuminate the invention and does not
pose a limitation on the scope of the invention unless otherwise
claimed. No language in the specification should be construed as
indicating any non-claimed element as essential to the practice of
the invention.
[0088] Preferred embodiments of this invention are described
herein, including the best mode known to the inventors for carrying
out the invention. Variations of those preferred embodiments may
become apparent to those of ordinary skill in the art upon reading
the foregoing description. The inventors expect skilled artisans to
employ such variations as appropriate, and the inventors intend for
the invention to be practiced otherwise than as specifically
described herein. Accordingly, this invention includes all
modifications and equivalents of the subject matter recited in the
claims appended hereto as permitted by applicable law. Moreover,
any combination of the above-described elements in all possible
variations thereof is encompassed by the invention unless otherwise
indicated herein or otherwise clearly contradicted by context.
* * * * *