Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02P—IGNITION, OTHER THAN COMPRESSION IGNITION, FOR INTERNAL-COMBUSTION ENGINES; TESTING OF IGNITION TIMING IN COMPRESSION-IGNITION ENGINES
  • F02P9/00—Electric spark ignition control, not otherwise provided for
  • F02P9/002—Control of spark intensity, intensifying, lengthening, suppression
  • F02P9/007—Control of spark intensity, intensifying, lengthening, suppression by supplementary electrical discharge in the pre-ionised electrode interspace of the sparking plug, e.g. plasma jet ignition
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T13/00—Sparking plugs
  • H01T13/20—Sparking plugs characterised by features of the electrodes or insulation
  • H01T13/32—Sparking plugs characterised by features of the electrodes or insulation characterised by features of the earthed electrode
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T13/00—Sparking plugs
  • H01T13/54—Sparking plugs having electrodes arranged in a partly-enclosed ignition chamber
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T21/00—Apparatus or processes specially adapted for the manufacture or maintenance of spark gaps or sparking plugs
  • H01T21/02—Apparatus or processes specially adapted for the manufacture or maintenance of spark gaps or sparking plugs of sparking plugs
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T13/00—Sparking plugs
  • H01T13/20—Sparking plugs characterised by features of the electrodes or insulation

Definitions

• lean fuel mixture which is a mixture of air and fuel containing an 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 which 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.
• the spark gap is confined in a cavity having a volume that may represent a relatively small fraction of the total engine cylinder displacement.
• a portion of the cavity is shaped as a dome and has various tangential induction/ejection holes.
• 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. [0008] Another challenge in spark plug design is premature spark plug wear.
• a spark plug can generate high velocity flame jets with low COV and long operating life - the benefits of which may include faster combustion in the main chamber, leading to improved NOx versus fuel consumption (or efficiency) trade-offs.
• a pre-chamber spark plug includes a metallic shell, 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 some implementations, 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 some implementations, the ground electrode is attached to the shell. In some implementations, 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.
• 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.
• the center electrode has an aerodynamic shape which improves the flow stream line through the gap from the center hole.
• the flame kernel is transported to a back chamber of the pre-chamber, and a second port permits 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 turbulence generated within the pre-chamber which further speeds 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.
• a pre-chamber spark plug includes a shell, and an end cap attached to the shell. Additionally, the pre-chamber spark plug includes an insulator disposed within the shell.
• 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 is defined by the shell and end cap.
• a ground electrode is attached to the shell.
• 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 holds the ring in place.
• the end of each spoke is attached to the shell.
• a pre-chamber spark plug is manufactured.
• a ground electrode is attached to the shell.
• the ground electrode includes a tubular electrode.
• the tubular electrode has an inner ring located in surrounding relation to the center electrode.
• precious metal is attached to the center electrode and to the ground electrode that represents the sparking surface.
• 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.
• the gapping tool is inserted between the center electrode and the ground electrode prior to final attachment of the ground electrode to the shell. In some instances, this gap is best maintained if this is the final heating step in the process.
• 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.
• EB electron beam
• the ideal new spark gap ranges from 0.15 mm to 0.35 mm.
• the 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.
• 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.
• a pre-chamber spark plug in another aspect, includes 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 surrounds a distil end of the center electrode.
• the ground electrode includes a tubular ring spaced in surrounding relation to the center electrode, and has a radial offset circumferential extension extending axially past the distil end of the center electrode forming a geometry which serves as an aerodynamic ram region.
• combustion in an internal combustion engine is facilitated.
• An air/fuel mixture is ignited in a pre-chamber of a pre-chamber spark plug. Igniting the air/fuel mixture includes 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.
• 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 which functions as a "flame holder" by creating a recirculation zone.
• 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.
• 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.
• a pre-chamber spark plug in another aspect, includes 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 includes an inner ring spaced in surrounding relation to the center electrode forming a spark gap.
• a laser light beam is 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.
• Some implementations include 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, whereas an electric spark requires higher voltage to achieve break-down and spark as the pressure increases.
• Laser ignition may enable ignition at pressures above the break-down voltage limits of conventional electric ignition systems.
• a method of facilitating combustion in operation of an engine comprises: receiving air/fuel mixture from a combustion chamber of the engine into an enclosure of a spark plug igniting the received air/fuel mixture in a spark gap within the enclosure; directing the ignited air/fuel mixture through the spark gap
• Aspect 4 according to any one of aspects 1 to 3, comprising directing air/fuel mixture in a swirling flow around the interior of the enclosure and to an end of the enclosure opposite the combustion chamber end; and shielding the air/fuel mixture igniting in the spark gap from the swirling flow.
• Aspect 5 according to aspect 4, comprising shielding the ignited air/fuel mixture exiting the spark gap from the swirling flow.
• Aspect 6 according to any one of aspects 1 to 5, where the spark plug is an Ml 4 to M24 size and comprising delaying maximum pressure in the enclosure due to combustion of the air/fuel mixture for 7 or more crank angle degrees of the engine after igniting the air/fuel mixture in the spark gap.
• Aspect 7 according to any one of aspects 1 to 6, comprising jetting ignited air/fuel mixture from inside the enclosure into a combustion chamber of the engine only after igniting substantially all of the air/fuel mixture in a half of the enclosure opposite the combustion chamber end. More of the air/fuel mixture is ignited than not, and in certain instances, all of the air/fuel mixture is ignited.
• a spark plug for an engine comprises: a spark gap in an enclosure of the spark plug; and a passage in the interior of the enclosure that during operation of the engine receives flow from outside of the enclosure and directs the flow through the spark gap predominantly away from a combustion chamber end of the enclosure, the spark plug adapted to produce a peak flow velocity (i.e., the maximum flow velocity) in the spark gap that is at least 10% of the peak flow velocity into the enclosure.
• the passage in the interior of the enclosure directs the flow away from the combustion chamber end of the enclosure. In certain instances, more of the flow is in this direction than not, and in certain instances, all of the flow is in this direction.
• Aspect 12 according to any one of aspects 8 to 1 1, where the spark plug is an M14 to M24 size spark plug and the passage extends at least 1.0 mm beyond an end of the spark gap toward the combustion chamber end of the enclosure.
• Aspect 15 according to any one of aspects 8 to 14, where the spark plug is an M14 to M24 size; and where the spark plug is adapted to reach maximum pressure in the enclosure due to combustion of air/fuel mixture in 7 or more crank angle degrees of the engine after a spark in the spark gap.
• Aspect 16 according to any one of aspects 8 to 15, comprising a metallic shell; an electric insulator in the shell; a central electrode extending from the insulator; and one or more ground electrodes defining the spark.
• Aspect 18 according to aspect 16 or 17, where the one or more ground electrodes comprises a tube defining the passage and comprising an arm extending from the tube, away from the combustion end of the enclosure, to the shell.
• Aspect 19 according to any one of aspects 16 to 18, where the central electrode is polygonal in axial cross-section.
• FIG. 1 illustrates a cross-sectional view of a portion of an example pre- chamber spark plug
• FIG. 2 is a perspective view of the example tubular electrode
• FIG. 4 is a plan view of the example tubular electrode
• FIG. 5 is a cross-sectional view of the example tubular electrode having a first electrode surface ring on a substrate material
• FIG. 6 is a perspective view of an example tubular electrode
• FIG. 7 is an end view of an example end cap for the pre-chamber spark plug
• FIG. 8 is a cross-sectional view of the example end cap of FIG. 7;
• FIG. 9 is a cross-sectional view of a portion of an example pre-chamber spark plug
• FIG. 10 is a cross-section view of an example pre-chamber pre-chamber spark plug assembly with dimensions labeled.
• FIGS. 11a and 1 lb show example pre-chamber spark plug assemblies with square and triangular electrodes.
• FIG. 12 shows an example spark plug assembly with multiple ground electrodes.
• FIG. 13 shows an example spark plug assembly with a velocity control tube centered over the spark gap.
• FIG. 14 is a cross-sectional view of an example large bore piston cylinder assembly and an example pre-chamber spark plug;
• FIG. 15 is a cross-sectional view of another example pre-chamber spark plug
• FIG. 16 is a cross-section view of the example pre-chamber spark plug of FIG. 15 illustrating fuel flow into the pre-chamber;
• FIG. 17 is a cross-sectional view of an example pre-chamber spark plug having a secondary fuel injector in the pre-chamber;
• FIG. 18 is a cross-sectional view of an example combined gas admission valve with igniter/spark plug
• FIG. 19 is a close up cross-sectional view of the example igniter/spark plug of FIG. 18;
• FIG. 20 is a close up cross-sectional view of a crevice of a pre-chamber
• FIG. 21 is a cross-sectional view of a portion of an example pre-chamber spark plug including a braze ring;
• FIG. 22 is an up-close view of the example braze ring disposed inside the pre-chamber spark plug of FIG. 21 ;
• FIGS. 23 a and 23b are top-down and cross-section views of a pre-chamber spark plug assembly without a velocity control tube;
• FIG. 24 is a cross-section view of the pre-chamber spark plug assembly of FIGS 23a and 23b with a front velocity control tube;
• FIG. 25 is a cross-section view of the pre-chamber spark plug assembly of FIGS 23a and 23b with a rear velocity control tube;
• FIG. 26 is a cross-section view of the pre-chamber spark plug assembly of FIGS. 23a and 23b with both front and rear velocity control tubes;
• FIGS. 27a-27c are output from a computational fluid dynamics analysis showing the velocity (FIG. 27a), velocity vectors (FIG. 27b) and air/fuel mixture distribution (FIG. 27c) in a pre-chamber spark plug lacking a velocity control tube;
• FIGS. 28a-28c are output from a computational fluid dynamics analysis showing the velocity (FIG. 28a), velocity vectors (FIG. 28b) and air/fuel mixture distribution (FIG. 28c) in a pre-chamber spark plug configured as in FIG. 10 at the same conditions as FIGS. 27a-27c; and
• FIG. 29 is output from a computational fluid dynamics analysis showing the velocity in a pre-chamber spark plug configured as in FIG. 10 at different conditions from FIGS. 28a and 28b.
• the concepts herein relate to a pre-chamber spark plug.
• aspects of the plug address challenges associated with providing a repeatable and controllable ignition delay time during the combustion process.
• the spark plug achieves a more efficient combustion process and longer life.
• the pre- chamber spark plug can include, for example, a tubular velocity control tube to control the flame kernel development, ignition delay time, flame jet evolution, main combustion chamber burn rate, and may consequently improve engine performance.
• the delay time refers to 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.
• 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.
• the tubular electrode 1 10 can be other tubular shapes (e.g., square tubing, triangular tubing, or other tubing) and, in certain instances, may match the axial cross section of the center electrode 102.
• the shell 1 12 is made from a high-strength metal capable of withstanding exposure to high temperatures.
• the shell 1 12 creates a portion of the pre-chamber volume of the spark plug 100.
• the shell 112 is attached to the insulator 104 and holds an end cap 116.
• the 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.
• the end cap 116 can be flat, have a domed shape, a conical "V" shape, or another shape. In certain instances, the end cap 116 can be integrated into the shell 1 12, as opposed to being a separate piece attached to the shell 112 as is shown.
• FIG. 2 is a perspective view of the example tubular electrode 1 10.
• the tubular electrode 110 has an inner ring 130 and an outer ring 132 imbedded within the tubular ground electrode 1 10. In the example of FIG. 2, the inner ring 130 and outer ring 132 are connected by three spokes 134.
• a tubular inner ring, or velocity control tube 136 Extending from the inner ring 130 in the center portion of the tubular electrode 1 10 is a tubular inner ring, or velocity control tube 136. As illustrated in FIG. 1, the velocity control tube 136 extends away from the disk portion 1 14 in one direction into the front chamber 108. A central opening 138 extends through the inner ring 130 and the velocity control tube 136.
• the ground electrode 110 has another design, such as a J-shape forming a spark gap with the end or sidewall of the center electrode 102 with a tube or walls welded or otherwise attached on the front and/or back side to create a velocity control tube.
• the example tubular electrode 110 can be made from a copper alloy, a nickel alloy, or some other relatively highly-conductive metal.
• 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.
• a first electrode surface ring 142 of, for example, platinum or alloys thereof, rhodium or alloys thereof, tungsten or alloys thereof, nickel or alloys thereof, iridium or alloys thereof lines the inner surface 140 of the inner ring 130.
• the inner surface 140 of the inner ring 130 is lined with an iridium-rhodium alloy or a nickel alloy.
• 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.
• the surface material makes up either the entire structural body of the center electrode 102 and/or the tubular electrode 110, or is attached via welding, brazing, or other suitable attachment method to the structural material.
• the alternative spark surface material may be made in the shape of a tube which is press fit, brazed, or welded into the structural body of the ground electrode.
• the tubular electrode 1 10 may have a ring of a different material inserted inside the inner diameter of the base structure of the tubular electrode 110.
• the different material can be different than the base material of the tubular electrode 1 10, for example a different material that is highly resistant to erosion or oxidation.
• the purpose of the inserted ring is to increase the erosion resistance and oxidation resistance of the electrode by adding expensive erosion and oxidation resistant material only to the spark surface.
• the example 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.
• the example tubular electrode 110 may be cast or machined substantially as a single piece (i.e. as a single piece or as a small number of pieces, such as 3 or 4 pieces), 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 some implementations, 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.
• 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 example 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.
• both the first and second electrode surface rings 142, 144 are assembled to the tubular electrode 1 10 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.
• 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 11 1 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 1 1 1 to the pre-chamber spark plug 100 without damaging other components of the tubular electrode 11 1 or the pre-chamber spark plug 100.
• the first electrode surface ring 142 can be attached to the example tubular electrode 1 10.
• the tubular electrode 1 10 is cast around the first electrode surface ring 142.
• 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.
• the electrode surface ring material can be deposited on a powdered metal substrate using physical or chemical vapor deposition.
• 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 1 10 having a first electrode surface ring 142 attached or deposited on a substrate material 143, for example a nickel alloy or highly conductive alloy.
• 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.
• the example tubular electrode 110 can be assembled from separate components. FIG.
• 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.
• the annular receiving portion 154 could be pressed inward into the notched portion 152 of the velocity control tube 136 holding it in place.
• the notched portion 152 includes an annular protrusion about its circumference that fits into a divot in the annular receiving portion 154 of the tubular electrode 1 10 to improve the attachment between the disk portion 114 and velocity control tube 136.
• 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 1 14.
• 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 1 16, and through a plurality of periphery holes 164 (see also FIGS. 7 and 8).
• the center hole 162 is oriented to direct its flow at and into the interior of the velocity control tube 136.
• 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 1 10 where it is ignited by an electric spark.
• the velocity control tube 136 collects the flow from the center hole 162 and causes the flow in the interior of the tube 136 to stagnate and create a higher pressure than the pressure around the exterior of the tube 136 and the pressure at the exit of the tubular electrode 1 10.
• the velocity of the flow from the center hole 162 together with the pressure differential creates high velocity flow, guided by the velocity control tube 136, through the spark gap towards the back chamber 106.
• the velocity of the air/fuel mixture causes the initial flame kernel to be transported into the back chamber 106.
• the flow through the primary central hole includes fresh air/fuel charge with a low level of residuals.
• the periphery holes 164 are oriented to introduce a swirling motion to the air/fuel mixture drawn in through 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.
• the flame kernel can consume all but a nominal amount of fuel in the back chamber 106. In certain instances, the flame kernel consumes all of the fuel in the back chamber 106.
• ignition can be delayed by the flow of the flame kernel to the back chamber 106.
• the combustion process starts in the back chamber 106 and progresses 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.
• the pre-chamber spark plug 100 is adapted to reach maximum enclosure pressure due to combustion of the air/fuel mixture in 7 or more crank angle degrees of the engine after a spark event in the spark gap.
• 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 specified (e.g., improved or optimized in some instances) 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.
• FIG. 6 is a perspective view of an example tubular electrode 180.
• 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.
• three spokes 134 extend radially outward from the exterior of the inner ring 130.
• 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.
• FIGS. 7 and 8 show an end view and a cross-sectional view, respectively, of the example end cap 1 16 for pre-chamber spark plug 100.
• 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 some
• the end cap 116 is centered on 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 and the velocity in the spark gap.
• 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 or the shell itself 112.
• the periphery holes 164 are configured to create a swirling motion of the air/fuel mixture in the pre-combustion chamber.
• the end cap 1 16 is attached to the shell 1 12 via welding, brazing, and the like.
• the end cap may also be flat (perpendicular to the shell) or "V" shaped.
• the shell 1 12 and end cap 1 16 may be shaped such that the end cap is 116 is flat and the majority of the insertion depth is due to the length of the shell 112.
• the shell 1 12 and end cap 1 16 may also be shaped such that the end cap 116 has a protruding shape (like a dome or "V" shape) and a portion of the insertion depth is due to the length of this end cap shape.
• FIGS. 7 and 8 show the example 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 1 16 that includes an example 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 some instances, when the end cap 1 16 is assembled to shell 1 12.
• FIG. 8 is a cross-sectional view of the end cap 1 16 and shows an example penetration angle for the periphery holes 164.
• the central hole sizes are likely to range from 0.1 mm to 2.0 mm in diameter, but larger holes sizes may also be prescribed.
• FIG. 7 illustrates a swirl angle for the periphery holes 164.
• 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.
• FIG. 8 illustrates a penetration angle for the periphery holes 164.
• 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.
• 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.
• FIG. 9 is a cross-sectional view of an example pre-chamber spark plug 200.
• 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 1 12, 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.
• an interior surface 1 18 of the shell 1 12 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.
• the ground electrode may also be constructed as a thin ring, which is suspended by legs attached anywhere on the shell including near the base where the core extends from the shell (112) or near the tip of the shell (108) or even attached from the end-cap itself (1 16). Any attachment method such as welding, brazing or laser welding or the like can be used to attach the tube.
• the example pre-chamber spark plug 200 operates in a manner similar to that described above for the operation of example pre-chamber spark plug 100.
• a tubular inner ring, or velocity control tube 236 extends axially both into the front chamber 108 and into the back chamber 106.
• the ignition delay time can be further increased.
• 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.
• the design can also accommodate the insertion of a precious or non- precious metal ring inside the ground electrode which is in electrical contact with the ground electrode body and thus in contact with the shell.
• the ring insert may be mounted via press-fit, interference fit, laser tack weld, laser weld or brazing. The design holds the ring insert in place even if the welds are to soften or break simply due to differential thermal expansion of the unconstrained section of the ground electrode tube relative to the section constrained by the spokes.
• FIG. 10 shows a cross section view of an example pre-chamber spark plug assembly similar to that of FIG. 9.
• Certain relevant dimensions in FIG. 10 are labeled as A-K.
• the dimensions are relevant to pre-chamber spark plug an Ml 4 to M24 sized plug (i.e., a spark plug where the threaded portion of the shell is a metric Ml 4 to M24 thread).
• the outer diameter of the shell is slightly smaller than a root diameter of the thread.
• the total volume of the back chamber 106 and the front chamber 108 can range between 1000 mm 3 and 3000mm 3 .
• dimension A is the length the ground electrode 210 extends past the spark surface of center electrode 102, forming part of a passage. In certain instances, dimension A has a minimum length of 1.0 mm.
• the extended ground electrode 210 creates the velocity control tube 236, and thus dimension A can characterize the length of the velocity control tube 236.
• the velocity control tube 236 creates a stagnation pressure zone which enables air/fuel mixture flow to sweep the flame kernel into the rear pre-chamber 106.
• the clearance between the end of the center electrode 102 and the end cap 116 can range between 1 mm and 12 mm.
• Dimension B is an extension of the ground electrode 210 away from the combustion chamber end of the spark plug enclosure.
• dimension B has a length of at least 0.1 mm.
• dimensions C and D define the cross-sectional area of an inlet tube notch in the velocity control tube 236.
• dimension C the depth of the notch
• dimension D the length of the notch
• the inlet tube notch minimizes flame kernel quenching effects under low speed operation and cold start.
• Dimension E defines the depth of a flame holder notch in the center electrode 102. In certain instances, dimension E has a range of 0.10 to 0.70 mm. The flame holder notch allows greater recirculation and also reduces quenching effects as a flame kernel travels to the rear pre-chamber 106.
• the example center electrode 102 can have a rounded front defined by dimensions F and G.
• dimension F is the radius of curvature of the rounded tip of the center electrode 102.
• a rounded tip enables more symmetric flow into the spark gap and reduces flow resistance.
• a flat tip with no curvature is easier to manufacture, and can be used in the implementations described herein, but permits greater flow turbulence and can reduce flow velocity.
• a curved tip may be used in some instances.
• the diameter of the center electrode 102 is defined by dimension G.
• dimension G has a length of 3 mm.
• a range of lengths of dimension F can be selected to satisfy the relation G/F ⁇ 1.
• the length of the spark gap surface is defined by dimension H.
• dimension H has a range between 2.50 to 6.00 mm.
• the spark gap is the distance between the center electrode 102 and the ground electrode 236 and is designated by dimension J. In some cases, the spark gap distance is not a single value along the length of the spark gap surface.
• the ground electrode 236 can have a conical profile defined by taper angle K. In certain instances, taper angle K can have a range between 0.10 and 2.5 degrees. In the example shown, the minimum spark gap distance is at the front of the ground electrode 236, and the maximum spark gap distance is at the rear of the ground electrode 236.
• the spark will occur in the region near the minimum gap at the front of the spark surface.
• dimension J can have a minimum in the range 0.10 to 0.20 mm.
• the front of the spark gap surface will be warmer than the rear of the spark gap surface. Greater thermal expansion of the front of the spark gap surface can cause the spark gap distance to become more uniform and parallel along the length of the spark surface.
• the spark gap dimension J during nominal warm operation can have a length of 0.42 mm.
• a spark gap with parallel surfaces can spark along its entire length and increase flame kernel generation.
• the ground electrode and center electrode can each have a cylindrical shape, a polygonal shape, an irregular shape, or some other shape.
• FIG. 10 shows a cross-section with a cylindrical center electrode 102 and a cylindrical ground electrode 236.
• the center electrode and ground electrode may be polygonal, such as the example square and triangular shapes shown in FIGS. 11a and lb.
• the velocity control tube on the front of the electrodes can have a shape similar to that of the electrodes (e.g., a triangular shape for FIG. 1 lb) or have a shape different to that of the electrodes.
• the electrodes also may have an irregular shape or parts of an electrode may have a different shape.
• the inner perimeter of an electrode may have a different shape than the outer perimeter of the same electrode.
• the electrodes can also have a variable shape along their axial length.
• the electrodes can taper, have step changes, or have other changes in dimension.
• the center electrode and ground electrode also need not be the same shape.
• the spark surface of the center electrode and corresponding surface of the ground electrode may match, and the portion ahead of the center electrode (i.e., the velocity control tube) may have a different shape.
• the electrodes can also have different shapes or include different or multiple parts, positions, locations, or spark surfaces.
• FIG. 12 shows an example spark plug assembly with multiple ground electrodes 704a, 704b surrounding a single center electrode 702.
• the example ground electrodes 704a, 704b are adjacent but do not meet.
• the multiple ground electrodes 704a, 704b define the flow passage through the spark gap.
• the ground electrodes 704a, 704b can have forward extending wall portions that, together, form a velocity control tube ahead of the spark gap.
• the electrodes 704a, 704b can also have rearward extending extensions. In other instances, a velocity control tube can be attached to the forward or rearward facing surfaces of the ground electrodes 704a, 704b.
• FIG. 13 shows a front cross-section of an example spark plug assembly.
• the velocity control tube 806 is a cylinder centered on the spark gap between the center electrode 802 and a J-shaped ground electrode 804.
• the example velocity control tube 806 can be attached to the ground electrode 804 or the center electrode 802. In certain instances, the tube 806 can have portions that extend downward over the sides of the gap.
• the velocity control tube can be cylindrical, polygonal, or some other shape. The velocity control tube need not be centered over the center electrode.
• FIG. 14 illustrates a cross-sectional view of an example pre-chamber spark plug assembly 300.
• 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.
• FIG. 15 illustrates a close up cross-sectional view of the pre-chamber 304 of the example pre-chamber spark plug assembly 300 of FIG. 14.
• the pre-chamber 304 is connected to the engine combustion chamber 302 by a series of ventilation holes 324 and bounded by a shell 334.
• 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 FIG. 15 shows three ventilation holes, more or less are contemplated. Additionally, the ventilation holes 324 (or any of the holes herein) could be in the form of slots or other shaped holes.
• the example 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.
• a center electrode 310 Around the center electrode, at the center electrode's 310 distil 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.
• the center electrode 310 connects to a voltage source (not shown), through the interior of the insulator 312, to the shell 334, which is electrically grounded.
• the ground electrode 308 forms a circular region around the distil end of the center electrode 310 forming spark gap 314. Further, 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. The insulator 312 acts as the velocity control tube. Additionally, above the spark gap 314 are two lateral slots or holes 318 drilled into the insulator 312. The lateral holes 318 act to ventilate a flame kernel after an ignition event.
• the area around the center electrode 310 and inside the insulator 312 is referred to as a first stage 320 of the pre-chamber 304.
• the first stage 320 can act 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 two lateral holes 318 are shown in the insulator 312, a greater or smaller number of lateral holes may be used.
• 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 engine combustion chamber 302 (i.e., cylinder).
• the example ground electrode 308 extends further into the pre-chamber 304 than the center electrode 310.
• the example ground electrode 308 includes a radial offset circumferential extension extending axially past the distil end of the center electrode 310 forming an aerodynamic nose cone.
• the shape of the aerodynamic nose cone is configured to facilitate a flow of an air/fuel mixture through spaces between the ground electrode 308 and the center electrode 310.
• the nose cone is aerodynamic in that it is designed to smoothly guide flow (and minimize separation of flow) around the leading edge of the ground electrode 308. In other instances, the nose of ground electrode 308 could be blunt.
• the extension creates an aerodynamic ram region 316 (i.e., velocity control tube).
• the aerodynamic ram region 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.
• the vapor through the spark gap 314 flows parallel to the spark gap 314 and can have a velocity range of 5 m/sec or greater, and in some instances 50 m/s.
• H/V*360*RPM can be less than or equal to 3 crank angle degrees of the engine.
• the spark gap 314 width can be altered to affect useable life of the spark plug, in some instances.
• FIG. 16 illustrates the flow physics of an example of how combustion is created and managed in the example pre-chamber 304.
• a 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 engine combustion 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.
• the primary and secondary flow 328, 300 purge residual fuel from previous ignition cycles from the spark gap 314 and the second stage 322 with fresh evenly dispersed fuel.
• the secondary flow disperses uniformly around the second stage 322 of the pre-chamber 304.
• the primary flow 328 is captured by the aerodynamic ram region 316.
• the aerodynamic ram region 316 gathers the primary flow around the spark gap 314.
• the velocity of the primary flow 328 into the spark gap 314 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 region 316 and the first stage 320, thereby causing the fuel to flow into the first stage 320 of the pre-chamber 304.
• the flow into the spark gap 314 also purges the spark gap 314 of residuals, replacing any residuals with a predominantly fresh charge.
• the residuals can be replaced by a mixture composed more of fresh charge than not.
• the mixture is composed of fresh charge and residuals, and in certain instances, the mixture is composed entirely of fresh charge.
• a distal end of the center electrode 310 is flat to facilitate the primary flow 328 into the spark gap 314.
• fuel will flow through the lateral holes 318. This flow is predominantly backward and away from the end cap. As such, more of the flow is in this direction than not, and in certain instances, all of the flow is in this direction.
• the lateral holes 318 are angularly offset such that they are not perpendicular to the center axis 301. This can prevent the air/fuel mixture from the secondary flow 330 from filling the first stage 320. Therefore, the pressure differential caused by aerodynamic ram region 316 is not disturbed by the lateral holes 318.
• the flow through the lateral holes 318 retains a measure of its entrance velocity. This maintains a pressure lower than the stagnation pressure of the fluid in the aerodynamic ram region 316. Thus, a pressure difference is created across the spark gap.
• the fuel in the spark gap 314 will ignite thus creating a flame kernel 332.
• the flame kernel 332 travels into the first stage 320 of the pre-chamber 304 where the flame kernel 332 is protected from the outside environment by the relatively small size of the first stage 320.
• the first stage 320 acts as a flame holder.
• 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.
• 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.
• the flame kernel 332 remains small. This keeps the temperature inside the first stage 320 low and minimizes damage to the spark gap 314, the ground electrode 308, and the center electrode 310.
• the flame kernel 332 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 332 is carried by the secondary flow 330 and wraps around the insulator 312. At this point the flame kernel 332 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 engine combustion chamber 302 where it ignites the fuel in the engine combustion chamber 302.
• the fuel to air ratio of the example 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.
• the secondary fuel injector 326 increases the fuel to air ratio.
• 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 atypical to enrich 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.
• the ignition process can run hotter.
• FIG. 18 illustrates a gas admission valve 402, integrally formed with a shell 416 of a pre-chamber 404, combined with a spark plug 400.
• a gas admission valve 402 integrally formed with a shell 416 of a pre-chamber 404, combined with a spark plug 400.
• FIG. 19 illustrates a close-up view of the pre-chamber 404 of FIG. 18.
• the pre-chamber 404 is connected to a cylinder of an engine (not shown) system by and end cap 440 with ventilation holes 412. Similar to implementations 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.
• 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.
• 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. 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.
• 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.
• the area expansion is created by a notch cut into the center electrode at the exit of the spark surface area.
• the recirculation zone can hold reactive particles in the recirculation loops and acts effectively as a flame holder - preventing the blow-out of the flame kernel which is swept out of the spark gap region.
• This flame kernel will burn the fuel in the first stage until it exits through the slots 418 into 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.
• Removal of the flame kernel from the spark gap region and into the flame holder can reduce the temperature of the spark surfaces. Reducing the temperature of the spark surfaces can reduce a primary factor in spark plug loss of life: 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 after the spark has occurred can extend the spark surface and thus the spark plug life, reducing the likelihood (or preventing) flame kernel quenching.
• another function of the central or primary hole flow is to cool the tubular ground electrode 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. This further extends spark plug surface life but also reduced the surface temperatures in the pre-chamber, keeping temperatures below the auto- ignition temperature of the fresh charge.
• a crevice 936 is created between an exterior surface of a ceramic insulator 912 and an interior surface of a shell 934 near a base or root 938 of the shell 934 and insulator 912, as illustrated in FIG. 20.
• the crevice 936 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 936 has a large surface area to volume ratio, which promotes cooling of the residual has and thus "quenching" of the residual gas reactivity.
• a further embodiment may include surface area enhancement of the crevice region by a means similar to "threading" the shell 934 in the crevice 936 to further enhance the heat removal capability of the crevice 936 to cool the residual gas.
• a braze ring may be used above or below the ground electrode and melted to give good heat transfer in a braze oven.
• a laser welder, friction welder, or the like can be used to weld the ground electrode to the shell
• FIG. 21 is a cross-sectional view of a portion of an example pre-chamber spark plug including a braze ring
• FIG. 22 is an up-close view of the braze ring disposed inside the pre-chamber spark plug, from FIG. 21.
• the outer ring 1032 of the ground electrode 1010 includes an angular cut out 1006, which creates the annular gap 1004 for the braze ring 1002 to sit in prior to laser welding.
• the ground electrode 1010 is pressed into the shell 1 12 such that the ground electrode 1010 seats onto the stepped portion 120. After seating the ground electrode 1010 onto the stepped portion 120, the braze ring 1002 is placed into the annular gap 1004.
• a laser welder may be utilized to melt the braze ring 1002 thereby allowing the melted braze ring 1002 to flow into the annular gap 1004 adhering the ground electrode 1010 to the shell 112 in a braze-welding process.
• This can create a strong bond between the ground electrode 1010 and the shell 1 12 such that no heat distortion is created between the two bodies once bonded together.
• only the braze ring 1002 is melted such that the ground electrode 1010 and the shell 1 12 do not have a distorted shape after the braze-welding process. Further, the angular cut out 1006 does not have to be angular.
• the center electrode may be made of either solid metal alloy or from the welding of two cylinders together where one of the cylinders may be called the base material and the other a precious metal material. Once proper alignment is generated via the manufacturing process, the precious metal and base metals can be joined by a variety of methods such as resistance welding, inertial welding and or laser welding. [00132] Similarly, a precious metal hollow cylinder may be created which is slipped over the base material center electrode having been reduced in diameter so that a cylinder outside a "pin" formation may be generated. The precious metal hollow cylinder is held in place by a retaining cap which is affixed by welding or mechanical means (such as threads).
• FIGS. 23a, 23b show a spark plug 500 with an end cap 512, but without a velocity control tube.
• FIG. 23a shows a view of the spark plug 500 showing the top of the end cap 512.
• FIG. 23b shows a cross-sectional view of the spark plug 500.
• a tubular ground electrode 505 is supported from the shell 503 by arms 506a, 506b. Rather than attaching to the sidewalls of the shell 503, the arms 506a, 506b extend backward and attach to a rearward surface of the shell 503.
• the ground electrode 506 surrounds center electrode 502 and is separated by center electrode 502 by spark gap 504.
• the end cap 512 surrounds the electrodes 502 and 506.
• the top of the end cap 512 has multiple center holes 510a-510f and multiple lateral holes 508a, 508b.
• FIG. 24 shows an example of how the spark plug 500 could be adapted according to the concepts herein to produce spark plug 520.
• Example spark plug 520 is substantially similar (without variation affecting the operation as described) to the spark plug 500 shown in FIG. 23, but with an included front velocity control tube 514.
• the velocity control tube 514 can be affixed to the front of the ground electrode 506, its arms 506a, 506b, or any supporting structure such as a ring.
• FIG. 25 shows an example of how the spark plug 500 could be adapted according to the concepts herein to produce spark plug 530.
• Example spark plug 530 is substantially similar (without variation affecting the operation as described) to the spark plug 500 shown in FIG. 23, but with an included rear velocity control tube 515.
• the velocity control tube 515 can be affixed to the rear of the ground electrode 506, its arms 506a, 506b, or any supporting structure such as a ring.
• FIG. 26 shows an example of how the spark plug 500 could be adapted according to the concepts herein to produce spark plug 540.
• Example spark plug 540 is substantially similar (without variation affecting the operation as described) to the spark plug 500 shown in FIG. 23, but with both front and rear velocity control tubes 514 and 515.
• the velocity control tubes 514, 515 can be affixed to the ground electrode 506, its arms 506a, 506b, or any supporting structure such as a ring.
• CFD computational fluid dynamics
• FIG. 27b shows a velocity vector plot of the spark plug lacking the velocity control tube and FIG. 28b shows a velocity vector plot of the spark plug configured as in FIG. 10.
• FIG. 28c shows the air/fuel mixture distribution plot of the spark plug lacking the velocity control tube and FIG. 28C shows the air/fuel mixture distribution plot of the spark plug configured as in FIG. 10.
• Both configurations are an Ml 8 plug, having a 3.0 mm diameter spark surface (i.e., the adjacent surfaces forming the spark gap), a 0.42 mm maximum spark gap and the same configuration of shell 1 12 and end cap.
• the flow conditions outside of the shell 112 were modeled to represent conditions at 20 crank angle degrees, before top dead center, in an engine having a 155 mm bore, and a 180 mm stroke operating at 750 rotations per minute (RPM).
• FIGS. 27a-27c lack a velocity control tube, and have a typical ring ground electrode 505 that does not extend forward beyond the end of the spark surface or the center electrode 502 or rearward of the spark surface.
• FIGS. 28a-28c have a ground electrode with a velocity control tube 236 that extends beyond the end of the center electrode 102 toward a combustion chamber end of the plug.
• the tube 236 surrounds and encircles the center electrode 102, and also extends rearward of the spark surface.
• the extent of the velocity control tube 236 beyond the end of the center electrode 102 was selected, by conventional fluid analysis, to produce the velocities discussed below.
• the extent of the velocity control tube 236 rearward of the spark surface was selected, by conventional fluid analysis, to shield flow exiting the spark gap from turbulent flow in the pre-chamber.
• the spark surface of FIGS. 28a-28c begins at the base of the radiused tip of the center electrode 102 and extends rearward to the diametrical step and is 3.5 mm long.
• FIGS. 27a, 28a the peak velocity of incoming fresh air/fuel mixture from the combustion chamber through the center hole 162 is nearly the same in both instances - 64 m/s in FIG. 27a and 54 m/s in FIG. 28a.
• the incoming flow impinges on the end of the center electrode 502 is predominantly directed laterally outward and then eventually cycles around the exterior of the ground electrode 505 to the rear of the pre-chamber. As such, more of the flow is is in this direction than not, and in certain instances, all of the flow is in this direction.
• a stagnation zone at the end of the center electrode 502 causes a high pressure that further tends to drive the incoming flow laterally outward.
• the high velocity in front of the ground electrode 505 creates a low pressure zone that draws flow up from the rear of the pre-chamber through the spark gap.
• the peak velocity at the midpoint of the spark surface is 8 m/s, that flow is traveling rearward to forward.
• residual gasses combustion air/fuel mixture
• this cycle feeds the spark gap with a flow from rearward to forward of residual gasses.
• Reference to FIG. 27c confirms this, showing that the highest lambda (i.e., leanest air/fuel mixture) is both rearward in the pre-chamber and behind and in the spark gap.
• FIGS. 28a, 28b the incoming flow impinges on the end of the center electrode 102 and, although initially directed laterally, the flow is captured by the walls of the velocity control tube 236 and directed rearward into the spark gap.
• a stagnation zone at the end of the center electrode 102 causes a high pressure that further tends to drive the flow into the velocity control tube and rearward.
• the extent of the velocity control tube 236 is selected to achieve this flow pattern.
• the peak velocity at the midpoint of the spark surface is 44 m/s.
• that flow is of fresh air/fuel mixture received directly from the combustion chamber via the center hole 162.
• this cycle feeds the spark gap with a flow from forward to rearward of fresh air/fuel for combustion.
• the fresh air/fuel mixture maintains enough velocity to flow through the entire spark surface and to the rear of the pre-chamber, sweeping out any residuals that might be in the spark gap (e.g. from the previous combustion cycle) and fueling the reward region of the pre-chamber.
• the spark plug is fired, the flame kernel produced by the electrical spark is moved quickly through the spark gap and into the reward portion of the pre-chamber to reduce the tendency of the kernel to quench on the spark surfaces.
• the velocity moving the flame kernel through the spark gap allows a larger spark surface without quenching the kernel than could be achieved with a zero or low flow velocity through the gap.
• a larger spark surface improves the life of the spark plug because there is more area over which to generate the electric spark and the material generating the spark wears less.
• the peak velocity of incoming fresh air/fuel mixture from the combustion chamber through the center hole 162 is 55 m/s.
• the peak velocity at the midpoint of the spark surface is 27 m/s.
• the peak velocity at the midpoint of the spark surface is 49% of the peak velocity of the incoming flow in the center hole 162.
• the spark gap is fed with a flow from forward to rearward of fresh air/fuel for combustion and the velocity continues through the entire spark surface and to the rear of the pre-chamber.

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