GB2541880A - Shield arrangement to enable reliable ignition for lean burn spark ignited engines - Google Patents

Abstract

Air flow around an electrode of a spark plug is shielded by a circumferential, eg cylindrical, shield 34 which may be part of the spark plug, fig.6, or an extension of a cooling adapter 18 (fig.1). The adapter 18 comprises a body 36 with an outer surface engaging the cylinder head 14 and a threaded inner surface for receiving the spark plug. The adapter 18 includes a longitudinally extending shield portion 34a having an open distal end forming an interior volume in which an electrode 42 is positioned. The shield 34a extends into the cylinder by a distance greater than the distance by which the electrode 42 extends into the cylinder. The shield 34 may have vents or orifices 38. The spark plug may be J-gap type or may have multiple ground electrodes.

Description

SHIELD ARRANGEMENT TO ENABLE RELIABLE IGNITION FOR LEAN BURN

SPARK IGNITED ENGINES

Technical Field [0001] The present disclosure relates generally to cooling adaptors for spark plugs in internal combustion engines and more specifically to cooling adapters that provide air flow shielding for spark plugs.

Background [0002] Spark plugs provide an ignition source in cylinders of internal combustion engines. The conditions within the cylinder impact the size and nature of the controlled explosions contained within the cylinder. Cooling adapters are provided to provide an interface between spark plugs and cylinder heads. The cooling adapters further provide a conduit through which coolant can be passed. The coolant mitigates the heat generated by combustion that is experienced by the spark plug. Cooling adapters engage the cylinder head and spark plugs engage the cooling adapter.

[0003] Engines can be fueled stoichiometrically, rich, or lean. Lean-burn refers to the burning of fuel with an excess of available air. Brake Mean Effective Pressure (BMEP) provides a manner of describing performance of an engine. In high BMEP engines running lean, flow conditions within cylinders are highly turbulent at the spark gap of the spark plug(s). To remove the spark gap from the turbulent conditions, the spark gap may be recessed within a wall of the cylinder. This recession increases a distance between the spark gap and the fuel to be ignited within the cylinder. This increase in distance generates a delay between the when the spark is provided and when ignition of the fuel is achieved. Additional solutions have provided enclosures or domes that surround the spark gap and offer small holes to communicate across the enclosure/dome. These enclosures/domes retain heat and provide increased bulk and weight. Additionally, the small holes are susceptible to being plugged by contaminants, thereby providing potential reduced effectiveness.

[0004] Accordingly, what is needed is a solution that reduces the turbulence seen by a spark gap without imparting significant delay of ignition and that is less susceptible to contaminant-related reductions in effectiveness.

Summary [0005] The present disclosure provides a spark plug adapter. In one embodiment, the adapter comprises a body with a circumferential wall having an inner surface forming an opening and an outer surface adapted to engage a cylinder head of an engine. The adapter also includes a shield portion extending longitudinally from the circumferential wall. The positioning of the shield portion permits placement thereof in a combustion chamber of the engine. The shield portion has an open distal end a first distance from the circumferential wall. The shield portion forms an interior volume from the circumferential wall to the open distal end. The opening of the adapter is sized and threaded to receive a spark plug having an electrode such that the electrode is positioned in the interior volume of the shield portion a second distance from the circumferential wall. The first distance (that the shield extends into the cylinder) is greater than the second distance (that the electrode extends into the cylinder).

[0006] Another embodiment of the present disclosure includes an internal combustion engine, comprising a combustion chamber formed by a cylinder block and a cylinder head, the combustion chamber including a wall surface defining a first plane; a cooling adapter coupled to the cylinder head and extending through the first plane into the combustion chamber, the cooling adapter including an open distal end positioned in the combustion chamber a first distance from the first plane; and a spark plug positioned in the cooling adapter and intersecting the first plane, the spark plug including an electrode positioned in an interior volume of the cooling adapter, the electrode being positioned in the combustion chamber a second distance from the first plane, the first distance being greater than the second distance.

[0007] Yet another embodiment includes a method, comprising: providing fuel into a combustion chamber of an engine; generating a spark in the combustion chamber at an electrode positioned a first distance from a flame deck of the combustion chamber; shielding, with a cylindrical shield, air flow in the combustion chamber around the electrode between the flame deck and a plane that is the first distance away from the flame deck; and combusting the fuel through an open distal end of the cylindrical shield.

Brief Description of the Drawings [0008] The above-mentioned and other features of this disclosure and the manner of obtaining them will become more apparent and the disclosure itself will be better understood by reference to the following description of embodiments of the present disclosure taken in conjunction with the accompanying drawings, wherein: [0009] Figure 1 is an cross sectional view of an engine assembly showing a spark plug cooling adapter with a shield portion; [0010] Figure 2 is the same cross-sectional view of Fig. 1 illustrating certain dimensions; [0011] Figure 3 is a cross-sectional view of the shield portion of Fig. 1; [0012] Figures 4 and 5 are cross-sectional views of alternative embodiments of a shield portion; [0013] Figures 6-8 are cross-sectional views of spark plugs having a shield portion integral therein; and [0014] Figure 9 is a cross-sectional view of the spark plug of Fig. 6 installed in a cylinder of an engine and showing certain dimensions.

[0015] Although the drawings represent embodiments of the various features and components according to the present disclosure, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the present disclosure. The exemplification set out herein illustrates embodiments of the disclosure, and such exemplifications are not to be construed as limiting the scope of the disclosure in any manner.

Detailed Description of Embodiments [0016] For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings, which are described below. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. The disclosure includes any alterations and further modifications in the illustrated device and described methods and further applications of the principles of the disclosure, which would normally occur to one skilled in the art to which the disclosure relates. Moreover, the embodiments were selected for description to enable one of ordinary skill in the art to practice the disclosure.

[0017] Referring to Figure 1, an engine cylinder 10 is shown for a spark ignited engine that is formed by a block 12 and a head 14. Engine cylinder 10 further includes a spark plug adapter 18 and a spark plug 20.

[0018] Head 14 illustratively provides an upper surface or flame deck 22 of cylinder 10. Head 14 also includes a spark plug bore 16 for each cylinder 10 of the engine. Spark plug bore 16 is sized and shaped to receive spark plug adapter 18. Spark plug bore 16 is illustratively internally threaded to engage with head spark plug adapter 18.

[0019] Spark plug adapter 18 is illustratively a cooling adapter. Adapter 18 comprises a body 36 and a shield 34. Body 36 includes an externally threaded lower portion 24 connected to an upper portion 25, a seal seat 28, an upper seal 30, an outer seat 48, and an internally threaded lower portion 32. An external surface of upper portion 25 cooperates with head 14 to define a flow path 26. Externally threaded lower portion 24 engages with threads of spark plug bore 16. However, embodiments are envisioned where adapter 18 is pressed-in or clamped to head 14. Outer seat 48 provides a limit on the extent of engagement of lower portion 24 within bore 16. In one embodiment, a seal 52 is abutted to seat 48. Adapter 18 is shown as a single piece, but embodiments are envisioned where adapter 18 is constructed from multiple pieces.

[0020] Upper seal 30 is illustratively an o-ring seal located within seal seat 28. When adapter 18 is mounted in spark plug bore 16, seal 30 engages spark plug bore 16 forming a seal therebetween. Seal 30 thus provides an upper sealed boundary for flow path 26. Flow path 26 is annular space that surrounds spark plug adapter 18. Coolant is routed through flow path 26 to absorb and carry away heat from spark plug adapter 18. The threads of spark plug adapter 18 and spark plug bore 16 seal to provide a lower boundary of flow path 26. Adapter 18 further includes an inner annular shoulder 44 that provides a seat for the spark plug 20. Accordingly, it should be appreciated that both spark plug adapter 18 and spark plug bore 16 provide walls that cooperate to define flow path 26. Internally threaded lower portion 32 is sized, shaped, and threaded to receive spark plug 20 therein. Shoulder 44 provides additional sealing and acts as a stop to limit further travel of the spark plug 20 within adapter 18. In certain embodiments, a seal member 46 is provided proximate shoulder 44. Embodiments are further envisioned in which indexing marks are provided on adapter 18 to allow a user to gauge the relative position of adapter 18 to head 14 and/or adapter 18 to plug 20. The indexing provides an indication of the positioning of the electrode 42 relative to the flame deck 22.

[0021] The bulk of spark plug adapter 18 is adapter body 36 that is generally a cylindrical/circumferential wall having various thicknesses and profiles that is illustratively constructed from steel. Shield 34 (or shroud) extends from lower portion 24 of adapter body 36. Figs. 1-5 show a plurality of embodiments of shield 34. Shield 34 is illustratively constructed from Nickel. However embodiments are envisioned where shield 34 is constructed from other temperature and corrosion resistant material. Indeed, other embodiments of shield 34 provide an end or other portion thereof constructed from metal having a relatively high thermal conductivity such as copper, brass, and aluminum. In one example, shield 34 comprises a bi-metal structure including a base and a core. The base is exposed to combustion gases. The base comprises a cavity and the core comprises the relatively high thermally conductive metal, e g. copper, brass, aluminum, and combinations thereof, in the cavity. In one variation, the cavity extends to upper portion 25 and opens to flow path 26, thereby enabling heat transfer from shield 34 via the core to the cooling fluid. The core may be poured through the opening into the cavity.

[0022] In certain embodiments, shield 34 is coupled to body 36 via friction welding. In one variation, shield 34 and body 36 comprise different base metals. Shield 34a of Figs. 1-3 is illustratively a cylindrical wall of constant thickness (excepting that it is rounded/tapered/ at its lower end). Shield 34a includes two rows of spaced vents 38 (orifices). Shield 34a illustratively includes two rows each having 16 vents 38 that are evenly spaced circumferentially. Shield 34b of Fig. 4 is substantially similar to shield 34a, excepting that it is devoid of vents 38. In some embodiments, vents 38 are drilled. Other embodiments are envisioned where vents 38 are formed through electrical discharge machining. Shield 34c differs from shields 34a-b in that it has a tapering (narrowing) wall thickness as it extends away from externally threaded lower portion 24. The addition of shield 34 can increase the temperature in the area of the electrode. Tapering of shield 34 reduces the amount of material that can absorb heat and therefore can reduce the temperature increase. The temperature increase can also be controlled using a bimetal shield (described above) to increase shield cooling. All versions of shield 34a-c have an open lower (distal) end. In each embodiment, the internal diameter and the lower opening 40 are substantially constant (only expanding a bit at the distal tip due to rounding of the end). Thus, in the shown embodiments, opening 40 of the open lower end has a diameter (width) that is at least as great as the rest of the internal width of shield 34a-c. As another point of reference, the width of opening 40 is equal to or greater than the internal width of shield 34a-c at a lower edge of an electrode 42 of spark plug 18 when spark plug 18 is mounted therein. Embodiments are envisioned where the width of opening 40 is less than the width of shield 34a-c at the lower edge of an electrode 42 of spark plug 18. Indeed, embodiments are envisioned where the width of opening 40 is greater than 50% (or any percent greater than 50%) of the width of shield 34a-c at the lower edge of an electrode 42 of spark plug 18. Spark plug 20 is illustratively a conventional spark plug with electrode 42 that threadably engages internally threaded lower portion 32. Figs. 1-5 show spark plug 20 with multiple ground electrodes.

[0023] In assembly, spark plug adapter 18 is mounted in spark plug bore 16. When so mounted, shield 34a-c extends into cylinder 10, through/past flame deck plane 50 defined by flame deck 22, by a length illustrated and denoted as “Y,” (Fig. 2). Similarly, when assembled, electrode 42 of spark plug 20 extends into cylinder 10, through/past flame deck plane 50 by a length illustrated and denoted as “X,” (Fig. 2). It should be appreciated that length Y is greater than length X so that electrode 42 is within the interior volume proscribed by shield 34. The interior volume proscribed by shield 34 is a portion of an overall interior volume proscribed by adapter 18. In one embodiment, length Y is twice as long as length X. The dimensions of X and Y are illustratively altered to achieve desired airflow and ignition propagation. In one set of embodiments, X ranges from .1 mm to .5 mm and Y ranges from 1 mm to 10 mm. The X/Y ratio is illustratively greater than 1, although embodiments where the ratio is below 1 are also envisioned. Shield 34a-c illustratively comprises a core material of high thermal conductivity (copper, brass, aluminum, etc.) with Nickel, 4140 SAE steel, or similar high temperature resistance, corrosion resistance material as a base.

[0024] Figs. 6-9 depict spark plug 20 as a J-gap style plug with integral shield 34 and depict the same variations in shield 34 shown in Figs. 3-5. Fig. 9 shows lengths “A” and “B” that are analogs of X and Y. Protrusion of the center electrode 42 into the main combustion chamber within the shield 34 from the head flame deck 22 is shown as “A.” Protrusion of the open end of the shield 34 into the main combustion chamber from the head flame deck 22 is shown as “B.” These dimensions are adjusted to give desired flame properties. In the provided examples, “A” ranges from . 1mm to 5mm and “B” ranges from 5.1mm to 10mm. The provided embodiments give a ratio of B to A of at least 2.

[0025] In operation, shield 34a-c at least partially impacts (i.e. reduces) air/charge flow around electrode 42. The inclusion of vents 38 allows further customization of the flow within shield 34b and around electrode 42. Indeed, embodiments are envisioned that alter the number, size, location, and attitude/angle/orientation of spaced vents 38 to achieve desired flow characteristics around electrode 42. Still further embodiments fashion vents 38 as nozzles. Overall, embodiments of vents 38 are envisioned to customize flow in any desired fashion. As shown, vents 38 are cylindrical and each include a central axis that intersects the central axes of all other vents 38 at a common point located at a center of the shield 34. Embodiments are further envisioned where the thickness of the wall of shield 34 is altered/chosen to provide a desired mass and heat capacity for the overall adapter 18.

[0026] While the embodiments have been described as having exemplary designs, the present disclosure may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.

Claims (23)

1. A spark plug adapter, comprising: a circumferential wall having an inner surface forming an opening and an outer surface adapted to engage a cylinder head of an engine, and a shield portion extending longitudinally from the circumferential wall permitting placement thereof in a combustion chamber of the engine, the shield portion having an open distal end a first distance from the circumferential wall, the shield portion forming an interior volume from the circumferential wall to the open distal end, wherein the opening of the adapter is sized and threaded to receive a spark plug having an electrode such that the electrode is positioned in the interior volume of the shield portion a second distance from the circumferential wall, and the first distance is greater than the second distance.

2. The spark plug adapter of claim 1, wherein the shield portion includes a cylindrical wall forming the interior volume.

3. The spark plug adapter of claim 2, wherein the cylindrical wall includes a plurality of spaced orifices.

4. The spark plug adapter of any preceding claim, wherein a width of an opening in the open distal end is at least 50% of a width of the interior volume at the second distance from the circumferential wall.

5. The spark plug adapter of any of claims 2 to 4, wherein the cylindrical wall tapers from the circumferential wall to the distal open end.

6. The spark plug adapter of any preceding claim, wherein the circumferential wall includes an annular shoulder that provides a seat for the spark plug.

7. An internal combustion engine, comprising: a combustion chamber formed by a cylinder block and a cylinder head, the combustion chamber including a wall surface defining a first plane; a cooling adapter coupled to the cylinder head and extending through the first plane into the combustion chamber, the cooling adapter including an open distal end positioned in the combustion chamber a first distance from the first plane; and a spark plug positioned in the cooling adapter and intersecting the first plane, the spark plug including an electrode positioned in an interior volume of the cooling adapter, the electrode being positioned in the combustion chamber a second distance from the first plane, the first distance being greater than the second distance.

8. The engine of claim 7, wherein the cooling adapter includes a perimeter wall forming the interior volume.

9. The engine of claim 8, wherein the cooling adapter has a longitudinal axis, and the perimeter wall is cylindrical and extends parallel to the longitudinal axis.

10. The engine of claims 8 or 9, wherein the perimeter wall includes a plurality of orifices forming flow paths between the combustion chamber and the interior volume of the cooling adapter.

11. The engine of any of claims 8 to 10, wherein at least one of an inner surface and an outer surface of the perimeter wall has a conical profile.

12. The engine of any of claims 8 to 11, wherein the perimeter wall tapers from the first plane to the distal open end.

13. The engine of any of claims 7 to 12, wherein the open distal end of the cooling adapter includes an end surface lying in a second plane and forming an opening in the second plane, and an area of the end surface is less than an area of the opening in the second plane.

14. The engine of any of claims 7 to 13, wherein a width of an opening in the open distal end is at least 50% of a width of the interior volume at the first distance from the first plane.

15. The engine of any of claims 7 to 13, wherein a width of an opening in the open distal end is at least equal to a width of the interior volume at the first distance from the first plane.

16. The engine of any of claims 7 to 15, wherein the cylinder head forms the wall surface of the combustion chamber.

17. The engine of claim 16, wherein the wall surface includes a flame deck.

18. The engine of any of claims 7 to 17, wherein the spark plug includes a center electrode and a ground electrode each positioned in the interior volume of the cooling adapter, a spark gap is formed between the center electrode and the ground electrode, and the cooling adapter extends from the plane beyond the center electrode and the ground electrode.

19. The engine of any of claims 7 to 18, wherein the cooling adapter includes an outer annular shoulder and an inner annular shoulder, and the spark plug is seated on the inner annular shoulder.

20. A method, comprising: providing fuel into a combustion chamber of an engine; generating a spark in the combustion chamber at an electrode positioned a first distance from a flame deck of the combustion chamber; shielding, with a cylindrical shield, air flow in the combustion chamber around the electrode between the flame deck and a plane that is the first distance away from the flame deck; and combusting the fuel through an open distal end of the cylindrical shield.

21. The method of claim 20, wherein a width of an opening in the open distal end is at least 50% of a width of an interior volume of the cylindrical shield at the first distance from the flame deck.

22. The method of claims 20 or 21, wherein the second plane is a second distance from the flame deck, and the second distance is greater than the first distance.

23. The method of any of claims 20 to 22, further including routing the air flow in the combustion chamber through a plurality of orifices in a perimeter wall of the cooling adapter.