Patent Application
20240337234
The present disclosure relates generally to a sparkplug, and more particularly to a sparkplug having an iridium cathode and an iron or steel anode configured for extended service life.
Sparkplugs have been used in internal combustion engines for well over a century. Sparkplugs are employed to generate an electrical spark that ignites a mixture of a fuel and air in an engine cylinder to cause a controlled combustion reaction that drives a piston to rotate a crankshaft. Many different sparkplug designs are known, including so-called J-gap or other open sparkplugs conventionally used in automobile engine, as well prechamber sparkplugs used in a variety of applications including heavy duty engine applications, commonly operated at stoichiometrically lean air-fuel ratios.
Sparkplugs are commonly considered consumable parts having a service life that can be considerably less than a service life of the overall engine platform. The physics involved in spark generation tend to cause ejection of ions of the spark electrode materials when a spark is produced, causing erosion of the electrodes over time. In most systems, as erosion of the electrodes proceeds a spark gap between a cathode electrode and an anode electrode eventually become so large that the voltage potential required to produce a spark that can bridge the spark gap becomes impracticably high. When the so-called breakdown voltage becomes too high the sparkplugs are typically replaced.
Sparkplugs employed in many modern engines often include electrodes formed of precious metals demonstrated to extend service life over conventional materials. For instance, it is conventionally known that an iridium cathode paired with a nickel anode provides a longer service life than certain other combinations of materials. Engineers have also experimented with a wide variety of other combinations of metallic materials, incrementally improving sparkplug service life but often with increased material costs.
In recent years many engine platforms have been developed or modified in an effort to achieve increased power density, where a relatively smaller or more lightweight engine produces increased power output as compared to conventional arrangements. Increased power density, where relatively more fuel and air is combusted in a given cylinder size in each engine cycle has resulted in new challenges relative to sparkplug service life, in some instances requiring more frequent sparkplug replacement. One known sparkplug strategy for extended service life is set forth in U.S. Pat. No. 11,035,334B1 to Cress.
In one aspect, a sparkplug includes a sparkplug housing defining a longitudinal axis, a first electrode including at least one electrode prong, and a second electrode including an electrode surface extending circumferentially around the longitudinal axis and spaced a spark gap distance from the at least one electrode prong. The first electrode is formed predominantly of iridium, and the second electrode is formed at least predominantly of iron or steel.
In another aspect, a prechamber sparkplug includes a sparkplug housing forming a prechamber, a center electrode, and a ground electrode. The ground electrode includes a ground electrode surface, and a spark gap within the prechamber is defined between the center electrode and the ground electrode surface. The center electrode is formed predominantly of iridium, and the ground electrode surface is formed at least predominantly of iron or steel.
In still another aspect, a method of operating an ignition system for an internal combustion engine includes energizing an iridium electrode prong positioned at a spark gap distance in a prechamber sparkplug from an iron or steel anode, producing a spark at a spark gap defined between the iridium electrode prong and the iron or steel anode, and igniting a mixture of a gaseous fuel and air in an engine cylinder via the spark.
Referring to
Engine system 10 also includes an air inlet 22 and a fuel supply 24 together structured to provide a flow of a fuel and air to cylinder 16. Engine system 10 may be turbocharged and might include a compressor in a turbocharger to compress intake air or a mixture of intake air and a fuel for conveyance to cylinder 16. Fuel may be admitted by fumigation, but could be port injected or direct injected, for example, in other embodiments. Exhaust from cylinder 16 is conveyed to an exhaust outlet 30 potentially by way of aftertreatment apparatus (not shown). An intake valve 26 movable in engine housing 14 controls a flow of intake air and fuel into cylinder 16. An exhaust valve 28 conventionally operates to control a flow of exhaust to exhaust outlet 30. In a practical implementation engine 12 operates on a gaseous fuel such as methane, ethane, natural gas, or various blends of hydrocarbon fuels and non-hydrocarbon fuels including hydrogen.
Engine system 10 also includes an ignition system 32. Ignition system 32 includes an electronic control unit 34 having or coupled to an ignition circuitry or coil 36. Ignition system 32 also includes a sparkplug 38 positioned to produce an electrical spark that ignites a mixture of a fuel such as a gaseous fuel and air in cylinder 16 for combustion. Sparkplug 38 may include a prechamber sparkplug.
Referring also now to
Sparkplug housing 40 may further include a prechamber tip 52 forming a prechamber 60 and including at least one outlet 54 from prechamber 60. As will be familiar to those skilled in the art moving of piston 18 in cylinder 16 can push a mixture of fuel and air through outlets 54 into prechamber 60 for ignition via a spark. The ignited fuel and air of an ignition charge in prechamber 60 can produce hot jets of combustion gases that exit sparkplug 38 through outlets 54 and ignite a larger main charge of a fuel and air in cylinder 16. Sparkplug housing 40 may further includes an outer surface 56 upon prechamber tip 52 and an inner surface 58 formed at least in part upon prechamber tip 52 that defines prechamber 60. The one or more outlets 54 extend from inner surface 58 to outer surface 56. Inner surface 58 may form an electrode surface including an anode or ground electrode surface as further discussed herein.
Sparkplug 38 further includes a first electrode 62 including at least one electrode prong 64. First electrode 62 may be electrically connected to terminal 44 and thus electrically connected in ignition system 32 to ignition coil 36. Ignition coil 36 may be structured to energize first electrode 62 as a cathode. In the illustrated embodiment first electrode 62 includes a plurality of electrode prongs 64, 65, 66, and 67. Each respective electrode prong may include a leg portion 68 that curves towards an electrode tip 70. Sparkplug 38 also includes a second electrode 72. Second electrode 72 may function as a ground electrode or anode, and includes an electrode surface extending circumferentially around longitudinal axis 42 and spaced a spark gap distance from the at least one electrode prong 64, 65, 66, 67. As noted above inner surface 58 may form the ground electrode surface of second electrode or anode 72.
As can be seen from
To this end, first electrode 62 may be formed predominantly of iridium. Second electrode 72 may be formed at least predominantly of iron or steel. In an embodiment, second electrode 72 consists essentially of iron or steel. In a further refinement, second electrode 72 may consist essentially of a low carbon steel with no alloying elements at all, such as ST523 mild steel. The second electrode or anode may be substantially free of nickel, meaning second electrode 72 may contain no more than trace amounts of nickel. In a refinement, first electrode 62 may be at least 90% iridium, and in a further refinement at least 95% iridium. In a still further refinement first electrode 62 may be approximately 97% iridium, with a balance made up of other elements. First electrode 62 may be formed in part of at least one of rhodium, hafnium, or niobium. One practical implementation includes a first electrode that is predominantly iridium with a balance of first electrode 62 including in whole or in part rhodium.
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Still referring to the drawings generally, but also now to
Referring now also to
As also noted above increased power density in certain engines has increased the challenges to extending sparkplug service life. Operating an ignition system according to the present disclosure can include energizing an iridium electrode prong positioned at a spark gap distance in a prechamber sparkplug from an iron or steel anode. Fuel and air has been urged into the prechamber based on movement of a piston, such that production of the spark triggers combustion of the fuel and air in the prechamber to cause ignition of a main charge in the associated cylinder as discussed herein. While the present disclosure is not limited to any particular firing density, in some applications the mixture of gaseous fuel and air in an engine cylinder may have a density of at least 20 kilograms per cubic meter, at least 25 kilograms per cubic meter, or potentially still higher.
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims. As used herein, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more.” Where only one item is intended, the term “one” or similar language is used. Also, as used herein, the terms “has,” “have,” “having,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.
