Patent Application
20180342855
Spark plugs deliver an electric spark into the combustion chamber of a spark-ignited piston engine. The internal combustion engine marketplace is froth with different types of spark plug configurations to serve a variety of functions. However, the spark plugs designed for piston-engine aircraft are particularly challenging due to the fact that bore sizes of the cylinder are generally larger (calling for 18 mm spark plugs) and each cylinder often utilizes 2 spark plugs, typically in a horizontally-opposed configuration, see
Aviation spark plugs have a number of important attributes. For example, the barrel sizes vary between Size E—shielded ⅝ in. with 24 threads, and Size H—shielded ¾ in. with 20 threads. Aircraft mounting threads (18 mm)—include the following: Size B—with 13/16 in. reach and ⅞ in. hex; Size M—with ½ in. reach and ⅞ in. hex; and Size U—with 1⅛ in. reach and ⅞ in. hex. By comparison, automotive mounting threads (14 mm) have different sizes: Size J—with ⅜ in. reach and 13/16 in. hex; Size L—with ½ in. reach and 13/16 hex; and Size N—with ¾ in. reach and 13/16 hex.
The electrode design of a spark plug typically uses a conventional single center electrode with variations of one, two, three, four or more ground electrodes on a single plug. There are different design features (fine-wire, iridium, nickel, etc.) to evoke different sparking characteristics.
There have been hundreds of publications, periodicals and patent applications dealing with spark plug design and manufacture for use in automotive engines (e.g., Heywood, John. Internal Combustion Engine Fundamentals. McGraw-Hill, 1988 and Schwaller, Anthony, Motor Automotive Mechanics. Delmar Publishers, 1988). Notable among the patent field are those that reference the suppression of radio-frequency electromagnetic interference (e.g. U.S. Pat. No. 4,713,582 and U.S. Pat. No. 4,568,855) and the use of unique electrode designs (e.g., U.S. Pat. No. 6,091,185, U.S. Pat. No. 7,309,951 and U.S. Pat. No. 7,528,534) that offer more chances for the electric impulse in the piston engine to spark with resistance to fouling. However, none of the references are targeted at the unique challenges of the aircraft piston engine, which has more complexity and dimensional aspects that nullify inventions of the past.
Internal combustion engines in piston aircraft differ greatly from those in automobiles. Automobiles utilize a high rpm transmission with a gear reduction system, where piston aircraft do not have a transmission but instead have a much larger crankshaft and thrust bearings to directly rotate the propeller. As a result, aircraft cylinders are larger and the rpms are lower for aircraft engines.
Automobiles utilize water-cooled cylinders which are maintained at a constant temperature for stable operation, whereas piston aircraft cylinders are air-cooled by the inflow of outside air controlled by the pilot's throttle and airspeed. Detonation will occur in the aircraft engine when the cylinder gets too hot, which can be impacted by high outside air temperature and/or slow speeds at too high a deck angle. Certain pilot operating conditions may not lend themselves to lowering the angle of ascent, which is why either cooling the inlet air, cooling the cylinder, or increasing the octane of the fuel is critical to prevent detonation. Accordingly, many automotive spark plugs do not perform to the requirements of an aircraft engine.
It is also noteworthy that automobile engines are now highly automated whereby the air-to-fuel ratio is maintained at a constant level, adjusted for octane. By comparison, piston aircraft are operated manually at rich and lean mixture configurations subject to pilot discretion. This fact contributes greatly to the existence of combustion fouling from carbon, lead, etc. in aircraft engines when the fuel mixture is momentarily too rich and forms unwanted deposits on spark plugs.
Automobiles are generally operated up to about 30% of their rated power, whereas piston aircraft are generally operated above 75% of their rated power. This infers that piston aircraft are much more vulnerable to detonation incidents because full power is needed at take-off, while cross-country cruise is generally at about 75% power. Accordingly, there are few options to safely lessen the load on the aircraft engine at full power during take-off to avoid detonation. Having a clean spark and unfouled plugs becomes a vital safety issue in an aircraft.
Automobiles use smaller spark plugs with a typical bore size of 2″ to 4″, while most piston aircraft use larger horizontally-opposed spark plugs (2 in each cylinder) with bore sizes between 3″ to 6″. Automobiles have engine rotation speeds ranging from 0-7,000 rpm but rarely operate above ⅓ the maximum rpm available. However, piston aircraft typically have a maximum rotation up to about 2,800 rpm and often operate at or near this maximum a high percentage of the time while in flight. This high rpm activity in propeller aircraft is intensified by the electronic pulse of the piston which can cause electromagnetic interference which can disrupt pilot radio signals and navigational systems—creating a dangerous condition in flight.
In the last several decades the compression ratio of most automotive engines, measuring the ratio of the max vs. min volume in the cylinder has ranged between 9:1 to as high as 14:1. Such ratios on high performance aircraft are lower, typically ranging between 7.5:1 up to 9:1 (with naturally aspirated engines having ratios the higher end and turbocharged engines at the lower end.)
All these factors and more impact the way fuel is combusted and pre-mature engine detonation (knock) is controlled. This is particularly the case when adding the complexity in aircraft at high altitudes needing low vapor pressure gasoline with very high octane levels to sustain peak performance.
Disclosed is a spark plug assembly for a spark plug having an external thread at one end and a terminal at the opposite end, the spark plug further including a hexagonal flange for use in rotating the spark plug to insert or remove the spark plug and a top insulator positioned between the hexagonal flange and the terminal. The assembly includes a housing comprising a sleeve having a first end defining an external thread sized and configured to couple with an ignition harness of a spark-ignited aircraft engine, and a second end defining a hexagonal-shaped cavity sized and configured to receive the hexagonal flange of the spark plug. Upon assembly, the top insulator and terminal of the spark plug are received within the sleeve and the hexagonal flange of the spark plug is received within the hexagonal-shaped cavity of the housing.
The housing further defines an external hexagonal flange for use in securing the housing to the spark plug port of an aircraft engine. A coupling is secured to the housing and includes an internal thread configured to receive the external thread of the spark plug, the external thread of the spark plug being threadingly received within the internal thread of the coupling. The coupling further includes an external thread configured to be received by the spark plug port of the aircraft engine. An insulator is received within the sleeve and surrounds the top insulator of the spark plug.
Described herein is a new approach to spark ignition in an internal combustion engine that improves the precision, reliability and firing impact of the spark in igniting industry-approved gasolines that meet international fuel standards (e.g. ASTM, ISO, GOST, etc.) in any piston-engine aircraft. This invention allows, for example, a uniquely specific 14 mm multi-channel (preferring the 4-electrode) automotive spark plug to be installed into an 18 mm piston aircraft cylinder using a durable shielded housing particularly designed for aircraft use. The design of this invention insulates and dampens sound waves and thereby eliminates electromagnetic interference.
The disclosed spark plug assembly reduces or eliminates any risk of carbon or lead fouling impacting the function of the spark-plug. The invention has applicability beyond aviation engines and is thereby adaptable to different sized cylinder ports, but the preferred embodiment of this unique assembly is tailored to an 18 mm cylinder port of a horizontally-opposed aircraft engine.
Referring to
The spark plug assembly 32 (
Spark plug assembly 32 is shown in assembled form in
Housing 34 may comprise one or more components secured together. Described herein is an embodiment in which housing 34 comprises two separate components with sleeve 38 secured to hex adapter 40. It will be appreciated, however, that these components may instead be fabricated as a single component.
Referring to
An illustrative hex adapter 40 is shown in perspective, second end and left side views, respectively, in
In the spark plug assembly, hex adapter 40 is secured to the end of member 42 opposite the external thread 44, with the first end portion 52 adjacent to member 42. In this combination, member 42 and hex adapter 40 constitute housing 34. In a preferred embodiment the attachment is by welding and is sufficient to provide a strong, sealed assembly. Also in the spark plug assembly, spark plug 10 is positioned with hexagonal flange 22 of spark plug 10 received within hexagonal cavity 60 to secure the two components against relative rotation.
Several views of coupling 36 are provided in
An insulator 70 is shown in perspective in
In an exemplary embodiment the invention combines a premium 14 mm, multi-channel automotive spark plug, with up to 4 electrodes, welded-in-place to an 18 mm spark-plug conversion coupling 36 to make it fully secure for high-vibration propeller aircraft operations. This assembly is then attached to a non-magnetic, metallic cylindrical member 42, preferably brass, which is further insulated and secured to eliminate radio-frequency interference. This is then connected to a standard aircraft ignition harness, a cable which receives an appropriate ignition impulse from the aircraft magneto (or similar starting device) to trigger the production of a spark.
The metallic and other parts may be machined or otherwise fabricated to the appropriate dimensions for either a short plug or a long plug application. In the preferred embodiment, sleeve 38 is non-magnetic, e.g. brass, and the hex adapter and cylindrical member are made from corrosion resistant metal, e.g. stainless steel, to prevent corrosion while in active use. Other metallic or non-metallic options may be utilized in other applications.
The spark plug assembly is suitably fabricated in a preferred embodiment as follows. Sleeve 38 is made of non-magnetic brass or another suitable material and is fabricated, e.g., machined, to the appropriate dimensions for either a long-plug or short plug to hold the 14 mm spark plug securely. Hex adapter 40, typically converting from ⅝ to ⅞ inches, is secured to sleeve 38 by suitable means, such as welding. Coupling 36 is threaded onto spark plug 10. The terminal nut end of spark plug 10 is then inserted into sleeve 38 to position the hexagonal flange of spark plug 10 within hexagonal-shaped cavity 60 of sleeve 10. Coupling 36, spark plug 10 and sleeve 38 are then joined together by induction brazing. This assembly is then pressure checked not to exceed 150 psi to assure there is no airflow leakage in the configuration. The appropriate heat range is also verified.
Finally, insulator 70 is pushed directly into the spark plug assembly between spark plug 10 and sleeve 38. Insulator 70 is sized to be received in an interference with the interior surface 48 of sleeve 38. The open end of sleeve 38 is closed upon attachment of the wiring harness to the spark plug assembly 32 by use of external thread 44.
A key objective of the invention is to produce sparks that minimize or eliminate fouling. It is well known that carbon fouling, MMT fouling and tetraethyllead fouling are common problems when these fuel components are combusted in a piston engine. Multi-day testing a wide range of plug designs on aircraft engines has revealed the unique outcome that the multi-electrode, multi-channel spark plug (either BKR6EQUA and BKR6EQUP) is the preferred plug design that best eliminates fouling in the aircraft. See chart below.
Testing trials were conducted over several months in a Cessna 150 aircraft. Weather conditions varied and the trials typically called for multi-day retests of each plug type to evaluate the outcomes for repeatability. The key verification point was the degree of lead or carbon fouling observed on each of the spark plugs after operation of the aircraft. The table above is a partial list of spark plugs that were evaluated for this trial. The BKR6EQU family of spark plugs was clearly the most effective of all the spark plugs tested. The spark plugs were not only clean of fouling, but also ran smoothly and started easily and received the highest satisfaction from the aircraft test pilot. The spark plugs were subsequently further tested on a Beechcraft 60 Duke with very similar results.
This application claims the benefit of U.S. Provisional Application No. 62/511,388 filed May 26, 2017, which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62511388 | May 2017 | US |
