Electric heating – Heating devices – Resistive element: igniter type
Patent
1981-09-25
1984-10-02
Mayewsky, Volodymyr Y.
Electric heating
Heating devices
Resistive element: igniter type
123145A, 219523, 219553, 338316, 361266, F23Q 722
Patent
active
044750307
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to a combustion system for a compression-ignition engine and, more particularly, to an improved glow plug which is adapted for igniting relatively lower-cetane-number fuels as well as conventional relatively higher-cetane-number fuels.
2. Background Art
In the face of ever-decreasing supplies of conventional diesel fuels, it would be very advantageous if conventional compression-ignition engines could be easily adapted to burn more plentiful alternative fuels such as, for example, alcohol, the light hydrocarbon fractions of petroleum, and synthetic fuels made from coal or shale oil. However, these relatively lower-cetane-number alternative fuels require an elevated or higher temperature for autoignition than that which is developed during the compression stroke of conventional compression-ignition engines. For example, methanol, a fairly plentiful alternative fuel which is attracting world-wide interest, will not autoignite in a conventional diesel engine because the cetane numer of methanol is only about 0 to 10 whereas conventional Grade 2-D diesel fuel has a cetane number of at least 40 and thus easily autoignites.
It is known, however, that relatively lower-cetane-number fuels can be ignited with a hot surface such as a glow plug by the phenomenon known as surface ignition. The required temperature of the hot surface, in order to facilitate ignition of a fuel, is not directly related to the cetane number of a given fuel but depends on other parameters including fuel composition, engine speed, and other engine operating conditions such as inlet air temperature.
I have found that a glow plug continuously maintained at a temperature of at least 871.degree. C. (1600.degree. F.) is required to facilitate ignition of methanol in an operating compression-ignition engine. Other investigators have determined that other alternative fuels such as ethanol and isooctane petroleum fuel require substantially greater glow plug temperatures to facilitate ignition.
Standard starting-aid glow plugs are designed to be electrically heated to about 816.degree. to 1038.degree. C. (1500.degree. to 1900.degree. F.) only during startup of an engine burning conventional diesel fuels. The ignition elements of known starting-aid glow plugs, such as described in U.S. Pat. No. 3,749,980 issued to Baxter on July 31, 1973, typically comprise a metallic casing which contains a helical electrical resistance wire embedded in a powdered electrically-insulative material, such as magnesium oxide. After engine startup and during engine operation these standard glow plugs are no longer electrically heated such that their temperature becomes merely a function of engine load or power output and thus normally relatively lower compared to their electrically-energized state. Consequently, when this type of glow plug is continuously electrically heated, to the elevated temperature range required to ignite a wide range of relatively lower-cetane-number alternative fuels in a conventional compression-ignition engine, the very hot metallic casing of this glow plug, which is exposed to the gases of the combustion chamber, rapidly deteriorates due to oxidation and other chemical attack.
It is well known that electrically-conductive ceramics, such as silicon carbide, adequately resist oxidation and other chemical attack at temperatures as high as about 1371.degree. C. (2500.degree. F.). However, ceramic material is also very brittle and therefore prone to failure when subjected to the severe cyclic thermal conditions of an engine. Another starting-aid glow plug, as described in U.S. Pat. No. 4,237,843 issued to Page et al on Dec. 9, 1980, has a small, solid, cylindrical, ceramic heating element substantially encased in a metallic-alloy body part and exposed to the gases of the combustion chamber through holes formed in the body part. The glow plug also has a two part electrode and conductive braid which is intended to accommodate any differential thermal expansion which may occur between the electrod
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Caterpillar Tractor Co.
Mayewsky Volodymyr Y.
Woloch Anthony N.
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