Abstract: A sheathed-element glow plug has a front resistance heating filament connected in series with a rear resistance regulating filament having a higher positive temperature coefficient (PTC) than the front filament. The rear filament is made of cobalt/iron alloy consisting of 44-80% by weight cobalt, 20-35% by weight iron, up to 1% miscellaneous components and nickel, if present, in an amount of 0 to less than 15% by weight. The alloy has a resistance ratio (20.degree.-1000.degree. C.) which is no more than approximately 7.5 in the range from about 100.degree. C. to between about 400.degree. C. to about 600.degree. C., and which ratio rises sharply to values from 7.5 to greater thin 12 in the range from 400.degree. C. to 600.degree. C. to about 900.degree. C.

Abstract: A glow plug for an air compressing internal combustion engine of the type having a tube which is closed at one end and connected to a plug housing on an opposite end with a wire filemant-like resistance element disposed in an insulating material within the tube and formed two series-connected resistance filaments, of which the rear resistance filament, serves as a regulating filament, having a higher positive temperature resistance coefficient than the front resistance filament, which serves as a heating filament, is improved so as to enable the heating up time to be reduced without adversely impacting upon the effective life of the glow plug. In accordance with various embodiments, this result is achieved through the use of, for example, special alloys for the material of the regulating filament which have a resitance at 1000.degree. C. that is greater than their resistance at 20.degree. C. by a resistance ratio over about 7.5:1, and preferably greater than 12:1, and in particular, about 14:1.