Image Number 5 for United States Patent #6794803.
At least one of a center electrode and a ground electrode of an engine spark plug is a Ni-base alloy containing, in weight percentage, 0.5.about.2.5% Si, 0.1.about.1.2% Mn, 3.2.about.5.0% Al, 0.9.about.2.8% Cr, 0.001.about.0.025% C in addition to Ni and unavoidable impurities. And, a value S/V is in a range from 1.7 mm.sup.-1 to 3.9 mm.sup.-1 when `S` represents a surface area of the ground electrode and `V` represents a volume of the ground electrode.
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