A radiofrequency plasma spark plug configured to equip a combustion chamber including: an annular shell with a main axis; a central electrode made of a conductive material, extending along the main axis and including an inner portion arranged inside the annular shell and an outer portion arranged outside the annular shell: an annular electrically insulating part extending at least about the inner portion of the central electrode so as to be interposed between the shell and the electrode, the insulating part only covering part of the outer portion of the central electrode. The insulating part includes an annular flange concealing the entire circular terminal surface of the shell relative to the uncovered part of the electrode
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http://www.faqs.org/patents/app/20090146542#ixzz0tTQ9byKe