is 20 millimeters then the electric field becomes 20 000 0 020 or one million volts per meter half its original value eventually distance d 2 becomes so great that the electric field does not reliably exceed the dielectric breakdown strength of the air fuel mixture and ionization ceases to occur fig7 illustrates one form of the invention an auxiliary electrode 72 is embedded in the insulator 75 the tip 78 is covered by the insulator material in region 81 as indicated by the insert 84 auxiliary electrode 72 may be connected to the shell 33 as at region 90 initially current enters electrode 27 as indicated by arrow 84 jumps to the shell 33 through the plasma 85 and exits the shell 33 into the engine through multiple paths such as through its mounting threads as indicated by arrow 86 as erosion occurs the insulator 75 departs from its initial shape indicated by phantom lines 92 in fig8 tip 78 of the auxiliary electrode 72 now becomes exposed now when a high voltage is applied to the igniter two paths exist for a plasma to follow one is the usual path p 5 in fig9 the other path is indicated as p 6 of fig9 and runs from the central electrode 27 to the now exposed auxiliary electrode 72 restated two current return paths are available to the central electrode 72 path p 5 runs to the shell 33 in the usual manner path p 6 runs to.