A corona igniter, comprising: an insulator formed of an insulating material, said insulator extending longitudinally along a center axis from an insulator upper end to an insulator tip, said insulator having a thickness extending from an insulator outer surface to an insulator inner surface, said insulator inner surface presenting a slot extending longitudinally along said center axis from said insulator upper end toward said insulator tip, and said insulator outer surface being round at said insulator tip; a central electrode disposed in said slot of said insulator and extending longitudinally from an electrode upper end to an electrode tip, said electrode tip being spaced from said insulator tip by said insulating material; a shell formed of metal surrounding a portion of said insulator and extending longitudinally from a shell upper end to a shell firing surface; and said insulator thickness tapering between said shell firing surface and said insulator tip, and said insulator thickness not increasing between a start of the taper and said insulator tip; wherein said insulator includes a core nose projection having a length extending from said shell firing surface to said insulator tip; and characterised in that said taper in said insulator thickness extends along a percentage of said length of said core nose projection, and said percentage of said length is greater than or equal to a calculated percentage defined according to the following equation: Y = − 2.9 % × R CE R INS − R CE + 59.56 % wherein Y is said percentage of said length of said core nose projection of said insulator, R CE is a radius of said center electrode, said radius of said center electrode is a distance extending from said center axis to an electrode outer surface, and R INS is a radius of said insulator, said radius of said insulator is a distance extending from said center axis to said insulator outer surface, and said radius of said insulator is measured along a portion of said insulator wherein said insulator thickness is constant. an insulator formed of an insulating material, said insulator extending longitudinally along a center axis from an insulator upper end to an insulator tip, said insulator having a thickness extending from an insulator outer surface to an insulator inner surface, said insulator inner surface presenting a slot extending longitudinally along said center axis from said insulator upper end toward said insulator tip, and said insulator outer surface being round at said insulator tip; a central electrode disposed in said slot of said insulator and extending longitudinally from an electrode upper end to an electrode tip, said electrode tip being spaced from said insulator tip by said insulating material; a shell formed of metal surrounding a portion of said insulator and extending longitudinally from a shell upper end to a shell firing surface; and said insulator thickness tapering between said shell firing surface and said insulator tip, and said insulator thickness not increasing between a start of the taper and said insulator tip; wherein said insulator includes a core nose projection having a length extending from said shell firing surface to said insulator tip; and characterised in that said taper in said insulator thickness extends along a percentage of said length of said core nose projection, and said percentage of said length is greater than or equal to a calculated percentage defined according to the following equation: Y = − 2.9 % × R CE R INS − R CE + 59.56 % wherein Y is said percentage of said length of said core nose projection of said insulator, R CE is a radius of said center electrode, said radius of said center electrode is a distance extending from said center axis to an electrode outer surface, and R INS is a radius of said insulator, said radius of said insulator is a distance extending from said center axis to said insulator outer surface, and said radius of said insulator is measured along a portion of said insulator wherein said insulator thickness is constant. wherein Y is said percentage of said length of said core nose projection of said insulator, R CE is a radius of said center electrode, said radius of said center electrode is a distance extending from said center axis to an electrode outer surface, and R INS is a radius of said insulator, said radius of said insulator is a distance extending from said center axis to said insulator outer surface, and said radius of said insulator is measured along a portion of said insulator wherein said insulator thickness is constant.