INTERNAL-COMBUSTION ENGINE IGNITION DEVICE AND IGNITION METHOD

An ignition device of the present invention repeatedly applies a high voltage across electrodes of an ignition plug with work of a high voltage generating circuit. In a combustion chamber that has a gas flow therein, active species produced by an initial discharge are forced to flow downstream by the gas flow, and thus a resistance Rdc of an air-fuel mixture of that portion is temporarily lowered, and thus, the high voltage application is carried out at a short discharge interval T in such a manner that a resistance ratio (Rdc/Rg) provided relative to a resistance Rg of an air-fuel mixture placed along the shortest distance lg between the electrodes is smaller than 1 (one). With this, a discharge channel produced is gradually extended toward the downstream side of the gas flow thereby elongating the length of the discharge channel. The extension of the discharge channel contributes to growth of a flame core and shortening of an initial combustion period and thus brings about assured ignition.