Abstract: An electrical igniter has two electrodes separated over the bore of a semiconductive annular element. One electrode is mounted at the operative tip of the igniter and has an orifice through which the bore opens from the igniter. A capillary tube extends from a supply of liquid, such as water or a hydrocarbon fuel, and opens into the cavity formed by the bore and the orifice. Small quantities of liquid are introduced into the cavity via the tube and electrical energy is applied to the electrodes to cause discharge within the cavity. The discharge causes a plasma to be ejected through the orifice, for igniting a fuel-air mixture externally of the igniter. The discharge causes vaporization and molecular disruption of liquid present in the cavity that increases the concentration of low activation energy species within the plasma and thereby improves the efficiency of ignition.