An igniter system for measuring gas velocity and/or gas composition within the combustion chamber of an internal combustion engine. The igniter has an insulator body and conductive shell around the top portion of the insulator body, configured so that the igniter can be installed in place of a conventional spark plug. The igniter has two pairs of electrodes, each pair of electrodes providing a spark gap and operable to generate a spark within the combustion chamber. An activation and measurement unit is operable to generate a sustained arc in each spark gap, and to measure the voltage, current and capacitance in a measurement circuit associated with each spark gap. From various electrical measurements, the velocity and composition of the gas in the combustion chamber can be determined.