The present invention relates to a method of monitoring the combustion chamber of a cyclically operating combustion engine in which an air-fuel-mixture is ignited by means of a corona discharge generated by exciting an electrical oscillating circuit.
Ignition devices in which an air-fuel-mixture is ignited by a corona discharge comprise an oscillating circuit in which the ignition electrode, electrically isolated from the combustion chamber walls, and the combustion chamber walls form a capacitor. Exciting the oscillating circuit leads to a corona discharge at the ignition electrode which then ignites the air-fuel mixture in the combustion chamber. Such a device for corona ignition is described for example in WO 2010/011838. The content of the combustion chamber is the dielectric medium of the capacitor between the ignition electrode and the combustion chamber walls. Evaluating the electrical parameters of this oscillating circuit, for example its resonance frequency, its impedance or its phase shift between current and voltage, allows the characterization of the condition of the combustion chamber and determining for example the combustion state.