Method for the analysis of an ion current signal in an auto-ignited internal-combustion engine

The method involves deriving the ignition delay from the offset of a local maximum (104,109) in the variation of the ion current signal (101) wrt. an injection time (105,107). The parameters for a main injection are controlled depending on evaluation of the measured ion current after a pre-injection. The main parameter can be adapted depending on the measured ion current following a preceding main injection.