Combustion engine and retrofit/conversion set for such a combustion engine

The internal combustion engine (1) has combustion chambers, into which liquid and gaseous fuel is introduced together with intake air. The internal combustion engine is operated with only one type of fuel in a range, in which a harmful hydrocarbon excess is produced. The internal combustion engine is operated with only one type of fuel or predominantly with only one type of fuel, particularly with liquid fuel, when starting. The liquid fuel is provided as diesel fuel of the internal combustion engine. An independent claim is included for a retrofitting or conversion kit for an internal combustion engine.