Abstract: An ignition onset sensor for internal combustion engines or the like including an optoelectric converter connected directly or indirectly with the combustion chamber of the engine, the converter having one side facing the combustion chamber which can be freed of soiling by being burned off or glow heated. The ignition onset sensor is particularly useful in internal combustion engines having direct injection as the onset of fuel supply by the fuel pump or the onset of injection at the fuel nozzle can be regulated on the basis of a signal of the ignition onset sensor. The burn-off of the side of the converter facing the combustion chamber is preferably accomplished by an electric arc and, in the case of glow heating, by means of a glow filament disposed in front of that side of the converter, the burn-off or glow heating process being controlled in accordance with the engine operational status, engine operational parameters, and/or at selected times.