PURPOSE: To provide a sensor which dispenses with a new bore in a combustion chamber and minimizes an arrangement cost, and a combustion engine equipped with such a sensor.

CONSTITUTION: This invention relates to a sensor 9 for detecting the degree of ionization in a combustion chamber of an engine with direct injection, and to a combustion engine equipped with such a sensor. The sensor is arranged around and concentrically to an injector 6 in a duct 5 of a cylinder head 1. A measuring electrode of the sensor 9 is substantially sleeve-shaped and is clamped firmly and centered by electrically insulating washers 11, 12, between a shoulder 7 in the duct 5 and a corresponding shoulder on the injector 6. The result is an inexpensive sensor which may easily be replaced without major modifications of the cylinder head or simultaneous replacement of the injector.