DETECTOR

To permit individual evaluation of the combustion processes in the respective cylinders (1a-d) of an internal combustion (IC) engine (2), individual optical pick-ups (3a-d; 4a-d) are coupled to the respective cylinders, the output signals either in optical or electrical form are conducted to separate pick-ups for individual evaluation or, alternatively, the output signals are combined and then again separated out by a steering circuit. Individual evaluation can be accomplished by locating light guide fibers from the sensors in a predetermined position with respect to opto-electrical transducers; by forming scanning windows, for example by a rotating disk (19, 20) rotating n in synchronism with the engine and permitting passage of light from the respective fibers of the light guides to respective pick-ups; or by combining the light outputs from the respective sensors (4) either optically by intermixing light guide fibers in a common cable (6'), or electrically in an equivalent OR-circuit (FIG. 8: RL) with subsequent correlation of the output signal with a specific cylinder by a scanning disk (FIG. 6: 20) with suitably placed openings (22a-d) therein, or an electrical time-multiplex steering circuit (FIG. 8: 30) operating in synchronism with rotation of the engine.