Abstract: The invention relates to a device for monitoring the combustion processes occurring in the combustion chamber of an internal combustion engine, which comprises a housing (1), which may be built into the wall of the combustion chamber, with a measuring sect-on which extends to the combustion chamber and with a number of drillings (3), which extend along the longitudinal axis of the housing, in each of which an optical guide (2) is arranged. A first end of an optical guide, lying at the first end of the drilling, receives light from inside the combustion chamber and a second end of said optical guide is linked to an opto-electronic analyzer. The drillings have an end section (3A), adjacent to the combustion chamber, which extend out of the housing, through an outer surface of the measuring section, at an angle (?) to the longitudinal axis of the housing.

Abstract: In order to determine the course of a varying internal pressure in the cylinder of a piston-type internal combustion engine using measurement sensors which are in interaction with the outside of the cylinder; an acceleration, velocity or displacement signal (X(t)) is produced and a transfer function (H(.omega.)) between the internal pressure (Y(t)) and the acceleration, velocity or displacement signal (X(t)) is determined once and thereafter an output signal representing the internal pressure is derived only from the acceleration, velocity or displacement signal X(t)) and the transfer function.