Concept of sagnac effect application in measurement of angular acceleration of piston engine crankshaft

In the paper results of conducted in Polish Naval Academy researches aiming to diagnostic using of measurement of engine crankshaft unsteady angular speed measurement will be presented. Similar works were many times started in different research centres. Up to now, adequate accuracy of measurement had not been achieved to make proper diagnostic decision. In commercial field, measurement of unsteady rotation speed has been used only in MAPEX –TV system (Torsional Vibration detector) dedicated to SULZER engines, which up to now without any mistakes detected only the one engine cylinder switch out of work. To the advanced diagnostic system, there are a lot off work to do. For several years in navigation, more often are used optic gyroscopes, which work on the base of Sagnac effect, assuring angular speed measurements, with 0.001 o/h resolution. Such resolution is absolutely higher than needed in piston engines diagnostic, but range of measured rotation speed is much lower than rpm of low speed marine diesel engines. In scope of conducted scientific work, it was decided to build of model of Sagnac interferometer prepared to measure rotational speed in range adequate to medium speed marine diesel engines. At rotational speed, equal 750 rpm 1 mV change in output voltage had been achieved for the difference of 0.4 o/sec of rotational speed. Time of measurement is equal the time, which need light to go through distance of 100 m fibber-optic line. In practice, this method does not introduce any significant phase shifts and does not limit the number of samples per revolution.