Applicability study of the fiber-optic gyro in piston engines diagnosing process

Abstract

The Polish Naval Academy has been involved in marine reciprocating combustion engines indication tests for many years. Results of researches aiming to diagnostic using of measurement of engine crankshaft unsteady angular speed are presented in the paper. Up to now, adequate accuracy of angular speed measurement had not been achieved to make proper diagnostic decision. Commercially, measurement of unsteady rotation speed has been used only in MAPEX –TV system (Torsional Vibration detector) dedicated to SULZER engines, which can detect only the one engine cylinder switch out of work without any mistakes. For several years, mostly in navigation, more often are used optic gyroscopes which work on the base of Sagnac effect, assuring angular speed measurements with resolution of 0.001o /h. Such resolution is too high than needed in piston engines diagnostic, but range of measured rotation speed is much much lower than rpm of mediumor low-speed marine diesel engines. In scope of conducted research it was decided to build a model of Sagnac interferometer prepared to measure of instantaneous angular speed in range adequate to medium speed marine diesel engines. At rotational crankshaft speed equal 750 rpm 1mV 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 ray to go through distance of 100 m fibber-optic line. In practice this method do not introduce any significant phase shifts and does not limit the number of samples per revolution.