Abstract. The article is devoted to the questions of technical operation of the internal combustion engines. Some questions of the technical diagnostics of the engine piston rings are considered. The authors propose a resonance method for the examination of the piston rings. The idea of the method is to cause oscillations in the ring at the frequency of its own mechanical resonance and at the multiple harmonics. The amplitude of the ring oscillations is measured in the gap by means of sensors according to two coordinates simultaneously. The frequency, phase and amplitude of the oscillations depend on the mechanical properties of the ring's material and its geometry. Micro-cracks, the areas with stresses, hardening defects, local overheating, loss of elasticity and other defects cause deviations of the frequency, phase and amplitude from the standard. One of the special features of the proposed method is registration of the frequency response of the piston ring oscillations simultaneously in two planes -radial (the plane of the ring) and in the direction of the axis. It allows to discover the defects (microcracks, thermal inhomogeneity, etc.) of the ring independently on their orientation along the assumed axes. This is a kind of non-destructive methods.Keywords: diagnostics, oscillations, frequency, amplitude, resonance. IntroductionThe piston rings are one of the important parts of the cylinder-piston group of internal combustion engines (ICE). A piston ring operates under very severe conditions -high temperatures, in the environment of aggressive chemical gases, with significant alternating mechanical stresses. The ring experiences continuous flexural-torsional vibrations in the grooves of the piston. The purpose of the piston ring is to segregate the combustion chamber and the crankcase space. The oil is supplied to the combustion chamber under the condition of increased gaps, the gases leak from the combustion chamber into the crankcase. This results in a significant deterioration of the technical and economic parameters of the engine and reduction of its service life.The paper suggests a method of present technical condition of the piston ring determination and analysing its frequency response plot (FRP) of its forced and self oscillations. The measurements are realized at the frequencies close to those of its own mechanical resonance and its harmonics. Thus, the piston ring plays a kind of tuning fork. Then the obtained FRP are compared with the reference plots.

This work is a further continuation of the investigations presented before at the previous conference. The basic attention is turned to improvement of the accuracy of the measurements of the oscillation changing, to development of a specified mathematical model of the oscillating process. The idea of the method is to cause oscillations in the ring at the frequency of its own mechanical resonance and at the multiple harmonics. The amplitude of the ring oscillations is measured in the gap by means of sensors according to two coordinates simultaneously. The frequency, phase and amplitude of the oscillations depend on the mechanical properties of the ring's material and its geometry. Micro-cracks, the areas with stresses, hardening defects, local overheating, loss of elasticity and other defects cause deviations of frequency, phase and amplitude from the standard. One of the special features of the proposed method is registration of the frequency response of the piston ring oscillations simultaneously in two planes-radial (the plane of the ring) and in the direction of axis. It allows to discover the defects (microcracks, thermal inhomogeneity, etc.) of the ring independently on their orientation along the assumed axes. This is a kind of non-destructive methods.

The electrochemical impedance spectroscopy (EIS) and corrosion behaviour of physical vapour deposited (PVD) TiAlN and TiCN coatings of 50 µm mesh shaped AISI 316 stainless steel were estimated under simulated marine conditions (3.5 wt. % NaCl solution). The coatings were prepared by creating adhesive Cr-CrN interlayer with the thickness of about 0.3 µm. The obtained thicknesses of produced coatings were measured to be in a range between 2 and 3.5 µm. The presence of protective coatings leads to corrosion potential (Ecorr ) shifting to more positive values as compared to the bare stainless steel. This effect indicates higher protection efficiency of coated steel under marine conditions. The protective behaviour of produced coating leads to the decreased corrosion current density (jcorr ) by indicating up to 40-fold higher polarization resistance as compared to resistance of the naturally formed oxide layer over the stainless steel. The Nyquist and Bode plots were obtained with the help of EIS measurements by applying alternating potential amplitude of 10 mV on observed Ecorr . The obtained plots were fitted by appropriate equivalent circuits to calculate pore resistance, charge transfer resistance and capacitance. The present study reveals that pore resistance was the highest in the case of TiCN coating (Rpore =3.22 kΩ·cm2). The increase in duration of the immersion up to 24 h leads to change in the capacitive behaviour of the coatings caused by the penetration of the aqueous solution into pore system of TiCN coating with low wettability and surface passivation of reactive TiAlN coating. The presence of defects was confirmed by examining the obtained samples with the help of the scanning electron microscope.

-A method of technical diagnostics of ship diesel engine -generator installation -is proposed. Spectral-power diagnostic parameters of the synchronous generator voltage and currents are used. The electric machine in this case is the multipurpose sensor of diagnostic parameters. A judgment on the quality of the operational processes in diesel engine cylinders and its technical condition is possible on the basis of these parameters. This method is applicable to piston compressor installations with electric drive. On the basis of such parameters as rotating torque, angular speed and angular acceleration it is possible to estimate the quality of the operating process in the cylinders of a diesel engine, the condition of its cylinder-piston group and the crank gear mechanism. The investigation was realized on the basis of a diesel-generator with linear load. The generator operation was considered for the case of constant RL load. Together with the above mentioned, the condition of bearings of synchronous machines, uniformity of the air gap, windings of the electric machine were estimated during the experiments as well. The frequency spectrum of the stator current of the generator was researched and analyzed. In this case the synchronous machine is becoming a rather exact multipurpose diagnostic sensor. The signal of nonuniformity in the operation process of diesel engine cylinders and its technical condition is the increasing of the amplitudes of typical frequencies.

Diesel generator sets (DGU) are very widely used in autonomous power supply systems. An example is marine power plants, diesel locomotives with electric power transmission, uninterruptible power supply units, etc. The power of ship DGUs reaches 2–6 or more MW in one unit. The number of units on ships can be different, but, as a rule, at least two. In this paper, we propose a method of monitoring the dynamic electromechanical system “diesel synchronous generator”. The method aims at using a synchronous generator machine as a multifunctional accurate and sensitive sensor for diagnostic parameters of the electromechanical system. The proposed method of technical diagnostics is based on continuous monitoring of non-uniformity of diesel torque, fluctuations in the instantaneous angular velocity and instantaneous angular acceleration of the diesel crankshaft. These data are the results of a spectral analysis of stator currents and voltages of a synchronous generator.