VIBROACOUSTIC DIAGNOSTICS OF MARINE DIESEL ENGINE TURBOCHARGER
Abstract
Introduction. Modern turbochargers of marine diesel engines enjoy a high boost pressure ratio in the compressor of up to 5 and above. They create high pressure of the charged air, thus providing high-specific power and high-efficiency operation of the marine engine with low-level emission of carbon oxides and soot. High efficiency of MAN MC and MAN ME diesel engines with actual specific fuel consumption of 160–170 g/kWh is ensured by the high pressure of the charged air, among other factors. In case the turbocharger loses in performance, the power and efficiency of the diesel engine rapidly decline while the emission level of carbon oxides and soot increases. The allowable hazardous emission level of marine diesel engines in operation is limited by the current requirements of the International Maritime Organization. Since the overwhelming majority of various maritime transport vessels use diesel power units, the matter of their efficient and safe operation is undoubtedly of current interest. The article presents the method of vibroacoustic diagnostics of the marine diesel engine turbocharger under operating conditions, when a prompt determination of instantaneous turbocharger speed and rotor vibration level is required. The method lies in the analysis of the vibroacoustic signal that is generated by the compressor of the turbocharger with the diesel engine running under load. Results. The spectral analysis reveals that the compressor blades generate acoustic oscillations that are always present in the overall vibroacoustic spectrum of the turbocharger regardless of its technical condition. The “blades” harmonic that corresponds to these vibrations can be detected in the spectrum using the method of limits. The calculated instantaneous turbocharger speed makes it possible to analyze the amplitude of the main harmonic in the spectrum. The method presented in the paper helps eliminate the Discrete Fourier Transform (DFT) spectral leakage, so that the amplitude of the main harmonic can be estimated. The further analysis of the amplitude of the main harmonic allows for efficient estimation of the turbocharger rotor vibration level when in operation. The method can be practically applied by the means of a smartphone or a computer that have the dedicated software installed. Conclusions. The proposed method can lay the foundation for the permanent monitoring system of the turbocharger speed and vibration level in the marine diesel engine.
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