Fault detection in internal combustion engines by the vibrations analysis method

Vibrations analysis methods are common as fault detection and diagnosis tools for rotating machines. The successful implementation of this method in various maintenance programs motivates its application to the class of SI engines. In this work, our goals in applying the method are to provide alerts for abnormal operation, to enable detection of the source of the abnormality, and to provide the means to estimate the severity of malfunctions evolving in the engine. Experiments were performed with a four-stroke, four-cylinder in-line, carbureted SI engine. The vibrations were measured at two points around the rear crankshaft bearings in addition to two opposing points on the sides of the engine-block. At each point the vibrations were measured along the axial, the radial and the tangential directions relative to the crankshaft axis. Various malfunctions were monitored and the resulting vibrations waveforms were transformed to the frequency domain by application of a fast Fourier transform. The results obtained in the course of the study demonstrate that various malfunctions can be detected with the proposed method and that few distinguish symptoms can provide conclusive criteria regarding the general health condition of the engine.