Engine Misfire Diagnosis Based on the Torsional Vibration of the Flexible Coupling in a Diesel Generator Set: Simulation and Experiment

Abstract

Flexible couplings are widely used for accommodating various imprecisions such as misalignments and torque fluctuations in a diesel generator set. However, excessive vibration due to common engine misfires can cause premature failures in both the couplings and the whole generator set. Moreover, the coupling also affects detection performance and the occurrences of early misfires due to such faults in fuel injections and cylinder seals. In this paper, the torsional vibration along with the dynamic torque of the flexible coupling connecting a 6-cylinder diesel engine to a dynamometer is studied theoretically and experimentally. This system represents a common diesel generator set which is modeled into a torsional dynamic system with 10-degree of freedom (DOF) by the Lagrange equation method. After a verification of the model by the measurement of vibration responses at the free end and the coupling with a magnetic speed sensor and a wireless torque sensor, it is then used to predict the influences of different misfire conditions on the dynamic torque on the coupling, which helps in determining reliable diagnostic features for misfire detection and diagnosis. Results show that the misfires of the diesel engine have significant influences (more than 5 times higher) on the torsional vibration and load of the flexible coupling than on the dynamic torque. Nevertheless, both the torsional vibration and torque of the flexible coupling can be used to detect the occurrence of the diesel engine misfires and the vibration provides slight better results in terms of localizing the misfired cylinders.