The diagnostic technique described in this paper is based on measuring the instantaneous angular speed of both the front end and the flywheel on internal-combustion engines, recording more than 400 speed measurements per engine cycle. Two noncontacting transducers are added to an existing drive train without requiring drive train modifications. A digital circuit, which includes a microprocessor, samples and processes the raw speed data. The numerical analysis includes data noise filtering, and the numerical determination of front end and flywheel speed waveforms. When operating without external load, the engine accelerates only the inertial load. When neglecting friction and the small amount of torsional energy in the crankshaft, it is shown that the engine energy can be modeled as a lumped parameter system consisting of inertia on both engine front and flywheel ends, coupled by a torsional spring. The results from measurements on an eight-cylinder diesel engine with various cylinder faults show that reduced cylinder performance produces a drop of kinetic energy for the faulty cylinder. An engine performance criterion evaluates the performance of each cylinder, based on its contribution to total engine kinetic energy. The results demonstrate that fault conditions are detected with high reliability.

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