In a single cylinder engine, the speed fluctuation during steady state operation of the engine is influenced only by the cylinder pressure variation, the engine friction and the dynamics of the crankshaft. This dependency is used to explore the capacity of the lumped mass model of the crankshaft to correctly represent its dynamics. Based on this model, the paper establishes the relationship between the cylinder pressure variation and the crankshaft speed fluctuation for steady state operation of the single cylinder diesel engine. Correlations are determined between the harmonic components of the tangential gas-pressure and the harmonic components of the angular speed of the free end of the crankshaft. These correlations are used to predict the angular speed variation of the crankshaft, when the cylinder pressure variation is known, or to reconstruct the cylinder pressure when the crankshaft speed fluctuation is known. The reverse calculation of the pressure variation from the measured crankshaft speed is strongly influenced by the elastic characteristics of the crankshaft. If the stiffness of the crankshaft is not accurately determined, the results are significantly distorted.

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