The torsional vibrations of marine Diesel engines under fault operation of its cylinders

Abstract

The torsional vibrations calculation of Diesel engines is usually performed for different speeds of revolutions but for uniform operation and behaviour of each cylinder. This condition is true only for new of very well maintained engines but generally the different cylinders operate with considerable deviations from its design conditions. This situation may influence strongly the torsional vibrations of the system, since the spectrum of the exciting forces is different. In some cases this non uniform operation of the different cylinders may induce severe torsional stresses leading to serious vibrations or even to damage. This contribution presents same theoretical and experimental results obtained on this subject taking into account usual engines conditions showing wrong injection timing, not proper operation of the turbocharging device, incorrect valve timing, excessive wear of piston rings and/or piston liners etc. All these faults result in an exciting force spectrum that is different in frequency and/or phase from the corresponding of uniform normal operation of each cylinder. This deviating spectrum can be predicted and practical measured by the thermodynamic behaviour and the indicators diagrams of the engine and the corresponding stresses can be calculated accordingly. The torsional stresses on the intermediated shaft can measured using strain gauges method and the bridge voltage output converting to numerical file stored on a miniature computer which running with the shaft. The method reported here has been verified for two identical ship engines MIRRLEES JVSS12 having different faults. The corresponding results after both engines has been tuned properly are reported too to show the influence of the improper maintenance.