Marine engines have been required higher power to fit the bigger and faster ships aiming at economical operation. To produce higher power, cylinder bore has been larger and the number of the cylinder has been increased. On the other hand, it has been continuously tried to develop components which has influence on engine power, as turbocharger, and to introduce a new fuel injection method etc. For this reason, the shafting system of the large scale diesel engine is getting complicated such that it is impossible to control the vibration in a simple way as before. By increasing the number of cylinders, the torsional vibration encounters another problem, 2-node torsional vibration in a crankshaft at the engine above 7 cylinders. As a solution of the problem caused by 2-node torsional vibration, a vibration damper has been usually applied. However, in the future, the vibration damper might not be able to solve the problem by only itself because the power of the engine will be much higher than now. If the engine has a higher power than present engine, the size of the damper could be bigger to have higher damping coefficient, which affects bearings due to heavy weight and the damper's life would be shorter by the influence of the big mass moment of inertia of the inertia ring. In this study, the methods of increasing the crank section and changing the excitation characteristics which can be adopted as an alternative solution to cope with the future requirements have been investigated. The basic concepts of these methods are as follows; the first concept is to lead to increase the modulus of section of a part of the crankshaft by increasing the diameters of one crank. With the increased section modulus, the torsional stress can be reduced. The second is to have proper excitation characteristics by changing the firing order. The firing order can influence on the sub-harmonic resonance. Generally, 2- node vibration is problem with minor order. So it could be effective to change the critical order. By these concepts, the combination of the proper diameters of the crank and the firing order has been found. To select the crank of which section to be increased, the variation tendencies of the torsional stress and the node position by the variation of the crank section, flywheel and tuning wheel mass moment of inertia have been investigated. Also, since the external force, the external moment and the guide force moment by the change of firing order can induce high excitation of engine, it has been also confirmed. In the result of the investigation, the node location becomes more distance from the crank which the diameter is increased due to the stiffness increase by the diameter change of the crank. On the other hand, the node location approaches the wheel which the mass moment of inertia is increased. Accordingly, the node movement by the stiffness increase could be controlled by changing the wheel's mass moment of inertia, so it could make the suggested method more effectively to control the 2-node vibration. Based on the above results, these methods have been applied at 8 cylinder engine shafting system and the effects have been confirmed.
Two node torsional vibration control in the multi-cylinder two stroke diesel engine
2010
10 Seiten, 27 Bilder, 5 Tabellen, 6 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch
Improvement in Crank Train Torsional Vibration (TV) Performance of Multi-Cylinder Diesel Engine
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