Active Vibration Control in Large Diesel Engines
The introduction of common-rail fuel injection system for medium-speed diesel engines has made control of cylinder-wise fuel injection durations and timings possible. At the same time, calibration of the fuel amounts injected into the cylinders has become an important problem. Due to pressure oscillations between the rail and cylinder, different characteristics of the fuel-injection solenoid valves and clogging of nozzles, the amount of injected fuel may differ significantly between cylinders. For automotive applications, deviations up to 25 % have been reported. The differences in cylinder-wise torque contributions cause significant torsional vibrations, resulting in a roughly running engine and thus increased wear and heating of mechanical components, and hence increased fuel consumption.
Although methods for automatic calibration of the fuel injection durations have been developed in the automotive industry, the methods are not directly applicable to large medium-speed engines. Firstly, compared to automotive applications, an important difference is the ratio between the rotational frequency and the natural frequency of the flexible coupling between the engine and the load. The engine can therefore not be regarded as decoupled from the load. The number of frequency components which should be analyzed in order to determine the optimal fuel injections also increases with the number of cylinders, and, moreover, engines with more than approximately 16 cylinders have overlapping firings, making the relating of the superposed torque to the consecutive firings more complex. For these reasons the cylinder-balancing methods developed for automotive applications are not applicable to large medium-speed engine applications, and continuing research in this area is therefore needed.
The purpose of this project is to develop active cylinder balancing methods for reducing torsional vibrations for large medium speed diesel engines. A technique is developed in which the frequency content of the angular speed is monitored on-line, and the cylinder-wise fuel injections are adjusted to reduce relevant frequency components using a model of the engine dynamics. An adaptive method is also being developed, where the engine dynamics is identified on line in order to compensate for model uncertainties and/or changes in the engine dynamics.
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|Ostman, Fredrik and Toivonen, Hannu T., Model-based torsional vibration control of internal combustion engines. In: IET Control Theory & Applications . 2008|