Crank shaft torsional vibration has impact on the crank angle measurement accuracy in large-bore Internal Combustion Engines (ICE). In large bore engine, the torsional vibration angular displacement can be up to 1 degree, which in turn can cause a fault of 2 bar in Indicated Mean Effective Pressure (IMEP) and a fault of 0.6 degrees in the Crank Angle of 50% burned (CA50). IMEP and CA50 are critical feedback parameters for closed-loop combustion control, therefore to compensate torsional vibration effect in real-time engine control system can not only provide higher accuracy crank angle data but especially improve the combustion analysis and closed-loop control accuracy. Thus, in this work, a torsional vibration dynamic model is established to improve the accuracy of the crank angle measurement. A lumped parameter model of torsional vibration is established for a Wärtsilä engine, the numerical computing method is determined, harmonic analysis is applied, the Transfer Matrix Method (TMM) result is verified with flexible Multibody Simulation (MBS) calculation and the accuracy of the torsional vibration model is estimated. For the trial of online crank angle correcting, the computation time of this model was found to be around 300 to 400 times heavier as IMEP calculation. A direct IMEP correcting model based on a linear dependence of cylinder number with an accuracy of ±0.1 bar compared with the reference was proposed.
Based on all those results, it is concluded that the TMM method can calculate the angular displacement from torsional vibration with high accuracy and correct the crank angle measurement from cylinder-wise and crank angle wise, and the torsional vibration calculation resolution needs to be considered based on performance and calculation capacity.