Application of Process Calculation of the Internal Combustion Engine for the Analysis of Torsional Vibrations in Marine Drives

Regarding driving units with combustion engines, it is primarily the torsional vibrations caused by the unsymetrical gas forces, inertial forces and out-of-balance forces which may cause harm to the driveline. The program DRESP was developed at the Institute of Machine Elements and Machine Design (IME) of the RWTH Aachen in order to simulate such nonlinear torsional vibration systems. The program has been established as an efficient simulation tool in numerous companies for driveline analysis. Fourier series of gas pressure moments are used for the simulation of torsional vibrations in order to simulate the periodic excitation of combustion engines. But this is only applicable at a certain stationary operation point of the engine. To avoid this disadvantage, a simulation model based on a combustion process calculation can be used instead. It computes the gas and mass excitation forces by modeling the combustion process and the kinematic of the crank drive for every cylinder. The theoretical basis is the so called One Zone Model according to Vibe which is a simplified thermodynamic model of the cylinder. The presentation shows a DRESP-simulation using the example of a modern marine drive with a two-stroke diesel engine. It shows the dynamic behavior of the power-train during an engine-startup process from zero to nominal speed.