Predictive Piston Cylinder Unit Simulation - Part I: Novel Findings on Cyclic Inter-Ring Pressure Measurements and Piston Ring Dynamic Simulation Validation 2021-01-0650

The increasing demand for environmentally friendly and fuel-efficient transportation and power generation requires further optimization and minimization of friction power losses. Calculating friction of internal combustion engines, especially the friction contribution from piston rings and skirt, requires detailed knowledge of the lubrication and relative motion of the components being in contact. This research presents a successful match of simulated and measured piston inter-ring pressures in several ring field locations. Good correlations demand excellent measurement results combined with a meticulous and comprehensive simulation model setup. This includes all data describing piston, piston rings, liner, and oil under real operating conditions within the entire engine performance map. To do so, the authors utilized a Floating-Liner-Engine - based on a heavy-duty diesel truck engine - to measure inter-ring pressures in the entire cascade from crown land down to third ring groove. In addition, the temperature of the Piston Cylinder Unit was measured, to provide reliable data for the calibration of the simulated temperature distribution and the thermal deformation of the piston and the liner. Detailed analysis of the measurement revealed a significant cycle to cycle variation of the inter-ring pressures. Therefore, the consideration of cyclically changing oil distribution, and damping effects in the piston ring dynamic simulation is necessary. An automatic optimizing strategy for fitting the uncertain oil distribution in the ring pack has been used for the first time within piston ring dynamics simulation. This empowered a matching comparison - for mean and individual pressure traces - with an overall simulation deviation of only 3%. Due to the strong dependency of ring motion, ring pressures and corresponding blow-by gas, it was possible to predict the local ring motion and to match the blow-by gases with the help of the verified simulation model. The comparison covers numerous operation points of a truck engine and shows the influence of oil damping on cycle to cycle pressure changes. The validated piston ring dynamics model constitutes the starting point for the downstream comparison of simulated and measured friction forces from Floating-Liner-Engine presented in part II of this publication series.