Increasing the roundness of deformed cylinder liner in internal combustion engines by using a non-circular liner profile

Abstract

Increasing the efficiency of internal combustion engines is of major interest for reduced greenhouse gas emission. A significant improvement potential is given with the reduction of friction losses. Here, especially the friction between the piston ring and the cylinder liner is of interest. This article describes a study with the target to enhance the piston ring–cylinder liner conformation through increasing the roundness of the deformed liner during the warm operation state. The approach is based on the assumption that a non-circular liner in the cold state can deform due to thermal and mechanical stresses toward a circular shape under typical hot operation conditions. To test this hypothesis, a computational model for a gasoline engine was built and simulated using advanced finite element methods. The simulation describes the deformation process of the liner from the thermal and mechanical stresses. First, the deformation of a circular liner is simulated, showing asymmetric deformations of up to 30 µm in the warm state for the cylinder positioned at the end of the four-cylinder bank. As experimental data are readily available, a comparison was possible, showing good agreement. Then, three liner configurations with non-circular shape in the cold stage are investigated. For an elliptically shaped configuration, a nearly circular-shaped liner is reached under typical operation conditions. This numerical approach shows the potential for reduced friction of the piston–liner arrangement within internal combustion engines. The planned next step is the extension of this method to three-dimensional shape aspects and the application to the geometry of our test engine of our lab where friction can be measured in detail with a floating-liner measurement system.

Enhancing the Geometrical Performance Using Initially Conical Cylinder Liner in Internal Combustion Engines—A Numerical Study

“…Both the trends and the values of the deformations have good agreement with experimental data described by the authors of [25]. The detailed model configuration, boundary conditions, temperature distributions, mesh properties, grid independence test, circumferential position dependent deformation, and model validation have been explained by the authors of [14].…”

“…Commonly, the cross section has a circular form. In a preceding work [14], it was shown that an elliptical liner cross section in the cold state can reduce the roundness error in the fired state by more than 75% for the terminal cylinder in four-cylinder gasoline engine due to the inhomogeneous thermal conditions. It was found that the deformation of a circular liner leads to a nearly elliptical shape in the fired state, while an initially elliptic liner with opposite ellipticity in the cold state deforms to an almost circular shape in the fired state.…”

“…The coolant temperature was 80 • C, and the used bolt pretension was 80,000 N. The top deck was restrained from the movement in the axial direction. Further details about the physical model have been described by the authors of [14]. The numerical study was done on the terminal cylinder located at the end of the four-cylinder engine.…”

“…To check if the use of the conical liner affected the roundness of the liner's cross sections, the roundness errors were calculated at different elevations. The roundness was evaluated with the least squares circle method [14]. Briefly, the roundness error is the difference between the maximum and minimum circles that confine all the data points in the cross section (see Figure 6a).…”

“…Increasing the roundness of the deformed liner in the fired state provides a significant opportunity for improving the PRCL performance [12,13]. The authors of [14] studied the performance of initially noncircular liners numerically. In this study, it was shown that an engine with noncircular liners in the cold state can increase the roundness of the liners in its fired state significantly.…”