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

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.