Effect of Skirt Structure on Vibro-Acoustic Characteristics of Engine Piston

The design of pistons is an important issue that opens research possibilities for reducing friction and noise in the field of tribology in Internal Combustion (IC) engines. It is widely known that the piston assembly is a major contributor to parasitic losses (up to 40%) due to rapidly changing loads and close contact in cylinder liner. Therefore, the study of piston dynamic characteristics is important to ascertain ways of reducing noise levels. This paper presents a vibro-acoustic analysis to show how the piston structure react. The studied engine piston was generated in CATIA CAD Software and consequentially this was simulated in ANSYS Workbench. The piston finite element model was built, and the relevant boundary conditions were supplied to predict the basic vibro-acoustic parameters such as: natural frequencies, vibration modes and Sound Pressure Level (SPL). To determine the vibrational behaviour of the piston, modal and harmonic analyses were performed. After, the acoustic analysis was coupled to obtain the sound waves of the piston structure by importing the velocity obtained in harmonic response as a boundary condition. The predictions of Sound Pressure Levels were validated with the experimental measurements in a fired engine. Good agreement was obtained. The validated model was then used to investigate the effect of skirt geometry. The full round piston model showed lower SPL’s of 7.3% at thrust side than the original piston with slipper skirt style. The proposed methodology can be easily used by a design engineer as a good prognostic tool.