Citation: Biswal, S.; Mishra, P.C. Piston Compression Ring Elastodynamics and Ring–Liner Elastohydrodynamic Lubrication Correlation Analysis. Lubricants 2022, 10, 356. https://doi.org/10.3390/ lubricants10120356 Received: 19 November 2022 Accepted: 5 December 2022 Published: 9 December 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). lubricants Article Piston Compression Ring Elastodynamics and Ring–Liner Elastohydrodynamic Lubrication Correlation Analysis Swagatika Biswal and Prakash Chandra Mishra * Department of Mechanical Engineering, Veer Surendra Sai University of Technology, Burla 768018, India * Correspondence: pcmishra_me@vssut.ac.in; Tel.: +91-8917-5354-45 Abstract: Friction loss in an internal combustion engine largely depends on elastohydrodynamic lubrication. The piston compression ring is a contributor to such parasitic losses in the piston subsystem. The complex elastodynamics of the ring are responsible for the transient and regime- altering film that affects the elastohydrodynamic lubrication of the ring liner contact conjunction. The current paper will discuss the ring radial, lateral deformation, and axial twist, and its effect on the film profile of the compression ring and its subsequent effect on tribological characteristics like elastohydrodynamic pressure, friction, and lubricant. A finite difference technique is used to solve the elastohydrodynamic issue of elastodynamic piston compression by introducing the elastodynamically influenced film thickness into the lubrication model. The results show that consideration of the elastodynamics predicts a 23.53% reduction in friction power loss in the power stroke due to the elastodynamic ring compared to the rigid ring. The elastodynamic effect improves the lubricant oil flow into the conjunction. A finite element simulation predicts a von-Mises stress of 0.414 N/mm 2 , and a maximum deformation of 0.513 μm at the core and coating interface is observed at the ring–ring groove contact. The sustainability of EHL in this case largely depends on the ring–liner elastodynamics. Keywords: compression ring; elastodynamics; ring–liner oil film thickness; fluid friction power; lubricant oil flow; sustainable elastohydrodynamic lubrication 1. Introduction The conformed engine piston top compression ring sits on the top ring groove and is subjected to various modal deformation during the operating cycle of an IC engine. Guided by the cylinder bore wall/liner, it elastically flexes its shape due to the combined action of gas pressure, ring tension, lubricant reaction, and oil friction during the reciprocation of the piston assembly, engaged to generate mechanical power. The dynamic ring governs the transient film shape responsible for the hydrodynamic action of the lubricant, due to which simultaneous sealing and sliding actions of the ring ensure durable piston assembly and engine performance. The hydrodynamic action in such a case is elastohydrodynamic in nature, not out of elastic deformation of the contiguous part due to extremely high concentrated contact as occurs in ball bearings, but because of the global deformation of the flexible compression ring (incompletely conformed to the cylinder bore). Therefore, there is a strong correlation between the elastodynamics of the compression ring and the elastohydrodynamic lubrication of the ring–liner conjunction. To explore such an interrelationship, it is required to understand the ring elastic deformation and how it replicates such a mode while in conformance with the piston–cylinder subsystem. The dynamics of an incomplete ring were first studied by Lamb [1], who considered the analysis of a bar of circular arc shape for the in-plane flexural strength. The vibration of such free–free curved was discussed considering the center as the origin and by deriving the motion equations in polar form. Subsequently, Den Hartog [2] derived the first and second natural frequencies of an incomplete ring which was either fixed or allowed to rotate Lubricants 2022, 10, 356. https://doi.org/10.3390/lubricants10120356 https://www.mdpi.com/journal/lubricants