24th International Colloquium Tribology - January 2024 157 Investigation of Wear Protection and Friction Losses in Ultralow Viscosity Lubricant Formulations: A Combined FEM-CFD Simulation- Javier Blanco-Rodríguez 1 *, Jacobo Porteiro 1 and Marti Cortada-Garcia 2 , Silvia Fernández 2 1 CINTECX, Universidade de Vigo, GTE, Lagoas-Marcosende s/ n, Vigo, 36310, Spain 2 Repsol SA, Madrid, Spain * Corresponding author: javier.blanco.rodriguez@uvigo.gal 1. Introduction For decades, researchers have delved into the realms of durability and reliability, relying heavily on trial-and-error experiments. Nonetheless, in certain application fields, the costs tied to this method have become prohibitive. In instances involving lubricated machines enduring strenuous dynamic loads, such as high-power-density engines, simulation tools bring to the forefront significant advantages over resource-intensive testing. They enable the economical simulation of prototypes and various scenarios for the evaluation of different lubricants and engine configurations. This work, as presented here, provides an in-depth examination of wear protection and friction losses, with its foundations resting on a well-established elastohydrodynamic (EHD) simulation model concerning the connecting rod journal bearing. This model thoughtfully considers elastic deformation by utilizing a finite element model (FEM) representing the connecting rod. In addition, it incorporates diverse properties of lubricants, as determined through specific experimental tests, which are subsequently integrated into the simulation software. Accordingly, a novel wear algorithm is introduced to forecast the progression of wear depth and roughness parameters over time within a typical wear cycle, aligning with the standard operating conditions of internal combustion engines (ICE). 2. Modelling A novel wear algorithm is developed based on experimental rig and data available in (1,2). The simulation model used for this study has been validated with experimental data in previous works (3). The following sections presents the case study selected and the proposed wear algorithm developed. 2.1 Case study In Figure 1, it is depicted the case study selected for this work, where: a) Describes the experimental rig selected to represent the engine load at the cone bearing. b) Shows a CAD model of the test machine where the lubricants are tested. c) Shows the specific simulation model validated for this machine. d) FE model used for the EHD simulation, where elastic deformation takes significant importance. e) 3D surface data from bearing and shaft, which are in contact when specific oil film thickness (SOFT) is below 3. f) Schematic representation of the real scenario where the oil film is crucial to avoid contact between surfaces. g) 2D scheme of the system to solve in the simulation model. Figure 1. Case study 2.2 Proposed algorithm To rectify the inaccuracies in predicting contact conditions within a bearing system, the authors devised and implemented a novel algorithm with the primary objective of calculating wear and interface evolution. The algorithm leverages GT- Suite V2023, a software developed by Gamma Technologies (Westmont, Illinois, USA), to conduct Elastohydrodynamic (EHD) calculations. Additionally, MATLAB R2023a, developed by MathWorks (Natick, Massachusetts, USA), is employed for managing shape evolution, executing wear computations, and postprocessing the resultant data. Figure 2 illustrates the underlying logic of the proposed model, where: a) Describes the lubricant data needed to carry out a detailed characterization. b) Represents the EHD simulation model, which has multiple input data from the lubricant and geometrical model. c) Shows a representation of the MATLAB code developed to predict wear, where the nonlocal averaging algorithm is applied. d) Presents a scheme of the wear evolution through the cycle. e) Updates the wear cycle boundary conditions before the simulation launch. Figure 2. Wear algorithm 158 24th International Colloquium Tribology - January 2024 Investigation of Wear Protection and Friction Losses in Ultralow Viscosity Lubricant Formulations: A Combined FEM-CFD Simulation This wear algorithm is also accounting surface topography variation within wear, though an in-house developed routine. Where the Greenwood-Tripp roughness parameters are recalculated each time that the surface vary with wear, as shown in Figure 3. Figure 3. Dynamic surface roughness routine 3. Results In this work, two different assessments will be carried out to compare the performance of 4 different lubricants in friction losses and wear protection. 3.1 Friction assessment A detailed analysis of friction losses will be undertaken to determine which lubricant candidate performance better in the selected case study. This analysis will go through oil film formation, contact incidence, and lubricants overall comparison. An example of this is depicted in Figure 4. Figure 4. Lubricants friction comparison 3.2 Wear assessment Following with the lubricants analysis, the wear protection capabilities of these candidates will be evaluated through the wear depth prediction carried out in the proposed wear algorithm. Several result will be used in this section to assess the performance, as it can be wear load, wear depth, roughness parameters variation, contours. Some of these results are shown in Figure 5 and Figure 6. Figure 5. Wear depth evolution Figure 6. Final wear depth contours 4. Conclusion In this work, an assessment procedure is presented to select the best lubricant candidate for sliding bearing applications in relation with its friction and wear protection performance. This procedure is a valid approach for OEMs and oil companies interested in carry out virtual lubricant testing as previous step to final validations, and as a great cost cut in experimental campaigns. References [1] Sander DE, Allmaier H, Priebsch HH, Witt M, Skiadas A. Simulation of journal bearing friction in severe mixed lubrication - Validation and effect of surface smoothing due to running-in. Tribol Int. 2016 Apr 1; 96: 173-83. [2] Sander DE, Allmaier H, Priebsch HH, Reich FM, Witt M, Skiadas A, et al. Edge loading and running-in wear in dynamically loaded journal bearings. Tribol Int. 2015 Dec 1; 92: 395-403. [3] Blanco-Rodríguez J, Porteiro J, López-Campos JA, Domínguez B, Cortada-Garcia M. Friction assessment of ultralow viscosity lubricant formulations based on a validated elastohydrodynamic simulation. International Journal of Engine Research. 2023 Mar 16; 146808742311621.