24th International Colloquium Tribology - January 2024 115 Simulation-Based Evaluation of Drive Cycle Fuel Efficiency Gains in Gasoline Engines through Engine Oil Viscosity Reduction X. Simón-Montero 1 , J. Blanco-Rodríguez 1 , J. Porteiro 1 , M. Cortada-Garcia 2 , S. Maroto 2 1 CINTECX, Universidade de Vigo, GTE, Lagoas-Marcosende s/ n, Vigo, 36310, Spain 2 Repsol SA, Madrid, Spain 1. Introduction In this study, a methodology for drive cycle performance evaluation combining numerical simulations and experimental lubricant data is presented. This methodology includes a simulation procedure where several simulation models are used to assess lubricants in transient conditions. In the core of this procedure, stationary simulations for each lubricant across a range of engine speed, engine load and oil temperature were run to generate a 4-D map of friction losses. This process significantly helped reduce the run time needed to perform transient real drive simulations. Three OEM approved lubricants for a representative European passenger car vehicle were included in this study, corresponding to three different SAE grades. This study also includes engine protection evaluation based on the Stribeck curve of the average type of lubrication obtained at each timestep of the driving cycle. The simulations were performed for the European standard homologation test WLTC. The results show significant reduction in friction totals when low viscosity engine oils are used. In terms of type of lubrication, the lowest values of specific oil film thickness were achieved for the least viscous of the engine oils, although the lubrication type was mainly hydrodynamic for the three lubricants. Results also include the comparative potential reduction in fuel consumption by using each lubricant. 2. Methodology Three lubricants (Table 1) were modelled in Gamma Technologies GT-Suite, to be ran at a transient model of passenger car, which main features are shown in Table 2. Table 1: Lubricants of the study Lubricant SAE grade Viscosity at 40-°C (cSt) Viscosity at 100-°C (cSt) Oil A- 0W-20- 40.78- 8.26- Oil B- 5W-30- 67.58- 12.00- Oil C- 5W-40- 81.68- 14.23- Additionally, stationary models of the main friction contributors, as bearings and the piston pack, where also created so the lubricants could be tested at specific conditions, and compared to references of similar vehicles and lubricants. Table 2: General features of the modelled vehicle Property Chosen vehicle Model VOLKSWAGEN T-ROC Engine displacement [L] 1.5 Engine configuration 4-inline Turbo Power [CV] 150 Fuel Petrol Weight [kg] 1330 Cx 0.38 Tyre rolling radius [mm] 334 Tyre rolling resisting factor 0.0155 In order to reduce computational time, friction losses were mapped by using the stationary models to create maps within the range of temperature, engine speed a load conditions of the WLTC driving simulations. In the figure below a friction loss map at full load is shown. Figure 1: Oil C Full load Engine Friction Loss Map To take into account the effects of the lubricant in wear and durability, the specific oil film thickness (SOFT) was also mapped, so its instantaneous values during transient simulations could be known. 3. Validation and results 3.1 Validation When performing studies concerning simulations, it is always key not to lose the link to real-world correlation. In this study, no specific test bench data was available, so as it was already mentioned, references of similar engines where taken, such as Taylor’s teardown test [1], featured in Figure-1 116 24th International Colloquium Tribology - January 2024 Simulation-Based Evaluation of Drive Cycle Fuel Efficiency Gains in Gasoline Engines through Engine Oil Viscosity Reduction and other authors [2-3], to cover different temperatures, loads and regimes. The validation process was performed for each of the engine oils, proving reasonable accuracy, thus leading to the driving simulations that led to the results shown on the following section. Figure 2: Oil B Crankshaft FMEP comparison to reference 3.2 Results The results showed that the introduction of Oil A, was an upgrade in terms of efficiency across all the components modelled, as it can be seen in Figure 3, which subsequently, led to a reduction in fuel consumption. Figure 3: WLTC friction energy loss distribution for the 3 oils Figure 4: Pie charts representing the percentage of bearings timesteps spent in each lubrication type The SOFT results (Figure 4), show that using oil A, there were more time steps in the elastohydrodynamic and mixed regimes, that were least common using any of the other lubricants. This was found coherent to the viscosity of the lubricants. 4. Conclusion In conclusion, this research introduced a comprehensive methodology that integrates simulations with experimental lubricant data to assess drive cycle performance. We evaluated three distinct lubricants and found that the low-viscosity oil (Oil A) notably decreased friction losses and fuel consumption. By comparing the simulation results with reference data, this study highlights its value as an effective tool for examining the impact of lubricant property variations on overall vehicle performance. Such insights may help in the development of novel lubricant formulations tailored to achieve optimal properties. References [1] R. I. Taylor, N. Morgan, R. Mainwaring, and T. Davenport, “How much mixed/ boundary friction is there in an engine — and where is it? ,” Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, vol. 234, no. 10, pp. 1563-1579, Oct. 2020, doi: 10.1177/ 1350650119875316 [2] K. Kalogiannis, P. Desai, O. Mian, and R. Mainwaring, “Simulated Bearing Durability and Friction Reduction with Ultra-Low Viscosity Oils,” in SAE Technical Papers, 2018, vol. 2018-September. doi: 10.4271/ 2018- 01-1802. [3] P. Lee and B. Zhmud, “Low friction powertrains: Current advances in lubricants and coatings,” Lubricants, vol. 9, no. 8, Aug. 2021, doi: 10.3390/ lubricants9080074.