23rd International Colloquium Tribology - January 2022 377 Tribological simulation of Friction Torque Test using SRV and EHD tribometer - A new approach for performance evaluation of energy efficient engine lubricant Rameshwar Chaudhary Indian Oil Corporation Ltd., R & D Centre, Faridabad, India Inder Singh Indian Oil Corporation Ltd., R & D Centre, Faridabad, India Punit Kumar Singh Indian Oil Corporation Ltd., R & D Centre, Faridabad, India S. Bhadhavath Indian Oil Corporation Ltd., R & D Centre, Faridabad, India Dr. S. Seth, R. Mahapatra Indian Oil Corporation Ltd., R & D Centre, Faridabad, India Corresponding author: mahapatrar@indianoil.in M. Sithananthan Indian Oil Corporation Ltd., R & D Centre, Faridabad, India A.K. Harinarain Indian Oil Corporation Ltd., R & D Centre, Faridabad, India Dr. P. Bhatnagar Indian Oil Corporation Ltd., R & D Centre, Faridabad, India Dr. D. Saxena Indian Oil Corporation Ltd., R & D Centre, Faridabad, India Dr. SSV Ramakumar Indian Oil Corporation Ltd., R & D Centre, Faridabad, India 1. Introduction This present study describes this approach to evaluate the frictional losses under hydrodynamic losses and boundary regimes of lubrication under simulated conditions present in IC Engines, and also validating it with a friction torque test in an engine configuration. Fuel efficient low viscosity candidate oil of 0W16 viscosity grade offering better fuel efficiency and long life was selected and compared against an industry reference product for the studies. A friction torque test (FTT) was carried out in a motorized gasoline engine under a wide range of speeds and lubricant temperatures. For validation of FTT results, simulated tribo tests under different regimes and conditions existing in the engine using EHD film thickness test apparatus and SRV tribometer were conducted. The frictional property under different lubrication regimes experienced in engine components was mapped in these simulated tribo tests. The EHD film thickness apparatus confirmed the fuel economy benefit on account of lower viscometrics simulating the FTT test result. However, the standard test protocol in SRV could not discriminate the oils in terms of coefficient of friction, therefore an extended test in SRV was carried out to find the wear track. Not only the wear volume with candidate oil was found to be lower than the reference oils, but also during the long duration test the friction coefficient was found to be significantly lower than the reference oils due to activation of surfaceactive additives. The results with the developed test protocol correlates well with the FTT test result with candidate oil showing lower friction in both hydrodynamic and boundary regimes as experienced in 378 23rd International Colloquium Tribology - January 2022 Tribological simulation of Friction Torque Test using SRV and EHD tribometer an engine configuration. Besides, lower wear volume in a long duration SRV test with candidate oil is expected to provide a better durability characteristic as compared to reference oil of same viscometrics. 2. Experimental Detail The comparative viscometrics of the candidate oil A visà-vis another candidate oil B and industry reference oil C is given below in Table 1. A full FTT test carried out under a wide range of speed and lubricant temperature showed lower friction torque with candidate oil A w.r.t. candidate B and reference oil C. Further, Tribo tests were carried out using SRV tribometer and EHD interferometry based film thickness test rig to investigate the friction and wear reduction capability of the candidate oil A visà-vis Oil B and Oil C of same viscosity grade. Table 1: Comparative viscometrics of the oils. Properties Candidate Oil A Candidate Oil B Reference Oil C K.V@ 100°C, cSt ASTM D 445 7.27 6.58 6.65 K.V@ 40°C, cSt ASTM D 445 34.14 28.15 25.95 VI ASTM D 2270 185 208 232 A) EHD Film thickness system The EHD interferometry based tribometer measures film thickness in the EHL contact formed between a 3/ 4 inch steel ball and a rotating 100 mm diameter disc. Tests were carried out at 10N and 20N load which corresponds to a contact pressure between the ball and disc of approximately 0.4 and 0.5 GPa respectively. The lubricant film thickness is measured by optical interferometry. B) SRV test Two test specimens (e.g., a cylinder and disk) are installed in the test chamber and pressed together with a specified normal force. The top specimen oscillates on the bottom specimen. Friction force is continually measured by a sensor. This test gives an indication of the boundary film forming tendency or lubricity of the lubricating oil under a simulated contact geometry 3. Result and Discussion EHD film thickness measurements have been done of the three candidates’ oils at two different temperatures 40 °C and 100 °C (Refer Fig.1 and Fig.2). These test conditions cover the range of temperature, load, and speed of the FTT. The oil film thickness increases with increase in speed and decrease in oil temperature and follows Stribeck curve. There is a significant difference in film thickness with the 3 oils with oil A giving lowest film thickness. This clearly indicates that due to lower viscometrics, high VI and suitable additive chemistry of oil A, the film thickness is lowest which will give lowest churning loss in hydrodynamic regime resulting in fuel efficiency for the engine components such as main and crank shaft bearing working in hydrodynamic regimes. Fig. 1: EHD Results at 10N load Fig. 2: EHD Results at 20N load Fig. 3: SRV friction trace in extended endurance test SRV test to measure the friction coefficient was conducted on the 3 oils using line contact (cylinder on flat steel 23rd International Colloquium Tribology - January 2022 379 Tribological simulation of Friction Torque Test using SRV and EHD tribometer disc) geometry at 400 N, 90 0C, for 45 minutes as per standard test condition. During the 45 minutes test, there was no difference in frictional behaviour of the oils. However, when the test was further extended for 2 hours to find out the wear track and to check whether there is any difference in the friction behavior a significant difference in friction coefficient was found as shown in Fig. 3. As shown in the figure, an interesting finding was observed with candidate oil A giving lower coefficient of friction as compared to oil B and C during the extended test. This may be because of the activation time required for the activation of surface-active additives. Further, the wear volume of worn part of cylinder after test was calculated. The results of cylinder worn volume along with the wear image of cylinder wear is shown in Fig.4. These results clearly indicate that the candidate oil A is having good frictional characteristics under boundary regime and is expected to give fuel efficiency for engine components working in boundary and mixed lubrication regime. Fig. 4: Wear volume of worn-out cylinder 4. Conclusions • Standard short duration test in SRV tribometer could not differentiate the candidate oil from the reference oils. However, the extended test could clearly differentiate the oils showing lower coefficient of friction and lower wear volume with candidate oil A vis a vis oil B and oil C. • The tribological test result with the developed test protocol is correlating the FTT test result with candidate oil A showing lower friction in both hydrodynamic and boundary regime due to the lower viscometrics along suitable additive chemistries. • Further lower wear volume in long duration SRV test with candidate oil A is in correlation with the lower COF and the oil is expected to provide a better endurance compared to oil B and C. References [1] Holmberg, K.; Andersson, P.; Erdemir, A. Global energy consumption due to friction in passenger cars. Tribol. Int. 47(0), 221−234, 2012. [2] Spikes, H.A.: Friction modifier additives. Tribol. Lett. 60, 5(2015). [3] Kenbeek D, Buenemann T, Rieffe H. Review of organic friction modifiers—Contribution to fuel efficiency? SAE Technical Paper 2000-01-1792, Society of Automotive Engineers, Warrendale, PA, 2000.