23rd International Colloquium Tribology - January 2022 207 The Effect of Friction Modifier and Viscosity on Piston Rings/ Cylinder Liner Friction in Floating Liner Single-Cylinder Engine Tests Abdullah Alenezi Institute of Functional Surfaces (iFS), School of Mechanical Engineering, University of Leeds, Leeds,UK Corresponding author: mn06ana@leeds.ac.uk Benoît Thiébaut Centre de Recherches de Solaize, TOTAL, Solaize, France Cayetano Espejo Institute of Functional Surfaces (iFS), School of Mechanical Engineering, University of Leeds, Leeds,UK Ardian Morina Institute of Functional Surfaces (iFS), School of Mechanical Engineering, University of Leeds, Leeds,UK 1. Introduction The AVL “floating liner” friction single-cylinder engine (FRISC) was used to perform tests at fired and motored modes at different loads and speeds using fully formulated oils. This extended abstract presents an analysis of friction force raw data to investigate the effect of molybdenum dithiocarbamate (MoDTC) concentration and oil viscosity on friction reduction throughout piston strokes, particularly at boundary regimes of reversal points at Top Dead Centre (TDC) and Bottom Dead Centre (BDC). 2. Methodology 2.1 Formulated Oils In this paper, the effect of two oil properties on friction performance have been investigated: the effect of small amount increments of MoDTC additive and the effect of two viscosity grades (HTHS 2.1 & 3). The HTHS1.7 and HTHS2.1 oils were used as reference oils. Table 1 provides the details of the first and second groups of the tested oils. The oils were provided by TOTAL. Table 1: Test Oils Description 1st Group of Oils 2nd Group of Oils A1 HTHS2.1 A2 HTHS1.7 (0W8) B1 HTHS2.1+ 0.5wt% Mo B2 HTHS1.7 + 0.1wt% Mo C1 HTHS2.1+ 1.0wt% Mo C2 HTHS1.7 + 0.3wt% Mo D1 HTHS3 D2 HTHS1.7 + 0.5wt% Mo E2 HTHS1.7 + 0.7wt% Mo 2.2 AVL FRISC Engine Tests Conditions/ procedure Both oil groups were tested at 90 °C for oil/ coolant. For the first group, each oil was tested at motored mode with four speeds and fired mode with four load/ speeds. Each condition was run for three stages (Loop 1  Stabilisation run 15 hrs  Loop 2). Frictional force was measured at every 0.2º crank angle. For the second group, a new liner was fitted for each test. All tests were at 1200 rpm/ 6.5 bar except the 4 th test was at 1000 rpm/ 12 bar. The first test was performed by ramping up MoDTC oils for one hour each (i.e., starting by no Moly oil  0.1% Mo  0.3% Mo  0.5% Mo  0.7% Mo). The 2 nd , 3 rd and 4 th tests were performed by HTHS1.7 oil first and then 0.1%, 0.5%, and 0.5% Mo, respectively. 3. Results and Discussion All lubrication regimes (e.g., boundary, mixed and hydrodynamic) exist at the contact between piston rings/ liner along each stroke and they control the friction force results [1, 2]. At the reversal points (TDC and BDC), the boundary and mixed lubrication regimes dominate the contact while at the mid stroke, the hydrodynamic regime exists because of high piston speed and the surfaces are expected to be not in contact, but the friction occurs because of shear force and pressure difference between oil film layers [2, 3]. Moreover, the profile of load, speed 208 23rd International Colloquium Tribology - January 2022 The Effect of Friction Modifier and Viscosity on Piston Rings/ Cylinder Liner Friction in Floating Liner Single-Cylinder Engine Tests and temperature along the stroke travel are changeable according to operating conditions [1]. MoDTC started to reduce friction significantly from 0.3% Mo and onwards while 0.1 % Mo had slight effect, as shown in Figure 1. In addition, MoDTC concentration was seen to contribute remarkably in friction reduction at the bottom one third of piston at BDCs. This indicates that 0.3 to 0.7% Mo oils have successed to form more low friction MoS 2 tribofilm than the 0.1% Mo oil. Overall, the 0.7% Mo has the highest friction reduction at all piston positions except at TDCs. However, all MoDTC concentrations showed insignificant effect at TDCs. This can be attributed to the dominant effect of the boundary lubrication regime which exists due to high combustion gases pressures and temperatures as well as the low piston speed [4]. Furthernore, it can be seen that the upwards strokes (Compression & Exhaust) show more friction reduction at the mid strokes and BDCs than downwards strokes (Intake & Exhaust). This can be attributed to the dominant effect of the boundary lubrication regime which exists due to high combustion gases pressures and temperatures as well as the low piston speed [4]. Furthernore, it can be seen that the upwards strokes (Compression & Exhaust) show more friction reduction at the mid strokes and BDCs than downwards strokes (Intake & Exhaust). This can be attributed to low pressure at the begining of the strokes. Figure 1: Friction reduction (%) at ramping up MoDTC A similar approach has been used to test the oils with different viscosity properties. Friction results from those tests will be shown and discussed in the main paper. 4. Conclusion In conclusion, 0.3 to 0.7% Mo have strong influence on friction reduction at BDCs. All MoDTCs showed insignificant friction reduction at TDCs Viscosity showed a significant effect on friction reduction with higher HTHS at reversal points especially at TDCs. References [1] Priest, M. and Taylor, C.J.W. Automobile engine tribology—approaching the surface. 2000, 241(2), pp.193-203. [2] Nagar, P. and Miers, S. Friction between Piston and Cylinder of an IC Engine: a Review. SAE Technical Paper, 2011. [3] Profito, F.J., Tomanik, E., Lastres, L.F. and Zachariadis, D.C. Effect of lubricant viscosity and friction modifier on reciprocating tests. SAE Technical Paper, 2013. [4] Priest, M. Factors influencing boundary friction and wear of piston rings. In: Tribology series. Elsevier, 2000, pp.409-416.