Proceedings of SerbiaTrib '13

Table 4. Typical composition of cylinder liner.ElementComposition % massFe 93.97P 0.3V 0.15C 3.00Si 2.00Mn 0.60Figure 2. Optical, SEM and EDS results of PC lubricant.3. RESULTS AND DISCUSSIONTop dead centre is the most complex surface forthe tribologists where the conditions are extreme.Combustion induced pressure gradient acts upon topring and hence contact between liner and ring surfacereaches top levels and conditions become severe.Furthermore, combustion gases and sootcontroversially affect the lubrication in TDC area,acidic compounds, unburned hydrocarbons and sootaccumulation on liner surface occurs with constantreplenishment cycle. In addition to the factorsexplained above, high gas temperature reduces oilviscosity which also has detrimental effect on linerringlubrication. Base number retention capability andhigh temperature and high shear rate viscosity(HTHS) of engine lubricant become excessivelyimportant on TDC lubrication as well as theperformance of anti-wear additive. Total base numberindicates the ability of engine oil to neutralize acidiccompounds which primarily originate fromcombustion chamber and transfer through the liner tothe crankcase. The more the base number retention,the lower the oxidative wear on liner surfaceespecially around TDC.Downsized engines with turbochargers are ongoingtrend to fulfil the requirements of CO 2 emissionreduction and fuel economy [10]. Low load fueleconomy and torque flexibility make these types ofengines favourable although increased boost levelsresult significantly higher contact pressures.Therefore, HTHS viscosity gains attention with risingin-cylinder pressure which is the wellness of lubricantperformance under severe operation conditions.Layer formation of anti-wear additive on TDCsurface is the main factor for decreasing the linerwear. Anti-wear additive acts like buffer between ringand liner asperities and prevents adhesion.Accumulated additives on surfaces can effectively bedetected through electron microscopy technique.Besides, it is possible to detect elemental distributionwith X-ray spectroscopy method.Equal tear-down processes were applied to testengines, which include dismantling of cylinder linersand piston rings. Scanning electron microscopy(SEM) and energy dispersive X-ray spectroscopy(EDS) were applied on TDC region of cylinder lineras shown in Figure 2 and Figure 3.Figure 3. Optical, SEM and EDS results of NPNAlubricant.Labels on figures indicate the location of theinspection: G1 designation borders the combustionchamber surface where the sweep motion of topring has ended G2 designation indicates linersurface covered by piston crown. Representation ofinspected surfaces are depicted in Figure 4, analysepoints were determined by considering the surfacelayers of additive accumulation.Figure 4. Schematic representation inspected surfaces.Figure 5. EDS result of combustion chamber surface.EDS measurements were applied for both of thesurfaces lubricated with test oils. Figure 5 showsthe elemental composition of layer on the surface ofcombustion chamber. Higher amount ofcarbonaceous deposit was detected with the PClubricant on combustion chamber surface. Similartrend observed for G2 surface as shown in Figure 6while atomic concentration is different.100 13 th International Conference on Tribology – Serbiatrib’13