The Effect on Soot Handling and Friction of Selected Dispersant Additives for Next Generation Transportation Sector Oils
Authors: Lattuada Marco , Manni Massimo , Notari Marcello , Ferraro Giovanni , Fratini Emiliano 
Published: November 2024

<div class="section abstract"><div class="htmlview paragraph">Next generation lubricating oils for transportation sector require higher durability in operation, compatibility with new engine technologies and aftertreatment devices as well as high fuel economy (FE), thus contributing to the reduction of CO<sub>2</sub> emissions, both in passenger cars and heavy-duty vehicles.</div><div class="htmlview paragraph">The current paper aims to highlight the impact of dispersant main properties in preventing sludge and deposits formation on engine surfaces. The effect on frictional properties of lubricating oils through a multi-step activity was evaluated.</div><div class="htmlview paragraph">Oil contamination by soot is a big concern not only for diesel but also for new generation of direct injection gasoline (GDI) engines. The presence of soot leads to oil thickening that heavily impacts on friction coefficient thus enhancing the role of dispersant in controlling soot and related viscosity increase and, indirectly, fuel consumption for long running periods.</div><div class="htmlview paragraph">After an introduction on dispersant technologies, the focus of the paper moves on an innovative lab-scale methodology based on optical microscopy for the direct assessment of the dispersing capacity of oil. This methodology was firstly applied to SAE Grade 15W-40 heavy duty (HD) oils contaminated with surrogate soot, where different dispersant systems were evaluated. In parallel, in order to simulate the soot effect on GDI oils, the aforementioned methodology was also applied on 0W-12 oils. Finally, the different dispersants were evaluated on the standard Mack T8E engine test for a duration of 300 hours, providing a ranking in terms of soot handling properties.</div><div class="htmlview paragraph">The second part of the paper deals with the investigation of the frictional properties of dispersants, both in GDI and HD engines. After a brief introduction on lubrication and tribology fundamentals, the authors considered an experimental activity based on a tribological test by using the Mini Traction Machine (MTM). For GDI engines, 0W-12 oils were tested at three different temperatures in order to evaluate the friction coefficient (COF) profile of oils as fresh. Afterwards, the authors considered the effect of the oil aging on friction losses, mainly consisting in soot loading and oxidation, through a two-step evaluation process: firstly, testing by MTM, the drained oil that achieved the low performance in soot handling at the Mack T8E. Secondly, from this oil, different candidates samples containing increasing amount of soot were derived and tested by MTM as fresh and after a laboratory ageing procedure: a performance comparison between aged oil vs fresh oils with and without soot was done in order to assess the effect of both soot content and ageing on frictional properties of lubricating oil.</div><div class="htmlview paragraph">The described experimental steps demonstrated that dispersant characteristics of engine oil play an important role not only in maintaining engine cleanliness but also in controlling the increase in friction during operation that influences fuel economy of finished product.</div></div>