Lube-Tech
Continuing with functionalised polymers, Hong et al. observed polymeric friction modifiers (Perfad XG 2500) combined with MoDTC and ZDDP at different temperatures to observe any tribological advancements [23]. Perfad XG 2500 is a relatively new polymeric friction modifier used for reducing friction throughout engines. In their results, researchers found that interactions between polymeric friction modifiers and this MoDTC/ZDDP decrease film thickness at higher temperatures, but the inherent properties of MoDTC and ZDDP allow the oil a prolonged service life and prevent wear over time. Also, researchers found that Perfad XG 2500 and MoDTC have synergistic effects and are optimal for antifriction applications, with reductions up to 20.83% [23]. More research into optimal ratios for adding oils must be conducted for replications of these results. For more alternatives to traditional friction modifiers, research into carbon nano-tubes has shown promise due to rising wear and increasing automotive engines. Carbon nanotubes may reduce friction due to their shape and optimal thermal conduciveness [24]. Further research is ongoing to better understand how graphene behaves mechanically and thermally when working in high-temperature environments as those found in engines. Earlier this year, researchers noted graphene’s tribological properties while in liquid form and working together with several other friction modifiers. Enhanced properties include decreased wear on material surfaces and maintained film thickness when exposed to high temperature- a key component in this discussion on friction modifiers [25].
ZDDP
The inverse relationship between engine efficiency and engine wear for film thickness observed within the aforementioned studies provides a basis for improved research. The examples above provide insight into how synergistic effects, individual modifier characteristics, and temperatures modify their effectiveness. Film thickness varies by application,
32 LUBE MAGAZINE NO.184 DECEMBER 2024
Volatility for friction modifiers plays a key role in engine oil’s effectiveness while in use. Indeed, temperature conditions affect oil and additive properties, changing how they interact with surfaces. Volatility, or how quickly the oil evaporates during operating conditions, is correlated with film thickness. Low volatility oils are harder to evaporate while in
PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.155 page 6
operating conditions, and viscosity of the base oil used [26]. As such, friction modifier addition would alter base oil operating conditions through chemically modifying friction coefficient and viscosity. For maintaining film thickness throughout the engine and maintaining operating conditions, ZDDP alternatives are growing in popularity due to ZDDP by itself increasing friction and potentially harming catalytic converters which shortens engine lifespan [21,26]. However, AMSOIL has found that reducing ZDDP has been found to reduce effectiveness between certain high-pressure components for older engines, including high-tension valve springs, amongst others [28]. Alas, the need for maintaining proper ZDDP ratios is crucial in maintaining engine efficiency, longevity, and wear.
Film thickness When addressing film thickness, Anghel et al. observed the characteristic behavior of certain friction modifiers between thick-film models for commercial applications [29]. Carboxylic acid and a dimer acid in hexadecane or mineral oil were used to form thick boundary films and demonstrated tribological properties; properties enhanced included forming boundaries 50-70 nm thick. However, such lubricants became either partially or wholly destroyed at high speeds, primarily above 0.08 m/s [29]. These conditions imply friction reduction at intermediate speeds for thicker oils; such results indicate certain industrial applications or older automotive engines. Applying these conditions to engine oils would be detrimental. Having film thickness decrease rapidly at high speeds, as in combustion engines, would immediately result in engine wear and destruction.
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