Lube-Tech
changing the ordering of the final boundary layer for a lubricant [13]. Anchoring chemistry observes how a molecule binds to a surface; for this context, how lubricant molecules react with mechanical surfaces. Surface stability and shear stress rates also have direct influences from anchoring chemistry. Also, research has observed whether synergies between two friction modifiers are tribologically sufficient [13]. Increased friction modifier efficiency within functionaliSed polymers allows for the oil lifecycle to be extended, decreasing the need for engine oil to be disposed of. Such functionaliSed polymeric friction modifiers would be able to prolong the life of engine lubricants, as well as the life of the engine, by reducing friction.
Challenges, Intro to Synergies/Antagonisms While friction modifiers of all classes exhibit great properties, certain challenges remain. This includes mixing with friction modifiers and their interactions with film thickness. For one, the increased use of low-friction engines in general has decreased the effectiveness of friction modifiers [15]. This has become paramount in finding “perfect” engine oils and lubricants. As such, the challenge of reducing friction in boundary and mixed lubrication blends, while retaining effectiveness over time, serves as a base for promising future research. Certain friction modifiers contain sulphur and phosphorus, which reduce the efficiency of catalysts within engines [16]. Current research has looked into OFMs as an alternative to traditional friction modifiers.
On top of these synergies involved, certain observed characteristics demonstrate antagonistic interactions between lubricants with friction modifiers and metal surfaces. These include corrosion, deposit formation, and decreasing antiwear performance. For corrosion, this involves the degradation of metallic surfaces due to repeated chemical exposure in conjunction with mechanical stress (i.e. friction over time). As for decreases in antiwear performance, one study implicated aminic dispersants as decreasing ZDDP’s
PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.155 page 3
antiwear performance due to reducing ZDDP’s adsorption abilities [17]. In decreasing antiwear performance, engines suffer from increased wear and possible failure while in operation. In conjunction with increased friction performance, decreased antiwear performance presents an interesting challenge to this relationship. Both synergies and antagonisms such as these will be highlighted by this review.
Recent advancements and inverse relationship OFMs and Organomolybdenum modifiers Despite these challenges, friction modifiers remain imperative in reducing friction and energy losses. In the pursuit of efficient engine lubricants, an interesting trend forms: increased efficiency leads to thinning of the lubricant’s film thickness as well as engine wear. For example, when relating to crank angle and film thickness, there is a decrease in film thickness; Figure 2 below shows this relationship at different engine speeds [16]. While this is expected, the challenge for researchers is to improve film thickness while maintaining efficiency and minimising wear. This challenge is key to understanding the need for improved friction modifiers.
Figure 2: Relationship between engine speed on oil thickness between top ring and cylinder liner using SAE 20W40 oil [16]
Recent advancements have shown great progress within this field. In the pursuit of better friction modifiers, researchers have analysed several properties to develop optimal blends for a variety of uses. One area of research looks into improving low-friction engines and their efficiency while maintaining efficient fuel economy. Several studies have shown
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