Interactions of Ethanol with Friction Modifiers in Model Engine Lubricants

Abstract

When employed as an engine fuel, ethanol can accumulate in the lubricant during use. Previous work has shown that ethanol contamination affects friction and elastohydrodynamic lubrication (EHL) film formation, and also the growth and stability of anti-wear tribofilms. The present work uses spacer-layer ultrathin interferometry and MTM tests to investigate how ethanol (both hydrated and anhydrous) interacts with friction modifiers in model lubricants. Small proportions (5 wt %) of ethanol were added to solutions of friction modifiers (one MoDTC and three organic friction modifiers) in a Group I base oil. For the three organic friction modifiers, the presence of ethanol promoted the formation of thick viscous boundary films so that very low friction coefficients were measured at low entrainment speeds. For the MoDTC additive, the presence of ethanol prevented the formation of a low friction film at low speeds at 70 °C, but this effect disappeared at 100 °C, probably due to ethanol evaporation.

Current Knowledge on Friction, Lubrication, and Wear of Ethanol-Fuelled Engines—A Review

“…Viscosity reduction due to fuel dilution has been observed by several researchers in both field [24,29] and lab tests [32][33][34], which is mostly due to the much lower viscosity of ethanol in comparison to usual engine lubricants. On the one hand, engine tests comparing gasoline and gasoline with different concentrations of ethanol showed that viscosity reduction over time depends much more on the lubricant type than the fuel type, as both gasoline and ethanol have much lower viscosity than engine lubricants [24].…”

“…Attempts to run laboratory tests with a mixture of ethanol and lubricant, such as those described in previous paragraphs, usually require attention to the test temperature. The selection of temperatures above the evaporation point of ethanol (around 69 • C) may result in quick ethanol evaporation which, while it may not invalidate the test, needs to be considered during analysis of the results [32][33][34]40]. As an alternative, in a study of the tribological impact of ethanol Lenauer, et al [43] conducted an artificial engine oil alteration process with addition of ethanol combustion products to the oil, which was later used in reciprocating sliding laboratory tests.…”

Significantly Affected Lubrication Behavior of Silicone Oil Lubricated Si3N4/Glass Contact after Cleaning with Different Solvents

“…Moreover, atomic force microscopy (AFM) studies conducted by Barthel et al 29 revealed that ethanol cleaning and its evaporatively deposited residues exhibited superior boundary lubrication, antifriction, and antiwear properties than UV/ozone cleaned surfaces. In addition, Costa et al 30 investigated the interaction between lubricating oil and ethanol (5 wt %) and discovered that ethanol increased the thickness of the boundary film of the organic friction modifier, thereby decreasing the boundary friction. Liu et al 31 achieved macroscopic superlubricity with basil seed gel (BSG)−ethanol (1:1), primarily because the mechanical strength of the adsorption layer was enhanced when the ethanol molecules entered the BSG network, and the lubricating film was prevented from being destroyed during the sliding process.…”

“…Since ethanol can be used as a biofuel additive, several researchers have examined its effect on friction and wear, − whereas petroleum ether and acetone have been the subject of very few comparable studies. Using DFT, Barnette et al investigated the friction and wear behavior of a SiO 2 surface in a 50% humidity and ethanol vapor environment.…”

Redução de atrito em motores de combustão interna com o uso do aditivo MoDTC: efeito da diluição de etanol.

“…Uma importante classe de aditivos modificadores de atrito são os compostos de molibdênio tais como o dialquilditiocarbamato de molibdênio (MoDTC), o qual se descompõe em condições de alta tensão de cisalhamento e temperatura, formando sobre a superfície deslizante um tribofilme rico em MoS2. A capacidade de redução de atrito deste aditivo já foi mostrada em diferentes trabalhos, apresentando reduções no valor de coeficiente de atrito de valores acima de 0,11 para valores tão baixos como 0,04 a 0,08 (BALARINI et al, 2020;DE BARROS'BOUCHET et al, 2005;ERDEMIR, 2005 SPIKES, 2019SPIKES, , 2016KHUONG et al, 2017;RUIZ, 2014). Apesar dos estudos realizados, ainda são escassos os conhecimentos em relação aos efeitos que o etanol causa nos tribofilmes formados pelos aditivos usados em óleos de motor, e a maioria destes trabalhos tem sido focados nos efeitos deste combustível no aditivo anti-desgaste ZDDP.…”