Effects of Ethanol Contamination on Friction and Elastohydrodynamic Film Thickness of Engine Oils

Abstract

ABSTRACT:The use of ethanol as engine fuel has increased for environmental reasons, both in flex-fuel engines, and as increasing amounts of ethanol blended with gasoline in conventional engines. This paper describes an investigation into the effects of ethanol contamination of lubricants during engine use with ethanol fuel. To facilitate this, a new technique was developed to measure small amounts of ethanol in lubricants.Elastohydrodynamic film thickness measurements and Stribeck curves were obtained for Group I base and formulated oils containing small added amounts of ethanol. The effect of the water present in hydrated ethanol was evaluated by carrying out tests using both 2 hydrated and anhydrous ethanol. Measurements were also carried out using a Group II base oil with added ethanol. These measurements showed that in the low entrainment speed region, where the elastohydrodynamic film is very thin so that boundary lubrication prevails, the addition of ethanol produced a boundary film, which was not present for the base oils. By contrast the addition of ethanol to formulated oil reduced film thickness in all lubrication regimes. The friction tests showed friction reduction due to addition of ethanol to the base oil, in particular at low speeds. For the formulated oil, ethanol reduced friction at high speeds, which was associated with a reduction in the viscosity of the lubricant, but at low speeds, ethanol reduced the formation of a boundary layer, increasing friction. The presence of water in hydrated ethanol did not change significantly film thickness and friction when compared with anhydrous ethanol.

Study of the interfacial mechanism of ZDDP tribofilm in humid environment and its effect on tribochemical wear; Part I: Experimental

“…On the other hand, at larger amount of dissolved or free water, viscosity is expected to increase, which is evident from the results of Liu et al [19]. The same results has also been found when hydrated ethanol was added to the lubricant [21]. This suggests that it is not sufficient to report only the relative humidity values but the exact amount of water in oil is required as well.…”

Effects of Ethanol on Film Thickness and Friction of Group One Engine Oils

“…Another possibility could be the occurrence of oxidation reactions of the ethanol when in contact with the hot metal surface. This seems to be the case, as reported in [7]. For the ethanol-free formulated oil, both the film thickness measurements under pure rolling and the Stribeck curves suggested the formation of a quite thick boundary film.…”

“…Chemical composition of the oil showed the presence of Zn, S and P and Ca. It was suggested in [7] that this film results from the formation of a CaCO3 film from an overbased detergent, as proposed in [15]. For the case of an organic friction modifier dissolved in base oil, friction coefficients below 0.06 were achieved for the region of low speeds.…”

“…* Technical contribution to the 2 nd International Brazilian Conference on Tribology -TriboBR 2014, November 3 rd to 5 th , 2014, Foz do Iguaçu, PR, Brazil. Although the viscosity of pure ethanol is higher than that of water, it was hypothesized that when both water and ethanol are present the true solubility of the ethanol in hydrocarbon is reduced, resulting in some of the ethanol being present as a microemulsion, thereby having little influence on viscosity [7].…”

“…After the tests, the amount of ethanol present in the lubricant was measured using refractive index measured of a sample of distilled water used to extract ethanol from the lubricant. This new technique has been proposed by Costa and Spikes and is fully described in [7]. For the EHD tests there was some loss of ethanol at 100 o C but more than half of the ethanol content remained to the end of the tests.…”