Assessment of boundary lubrication in biodiesels by nanotribological tests

Marcia M. Maru, Clara M. Almeida, Rui F. Silva and Carlos A. Achete

Energy, 2013, vol. 55, issue C, 273-277

Abstract: Nanoscale measurements using atomic force microscopy are performed in order to scrutinize the friction phenomena observed in microscale ball-on-disc tribological tests under (boundary lubrication) BL regime. Two reference biodiesels, one derived from a vegetable source (soybean) and the other from animal fat, are compared. A linear dependence of the friction coefficient (μ) with the Stribeck parameter (S = viscosity × velocity/load) is observed: μ = 0.11 − 26.54 × S for the animal fat and μ = 0.12 − 51.56 × S for the soybean biodiesel. The nanotribological tests allowed highlighting the cohesion component of friction force in the BL regime that is associated to the intrinsic characteristics of the biodiesels, the respective friction coefficients being μ = 0.0206 for the animal fat and μ = 0.0233 for the soybean biodiesel. The better lubricity of the animal fat biodiesel compared to the soybean observed in microscale is attributed to the presence of sulfur and to the higher amount of mono- and di-glycerides contaminants in it. The polarity and/or chemical affinity of the respective sulfur and OH groups facilitate them to reacting with the steel surfaces during the rubbing action. At nanoscale level, the same ranking in friction is observed among the biodiesels, being that here the friction phenomena are attributed to the cohesive forces other than those related to viscosity.

Keywords: Nanotribology; Boundary lubrication; Biodiesel; Friction (search for similar items in EconPapers)
Date: 2013
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (2)

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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:55:y:2013:i:c:p:273-277

DOI: 10.1016/j.energy.2013.03.036

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