Assessment of the lubricant behaviour of biodiesel fuels using Stribeck curves

• Published in: Fuel processing technology Vol. 116; pp. 130 - 134
• Main Authors: Maru, Marcia M., Trommer, Rafael M., Almeida, Flávia A., Silva, Rui F., Achete, Carlos A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.12.2013; Elsevier
• Subjects: Alternative fuels. Production and utilization; animal fats and oils; Applied sciences; Biodiesel; Biofuel production; Biological and medical sciences; Biotechnology; carbon; chemical structure; Energy; equations; Exact sciences and technology; Friction; Fuels; Fundamental and applied biological sciences. Psychology; Industrial applications and implications. Economical aspects; Lubricant behaviour; Miscellaneous; soybeans; sulfur; viscosity; Lubricant behaviour; Friction; Biodiesel; Biofuel; Vegetable oil; Soybean oil; Fatty acid methyl ester; Animal fat; Stribeck effect; Lubricant
• ISSN: 0378-3820; 1873-7188
• DOI: 10.1016/j.fuproc.2013.05.010

The molecular structure (carbon chain length, degree of unsaturation and branching of the chains) and the presence of contaminants in a biodiesel have a critical influence on their lubricant behaviour. Ball-on-disc tribological tests were performed with two different standard reference materials for biodiesel — NIST SRM 2772 (soybean) and NIST SRM 2773 (animal fat). It is demonstrated that the Stribeck curves, the plots of coefficient of friction (μ) vs. Stribeck parameter S (the product of viscosity with speed divided by the normal contact load), fit to a general polynomial equation of the type μ=μ0 (1−KBL×S+KEHL×Sn). Constants KBL and KEHL reveal the contributions of the boundary lubrication (BL) and the elastohydrodynamic (EHL) phenomena, respectively. The animal fat biodiesel is the most effective fuel as it shows the highest KBL and the lowest KEHL values leading to the most stable coefficient of friction regarding speed variation. This behaviour is attributed to the higher content of contaminants, namely mono- and di-glycerides, and the presence of sulphur in the animal fat biodiesel. •Frictional behaviour of standard reference biodiesels is studied by Stribeck curves.•A polynomial equation is proposed to govern the friction coefficient of the fuels.•Contributions of boundary and EHL regimes to mixed lubrication are discriminated.•Animal fat biodiesel lubrication leads to lower friction than with soybean biodiesel.•Biodiesel contaminants (glycerides, sulphur) play a major role in friction.