The Lubricity of Glycerol and its Solutions

Glycerol has been recognised as an excellent diesel fuel and lubricant. It is a liquid that can originate from the transesterification of plant oil that also results in plant oil metyl (or ethyl) ester (biodiesel). Machine elements lubricated by glycerol show very low friction, in fact lower than the one predicted by hydrodynamic lubrication calculations. Addition of water to glycerol lowers the friction but increases the wear. In the present paper the lubricity (boundary lubrication performance) of glycerol and its solutions with water, ethanol and methanol is investigated. Dilution of glycerol up to 15% shows no wear in a standard wear test. Decrease in the glycerol content below 85% reveals significant wear and solutions with less than 15% glycerol show nearly the same wear as the solvent itself. The conclusion is that glycerol may be an excellent lubricant in hydrodynamics but when it is operated in boundary lubrication it is not very effective in reducing the wear levels induced by the pure solvents.