Viscosity of biodiesel: experiments and modeling

Abstract

A model has been developed to predict the viscosity of biodiesel fuel. It is based on the extended hard-sphere (EHS) model that assumes conformal viscosity behavior and makes use of the mole average mixing rules. The relevant mixture parameters for unsaturated esters were obtained by means of the effective molecular mass concept, while those for saturated esters were obtained by recourse to previously published correlations. In order to validate the developed model, the density and viscosity of three synthetic biodiesel mixtures, composed of up to five components, were measured at atmospheric pressure at temperatures between (288.15 and 353.15) K. The density was measured by means of a vibrating U-tube densimeter with the combined expanded uncertainty (k ≈ 2) of 2.5 kg⋅m−3. The viscosity was measured with a Stabinger viscometer, with a relative uncertainty of 3.5 %. The data measured in this work, together with the literature viscosity data on both synthetic biodiesel mixtures and real biodiesel fuel was used to validate the developed EHS model. The experimental data, consisting of 84 data points, were represented with the average absolute deviation of 3.5 % and a maximum deviation of 12 %