Density of biodiesel is an important physical property of liquid fuel and biodiesel. A slight change in density can affect engine output power. In this work, density of a saturated, unsaturated fatty acid methyl ester or a biodiesel can be estimated from either (1) its number of carbon atoms (of fatty acid, z) and number of double bonds (n d ): ln ρ = −0.435 − 0.0025z + 85.98/T + 0.792z/T + 4.0 n d /T or (2) its saponification number (SN) and iodine value (IV): ln ρ = −0.427 − 10/SN + 83.38/T + 3168.95/(T × SN) + 11 IV/(T × SN), where T is absolute temperature. The predicted densities at different temperatures from both equations agree well with the reported literature values.

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proposed model would be good for estimation of viscosity of biodiesel containing normal fatty acids, generally found in biodiesel feed stocks.

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Viscosity is an important physical property of fatty acid methyl esters (FAME) and biodiesel (mixture of FAMEs). In this work, quantitative structure–property relationship (QSPR) for estimation of dynamic viscosity of FAMEs and biodiesel is approached via the Gibbs energy additivity method. The Gibbs energy of dynamic viscous flow is simply derived from the sum of the Gibbs energy of kinematic viscous flow and Gibbs energy of volumetric expansion. The derived model can be used for estimation of dynamic viscosity of saturated and unsaturated FAMEs commonly found in nature. Also, the proposed model can be extended to a mixture of FAMEs or biodiesel as well as biodiesel blends. Thus, the dynamic viscosity of FAMEs as well as neat and blended biodiesels can be estimated by the same equation from the carbon number (z) and number of double bonds (nd) at different temperature (T). The average absolute deviation (AAD) values for saturated, unsaturated FAMEs, biodiesels, and biodiesel blends (at 20–100 °C) are approximately the same as the original model for estimation of kinematic viscosity.