Biodiesel has a color varying from golden or light brown to dark brown. The color depends upon the originating biodiesel feedstock. Biodiesel is immis­cible with water, and has a high boiling point and a low vapor pressure. The boiling point data of biodiesel are very scarcely reported in the literature

[48] because a smoke point is usually reached before a boiling point during its measurement, thus making the measurement itself quite difficult. At a smoke point, ingredients of biodiesel are degrading, that is, going through pyrolytic decomposition. Based on the published literature values, pure methyl esters of C18:0, C18:1, and C18:2 are 625, 622, and 639 K, respectively

[49] . Yuan, Hansen, and Zhang [48] developed models, based on the Antoine equation and a group contribution method, for predicting vapor pressure and the normal boiling point of pure methyl esters and biodiesel fuels. The flash point of biodiesel (>130°C) is significantly higher than that of petroleum diesel (64°C) or gasoline (-45°C), which makes biodiesel substantially easier to handle and less flammable. Biodiesel has a density of approximately 0.880 g/cm3, which is higher than that of petrodiesel (0.85 g/cm3) or gasoline (0.71­0.77 g/cm3).