Why Are Vegetable Oils and Animal Fats Transesterified to Alkyl Esters (Biodiesel)

The major reason that vegetable oils and animal fats are transesterified to alkyl esters (biodiesel) is that the kinematic viscosity of the biodiesel is much closer to that of petrodiesel. The high viscosity of untransesterified oils and fats leads to operational problems in the diesel engine such as deposits on various engine parts. Although there are engines and burners that can use untransesterified oils, the vast majority of engines require the lower-viscosity fuel.