Why Can Vegetable Oils and Animal Fats and Their Derivatives Be Used as (Alternative) Diesel Fuel?

The fact that vegetable oils, animal fats, and their derivatives such as alkyl esters are suitable as diesel fuel demonstrates that there must be some similarity to petrodiesel fuel or at least to some of its components. The fuel property that best shows this suitability is called the cetane number In addition to ignition quality as expressed by the cetane scale, several other properties are important for determining the suitability of biodiesel as a fuel. Heat of combustion, pour point, cloud point, (kinematic) viscosity, oxidative stability, and lubricity are among the most important of these properties.

Believe it or not, the original diesel engines were designed to run on peanut oil! Today's engines are designed with petro-diesel in mind and therefore require a fuel with similar physical properties. Vegetable oil will burn in a diesel engine but only if its viscosity (how thick a liquid is) can be brought down to a level similar to petro-diesel.

To do this you can mix it with another fuel such as kerosene or petro-diesel, but you can also do it by heating it to about 160 °F. This option can allow you to run on pure vegetable oil, including waste vegetable oil.