Biodiesel conversion can seem like a very complex subject, since there are many different types of engines and fuels available. Most diesel engines can actually run on biodiesel without any type of conversion, though that assumes the fuel itself has undergone a transesterification process to give it qualities similar to petrodiesel. Conversions are only necessary in this case if the temperatures are likely to drop low enough for the biodiesel to crystallize or if the fuel system uses certain incompatible materials. More extensive biodiesel conversion can be necessary to run waste vegetable oil (WVO) and other products that have not undergone transesterification. The WVO may need to be heated before injection, and it is often necessary to install a different fuel filter system.
The term "biodiesel" can be used to refer to any number of petrodiesel substitutes, though it is usually used in a more tightly controlled context. In most cases, biodiesel consists of oil that has undergone a transesterification process involving alcohol. This process transfers certain chemical elements from the alcohol to the oil, which gives it similar characteristics to petrodiesel.
Modern diesel engines can typically run on biodiesel without any conversions, as long as the fuel has undergone transesterification. It can be helpful to contact the manufacturer of a vehicle to verify this, though the user's manual will typically also state whether the engine is designed to use biodiesel. In certain cases, some type of biodiesel conversion is necessary. One type of modification that some engines require involves certain portions of the fuel system. If the vehicle uses nitrite rubber for fuel lines or seals, a biodiesel conversion will typically involve replacing them.
Biodiesel can also crystallize in especially low temperatures, though high quality products are less likely to do so. A biodiesel conversion intended for use in low temperature environments will typically include some type of heating system. This can prevent the fuel in the tank, lines, filter and other areas of the system from becoming too cold and crystallizing.
Products such as waste vegetable oil are sometimes referred to as biodiesel, and many vehicles require more extensive modifications to run on these fuels. Heating systems intended for use with WVO are typically designed to warm the oil up and lower its viscosity prior to injection. Straight vegetable oil can solidify at substantially warmer temperatures than biodiesel that has undergone transesterification, so it is sometimes necessary to use two fuel tanks. One tank can be used for WVO in warmer weather, while the other holds petrodiesel or biodiesel for use during the colder months.