Biodiesel is a clean burning alternative fuel, produced from domestically grown, renewable resources. Biodiesel contains no petroleum products, but can be blended at any concentration with diesel from traditional sources to create a biodiesel blend. It can be used in compression-ignition engines with little or no modification. Biodiesel is simple to use, biodegradable, non-toxic, and intrinsically free of sulphur compounds and aromatics.
Biodiesel is made in a chemical process called transesterification, where glycerine is separated from the vegetable oil. The process results in two products -- methyl esters (the chemical name for biodiesel) and glycerine (a by-product used in soap manufacture).
Looking at the disadvantages, biodiesel does not supply the same energy yield per unit area that simple green plants used in a biodigester would. The biogas produced there would give about twice the energy that the same area devoted to oil plants for biodiesel production.
Biodiesel is so attractive because it can be used in existing engines with very little needed in the way of adaptation. At very low temperatures it will probably prove impossible to use pure biodiesel (B100), but mixtures up to 20 % biodiesel (B20) should cope with most climates. This advantage means that the technology can be applied generally without any preparation stage. Converting fleets of vehicles to gas propulsion is a very costly and time-consuming business, to say nothing of the down-time caused.