Biodiesel is a processed fuel derived from vegetable oils, such as rapeseed/canola, that can be readily used in diesel-engine vehicles. Some modified diesel engines can run on straight vegetable oils (SVO) or waste vegetable oils (WVO), but processed biodiesel fuels can run in any diesel engine designed for petroleum-based fuels. Although biodiesel runs in unmodified diesel engines and can be distributed through normal channels, it is generally more expensive to produce than petroleum diesel, although because of taxes and subsidies in some countries, such as Germany, biodiesel can actually be cheaper to buy than regular diesel fuel.
Biodiesel is biodegradable and non-toxic, and has significantly fewer emissions than petroleum-based diesel. It also has a higher lubricity index than petrodiesel fuels which can help to prolong the life of fuel injectors. Biodiesel is a better solvent than petrodiesel, so it helps to clean the fuel system, and it can break down and flush out residue deposits in vehicles that have been running on petrodiesel. Switching over to biodiesel fuel will therefore quickly clog up the fuel filter in older and dirty engines, so this will need to be changed after the lines have been cleaned by the fuel.
Biodiesel is oil-based so it does not mix with water, but it is hygroscopic, which means that it attracts water from the atmosphere. Contamination with moisture can corrode fuel system components such as pumps or injectors, it can make the engine harder to start and produce less power and more smoke, and it can encourage the growth of microbes in the vegetable-based fuel. The fuel will also degrade rubber gaskets and hoses, although it does not affect synthetic rubber, from which most components are now made.
Biodiesel is a light yellow to dark yellow liquid, and it has a viscosity similar to petrodiesel. It can be used by itself or mixed with regular diesel in any concentration as an additive. The 'B' rating of the fuel indicates the amount of biodiesel in any fuel mix. Fuel containing 20% biodiesel is therefore labeled B20. Pure biodiesel is labeled B100.