Biodiesel vehicles can run on B100 or B99.9 fuel blends. Image from Wikimedia Commons.

Biodiesel fuel is an arguably more environmentally friendly alternative to the “petrodiesel” most diesel cars run on. Some forms of biodiesel are already manufactured and sold commercially in the United States, while others are do-it-yourself specials. Is biodiesel a legitimate alternative to petrodiesel, or should you keep the vegetable oil out of your gas tank?

Telling the difference between biodiesel fuels

Biodiesel, in general, is diesel fuel made from biological, rather than oil-based, materials. Vegetable oil is the most commonly used raw material for biodiesel. B10 or B20 are biodiesel blends – 10 or 20 percent biodiesel mixed with petrodiesel. On the other hand, B100, or the “biodiesel” most often discussed in environmental circles, is made of 100 percent vegetable or biological sources. B10 and B20 are very different from B100 and must be treated differently.

Biodiesel blends — B10 and B20

A blended biodiesel fuel can be used in most standard diesel engines. B10 and B20 blends are federally regulated fuels. There are about 1,000 filling stations, mostly in the Midwest, that offer this blended fuel. Biodiesel blends can also be specially ordered if you live in an area that doesn’t have a B10 or B20 filling station. Blended biodiesel fuel has the benefit of being able to run in a standard diesel engine with no modifications necessary.

Pure biodiesel fuel — B100

B100, otherwise known as “pure” biodiesel, is very different from blended B10 or B20. A standard diesel engine can run on pure biodiesel, but only with modifications. Biodiesel tends to coagulate at cold temperatures and can eat away at the seals in old diesel vehicles. Converting a diesel vehicle to run on biodiesel involves adding an extra tank, altered fuel lines and injectors and replacing any natural rubber in the engine. Converting a diesel engine to run on biodiesel is a project that can be done on your own, with time and money. Remember that pure biodiesel gels at freezing temperatures. This means a B100 engine must never be exposed to temperatures lower than 32 degrees unless it has a separate petrodiesel tank to get the engine and biodiesel warmed up.

Biodiesel is much like ethanol blended fuels; at low concentrations, a standard engine designed to run on that fuel can run a blend. At higher concentrations, though, you need a specialty engine.