What Is Biodiesel?

This alternative fuel has been available at the pump for decades.

Benjamin Hunting | 

Nov 18, 2024 | 3 min read

Getty Images

Although the vast majority of diesel fuel is refined from oil, diesel engines can also run alternative fuels derived from other sources. Of these, one of the most common is biodiesel, a small quantity of which has been mixed in with almost all diesel fuel sold in the United States since the early 2000s.

Biodiesel Is Not Based in Petroleum

It might surprise you to learn that the original diesel-engine design of the early automotive industry didn't run on fossil fuels but on peanut oil, indicating just how versatile the concept is.

Biodiesel is a catchall term used to describe non-petroleum-based fuel that can be used to power modern diesel engines. Most of the time, it's made from vegetable oil or soy oil, but it can also be derived from animal fats, cooking grease, and even algae.

These oils are refined in order to remove any impurities that could leave deposits behind in an engine or interfere with the combustion process. They are then combined with alcohol and a catalyst, which creates B100, otherwise known as pure biodiesel fuel. This process isn't any more expensive than refining and creating petroleum-based diesel, according to automotive-enthusiast publication Car and Driver.

There Are a Few Available Biodiesel Blends

B100 is most often blended with oil-derived diesel to create different types of fuel. B5 biodiesel is petro-diesel mixed with up to 5% B100 and is found at many diesel pumps in the U.S. It can be used in any engine designed for oil-only No. 2 diesel fuel and doesn't require any special labeling.

In the world of commercial fleets, the most commonly found blend is B20, which contains 20% B100 and 80% petroleum diesel. It is not as easy to find as B5 but is most common along the West Coast and in the Midwest. B20 biodiesel is popular with fleet managers because its high cetane content helps lubricate and protect diesel engines from wear, potentially reducing maintenance costs. Many modern diesel engines are compatible with B20 biodiesel.

Pure B100 fuel is less common, but it can be used in modified vehicles that have a separate tank for holding oil-derived diesel that is used during startup. This dual-tank setup is necessary because pure biodiesel congeals at much higher temperatures than conventional diesel, which can lead to hard-start issues in colder weather.

This issue of fuel flow at lower temperatures is one key disadvantage of biodiesel compared with diesel, as is the need to change filters more frequently to avoid deposit buildup in traditional diesel engines due to the solvent nature of B100.

Biodiesel Can Be Seen as a Green Fuel

Biodiesel can help reduce atmospheric carbon, with pure B100 fuel offering up to 85% fewer greenhouse gases than petroleum throughout its production and use life cycle. Even more mild biodiesel formulations provide useful reductions in tailpipe emissions.

Benjamin Hunting

Benjamin Hunting is a writer and podcast host who contributes to a number of newspapers, automotive magazines, and online publications. More than a decade into his career, he enjoys keeping the shiny side up during track days and always has one too many classic vehicle projects partially disassembled in his garage at any given time. Remember, if it's not leaking, it's probably empty.