Biodiesel is a liquid fuel made up of fatty acid alkyl esters, fatty acid methyl esters (FAME), or long-chain mono alkyl esters. It is produced from renewable sources such as new and used vegetable oils and animal fats and is a cleaner-burning replacement for petroleum-based diesel fuel. It is nontoxic and biodegradable. Biodiesel has physical properties similar to those of petroleum diesel:

Like petroleum diesel, biodiesel is used to fuel compression-ignition (diesel) engines. Low-level blends of biodiesel with petroleum diesel also provide benefits.

Related articles:

• B20 & B100: Alternative Fuels
• Biodiesel Production
• Benefits
• Biodiesel Emissions

When biodiesel is blended with petroleum diesel, it produces a fuel that is compatible with diesel engines, displaces imported petroleum, and reduces harmful emissions. Blends like B2 (2% biodiesel and 98% diesel) and B5 (5% biodiesel and 95% diesel) are becoming increasingly common as drivers become more aware of the many benefits. Higher-level biodiesel blends, such as B20, are also becoming more widely available and can qualify for credits under the Energy Policy Act of 1992.

Benefits

As of 2006, most U.S. highway diesel fuel is limited to 15-ppm sulfur, down from a 500-ppm limit. This new ultra-low sulfur diesel fuel (ULSD) might have reduced lubricating properties before additives. Adding as little as 0.25% biodiesel, which is very low in sulfur, can significantly increase fuel lubricity. B2 and B5 are becoming increasingly popular for this reason.

Another reason for using B2 or B5 is to introduce a large quantity of renewable fuel into the diesel fuel market with no noticeable impact on users or fuel properties. Using 100 gallons of B5 brings roughly the same air-quality and alternative fuel use benefits as using 25 gallons of B20 or 5 gallons of B100. Minnesota adopted a statewide requirement for B2 use in 2005. After some problems from out-of-specification fuel the first winter, the program is working well. Louisiana, Maryland, and Washington have enacted similar programs contingent on state biodiesel production reaching certain levels.

What Types of Vehicles Can Run on Biodiesel Blends?

As long as the biodiesel used for blending meets ASTM D6751 standards, low-level biodiesel blends such as B2 and B5 can be used safely in any compression-ignition engine designed to be operated on diesel fuel. This can include light-duty and heavy-duty diesel cars and trucks, tractors, boats, and electrical generators.

Biodiesel is a domestically produced, clean-burning, renewable substitute for petroleum diesel. Using biodiesel as a vehicle fuel increases energy security, improves public health and the environment, and provides safety benefits.

Increasing Energy Security

The United States imports more than 60% of its petroleum, two-thirds of which is used to fuel vehicles in the form of gasoline and diesel. The demand for petroleum imports is increasing. With much of the worldwide petroleum reserves located in politically volatile countries, the United States is vulnerable to supply disruptions.

Biodiesel can be produced domestically and used in conventional diesel engines, directly substituting for or extending supplies of traditional petroleum diesel. (Remember to consult with your auto manufacturer and engine warranty statement before using biodiesel in your vehicle.) It also has an excellent energy balance: biodiesel contains 3.2 times the amount of energy it takes to produce it.

Protecting Public Health and the Environment

Compared with using petroleum diesel, using biodiesel in a conventional diesel engine substantially reduces emissions of unburned hydrocarbons (HC), carbon monoxide (CO), sulfates, polycyclic aromatic hydrocarbons, nitrated polycyclic aromatic hydrocarbons, and particulate matter (PM). The reductions increase as the amount of biodiesel blended into diesel fuel increases. B100 provides the best emission reductions, but lower-level blends also provide benefits. B20 has been shown to reduce PM emissions 10%, CO 11%, and unburned HC 21% (see graph). Learn more about Biodiesel Emissions.

Average emission impacts of biodiesel for heavy-duty highway engines (Source: U.S. Environmental Protection Agency, A Comprehensive Analysis of Biodiesel Impacts on Exhaust Emissions)

Using biodiesel also reduces greenhouse gas emissions because carbon dioxide released from biodiesel combustion is offset by the carbon dioxide sequestered while growing the soybeans or other feedstock. B100 use reduces carbon dioxide emissions by more than 75% compared with petroleum diesel. Using B20 reduces carbon dioxide emissions by 15%.

Providing Safety Benefits

Biodiesel is nontoxic, so it causes far less damage than petroleum diesel if spilled or otherwise released to the environment. It is also safer than petroleum diesel because it is less combustible. The flashpoint for biodiesel is higher than 150°C, compared with about 52°C for petroleum diesel. Biodiesel is safe to handle, store, and transport.

Analysis completed by the Environmental Protection Agency (EPA) in 2002 compiled the most robust data set on biodiesel tailpipe emissions from heavy-duty engines. The findings were published in A Comprehensive Analysis of Biodiesel Impacts on Exhaust Emissions (PDF 765 KB), a report that analyzes data from 39 studies. Download Adobe Reader. It concludes that biodiesel decreases emissions of particulate matter (PM), carbon monoxide (CO), and hydrocarbons (HC) commensurately with its blend level, as shown in the figure below.

Source: EPA 2002

Later studies show that biodiesel particulate matter (PM) emissions are not only reduced but are less toxic. These studies are analyzed in Impact of Biodiesel Fuels on Air Quality and Human Health (PDF 615 KB), which concluded that the PM from B100 (100% biodiesel) and B20 (20% biodiesel, 80% diesel) is 20% and 5%, respectively, less toxic than PM from diesel. Download Adobe Reader.

EPA’s study also found a slight increase in NOx emissions (2% for B20). However, Effects of Biodiesel Blends on Vehicle Emissions (PDF 1.8 MB), published by the National Renewable Energy Laboratory (NREL), presented data and analysis suggesting that B20 has no net impact on oxides of nitrogen (NOx) emissions. Download Adobe Reader. This study attributes EPA’s reported increase to a dataset that was not adequately representative of all on-highway engines. The following table combines EPA’s results with those of NREL.

These and nearly all other diesel and biodiesel emissions studies do not include evaporative emissions. This is because an inconsequential amount of these fuels evaporates due to their extremely low Reid vapor pressure.

Lifecycle Emissions and Petroleum Use

A lifecycle analysis completed by NREL found that carbon dioxide emissions for B100 were 78.5% less than those from petroleum diesel. It also showed that biodiesel reduces petroleum use by 95% throughout its lifecycle.