Biodiesel Basics

Biodiesel vs Petroleum Diesel

Biodiesel is a renewable energy resource commonly produced from vegetable oil, soybean oil, or animal fat, though the fuel source has been created from other organic materials as well. Biodiesel is compatible with and most commonly available blended with petroleum based diesels. With some restraints, Biodiesel is safe to use as a fuel in diesel engines. Biodiesel is advertised by the ratio of its blend with petroleum based diesel fuel. Biodiesel is commonly made available in B5 or B20 blends - B5 biodiesel contains 5 percent biodiesel and 95 percent petroleum diesel, while B20 contains 20 percent biodiesel to 80 percent standard diesel fuel by volume. B100 biodiesel is pure, 100 percent unblended biodiesel.

Properties of Biodiesel

Biodiesel has a lower energy content than petroleum based diesel, though studies have found that when using a B20 or less blend, the effects on fuel economy and performance are small, even negligible at times. B20 biodiesel has an 8-9 percent lower energy content by volume than petroleum based diesel fuel, while B5 only has a 1-2 percent lower energy content. The higher the blend, the lower the energy content. On the positive side, biodiesel has a higher cetane level and better lubricity than petroleum based diesel. Studies suggest that using B100 biodiesel may yield up to a 5% decrease in fuel economy.

A study by the U.S. Environmental Protection Agency (EPA) suggests that emissions from biodiesel are favorable over conventional petroleum based diesel. Their study found that a B20 blend of biodiesel yielded a 10% reduction in particulate matter, 21% reduction in hydrocarbon, and 11% reduction in carbon monoxide emissions. On the contrary, biodiesel tends to result in greater NOx emissions.

Carbon dioxide emissions remain relatively constant regardless of the fuel being consumed. However, proponents of biodiesel tend to offset the CO2 emissions produced by biodiesel under the circumstance that plants grown specifically for the production of biodiesel consume roughly the same quantity of CO2 through their life cycle as the emissions produced from the fuel they yield. From this perspective, it could be said that CO2 emissions resulting from the combustion of biodiesel alone eventually zero out - for every unit of CO2 emitted, there is an equal unit of CO2 consumed by the plant stock. In reality, this pattern of thought is unrealistic and fails to take into account the overall "carbon footprint" of the process of harvesting, refining, and transporting biodiesel. Regardless, it is widely accepted that CO2 emissions are significantly reduced by the use of biodiesel.

How Biodiesel is Produced

Biodiesel is made by a process called transesterification. During this process, glycerin is separated from the vegetable oil or animal fat and discarded leaving fatty acids called methyl esters, or what is simply classified as biodiesel. Raw vegetable oil cannot be used in conjunction with or as a replacement for diesel fuel until the glycerin has been separated and removed. Waste vegetable oil is commonly used to make biodiesel using home-based, DIY kits, where as raw, unused materials are more common in the commercial production of biodiesel.

Biodiesel Pros, Cons, & Concerns

Many studies suggest that using a biodiesel blend of B20 or less has limited or only negligible effects on an engine. Biodiesel may act as a detergent in fuel systems and therefore may remove deposits left from conventional petroleum based diesel fuel. For this reason, it is important to replace your fuel filters shortly after switching to biodiesel or any biodiesel blended fuels.

Another concern with concentrated biodiesel (generally accepted to be anything more than B20) is that is may soften rubber fuel hoses and increase the rate of deterioration to seals/gaskets. The current diesels offered by Ford, General Motors, and Ram Trucks are rated for up to B20 biodiesel. Using biodiesel above the OEM's maximum recommended blend may result in denial of warranty claims and long term reliability issues.


Biodiesel Advantages

Biodiesel Disadvantages

• Reduced environmental impact by means of cleaner emissions and smaller overall carbon footprint

• Lower energy content by volume than petroleum based diesel fuels and therefore may negatively impact fuel economy

• 100% compatible with petroleum based diesel fuel, most commercially available biodiesels are blended with conventional diesel fuel

• May soften and/or deteriorate certain rubbers, including fuel lines and seals in a fuel injection system

• Higher cetane rating (ignition delay) and lubricity. Favorable lubrication properties promote longevity/reliability of fuel injectors and injection pumps

• May remove deposits left from petroleum based diesel fuel and overburden the fuel filtration system

• May be less expensive than #2 diesel (not always true)

• Poor characteristics in cold weather - prone to gelling


Biodiesel is a readily available alternative to traditional #1 and #2 diesel fuels. Despite its inherent drawbacks, the fact that it is ultimately a much cleaner fuel has driven its desirability. Biodiesel is available at many fuel stations around the United States, and look for availability to increase exponentially as the world turns more and more to renewable energy resources.