Biodiesel is a renewable fuel source derived from organic materials, offering a domestic alternative to traditional petroleum diesel. It is produced through a chemical process that converts vegetable oils, animal fats, or recycled greases into fuel-grade esters. Among the various mixtures available, B20 has become the most common blend utilized in the United States transportation market. This blend balances the environmental benefits of renewable content with the operational familiarity of conventional diesel.
Understanding the B20 Blend
The designation “B20” indicates the volumetric composition of the fuel mixture: 20% pure biodiesel and 80% petroleum-based diesel fuel (B0). The biodiesel component is chemically known as Fatty Acid Methyl Ester (FAME), which is produced via a reaction called transesterification. This process uses an alcohol, typically methanol, to separate fatty acids from the triglycerides found in organic oils or fats.
The primary sources, or feedstocks, used to create FAME in the United States come from agricultural and waste sources. Soybean oil accounts for the largest share of production feedstock. Other significant sources include recycled cooking oil (yellow grease) and rendered animal fats like tallow. These renewable sources provide the long-chain fatty acids chemically modified to create the fuel molecules.
FAME is a clean-burning hydrocarbon fuel that must meet the ASTM specification D6751 before blending. The final B20 blend must also adhere to the ASTM D7467 specification, ensuring fuel quality is consistent with operational standards. B20 leverages the lubricity and environmental advantages of biodiesel while maintaining the energy density and handling characteristics of conventional diesel fuel.
Engine Compatibility and Use
B20 is considered a “drop-in” fuel for a large majority of modern diesel engines without requiring modifications. This seamless integration is a primary reason B20 is favored over higher-concentration blends, which might necessitate material changes to fuel system components. Many engine manufacturers, particularly those producing heavy-duty engines, have formally approved B20 use, often covering it under the original equipment manufacturer (OEM) warranty.
B20 use is prevalent in high-volume, regulated fleets where its environmental and operational profile is beneficial. Typical users include municipal transit buses, government vehicle fleets, and commercial trucking operations. These applications benefit from B20’s enhanced lubricity, which helps reduce wear on high-pressure fuel pumps and injectors. This lubricity is important since the removal of sulfur from petroleum diesel reduced its natural lubricity.
B20 is a strategic choice because it offers a significant reduction in tailpipe emissions, such as particulate matter and unburned hydrocarbons, compared to pure petroleum diesel. While it contains slightly less energy per gallon than B0, the difference in power and fuel economy is typically marginal, often less than a 2% reduction. For fleet operators, the balance of operational parity, environmental compliance, and renewable content makes B20 the most practical blend for general transportation use.
Practical Considerations for Storage and Handling
While B20 is highly compatible with most diesel systems, its unique chemical properties introduce specific considerations for storage and handling. One notable characteristic is its solvent effect, meaning that FAME naturally begins to clean out old fuel tanks and lines. This solvency can dissolve varnish and accumulated sediment left by prior petroleum diesel use. This cleaning action may lead to initial filter clogging, often requiring more frequent filter changes during the first few weeks of B20 adoption.
A second concern is the fuel’s cold flow performance, which is defined by its cloud point and pour point. The cloud point, the temperature at which wax crystals begin to form and make the fuel appear cloudy, is generally higher for B20 than for B0. In colder climates, this means B20 will begin to gel sooner than pure diesel, necessitating the use of specialized cold flow improver additives or blending with No. 1 diesel or kerosene to maintain fluidity and prevent fuel line or filter blockage.
Storage stability also requires attention, as B20 has a shorter shelf life than petroleum diesel, typically around six to eight months without stabilizers. Biodiesel is hygroscopic, meaning it attracts and holds more moisture than conventional diesel fuel. The presence of water provides an environment conducive to microbial growth, often called “diesel bug,” which can lead to filter plugging and fuel system corrosion. To mitigate these issues, storage tanks must be kept dry and clean, and long-term storage often requires the periodic use of biocides and antioxidants.