Fundamentals of Biodiesel Quiz

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Commonly used blends are limited to B20 in the United States because this level provides a good balance between material compatibility, cold weather operability, performance, and emission benefits, as studied. B20 is also the minimum blend level allowed for compliance with the Energy Policy Act of 1992 (EPAct), which requires the use of renewable fuels and/or alternative fuel vehicles (AFVs) by certain covered fleets. Equipment that can use B20 includes diesel engines, fuel oil and heating oil boilers, and turbines.

Higher blend levels such as B50, and B100 require special handling and may require equipment modifications. These issues can potentially be managed with heaters and/or changing engine seal and gasket materials. Consult your engine or combustion equipment manufacturer for further information about procedures before using biodiesel blends higher than B20.

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“A fuel comprised of mono-alkyl esters of long-chain fatty acids derived from vegetable oils or animal fats, designated B100, and meeting the requirements of ASTM D6751.”

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The biodiesel manufacturing process converts oils and fats into chemicals called long-chain mono alkyl esters, or biodiesel. These chemicals are also referred to as fatty acid methyl esters (FAME), and the process is referred to as esterification. Figure 1 provides a simplified diagram of the esterification process. Roughly speaking, 100 pounds of oil or fat are reacted with 10 pounds of a short-chain alcohol (usually methanol) in the presence of a catalyst (usually sodium hydroxide or potassium hydroxide) to form 100 pounds of biodiesel and 10 pounds of glycerin (or glycerol). Glycerin is a sugar and is a co-product of the biodiesel process.

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Specification D6751 is based on a compilation of efforts from researchers, engine manufacturers, petroleum companies and distributors, and many other fuel-related entities and is intended to ensure the quality of biodiesel used as a blendstock at 20% (B20) and lower blend levels. Any biodiesel used in the United States for blending should meet ASTM D6751 standards. The ASTM standards provide a minimum level of quality for biodiesel regardless of the source of the fuel. Purchasers and sellers can require that biodiesel meet more stringent requirements in purchasing specifications. Both parties must agree to these more stringent requirements, and this is becoming an increasingly common practice.

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When biodiesel displaces petroleum, it significantly reduces life-cycle greenhouse gas emissions. Life cycle analysis completed by Argonne National Laboratory found that greenhouse gas emissions for B100 are 74% lower than those from petroleum diesel. More recently, the California Air Resources Board (CARB) reported similar values for its life-cycle analysis of biodiesel from various sources.

When oilseed plants grow, they take carbon dioxide (CO2) from the air to make the stems, roots, leaves, and seeds. After the oil is extracted from the oilseeds, it is converted into biodiesel. When the biodiesel is burned, CO2 and other emissions are released and returned to the atmosphere. On balance, most of this emitted CO2 does not add to the net CO2 concentration in the air because the next oilseed crop will reuse the CO2 as it grows. A small fraction of the emitted carbon is fossil derived because of fossil fuel and chemicals used in farming and in the biodiesel production process.

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Neat biodiesel contains about 8% less energy per gallon than typical No. 2 diesel in the United States, or 12.5% less energy per pound. The difference between these two measurements is due to the higher density of biodiesel compared to diesel fuel. All biodiesel, regardless of its feedstock, provides about the same amount of energy per gallon or per pound. The energy content of petroleum diesel fuel typically varies more widely than that of biodiesel. However, some reference values are:

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Cetane number is a measure of the ignition delay (the time from fuel injection into the combustion chamber to ignition); higher cetane numbers are believed to provide easier starting and quieter operation. ASTM D6751 for biodiesel requires a minimum cetane number of 47; the cetane number required of petroleum diesel fuel is 40. B100 produced from highly saturated feedstocks can have a cetane number of 60 or higher. Figure 3 shows the cetane numbers of various biodiesel samples and compares them to diesel cetane numbers. While it is interesting to know the cetane numbers of biodiesels from different feedstock oils, biodiesel is most commonly a blend from two or more feedstocks. Thus, buyers should focus on measured fuel properties rather than trying to determine the feedstock source.

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• Pour point. The temperature at which the fuel contains so many agglomerated crystals it is essentially a gel and will no longer flow (ASTM D97, D5949, orD5950). Distributors and blenders use pour point as an indicator of whether the fuel can be pumped,even if it would not be suitable for use without heating or taking other steps.

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Methyl esters have been used as low volatile organic compound cleaners and solvents for decades. Methyl esters make excellent parts cleaners, and several companies offer methyl esters as a low volatile organic compound, nontoxic replacement for the volatile solvents used in parts washers. B100 will dissolve the accumulated sediments in diesel storage and engine fuel tanks. These dissolved sediments can plug filters. If this happens, it can cause injector deposits and even fuel injector failure. If you plan to use or store B100 for the first time, clean the tanks and any parts in the fuel system where sediments or deposits may occur before filling with B100.

The level of cleaning depends on the amount of sediment in the system (if the system is free of sediment, there should be no effect) as well as the biodiesel blend level—the higher the blend level, the greater the cleaning potential. The cleaning effect is much greater with B100 and blends with 35% or more biodiesel, compared to B20 and lower blends.

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• Pour point. The temperature at which the fuel contains so many agglomerated crystals it is essentially a gel and will no longer flow (ASTM D97, D5949, orD5950). Distributors and blenders use pour point as an indicator of whether the fuel can be pumped, even if it would not be suitable for use without heating or taking other steps.

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In general, blending biodiesel is not difficult if you remember that biodiesel is slightly heavier and more viscous than diesel fuel and the more it is mixed, the better.

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Blending biodiesel into petroleum diesel even at low levels can improve the lubricity of diesel fuel (i.e., reduce wear scar diameter). As little as 0.25% biodiesel can significantly improve lubricity. Figure 10 shows results of lubricity testing using the HFRR, the test used to determine if diesel fuels meet the ASTM lubricity requirement of a maximum 520-micron wear scar diameter. The exact blending level required to achieve adequate lubricity depends on the properties of the conventional diesel. Preliminary evidence suggests that 2% biodiesel almost always imparts adequate lubricity.

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B100 should not be stored longer than four months unless it has been treated with synthetic antioxidants and has an oxidation stability of 6 hours or longer. Non-oxidizing storage conditions in containers with little head space or under a nitrogen blanket will also be helpful. In fact, when B100 is being stored longer than about two months, it should be tested for oxidation stability every two weeks. One of the best ways to stabilize biodiesel is to blend it with petroleum diesel.

B5 blends made from in-specification B100 can be stored for one year or longer. However, as storage conditions can influence stability, we recommend that you consider adding a synthetic antioxidant and monitoring the condition of the fuel periodically if you store fuel for longer than 6 months.

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Neat biodiesel contains no hazardous materials and is generally regarded as safe. A number of studies have found that biodiesel biodegrades much more rapidly than conventional diesel. Users in environmentally sensitive areas such as wetlands, marine environments, and national parks have taken advantage of this property by replacing toxic petroleum diesel with biodiesel.

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Viscosity: A measure of the resistance to flow of a liquid.

 (the higher the viscosity, the less easily a fluid can flow)

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Neat biodiesel can be extinguished with dry chemical, foam, Halon, CO2, or water spray, although the water stream may splash the burning liquid and spread the fire. Oil-soaked rags can cause spontaneous combustion if not handled properly. Before disposal, wash rags with soap and water and dry in a well-ventilated area. Because biodiesel will burn if ignited, keep it away from oxidizing agents, excessive heat, and ignition sources.

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• Viscosity. A minimum viscosity is required for some engines because of the potential for power loss caused by injection pump and injector leakage.This is not an issue for B100, and the minimum is set at the same level as for petroleum diesel.The maximum viscosity is limited by the design of engine fuel injection systems. Higher viscosity fuels can cause poor fuel combustion that leads to deposit formation as well as higher in-cylinder penetration of the fuel spray, which can result in elevated engine oil dilution with fuel. The maximum allowable viscosity in ASTM D975 for No. 2 diesel is 4.1 mm2/s at 40°C (104°F). ASTM D6751 allows for slightly higher viscosity than D975, primarily because the normal viscosity of B100 is slightly higher than that of diesel fuel. Biodiesel blends of 20 vol% or lower should have viscosities between 1.9 and 4.1 mm2/s, within the range allowed by D975.

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Certain metals may affect the biodiesel by accelerating its oxidation process and creating fuel insolubles. Lead, tin, brass, bronze, and zinc significantly increase sediment formation in both B100 and B20. Galvanized metal and terne-coated sheet metal are not compatible with biodiesel at any blend level.