Biodiesel: Encyclopedia II - Biodiesel - Fuel quality standards and properties

Biodiesel - Fuel quality standards and properties

Biodiesel is a clear amber-yellow liquid with a viscosity similar to petrodiesel, the industry term for diesel produced from petroleum. It can be used as an additive in formulations of diesel to increase the lubricity of pure ultra-low sulfur petrodiesel (ULSD) fuel. Much of the world uses a system known as the "B" factor to state the amount of biodiesel in any fuel mix, in contrast to the "BA" system used for bioalcohol mixes. For example, 20% biodiesel is labeled B20. Pure biodiesel, 100%, is referred to as B100.

The common international standard for biodiesel is EN 14214.

There are additional national specifications. The standard ASTM D 6751, which is the most common standard referenced in the United States. In Germany, the requirements for biodiesels are fixed in a DIN standard. There are standards for three different varieties of biodiesel, which are made of different oils:

• RME (rapeseed methyl ester, according to DIN E 51606)
• PME (vegetable methyl ester, purely vegetable products, according to DIN E 51606)
• FME (fat methyl ester, vegetable and animal products, according to DIN V 51606)

The standards ensure that the following important factors in the fuel production process are satisfied:

• Complete reaction.
• Removal of glycerin.
• Removal of catalyst.
• Removal of alcohol.
• Absence of free fatty acids.

Basic industrial tests to determine whether the products conform to the standards typically include gas chromatography, a test that verifies only the more important of the variables above. More complete testings are more expensive. Fuel meeting the quality standards is very non-toxic, with a toxicity rating (LD50) of greater than 50 ml/kg. This toxicity rating would mean that an average 60 kg person would need to consume more than 3 litres to cause death 50% of the time, making biodiesel ten times less toxic than table salt.

Biodiesel can be mixed with petroleum diesel at any concentration in most modern engines, although it has the disadvantage of degrading rubber gaskets and hoses in vehicles manufactured before 1992. Biodiesel is a better solvent than petrodiesel and has been known to break down deposits of residue in the fuel lines of vehicles that have previously been run on petroleum. Fuel filters may become clogged with particulates if a quick transition to pure biodiesel is made, but biodiesel cleans the engine in the process.

In a study at a U.S. military base, a biodiesel blend was used as a replacement for heating oil at housing on the base. Due to the solvent power of biodiesel, residues that had been present in fuel tanks for decades were dissolved. The particulate component of the residues caused repeated clogging of fuel strainers, requiring repeated replacement, cleaning, and in some cases installation of higher capacity filters. Due to the relatively smaller surface area and service life of fuel tanks in motor vehicles and mobile equipment, filter clogging is less prevalent but still a factor to be considered.

Environmental benefits in comparison to petroleum based fuels include:

• Biodiesel reduces emissions of carbon monoxide (CO) by approximately 50% and carbon dioxide by 78.45% on a net lifecycle basis because the carbon in biodiesel emissions is recycled from carbon that was already in the atmosphere, rather than being new carbon from petroleum that was sequestered in the earth's crust. (Sheehan, 1998)
• Biodiesel contains fewer aromatic hydrocarbons: benzofluoranthene: 56% reduction; Benzopyrenes: 71% reduction.
• It also eliminates sulfur emissions (SO₂), because biodiesel does not include sulfur.
• Biodiesel reduces by as much as 65% the emission of particulates, small particles of solid combustion products.
• Biodiesel does produce more NO_x emissions than petrodiesel, but these emissions can be reduced through the use of catalytic converters. The increase in NO_x emmisions may also be due to the higher cetane rating of biodiesel. Properly designed and tuned engines may eliminate this increase.
• Biodiesel has a higher cetane rating than petrodiesel, and therefore ignites more rapidly when injected into the engine.

Pure biodiesel (B100) can be used in any petroleum diesel engine, though it is more commonly used in lower concentrations. Some areas have mandated ultra-low sulfur petrodiesel, which reduces the natural viscosity and lubricity of the fuel due to the removal of sulfur and certain other materials. Additives are required to make ULSD properly flow in engines, making biodiesel one popular alternative. Ranges as low as 2% (B2) have been shown to restore lubricity. Many municipalities have started using 5% biodiesel (B5) in snow-removal equipment and other systems. Since biodiesel is more often used in a blend with petroleum diesel, there are fewer formal studies about the effects on pure biodiesel in unmodified engines and vehicles in day-to-day use. Fuel meeting the standards and engine parts that can withstand the greater solvent properties of biodiesel is expected to--and in reported cases does--run without any additional problems than the use of petroleum diesel. The flash point of biodiesel (150 °C) is significantly higher than that of petroleum diesel (64 °C) or gasoline (−45 °C). The gel point of biodiesel varies depending on the proportion of different types of esters contained. However, most biodiesel, including that made from soybean oil, has a somewhat higher gel and cloud point than petroleum diesel. In practice this often requires the heating of storage tanks, especially in cooler climates.

Adapted from the Wikipedia article "Fuel quality standards and properties", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki