The name biodiesel comes from the fact that the fuel is derived from biologi­cal sources and the fuel is, at least originally, meant to be used in diesel engines. Biodiesel is considered a renewable fuel as it is produced from plant oils and animal fats [40]. However, it should be noted that "biodiesel" as a name potentially implies and encompasses more than what is technologi­cally defined as biodiesel. In other words, biodiesel is far more specific than simply "a biologically derived fuel that can be used on diesel engines."

Biodiesel is a renewable alternative fuel for diesel engines comprised of a long-chain mono-alkyl ester and is the product of the transesterification reaction of triglycerides with low molecular weight alcohols such as metha­nol and ethanol. According to the National Biodiesel Board (NBB), which is the national trade association representing the biodiesel industry in the United States, biodiesel is defined as "a domestic, renewable fuel for die­sel engines derived from natural oils like soybean oil, and which meets the specifications of ASTM D 6751" [41]. Although ASTM D 6751 provides the original specifications for 100% pure biodiesel (B100), there are other objec­tive fuel standards and specifications for biodiesel fuel blends such as:

• Biodiesel blends up to 5% (B5) to be used for on — and off-road diesel applications (ASTM D975-08a)

• Biodiesel fuel blends from 6 to 20% (B6-B20; ASTM D7467-09)

• Residential heating and boiler applications (ASTM D396-08b)

There is a major global push enacted by the Kyoto Protocol (adopted on December 11, 1997; entered into force on February 15, 2005) to reduce emis­sions of greenhouse gases (GHGs), more particularly, carbon dioxide [42]. Currently, the world is seriously concerned with energy sustainability and affordability, as many industrialized and developing nations are economi­cally hurting from escalating costs of energy and fuels, in particular, petro­leum-based transportation fuels. Biodiesel is one of the alternative fuels that can help the world address these issues. Biodiesel is considered a mostly carbon-neutral fuel and is completely biodegradable.