Diesel is any fuel used in diesel engines. These engines are used in various machines with engines including cars and trucks. The fuels are produced from distilling crude oil which results in a mixture of carbon chains varying from 8 to 21 carbons in length.
Biodiesels can also be used in any engine where diesel is used without modification. The primary from differences from ordinary diesel is its origin and its composition. It is derived from reacting fats or lipids (e.g., vegetable oil, animal fat (tallow)) with an alcohol and composed of (FAME) Fatty Acid Methyl Esters consisting of long-chain alkyl (methyl, propyl or ethyl) esters.
Why do both fuel work in diesel engines if one is based on petroleum and the other from vegetable oil?
The answer is provided by examining the structure of these two materials. After being processed from feedstock of crude oil Diesel fuel is typically composed of cetane, or n-hexadecane (C16H34),
A typical molecule of biodiesel after processing from its feedstock of vegetable oils is composed of a long chain of carbon atoms, with hydrogen atoms attached, similar to the diesel molecule except the end grouping identified as an ester functional group.
The energy from both diesel and biodiesel comes from the carbon hydrogen (C-H) bonds which comprise both of the molecules.
Diesel engines can burn biodiesel fuel with no modifications (except for replacing some rubber tubing inside the automobile that may soften with biodiesel). This is possible because biodiesel is very similar in its composition to regular diesel, shown above. Notice diesel also has the long chain of carbon and hydrogen atoms, but doesn't have the ester group shown in blue above.
Diesel is used in general as is while Biodiesel is blended in various proportions with gasoline. Blends of biodiesel and traditional hydrocarbon-based diesel are products most distributed for use in the retail diesel fuel marketplace. Much of the world uses a system known as the "B" factor to state the amount of biodiesel in any fuel mix: fuel containing 20% biodiesel is labeled B20, while pure biodiesel is referred to as B100. Blends of 20 percent biodiesel with 80 percent petroleum diesel (B20) can fuel unmodified diesel engines. Biodiesel can also provide power in its pure form (B100), but may require certain engine modifications to avoid maintenance and performance problems.
The future will see more biodiesels being used in place of conventional diesel in many applications including jet fuel. The adoption rate will be faster if the price of biodiesel becomes comparable or less to that of ordinary diesel. The transition had already begun as many applications, since jet fuel is the structurally the same was diesel, are beginning to use biodiesel to power their airplane fleets.
Images courtesy of http://www.goshen.edu/chemistry and http://www.dreamstime.com
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