Isomers are certain classes of chemical compounds; some of these are useful in the production of fuels which are used to power the vehicles we use everyday. Isomers are used primarily to create stability and smooth burning properties in fuel.
Isomers are any two or more chemical compounds which share the same formula, but have different physical structures. For example, imagine a compound that has the formula C3H2, which means it has 3 carbon atoms and 2 hydrogen atoms per molecule. Two possible isomers of this compound are the structures C-C-C-H-H and C-H-C-H-C. The formulas are the same, but the pattern of how the elements bond is different. Therefore, these two compounds are called isomers of C3H2.
A common fuel used today is octane, which has the formula CH3(CH2)6CH3. It is the primary component of gasoline. This particular fuel has 18 isomers, each of which is useful for different applications. For most applications, stable burning is the goal in creating fuels. Certain isomers of octane are more useful in achieving this result.
In fuel design, the most useful octane isomers are those which have "branched" structures. These isomers are distinguished from those that have more linear structures. A linear isomer has all its elements connected in a line, whereas a branched may resemble a tree in structure, with each element not necessarily touching other branches. This branched structure causes the octane to burn more slowly and evenly, therefore, the most commonly used octane isomers in fuels are those with branched structures.
When gassing your car, you may notice the "octane rating" of the fuel you are using. This rating is a measure of how fast the fuel will burn. The rating is determined both by the isomers used in the octane, as well as the percentage of fuel which is not octane due to the addition of an additive such as ethanol. The octane rating is largely a measure of the isomers in a given fuel.
In general, isomers are very important to fuel design. The choice of the isomer mix in a given fuel determines pretty much all of the properties that the fuel will have. The only other important concern in fuel manufacture are the additives which are put in, usually only to increase the amount of available fuel. To all intents and purposes, fuel properties are determined by isomer mixtures.
