Your Complete Guide to Gasoline

You know what gasoline is, it’s that stuff that you pump in your car and makes it go. But do you know the finer points about gasoline? Do you know what Octane is all about? Do you really need those “cleaning” additives? In this article, we will take a closer look at these interesting topics.

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What is gasoline?

­Gasoline is a fluid that that is made up of liquid hydrocarbon chains. In each chain, they have some 7 to 11 carbon atoms that are flanked by hydrogen atoms. When you burn gasoline under “ideal conditions,” you produce carbon dioxide, water and lots of heat. Of course, internal combustion engines don’t burn gasoline under ideal conditions. The result is that various atmospheric pollutants are produced too.

Where does gasoline come from?

­ ­Gasoline is made from crude oil pumped out of underground oil fields. The problem with crude oil is that it contains many different kinds of hydrocarbons all mixed together, gasoline isn’t the only component. Fortunately there is an easy way to separate all the other components out because they have different boiling points. This means that they can all be separated by “fractional distillation.”

What is octane?

Engines produce power through the combustion of gasoline and air. In the standard four-stroke engine, there are four different stages involved. One of the strokes is the compression stroke, where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it. The amount of compression is called the compression ratio of the engine.  Typical engines have compression ratios of 8-to-1.

The octane rating of gasoline is a measurement that tells you how much the fuel can be compressed before it self- ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes pre-ignition in the engine. Pre-ignition if it occurs long enough can damage an engine. Lower octane gas, like “regular” 87-octane gasoline, can handle the least amount of compression before self-igniting. As Len Stoler Dodge of Westminster, MD, a Chrysler, Dodge, Jeep, Ram dealer explained to us high performance engines have higher compression ratios so they need special gas to prevent self-igniting.

Octane is the name of one of the hydrocarbon liquids that is distilled when gasoline is produced from petroleum. As it turns out, Octane is relatively resistant to self-ignition under pressure so high performance gasoline has a larger percentage of octane in it than regular gas does.

Gasoline additives

­ Dur­ing WWI, it was discovered that you can add a chemical called tetraethyl lead to gasoline and significantly improve its octane rating without adding actual Octane. Cheaper grades of self-igniting resistant gasoline could be made by adding this chemical. This led to the widespread use of “ethyl” or “leaded” gasoline. Unfortunately, the side effects of adding lead to gasoline are that lead was released into the atmosphere. The Federal Government banned lead additives in gasoline starting in 1974.

Another common additive is Methyl Tertiary Butyl Ether (MTBE). MTBE is a fairly simple molecule that is created from methanol.  It is added to gasoline because it boosts octane and it is an oxidizer that helps burn the gas and air in the cylinder more completely. The problem with MTBE is that it is carcinogenic and easily mixes with water.  If a gas station tank leaks gasoline, the MTBE is likely to contaminate nearby water sources.

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