A Moment of Science

Some Fuel For Thought

The number of carbon atoms in fuel determines its chemical properties.

An abandoned gas pump with handle.

Photo: Amanda Azzi (Flickr)

Gas, diesel and jet fuel aren't carbon copies.

Ever wonder what makes the unleaded gasoline you put in your car different from diesel or jet fuel? Here’s a — excuse the pun — crude explanation.

All About The Carbons

The crude oil, or petroleum, that’s pumped out of the ground contains molecules known as hydrocarbons. These molecules contain hydrogen and carbon atoms, which are linked together in chains of varying lengths and shapes.

Different carbon chains posses different chemical properties. For example, methane contains only one carbon atom per molecule and is a gas at room temperature. In contrast, isooctane, one of the main hydrocarbons in the gasoline you put in your car contains eight carbon atoms and is liquid at room temperature.

Gas Versus Diesel

The difference between diesel and gasoline has to do with the average length and shape of the carbon chains each contains. Diesel consists of more carbon atoms; it therefore provides more energy and is more efficient than gasoline.

On the down side, diesel’s longer carbon chains are more likely to form branches or rings, which tend not to burn completely. That’s why diesel creates more pollutants than gasoline.

Jet Fuel

Airplanes use kerosene, which falls between gasoline and diesel in terms of the average length of its hydrocarbon chains. Kerosene is good for jets because it has a low freezing temperature, which comes in handy at high altitudes, and because it burns cleanly.

So the next time you’re filling up, don’t mince your hydrocarbons. A little carbon makes a world of difference.

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