Gasoline

Gasoline is the most common type of fuel used in cars today, and is made from a blend of hundreds of different hydrocarbon compounds. Unfortunately, gasoline is also one of the major causes of pollution, producing carbon monoxide, carbon dioxide and nitrogen oxides. Not only do these pollutants contribute to global warming, but they can also cause acid rain and can damage human health.

Gasoline is given an octane rating (RON) as a measurement of its ability to resist engine knocking, i.e. when the fuel-air mix in the cylinder explodes instead of burning in a controlled way. The higher the octane number; the greater the resistance to engine knocking. In the US, the number given at the pump is the average of the RON and the MON (Motor Octane Number - measured using a a preheated fuel mixture), sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON) or Pump Octane Number (PON). This means that the octane in the US is about 4 to 5 points lower than the same fuel in parts of the world that use the RON system: 87 octane fuel, the 'regular' gasoline in the US and Canada, would be rated 91-92 in Europe.

Regular gasoline has an AKI greater than or equal to 85 and less than 88, midgrade gasoline an AKI greater than or equal to 88 and less than or equal to 90, while premium gas has an AKI greater than 90. However, octane ratings can vary greatly from region to region. For example, in the Rocky Mountain (high altitude) states, octane ratings are lower than in other parts of the country. This is because in higher-altitude areas, a typical combustion engine draws in less air per cycle due to the reduced density of the atmosphere. This directly translates to reduced absolute compression in the cylinder, therefore deterring knock. It is worth noting that although it is safe to fill up a car that normally takes 87 AKI fuel at sea level with 85 AKI fuel in the mountains, if it carried back to sea level, the fuel may cause damage to the engine.

Leaded Gas

In the past, lead was added to gas to improve combustion; however it was found to be harmful to the environment and toxic to humans, and from January 1, 1996, the Clean Air Act banned the sale of leaded fuel for use in on-road vehicles. Possession and use of leaded gasoline in a regular on-road vehicle now carries a maximum $10,000 fine in the United States. However, fuel containing lead may continue to be sold for off-road uses, including aircraft, racing cars, farm equipment, and marine engines until 2008.

Reformulated Gasoline (RFG)

This is gasoline blended to burn cleaner and reduce smog-forming and toxic pollutants. The Clean Air Act requires that RFG be used in cities with the worst smog pollution to reduce harmful emissions of ozone.