Gasoline the fuel that is used in cars comes from crude oil, Petroleum refers to the crude oil that is pumped out of the ground in the form of a black liquid. Petroleum contains hydrocarbons. The carbon atoms present in crude oil are present in chains of different lengths. The molecules preset in the different lengths posses different properties and behaviors. Each chain length has a higher boiling point which allows the oil refineries to separate them out by distillation. Petroleum is a nonrenewable resource, meaning that it is created by naturally occurring processes.

Most cars run by using a four-stroke gasoline engine. The compression stroke is where the engine takes a cylinder-full of air and gas and compresses it into a smaller volume. It is then ignited by using a spark plug. The rate of compression is called the compression ratio of the engine, different engines compress at different rates. The octane rating of gasoline is used to inform the public how much fuel can be compressed before it suddenly ignites. Deflagration is the term that is used to describe the normal type of combustion. Gasoline that is ignited by compression rather than from the spark of the spark plug, causes knocking in the engine. Different engines require different fuel octane requirements. Engine with a higher engine compression ratios generate more heat in the cylinder during the compression stroke. When the fuel octane rating is too low for a particular compression ratio, the fuel ignites prematurely and the fuel charge explodes instead of burning. Gasoline that is ignited by compression rather than from the spark of the spark plug, causes knocking in the engine. This incomplete combustion causes the knocking which is referred to as detonation.

Octane number is measured by comparing gasoline to isooctane and heptane. For all purposes isooctane, which burns smoothly, has an octane rating of 100 and heptane, which can cause knocking, has an octane rating of zero. Gasoline that comes directly from the refinery distillation column has an octane number of 70. This means that the volume of the mixture is 70% isooctane and 30% heptane. The gasoline is taken through additional refining processes to increase the octane rating. The numbers that you see at the pump for regular, super and premium fuel refer to their respect octane number. Most gas pumps range in octane number from 87-93 with 87 being regular and 93 being premium.

Regular gas generally has an octane rating of 87 and what this means is that it is 87% isooctane and 13% heptanes and it is made for engines that do not exceed this compression ratio. For most cars this ratio is fine and regular gas can be used unless otherwise noted. The horsepower of an engine can be increased by increasing its compression rate. This is why high performance engines such as some V6 and V8 engines require a higher octane fuel level. 89 is generally the octane rating for Super gasoline in some places and is generally therefore recommended for higher performance engines. The octane number 91 and up usually refers to premium gas and those cars that have an engine with this type of compression ratio are urged to use this higher grade.

If your car does not call for super or premium using regular is sufficient. Regardless of what you may have been told using the higher octane gas will not cause your car to go faster or give you better gas mileage. If your car manual says to use the higher octane rating you should follow that suggestion. If you do not your car probably will still run but your gas mileage as well as your car’s performance will definitely decrease.