| MadSci Network: Chemistry |
Greetings: There are many drivers who believe that the higher the octane rating of the gasoline they put in their vehicle, the greater the power and the better the performance. In reality a fuel's octane rating is totally unrelated to power. A fuel's octane number is simply a numeric description of its ability to resist engine knocking. When unburned gasoline vapors spontaneously explode in the cylinder before the expanding flame in the combustion cylinder reaches them, it actually causes two simultaneous explosions (the other is from the spark plug). This results in a knocking or pinging sound. The higher a fuel's octane number -- or anti-knock index, which is a more accurate term -- the higher its resistance to engine knock. A car's engine is designed by its manufacturer for fuel of a particular octane number which is always specified in the owner's manual. Operating a car at a lower octane number can cause deposits in the engine leading to incomplete burning and increased hydrocarbon emissions. Operating a car at a higher octane number then specified in the owner’s manual does not produce more hydrocarbons but it does cost more to operate. Also, operating older engines with higher octane numbers does reduce emissions. Industry surveys indicate that American drivers do not use high enough octane ratings. Consumer group surveys indicate that American drivers use to high an octane rating. You can read the arguments for yourself at the following URLs. http://www.api.org/index.htm http://205.233.109.119/oshell/cmarket/gasoline.htm http://www.landfield.com/faqs/autos/gasoline-faq/part3/preamble.html Best regards, Your Mad Scientist Adrian Popa
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