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Speaker 1: m z y dot com. Welcome to brain Stuff from
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Speaker 1: Marshall Brand with today's question what does octane mean? If
Speaker 1: you've read how car engines work, you know that almost
Speaker 1: all cars use four stroke gasoline engines. One of the
Speaker 1: strokes is the compression stroke, where the engine compresses a
Speaker 1: cylinder full of air and gas into a much smaller
Speaker 1: volume before igniting it with the spark plug. The amount
Speaker 1: of compression is called the compression ratio of the engine.
Speaker 1: A typical engine might have a compression ratio of eight
Speaker 1: to one. The octane rating of gasoline tells you how
Speaker 1: much the fuel can be compressed before it's spontaneously ignite.
Speaker 1: When gas ignites by compression rather than because of the
Speaker 1: spark plug, it causes knocking in the engine. Knocking can
Speaker 1: damage and engine, so it's not something you want to
Speaker 1: have happening. Lower octane gas like regular eight seven octane
Speaker 1: gasoline can handle the least amount of compression before it
Speaker 1: starts igniting. The name octane comes from the following fact.
Speaker 1: When you take crude oil and crack it in a refinery,
Speaker 1: you end up getting hydrocarbon chains of different links. These
Speaker 1: different chain links can then be separated from each other
Speaker 1: and blended to form different fuels. For example, you may
Speaker 1: have heard of methane, propane, and butane. All three of
Speaker 1: them are hydrocarbons. Methane has just a single carbon atom,
Speaker 1: Propaine has three carbon atoms chained together, and butane has
Speaker 1: four carbon atoms chained together. Pentane has five, hexane has six,
Speaker 1: heptane has seven, and logically octane has eight carbon atoms
Speaker 1: chained together. It turns out that heptane handles compression very poorly.
Speaker 1: Compress it just a little and it ignites spontaneously. Octane,
Speaker 1: on the other hand, handles compression very well. You can
Speaker 1: compress it a lot and nothing happens. Eighty seven octane
Speaker 1: gasoline is gasoline that contains eight seven percent octane and
Speaker 1: thirteen percent heptane, or some other combination of fuels that
Speaker 1: has the same performance as eight thirteen combination of octane
Speaker 1: and heptane. It's spontaneously ignites at a given compression level,
Speaker 1: and it can only be used in engines that do
Speaker 1: not exceed that compression ratio. Do you have any ideas
Speaker 1: or suggestions for this podcast? If so, please send me
Speaker 1: an email at podcast at how stuff works dot com.
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