This is something different but well worth reading.
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It was written by our learned friend in Stoke and we think is of interest to any car or bike owner.
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Well
! In The Beginning there was Carbon and Hydrogen.
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These got together in accordance with rules forged in the Big Bang
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(yes, really!) to make methane, one carbon atom with 4 hydrogens stuck on.
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A bit later,
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(only 4000 million years) other atoms started getting together and finally came up with Life, a self-reproducing chemical mix.
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The reproducing bit was quite fun, but after 600 million years even that gets boring.
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So, a more or less intelligent life-form invented The Car and the Motorcycle, the ultimate boredom cure.
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This was, and is, powered by the Internal Combustion Engine, which must have fuel.
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Methane is a fuel, which means it burns in air to produce energy, but unfortunately its a gas; a tank-full would propel a Honda 50 for about half a mile.
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But! Methane had not been idle since the formation of planet Earth, and had joined up with more carbons and hydrogens to make chains called
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hydrocarbons.
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Well, they werent called that at the time.
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They had to wait for a life-form to evolve that liked giving things names, and a hundred and 20-odd years ago chemists had to learn Latin, so they called the one with five carbons
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pentane, the 6-carbon one
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hexane, then
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heptane then
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.wait for it
.
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the 8-carbon one
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octane and so on.
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(If we were naming them now the last one would be called
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eightane so you would need 95 minimum REN for your engine.
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)
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All these things were liquids, very thin and volatile, and pure concentrated energy.
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The Hildebrand and Wolfmuller
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(rough 1894 equivalent of the Honda 50) now did 100 miles to the tank full.
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Unlike water, these liquids dont stand around in lakes.
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They are hidden underground in porous rock so you have to drill for them.
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The old name was
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petroleum meaning
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rock oil but this was soon shortened to
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petrol.
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The petrol came out of the wells mixed with heavy oil, so it had to be distilled off in an oil refinery.
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Early on, the pale coloured stuff that evaporated easily and caught fire very easily was sold as internal combustion engine fuel.
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It was a simple as that.
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Octane Number hadnt been invented, but in modern terms this
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light petroleum fraction was about 50 Octane.
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Now we all know that in the GCSE Science engine The Piston squeezes the air/fuel mixture, then The Spark Plug ignites it to produce The Power Stroke.
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The trouble is, with 50 octane fuel if The Piston squeezes too much the heat generated by compression makes the stuff Go Bang prematurely before The Spark Plug gets a look in, giving a Power Stroke with as much push as a fairys fart.
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This is why early engines couldnt use compression ratios above 4
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: 1, and 10BHP per litre was seen as hot stuff.
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Engines improved but petrol didnt and even some time after WW 1 a touring 1000cc engine only turned out about 25BHP, and a hot-shot Sport version with the latest overhead valves would need a good tuner to get 50BHP.
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So finally some effort was made to stop primitive petrol going bang too soon, and a variable compression engine was invented for research.
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(The
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CFR engine, as used for finding Research and Motor Octane Numbers, RON and MON, to this very day.
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) Early on researchers found that the bung in the CFR head could be really screwed down if a heavy liquid called
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TEL
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(tetra ethyl lead) was added.
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This was really effective and cheap, and allowed the
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straight petrol to be upped to 90 or even 100 octane, and a whole load of exciting high-power engines were designed around these fuels.
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This leaded fuel survived into the late 1990s, but much earlier an amazing discovery had been made.
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The shape of the petrol molecules was very important.
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Octane if the
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straight eight version with 8 carbons in a row had an
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octane number of 25.
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It was only the mutant octane with 5 carbons down the middle and the others sticking out from the sides that gave the best results at high compression.
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(This special octane is still used as a standard for 100 octane.
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Proper name is 2,2,4-trimethyl pentane.
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)
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Today,
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petrol is really a synthetic fluid built up from oil industry feedstocks.
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Very little of it is unmodified distillate from crude oil.
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It is tailor made to include the best compression-resisting molecules so that no poisonous and polluting lead compounds are needed to reach 95 or even 98 octane.
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Nothing much is added, apart from a touch of detergent to keep the engine top end clean.
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Quite a lot of petrol now has 5%
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renewable alcohol as a planet-saving gesture, but this also improves the octane number
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(by about 1
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) so theres nothing wrong with that.
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Anyway, if you have a motoring holiday instead of flying ComaJet, you are keeping that carbon footprint down
.and paying too much tax as well
.
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.but thats another story.
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Fascinating stuff.
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Cheers
Guy