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Distillation of gasoline these days is quite a sophisticated procedure.
In the old days when petrol was required for the evolving motor car petrol was obtained by a fairly simple process of fractional distallation.
This basic petrol had elements of the fuel that ignited (flash point) over a range of temperatures. With the lower compression of the early cars the compressed gas to be ignited by a spark did not reach the flash temperature so combustion was quite smooth. However as the compression of engines was increased to improve efficiency a problem arose where elements of the fuel reached flash point before proper ignition. This caused pinking (a nasty knocking sound in the engine) as the uncontrolled ignition of the gas took over.
By further refining of the petrol these volatile elements were removed (improving the octane rating) particularly for aviation engines that needed the higher efficiency of higher compression ratios. This of course led to an increase in the cost of refining so many experiments were carried out to find a way of making a higher octane without the expense of re-refining. Quite by accident it was found that lead (in one of its forms) stopped the pinking so the tetra-ethyl-lead company came into production and made zillions regardless of the lead pollution it caused. Another way to improve octane was by water alcohol injectors that cooled the mixture so that combustion temperature was reached later in the stroke.
As development of the internal combustion engine continued there was also development in the refining industry and catalyctic cracking came into being where the lighter elements that caused the problem were made to combine into heavier elements by use of a catalyst so creating a higher octane. Improvements in the refining process produced more and more petrol of a higher octane rating to the point where the government was able to say "no more lead". Of course the manufacturer of lead for gasoline was not very happy because it cut out a "nice little earner" but that is progress.
Barry
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