Quote:
Originally Posted by Old Tele man
...OCTANE rating is a "referenced" number that equates to the gasoline's ability to resist "pre-ignition" prior to the precise moment that ignition IS DESIRED to occur. NOTE that "pre-ignition" is any combustion that occurs before it was intended to occur, ie: pinging, detonation, etc.
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That's the misleading part... Based on what I read on the Gasoline FAQs, the 'ping' / 'knock' is not a result of pre-ignition of the fuel prior to the ignition point... from the link:
Quote:
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...the knock did not arise from preignition, as was commonly supposed, but arose from a violent pressure rise *after* ignition...
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The knock happens when the fuel is ignited by the spark, and then after that point the unburnt portion of the fuel (at the outside edges of the mixture) pre-ignites and produces a secondary wave front. The point at which the two (or potentially more) wave fronts meet create the 'knock', producing much higher pressures at the wrong time.
Indicating that the fuel pre-ignites *before* any ignition source is exactly what confused FourBinLabs ... quite understandable. But that is
not what the octane rating is measuring.
Read the FAQ... no, really, read it. It is quite good and very understandable. Link again:
Gasoline FAQ - Part 3 of 4