| Glide, you're getting yourself into an odd vortex.
Octane ratings, as posted on the pumps, is RON + MON / 2 . What that means is the Research Octane Number -the octane rating as determined by chemical evaluation, and the Motor Octane Number -the actual rating of the fuel's octane as determined by being run in a Research Engine (a variable-compression, single-cylinder engine outfitted with more gizmos and sensors than you can wag a tree at) and having its knock resistance determined. Since the numbers are almost never the same, but are the methods used which the industry members agree on, the two are added up and averaged. I believe the Research number is usually higher, but that may be information from the previous century.
However, mixing various octane gasolines isn't a matter of adding up and dividing. There are chemical events which occur both in the mixing of the fuels and during what goes on in the contained hell of a varying-displacement cylinder (which in itself is one of the internal combustion engine's Achille's heels as regards emissions: by the time the flame front gets to the bitter end of the available fuel, its composition has been so altered by the heat and pressures involved that it's no longer anything like gasoline) that simple math does nothing to determine what your fuel's octane rating actually is. Whether it winds up being higher than the lower, lower than the higher, or even higher than the higher will depend on the nuance of variation in the two mixes' composition. |