Thread: Octane and Oxygen

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There are at least two effects here. First, yes more oxygen helps combustion. The more complicated second part has to do with the rate/speed of the burning of the fuel; slower is better relative to the mechanical speed of the engine parts. The combustion reaction can be much faster than the mechanical motion of the engine parts so it is better to have a slow "wooomf" rather than a sudden "bang". I once saw a Mr. Wizard demonstration of a soft rubber hammer hitting a piston on a rod and crank mockup where a single hit with the soft rubber mallet would get the piston going up and down many times with the crank spinning many revolutions while with a hard metal/plastic mallet hitting the piston the crank would only revolve one time or less. The smooth combustion explosion is better when it is slow and matched to the engine speed. Basically chemical explosions can be much faster than the mechanical parts of an engine can respond, so a slow continuous burn lasting longer is more effective to push that piston down. Probably in your case the oxygen levels at various altitudes is more important but slow burning high octane fuel is better too. Low octane fuels use long straight chain hydrocarbons which burn fast linearly like a fuse. The high octane fuels are highy branched hydrocarbons which burn slower and are more nearly matched to the timing of the events in the mechanical parts of the engine. 6,000 rpm might seem like a fast situation but with only an explosion every two revolutions for an explosion every 1/3000 of a minute which is 60/3000=0.02 seconds, that is "forever" compared to chemical reactions which can occur in less than 0.000001 seconds so slowing the reaction is needed to match the chemistry to the mechanical parts of the engine.

Don Shillady
Retired Scientist/teen rodder