Posted by R.Davis on March 10, 1999 at 19:43:41:
In Reply to: Re: More avgas lead questions... posted by Bob Fetters on March 10, 1999 at 14:11:50:
As referring to gasoline,octane is a rating,not an additive or compound.The octane rating of a particular batch of fuel is determined by testing that fuel in a test engine.After the point at which the tested fuel knocks is determined,it is compared with that of a known mixture of isooctane plus heptane.Isooctane is a hydrocarbon that has extremely high resistance to knocking.Heptane is a hydrocarbon that knocks even at very low compression pressures.These check fuels are mixed and burned in the same test engine.The percentage of isooctane to heptane is adjusted until the engine runs with the same knock characteristic as the tested fuel.The final percentage becomes the rating of the fuel.For example,80 octane means it took 80%isooctane and 20%heptane to produce the results obtained w/the tested fuel.The octane rating of a fuel depends on its blend and method of refining.The addition of ethyl lead or other anti-knock compounds increases the octane rating of any gasoline.If an engine knocks at a lower octane rated gasoline,it is advisable to use a higher test or octane rated fuel.Lead was and is simply something that was found that would raise the octane rating (or the anti-knock characteristic)of gasoline fuel w/out speeding up or slowing down the burning of the fuel.