Octane and burn rate

["Storhok, Eric (E.M.)" <estorhok@domain.elided>]

I'm not sure where Fred is going with the Octane requirement for the 164, but I'll guess that it has something to do with the RON rating used in Europe vs the pump octane used here- Scott's been over this already.

But, I would like to address the whole myth that high octane fuel burns slower than low octane fuel.  If the 2 blends of fuel have the same amount of non gasoline additives (MTBE, Alcohol, etc), then they will burn at exactly the same rate.

For "pure" gasoline, the difference between high and low octane fuel is that the higher octane has fewer long-single chain HC's in it.  These long chain HC's are less stable than double chain or "round" chain HC's, and will spontaneously react at a lower temperature and pressure.  So the higher octane fuel should be more refined than the lower octane fuel.

I say should because its quite common to use various versions of alcohol's to raise the octane.  Alcohol fuel does burn slower AND has lower specific energy, which means that you will lose both fuel economy and power under EQUAL running conditions (air, spark, and fuel).

So, if you lose power or fuel economy running high octane fuel, find a new source.  If your car does not knock with low octane fuel, stick with it.  If you have a modern car that has a knock sensor AND a cool control strategy that takes advantage of it, PLUS it tells you that you require 98 RON or 93 Pump octane, then use high octane and have fun.

Eric Storhok
Core Emissions and Fuel Economy Team
Advanced Powertrain Engineering
(313)33x75011
MD 35, FPC-B
Ford Motor Company
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