There are basically two ways to calculate octane ratings, both based on the arbitrary assignment of 100 to pure iso-octane. The European de facto standard is something called Research Octane Number, and it’s determined by comparing engine-knock resistance of a fuel to the known resistance of iso-octane. On the Continent generally, gasoline (diesel is different) is generally a minimum of 95 RON.
Just different enough is something called the Motor Octane Number, which uses a more complicated test regimen and produces numbers typically 9 to 12 less than the RON. Inexplicably, North America splits the difference and calls it the Anti-Knock Index; this is the number you see on US and Canadian pumps.
This matters because the auto industry wants to switch to a single fuel, rated at 95 RON:
On Friday, Dan Nicholson, General Motors’ vice president of global propulsion systems, told the House Energy and Commerce Committee’s environment subcommittee that switching to 95 octane would align the U.S. with Europe and is one of the most affordable ways to boost fuel economy and lower greenhouse emissions.
Well, they can afford it, anyway. Most of the stuff sold in Europe as RON 95 is 90 or 91 AKI, and Joe and Susan Sixpack will not be happy to hear that 87 AKI, which we laughingly call “regular,” might be replaced by something half a buck per gallon more expensive.
Which is not to say that Detroit is unaware of this situation:
David Filipe, vice president of Ford’s powertrain engineering, joined Nicholson to say 95 octane fuel must become more affordable for this strategy to work. “That’s been something that has been important to us. How do we do this without having a big impact on the customer?” he said. “We don’t want to put the burden onto the customer.” Filipe explained the cost must not add more than 5 cents per gallon.
Yeah, good luck with that. Selling only one grade doesn’t cut costs that much: as it stands, they sell only two grades, highest and lowest, and mix and match as needed to come up with intermediate grades.
Straight ethanol, incidentally, runs 99 RON. However, the loss in energy density offsets, and then some, the higher octane rating.