Ethanol boosts the octane number of fuel, which helps prevent pre-ignition knock. Incidentally, the octane rating system for fuels was originally developed by Penn State chemist Russell Marker in the 1920s. The octane rating (Anti-Knock Index, AKI) of normal unleaded gasoline in the United States is 87. The octane rating of pure ethanol is 100. What's interesting is that when ethanol is blended with gasoline, it performs as if its octane rating is 112, making ethanol a very effective octane booster when used in gasoline. High octane is one reason why NASCAR uses ethanol for their high-compression racing engines. Engines that are designed and optimized for ethanol fuel have the potential to run at higher efficiencies than engines designed for and using gasoline.
