Why is ethanol considered a high octane fuel ?
It’s not “considered” it’s scientifically proven. There are two ways to find the octane rating of a fuel. One is research octane, the other is motor octane. They both use an engine, Research Octane Number (RON) varies the compression and runs at 600rpm, until knock (pre-ignition or detonation) occurs, to determine the RON. The Motor Octane Number (MON) method works similar, but with a static compression, higher engine speed (900rpm), and varies the ignition timing instead of the compression, to simulate more real-world scenarios. Generally, MON is a bit lower than RON, but the US uses an average between the two numbers, called the anti-knock index (AKI). Ethanol has a RON of 129 and a MON of 116, giving an AKI rating of 122. As you can see, compared to regular pump gasoline, even our “high octane” pump gas, it’s very high (with the average high octane gasoline being 91-93 octane).
