The MIT researchers focused on a key property of ethanol: when it vaporizes, it has a pronounced cooling effect, much like rubbing alcohol evaporating from skin. Increased turbo�charging and cylinder compression raise the temperature in the cylinder, which is why they lead to knock. But Cohn and his colleagues found that if ethanol is introduced into the combustion chamber at just the right moment through the relatively new technology of direct injection, it keeps the temperature down, preventing spontaneous combustion. Similar approaches, some of which used water to cool the cylinder, had been tried before. But the combination of direct injection and ethanol, Cohn says, had much more dramatic results.

Neat.