8.3 Ethanol and Gasoline
Early on in the development of the automobile, there was no standardized fuel. Early cars ran on gasoline, kerosene, ethanol, or even steam engines! Some cars, like Ford’s wildly popular Model T could run on different fuels as needed, whether it was kerosene, ethanol, gasoline, or some mixture of the three. 
Chemicals have always been added to gasoline to reduce what’s called “engine knocking,” which is a problem where the fuel doesn’t light correctly, potentially damaging the engine. Tetraethyllead (TEL) used to be one such chemical, but the lead in it acts as a neurotoxin, and all gasoline used today must be “unleaded.”
Ethanol has emerged as an alternative anti-knocking chemical, and is much less environmentally harmful than TEL. It can be mixed with gasoline in concentrations up to 20% without requiring any modifications to the gasoline engine. But ethanol can also be used as a fuel itself, both by burning it in an internal combustion engine and in a fuel cell.