The article seems mistaken on a point. A "lean burn" lets in _more_ oxygen than is required, whereas a rich burn provides too much fuel (wasting it), usually to

The article seems mistaken on a point. A "lean burn" lets in _more_ oxygen than is required, whereas a rich burn provides too much fuel (wasting it), usually to help cool down the engine through evaporation. Adding water to the intake mix helps keeping the engine cool and increases the efficiency because of the expansion of droplets into water vapor before going through the turbo exit.