Results of NASA’ s experiments with hydrogen in internal combustion engines
Direct from 1977 article by *NASA: "Lean-mixture-ratio combustion in internal-combustion engines has the potential of producing low emissions and higher thermal efficiency for several reasons. First, excess oxygen in the charge further oxidizes unburned hydrocarbons and carbon monoxide.
Second, excess oxygen lowers the peak combustion temperatures, which inhibits the formation of oxides of...