You should look into oxygenated fuels before you look at direct injecting oxygen. Specifically, alcohols like Ethanol and Methanol. Not only are they cleaner and more efficient than Gasoline but they make more power. Their biggest disadvantages are less energy in a gallon and cold starting problems with early FFVs. Newer higher compression engines work even better and current FFVs have special startup routines in addition to more Gasoline content in the winter. The earliest FFVs were designed to run on Gasoline, E85, or even M85. Methanol has an octane value of 112 while Ethanol has an octane value of 110. But it drops to about 96 octane in E85, M85 is unknown.
Newer Direct injection engines are perfectly suited to alcohols, tuning has shown some promising results. But the market is limited and competes directly with Gasoline for market share. Plus there just isn't enough positive information about them.
