I have been wondering about why oxyhydrogen (HHO) (a ~2:1 H2/O2 stoichiometric mixture) hasn't been used as a fuel? I know it has been used for bottle rockets and other types of small scale rockets, and I know hydrogen and oxygen have been used as fuel (like in the delta IV) but could it be used for a large scale rocket? Would there be any problems with just one fuel tank holding both the oxidizer and fuel (maybe it would be dangerous to keep them together?) Would there be any changes needed to engines to use HHO as a fuel?
Oxyhydrogen is an extremely bad idea for a fuel. It is highly explosive, and too dangerous to be used on rockets.
But rockets today do use liquid hydrogen as fuel which is oxidized by liquid oxygen(Lox/LH2) as it is cheap and provides extremely high thrust and can be controlled to burn steadily. It is one of the most powerful liquid propellants.It also yields the highest specific impulse of any currently used rocket propellant.