This guy makes HHO electrolyzer units in Paraguay, in this video he runs a small genset with the HHO produced with the electrolyzer powered by the output of the same Genset (closed loop). However he says if you keep doing this the genset eventually starts failing because the HHO explosion within the combustion chamber starts breaking up the cylinder and piston metals. This would require a turbine of special material to be used as an self sustaining energy source.