Abstract: The objective of this invention, on demand hydrogen enhancement system for internal and external combustion engine, is to develop a continuous non pressurized water electrolyzer from clean water (not pure water or distil water) generator system. The mixed hydrogen gas and oxygen gas called “Oxyhydrogen”. Oxyhydrogen use as catalyse for internal and external combustion engine to increase fuel flame speed. It can use with variety fuels such as Ethanol, Methanol, Gasohol, Gasoline, Diesel, Bio Diesel, LPG, CNG, and LNG. This system can reduce fuel consumption, increase fuel efficiency, increase torque, reduce emissions, and reduce engine temperatures. The system required no cooling fan and electrolytic solution circulating pump. The system has less heat loss and very low electrical consumption. Oxyhydrogen will produce on demand as the engine RPM and load of generator. The control unit detects signal frequency from the alternator.