A portable, on-demand hydrogen generation system producing hydrogen and injecting the hydrogen into the air intake of internal combustion engines. Hydrogen and oxygen is produced with an electrolyzer from nonelectrolyte water in a supply tank. The hydrogen and oxygen is passed back thru the supply tank for distribution and water preservation. The gases are kept separate by a divider in the tank. The device is optionally powered by the vehicle battery, a stand alone battery, waste heat of the internal combustion engine or solar energy. The system utilizes a vacuum switch or other engine sensor that permits power to the device and therefore hydrogen production only when the engine is in operation.