NOVELTY - The generator (110) has cylindrical enclosure made of metal that operates as a cathode when coupled to first terminal of a power source. A fuel cell unit is located within the cylindrical enclosure. An anode provided in fuel cell unit is coupled to a positive terminal of the power source. Several passive conductive tubular cells are provided along the longitudinal direction of the cylindrical enclosure and are not coupled to the negative and positive terminals. A metal rod made of stainless steel is located within the innermost tubular cell.    USE - Hydrogen fuel generator used in supplementary fuel system (claimed) for delivering hydrogen to motor vehicle engine.    ADVANTAGE - The compact fuel generator is simple in structure and produce oxyhydrogen (HHO) gas easily. The miles per gallon (MPG) performance and the burn quality of the fuel can be improved so that unwanted emissions can be reduced and more power can be produced to clean out old carbon deposits inside the engine. The generator can be operated along with an existing fuel source to compliment the efficiency of fuel burn within the combustion chamber, so that emission and fuel economy can be reduced. The viscosity of the engine's oil cannot break down quickly, longer periods are taken between oil changes and less wear to the cylinders so that overall maintenance costs of the engine can be reduced. The toxic or non-toxic engine emissions can be reduced so that greenhouse gas emission can be reduced. The injection control system is programmed for each specific engine to optimize the amount of hydrogen gas injected into the engine so that emission and fuel economy can be reduced. The amount of reactive surface exposed to the aqueous solution can be increased by microscopic indentations so that the excitation of hydrogen molecules and efficiency of the electrolysis towards optimal hydrogen gas production can be improved. The arcing due to the melted or changed shape of the rubber insulator can be avoided by the anode located in the innermost tube cell.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for supplementary fuel system.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of the supplementary fuel system having hydrogen fuel generator.    Hydrogen fuel generator (110)    Safety valve (111)    Injection controller (122)    Breaker (161)    Relay (162)