NOVELTY - The gas generator (1) is operated using a fuel, which may be mixed. In a first mode it is operated with a fuel selected from a first group, in a second it is operated with a fuel selected from another group. The first gas purification unit (4) is a CO shift reactor, which is operated as such, in the first mode. In the second mode, fuel is introduced (16) from the second group, operating it as a reforming unit.    USE - To generate a hydrogen-rich gas for use in a fuel cell for e.g. vehicular applications.    ADVANTAGE - The method and the fuel cell system offered, allow methanol/dimethyl ether, and also other hydrocarbons, to be converted into a hydrogen-rich gas with acceptable efficiency.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for the corresponding gas generator, operating as described. Preferred features: In the second mode the reformer is operated as a POX (partial oxidation of hydrocarbons) reformer. A limited quantity of fuel is converted, such that the waste heat liberated, is sufficient to convert much of the fuel supplied to the CO shift reactor into hydrogen-rich gas by steam reforming. In both modes, during a cold start, the reformer is operated with liquid fuel and air as POX reformer. The gas generator includes an evaporator (8). Following a cold start, in hot running, the reformer is operated with gaseous fuel and steam. Fuel and water are vaporized in the evaporator, heated by the burner (6). They are then supplied in gaseous form to the reformer. Air supplied to the reformer (2) is heated by means of a heat exchanger (7) at the burner and/or evaporator. A heat exchanger (3) is provided between reformer and CO shift reactor (4). This cools reformer product gases and heats fuel and water from the evaporator, before supply to the reformer. The gas generator includes a water tank, into which methanol has been mixed, in a quantity suitable to confer frost protection. The second gas purification unit (5) is a CO shift reactor, a selective CO oxidation reactor, a CO methanization reactor or a membrane unit for hydrogen separation. The burner is catalytic. A variant procedure based on the foregoing principles is also described. In the preferred equipment, effluent air from the fuel cell is put to use for cooling and combustion duties.    DESCRIPTION OF DRAWING(S) - A block diagram of the equipment is presented.    Gas generator (1)    Reformer (2)    Heat exchanger (3)    Gas purification unit (4)    Second gas purification unit (5)    Burner (6)    Heat exchanger (7)    Evaporator (8)    Fuel introduction (16)