NOVELTY - Fuel cell system comprises two direct water-vaporizing combustors for burning fuel to produce high-temperature fuel combustion by-product exhaust and to produce steam from water sprayed into the byproduct exhaust, fuel-reforming reactor, water-gas shift reactor, oxidation reactor and fuel cell stack.    USE - For use in e.g. automobiles and trucks.    ADVANTAGE - The system is capable of rapidly producing substantial amount of heat and hydrogen to quickly achieve high operating temperature necessary for start-up and to respond to dramatic increases in electrical load demand on the fuel cell during transient conditions.    DETAILED DESCRIPTION - Fuel cell system comprises:    (1) a fuel-reforming reactor (18) comprises a catalyst for producing reformate stream including hydrogen and carbon;    (2) a water-gas shift reactor (22) downstream of the fuel-reforming reactor, and comprising a catalyst for reducing the amount of carbon monoxide in the reformate stream;    (3) a preferential oxidation reactor (24) downstream of the water-gas shift reactor, and comprising a catalyst for oxidizing carbon monoxide into carbon dioxide and for producing hydrogen-rich stream;    (4) a fuel cell stack (32) downstream of the oxidation reactor for producing electricity from the hydrogen-rich stream;    (5) a first direct water-vaporizing combustor (36) for combusting fuel to produce high-temperature fuel combustion byproduct exhaust and to produce steam from water sprayed into the combustion byproduct exhaust; and    (6) a second direct water-vaporizing combustor (64) for combusting fuel to produce high-temperature fuel combustion byproduct exhaust and to produce steam from water sprayed into the fuel combustion byproduct exhaust.    The first combustor is plumbed to the fuel-reforming reactor for charging steam. The second combustor is plumbed to the water-gas shift reactor for charging steam.    An INDEPENDENT CLAIM is included for a method of direct water vaporization including instantaneously vaporizing sprayed water to produce first steam stream and charging the first stream into fuel-reforming reactor and water-gas shift reactor.    DESCRIPTION OF DRAWING(S) - The figure is a schematic view of the fuel cell system.    Fuel-reforming reactor (18)    Second heat exchanger (20)    Water-gas shift reactor (22)    Preferential oxidation reactor (24)    Fuel cell stack (32)    First direct water-vaporizing combustor (36)    Water tank (44)    Bypass valve (49)    First Heat exchanger (56)    Second direct water-vaporizing combustor (64)    Third heat exchanger (68)    Catalytic combustor (82)    Steam heat exchanger (206)