TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Component: The coolant stream comprises a mixture of air and water to be fed to the autothermal reformer.    TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Method: The temperature of the autothermal reformer is maintained by adjusting the oxygen to carbon ratio, the steam to carbon ratio, and the temperatures of the fuel, air and water feeds entering the autothermal reformer. A flow path of the coolant streams that is continuously adjusted to maintain a desirable temperature at each critical zone in the fuel processing train. The flow rates of the coolant streams flowing through or bypassing the heat exchangers in the fuel processing train are continuously adjusted to maintain a desirable temperature of the reformate at the critical zone in the fuel processing train. The reformate temperature is lowered to the desired value by injecting liquid water through a sparger, such that the endothermic phase change of the injected water leads to cooling of the gas stream. The reformate temperature is raised to the desired value by injecting oxygen-containing gas through the sparger, such that the oxygen reacts with the combustible gases to generate heat. Autothermal reformer temperature is maintained by adjusting the temperatures of the fuel, air, and steam feeds entering the autothermal reformer. The average temperature in the autothermal reformer is maintained by adjusting the steam to carbon ratio and oxygen to carbon ratio of the fuel, air, and steam feeds entering the autothermal reformer. The water gas shift reactor and the preferential oxidation reactor are heated in parallel by distributed combustion of hydrogen gas and carbon monoxide. The heat exchanger is water bypassed unless a gas temperature at a stage following it exceeds its design value. Air supply is cut off for a stage when the temperature for the stage exceeds a predetermined maximum.    TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Component: The control(s) comprises heat exchangers, liquid injection ports, liquid injection spargers, air injection ports, or air injection spargers. The critical zone is located downstream of the reformer in the fuel processing train. An anode gas burner is provided where a combustible gas present in a fuel cell anode effluent is oxidized to generate heat, which energy is then transferred to the autothermal reformer, such that the fuel processor can be operated at a higher thermal efficiency. An electronic chip determines an optimal temperature profile.