NOVELTY - A reformer arrangement comprises a mixture preparation portion and a reaction portion. The reaction portion includes processing stage(s), and heat exchanger(s) arranged with respect to the processing stages so that heat may be extracted from a fluid mixture emanating from a corresponding processing stage and used according to a particular distribution strategy to enable certain level of preheating of fluid input(s) required by reforming process.    USE - The reformer arrangement is used for processing fluid mixture. It may be a fuel reformer for use with a fuel cell.    ADVANTAGE - The reformer arrangement incorporates a dynamically responsive, compact, and effective mixing chamber that provides uniform mixing of main fluid flow with second fluid flow. It has the capability of operating more effectively immediately following start-up. Excess heat from the reaction stages is used to improve the overall thermal efficiency of the reforming process.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (a) a mixing chamber arrangement comprising a mixture preparation section, a mixture diffusing section downstream of the preparation section, a first inlet for directing flow of first fluid into the mixture preparation section, fluid delivery mechanism(s) for directing flow of second fluid(s) into the mixture preparation section, and a second inlet for directing flow of fluid into the mixture diffusing section, where initial mixing is effected in the mixture preparation section and subsequent mixing and diffusion of fluids are effected by the mixture diffusing section; and    (b) a method of controlling a dual fluid injection system for use with a reformer arrangement, by delivering high-frequency delivery injection events, including metering (in a single event) a volume of fluid sufficient to satisfy the requirements of at least two delivery injection events, and delivering the volume of fluid by using the two delivery injection events.    DESCRIPTION OF DRAWING(S) - The figure is a schematic representation of different processing stages in a fuel reformer.    Autothermal reactor (16)    Heat exchangers (30-34)