NOVELTY - The fuel processor comprises a fuel inlet port (103), an oxidant inlet port (101), a product outlet port, a shell (114) housing a reaction chamber (108), and an annular particulate filter assembly located upstream of the product outlet port. The particulate filter assembly (111) comprises two segments with an expansion joint between adjacent segments. The expansion joint is partially filled with a resilient material, which comprises a ceramic-containing material. The fuel processor further comprises a critical flow venturi (105), and a thermal insulating layer.    USE - The fuel processor such as non-catalytic syngas generator is useful for producing a hydrogen-containing product stream such as syngas stream from a fuel stream and an oxidant stream, and in engine system for vehicular or other mobile applications, where the hydrogen is useful to regenerate, desulfate and/or heat engine exhaust after-treatment devices, and as a supplemental fuel for the engine and a secondary power source such as fuel cell.    ADVANTAGE - The fuel processor is compact and lightweight, has high reliability and durability and improved fuel conversion efficiency, and can be economically manufactured with reduced thermal stress and without any fatigue and premature failure of materials, components and assemblies.    DETAILED DESCRIPTION - The fuel processor comprises a fuel inlet port (103), an oxidant inlet port (101), a product outlet port, a shell (114) housing a reaction chamber (108), and an annular particulate filter assembly located upstream of the product outlet port. The particulate filter assembly (111) comprises two segments with an expansion joint between adjacent segments. The expansion joint is partially filled with a resilient material, which comprises a ceramic-containing material. The fuel processor further comprises a critical flow venturi (105), a thermal insulating layer disposed between the critical flow venturi and the annular particulate filter, a two-sleeve concentric type heat exchanger (102) connected to the reaction chamber to transfer heat a portion of time from the product stream to the oxidant stream during operation of the fuel processor, a mixing tube (107) fluidly connected to receive the oxidant stream from the oxidant inlet port and the fuel stream from the fuel inlet port, for forming a combined reactant stream and directing the combined reactant stream axially into the reaction chamber, a wet blanket type insulation defining a portion of the reaction chamber, a flame rod connected to sense a temperature of the reaction chamber periodically during operation of the fuel processor, a controller with an analog-to-digital converter with digital filtering capabilities. The particulate filter assembly is positioned to trap particulates from a gas stream flowing through it in a flow direction between the reaction chamber and the product outlet port, is located partially within the reaction chamber, downstream of the reaction chamber and within the shell of the fuel processor, and is disposed partially around the critical flow venturi. The expansion joints are oriented parallel to the flow direction through the particulate filter assembly. A radiative heat transfer mechanism from the product stream to the hot side of the heat exchanger is 60-99%. The mixing tube is manufactured from a soft ceramic material, which has a porosity of 60-86%, and comprises an alumina-silica based material. The temperature of the reaction chamber is a measurement of a primary reaction process in the reaction chamber. The analog-to-digital converter is 24 bit, and is two differential inputs. INDEPENDENT CLAIMS are included for:    (1) a method of operating a fuel processor; and    (2) a method of assembling a fuel processor.    DESCRIPTION OF DRAWING(S) - The diagrams show top cross-sectional views of a syngas generator.    Oxidant inlet port (101)    Heat exchanger (102)    Fuel inlet port (103)    Critical flow venturi (105)    Mixing tube (107)    Reaction chamber (108)    Particulate filter assembly (111)    Shell. (114)