NOVELTY - Multi-tubular chemical reactor comprises: many spaced-apart reactor units (109), each comprising an elongate tube having a wall with internal and external surfaces, an inlet at one end and an outlet at the opposing end, where the wall encloses a gaseous flow passageway at least a portion of which defines a gas phase reaction zone (110); and at least one igniter (123) for initiation of gas phase exothermic reaction, where the igniter comprises a radiant heat-producing element positioned in thermal communication with and proximity to, but in physical isolation from, the gas phase reaction zone.    USE - The multi-tubular chemical reactor is useful: as partial oxidation reformer or autothermal reformer for carrying out gas phase exothermic reaction (all claimed) for reforming liquid reformable fuels including methanol, ethanol, naphtha, distillate, gasoline, kerosene, jet fuel, diesel or biodiesel, and gaseous reformable fuels including methane, ethane, propane, butane, isobutane, ethylene, propylene, butylene, isobutylene or dimethyl ether to produce hydrogen-rich reformates.    ADVANTAGE - The multi-tubular chemical reactor utilizes igniter, which easily deactivates and reactivates the exothermic gas phase reaction.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for carrying out a gas phase exothermic reaction within a multi-tubular chemical reactor to produce desired product, comprising introducing gaseous reactants into a reactor unit, initiating with radiant heat an exothermic reaction of the gaseous reactants within a gas phase reaction zone of the reactor unit, thus commencing the production of desired product, and transferring heat produced by the exothermic reaction occurring within the gas phase reaction zone of the reactor unit to the gas phase reaction zone or at least one adjacent reactor units, thus initiating an exothermic reaction within the adjacent reactor unit until in such manner an exothermic reaction has been initiated in the spaced-apart reactor units.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of gas phase exothermic chemical reactor.    Catalytic partial oxidation reformer (100)    Thermocouple (105)    Tubular Catalytic partial oxidation reactor units (109)    Catalytic partial oxidation reaction zones (110)    Igniter (123)