NOVELTY - Start-up of a thermally self-sustaining reaction comprises introducing a reactant stream to a reactor comprising a reaction zone for conducting the thermally self-sustaining reaction, and an ignition zone in thermal contact with the reaction zone. At least a portion of the ignition zone is downstream of at least a portion of the reaction zone. The ignition zone comprises an igniter that ignites the reactant stream.    USE - For start-up of a thermally self-sustaining reaction, e.g. partial oxidation reaction, oxidative dehydrogenation reaction, or sulfur partial oxidation reaction (claimed).    ADVANTAGE - The ignition system minimizes the loss of selectivity, loss of production of carbon monoxide and hydrogen, and premature deactivation of the catalyst and requires minimal (if any) additional handling equipment or cost.    DETAILED DESCRIPTION - Start-up of a thermally self-sustaining reaction comprises introducing a reactant stream to a reactor comprising a reaction zone for conducting the thermally self-sustaining reaction, and an ignition zone in thermal contact with the reaction zone. At least a portion of the ignition zone is downstream of at least a portion of the reaction zone. The ignition zone comprises an igniter that ignites the reactant stream and starts-up the thermally self-sustaining reaction in the reaction zone.    INDEPENDENT CLAIMS are also included for:    (1) a process for the production of liquid hydrocarbons, comprising introducing a stream comprising a hydrocarbon-containing gas and an oxygen-containing gas to a reactor comprising a reaction zone and an ignition zone; igniting the stream to initiate the partial oxidation reaction on the reaction zone to produce a product stream comprising synthesis gas; and contacting at least a portion of the product stream with a catalyst in a hydrocarbon synthesis reactor to convert at least a portion of the synthesis gas to liquid hydrocarbons; and    (2) a reactor for producing synthesis gas, comprising reaction zone for partially oxidizing the hydrocarbon gas to a product stream comprising synthesis gas; and igniter in thermal contact with the reaction zone and igniting the hydrocarbon in the reaction zone to start-up the partial oxidation reaction in the reaction zone.    DESCRIPTION OF DRAWING(S) - The figure is a schematic drawing of a laboratory scale reactor.