Methods and systems are provided for converting methane in a feed stream to acetylene. The method includes removing at least a portion of carbon dioxide from a hydrocarbon stream. The hydrocarbon stream is introduced into a supersonic reactor and pyrolyzed to convert at least a portion of the methane to acetylene. The reactor effluent stream may be treated to convert acetylene to another hydrocarbon process. The method according to the invention provides certain aspects includes controlling the level of carbon dioxide in the hydrocarbon stream and in a fuel stream that is first sent to a combustion zone and then to the supersonic reactor. The results of removal of carbon dioxide include maintaining the shock location in the supersonic reactor and maintaining the acetylene yield without the production of undesired products such as carbon monoxide.