Methane Oxy-Combustion for Low CO₂ Cycles: Blowoff Measurements and Modeling

Increasing concerns about climate change have encouraged interest in zero-CO₂ emission hydrocarbon combustion techniques. In one approach, nitrogen is removed from the combustion air and replaced with another diluent such as carbon dioxide or steam. In this way, formation of nitrogen oxides is prevented and the exhaust stream can be separated into concentrated CO₂ and water by a simple condensation process. The concentrated CO₂ stream can then be sequestered or used for enhanced oil recovery. Burning fuels in an O₂/CO₂ diluent raises new combustion opportunities and challenges for both emissions and operability: this study focuses on the latter aspect. CH₄/O₂/CO₂ flames are known to be characterized by slower chemical kinetics than methane-air flames and as such, flame stability is more problematic as they are easier to blow off. This issue was investigated experimentally by characterizing the stability boundaries of a swirl stabilized combustor. Near stoichiometric CO₂ and N₂ diluted methane/oxygen flames were considered and compared with baseline methane/air flames. Numerical modeling of chemical kinetics was also performed to analyze the dependence of laminar flame speeds and extinction strain rates upon dilution by different species and to develop correlations for blowoff boundaries. Finally, blowoff trends at high pressure were extrapolated from atmospheric pressure data to simulate conditions closer to those of gas turbines.