EVALUATION OF KINETIC MECHANISMS FOR DIRECT FIRED SUPERCRITICAL OXY- COMBUSTION OF NATURAL GAS

摘要

Existing kinetic mechanisms for natural gas combustion are not validated under supercritical oxy-fuel conditions because of the lack of experimental validation data. Our studies show that different mechanisms have different predictions under supercritical oxy-fuel conditions. Therefore, preliminary designers may experience difficulties when selecting a mechanism for a numerical model. This paper evaluates the performance of existing chemical kinetic mechanisms and produces a reduced mechanism for preliminary designers based on the results of the evaluation. Specifically, the mechanisms considered were GRI-Mech 3.0, USC-Ⅱ, San Diego 204-10-04, NUIG-Ⅰ, and NUIG-Ⅲ. The set of mechanisms was modeled in Cantera and compared against the literature data closest to the application range. The high pressure data set included autoignition delay time in nitrogen and argon diluents up to 85 atm and laminar flame speed in helium diluent up to 60 atm. The high carbon dioxide data set included laminar flame speed with 70% carbon dioxide diluent and the carbon monoxide species profile in an isothermal reactor with up to 95% carbon dioxide diluent. All mechanisms performed adequately against at least one dataset. Among the evaluated mechanisms, USC-Ⅱ has the best overall performance and is preferred over the other mechanisms for use in the preliminary design of supercritical oxy-combustors. This is a significant distinction; USC-Ⅱ predicts slower kinetics than GRI-Mech 3.0 and San Diego 2014 at the combustor conditions expected in a recompression cycle. Finally, the global pathway selection method was used to reduce the USC-Ⅱ model from 111 species, 784 reactions to a 27 species, 150 reactions mechanism. Performance of the reduced mechanism was verified against USC-Ⅱ over the range relevant for high inlet temperature supercritical oxy-combustion.