Skeletal Reaction Models for Atmospheric and High Pressure Combustion of Methane*

Skeletal reaction mechanisms for atmospheric and high pressure combustion of methane are generated from the foundational fuel chemistry model (FFCM-1) via the forced-optimally time dependent (f-OTD) methodology. In the f-OTD methodology, the sensitivity matrix, i.e., a large matrix containing all local sensitivities of a system, is modeled as the multiplication of two low-rank time-dependent matrices. The evolution equations of these matrices are derived from the governing equations of the system. For skeletal mechanism reduction, the sensitivity of mass fractions and temperature with respect to the reaction rates are considered. These modeled sensitivities are computed for the auto-ignition problem with different sets of initial temperatures, pressures, and equivalence ratios. The calculated sensitivities are then analyzed to rank the most sensitive species. A series of skeletal mechanisms with different levels of accuracy in reproducing the results of the detailed kinetics model, i.e. FFCM-1 are then produced. This skeletal reduction technique is conducted both for atmospheric and high pressure combustion of methane. The performances of the generated models are compared against FFCM-1 based on their abilities in predicting ignition delays, laminar flame speeds, and diffusion flame extinctions. Results suggest a skeletal model with 27 species can accurately reproduce the results of FFCM-1 for both atmospheric and high pressure test cases.