Combustion and Flame, Vol.224, 54-65, 2021
Competitive oxidation of methane and C-2 hydrocarbons discerned by isotopic labeling and laser absorption spectroscopy of CO isotopologues in shock-heated mixtures
The competitive oxidation of methane with C-2 hydrocarbons of differing functional groups (alkane, alkene, and alkyne) was examined experimentally via combustion of isotopically-labeled fuel mixtures and laser absorption spectroscopy of carbon monoxide isotopologues. Quantitative species time-histories of the (CO)-C-12 and (CO)-C-13 isotopologues were measured simultaneously and in situ using laser absorption spectroscopy behind reflected shock waves, used for near-instantaneous heating and auto-ignition of binary mixtures containing equal carbon fractions of the different fuels. A driver extension and gas tailoring were employed on the shock tube facility to extend test times up to 30 milliseconds, enabling dilute ignition of the fuel blends over a range of temperatures from 1100-1800 K. Tested fuel mixtures were primarily fuel-rich to force the competition of carbon oxidation between the fuel components. The novel dataset of multi-isotopologue species time-histories were compared to available chemical mechanisms, revealing insights on the influence of each C-2 fuel on methane ignition. The GRI-MECH 3.0 and Foundational Fuel Chemistry Model (FFCM-1) reaction models were modified to incorporate C-13 reactions and species. Detailed comparison of the measurement data with FFCM-1 simulations revealed generally good agreement at elevated temperatures (>1500 K), with increasing divergence at lower temperatures, particularly for mixtures involving ethane and acetylene. Reaction pathway and sensitivity analysis of the variance between data and the modified mechanisms reveal key reactions likely responsible for the disagreements. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.