Effect of oxygen enrichment on methane ignition

Abstract

Oxygen-enriched combustion has attracted interest in the energy sector due to its increased thermal efficiency and low carbon capture cost compared to ‘air’ combustion. Experimental data on the ignition of oxygen-enriched mixtures are limited in literature. In this work, ignition delay times (IDTs) of various methane/oxygen mixtures diluted in argon/nitrogen were measured using a low- and a high-pressure shock tube over a temperature range of 1200 – 1700 K, three pressures of 1, 10, and 20 bar and an equivalence ratio range of 0.21 - 4. The oxygen mole fraction in the mixtures was varied from 19% (‘air’) to 90.5%, and dilution levels from 71% to zero. The reported IDTs were extracted from pressure and OH* emission profiles. To the best of our knowledge, this is the first comprehensive IDT study on the effect of oxygen enrichment on methane ignition. High-speed imaging experiments were performed to determine the possible presence of non-ideal ignition in these unconventional mixtures. The Bifurcation Damköhler number was found to be a good indicator of non-ideal ignition observed in some imaging experiments. Measured IDTs were compared with the predictions of AramcoMech 3.0 model as well as with GRIMech 3.0 and NUIGMech 1.1 for few cases. In general, AramcoMech 3.0 overestimated IDTs for the investigated methane mixtures. Brute force sensitivity analyses were conducted with AramcoMech 3.0 to identify reactions with a strong influence on IDT prediction for the investigated mixtures. Minor modifications were made to AramcoMech 3.0 resulting in improved predictions of ignition behavior in oxygen-enriched methane mixtures.