Modeling of nitric oxide formation in high-pressure premixed laminar ethane flames

Abstract

The GRIMECH version 2.11 chemical kinetics mechanism is modified to provide improved predictions of NO concentrations in high-pressure (1 < P < 15), low-temperature (1600 K–1850 K), premixed, flat, laminar, C 2H 6/O 2/N 2 flames. The modifications include adding 38 reactions to expand the C 2 submechanism and using different reaction rate coefficients for the CH + N 2 ↔ HCN + N reaction. The unmodified GRIMECH mechanism significantly underpredicts the NO concentrations in rich flames. In addition, the predictions from the original mechanism are poor qualitatively, particularly at the lower pressures studied. As the prompt-NO mechanism has been shown to be significant in the rich flames in this study, it is expected that the predictive errors of the unmodified mechanism are a result of deficiencies in the modeling surrounding the prompt-NO formation pathway. To account for the underprediction of prompt-NO, a different set of proposed reaction rate coefficients for the CH + N 2 ↔ HCN + N are used in the revised model. The expansion of the C 2 submechanism reactions enhances the existing C 2 chemistry in the original mechanism, which was designed primarily for methane combustion. The modified mechanism provides good agreement with published NO concentration data from the postflame regions of flames from 1 to 9.16 atm. The revised mechanism does continue to underpredict the NO concentrations in 14.6-atm flames, although the predictions are improved qualitatively from the original mechanism at that pressure.