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Abstract
Modern gas turbines use combustion chemistry during the design phase to optimize their efficiency and reduce emissions of regulated pollutants such as NOx. The detailed understanding of the interactions during NOx and natural gas during combustion is therefore necessary for this optimization step. To better assess such interactions, NO2 was used as a sole oxidant during the oxidation of CH4 and C2H6 (the main components of natural gas) in a shock tube. The evolution of the CO mole fraction was followed by laser-absorption spectroscopy from dilute mixtures at around 1.2 atm. The experimental CO profiles were compared to several modern detailed kinetics mechanisms from the literature: models tuned to characterize NOx-hydrocarbons interactions, base-chemistry models (C0–C4) that contain a NOx sub-mechanism, and a nitromethane model. The comparison between the models and the experimental profiles showed that most modern NOx-hydrocarbon detailed kinetics mechanisms are not very accurate, while the base chemistry models were lacking accuracy overall as well. The nitromethane model and one hydrocarbon/NOx model were in relatively good agreement with the data over the entire range of conditions investigated, although there is still room for improvement. The numerical analysis of the results showed that while the models considered predict the same reaction pathways from the fuels to CO, they can be very inconsistent in the selection of the reaction rate coefficients. This variation is especially true for ethane, for which a larger disagreement with the data was generally observed.
Highlights
The combustion of hydrocarbons in air in internal combustion engines and gas turbines can lead to the formation of NOx (NO, NO2, N2 O), which are regulated pollutants.Thanks to a large number of fundamental studies conducted over the past few decades, the chemistry of several NOx formation mechanisms was identified (Zeldovich, Fenimore, N2 O, etc.) [1,2], which allowed for the implementation of strategies to limit NOx emissions during combustion
One common method used in gas turbines and internal combustion engines consists of re-circulating the exhaust gases in the combustion chamber, to limit the combustion temperature and minimize NOx formation via the Zeldovich mechanism (so-called exhaust gas recirculation method)
Within the test time of the 4 forand (a) methane (b) ethane. Both fuels the show similar the increasing shock tube within theand conditions investigated, higher thebehavior: temperature, the higher slope corresponding to the formation of CO, which becomes steeper as the temperature the maximum CO mole fraction
Summary
Thanks to a large number of fundamental studies conducted over the past few decades, the chemistry of several NOx formation mechanisms was identified (Zeldovich, Fenimore, N2 O, etc.) [1,2], which allowed for the implementation of strategies to limit NOx emissions during combustion. To design better combustion devices and reduce NOx emissions, it is important to accurately know the chemistry for both NOx formation and NOx-fuel interaction mechanisms. This goal has been the purpose of the many detailed kinetics mechanisms that have been developed and refined continuously over the past 20+ years. To validate these detailed kinetics mechanisms, typically, a fuel/oxidizer (O2 and diluent or air) mixture is
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