Study on the Combustion Characteristics of Carbon Monoxide-Hydrogen-Nitrogen Mixture

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In this study, the combustion characteristics and the NOx emission of the CO-H_2-N_2 mixture, which can be produced by the partial oxidation of methane with air, were investigated by a numerical calculation with detailed chemical kinetics. The results were compared with those of the CH_4-N_2 mixture and H_2-N_2 mixture. In each case air was used as the oxidizer. The compositions of the above three fuel mixtures were determined so that the adiabatic flame temperatures of the stoichiometric combustion should be identical with each other. The one-dimensional premixed flame and the coflow diffusion flame were adopted respectively as the representative premixed flame and the representative diffusion flame. Experiments were also conducted for the coflow diffusion flame, and the flame structure and the NOx concentration distribution were measured and compared in detail with the numerical results. For the one-dimensional premixed flame, it was found that the burning velocity, the flammability limits and the emission index of NOx of the CO-H_2-N_2 flame are much different from those of the CH_4-N_2 flame, and similar to those of the H_2-N_2 flame. For the coflow diffusion flame, on the other hand, it was found that the temperature distribution, the flame length and the NOx emission are much different from those of the CH_4-N_2 flame, and similar to those of the H_2-N_2 flame. That is, as compared to the CH_4-N_2 flame the CO-H_2-N_2 flame has much shorter flame length and lower NOx emission. In addition, QRPD (Quantitative Reaction Path Diagram) for NO formation was drawn based on the numerical results, in order to investigate the cause of the low NOx emission of the CO-H_2-N_2 flame. As a result, it was found that NO is formed mainly via NNH and any large reaction pathway related with C such as prompt NO does not exist in the CO-H_2-N_2 flame.