In this study, numerical simulation of high temperature combustion in CO–H
2 mixture with oxygen jet has been conducted to consider post combustion in a converter for steel making process. In the numerical model, a detailed reaction model and mixture fraction model were used. The flammability characteristics and flame structure were compared between both calculation results. The influence of H
2 content in the mixture and the reaction mechanism of the combustion were discussed. In mixture fraction model, the post combustion ratio decrease with an increase of H
2 content, but the influence of H
2 content on post combustion ratio is small. On the other hand, in the detailed reaction model, the influence H
2 content on post combustion ratio is bigger, and the post combustion ratio takes its maximum when the molar hydrogen concentration is 2%. When the molar hydrogen concentration is 20% in CO–H
2 mixture, CO
2 is decomposed around the edge of combustion zone, where the endothermic reaction occurs. Resultantly, the temperature in the downstream region is reduced. In the CO–H
2 combustion, water vapor is also decomposed by the shift reaction through CO+H
2O→CO
2+H
2.
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