Effect of CO_2 diluent on the formation of pollutant NOx in the laminar non-premixed methane-air flame

摘要

In this paper, the effects of changes in the concentration of diluent CO_2 in methane and air fuels are investigated. A finite volume method (FVM) with staggered grids is used for numerical solution. Equations of continuity, momentum, energy, ideal gas state and kinetic equations with thermodynamic and thermo-chemical information of chemical species are solved using the numerical method of SIMPLE. The convective terms are discretized using Power Law scheme (PLS). The under-relaxation factor dependent on temperature has been utilized to solve the chemical kinetic equations. In this research, by increasing the diluent mass fraction, the mass fraction of the fuel is diminished to the same extent. Therefore, the sum of the diluent and fuel mass fraction values remains constant. The results depicted that as the amount of CO_2 diluent in the fuel increases, the total lift-off height and flame length decreases linearly, and the maximum temperature in the combustion chamber becomes smaller than that at the inlet of the chamber. When the concentration of CO_2 increases in the fuel, the temperature changes become negligible at the inlet of the combustion chamber. By using the CO_2 diluent, shorter combustion chambers can be used. While the diluent is used, the increase in the length of the combustion chamber will not have any effect on the NOx emissions reduction. Therefore, the more concentration of the diluent is used, the smaller the combustion chamber can be selected. Moreover, by increasing the diluent, NOx pollutant decreases in the combustion chamber.