Numerical study of the effect of carbon dioxide injection on flame structure in flameless combustion regime

The aim of the present study is to investigate the effect of carbon dioxide injection on the flame structure using numerical simulation of flameless furnace. Using different amounts of carbon dioxide injection leads to the formation of three air-fuel, oxygen enrich and oxy-fuel combustion modes. Numerical simulations are performed using OpenFoam software. The standard k-εmodel for turbulence modeling and the discrete ordinate model for radiation modeling are used, respectively. Four combustion models based on the eddy dissipation concept model have also been used to validation of combustion model. Studies are performed on temperature distribution, ignition delay, flame color, and hydroxyl radical in order to the investigation of flame structure. The results show that by switching from air-fuel flameless combustion to oxygen enrich and oxy-fuel flameless combustions coupled with the replacement of part or all of the mass fraction of nitrogen with carbon dioxide, the maximum flame temperature is reduced due to higher carbon dioxide heat capacity and active presence in the chemical reactions. Moreover, the presence of carbon dioxide in oxygen enrich and oxy-fuel combustion conditions results in a delayed in ignition process and significantly reduces the concentration of methylene radical, which is the driving factor of visible light.