Effects of CO2 dilution on the interactions of a CH4–air nonpremixed jet flame with a single vortex

We carried out numerical simulations to understand how CO2 dilution in either fuel or oxidizer stream changes the flame-vortex interactions in terms of hydrodynamic effects in CH4–air nonpremixed jet flames. The simulation used a time-dependent, axisymmetric computational model and a low Mach number approximation. Reaction rates were calculated from a two-step global reaction mechanism that considered six species. Studies were conducted with fixed initial velocities for three different cases of CO2 introduction: (1) without dilution, (2) dilution in a fuel stream, and (3) dilution in an oxidizer stream. A single vortex was generated by an axisymmetric jet driven of cold fuel, after a flame development was reached to quasi steady-state condition. The simulation shows that CO2 dilution in a fuel stream leads to a slightly increased vortex radius and more entrainment of surrounding fluids compared to the other dilution methods tested. Thus, dilution of CO2 in a fuel stream enhances the mixing inside a single vortex and increases the stretching of the flame surface. The vorticity transport equation budgets were examined to reveal the mechanisms of vortex formation in the presence of CO2. In the stage of vortex formation, vortex production due to baroclinic torque and vortex destruction due to volumetric expansion were found to be greater in the case of CO2 dilution in a fuel stream than in the other dilution cases. However, after vortex formation, there terms showed the opposite tendencies.