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The effect of the injection of externally sourced carbon dioxide (CO2) on the stability of the flameless combustion regime was evaluated numerically taking thermal uniformity and NO and CO emissions as criteria. Natural gas was used as fuel with normal air as the oxidizer. The CO2 was injected into the lower part of the furnace in order to directly affect the reaction zone. CFD simulations were performed using the ANSYS-Fluent software. The models used to estimate the turbulence, radiation, and chemical kinetic-turbulence interaction were the standard k-e model, Discrete Ordinate model, and Eddy Dissipation Concept (EDC) model, respectively. For modeling combustion, the EDC model was paired with a 7-step global reaction mechanism. A 20 kW output was simulated based on the LHV of the fuel. The excess air was set to 20%, 25%, or 30%, and combined with various CO2 flows. At 30% excess air, without the addition of CO2, the flame exhibited destabilization in the form of flashes. Adding CO2 was found to attenuate the destabilization due to the effect of dilution. Furthermore, increasing either the CO2 or excess airflow resulted in a considerable decrease in the global temperature of the process, consequently generating an increase in CO and a decrease in NO emissions. Finally, for the conditions studied, increasing the mass flow of externally sourced CO2 did not destabilize combustion.