H-2-CH4 mixture fuels can be promising for reducing carbon-based emissions. However, because of higher pollutant emission (such as NOX) problems during hydrogen combustion, a new combustion method can be favorable. Colorless distributed combustion (CDC) is emerging here. CDC enables ultra-low pollutant emissions along with reduced flame instabilities, combustion noise, improved combustion efficiency, etc. Considering those benefits, methane and the hydrogen-enriched methane (60% CH4-40% H-2, 50% CH4-50% H-2, 40% CH4-60% H-2) fuels have been consumed using a cyclonic burner providing more residence time at an equivalence ratio of 0.83 under distributed regime. For the modelings, Reynolds Stress Model (RSM) turbulence model, the assumed-shape with b-function Probability Density Function combustion model, and P-1 radiation model have been selected. To seek CDC, the oxygen concentration in the oxidizer was reduced with N-2 or CO2 diluent from 21% O-2 to 13% O2 at an interval of 2%. The air and the fuel temperatures were kept constant at 300 K. Besides, for seeking high-temperature air combustion (HiTAC) conditions the oxidizer temperature was changed to 600 K to simulate flue gas recirculation. The results showed that the temperature distributions changed to be more uniform considerably with a decrease in oxygen concentration for all cases. CDC also provided a considerable decrease in NOX and a favorable reduction in CO at a certain oxygen concentration. It has been concluded that CO2 as the diluent was more effective for reducing temperature levels and NOX levels due to its greater heat capacity. (C)& nbsp;2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.