This work presents a numerical simulation of the non-premixed combustion of natural gas in atmospheric air in an axis-symmetric cylindrical chamber, focusing on the effect of thermal radiation on the temperature and chemical species concentration fields and the heat transfer. The simulation is based on the solution of the mass, energy, momentum and the chemical species conservation equations. Thermal radiation exchanges in the combustion chamber is computed through the zonal method, and the gas absorption coefficient dependence on the wavelength is resolved by the weighted-sum-of-gray-gases model. The turbulence is modeled by the standard kappa - epsilon model, and the chemical reactions are described by the E-A (Eddy Breakup-Arrhenius model). The finite volume method is employed to treat the differential equations. Among other results, the solution of the governing equations allows the determination of the region where combustion takes place, the distribution of the chemical species, the velocity fields and the heat transfer rate by convection and radiation. The results indicate that while thermal radiation has a strong effect on the temperature field and heat transfer, its effect on the chemical reactions rates is of less importance. The numerical results are compared to experimental results obtained by Garreton and Simonin (1994).