An atmospheric diffusion oxy-combustion flame in a gas turbine model combustor has been investigated experimentally and numerically. Oxy-combustion and emission characterization, flame stabilization and oxy-combustion model validation analyses are the main goals of the present research work. The combustor is fuelled with CH4 and a mixture of CO2 and O-2 as oxidizer. A modified two-step oxy-combustion reaction kinetics model for methane-oxygen combustion has been used in order to predict accurately the oxy-combustion characteristics. The conducted experimental results were used to validate the numerical model. Wide ranges of different operating parameters have been considered including equivalence ratio, percentage of O-2/CO2 in the oxidizer mixture and fuel volume flow rate. The stability of the oxy-combustion diffusion flame is also investigated both experimentally and numerically. The experimental and numerical results showed that the stability of the oxy-combustion flame is affected when the operating percentage of oxygen in the oxidizer mixture is reduced below 25%. In all cases, flame was extinct for conditions of less than 21% oxygen in the oxidizer mixture. Flame visualization over a wide range of operating parameters has been carried out experimentally and comparisons with the numerical results have been conducted. The flames have been characterized in detail by measuring the exhaust gas temperatures and emissions and comparing them with those from the numerical model. The combustion was found to be improved with increasing the percentage of O-2 at inlet however there is a limitation in temperature. Both experimental and numerical results are in good agreement. The modified two step reaction kinetics model was found to be capable of capturing the trends of temperature and the overall flame shape of the experimental data. Flame zone is also characterized in details by plotting the axial and radial temperatures, species concentrations and flow velocities using the numerical model. (C) 2013 Elsevier Ltd. All rights reserved.