In this paper, the numerical simulation of a turbulent non-premixed hydrogen (H-2) diffusion flame has been performed in a model combustor. CFD studies using Fluent code were carried out changing fuel composition from pure hydrogen to natural gas (100% H-2, 70% H-2+ 30% CH4, 10% H-2 + 90% CH4, and 100% CH4). The model prediction studies have been extended to combustion air staging. Air 25% was staged and introduced through the two tangential inlets. The predictions are validated and compared against the experimental results obtained in this study and results from the literature. Turbulent diffusion flames are investigated numerically using a finite volume method for the solution of the conservation and reaction equations governing the problem. The standard k-epsilon model is used for modelling of turbulent flow as the model was far enough for the turbulence phenomena in the combustor. The chemical combustion reactions are described by seven species and three steps. A NOx post-processor has been used for predicting NO, emissions from the combustor. The temperature and major pollutant concentration (CO and NOx) distributions are in good agreement with the experimental measurements. The overall flame temperature increases as hydrogen is added or decreases as methane is added to the fuel mixture. The addition of methane to hydrogen decreases the flame temperature and thus NOx emissions considerably. Air staging causes rich and lean combustion regions and thus lower NOx emissions through the combustor exit. (c) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.