The present work is numerical simulat ion results from the modeling of a non-premixed natural gas flame performed
in a combustor model. CFD studies using FLUENT code were carried out for different air swirl numbers and inlet
thermal load with constant A/F. The isothermal flow field was simulated using (SST) k-ω turbulence model and the
reacting flow was simulated by the non-premixed combustion model with the P-1 radiation model available in the
computational fluid dynamics package Fluent 6.3. The model geometry was created and meshing arrangement was
generated using Gambit pre-processing software. The domain of the model was based on the dimension of the
combustor and burners. The case studied is a cylindrical enclosure of 0.1 m radius and 1.0 m length. Two reactant
streams emerge from two separate coaxial jets producing a swirling diffusion flame. The natural gas is issued axially
into the combustor from the annulus area between the swirler outer diameter and the burner hub diameter whereas the
combustion air is introduced through an annular swirler having uniform swirl vanes. The results show a reasonable
agreement of the measured and the calculated reverse flow zone sizes using the shear stress transport (SST) k -ω model.
The boundary of the reverse flow zone for weak air swirl number of 0.5 is formed completely inside the combustor with
closed loop, while for air swirl numbers of 0.87 and 1.5 the boundaries fill the combustor and its size increased as the
air swirl number increased. Increasing the air swirl number, the high temperature regions size, the flame length, and the
CO2 and CO concentrations decreased while the O2 concentration increased. Increasing the thermal load, the high
temperature regions size, the flame length, CO2 and CO concentrations increased, while the O2 concentration decreased.