Comparative CFD Analysis of Natural Gas, Syngas, and Biogas Combustion in an Industrial Burner: Effects of Air/Fuel Ratio on Flame Characteristics and Thermal Performance
Aniekan, Okon
Department of Mechanical and Aerospace Engineering, Faculty of Engineering, University of Uyo, Uyo, Nigeria.
Arua, Julius Egwu *
Department of Mechanical and Aerospace Engineering, Faculty of Engineering, University of Uyo, Uyo, Nigeria.
Alexander Aniekan Offiong
Department of Mechanical and Aerospace Engineering, Faculty of Engineering, University of Uyo, Uyo, Nigeria.
Ukoima, Katoubokmelek Thompson
Department of Mechanical and Aerospace Engineering, Faculty of Engineering, University of Uyo, Uyo, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
This study presents a comparative computational fluid dynamics (CFD) investigation of natural gas, syngas and biogas combustion in a common industrial burner geometry under systematically varied air/fuel conditions. The burner was modelled parametrically and analysed in ANSYS Fluent using the Eddy Dissipation Model for turbulent combustion. The three fuels were simulated at air equivalence ratios of 1.11, 1.0, 0.91, 0.83, 0.77, 0.71, 0.67, 0.62 and 0.59. Flame-temperature distribution, thermal output, combustion efficiency and flame stability were used as the principal performance indicators, with 1.0 representing the stoichiometric air/fuel ratio. The simulations showed a clear fuel-dependent response to excess air. The 1.0 ratio produced the highest static flame-temperature field, whereas the 0.59 equivalence ratio (very lean) produced the best overall performance in terms of flame stability, useful heat output and combustion efficiency. Under this condition, natural gas produced 9.584 kW at 95.94% efficiency, biogas produced 3.325 kW at 94.25%, and syngas produced 2.994 kW at 85.59%. Natural gas therefore provided the highest thermal capacity, while biogas approached its combustion efficiency despite having a lower energy density. Syngas maintained relatively better flame stability but delivered the lowest thermal output because of its lower effective energy content and highly reactive hydrogen content. Validation of the natural-gas case gave a CFD stoichiometric flame temperature of 2300 K, compared with a theoretical reference value of 2236 K, corresponding to a difference of approximately 2.86%; the stoichiometric air/fuel ratio also differed from the cited theoretical value by approximately 0.58%. These results demonstrate that flame temperature, combustion efficiency and thermal output should be treated as separate but interacting indicators, and that the optimum air/fuel condition depends on the fuel considered. The study provides a CFD-based basis for selecting air-supply conditions when natural gas, syngas or biogas is used in industrial burners.
Keywords: Computational fluid dynamics, industrial burner, natural gas, syngas, biogas, air/fuel ratio, combustion efficiency, thermal output, flame temperature