Hydrogen as burner fuel:: modelling of hydrogen-hydrocarbon composite fuel combustion and NOx formation in a small burner

The objective of this work is to investigate numerically the turbulent non-premixed hydrogen (H-2) and hydrogen-hydrocarbon flames in a small burner. Numerical studies using Fluent code were carried out for air-staged and non-staged cases. The effects of fuel composition from pure hydrogen to natural gas (100% H-2, 70% H-2 + 30% CH4, 10% H-2 + 90% CH4, and 100% CH4) were also investigated. The predictions are validated and compared against the experimental results previously obtained and results from the literature. Turbulent diffusion flames are investigated numerically using a finite volume method for the solution of the conservation equations and reaction equations governing the problem. Although, three different turbulence models were tested, the standard k-epsilon model was used for the modelling of the turbulence phenomena in the burner. The temperature and major pollutant concentrations (CO and NOx) distributions are in good agreement with the existing experimental results. Air staging causes rich and lean combustion regions thus lower NOx emissions through the combustor exit. Blending hydrogen with methane causes considerable reduction in temperature levels and thus NO emissions. Increasing the mixture ratio from stoichiometric to leaner mixtures also decreases the temperature and thus NO emissions. Hydrogen may be considered a good alternative fuel for burners, as its use reduces the emission of pollutants; and as it is a renewable synthetic fuel. Copyright (c) 2005 John Wiley & Sons, Ltd.