A computational fluid dynamics (CFD) modelling study is undertaken integrating the air-fired and oxy-fuel combustion cases for chemical reactions, radiative heat transfer, and gas compositions into a 3-D hybrid unstructured grid CFD code.... more
A computational fluid dynamics (CFD) modelling study is undertaken integrating the air-fired and oxy-fuel combustion cases for chemical reactions, radiative heat transfer, and gas compositions into a 3-D hybrid unstructured grid CFD code. A swirl injection system is used to achieve the flame stability of the turbulent non-premixed combustible gases. An Eddy Breakup (EBU) combustion model with appropriate empirical coefficients is employed for this study. Validation and comparison of both combustion cases with the experimental data, which conducted on a 100 kW facility unit, were made by comparing the temperature distribution levels and species concentration levels. The oxy-fuel combustion case showed that the flame is obviously concentrated in the central region, and it is not spread inside the furnace compared to the air-fired flame. The swirl effect is certainly used to enhance the turbulent mixing and to achieve the internal recirculation of flames. By switching to oxy-fuel fired...
The laminar flame characteristics of natural gas–hydrogen–air–diluent gas (nitrogen/CO2) mixtures were studied in a constant volume combustion bomb at various diluent ratios, hydrogen fractions and equivalence ratios. Both unstretched... more
The laminar flame characteristics of natural gas–hydrogen–air–diluent gas (nitrogen/CO2) mixtures were studied in a constant volume combustion bomb at various diluent ratios, hydrogen fractions and equivalence ratios. Both unstretched laminar burning velocity and Markstein length were obtained. The results showed that hydrogen fraction, diluent ratio and equivalence ratio have combined influence on laminar burning velocity and flame instability. The unstretched laminar burning velocity is reduced at a rate that is increased with the increase of the diluent ratio. The reduction effect of CO2 diluent gas is stronger than that of nitrogen diluent gas. Hydrogen-enriched natural gas with high hydrogen fraction can tolerate more diluent gas than that with low hydrogen fraction. Markstein length can either increase or decrease with the increase of the diluent ratio, depending on the hydrogen fraction of the fuel.
The laminar burning velocities and Markstein lengths of the hydrogen-air-diluent mixtures were measured at different equivalence ratios (0.4–1.5), different diluents (N2, CO2 and 15%CO2+85%N2) and dilution ratios (0, 0.05, 0.10 and 0.15)... more
The laminar burning velocities and Markstein lengths of the hydrogen-air-diluent mixtures were measured at different equivalence ratios (0.4–1.5), different diluents (N2, CO2 and 15%CO2+85%N2) and dilution ratios (0, 0.05, 0.10 and 0.15) by using the outwardly expanding flame. The influences of flame stretch rate on the flame propagation characteristics were analyzed. The results show that both the laminar burning velocities and the Markstein lengths of the hydrogen-air-diluent mixtures decrease with the increase of dilution ratio. The decrease in Markstein lengths means that adding diluents into the hydrogen-air mixtures will decrease the diffusional-thermal instability of the flame front. For a specified dilution ratio, the laminar burning velocities give their maximum values at an equivalence ratio of 1.8. The Markstein lengths increase with the increase of the equivalence ratio monotonously regardless of the diluents. The study shows that CO2 as the diluent has a greater impact on the laminar flame speed and the flame front stability than N2 as the diluent.
