CFD Study on Influence of O2/CO2, O2/H2O Atmospheres and Shape of Furnace on Methane MILD Combustion

In this study, CFD modeling of a combustion system with internal gas circulation technology was carried out for a cylindrical chamber with 0.33 m height and a 0.025 m radius in which feed enters from a nozzle with 0.003 m diameter. The simulation implements the DRM-22 chemical mechanism, modified k? turbulence model, and EDC combustion model. The effect of chamber shape and diameter, nitrogen and carbon dioxide concentration of the input feed in MILD combustion was evaluated. The results indicated that by changing the combustion chamber shape from cylindrical to convergent, the temperature contour is more uniform and CO mass fraction at the output of the combustion chamber decreases. The maximum temperature for 901.4 Nml & BULL;min(-1) methane and 9148 Nml & BULL;min(-1) for divergent, cylindrical, and convergent cone chambers are 1820 K, 1663 K, and 1655 K, respectively. By increasing the radius of the combustion chamber, the temperature distribution becomes more uniform due to increasing the return flow, and the maximum temperature and CO emission at the chamber outlet decrease. By decreasing the nitrogen concentration on the input feed and increasing H2O and CO2 concentration, the temperature profile becomes more uniform so that the maximum temperature in the case without nitrogen (with 0.37 carbon dioxide and water vapor mass fraction) is 1510 K, while for a case with a 0.75 nitrogen mass fraction (without carbon dioxide and water vapor) is 1630 K. The results show that increasing H2O percentage and decreasing CO2 percentage causes temperature uniformity and CO mass fraction decreasing at the chamber outlet.