Numerical study on the heat transfer characteristics, flame structure, and pollutants emission in the MILD methane-air, oxygen-enriched and oxy-methane combustion

Abstract

Present study provides the comprehensive investigation on the different characteristics of MILD oxygen-enriched and oxy-methane combustion such as heat transfer, ignition delay, flame color, flame structure, emissions of CO and NOx (as air pollutants) by the adding of CO2 to the oxidizer. The MILD furnace of the University of Lisbon is modeled using the standard k-ε turbulence model and detailed chemical mechanism of GRI2.11. Original, extended and new optimized EDC (“EDC2020”) models are applied for the turbulence-chemistry interaction modeling. Additionally, a perfectly stirred reactor (PSR) analysis alongside with CFD simulation is used for better understanding the combustion process. The results indicate that by replacing of CO2 with N2, emission of visible light is reduced significantly and maximum temperature drops noticeably until flame reaches to nozzle shape section of furnace. Moreover, it is found that MILD oxygen-enriched and oxy-methane combustion have regarded advantages than MILD methane-air combustion involving enhancing the temperature uniformity about 10–15%, more distributed reaction zone and a significant reduction of NOx emission. CO emission shows different behavior and is unchanged under MILD oxygen-enriched regime while it increases from 11 ppm in MILD methane-air to 140 ppm in MILD oxy-methane with injection of 90% CO2 mass fraction.