Numerical Simulation Of A CH4/H₂Jet Diffusion Flame In Dilution Hot Coflow

Moderate and Intense Low Oxygen Dilution (MILD) Combustion is a moderate combustion mode under the condition of the dilution. MILD combustion technology can significantly reduce the maximum temperature of reaction area and emissions of pollutants, and the reaction occurs in the larger area, even in the whole combustion chamber, and then the overall reaction efficiency is also improved. It is a typical high efficiency low pollution combustion technology.Hot flue gas coflow as oxidant and the center high-speed jet as fuel, is an important way to achieve MILD combustion. By simplifying the university of Adelaide jet burner, this article uses the custom K-ε model (C1ε=1.6), and selects EDC model based on a detailed chemical mechanism Gri-Mech3.0to simulate the combustion process of a CH4/H2jet flame in hot coflow. Compared with the experimental results, the simulation results verify the rationality of the numerical model.By changing the simulation calculation of the hot coflow oxygen concentration, we can get the influence to the combustion efficiency and the pollutant emissions under the condition of dilute oxygen concentration. The research shows that under the condition of the dilution, the highest temperature of reaction zone and CO emissions are linear with the increase of oxygen concentration of hot coflow, but the relationship to the NO emissions are growing exponentially. For the realization of the dilute jet MILD combustion process, increasing oxygen concentration of hot coflow can make the temperature rise of the reaction zone bigger, at the same time greatly increase the pollutant of CO and NO emissions, and so we should try to reduce the oxygen concentration of the hot coflow. For the burner of this article, we can get MILD combustion process when the oxygen concentration selects3%.Through the research of the coflow temperature in the jet MILD combustion, it should be higher than the ignition of the fuel mixture, generally should be higher than1000K, to make chemical reactions happen; When increasing the coflow temperature, the efficiency of the chemical reaction rises, and at a certain temperature, it reaches the maximum; Continue to rise the coflow temperature, the efficiency of chemical reaction will reduce, and CO and NO emissions will be in great quantities. So for jet MILD combustion process in hot coflow, the coflow temperature should choose the proper one.For the CH4/H2jet MILD combustion in hot coflow in this article, it is advisable to take a value of1250K for the hot coflow temperature.