Large Eddy Simulation of Hydrogen/Air MILD combustion in a cyclonic burner

Abstract

In this work Large Eddy Simulation (LES) of a Hydrogen/Air cyclonic burner operating in the MILD combustion regime at 1 atm is performed. The cyclonic flow configuration may represent a proper way to enhance the mixing process in a very short time while allowing for residence times long enough to achieve complete oxidation of diluted and preheated mixtures. Accurate molecular transport properties and a reduced chemical mechanism for hydrogen-air combustion, consisting of 18 transported species and 244 elementary reactions are considered. Results show that at the center of the combustor, where MILD combustion occurs, temperature exhibits a statistically steady trend (a mean of 1450 K) with peak values lower than 1700 K. This implies that the Zeldovich mechanism for thermal NO formation is negligible, so NO levels are low and statistically steady with a maximum peak of 20 ppm. These values are lower than those observed in standard combustion, confirming the ability of MILD to reduce NOx pollutants also with hydrogen as fuel. Finally, the simulations outcomes are in very good agreement with the experimental results, in particular radiative heat transfer must be taken into account to better capture the preheating of the reactants and consequently fit the experimental temperature profiles in the combustion chamber.