Assessment of combustion paradigms for modeling a cyclonic burner under mild combustion conditions

The development of MILD Combustion systems in several practical applications is hampered by a lack of understanding into such regime and thus novel tools are required compared to conventional combustion systems. In MILD combustion technologies, reactants are diluted with large amounts of burnt reaction products prior to ignition, which enables reactive structure stabilization under diluted conditions, thereby avoiding high-temperature regions that promote enhanced thermal NOx formation. In this background, computational fluid dynamics (CFD) for the prediction of the burner behavior and its optimization, appears essential for a successful introduction of such a concept in some industries. A major issue in the modeling of diluted combustion is the pronounced sensitivity of the reactive structure to the reaction chemistry and therefore detailed kinetic schemes are necessary when a gas mixture is subjected to dilution by hot reaction products. In order to include detailed chemistry in fluid-dynamics simulations several turbulent combustion models were used and they are represented by the Eddy Dissipation Concept (EDC), PaSR and the Flamelet Generated Manifold (FGM). In particular, this study investigates the combustion characteristics of MILD Combustion in a novel cyclonic lab-scale burner. The numerical computations were performed incorporating turbulent combustion models in RANS simulations in order to determine the effect of several different main parameters such as inlet oxidizer temperature, and mixture composition on models performance. Therefore, an assessment of models was carried out on the basis of an experimental/numerical comparison by evaluating the temperature inside the burner for a fixed condition. Results suggest that both the modified EDC and PaSR represent promising tool for modeling the complex flame structures of cyclonic MILD burner, although in several conditions they depict some aspects that need to be further investigated.