CHEMISTRY REDUCTION FOR THE MODELING OF AN ETHYLENE JET FLAME IN DILUTED AND HEATED COFLOW

Flameless combustion, also known as moderate or intense low oxygen dilution (MILD), ensures high combustion efficacies with low pollutant emissions thanks to the dilution of reactants, usually achieved through recirculation of combustion products. The technology has been successfully applied in several processes and has been found to be able to handle a large variety of fuels, including low grade fuels, industrial by-products and hydrogen. Further development of this innovative combustion technology would benefit of Computational Fluid Dynamics (CFD) tools; however, modeling flameless combustion is much more challenging than conventional flames, because of the strong coupling between turbulent mixing and chemical kinetics. It is well known that chemical kinetics plays a fundamental role, even though there no common opinion on the degree a mechanism can be reduced. Some useful works may be found on flameless burners fed with methane, but there is lack of information on different fuels. The present work describes the numerical modelling of an ethylene jet flame issuing in a hot coflow burner, which is fully characterised in literature and emulates flameless conditions (Medwell and Dally, 2012). The modelling activities are aimed at validating different aspects of turbulent combustion modelling, through a Verification, Validation and Uncertainty Quantification approach. (VV&UQ). The following sources of uncertainties will be considered: - boundary conditions (e.g. turbulence levels of the inlet streams); - turbulence model; - combustion model; - chemical kinetics. Values and options for the above models were selected through a proper Design of Experiments, to optimize the number of simulations to be performed. Special attention was devoted to the chemical kinetics. A Principle Component/Variable Analysis was used to investigate the most important species in the chemical mechanism and thus reduce the complexity of detailed mechanisms