Large eddy simulation of fuel variability and flame dynamics of hydrogen-enriched nonpremixed flames

Abstract

In this study large eddy simulation (LES) technique has been used to predict the fuel variability effects and flame dynamics of four hydrogen-enriched turbulent nonpremixed flames. The LES governing equations are solved on a structured non-uniform Cartesian grid with the finite volume method, where the Smagorinsky eddy viscosity model with the localised dynamic procedure is used to model the subgrid scale turbulence. The conserved scalar mixture fraction based thermo-chemical variables are described using the steady laminar flamelet model. The Favre filtered scalars are obtained from the presumed beta probability density function approach. Results are discussed for the instantaneous flame structure, time-averaged flame temperature and combustion product mass fractions. In the LES results, significant differences in flame temperature and species mass fractions have been observed, depending on the amount of H2, N2and CO in the fuel mixture. Detailed comparison of LES results with experimental measurements showed that the predicted mean temperature and mass fraction of species agree well with the experimental data. The high diffusivity and reactivity of H2 largely affect the flame temperature and formation of combustion products in syngas flames. The study demonstrates that LES together with the laminar flamelet model is capable of predicting the fuel variability effects and flame dynamics of turbulent nonpremixed hydrogen-enriched combustion including syngas flames.