A novel flamelet-based model for 3D DNS of Mild combustion with CH₄/H₂ fuels

MILD combustion, also known as Flameless combustion, is a relatively new combustion concept which has a unique potential in enhancement of efficiency and reduction of emissions, in particular NOx. Very recently, the idea of using alternative fuels such as Syngas in MILD combustion has been emerged as a very clean combustion technology which has notable environmental and economic advantages. Exploitation ofMILD/Syngas combustion in industrial applications has been largely hindered by the lack of knowledge in complex processes associated with its stabilization. The stabilization mechanism of MILD combustion is mainly based on autoignition and presence of H2 introduces preferential diffusion effects. In this study, we conduct 3D DNS of MILD combustion with CH4/H2 fuels using detailed chemistry and transport models in order to obtain a better understanding of autoignition and preferential differential effects in MILD/Syngas combustion condition. A reduced flamelet-based chemistry model is developed to include these effects using Igniting Mixing Layer (IML) Flamelets. This model shows a considerable improvement compared to the commonly-used Igniting Counterflow (ICF) Flamelets. Findings of this study will broaden our knowledge on such a complex combustion regime, and provide reduced models for accurate RANS/LES simulations of turbulent Mild flames in the future.