Modeling MILD combustion with flamelet-generated manifolds

MILD combustion has the potential to deliver high thermal efficiency with low levels of pollutant emission. In MILD combustion systems a high degree of preheating of the reactants is coupled with a high degree of dilution. Since the temperature of the reactants is above the self-ignition temperature, a complex interplay between turbulent mixing, molecular transport and chemical kinetics occurs. The presence of thin reaction layers in MILD combustion makes the use of flamelet-based models such as FGM very attractive. In this work, modeling self-ignition with FGM under MILD conditions is investigated focusing on methane-carbon dioxide fuel mixtures. The influence of carbon dioxide level on ignition behavior is investigated, which is relevant for understanding MILD combustion behavior of biogas. Furthermore, the effect of the choice of progress variable is discussed and an automatic procedure to optimize the progress variable definition is presented.