Multi-environment Probability Density Function Modeling for Turbulent CH4 Flames under Moderate or Intense Low-Oxygen Dilution Combustion Conditions with Recirculated Flue Gases

The present study has adopted the multi-environment probability density function (MEPDF) approach to simulate the turbulent CH4 flames under flameless combustion conditions with recirculated flue gases. The MEPDF approach is based on an Eulerian PDF formulation with computational efficiency. Micromixing can be represented via the IEM (interaction by exchange with the mean) model, and the chemistry is based on the GRI 2.11 mechanism including the NO x chemistry. Special emphasis is given to the effects of the micromixing model constants on the structure and characteristics of recirculated moderate or intense low-oxygen dilution (MILD) combustion processes. In terms of the temperature and species mole fraction, the multi-environment PDF model with a micromixing constant of 0.5 yields reasonably good agreement with experimental data. In terms of the integrated NO production rate for the MILD combustion condition, the N2O path yields the highest level, followed by the prompt, reburn, NO2, thermal, and NNH mechanisms in that order. Moreover, detailed discussions are made for the flame stabilization and autoignition processes in terms of recirculation rate, distribution of Damköhler number, scalar dissipation rate, and H2CO mass fraction.