Large eddy simulations (LESs) of turbulent mixing and combustion in non-premixed and premixed Colorless Distributed Combustion (CDC) systems are conducted with a hybrid Eulerian-Lagrangian mathematical/computational methodology. The CDC has shown to significantly reduce NOx and hydrocarbon emissions while improving the reaction pattern and stability with low-pressure drop and noise. The flow and combustion in CDC are characterized by a wide range of fluctuations in flow variables like velocity, temperature and chemical species concentrations. The flame is distributed in the entire combustor instead of the limited flame zone or thin flamelets seen in ordinary combustion systems. In the hybrid Eulerian-Lagrangian methodology used in this study, a high-order finite difference (FD) multi-block method is used to solve the Eulerian filtered Navier-Stokes equations while the composition field is obtained from the filtered mass density function (FMDF) and its equivalent stochastic equations, which are solved by a Lagrangian Monte Carlo (MC) method. The consistency of the Eulerian and Lagrangian parts of the LES/FMDF is established for non-reacting and reacting CDC. The LES/FMDF results are also shown to be in good agreement with the available experimental data, indicating the accuracy and reliability of the LES/FMDF model. The numerical results show that the variation in inflow air temperature (or the air and fuel jets momentum flux ratio) has a significant effect on the flow, mixing and combustion in CDC. They also indicate the importance of the configuration and jet layout in the combustor.
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