Combustion and emission modelling near lean blow-out in a gas turbine engine

Large Eddy Simulations (LES) of turbulent premixed combustion have been performed for conditions close to Lean Blow Out (LBO), where the flame propagates in the broken-reaction zone (BRZ) regime. LES using a thin-flame model (G-equation) and a sub-grid linear-eddy mixing (LEM) model are compared. Their ability to predict global heat release and flame characteristics in the BRZ regime is discussed. In both approaches, a flamelet library model is employed to predict CO, NO and UHC emission. Contrary to the LEM approach, the flame length obtained with the G-Equation method can be modified by adjusting the model parameters. It is shown that the presence of UHC has to be included to obtain the experimental CO emission trend. Although both approaches show similar agreement in overall features, the inherent limitation of the thin-flame model in the BRZ regime is highlighted and discussed.