Numerical investigation of main characteristics of Mild combustion flames with different diluted boundaries

In this study main characteristics of MILD combustion process has been investigated in cases where the fuel and/or oxidizer streams were diluted with various amounts of product gas. For this purpose, a one-dimensional counterflow diffusion flame (CFDF) is used to investigate characteristics of diffusion flamelets in MILD burners using CHEM1D code. Detailed chemistry of GRI Mech 3.0 and complex multi-component transport model including Soret and Dufour effects has been used for modeling of methane combustion in dilute condition. The applied strain rate was set to 100 s-1 which is a value often observed in turbulent flames. A non-adiabatic case was also studied, in which the exhaust gas was assumed to be cooled down to 1400 K. Results showed that the maximum temperature decreases with increasing of recirculation ratio for non-adiabatic cases while for adiabatic case it remains approximately constant for all dilution cases including air, fuel and both diluted streams. In addition, Lower peak temperatures are accompanied by lower amounts of NO. Unsteady analysis of the flamelets showed that ignition delays decreases with increasing of recirculation ratio due to increased initial temperature. In cases where the fuel is diluted, a much shorter ignition delay is observed than when only the air stream is diluted.