Numerical Simulation of CO Concentration on Flame Propagation in the Vicinity of the Wall -Validity of Non-Adiabatic FGM Approach-

Abstract

To design a gas turbine combustor for low emissions, carbon monoxide (CO) generated near the cooled wall is one of the important indexes. However, the measuring of CO concentration is difficult in experiments in actual conditions of high pressure and temperature. In this study, in order to take the heat loss effect on the cooled wall into account, a non-adiabatic flamelet generated manifolds (NA-FGM) approach, which can account for the change of gas composition due to the heat loss, is applied to two-dimensional numerical simulations of premixed flame near the cooled wall and the effect of equivalence ratio variation on the CO concentration is investigated. The results show that the CO concentrations predicted for the equivalence ratio of 1.0 using the NA-FGM approach are in good agreements with those using the detailed reaction approach, and that the NA-FGM approach can adequately catch the tendency of CO generation in the vicinity of the wall with heat loss. NOMENCLATURE Progress variable Isopiestic specific heat ℎ Thermal diffusivity Diffusion coefficient � = ⁄ � ℎ Enthalpy Pressure ̇ Source term of heat loss Gas constant Laminar flame velocity Temperature Velocity vector Diffusion velocity of chemical species Molecular weight Mass fraction of chemical species Z Mixture fraction Greeks Adjustment parameter δ Laminar flame thickness λ Thermal conductivity Shear stress tensor φ Equivalence ratio Density ̇ Generation rate of progress variable ̇ Chemical reaction rate of chemical species Subscripts k Chemical species

Prediction of CO emissions in turbulent super lean premixed combustion under pressurized conditions using an LES/non-adiabatic FGM approach

“…Therefore, we apply the NA-FGM approach [14] to include the effect of heat loss. The flamelet library, using the effect of the considered heat loss [16], is calculated using equations ( 6), (7) and (9).…”

“…However, no comparisons were made with the experiments. To take the heat loss effect into account in the flamelet approach, a non-adiabatic procedure [14] has been introduced in some previous studies for both non-premixed and premixed flames [15][16][17][18][19]. However, to assess the validity, comparisons with the experiment results are essential because of procedural complications.…”

“…The purpose of this study is, therefore, to apply an LES by employing a non-adiabatic FGM approach (referred to as "NA-FGM approach", hereafter), which can consider the effect of heat loss on the chemical species composition [14][15][16][17], to CH4-air super lean premixed flames for equivalence ratios of φ = 0.43, 0,45 and 0.50 under pressurized conditions with heat loss through a cooled wall, and to examine the validity to predict the CO emissions based on a comparison with the experiment results. In addition, the effects of heat loss and equivalence ratio on CO emissions were investigated in detail.…”