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

Abstract

A large eddy simulation (LES) employing a non-adiabatic flamelet generated manifolds (NA-FGM) approach, which can account for the effects of heat loss, is applied to CH4-air super lean premixed combustion fields generated by an axisymmetric jet burner with cooled walls under pressurized conditions. In addition, the validity in predicting the CO emissions is examined. The NA-FGM approach captures the trends of CO emissions well during the experiments, in which the CO emissions increase with a decreasing equivalence ratio. It is shown that the increase in CO emissions for low equivalence ratios is not due to the increase in the CO production, but to the slow rate of CO consumption, which keeps the CO concentration high downstream. The results suggest that capturing such a sensitive reduction of CO consumption rate by heat loss is important for accurately predicting the CO emissions in developing a low-emissions gas turbine combustor at low load. NOMENCLATUREProgress variable [-] Isobaric specific heat [J/kg/K] ℎ Thermal diffusivity [m 2 /s] Diffusion coefficient �D γ = λ ρC p ⁄ � [m 2 /s] ℎ Enthalpy of species k [J/kg] Mass diffusion flux of species [kg/m 2 s] ̇ Mass production rate of species [kg/m 3 s] Pressure [Pa] ̇ Source term of heat loss [W/m 3 ] Temperature [K] Velocity vector [m/s] Mass fraction of chemical species [-] Mixture fraction [-] Greeks Adjustment parameter λ Thermal conductivity φ Equivalence ratio [-] Viscosity [Pa•s] Density [kg/m 3 ] Shear stress tensor ̇ Generation rate of progress variable+ ̇ Chemical reaction rate of chemical species Subscripts f Fuel k Chemical species st Stoichiometric air-to-fuel ratio wall Wall

Prediction of boundary layer flashback limits of hydrogen flame using an LES/non-adiabatic FGM approach

“…Although there have been researches on CFD simulations applying the detailed chemistry to reproduce the flashback phenomenon [11][12][13][14][15][16][17], the calculation cost is too high to study the actual combustor with the large size and the complicated geometry. On the other hand, it has been reported that the flamelet-generated manifold (FGM) approach can simulate the partially premixed combustion with the relatively low calculation cost and the satisfactory accuracy [18][19]. In addition, the heat loss process, which is important for boundary layer flashback, could be taken into account in the FGM approach [18][19][20].…”

“…On the other hand, it has been reported that the flamelet-generated manifold (FGM) approach can simulate the partially premixed combustion with the relatively low calculation cost and the satisfactory accuracy [18][19]. In addition, the heat loss process, which is important for boundary layer flashback, could be taken into account in the FGM approach [18][19][20].…”