An Experimental and Modeling Study of Humid Air Premixed Flames

An experimental and modeling study has been performed jointly by UTRC and DOE-FETC to determine the effect of humidity in the combustion air on emissions and stability limits of gas turbine premixed flames. This study focuses on developing gas turbine combustor design criteria for the Humid Air Turbine (HAT) cycle. The experiments were conducted at different moisture levels (0 percent, 5 percent, 10 percent, and 15 percent by mass in the air), at a total pressure of 200 psi, pilot levels (0 percent, 1 percent, 3 percent, and 5 percent total fuel), and equivalence ratio (0.4 to 0.8 depending on the moisture levels). The moisture levels were achieved by injecting steam into dry air well upstream of the fuel-air premixing nozzle. Computations were made for comparison to the experiments using GRI Mech 2.11 kinetics and thermodynamic database for modeling the flame chemistry. A Perfectly Stirred Reactor (PSR) network code was used to create a network of PSRs to simulate the flame. Excellent agreement between the measured and modeled $NOx$ (5–10 percent) was obtained. Trends of added moisture reducing $NOx$ and the effects of equivalence ratio and piloting level were well predicted. The CO predictions were higher by about 30–50 percent. The CO discrepancies are attributed to in-probe oxidation. The agreement between the data and model predictions over a wide range of conditions indicate the consistency and reliability of the measured data and usefulness of the modeling approach. An analysis of $NOx$ formation revealed that at constant equilibrium temperature, $Teq,$ the presence of steam leads to lower O-atom concentration which reduces “Zeldovich and $N2O$” $NOx$ while higher OH-atom concentration reduces “Fenimore” $NOx.$[S0742-4795(00)00703-1]