Numerical prediction of Nitrogen Oxides (NOx) from combustion processes has been a challenging task to the combustion community, yet necessary to reduce environmental impact. Turbulent nonpremixed combustion is characterized by wide ranges of overlapping length and time scales associated with the mixing and chemical reaction processes. In practice, averaged governing equations are solved with subgrid scale models to account for the unresolved scales and interactions among them. A validation study of subgrid scale models is made for a turbulent nonpremixed CO/H2/N2 jet flame. Numerical predictions of Nitric Oxide (NO) quantities are compared with experimental data to evaluate the accuracy of subgrid scale models. Factors significantly affect NO formation are identified and studied thoroughly. In addition to thermal NO pathway, N2O-intermediate pathway is also dominant for this fuel composition. Even though this flame has a very low radiant fraction, the heat loss has a significant effect on NO formation because of the highly temperature dependent NO formation rates. Superequilibrium O-atom & OH radical levels showed high sensitivity to the thermal NO formation in high-temperature zones. An order of magnitude differences are observed in thermal NO by neglecting subgrid scale fluctuations on NO formation with some what less sensitivity to NO formation by the N2O pathway. For reliable and accurate NO numerical predictions, the following should be accounted for; NO formation pathways, radiation effects, nonequilibrium O-atom & OH-radicals and subgrid scale turbulence effects. Overall, the Zeldovich mechanism predicted thermal NO very closely and overpredictions resulted from the N2O-intermediate pathway.
Simulation of A Confined Turbulent Nonpremixed Piloted Methane Jet Flame
