Evaluation, development, and application of a new skeletal mechanism for fuel-NO formation under air and oxy-fuel combustion

Although fuel-NO formation is significant for the combustion of pulverized coal, biomass, and heavy distillate fuels, its mechanism has not been systematically validated under air and oxy-fuel combustion. This is the first study that quantitatively evaluates detailed fuel-NO mechanisms against large experimental datasets from a jet stirred reactor (JSR) under both air and oxy-fuel combustion. The mechanism with the best overall performance is thoroughly reduced and validated. A skeletal fuel-NO mechanism including only 35 species is obtained using methods of directed relation graph with error propagation (DRGEP), DRGEP-aided sensitivity analysis, and computational singular perturbation. The skeletal mechanism is comprehensively validated and agrees well with the detailed mechanism and experiments predicting the ignition delay, temperatures, and concentrations of important species in JSRs, laminar flame speeds, and flame extinction under both air and oxy-fuel combustion. Moreover, the skeletal mechanism is successfully applied to the finite-rate modeling of moderate or intense low-oxygen dilution (MILD) combustion of pulverized coal. Unlike conventional semi-empirical post-processing modeling of fuel-NO production, the fuel-NO calculation in this study is coupled with coal combustion by using the well-validated skeletal mechanism. A highly precise in-furnace distribution of fuel-NO critical precursors (i.e., NH3 and HCN) and detailed fuel-NO reaction pathway under the MILD combustion are obtained.