A priori study of an extended flamelet/progress variable model for NO prediction in pulverized coal flames

Highlights: • An extended flamelet/progress variable model for NO prediction in pulverized coal flames is developed. • The validity of the flamelet model is evaluated through an a priori analysis. • The model is sensitive to the progress variable definition. • The effects of strain rate and initial temperature are investigated. -- Abstract: An extended flamelet/progress variable (FPV) model is developed in this work to predict the NO formation in pulverized coal flames with a newly defined progress variable. The validity of the model is assessed through an a priori analysis, in which the thermo-chemical values predicted with the extended FPV model are compared with the corresponding reference results. It is found that the NO mass fraction in the pulverized coal flames can be well predicted with the extended model, which is sensitive to the progress variable. The prediction accuracy can be further improved by optimizing the definition of progress variable. The effects of strain rate and initial temperature on the performance of the extended FPV model are also investigated. The overall good agreements between the developed model predictions and the detailed chemistry solutions demonstrate that the extended FPV model has a better performance for NO prediction than the conventional one in pulverized coal flames. Compared with the conventional model, the deviations of maximum NO mass fraction predicted with the extended FPV model are decreased by 92.97%, 86.80% and 95.14% for three different strain rate cases as well as 86.80%, 82.81% and 87.45% for three different initial temperature cases, respectively.