Direct Numerical Simulation and Flamelet Modeling of Coal/Ammonia Cofiring Flame

Combusting ammonia with coal is regarded as an effective technical approach for reducing carbon emissions. This process involves multiple fuel streams and nitrogen sources, posing challenges for accurate and efficient modeling of combustion and NO formation. The present paper presented a point-particle direct numerical simulation (PP-DNS) work with detailed chemistry for a coal/ammonia co-firing flame, and a flamelet/progress variable (FPV) model for ammonia/coal co-firing was applied to consider the multiple fuel streams and reacting stages. The performance of the extended FPV model was evaluated by conducting a priori analyses with the PP-DNS solution as benchmarks. The gas temperature, major species, and CO profiles in the PP-DNS can be well reproduced by the extended FPV model. The reaction time scale analysis indicated that NO is formed on the same order of time scale as those of the major species in this flame. Therefore, it can be acceptably predicted by directly extracting data from the flamelet tables. Incorporating NO in the progress variable does not enhance the NO prediction and lowers the accuracy of the temperature and major species predictions. The main deviations of NO prediction can be attributed to the multi-dimensional effect.