Local extinction in piloted turbulent partially premixed ammonia/hydrogen/nitrogen-air jet flames

This work investigates local extinction in piloted turbulent, partially premixed ammonia/hydrogen/nitrogen-air flames at Reynolds numbers of 24,000 (Flame D) and 36,000 (Flame F). 1D Raman/Rayleigh/LIF techniques provide quantitative measurements of major species, mixture fraction, temperature, OH mole fraction, and qualitative NH₂-LIF detection. Flame D, exhibiting minimal extinction events, serves as a reference for Flame F, which has significant levels of local extinction. Laminar flame simulations reveal three local peaks in heat release rate within the mixture fraction space: Zone 1 near stoichiometry with peak OH, Zone 2 at peak temperature, and Zone 3 at peak NH₂. Scatter plots of temperature, OH, NH₂, and major species highlight differing local extinction behaviors across these zones at various axial heights. The quantitative Extinction Probability based on thresholds of OH, temperature, and NH₂ corroborates observations from the scatter plots. Zones 1 and 2 predominantly exhibit extinction events at downstream distance relative to jet diameter, Z/D, of 4 to 6, whereas Zone 3′s extinction probability peaks farther downstream, indicating that both extinction and re-ignition are driven by the leaner heat release regions. Detailed Probability Density Function (PDF) distributions are analyzed, focusing on Z/D of 4 and 10, the heights where the local extinction is most evident. The PDF profiles for burnt samples in Flames D and F are nearly identical at both axial heights. While the distinct shift to lower of species concentration and temperature are observed in the extinction samples at Z/D = 10. These turbulent flames may serve as interesting test cases for models aimed at predicting the stability of practical ammonia-based combustors.