Ammonia oxidation regimes and transitional behaviors in a Jet Stirred Flow Reactor

Abstract The present work was devoted to the experimental identification of combustion regimes for NH3/O2 mixtures diluted in N2 in a Jet Stirred Flow Reactor (JSFR). Low Temperature (LT) combustion and High Temperature (HT) combustion regimes were identified as a function of reactor temperature (Tr) and mixture equivalence ratio (ϕ). The shift between the identified regimes occurs at a noticeable system working temperature (1300 K), independently of the mixture composition. This shift may occur through a transitional Lower Reactivity (LR) regime for ϕ≤1 in-between 1300 and 1310 K. For fuel-lean conditions, damped temperature oscillations were recognized between 1310 and 1320 K. Different detailed kinetic mechanisms were used to simulate system reactivity. To some extent, kinetic models were able to reproduce the establishment of different kinetic regimes along with the dependence on system temperature and mixture composition. Kinetic analyses suggested that NH2 oxidation routes control the shift between LT and HT regimes along with the establishment of dynamic behaviors. The experimental results obtained in this work represent important constraints for a fine tuning of ammonia chemical kinetic mechanisms, with particular regards to intervals of parameters where the transition from LT to HT regimes occurs. Indeed, improving the models in these critical ranges will help seeking for possible fluid-dynamical and chemical strategies to improve combustion stability while reducing pollutants emissions.