A Comprehensive Numerical Study on the Inhibition Effect of Ammonia on Various (Un)strained Premixed Stoichiometric Hydrogen/Air Flame Systems

This study numerically investigates the potential use of ammonia as a chemical inhibitor in hydrogen/air premixed combustion systems, aiming to reduce the risks associated with hydrogen use. Various flame configurations are explored using zero-dimensional and one-dimensional reacting models, including the homogeneous reactor, perfectly stirred reactor, unstrained premixed flame (freely propagating and quenching), and strained premixed flame in counterflow. The impact of ammonia addition on key flame behaviors, such as the ignition delay time, laminar burning velocity, flame thickness, and extinction strain rate, is evaluated. Results show that adding 20% ammonia achieves up to 50% inhibition efficiency across these metrics. Furthermore, heat release rate analysis is conducted for unstrained premixed flames during both free propagation and head-on quenching. It is found that the controlling elementary reactions contributing to the heat release rate differ significantly between these two phases. The study also examines the environmental implications of ammonia addition, particularly regarding NOx and N₂O emissions. While pure stoichiometric hydrogen/air combustion produces minimal NOx and N₂O, the addition of ammonia results in emissions on the order of $O\left(10^3\right)$ ppm or higher, indicating significant environmental challenges. This dual focus on inhibition and emission informs future strategies to balance the efficiency and environmental impact of hydrogen combustion systems. This study emphasizes the importance of experimental validation and encourages future experiments to collect data for further research.