A simplified chemical kinetic model with a reaction mechanism based on a multidimensional average error iteration method for ammonia and ammonia/hydrogen combustion

Abstract

Ammonia (NH₃) is emerging as a promising fuel due to its high energy density, high hydrogen content, and zero carbon emissions from combustion. The study of chemical kinetics in NH₃ combustion offers theoretical approaches to address its low reactivity and high nitrogen oxide (NO_x) emissions, especially in binary fuels with hydrogen (H₂), which have been shown to positively affect NH₃ combustion systems. However, existing NH₃/H₂ models have various defects under different conditions. In this study, we develop a simplified NH₃/H₂ chemical kinetics model that is comprehensively validated using a large amount of representative experimental literature data, including ignition delay time, laminar flame speeds, and species concentration profiles. The model is analyzed using an innovative multidimensional average error iteration method, ensuring that the overall average error remains within 5%. Subsequently, the model is simplified by removing unnecessary components and reaction steps through the direct relation graph with error propagation method, reducing computational consumption. The combustion results of the pure NH₃ and NH₃/H₂ mixtures under most conditions are highly consistent with those of the new model. By conducting sensitivity and productivity analyses, we determined the key reactions controlling fuel reactivity under different H₂ ratios and the important interactions between intermediate products are described in detail. Additionally, the different reaction directions of NH₃ and the principle of NO_x generation under high H₂ conditions are elucidated through these analyses and reaction pathway diagrams.