Chemical Kinetic Modeling of the Combustion of NH3/H2 and NH3/syngas Fuel Mixtures Using a Large Amount of Experimental Data

Abstract: Nowadays, due to the global climate change, it is extremely important to find alternative fuels to reduce the utilization of fossil fuels and the emission of air pollutants such as carbon dioxide (CO2), hydrocarbon pollutants, and soot. Ammonia (NH3) is a promising carbon free fuel candidate that can store and transport renewable hydrogen (H2) energy. Ammonia has several advantages over hydrogen in practical applications, but the combustion characteristics of NH3 are different from traditional hydrocarbon fuels. A possible solution to improve the disadvantageous combustion properties of ammonia is to blend it with other fuels. For this purpose, two of the most usually used co fuels are hydrogen and syngas (H2/CO). This study reports a collection of currently available chemical kinetic mechanisms from the literature that can be applied for modeling the combustion of NH3/H2 and NH3/syngas fuel mixtures. An indirect experimental data collection is also presented which can be used for testing the performance of these combustion mechanisms. In this work, 19 detailed reaction mechanisms were investigated that had been published in the last 13 years. Their performance was quantitatively assessed based on how well they can reproduce the results of indirect experiments. Almost 5000 experimental data points were utilized in the mechanism comparison including ignition delay times measured in shock tubes, concentration measurements in jet stirred and flow reactors, and laminar burning velocity measurements. Based on the results, it can be concluded that there are significant differences between the performances of the different models, and the performance of a mechanism may also vary significantly with the type of experiments. Local sensitivity analysis was carried out on the best performing mechanisms to identify the kinetic and thermodynamic parameters to which model outputs are most sensitive. Even though the investigated models are different, sensitivity analysis identified largely the same set of important reactions and thermodynamic data in these mechanisms. Results presented in this work may serve as a good basis for further mechanism development for the combustion of NH3/H2 and NH3/syngas fuel mixtures.