Comparison of chemical mechanisms for the oxidation of hydrogen/ammonia mixtures based on different evaluation methods

Abstract

For net-zero carbon emissions, hydrogen/ammonia blends have drawn considerable attention for the application in industrial combustion devices. Various chemical mechanisms have been developed to describe the oxidation and combustion of hydrogen/ammonia mixtures at certain conditions. A comprehensive evaluation and comparison of the performance of these mechanisms is thus of high interest, especially in terms of their application for particular computational studies. Thus, this work aims to compare the existing chemical mechanisms in terms of their performance for the combustion of hydrogen/ammonia mixtures over a wide range of experimental conditions. In addition to previous literature studies, the model performance is evaluated by using two different methods for the assessment of prediction accuracy. Besides the conventional measure of point-wise differences between model and data, the curve-matching method is also applied, which quantifies the dependence of model response on physical conditions additionally, by comparing the similarity between the curve shapes of the predicted and measured results. Extensive experimental data are taken into account in the model evaluation, including 136 datasets obtained from various facilities in the past 10 years. Nineteen mechanisms are compared, which were published in recent five years. It is revealed that these models give strongly different numerical results for combustion targets, such as laminar burning velocities, ignition delay times, and species concentrations. The chemical mechanisms of Zhang et al. (2021), Han et al. (2023), Mei et al. (2019), Li et al. (2019), and Stagni et al. (2020) show relatively satisfactory performance over the entire investigated domain. Moreover, it is found that the estimated prediction accuracy of chemical mechanisms is highly sensitive to model evaluation methods.