The combustion chemistry of ammonia and ammonia/hydrogen mixtures: A comprehensive chemical kinetic modeling study

Ammonia (NH₃) is relatively less reactive compared to hydrocarbon fuels. Therefore, ammonia mixtures blended with hydrogen (H₂) have been shown to be a promising fuel for internal combustion engines. In this study, a detailed NH₃/H₂ chemical kinetic model is developed over a wide range of engine-relevant conditions and comprehensively validated to describe the combustion of NH₃/H₂ mixtures using available experimental literature data, including ignition delay times, laminar flame speeds and species concentration profiles. The new model captures very well the combustion properties of pure NH₃ and NH₃/H₂ mixtures at most conditions. By performing sensitivity and reaction path flux analyses the key reactions controlling fuel reactivity at high-temperature (≥ 1500 K) and low-to-intermediate temperature (1000 ≤ T ≤ 1500 K) regimes are identified. Moreover, the formation and consumption pathways of nitrogen oxides (NO_x) in NH₃/H₂ combustion at different conditions have also been investigated, which are found to be highly coupled to the underlying chemical reactions that dictate fuel reactivity. The kinetic data for the important reactions and species thermochemistry data used in our model are rigorously evaluated and are discussed in detail.