Emissions Performance of Staged Premixed and Diffusion Combustor Concepts for an NH₃/Air Flame With and Without Reactant Humidification

Renewably generated ammonia offers a form of carbon-free chemical energy storage to meet the differences between uncertain supply and fluctuating demand and has the potential to support future energy requirements. The storage/transportation characteristics of NH₃ are favorable compared with H₂; however, there are combustion research challenges to enhance fuel reactivity while reducing harmful emissions production. The purpose of this work was to evaluate different fuel delivery concepts for a representative gas turbine combustor. An experimental and numerical comparison was made between swirl-stabilized premixed and diffusion NH₃–air flames at elevated inlet temperature (473 K). The exhaust NO_x and NH₃ emissions generated from each concept were quantified to optimize combustor performance. High-speed OH* and NH₂* chemiluminescence was employed to characterize the change in flame topology with variation in fuel–air equivalence ratio, and the resultant influence on measured emission concentrations. Chemiluminescence intensities were shown to elucidate changes in sampled exhaust emissions, enabling detailed analysis of intermediate chemistry. A comparison was made between experimental data and kinetic simulations, demonstrating the sensitivity of NO_x emissions to premixed fuel–air equivalence ratio. A comparison was also made between exclusive primary airflow, and the staged introduction of secondary air, to quantify the change in NO_x production between each configuration and improve fuel burnout. Secondary air loadings were incrementally increased through the combustor. Finally, reactant humidification was employed as a secondary process for NO_x reduction, having shown favorable performance with NH₃–H₂ mixtures, with the efficacy compared for both premixed and diffusion configurations.