Combustion regime identification and characteristics of nitrogen-diluted ammonia with hot air oxidizer: Non-premixed counterflow flame

Abstract

In this study, a numerical investigation was done to study the characteristics of N2-diluted ammonia combustion in a counterflow diffusion configuration with an elevated oxidizer temperature. The flame structures have been characterized in a steady laminar, unidimensional configuration in which hot oxidant and diluted fuel are representative of recirculating flow required to achieve High Temperature Air Combustion (HiTAC) and moderately or intense low-oxygen dilution (MILD) combustion. Investigations were done from a combustion-regime viewpoint to find the effect of each regime on the ammonia flame structure and emission. The specific working conditions of each regime were also identified. The heat release rate typology and temperature rise were analyzed with respect to external parameters such as dilution, oxidizer temperature, and thermal power to determine the boundaries of each regime of ammonia combustion. The results suggest the desired fuel dilution and oxidizer temperature to achieve a favorable combustion regime. It has been found that a high dilution of 0.8 is at least required for the MILD combustion of ammonia to occur. An enhancement has been found in the heat release rate, temperature, and main intermediate and final species in correspondence with combustion regime transition. It is shown that ammonia combustion characteristics in HiTAC and MILD regimes can be favorable in terms of stability and Emissions.