Abstract
Ammonia (NH3) is increasingly recognized as a promising alternative fuel. Various blending options have been proposed that are aimed at improving its flammability and applicability across diverse energy systems. This study conducts a comprehensive investigation, employing both experimental and numerical approaches, to understand the impact of blending ammonia with CH3OH or syngas, at various H2:CO ratios, on flame extinction limits, structure, and NOx emissions in counterflow laminar diffusion flames. Concentration profiles of ammonia and intermediate species (O2, CO, CO2, H2, NO, and N2O) were measured using Fourier-transformed infrared (FTIR) and gas chromatographic (GC) techniques. The findings indicate that increasing the H2:CO ratio in syngas-blended flames increases the extinction limits and reduces NO and N2O emissions. Compared with ammonia/methanol flames the ammonia/syngas flames exhibit higher extinction limits, flame temperatures, and lower NO and N2O emissions. Multiple kinetic models were found to underestimate the extinction strain limits, with Wang et al.’s 2021 model offering the closest predictions. Notably, discrepancies in ammonia dissociation and oxygen leakage to the rich side of stoichiometry impact reaction zone characteristics, extinction limits, and NOx predictions. Further kinetic analyses reveal that reactivity in syngas-blended flames is dominated by heat and radicals-producing reactions, while methanol-blended flames are sensitive to reactions involving ammonia fragments, resulting in decreased reactivity compared to syngas-blended flames. The results and findings from this study yield valuable insights into optimizing ammonia blends for enhanced flame stability and reduced emissions across various energy applications. It also provides data for chemical kinetics model validation in non-premixed diffusion environment where both species chemistry and transport are encountered.
Published Version
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