This study investigates nozzle diameter and fuel type effects on combustion characteristics and NOx emissions in radiant tube heating systems through numerical simulation. Four fuels were analyzed: LPG, natural gas, coke oven gas, and hydrogen under varying nozzle conditions using computational fluid dynamics with energy conservation, species transport, and thermal NOx formation models. Results show that nozzle diameter optimization significantly enhances internal recirculation, improving fuel-air mixing and reducing NOx formation. Hydrogen exhibits higher flame temperatures, potentially increasing thermal NOx generation, but optimal nozzle design controls this effect through enhanced mixing patterns. The optimized configuration achieved substantial NOx reduction while maintaining combustion stability across all tested fuels.

In this study used Computational Fluid Dynamic analysis to examine NOx reduction in hydrogen combustion, analyzing six conditions with varying air/fuel ratios, temperatures, and concentrations. Results were compared between two combustor shapes and previous experimental data. Findings showed increased air/fuel ratios decreased flame temperature and increased post-combustion O2. NOx emissions peaked at high temperatures and low O2. Numerical results aligned with previous experimental trends, validating the approach. Combustor shape differences, reflecting variations in fuel and air pipes, significantly affected flow rates and combustion positions. This reduced NOx emissions up to a certain air/fuel ratio, but excessive increases diminished this effect. The study highlights the complex relationship between combustor design, operating conditions, and NOx emissions. Further research is needed to optimize NOx reduction by considering pipe numbers and combustion locations. Future studies should explore various combustor geometries, fine-tune air/fuel ratios, and investigate additional parameters influencing NOx formation and reduction in hydrogen combustion systems.