Optimizing iron powder combustion: Influence of particle size on flame stability, nanoparticle formation, and nitric oxide emission

• Iron flame characterization, focusing on flame stability, temperature profiles, and combustion completeness, using a small-scale semi-practical burner. • Analyzed nanoparticle formation and NO x emissions during iron powder combustion, utilizing a small-scale burner to simulate practical conditions. • Determined the threshold iron powder size required for stable combustion by conducting a comprehensive evaluation of flame characteristics and emission profiles. • Established the minimum iron fuel-air ratio necessary to sustain stable combustion without the need for external heat sources. • Examined the morphology of combustion by-products, assessing solid residue across different iron powder sieve ranges to understand product formation mechanisms. This study utilizes a small-scale semi-practical burner “Metal Cyclonic Combustor (MC 2 )” to investigate the combustion behavior of iron powder as a potential clean energy carrier, focusing on varying powder sieve ranges and input equivalence ratios. The iron aerosol burner, used previously, can stabilize iron-air flames without a pilot flame or external heat supply. Experimental results demonstrate that smaller iron powder sizes produce stable and steady iron flames with higher degrees of oxidation. The critical powder sieve size for achieving steady iron flames in the current small-scale semi-practical burner (MC 2 ) was found to be below 75 µm, ensuring adequate residence time for combustion. Additionally, nanoparticle formation and nitric oxide (NO) emissions are significantly influenced by the size of the iron particles and combustion conditions, with smaller sizes and leaner conditions producing higher nanoparticles and NO emissions. A critical parameter identified is the average distance between particles being less than 1 mm for studied powder sizes to sustain a steady and stable iron flame without external heat support. These findings provide valuable data for developing commercial iron powder-firing burners and advancing iron powder as a sustainable energy carrier, offering practical guidance for efficient and environmentally friendly combustion processes. Novelty and Significance Statement This study provides an investigation into the combustion behavior of micron-sized iron powder using a practical burner, exploring its potential as a clean energy carrier. The novelty of this research lies in the detailed analysis of iron flame characteristics, nanoparticle formation, and NO formation under varying powder sieve ranges and combustion conditions. Unlike previous studies that focused much more on single-particle characteristics, this study examines larger-scale continuous combustion, highlighting critical parameters needed to achieve stable and steady iron flames without external heat support. The findings indicate that specific particle spacing is essential for sustaining stable and steady iron flames for practical particle size ranges employed in this study. These insights are pivotal for optimizing iron powder combustion processes, advancing the development of commercial iron powder burners, and promoting iron powder as a viable, sustainable alternative to fossil fuels. This research offers practical guidance for achieving efficient and environmentally friendly combustion, contributing significantly to the iron energy carrier cycle.