Iron Energy Carrier: Experimental Characterisation, Combustion Diagnostic and Benchmarking with Other Clean Metal Fuels

ABSTRACT This study presents an experimental investigation into the combustion of iron particles over a substantially extended size range (10–250 µm), addressing the limitations of prior research constrained to smaller particles (typically < 100 µm). Using a drop tube burner setup, individual iron particles were released through a fuel‐lean, laminar flat flame, and their combustion dynamics were observed via high‐speed imaging and photomultiplier tube (PMT) measurements. The primary objective was to determine whether a single power‐law scaling (τ b = mdⁿ) could describe the burn time ( τ b ) across the full particle size (d) spectrum. The results reveal that a single scaling law is insufficient; instead, two distinct combustion regimes emerge. For particles between 13 and 118 µm, burn time exhibits a weak dependence on particle size, indicative of rapid heating and diffusion‐limited combustion. Above 118 µm, a stronger particle size dependence is observed, reflecting the increasing influence of internal heat conduction. This transition in scaling behaviour aligns with analogous trends found in aluminium and titanium combustion, suggesting a potential shift in the governing mechanisms at critical particle sizes specific to each metal. Additionally, high‐resolution PMT diagnostics identified key sub‐timescales constituting the ignition delay phase, including heating, melting, and thermal runaway. High‐resolution imaging revealed unexpected nanoparticle formation during the burnout phase. This phenomenon challenges the conventional understanding of liquid‐phase iron combustion. Scanning electron microscopy (SEM) confirmed the presence of nanoparticles and explosive fragmentation events, the latter attributed to structural heterogeneities within the iron particles.