The role of particle size on the combustion regimes of iron in dust flames

Unlike gaseous fuels, which are fully characterized by chemical composition, metal fuels also vary in particle size. This paper investigates the effect of particle size on laminar flame propagation in iron particle suspensions with oxygen–argon and oxygen–helium carrier gases. Using a McGill Bunsen-type metal-fuel burner, pure iron flames are stabilized across a broad range of fuel concentrations. Particle size significantly influences the laminar burning velocity, flame temperature, and their sensitivity to fuel concentration. Evidence consistent with a transition from a diffusion-limited to a predominantly kinetically controlled combustion regime is observed as the mean particle size decreases. This transition is hypothesized to be governed by the diffusion resistance across a molten FeO surface layer, leading to arrested ignition in fine particles.