A study on surface deposition of combusting iron particles

Iron powder, as a recyclable and carbon-free fuel, is a promising alternative to fossil fuels and other energy carriers. One challenge in developing a practical iron-powder combustor is the deposition of particles on the inner surfaces of the combustion chamber. The objective of this study is to understand the mechanism underlying the surface deposition of combustible iron particles in a size range between 20 µm and 70 µm. The effects of the temperature and different material properties of the surface, including melting point and thermal conductivity, on the deposition behavior are examined experimentally and further analyzed via numerical modeling. For the experimental study, a Jet-in-Hot-Coflow (JHC) burner is used to heat and inject iron particles onto a plate. Various surface materials, including carbon steel, stainless steel, aluminum, and brass, are analyzed. The experiments reveal that unignited solid iron particles cannot deposit on any surface. When particle ignition occurs, molten iron particles can deposit on all of the herein considered surface materials. The experimental measurements show that a higher temperature, lower melting point, and lower thermal conductivity of the surface material enhance deposition, suggesting that the key deposition mechanism (at least, for sufficiently smooth surfaces) is likely a local melting and fusion (or welding) process. An overall positive correlation between the experimentally measured deposition degree for different surface materials and the theoretically estimated local melting parameter ((Formula presented.)) supports the hypothesis of the deposition mechanism.