Burning Velocity Measurements for Flat Hybrid Iron-Methane-Air Flames

Recently, a cyclic energy storage concept was proposed involving the use of metal powder as
CO2-free energy carrier, known as the metal fuel cycle. In this cycle, the burning of iron powder is considered as the discharge agent of the energy carrier. However, for this cycle to be an
efficient one, better understanding of the laminar burning velocity of iron powder is required.
Earlier findings regarding the burning velocities of iron flames in literature are not easily compared since the powders and experimental equipment vary widely from Bunsen flames [1, 2]
to counterflow [3] and spherical expanding flames [4, 5]. In gaseous flames, these methods of
measuring the laminar burning velocity are all subjected to stretch, and extrapolation to nonstretched flames is needed for proper comparison. However, for iron loaded flames, the effects
of stretch are still unknown. Furthermore, measurements are in many cases also subjected to
scatter from which the source is in many cases only partially quantified.
This study presents a newly developed burner based on the Heat Flux Method (HFM) [6]
which can measure the burning velocities of flat hybrid iron-methane-air flames, as illustrated
in Figure 1a. Since laminar iron flames are particularly difficult to stabilize and have - even for
micron-sized particles - burning velocities in close proximity to their terminal velocity, methane
is used as stabilizing agent. Due to the different properties is the hybrid flames and corresponding unburned mixture, the Heat Flux Burner (HFB) was redesigned to create a flat particle-laden
flow profile, which was validated using PIV. For the seeding of iron to to gaseous mixture, an
in-house developed