The combustion behavior of iron particles in a turbulent jet with concentric plasma-heated co-flow is investigated experimentally. Co-flow temperature, particle injection rate, and particle size distribution are systematically varied to gain a deeper understanding on the coupling between turbulent flow, particle-phase, and combustion chemistry. Simultaneous high-speed planar Mie scattering and broadband luminosity imaging were used to characterize particle-phase dynamics including scalar mixing and ignition locations. Two iron powders with distinct size distributions and jet exit Stokes numbers St D of 1.2 and 80.7 were examined at co-flow temperatures ranging from 900 ∘ C to 1050 ∘ C, with matched bulk velocities between jet and co-flow. Particle-phase jet exit velocity and Mie scattering intensity profiles revealed a distinct Stokes-number-dependent particle distribution at the jet exit, consistent with particle-laden jet flows reported in the literature. Particle ignition is caused by convective heating of the entraining hot co-flow, causing distinct ignition zones in the shear layer. The ratio between ignited and injected iron particles is positively correlated with co-flow temperature and increases non-linearly with injection rate, following a power-law correlation. Larger particles, concentrated near the jet centerline, ignite less frequently due to their higher thermal inertia and greater distance from the hot shear layer where mixing with the hot co-flow occurs. Conversely, the preferential migration of small particles toward the jet walls is beneficial for the transport of iron particles into the shear layer. This demonstrates the importance of Stokes-number-dependent particle dynamics on the combustion behavior in turbulent jets, which can be exploited to enhance fuel conversion in technical burner systems. • Investigation of ignition in a turbulent iron particle-laden jet with hot co-flow. • Impact of co-flow temperature, particle size distribution and particle injection rate on iron particle ignition and dispersion. • Simultaneous high-speed Mie-scattering and luminosity imaging of iron particles. • Stokes-dependent exit distribution affects ignition in the shear layer. • Ignition event scaling indicates the role of inter-particle heat transfer.
Hebel et al. (Thu,) studied this question.