Influence of turbulence on iron dust flame propagation

We investigate the effect of turbulence and particle slip on propagating flames from micron-sized iron particles through carrier-phase direct numerical simulations (CP-DNS). We use a pseudo-spectral multiphase solver for the fluid equations, including heat, mass, and momentum transfer between the fluid and the particles, and model the iron combustion through a point-particle approach. In differently elongated domains with triply periodic boundary conditions, we initially let particles evolve and cluster in forced homogeneous isotropic turbulence (HIT) without chemical reaction. Then, we heat up a slice of particles to initiate combustion and examine flame propagation through forced turbulence. We vary the integral-scale Reynolds number Re𝓁 , ranging from 57 to 250, independently from the Kolmogorov-based Stokes number St = 1∕4 to 4, and compare the results to a case with planar flame propagation. The Stokes number has a strong impact on flame propagation speed, while no significant influence of the Reynolds number is observed across the investigated range. Particles at St = 4 reach a global oxidation progress of 80% around six times faster compared to the planar flame. ... mehrThe turbulent mixing at the smallest scales increases with St for a fixed initial particle size 𝑑𝑝, increasing the flame propagation speed. For a planar flame, particle slip enhances the propagation We observe flame speeds in the range 7–13 cm s−1 for the planar flame, which is in a range similar to previous works. Moreover, we characterize turbulent flame fronts using temperature isocontours of the gas phase, and provide a first estimate for the turbulent flame front speed in HIT relative to the planar speed. Novelty and significance statement: Iron particle cloud combustion is a promising concept for renewable energy storage and transportation. Many studies investigate single iron particle reaction properties or the combustion of small particle groups. This study aims to connect the knowledge from those models to more realistic, but generic turbulence, namely the flame propagation through homogeneous isotropic turbulence. We compute turbulent flame speeds for iron dust flames, connect them to the flame surface area, and investigate the effect of particle slip and small scale turbulence, which to the best of our knowledge has not yet been done before. These features need to be well understood for future designs of iron combustion chambers.