Large eddy simulation of iron(III) oxide nanoparticle synthesis in spray flames

The SpraySyn burner has been developed to investigate nanoparticle synthesis from spray flames by various diagnostic methods and simulations from research groups within the DFG (German Research Foundation) priority program SPP1980. We investigate the formation of iron oxide nanoparticles from iron nitrate dissolved in a mixture of ethanol and ethyl hexanoic acid. In the SpraySyn experiment, the nanoparticle precursor solution is injected and atomized via an air-blast nozzle, surrounded by a pilot flame. The solvent itself is combustible, such that the droplets evaporate at high heating rates in a highly reactive environment. We investigate the synthesis flame in large eddy simulations. The liquid droplets are described by Lagrangian particles, and gas-phase combustion is modeled by the flamelet-generated manifold approach with adaptations for particle inception. The nanoparticle dynamics are predicted by three models: a monodisperse model, a bimodal model, and a sectional model. The monodisperse and bimodal models account in terms of number-, surface-, and volume-concentration from inception, coagulation, and sintering processes, while the sectional model accounts for inception and coagulation and provides the particle size distribution. The comparison of nanoparticle sizes with the in-situ measurements shows that the bimodal model can be a suitable alternative approach to the computationally expensive sectional model.