Ethanol droplet formation, dynamics and combustion mode in the flame of the SpraySyn-nozzle

The synthesis of nanoparticles via flame spray pyrolysis (FSP) is based on a couple of physicochemical steps such as precursor atomization, droplet evaporation, fuel combustion, particle nucleation and growth. Most recent studies on FSP are focused on the particle formation without taking the antecedent precursor atomization and spray formation into account. In the present work, the atomization characteristics under burning and non-burning conditions are investigated by means of laser sheet Mie-scattering images and phase Doppler anemometry. The influence of the gas to liquid volume ratio on the spray formation, jet morphology and scales of turbulence in the nozzle far-field are studied to assess the performance of the external-mixing gas-assisted SpraySyn-nozzle. The turbulent flame spray is characterized by the Kolmogorov length scale and the Kolmogorov shear rate. The droplet–droplet interaction and group combustion behaviour, enabling clouds of merely vaporizing droplets surrounded by a flame sheath, are investigated. The experimentally determined droplet velocities, turbulence length scales and the analysis of group combustion modes allow a deeper insight into the spray flame dynamics and droplet mixing zones.