Particle formation by flame spray pyrolysis is investigated theoretically and compared with particle size distribution data of ZrO₂ production at 100 to 300 g/h. Spray droplet size distributions as well as droplet and gas velocities are measured by Phase Doppler Anemometry along the axis and radius of the solid cone type spray. Multi-component droplet combustion is simulated accounting for droplet polydispersity, transport and evaporation. The dynamics of the product particle size distributions are investigated accounting for coagulation and sintering by population balance equations. The effect of initial droplet size and liquid feed rate on the evolution of product particle size and polydispersity is analyzed.