Generation of Silica Nanoparticles in Turbulent Non-premixed Flames with Oxygen Enrichment

Abstract

Silica nanoparticles were made via the gas-to-particle conversion of tetraethylorthosilicate (TEOS) in co-flowing turbulent methane-oxygen-enriched non-premixed flames. The effects of fuel velocity, oxygen concentration, flame residence time, and temperature distribution on the characteristics of the silica nanoparticles were investigated. The flame length was measured by OH chemiluminescence, using an intensified charge-coupled device (ICCD) camera. The primary particle diameter of the silica nanoparticles was quantitatively measured by transmission electron microscopy (TEM). Particle number concentration, as well as the geometric mean diameter and standard deviation, were measured by it scanning mobility particle sizer (SMPS) spectrometer. Adiabatic temperatures according to oxygen concentration and mixture fraction were calculated from thermodynamic equilibrium calculations, considering chemical species using CHEMKIN EQUI L code. Flame temperature, velocity, and turbulent intensity distributions were calculated using Fluent software adapted to the presumed probability density function (PDF) model, considering chemical species in the turbulent non-premixed methane-oxygen-enriched flame burner without including the particles. For each oxygen concentration condition, the flame residence time, average primary particle diameter, and geometric mean diameter decreased as the fuel velocity increased. Typically, agglomerates or silica nanoparticles were made on averaged primary particle diameters of 9-15 rim and geometric mean diameters of 60-100 nm, according to the oxygen concentration, which varied from 50% to 100% for first jet velocities of 40 and 70 m/s.