Measurement of the soot concentration and soot particle sizes in propane oxygen flames

Abstract

Soot concentrations and particle sizes were measured by light scattering and probe measurements in the burnt gas region of atmospheric pressure propane-oxygen flames and propane-oxygen flames to which hydrogen or ammonia were added. The results show that the soot concentrations in propane-oxygen flames, to which hydrogen is added are lower compared to propane-oxygen flames. The decrease of soot concentration is much stronger when ammonia is added. Associated with the reduction of soot concentration is a reduction of mean particle size of the soot particles and a lower breadth of the particle size distributions. Electron micrographs of soot particles from the probe measurements showed that soot particles from flames with high soot concentrations (propane oxygen flames) are aggregates with chain or cluster structure while the structure of the particles from flames with lower soot concentration (propane oxygen flames with hydrogen or ammoniaadded) is more compact. Light scattering measurements were evaluated by nonlinear regression analysis of the scattering curves using different scattering models. Light scattering measurements and probe measurements which give high consistency for flames with low soot concentration and a more compact structure of the particles are discussed with respect to particle structure. The soot inhibiting effect of hydrogen and ammonia added to propane oxygen flames and their influence on the soot particle sizes are discussed as a strong deceleration of the reactions which lead to nucleation and a deceleration of the surface growth reactions for the built nuclei. This can be elucidated by simulation of particle growth of soot particles in these flames by a model including nucleation, surface growth and coagulation.