Particle size measurements using diffusion broadening spectroscopy

The use of monochromatic laser line broadening due to random particle motion to determine the sizes of submicron particles is investigated as part of a study of the condensation of Al2O3 in solid rocket exhaust. Mean particle diameters were measured as a function of mixture ratio and height above a flat-flame burner which was operated as a premixed acetylene/oxygen/nitrogen flame. Particle sizes are found to vary from 40 to 250 nm as height above the burner varied from 0.5 to 3.0 cm, in agreement with electron microscope photographs of particulates collected above the flame. The application of the diffusion broadening spectroscopy system to aluminum/oxygen flames is planned, and operational parameters for the system are estimated.