Particle sizing from forward scattered light at two angles using a variable-focal-length optical system

Abstract

The theory of operation and description of a particle sizing device which indirectly determines the size of small particles from forward scattered light at two angles is presented. The device incorporates a fixed detector geometry and maintains a fixed intensity ratio at two photodiode detectors by adjusting the optical system focal length. Simple analogue signal processing is used with a servomotor to make continuous adjustments automatically. The optical device is used to investigate the effects of an applied high intensity electric field on a fuel spray from a turbine engine fuel nozzle for changes in droplet size. Preliminary results on a T-56 nozzle spraying DF-2 fuel at 75 psig with the sample volume 8 centimeters from the nozzle and using a sharp electrode with the point 10 millimeters from the nozzle at a potential of 16 kV showed no conclusive changes in droplet size. The Sauter mean diameter of the fuel spray varied from 42 to 47 microns. Keywords include: Particle measurement, and Variable-focal-length optical system