The Use of Small Probe Volumes with Phase Doppler Interferometry

Abstract

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The effects of LOX post biasing on SSME injector wall compatibility

“…A ten-to-one intensity validation scheme was implemented to reject erroneous measurements associated with the relatively small beam waist in comparison to the droplet sizes being measured (2<D<350 (im). 3 The PDI was fixed in location with respect to the chamber windows and the injector was traversed through the probe volume at 1 mm steps for the axial location of 5 mm and 3 mm steps for all other axial locations. This yielded a radial profile of the gas phase velocity and droplet diameter from the outside edge of the spray to the wall, through the centerline of the spray as defined by the center of the LOX post.…”

Phase Doppler Measurements in Dense Sprays

“…The authors have demonstrated in a separate paper being presented at this conference, that the probe diameter can be made much smaller than the largest droplet being measured by using an intensity validation technique which limits the minimum scattering intensity to one tenth the maximum intensity in each particle size class [4].…”

“…The degree of attenuation is a function of both the droplet number densities and the path length through the spray. Laser transmission rates through dense sprays can typically be less than 10" 4 . The loss in signal, however, can usually be overcome by increasing the intensity of the probe beams or by increasing the photomultiplier tube (PMT) voltage.…”

“…Sankar et al [2] have used a PDPA in a shear coaxial rocket injector spray similar to the type of injector used in the present study. Peak number densities of about 2xl0 4 cm" 3 were measured. It was also reported that the measured volume flux decreased with increasing gas flowrate through the injector which was attributed to evaporation of the smaller droplets.…”

“…Unfortunately, laser diagnostic techniques for measuring droplet size, velocity and volume flux generally do not work well in dense sprays where droplet number densities, N, can reach 10 cm" , and light transmission rates through the spray, I/I 0 , fall below 10" 4 . Laser diffraction techniques generally require that I/I 0 be greater than 10" 1 in order to avoid errors associated with multiple scattering, while phase Doppler interferometry usually requires that the droplet number densities are less than 10 3 cm" 3 in the size range of 5-300 pi.…”