ID 394

Conversion of Scattering Phase Function to SMD in Scattering/Extinction Tomography

 

Abstract:

The combined scattering and extinction tomography technique provides the planar distribution of scattering phase function of drops within a spray. The scattering phase function of drops, at a specific angle, is a unique function of individual sizes of the drops based on the MIE theory. Therefore, the phase function obtained using combined scattering and extinction tomography can be converted to the Sauter Mean Diameter (SMD) of the spray. A conversion method from to obtain the SMD of the spray from the phase function was developed and evaluated by using a mono-disperse droplet generator. The extinction and scattering intensity at 30 degree from the incident laser was measured simultaneously for the drops. The size distribution from the drops obtained with the mono-disperse droplet generator is known. This information was utilized to calibrate the optical efficiency of the measuring system. A scattering/extinction tomography and a grid scan of PDA measurement were conducted for a pressure atomized nozzle, at two different pressure conditions. The uncertainty associated with converting the measured phase functions to the SMD of the spray was also analyzed using MIE theory. A lognormal distribution of drop size was assumed for the drops in the spray. It was discovered that the SMD of the spray was a strong function of mean scattering phase function, and a weak function of second order moment of the measured phase function. The planar SMD distributions estimated with scattering/extinction tomography agreed with the grid scan of the PDA measurement for both the pressure conditions.