THREE-DIMENSIONAL HIGH-SPEED TOMOGRAPHY OF DENSE SPRAYS USING BALLISTIC IMAGING

ABSTRACT: The primary objective of this research effort is to develop a next-generation time-gated ballistic imaging (BI) system for three-dimensional characterization of liquid breakup within dense fuel sprays. The temporal resolution will be varied using nonlinear time gating and pulse shaping techniques to optimize image contrast for a range of optical densities in sprays for propulsion applications, including augmentors, rockets, scramjets, and IC engines. The unique feature of BI is that it can circumvent the difficulties associated with propagating light through dense media by eliminating diffuse light that has undergone multiple scattering within the dense field of droplets. In contrast with X-ray or conventional tomography, BI greatly reduces the number of elements that must be reconstructed to satisfy the Shannon/Nyquest criterion and allows 3D reconstruction using discrete tomography. Borrowing largely from advancements in medical imaging and non-destructive testing, several inversion algorithms will be tested to solve the discrete tomography problem. This approach can potentially allow measurements with very limited viewing angles for high-speed 3D imaging of liquid breakup in dense sprays. BENEFIT: We anticipate that three-dimensional ballistic imaging tomography will provide new measurement capabilities for studying liquid-breakup dynamics in a variety of propulsion systems, including augmentors, gas turbines, scramjets, and rockets. This will enable improved fundamental understanding and modeling of dense sprays, which is of significant practical and scientific interest. The understanding developed from the proposed tomography system is critical for improving the speed and efficiency of the design process, ultimately helping to avoid and or solve problems associated combustion dynamics brought on by transient, non-uniform fuel-air mixture preparation. This measurement capability is applicable for military and commercial propulsion systems, as well as industrial furnaces and internal combustion engines. The increasing availability of compact, ultrafast laser systems indicates that a ballistic imaging approach based on these advanced laser sources will be commercially feasible.