Ballistic Imaging of Transient Phenomena in Turbid Media

Ballistic imaging (BI) was developed as an optical diagnostic capable of ascertaining velocity and spatial information within dense sprays with relevance to liquid-fuel injection and combustion. This development includes a full model of light scattering within the complete imaging system, enabling the performance of the instrument to be examined, optimized and quantified. BI is a laser-based measurement for enhanced visualization of strong gradient disturbances within inhomogeneous highly scattering media. The technique is a specialized shadow-imaging method, closely related to schlieren and shadowgraph techniques, which focuses on eliminating stray and multiply-scattered source light from a line-of-sight integrated 2-D signal, detected in a forward-collection geometry. Experimental investigations of two turbulent sprays were conducted, and new spray behavior was observed over the course of both measurement campaigns: Bifurcation in a two-phase flow was observed for the first time, in a jet-in-crossflow, and overall flowrate effects were shown to influence the breakup characteristics in an effervescent spray. Analysis methods were developed to apply spatial correlation to BI results, enabling the determination of velocity vectors throughout a dense spray