Fast-framing ballistic imaging of velocity in an aerated spray

We describe further development of ballistic imaging adapted for the liquid core of an atomizing spray. To fully understand spray breakup dynamics, one must measure the velocity and acceleration vectors that describe the forces active in primary breakup. This information is inaccessible to most optical diagnostics, as the signal is occluded by strong scattering in the medium. Ballistic imaging mitigates this scattering noise, resolving clean shadowgram-type images of structures within the dense spray region. We demonstrate that velocity data can be extracted from ballistic images of a spray relevant to fuel-injection applications, by implementing a simple, targeted correlation method for determining velocity from pairs of spray images. This work presents the first ballistic images of a liquid-fuel injector for scramjet combustion, and the first velocity information from ballistic images relevant to breakup in the near-field of a spray.