Non-intrusive measurement techniques for the near field of dense fuel sprays

• This is an invited review article. It is mostly devoted to published work, some of it by the author but much of it by others. • New results include the application of wavelet-based optical flow velocimetry to ballistic images, for the detection of acceleration in the liquid-gas interface. • A section on transitional jets discusses difficult issues associated with supercritical states. The results are not new but may not have been noticed by others. • New work on X-ray radiography using a laser plasma accelerator is presented and discussed. This paper presents a review of recent developments in non-intrusive, dense fuel spray measurement; covering both optical and X-ray techniques. It emphasizes: the flow inside a fuel injector, flow in the near field, primary breakup, and to a lesser extent secondary breakup. Spatial and temporal measurement of parameters such as cavitation, mass, interfaces, breakup mechanics, drop sizing, drop temperature, and drop/vapor distributions are discussed.