Combined two-photon optical connectivity and planar laser induced fluorescence for instantaneous characterisation of liquid interface during primary atomisation

A technique that combines two-photon excitation (TPE), planar laser induced fluorescence (PLIF) and optical connectivity (OC) has been applied to capture the instantaneous geometry of a cross-section normal to the main direction of the core of a liquid jet exposed to a crossflow of air during atomisation. This paper demonstrates that a nanosecond pulse laser can excite two-photon fluorescence in an atomising Rhodamine B-dyed water jet. It shows that TPE-PLIF on its own has limitations to capture the liquid interface during air-crossflow atomisation. The combination of TPE-PLIF and TPE-OC excites TPE-fluorescence at a targeted cross-section normal to the liquid jet axis at a fixed distance from the liquid jet exit and eliminates the limitations of the individual techniques. The optimisation of the instrumentation of the combined techniques and the associated image processing are described and the quantification of the instantaneous cross-section structures, developing during atomisation, on the surface of the liquid jet is demonstrated.