Comparative measurement of the breakup length of liquid jets in airblast atomisers using optical connectivity, electrical connectivity and shadowgraphy

A comparative examination of the optical connectivity, electrical connectivity and shadowgraphy techniques for the measurement of the break-up length of atomising liquid jets from a co-axial airblast atomiser is presented. The atomiser was operated over air-to-liquid Momentum Ratios between 27 and 335 and Momentum Flux Ratios between 0.67 and 8.27. Shadowgraphy records instantaneous images of the shadow of the atomising liquid jet when it is back-illuminated by a light source. The electrical connectivity uses the continuity of an electrically conducting atomising liquid jet to measure the potential during the presence of an electrical connection between the spray nozzle and a probe further downstream. The optical connectivity visualises the atomising liquid jet, doped with a fluorescing dye, as it is illuminated from within the nozzle using a laser beam. Comparison of the measured breakup lengths with time resolved shadowgraphy, optical connectivity and electrical connectivity, following the proposed novel processing of the time-dependent potential, showed that the mean values are all within ±15% of each other. The advantages and limitations of each technique are discussed.